reliability of unreinforced masonry bracing walls · 2012. 4. 2. · din 1055-100. there, a value...
TRANSCRIPT
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
RELIABILITY OF UNREINFORCED MASONRY BRACING WALLS
Brehm Eric1 Lissel Shelley L
2
1 Dr-Ing Forensic Engineer TUumlV SUumlD Munich Germany ericbrehmtuev-suedde
2PhD Associate Professor Dept of Civil Engineering University of Calgary sllisselucalgaryca
Bracing walls are essential members in typical masonry structures However design checks
are only performed rarely in Germany The reason for this is a paragraph in the German
design code DIN 1053-1 which allows for neglecting of this design check This mentioned
paragraph is based on construction methods different from the current state of the art
Additionally design codes have mostly been calibrated on the basis of experience
Consequently the provided level of reliability remains unknown
In this paper a systematic analysis of the provided level of reliability is conducted Analytical
models for the prediction of the shear capacity of the walls are analyzed and assessed with test
data to identify the most realistic model A complete stochastic model is developed and the
reliability of typical bracing walls is determined The difference between the theoretical level
of reliability and the ldquoactualrdquo level of reliability is evaluated taking into account the realistic
utilization of the walls Subsequently the derived level of reliability is presented and
assessed
Keywords reliability masonry target reliability probabilistic
INTRODUCTION
The key objective in structural design is the design of sufficiently safe and reliable structures
While safety commonly refers to the absence of hazards reliability is a quantifiable value and
can be determined by probabilistic methods In current structural design codes the demands
of safety are incorporated through the use of partial safety factors which can be derived from
probabilistic analysis Unlike other materials in construction the reliability of masonry
members has not been subjected to extensive research in the past Recent research (see
Glowienka (2007)) showed the necessity for a probabilistic approach to masonry structures
However most studies are focussed on masonry subjected to axial stress and flexure Since
masonry shear walls exhibit a much more complex load-carrying behaviour and are even
more important to structural integrity this paper focuses on masonry shear walls subjected to
wind loading The structural reliability of these walls will be analysed by assessing different
analytical models and probabilistic modelling
RELIABILITY OF STRUCTURES
The most important requirement for structures is reliability The term reliability concerns
every aspect of a structure structures have to be reliable when it comes to load bearing
capacity as well as serviceability In design every parameter is uncertain to some extent The
uncertainty may be in the strength of materials as well as in dimensions and quality of
workmanship All parameters further referred to as basic variables influence the properties of
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
a member Reliability is linked to the probability that a member will exceed a certain limit
state This can be described by so called limit state functions which can be written as in
Eq (1)
Z(RE) = R - E (1)
where R is the resistance and E is the load effect
In the case where R = E the ultimate limit state is reached It can be seen from this equation
that the safety of a member can be defined as the difference between the resistance and the
load effect It has to be noted that R and E are independent random variables in many cases
so they have to be described by means of stochastics Therefore a stochastic model mostly
consisting of a probability distribution and the corresponding moments (eg mean standard
deviation) is required for every basic variable Figure 1 presents this for the simplified two-
dimensional case
Figure 1 Definition of failure probability (Glowienka (2007))
The failure probability can be computed by probabilistic methods such as SORM (Second
Order Reliability Method) or Monte Carlo-simulation For further information see
Rackwitz (2004)
For the description of the resistance appropriate models are required that describe the load
carrying behaviour realistically Contrary to design models a model that underestimates the
load carrying behaviour is not appropriate for probabilistic analysis
To find a measure for reliability that can be defined independently from the type of
distribution of the basic variables the reliability index βR according to Cornell (1969) has
proven useful see Eq (2) The major advantage of this definition is that only the mean mz
and standard deviation z of the basic variables need to be known
Z
ZR
m
(2)
load effect E
resistance R safety margin
failure
probability Pf
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
With this measure target reliabilities can be defined Ideally target reliabilities are based on a
complex optimization process accounting for aspects of safety as well as economic
requirements In the past target reliability has mostly been determined on an empirical basis
Since the target reliability has a major influence on safety factors setting too large of a target
reliability will lead to uneconomic design More information can be found in Brehm (2011)
GruSiBau (1981) and Rackwitz (2004)
The Joint Committee on Structural Safety (JCSS) gives the target reliabilities depending on
the failure consequences as shown in Table 1
Table 1 Target reliabilities according to JCSS (2001) for an observation period of 50
years
Relative cost for
enhancing the structural
reliability
Failure consequences
Minora)
Averageb)
Majorc)
large β=17 (Pf ∙510-2
) β=20 (Pf ∙3∙10-2
) β=26 (Pf 510-3
)
medium β=26 (Pf 510-3
) β=32 (Pf 710-4
)d)
β=35 (Pf 3∙10-4
)
small β=32 (Pf ∙710-4
) β=35 (Pf 3∙10-4
) β=38 (Pf 10-5
) a)
eg agricultural building b)
eg office buildings residential buildings or industrial buildings c)
eg bridges stadiums or high-rise buildings d)
recommendation for regular cases according to JCSS 2001
These target reliabilities are considered to be sufficient for most cases and will be taken as
reference for further calculations Another recommendation is given by the German code
DIN 1055-100 There a value of βtarget = 38 is given for a 50 year observation period
A full probabilistic approach for design is difficult since stochastic models have to be known
for all basic variables and good prediction models are required To simplify design the semi-
probabilistic partial safety concept is applied in most design codes In this concept the partial
safety factors for different basic variables make it possible to account for different scatter of
the variables A typical application of partial safety factors is presented by the following
equation
R
E
RE
(3)
where E is the load effect and R is the resistance both are usually defined as characteristic
values The safety factors which are greater than unity are represented by γi
LOAD-CARRYING BEHAVIOUR OF URM BRACING WALLS
To be able to determine the resistance and capacity of a member the load-carrying behaviour
has to be known Masonry members subjected to shear exhibit a complex load-carrying
behaviour There is however a general consensus on the 3 main in-plane failure modes in
masonry which include flexural failure (tension at the heel or crushing at the toe) sliding
failure in one or multiple bed joints and diagonal tensile failure of the panel which may be
combined with sliding failure of the joints Cracks are typically diagonal and stepped in nature
but may also transverse through units as shown in Figure 2
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 2 Typical failure modes for in-plane shear failure of masonry
Many models have been developed in the past for the prediction of the shear capacity of
Unreinforced Masonry (URM) walls In this study a variety of models was compared to test
