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    TABLE OF CONTENTS

    Synthesis report 5

    1. Objectives of the project 5

    2. Comparison of initially planned activities and work accomplished 5

    3. Description of activities and discussion 63.1 General 6

    3.2 WP1 Available design methods and new technologies for seismic design 6

    3.3 WP2 Seismic testing of joints 9

    3.4 WP3 Seismic testing of shear walls 12

    3.5 WP4 Analysing of test results 15

    3.6 WP5 Recommendations for practical design 18

    4. Conclusions 22

    5. Future works 23

    6. Exploitation and impact of the results 23

    7. List of most relevant figures and tables 25

    8. List of references 26

    ANNEX 1 Available design methods and new technologies for seismic design 27

    ANNEX 2 Joint testing and analysis 45

    ANNEX 3 Shear wall testing 85

    ANNEX 4 Earthquake analysis and modelling of shear walls 121

    ANNEX 5 Development of simplified formulas for calculating shear walls 153

    ANNEX 6 Design guide 167

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    Synthesis report

    1. Objectives of the project

    The commercial objective is to increase the use of cold- formed steel components in the light gauge

    steel framed buildings especially in the earthquake zones. The technical objective is to develop guid-

    ance for codified design rules, guidance on analysis methods and guidance on detailing. This will en-able engineered light gauge steel building solutions to be promoted in seismically vulnerable locations.

    The expected results of the project are:

    Codified design rules: a design methodology and associated design equations for use in manual de-

    sign of light gauge steel buildings. The design recommendations will be written in a fashion that is

    suitable for adoption by code drafters to facilitate future coverage of seismic design of light gauge steel

    buildings in Standards, particularly the Eurocodes (EC8).

    Guidance on analysis methods: guidance on the analysis (including FE analysis) of light gauge steel

    buildings subjected to earthquake loading.

    Guidance on detailing: recommendations for the detailing of joints and shear walls.

    The requirements for the development work in this project are:

    The rules developed should be practical and easy to use guidelines for seismic design of light gauge 1-

    and 2-storey steel buildings. Because design rules are not available there is urgent need for such rules in

    the steel construction industry.

    The rules should be clear and simple international design rules that will encourage the use of light

    gauge steel framed construction techniques.

    2. Comparison of initially planned activities and work actually accomplished

    The work was accomplished mainly according to original plan, but following deviations have been re-

    corded in some work packages.

    WP2 Seismic testing of joints.

    A wide range of shear tests for screwed and bolted connection between two steel straps were performed.

    Number of connectors and number of connector columns in the connection were varied. The bending

    tests were excluded from the test series because the preliminary analyses have shown that the bending

    stiffness of the connection is not a significant parameter in the shear wall design. Instead of them, sev-

    eral types of corner details of shear walls have been tested (upper and lower corners, with and without

    gusset plate). Furthermore, two tests were performed to small scale shear walls in order to study global

    behaviour of connections. Altogether 190 axial joint tests were performed to screw, bolt and Rosette

    connectors. Furthermore, totally 28 corner details and small scale shear wall tests were performed. The

    test set-ups to the corner details were much more complicated than corresponding set-ups for bending

    tests. Thus, although the number of performed test (218) was lower than estimated (380) in the Techni-

    cal Annex, the total work amount of the modified test series was at least the same than the work amount

    of the original test plan.

    WP3 Seismic testing of shear walls

    Only quasi-static, cyclic tests were planned to be performed in this work package. Finally, two different

    test procedures were used in the project. Further to cyclic tests, a comprehensive series of dynamicseismic tests on vibration table were also carried out. The purpose of seismic testing was to get informa-

    tion of the behaviour of the shear walls during an different accelerogams. The damping of the all seis-

    mic test specimens were also measured in specific damping tests. The total amount of the different test

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    specimens (different sheathings or diagonal stiffening systems) has been 31 that is almost the same as

    originally planned (30).

    WP4.1 Analysing the results of joint tests

    The work in this sub-WP has been carried out as planned. Finite element analyses of structural details

    (e.g. frame corners) were a useful tool for design. However, detailed geometrical FE modelling of all

    joint configurations was deemed inappropriate to capture the global response of the shear walls. For this

    reason, the main effort was put in the analysis of joint results (identification of failure modes and theirseismic suitability), the comparison of experimental ultimate loads with Eurocode 3 predictions and the

    development of general guidelines for the design and testing of joints.