data aiming at the identification of the most realistic model For further information on the
load-carrying behaviour of masonry shear walls and shear models see Kranzler (2008)
STRUCTURAL MODEL
To apply the different shear models and to assess the test data an appropriate structural model
is required The model is considered appropriate if it allows for the modelling of a large
number of walls with variation of only a few parameters and takes into account the coupling
moments of the concrete slabs Such a model has been proposed by Kranzler (2008) and is
presented in Figure 3 The shear slenderness v can then be computed from Eq (4)
Figure 3 Structural Model
(4)
SHEAR CAPACITY PREDICTION MODEL UNCERTAINTIES
The previously mentioned structural model was combined with a number of prediction
models to assess a test database The goal was the determination of the uncertainties linked to
Tension Crushing
(a) (b) (c)
Diagonal Tension
(a) (b) (c)
Sliding
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
the different prediction models to finally be able to identify the most accurate model This
model should then be used for the analysis of the reliability of the walls
To achieve more realistic results and to eliminate stochastic uncertainties a Bayesian update
has been performed taking into account prior information This prior information mainly
consisted of expert opinions found in the literature More information on this can be found in
Rackwitz (2004)
In Table 2 the results in form of the mean and scatter of the test-to-prediction ratio are
presented for Calcium Silicate (CS) Autoclaved Aerated Concrete (AAC) and Clay Brick
(CB) walls For detailed information about the different models please see Brehm (2011)
Table 2 Stochastic moments of test-to-prediction ratios for different models after
Bayesian Update
Failure mode Model Unit m CoV
Diagonal
tension
Mann amp Muumlllera
CS 121 025 21
AAC 112 022 20
CB 140 023 16
DIN EN 1996-1-1NA
CS 115 028 24
AAC 114 020 18
CB 103 018 18
Kranzler
CS 112 030 27
AAC 117 027 23
CB 099 019 19
DIN 1053-100
CS 123 027 22
AAC 115 030 26
CB 139 023 16
Sliding shear
Mann amp Muumlllera
CS 127 021 17
AAC 123 024 19
CB 141 024 17
DIN EN 1996-1-1NA
CS 115b 024 21
AAC 121b 025 20
CB 124 024 20
DIN 1053-100
CS 115 022 19
AAC 112 027 23
CB 140 024 17
Flexure ideal-plastic
CS 100 018 18
AAC 105 016 15
CB 110 020 18 aideal-plastic stress-strain relationship
bupdated with a mean of 10 (Likelihood)
It was found that every model performed differently depending on unit material and possible
failure mode Thus just a single ldquomost appropriate modelrdquo could not be determined
Therefore a combination of models was chosen for the most realistic representation of the
behaviour of masonry subjected to in-plane shear The corresponding model uncertainties are
summarized in Table 3
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Table 3 Model uncertainties
Failure mode Unit Model Dist m CoV
Diagonal tension Θdt
CS Mann amp Muumlller
LN
121 025 21
AAC DIN EN 1996-1-1NA
114 020 17
CB 103 018 17
Sliding shear Θs
CS DIN EN 1996-1-1NA 115 024 21
AAC Mann amp Muumlller 123 024 20
CB DIN EN 1996-1-1NA 124 024 19
Flexure Θf
CS
fully-plastica
100 018 18
AAC 105 016 15
CB 110 020 18
Shear crushing Θc all DIN EN 1996-1-1NA 100 020 20 astress-strain relationship
STOCHASTIC MODEL
For the reliability analysis every significant basic variable has to be modelled as a random
variable In this study every parameter related to shear design of masonry walls subjected to
wind load has been assessed thoroughly to obtain the relevant stochastic moments Note that
these variables are related to both sides of the limit state function resistance and loads A
summary of the stochastic model is presented in Table 4 Note that the model uncertainties for
the resistance are displayed in Table 3 The model uncertainties are modelled differently for
every unit material and failure mode according to the previously presented assessment of the
test database
Table 4 Stochastic model
Basic variable Material Distr mXiXki CoV
Res
ista
nce
Compressive strength of masonry fm
CS
LN
155 19
AAC 181 16
CB 143 17
Tensile strength of unit fbt
CS 184 26
AAC 155 16
CB 131 24
Cohesion fv0 TLM 214 35
GPM 357 40
Friction Coefficient all 133 19
Load
Model uncertainty on the shear load Ev
all
100 10
Model uncertainty on the axial load Ea 100 5
Wind load vab
Weibull 103 7
Live load nQa Gumbel 110 20
Dead load nG N 100 6 aobservation period of 50 yrs
b = 0073
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
RELIABILITY ANALYSIS
The reliability analysis has been performed for selection of over 400 walls which were
previously designed according to German design codes This made it possible to determine
the realistically provided reliability of shear walls in Germany
The reliability has been determined by SORM Basically the failure probability for every
possible failure mode for every wall has been determined and then the obtained failure
probabilities for every failure mode have been summed up Since one failure mode clearly
always governs the analysis the effects of possible overlap are small (lt 1) Figure 4
illustrates the determination of the failure probability By applying this method time-
consuming Monte-Carlo-Simulation could be avoided The reliability of the walls was
determined for full utilization of the cross-section to model walls in ultimate limit state and to
obtain comparable results for the different unit materials
Figure 4 Approach for Probabilistic Analysis
RESULTS THEORETICAL RELIABILITY
It quickly became obvious that the walls do not fulfil the code requirements in terms of target
reliability when the examined walls were slender Squat walls however reached very large
values of the reliability Note that every wall assumed to be 100 utilized
The reason for the differences in reliability between slender and squat walls is the
eccentricity Slender walls reach a much larger eccentricity than squat walls In the following
the axial and shear loads according to Eq (5) and Eq (6) will be used
mw
Gk
Gkflt
Nn
(5)
mw
Ek
Ekflt
Vv
(6)
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
where fm is the masonry compressive strength NGk is the axial dead load and VEk is the shear
load
Figure 5 shows the reliability and eccentricity for a slender CS wall related to the axial dead
load nGk
Figure 5 Reliability vs Eccentricity for a slender CS wall (v = 30) and full utilization
of the cross-section (100)
In general a large eccentricity leads to small reliability In Figure 6 the reliability for a squat
CB wall is shown It can be seen that the reliability is consistently very high and above the
target region
Figure 6 Reliability vs Eccentricity for a squat CB wall (v = 05) and full utilization of
the cross section (100)
Figure 7 shows a comparison of the reliabilities obtained for different unit materials and
slender walls It can be seen that the reliabilities are similarly distributed and stay below the
target values The larger reliability for AAC walls is due to a peculiarity in the German code
DIN 1053-1 where the tensile strength of AAC units was massively underestimated
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
a member Reliability is linked to the probability that a member will exceed a certain limit
state This can be described by so called limit state functions which can be written as in
Eq (1)
Z(RE) = R - E (1)
where R is the resistance and E is the load effect
In the case where R = E the ultimate limit state is reached It can be seen from this equation
that the safety of a member can be defined as the difference between the resistance and the
load effect It has to be noted that R and E are independent random variables in many cases
so they have to be described by means of stochastics Therefore a stochastic model mostly
consisting of a probability distribution and the corresponding moments (eg mean standard
deviation) is required for every basic variable Figure 1 presents this for the simplified two-
dimensional case
Figure 1 Definition of failure probability (Glowienka (2007))
The failure probability can be computed by probabilistic methods such as SORM (Second
Order Reliability Method) or Monte Carlo-simulation For further information see
Rackwitz (2004)
For the description of the resistance appropriate models are required that describe the load
carrying behaviour realistically Contrary to design models a model that underestimates the
load carrying behaviour is not appropriate for probabilistic analysis
To find a measure for reliability that can be defined independently from the type of
distribution of the basic variables the reliability index βR according to Cornell (1969) has
proven useful see Eq (2) The major advantage of this definition is that only the mean mz
and standard deviation z of the basic variables need to be known
Z
ZR
m
(2)
load effect E
resistance R safety margin
failure
probability Pf
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
With this measure target reliabilities can be defined Ideally target reliabilities are based on a
complex optimization process accounting for aspects of safety as well as economic
requirements In the past target reliability has mostly been determined on an empirical basis
Since the target reliability has a major influence on safety factors setting too large of a target
reliability will lead to uneconomic design More information can be found in Brehm (2011)
GruSiBau (1981) and Rackwitz (2004)
The Joint Committee on Structural Safety (JCSS) gives the target reliabilities depending on
the failure consequences as shown in Table 1
Table 1 Target reliabilities according to JCSS (2001) for an observation period of 50
years
Relative cost for
enhancing the structural
reliability
Failure consequences
Minora)
Averageb)
Majorc)
large β=17 (Pf ∙510-2
) β=20 (Pf ∙3∙10-2
) β=26 (Pf 510-3
)
medium β=26 (Pf 510-3
) β=32 (Pf 710-4
)d)
β=35 (Pf 3∙10-4
)
small β=32 (Pf ∙710-4
) β=35 (Pf 3∙10-4
) β=38 (Pf 10-5
) a)
eg agricultural building b)
eg office buildings residential buildings or industrial buildings c)
eg bridges stadiums or high-rise buildings d)
recommendation for regular cases according to JCSS 2001
These target reliabilities are considered to be sufficient for most cases and will be taken as
reference for further calculations Another recommendation is given by the German code
DIN 1055-100 There a value of βtarget = 38 is given for a 50 year observation period
A full probabilistic approach for design is difficult since stochastic models have to be known
for all basic variables and good prediction models are required To simplify design the semi-
probabilistic partial safety concept is applied in most design codes In this concept the partial
safety factors for different basic variables make it possible to account for different scatter of
the variables A typical application of partial safety factors is presented by the following
equation
R
E
RE
(3)
where E is the load effect and R is the resistance both are usually defined as characteristic
values The safety factors which are greater than unity are represented by γi
LOAD-CARRYING BEHAVIOUR OF URM BRACING WALLS
To be able to determine the resistance and capacity of a member the load-carrying behaviour
has to be known Masonry members subjected to shear exhibit a complex load-carrying
behaviour There is however a general consensus on the 3 main in-plane failure modes in
masonry which include flexural failure (tension at the heel or crushing at the toe) sliding
failure in one or multiple bed joints and diagonal tensile failure of the panel which may be
combined with sliding failure of the joints Cracks are typically diagonal and stepped in nature
but may also transverse through units as shown in Figure 2
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 2 Typical failure modes for in-plane shear failure of masonry
Many models have been developed in the past for the prediction of the shear capacity of
Unreinforced Masonry (URM) walls In this study a variety of models was compared to test
data aiming at the identification of the most realistic model For further information on the
load-carrying behaviour of masonry shear walls and shear models see Kranzler (2008)
STRUCTURAL MODEL
To apply the different shear models and to assess the test data an appropriate structural model
is required The model is considered appropriate if it allows for the modelling of a large
number of walls with variation of only a few parameters and takes into account the coupling
moments of the concrete slabs Such a model has been proposed by Kranzler (2008) and is
presented in Figure 3 The shear slenderness v can then be computed from Eq (4)
Figure 3 Structural Model
(4)
SHEAR CAPACITY PREDICTION MODEL UNCERTAINTIES
The previously mentioned structural model was combined with a number of prediction
models to assess a test database The goal was the determination of the uncertainties linked to
Tension Crushing
(a) (b) (c)
Diagonal Tension
(a) (b) (c)
Sliding
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
the different prediction models to finally be able to identify the most accurate model This
model should then be used for the analysis of the reliability of the walls
To achieve more realistic results and to eliminate stochastic uncertainties a Bayesian update
has been performed taking into account prior information This prior information mainly
consisted of expert opinions found in the literature More information on this can be found in
Rackwitz (2004)
In Table 2 the results in form of the mean and scatter of the test-to-prediction ratio are
presented for Calcium Silicate (CS) Autoclaved Aerated Concrete (AAC) and Clay Brick
(CB) walls For detailed information about the different models please see Brehm (2011)
Table 2 Stochastic moments of test-to-prediction ratios for different models after
Bayesian Update
Failure mode Model Unit m CoV
Diagonal
tension
Mann amp Muumlllera
CS 121 025 21
AAC 112 022 20
CB 140 023 16
DIN EN 1996-1-1NA
CS 115 028 24
AAC 114 020 18
CB 103 018 18
Kranzler
CS 112 030 27
AAC 117 027 23
CB 099 019 19
DIN 1053-100
CS 123 027 22
AAC 115 030 26
CB 139 023 16
Sliding shear
Mann amp Muumlllera
CS 127 021 17
AAC 123 024 19
CB 141 024 17
DIN EN 1996-1-1NA
CS 115b 024 21
AAC 121b 025 20
CB 124 024 20
DIN 1053-100
CS 115 022 19
AAC 112 027 23
CB 140 024 17
Flexure ideal-plastic
CS 100 018 18
AAC 105 016 15
CB 110 020 18 aideal-plastic stress-strain relationship
bupdated with a mean of 10 (Likelihood)
It was found that every model performed differently depending on unit material and possible
failure mode Thus just a single ldquomost appropriate modelrdquo could not be determined
Therefore a combination of models was chosen for the most realistic representation of the
behaviour of masonry subjected to in-plane shear The corresponding model uncertainties are
summarized in Table 3
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Table 3 Model uncertainties
Failure mode Unit Model Dist m CoV
Diagonal tension Θdt
CS Mann amp Muumlller
LN
121 025 21
AAC DIN EN 1996-1-1NA
114 020 17
CB 103 018 17
Sliding shear Θs
CS DIN EN 1996-1-1NA 115 024 21
AAC Mann amp Muumlller 123 024 20
CB DIN EN 1996-1-1NA 124 024 19
Flexure Θf
CS
fully-plastica
100 018 18
AAC 105 016 15
CB 110 020 18
Shear crushing Θc all DIN EN 1996-1-1NA 100 020 20 astress-strain relationship
STOCHASTIC MODEL
For the reliability analysis every significant basic variable has to be modelled as a random
variable In this study every parameter related to shear design of masonry walls subjected to
wind load has been assessed thoroughly to obtain the relevant stochastic moments Note that
these variables are related to both sides of the limit state function resistance and loads A
summary of the stochastic model is presented in Table 4 Note that the model uncertainties for
the resistance are displayed in Table 3 The model uncertainties are modelled differently for
every unit material and failure mode according to the previously presented assessment of the
test database
Table 4 Stochastic model
Basic variable Material Distr mXiXki CoV
Res
ista
nce
Compressive strength of masonry fm
CS
LN
155 19
AAC 181 16
CB 143 17
Tensile strength of unit fbt
CS 184 26
AAC 155 16
CB 131 24
Cohesion fv0 TLM 214 35
GPM 357 40
Friction Coefficient all 133 19
Load
Model uncertainty on the shear load Ev
all
100 10
Model uncertainty on the axial load Ea 100 5
Wind load vab
Weibull 103 7
Live load nQa Gumbel 110 20
Dead load nG N 100 6 aobservation period of 50 yrs
b = 0073
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
RELIABILITY ANALYSIS
The reliability analysis has been performed for selection of over 400 walls which were
previously designed according to German design codes This made it possible to determine
the realistically provided reliability of shear walls in Germany
The reliability has been determined by SORM Basically the failure probability for every
possible failure mode for every wall has been determined and then the obtained failure
probabilities for every failure mode have been summed up Since one failure mode clearly
always governs the analysis the effects of possible overlap are small (lt 1) Figure 4
illustrates the determination of the failure probability By applying this method time-
consuming Monte-Carlo-Simulation could be avoided The reliability of the walls was
determined for full utilization of the cross-section to model walls in ultimate limit state and to
obtain comparable results for the different unit materials
Figure 4 Approach for Probabilistic Analysis
RESULTS THEORETICAL RELIABILITY
It quickly became obvious that the walls do not fulfil the code requirements in terms of target
reliability when the examined walls were slender Squat walls however reached very large
values of the reliability Note that every wall assumed to be 100 utilized
The reason for the differences in reliability between slender and squat walls is the
eccentricity Slender walls reach a much larger eccentricity than squat walls In the following
the axial and shear loads according to Eq (5) and Eq (6) will be used
mw
Gk
Gkflt
Nn
(5)
mw
Ek
Ekflt
Vv
(6)
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
where fm is the masonry compressive strength NGk is the axial dead load and VEk is the shear
load
Figure 5 shows the reliability and eccentricity for a slender CS wall related to the axial dead
load nGk
Figure 5 Reliability vs Eccentricity for a slender CS wall (v = 30) and full utilization
of the cross-section (100)
In general a large eccentricity leads to small reliability In Figure 6 the reliability for a squat
CB wall is shown It can be seen that the reliability is consistently very high and above the
target region
Figure 6 Reliability vs Eccentricity for a squat CB wall (v = 05) and full utilization of
the cross section (100)
Figure 7 shows a comparison of the reliabilities obtained for different unit materials and
slender walls It can be seen that the reliabilities are similarly distributed and stay below the
target values The larger reliability for AAC walls is due to a peculiarity in the German code
DIN 1053-1 where the tensile strength of AAC units was massively underestimated
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
With this measure target reliabilities can be defined Ideally target reliabilities are based on a
complex optimization process accounting for aspects of safety as well as economic
requirements In the past target reliability has mostly been determined on an empirical basis
Since the target reliability has a major influence on safety factors setting too large of a target
reliability will lead to uneconomic design More information can be found in Brehm (2011)
GruSiBau (1981) and Rackwitz (2004)
The Joint Committee on Structural Safety (JCSS) gives the target reliabilities depending on
the failure consequences as shown in Table 1
Table 1 Target reliabilities according to JCSS (2001) for an observation period of 50
years
Relative cost for
enhancing the structural
reliability
Failure consequences
Minora)
Averageb)
Majorc)
large β=17 (Pf ∙510-2
) β=20 (Pf ∙3∙10-2
) β=26 (Pf 510-3
)
medium β=26 (Pf 510-3
) β=32 (Pf 710-4
)d)
β=35 (Pf 3∙10-4
)
small β=32 (Pf ∙710-4
) β=35 (Pf 3∙10-4
) β=38 (Pf 10-5
) a)
eg agricultural building b)
eg office buildings residential buildings or industrial buildings c)
eg bridges stadiums or high-rise buildings d)
recommendation for regular cases according to JCSS 2001
These target reliabilities are considered to be sufficient for most cases and will be taken as
reference for further calculations Another recommendation is given by the German code
DIN 1055-100 There a value of βtarget = 38 is given for a 50 year observation period
A full probabilistic approach for design is difficult since stochastic models have to be known
for all basic variables and good prediction models are required To simplify design the semi-
probabilistic partial safety concept is applied in most design codes In this concept the partial
safety factors for different basic variables make it possible to account for different scatter of
the variables A typical application of partial safety factors is presented by the following
equation
R
E
RE
(3)
where E is the load effect and R is the resistance both are usually defined as characteristic
values The safety factors which are greater than unity are represented by γi
LOAD-CARRYING BEHAVIOUR OF URM BRACING WALLS
To be able to determine the resistance and capacity of a member the load-carrying behaviour
has to be known Masonry members subjected to shear exhibit a complex load-carrying
behaviour There is however a general consensus on the 3 main in-plane failure modes in
masonry which include flexural failure (tension at the heel or crushing at the toe) sliding
failure in one or multiple bed joints and diagonal tensile failure of the panel which may be
combined with sliding failure of the joints Cracks are typically diagonal and stepped in nature
but may also transverse through units as shown in Figure 2
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 2 Typical failure modes for in-plane shear failure of masonry
Many models have been developed in the past for the prediction of the shear capacity of
Unreinforced Masonry (URM) walls In this study a variety of models was compared to test
data aiming at the identification of the most realistic model For further information on the
load-carrying behaviour of masonry shear walls and shear models see Kranzler (2008)
STRUCTURAL MODEL
To apply the different shear models and to assess the test data an appropriate structural model
is required The model is considered appropriate if it allows for the modelling of a large
number of walls with variation of only a few parameters and takes into account the coupling
moments of the concrete slabs Such a model has been proposed by Kranzler (2008) and is
presented in Figure 3 The shear slenderness v can then be computed from Eq (4)
Figure 3 Structural Model
(4)
SHEAR CAPACITY PREDICTION MODEL UNCERTAINTIES
The previously mentioned structural model was combined with a number of prediction
models to assess a test database The goal was the determination of the uncertainties linked to
Tension Crushing
(a) (b) (c)
Diagonal Tension
(a) (b) (c)
Sliding
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
the different prediction models to finally be able to identify the most accurate model This
model should then be used for the analysis of the reliability of the walls
To achieve more realistic results and to eliminate stochastic uncertainties a Bayesian update
has been performed taking into account prior information This prior information mainly
consisted of expert opinions found in the literature More information on this can be found in
Rackwitz (2004)
In Table 2 the results in form of the mean and scatter of the test-to-prediction ratio are
presented for Calcium Silicate (CS) Autoclaved Aerated Concrete (AAC) and Clay Brick
(CB) walls For detailed information about the different models please see Brehm (2011)
Table 2 Stochastic moments of test-to-prediction ratios for different models after
Bayesian Update
Failure mode Model Unit m CoV
Diagonal
tension
Mann amp Muumlllera
CS 121 025 21
AAC 112 022 20
CB 140 023 16
DIN EN 1996-1-1NA
CS 115 028 24
AAC 114 020 18
CB 103 018 18
Kranzler
CS 112 030 27
AAC 117 027 23
CB 099 019 19
DIN 1053-100
CS 123 027 22
AAC 115 030 26
CB 139 023 16
Sliding shear
Mann amp Muumlllera
CS 127 021 17
AAC 123 024 19
CB 141 024 17
DIN EN 1996-1-1NA
CS 115b 024 21
AAC 121b 025 20
CB 124 024 20
DIN 1053-100
CS 115 022 19
AAC 112 027 23
CB 140 024 17
Flexure ideal-plastic
CS 100 018 18
AAC 105 016 15
CB 110 020 18 aideal-plastic stress-strain relationship
bupdated with a mean of 10 (Likelihood)
It was found that every model performed differently depending on unit material and possible
failure mode Thus just a single ldquomost appropriate modelrdquo could not be determined
Therefore a combination of models was chosen for the most realistic representation of the
behaviour of masonry subjected to in-plane shear The corresponding model uncertainties are
summarized in Table 3
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Table 3 Model uncertainties
Failure mode Unit Model Dist m CoV
Diagonal tension Θdt
CS Mann amp Muumlller
LN
121 025 21
AAC DIN EN 1996-1-1NA
114 020 17
CB 103 018 17
Sliding shear Θs
CS DIN EN 1996-1-1NA 115 024 21
AAC Mann amp Muumlller 123 024 20
CB DIN EN 1996-1-1NA 124 024 19
Flexure Θf
CS
fully-plastica
100 018 18
AAC 105 016 15
CB 110 020 18
Shear crushing Θc all DIN EN 1996-1-1NA 100 020 20 astress-strain relationship
STOCHASTIC MODEL
For the reliability analysis every significant basic variable has to be modelled as a random
variable In this study every parameter related to shear design of masonry walls subjected to
wind load has been assessed thoroughly to obtain the relevant stochastic moments Note that
these variables are related to both sides of the limit state function resistance and loads A
summary of the stochastic model is presented in Table 4 Note that the model uncertainties for
the resistance are displayed in Table 3 The model uncertainties are modelled differently for
every unit material and failure mode according to the previously presented assessment of the
test database
Table 4 Stochastic model
Basic variable Material Distr mXiXki CoV
Res
ista
nce
Compressive strength of masonry fm
CS
LN
155 19
AAC 181 16
CB 143 17
Tensile strength of unit fbt
CS 184 26
AAC 155 16
CB 131 24
Cohesion fv0 TLM 214 35
GPM 357 40
Friction Coefficient all 133 19
Load
Model uncertainty on the shear load Ev
all
100 10
Model uncertainty on the axial load Ea 100 5
Wind load vab
Weibull 103 7
Live load nQa Gumbel 110 20
Dead load nG N 100 6 aobservation period of 50 yrs
b = 0073
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
RELIABILITY ANALYSIS
The reliability analysis has been performed for selection of over 400 walls which were
previously designed according to German design codes This made it possible to determine
the realistically provided reliability of shear walls in Germany
The reliability has been determined by SORM Basically the failure probability for every
possible failure mode for every wall has been determined and then the obtained failure
probabilities for every failure mode have been summed up Since one failure mode clearly
always governs the analysis the effects of possible overlap are small (lt 1) Figure 4
illustrates the determination of the failure probability By applying this method time-
consuming Monte-Carlo-Simulation could be avoided The reliability of the walls was
determined for full utilization of the cross-section to model walls in ultimate limit state and to
obtain comparable results for the different unit materials
Figure 4 Approach for Probabilistic Analysis
RESULTS THEORETICAL RELIABILITY
It quickly became obvious that the walls do not fulfil the code requirements in terms of target
reliability when the examined walls were slender Squat walls however reached very large
values of the reliability Note that every wall assumed to be 100 utilized
The reason for the differences in reliability between slender and squat walls is the
eccentricity Slender walls reach a much larger eccentricity than squat walls In the following
the axial and shear loads according to Eq (5) and Eq (6) will be used
mw
Gk
Gkflt
Nn
(5)
mw
Ek
Ekflt
Vv
(6)
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
where fm is the masonry compressive strength NGk is the axial dead load and VEk is the shear
load
Figure 5 shows the reliability and eccentricity for a slender CS wall related to the axial dead
load nGk
Figure 5 Reliability vs Eccentricity for a slender CS wall (v = 30) and full utilization
of the cross-section (100)
In general a large eccentricity leads to small reliability In Figure 6 the reliability for a squat
CB wall is shown It can be seen that the reliability is consistently very high and above the
target region
Figure 6 Reliability vs Eccentricity for a squat CB wall (v = 05) and full utilization of
the cross section (100)
Figure 7 shows a comparison of the reliabilities obtained for different unit materials and
slender walls It can be seen that the reliabilities are similarly distributed and stay below the
target values The larger reliability for AAC walls is due to a peculiarity in the German code
DIN 1053-1 where the tensile strength of AAC units was massively underestimated
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 2 Typical failure modes for in-plane shear failure of masonry
Many models have been developed in the past for the prediction of the shear capacity of
Unreinforced Masonry (URM) walls In this study a variety of models was compared to test
data aiming at the identification of the most realistic model For further information on the
load-carrying behaviour of masonry shear walls and shear models see Kranzler (2008)
STRUCTURAL MODEL
To apply the different shear models and to assess the test data an appropriate structural model
is required The model is considered appropriate if it allows for the modelling of a large
number of walls with variation of only a few parameters and takes into account the coupling
moments of the concrete slabs Such a model has been proposed by Kranzler (2008) and is
presented in Figure 3 The shear slenderness v can then be computed from Eq (4)
Figure 3 Structural Model
(4)
SHEAR CAPACITY PREDICTION MODEL UNCERTAINTIES
The previously mentioned structural model was combined with a number of prediction
models to assess a test database The goal was the determination of the uncertainties linked to
Tension Crushing
(a) (b) (c)
Diagonal Tension
(a) (b) (c)
Sliding
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
the different prediction models to finally be able to identify the most accurate model This
model should then be used for the analysis of the reliability of the walls
To achieve more realistic results and to eliminate stochastic uncertainties a Bayesian update
has been performed taking into account prior information This prior information mainly
consisted of expert opinions found in the literature More information on this can be found in
Rackwitz (2004)
In Table 2 the results in form of the mean and scatter of the test-to-prediction ratio are
presented for Calcium Silicate (CS) Autoclaved Aerated Concrete (AAC) and Clay Brick
(CB) walls For detailed information about the different models please see Brehm (2011)
Table 2 Stochastic moments of test-to-prediction ratios for different models after
Bayesian Update
Failure mode Model Unit m CoV
Diagonal
tension
Mann amp Muumlllera
CS 121 025 21
AAC 112 022 20
CB 140 023 16
DIN EN 1996-1-1NA
CS 115 028 24
AAC 114 020 18
CB 103 018 18
Kranzler
CS 112 030 27
AAC 117 027 23
CB 099 019 19
DIN 1053-100
CS 123 027 22
AAC 115 030 26
CB 139 023 16
Sliding shear
Mann amp Muumlllera
CS 127 021 17
AAC 123 024 19
CB 141 024 17
DIN EN 1996-1-1NA
CS 115b 024 21
AAC 121b 025 20
CB 124 024 20
DIN 1053-100
CS 115 022 19
AAC 112 027 23
CB 140 024 17
Flexure ideal-plastic
CS 100 018 18
AAC 105 016 15
CB 110 020 18 aideal-plastic stress-strain relationship
bupdated with a mean of 10 (Likelihood)
It was found that every model performed differently depending on unit material and possible
failure mode Thus just a single ldquomost appropriate modelrdquo could not be determined
Therefore a combination of models was chosen for the most realistic representation of the
behaviour of masonry subjected to in-plane shear The corresponding model uncertainties are
summarized in Table 3
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Table 3 Model uncertainties
Failure mode Unit Model Dist m CoV
Diagonal tension Θdt
CS Mann amp Muumlller
LN
121 025 21
AAC DIN EN 1996-1-1NA
114 020 17
CB 103 018 17
Sliding shear Θs
CS DIN EN 1996-1-1NA 115 024 21
AAC Mann amp Muumlller 123 024 20
CB DIN EN 1996-1-1NA 124 024 19
Flexure Θf
CS
fully-plastica
100 018 18
AAC 105 016 15
CB 110 020 18
Shear crushing Θc all DIN EN 1996-1-1NA 100 020 20 astress-strain relationship
STOCHASTIC MODEL
For the reliability analysis every significant basic variable has to be modelled as a random
variable In this study every parameter related to shear design of masonry walls subjected to
wind load has been assessed thoroughly to obtain the relevant stochastic moments Note that
these variables are related to both sides of the limit state function resistance and loads A
summary of the stochastic model is presented in Table 4 Note that the model uncertainties for
the resistance are displayed in Table 3 The model uncertainties are modelled differently for
every unit material and failure mode according to the previously presented assessment of the
test database
Table 4 Stochastic model
Basic variable Material Distr mXiXki CoV
Res
ista
nce
Compressive strength of masonry fm
CS
LN
155 19
AAC 181 16
CB 143 17
Tensile strength of unit fbt
CS 184 26
AAC 155 16
CB 131 24
Cohesion fv0 TLM 214 35
GPM 357 40
Friction Coefficient all 133 19
Load
Model uncertainty on the shear load Ev
all
100 10
Model uncertainty on the axial load Ea 100 5
Wind load vab
Weibull 103 7
Live load nQa Gumbel 110 20
Dead load nG N 100 6 aobservation period of 50 yrs
b = 0073
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
RELIABILITY ANALYSIS
The reliability analysis has been performed for selection of over 400 walls which were
previously designed according to German design codes This made it possible to determine
the realistically provided reliability of shear walls in Germany
The reliability has been determined by SORM Basically the failure probability for every
possible failure mode for every wall has been determined and then the obtained failure
probabilities for every failure mode have been summed up Since one failure mode clearly
always governs the analysis the effects of possible overlap are small (lt 1) Figure 4
illustrates the determination of the failure probability By applying this method time-
consuming Monte-Carlo-Simulation could be avoided The reliability of the walls was
determined for full utilization of the cross-section to model walls in ultimate limit state and to
obtain comparable results for the different unit materials
Figure 4 Approach for Probabilistic Analysis
RESULTS THEORETICAL RELIABILITY
It quickly became obvious that the walls do not fulfil the code requirements in terms of target
reliability when the examined walls were slender Squat walls however reached very large
values of the reliability Note that every wall assumed to be 100 utilized
The reason for the differences in reliability between slender and squat walls is the
eccentricity Slender walls reach a much larger eccentricity than squat walls In the following
the axial and shear loads according to Eq (5) and Eq (6) will be used
mw
Gk
Gkflt
Nn
(5)
mw
Ek
Ekflt
Vv
(6)
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
where fm is the masonry compressive strength NGk is the axial dead load and VEk is the shear
load
Figure 5 shows the reliability and eccentricity for a slender CS wall related to the axial dead
load nGk
Figure 5 Reliability vs Eccentricity for a slender CS wall (v = 30) and full utilization
of the cross-section (100)
In general a large eccentricity leads to small reliability In Figure 6 the reliability for a squat
CB wall is shown It can be seen that the reliability is consistently very high and above the
target region
Figure 6 Reliability vs Eccentricity for a squat CB wall (v = 05) and full utilization of
the cross section (100)
Figure 7 shows a comparison of the reliabilities obtained for different unit materials and
slender walls It can be seen that the reliabilities are similarly distributed and stay below the
target values The larger reliability for AAC walls is due to a peculiarity in the German code
DIN 1053-1 where the tensile strength of AAC units was massively underestimated
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
the different prediction models to finally be able to identify the most accurate model This
model should then be used for the analysis of the reliability of the walls
To achieve more realistic results and to eliminate stochastic uncertainties a Bayesian update
has been performed taking into account prior information This prior information mainly
consisted of expert opinions found in the literature More information on this can be found in
Rackwitz (2004)
In Table 2 the results in form of the mean and scatter of the test-to-prediction ratio are
presented for Calcium Silicate (CS) Autoclaved Aerated Concrete (AAC) and Clay Brick
(CB) walls For detailed information about the different models please see Brehm (2011)
Table 2 Stochastic moments of test-to-prediction ratios for different models after
Bayesian Update
Failure mode Model Unit m CoV
Diagonal
tension
Mann amp Muumlllera
CS 121 025 21
AAC 112 022 20
CB 140 023 16
DIN EN 1996-1-1NA
CS 115 028 24
AAC 114 020 18
CB 103 018 18
Kranzler
CS 112 030 27
AAC 117 027 23
CB 099 019 19
DIN 1053-100
CS 123 027 22
AAC 115 030 26
CB 139 023 16
Sliding shear
Mann amp Muumlllera
CS 127 021 17
AAC 123 024 19
CB 141 024 17
DIN EN 1996-1-1NA
CS 115b 024 21
AAC 121b 025 20
CB 124 024 20
DIN 1053-100
CS 115 022 19
AAC 112 027 23
CB 140 024 17
Flexure ideal-plastic
CS 100 018 18
AAC 105 016 15
CB 110 020 18 aideal-plastic stress-strain relationship
bupdated with a mean of 10 (Likelihood)
It was found that every model performed differently depending on unit material and possible
failure mode Thus just a single ldquomost appropriate modelrdquo could not be determined
Therefore a combination of models was chosen for the most realistic representation of the
behaviour of masonry subjected to in-plane shear The corresponding model uncertainties are
summarized in Table 3
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Table 3 Model uncertainties
Failure mode Unit Model Dist m CoV
Diagonal tension Θdt
CS Mann amp Muumlller
LN
121 025 21
AAC DIN EN 1996-1-1NA
114 020 17
CB 103 018 17
Sliding shear Θs
CS DIN EN 1996-1-1NA 115 024 21
AAC Mann amp Muumlller 123 024 20
CB DIN EN 1996-1-1NA 124 024 19
Flexure Θf
CS
fully-plastica
100 018 18
AAC 105 016 15
CB 110 020 18
Shear crushing Θc all DIN EN 1996-1-1NA 100 020 20 astress-strain relationship
STOCHASTIC MODEL
For the reliability analysis every significant basic variable has to be modelled as a random
variable In this study every parameter related to shear design of masonry walls subjected to
wind load has been assessed thoroughly to obtain the relevant stochastic moments Note that
these variables are related to both sides of the limit state function resistance and loads A
summary of the stochastic model is presented in Table 4 Note that the model uncertainties for
the resistance are displayed in Table 3 The model uncertainties are modelled differently for
every unit material and failure mode according to the previously presented assessment of the
test database
Table 4 Stochastic model
Basic variable Material Distr mXiXki CoV
Res
ista
nce
Compressive strength of masonry fm
CS
LN
155 19
AAC 181 16
CB 143 17
Tensile strength of unit fbt
CS 184 26
AAC 155 16
CB 131 24
Cohesion fv0 TLM 214 35
GPM 357 40
Friction Coefficient all 133 19
Load
Model uncertainty on the shear load Ev
all
100 10
Model uncertainty on the axial load Ea 100 5
Wind load vab
Weibull 103 7
Live load nQa Gumbel 110 20
Dead load nG N 100 6 aobservation period of 50 yrs
b = 0073
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
RELIABILITY ANALYSIS
The reliability analysis has been performed for selection of over 400 walls which were
previously designed according to German design codes This made it possible to determine
the realistically provided reliability of shear walls in Germany
The reliability has been determined by SORM Basically the failure probability for every
possible failure mode for every wall has been determined and then the obtained failure
probabilities for every failure mode have been summed up Since one failure mode clearly
always governs the analysis the effects of possible overlap are small (lt 1) Figure 4
illustrates the determination of the failure probability By applying this method time-
consuming Monte-Carlo-Simulation could be avoided The reliability of the walls was
determined for full utilization of the cross-section to model walls in ultimate limit state and to
obtain comparable results for the different unit materials
Figure 4 Approach for Probabilistic Analysis
RESULTS THEORETICAL RELIABILITY
It quickly became obvious that the walls do not fulfil the code requirements in terms of target
reliability when the examined walls were slender Squat walls however reached very large
values of the reliability Note that every wall assumed to be 100 utilized
The reason for the differences in reliability between slender and squat walls is the
eccentricity Slender walls reach a much larger eccentricity than squat walls In the following
the axial and shear loads according to Eq (5) and Eq (6) will be used
mw
Gk
Gkflt
Nn
(5)
mw
Ek
Ekflt
Vv
(6)
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
where fm is the masonry compressive strength NGk is the axial dead load and VEk is the shear
load
Figure 5 shows the reliability and eccentricity for a slender CS wall related to the axial dead
load nGk
Figure 5 Reliability vs Eccentricity for a slender CS wall (v = 30) and full utilization
of the cross-section (100)
In general a large eccentricity leads to small reliability In Figure 6 the reliability for a squat
CB wall is shown It can be seen that the reliability is consistently very high and above the
target region
Figure 6 Reliability vs Eccentricity for a squat CB wall (v = 05) and full utilization of
the cross section (100)
Figure 7 shows a comparison of the reliabilities obtained for different unit materials and
slender walls It can be seen that the reliabilities are similarly distributed and stay below the
target values The larger reliability for AAC walls is due to a peculiarity in the German code
DIN 1053-1 where the tensile strength of AAC units was massively underestimated
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Table 3 Model uncertainties
Failure mode Unit Model Dist m CoV
Diagonal tension Θdt
CS Mann amp Muumlller
LN
121 025 21
AAC DIN EN 1996-1-1NA
114 020 17
CB 103 018 17
Sliding shear Θs
CS DIN EN 1996-1-1NA 115 024 21
AAC Mann amp Muumlller 123 024 20
CB DIN EN 1996-1-1NA 124 024 19
Flexure Θf
CS
fully-plastica
100 018 18
AAC 105 016 15
CB 110 020 18
Shear crushing Θc all DIN EN 1996-1-1NA 100 020 20 astress-strain relationship
STOCHASTIC MODEL
For the reliability analysis every significant basic variable has to be modelled as a random
variable In this study every parameter related to shear design of masonry walls subjected to
wind load has been assessed thoroughly to obtain the relevant stochastic moments Note that
these variables are related to both sides of the limit state function resistance and loads A
summary of the stochastic model is presented in Table 4 Note that the model uncertainties for
the resistance are displayed in Table 3 The model uncertainties are modelled differently for
every unit material and failure mode according to the previously presented assessment of the
test database
Table 4 Stochastic model
Basic variable Material Distr mXiXki CoV
Res
ista
nce
Compressive strength of masonry fm
CS
LN
155 19
AAC 181 16
CB 143 17
Tensile strength of unit fbt
CS 184 26
AAC 155 16
CB 131 24
Cohesion fv0 TLM 214 35
GPM 357 40
Friction Coefficient all 133 19
Load
Model uncertainty on the shear load Ev
all
100 10
Model uncertainty on the axial load Ea 100 5
Wind load vab
Weibull 103 7
Live load nQa Gumbel 110 20
Dead load nG N 100 6 aobservation period of 50 yrs
b = 0073
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
RELIABILITY ANALYSIS
The reliability analysis has been performed for selection of over 400 walls which were
previously designed according to German design codes This made it possible to determine
the realistically provided reliability of shear walls in Germany
The reliability has been determined by SORM Basically the failure probability for every
possible failure mode for every wall has been determined and then the obtained failure
probabilities for every failure mode have been summed up Since one failure mode clearly
always governs the analysis the effects of possible overlap are small (lt 1) Figure 4
illustrates the determination of the failure probability By applying this method time-
consuming Monte-Carlo-Simulation could be avoided The reliability of the walls was
determined for full utilization of the cross-section to model walls in ultimate limit state and to
obtain comparable results for the different unit materials
Figure 4 Approach for Probabilistic Analysis
RESULTS THEORETICAL RELIABILITY
It quickly became obvious that the walls do not fulfil the code requirements in terms of target
reliability when the examined walls were slender Squat walls however reached very large
values of the reliability Note that every wall assumed to be 100 utilized
The reason for the differences in reliability between slender and squat walls is the
eccentricity Slender walls reach a much larger eccentricity than squat walls In the following
the axial and shear loads according to Eq (5) and Eq (6) will be used
mw
Gk
Gkflt
Nn
(5)
mw
Ek
Ekflt
Vv
(6)
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
where fm is the masonry compressive strength NGk is the axial dead load and VEk is the shear
load
Figure 5 shows the reliability and eccentricity for a slender CS wall related to the axial dead
load nGk
Figure 5 Reliability vs Eccentricity for a slender CS wall (v = 30) and full utilization
of the cross-section (100)
In general a large eccentricity leads to small reliability In Figure 6 the reliability for a squat
CB wall is shown It can be seen that the reliability is consistently very high and above the
target region
Figure 6 Reliability vs Eccentricity for a squat CB wall (v = 05) and full utilization of
the cross section (100)
Figure 7 shows a comparison of the reliabilities obtained for different unit materials and
slender walls It can be seen that the reliabilities are similarly distributed and stay below the
target values The larger reliability for AAC walls is due to a peculiarity in the German code
DIN 1053-1 where the tensile strength of AAC units was massively underestimated
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
RELIABILITY ANALYSIS
The reliability analysis has been performed for selection of over 400 walls which were
previously designed according to German design codes This made it possible to determine
the realistically provided reliability of shear walls in Germany
The reliability has been determined by SORM Basically the failure probability for every
possible failure mode for every wall has been determined and then the obtained failure
probabilities for every failure mode have been summed up Since one failure mode clearly
always governs the analysis the effects of possible overlap are small (lt 1) Figure 4
illustrates the determination of the failure probability By applying this method time-
consuming Monte-Carlo-Simulation could be avoided The reliability of the walls was
determined for full utilization of the cross-section to model walls in ultimate limit state and to
obtain comparable results for the different unit materials
Figure 4 Approach for Probabilistic Analysis
RESULTS THEORETICAL RELIABILITY
It quickly became obvious that the walls do not fulfil the code requirements in terms of target
reliability when the examined walls were slender Squat walls however reached very large
values of the reliability Note that every wall assumed to be 100 utilized
The reason for the differences in reliability between slender and squat walls is the
eccentricity Slender walls reach a much larger eccentricity than squat walls In the following
the axial and shear loads according to Eq (5) and Eq (6) will be used
mw
Gk
Gkflt
Nn
(5)
mw
Ek
Ekflt
Vv
(6)
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
where fm is the masonry compressive strength NGk is the axial dead load and VEk is the shear
load
Figure 5 shows the reliability and eccentricity for a slender CS wall related to the axial dead
load nGk
Figure 5 Reliability vs Eccentricity for a slender CS wall (v = 30) and full utilization
of the cross-section (100)
In general a large eccentricity leads to small reliability In Figure 6 the reliability for a squat
CB wall is shown It can be seen that the reliability is consistently very high and above the
target region
Figure 6 Reliability vs Eccentricity for a squat CB wall (v = 05) and full utilization of
the cross section (100)
Figure 7 shows a comparison of the reliabilities obtained for different unit materials and
slender walls It can be seen that the reliabilities are similarly distributed and stay below the
target values The larger reliability for AAC walls is due to a peculiarity in the German code
DIN 1053-1 where the tensile strength of AAC units was massively underestimated
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
where fm is the masonry compressive strength NGk is the axial dead load and VEk is the shear
load
Figure 5 shows the reliability and eccentricity for a slender CS wall related to the axial dead
load nGk
Figure 5 Reliability vs Eccentricity for a slender CS wall (v = 30) and full utilization
of the cross-section (100)
In general a large eccentricity leads to small reliability In Figure 6 the reliability for a squat
CB wall is shown It can be seen that the reliability is consistently very high and above the
target region
Figure 6 Reliability vs Eccentricity for a squat CB wall (v = 05) and full utilization of
the cross section (100)
Figure 7 shows a comparison of the reliabilities obtained for different unit materials and
slender walls It can be seen that the reliabilities are similarly distributed and stay below the
target values The larger reliability for AAC walls is due to a peculiarity in the German code
DIN 1053-1 where the tensile strength of AAC units was massively underestimated
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Figure 7 Reliability of slender masonry walls for different materials (v = 30) and full
utilization of the cross section (100)
RESULTS ACTUAL RELIABILITY
The reliabilities obtained for slender walls are small much smaller than one would expect
considering the fact that there are actually no structural failures of masonry shear walls due to
wind load reported The most likely reason for this is the low actual level of utilization in
reality In this study every wall was designed for full utilization However CS and CB walls
provide much larger strength than AAC walls so that higher loads are required to reach full
utilization The wind load acting on a structure in reality will be more or less the same no
matter which material is used Thus levels of utilization are different for every unit material
The typical effect is shown in Figure 8
Figure 8 Reliability vs Eccentricity for a slender CS wall (v = 30) and different
utilization levels of the cross section
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
To assess this effect a typical town house was modelled using FE software Different unit
materials were investigated and the actual level of utilization due to wind and axial load was
determined for every wall Subsequently the reliability taking into account the actual level of
utilization has been determined It was found that the reliability reaches similar values for
every wall material and that these values are significantly higher than the theoretical values of
reliability The results are summarized in Table 5
The ldquoactualrdquo value of reliability determined on the basis of DIN 1053-1 does not reach the
target values of DIN 1055-100 Nonetheless it matches the recommendations of JCSS (2001)
see Table 1 However the target values have to be analysed and assessed since there is no
difference in target reliability depending on the failure consequences linked to a structure
These values are valid for a skyscraper as well as for agricultural buildings In a future study
a full-probabilistic optimization of typical masonry structures will be conducted to determine
the socio-economic optimum target reliability for masonry structures
Table 5 Results for average theoretical and actual reliability
Material
Average reliability index provided
in common masonry constructiona
theoreticalb
actualc
DIN 1053-1 DIN 1053-100 DIN EN 1996-1-1NA
CS (20TLM) 20 27 26 32d
CB (12GPM IIa) 21 30 30 31e
AAC (4TLM) 30 37 33 30f
acorresponding to v = 30 and nGk = 00502
bfull (100) utilization of the wall
cdetermined on the basis of DIN 1053-1
dcorresponding to a utilization of 70
ecorresponding to a utilization of 80
fcorresponding to a utilization of 100
SUMMARY
The reliability of masonry shear walls subjected to wind loading has been determined The
walls were designed according to German design codes so that the provided level of reliability
in Germany could be derived It was shown that the theoretical reliability of slender masonry
walls falls short of the target values of DIN 1055-100 if full utilization of the cross-section is
assumed For realistic values of the utilization reliability is much larger and the three
investigated unit materials reach similar values
REFERENCES
Brehm E rdquoReliability of Unreinforced Masonry Bracing Walls ndash Probabilistic Approach and
Optimized Target Valuesrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2011
Cornell CA rdquoA reliability-based structural coderdquo ACI Journal Vol 66 No 12 1969
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004
15th International Brick and Block
Masonry Conference
Florianoacutepolis ndash Brazil ndash 2012
Glowienka S rdquoZuverlaumlssigkeit von Mauerwerkswaumlnden aus groszligformatigen Steinenrdquo
Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt Germany 2007
GruSiBau rdquoGrundlagen zur Festlegung von Sicherheitsanforderungen fuumlr bauliche Anlagenrdquo
NA Bau Beuth Verlag Berlin Germany 1981
Joint Committee on Structural Safety (JCSS) rdquoProbabilistic Assessment of Existing
Structuresrdquo RILEM publucations SARL 2001
Kranzler T rdquoTragfaumlhigkeit uumlberwiegend horizontal beanspruchter Aussteifungsscheiben aus
unbewehrtem Mauerwerkrdquo Doctoral Thesis Technische Universitaumlt Darmstadt Darmstadt
Germany 2008
Mann W Muumlller H rdquoSchubtragfaumlhigkeit von Mauerwerkrdquo in Mauerwerk-Kalender 3
Ernst amp Sohn Berlin 1978
Rackwitz R rdquoZuverlaumlssigkeit und Lasten im konstruktiven Ingenieurbaurdquo Technical
University of Munich Munich Germany 2004