    WP4.2 Analysing the results of shear wall tests

    In the original plan (Tasks 2 and 3), the modelling of shear walls was assumed to be based solely on

    finite element computations. However, a simplified model for shear walls has also been developed by

    UPC. The shear wall is treated as a single-degree-of-freedom system and its hysteretic response is de-

    scribed by means of an appropriate constitutive model (for either unsheathed x-braced frames or

    sheathed frames). This approach is computationally more efficient and simpler to use than a full nonlin-

    ear finite element analysis. This simplified approach has been extended to model whole buildings, ei-

    ther symmetrical or non-symmetrical. In order to validate the simplified model, a large number of finite

    element analyses were also carried out.

    3. Description of activities and discussion

    3.1 General

    The summary of the project activities and main results are described below work package by work

    package. The more comprehensive description of the activities and the results are given in Annexes at-

    tached to the report. In order to improve the readability of the document, the content of annexes are not

    following directly the order of the work packages in the project plan in Technical Annex. The table be-

    low shows the corresponding Annex to each work package or task.

    Work Package Work described in

    WP 1 Annex 1

    WP 2 Annex 2

    WP 3 Annex 3

    WP 4.1 Annex 2

    WP 4.2, Tasks 1&5 Annex 3

    WP 4.2, Tasks 2,3,4&6 Annex 4

    WP 4.2, Task 7 Annex 5

    WP 5 Annex 6

    3.2 WP1 Available design methods and new technologies for seismic design

    3.2.1 Objectives of the WP 1

    Objectives of the WP1 were to review the current methods of seismic analysis and design of light-gauge

    structures. Furthermore one objective of the WP1 was a preliminary design of test programmes and test

    specimens used in WP 2 and WP3 concerning of joint testing and shear wall testing

    The goals of this work baggage are:

    To go through some main standards concerning seismic design

    To collect information of shear wall testing methods and testing facility To collect information of stiffening system and sheathings used in steel stud shear walls To collect main results of steel stud shear walls To obtain information of analyzing of test results

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    3.2.2 Activities and results obtained

    The bibliographic review was made at the beginning of the project in order to have knowledge of

    standards and test methods of steel stud shear walls. The technical report and Annex 1 is shown in

    Table WP1.1:

    Table WP1.1.Technical reporst of WP 1.

    Phase Description Technical report

    1State of art

    (Standards, testing)

    WP1/E001 Bibliographic review of scientific journals and

    standards of light gauge steel constructions

    Annex 1

    At the beginning of the project in 2002 the standard of Eurocode 8 was developing and the latest ver-

    sion was published in 2004 (EN1998-1:2004). Other standards reviewed in the project are Uniform

    building code (UBC) 1997 and International building code (IBC) 2003. At the beginning of the project

    the interest of research was to find technical articles of shear wall structures and testing methods. The

    technical report WP1/E001 does not include all the information used in the project, because most in-

    formation is collected after the report is written, but that information is given in Annexes and other

    technical reports of the project.The main results obtained are as follows:

    Eurocode 8 (EN1998-1 2004, ), / Annex 1/

    Eurocode 8 /1/ does not give exact value for behavior factor q when light gauge steel structures (LGS)

    are used in a one or two storey small buildings. In chapter 8 of Eurocode 8 q values are given e.g. for

    nailed wall panels, but these values cannot be used without further investigations for LGS structures,

    because the ductility behavior of the nails if different from screws behavior in cyclic tests. The seismic

    forces are calculated using acceleration response spectrum and design ground acceleration.

    Uniform Building Code (UBC) 1997, /Annex 1/

    In table 16 N (Structural systems) of UBC is given factors for various structural systems. The LGS

    structures belong to system 2 (Building frame system). The standard of UBC gives values of forcemodification factor R, but it is not quite the same as the behavior factor q of EC 8. According to

    Eurocode 8 the design response spectrum is divided by q but according to UPC the design forces are

    divides by R

    International Building Code (IBC) 2003, /Annex 1/

    The IBC gives two methods to calculate seismic events: General procedure and Site-specific procedure.

    The site-specific procedure is used for Site Class F buildings. In IBC 2003 the mapped maximum

    considered earthquake spectral response accelerations at short period (SS) and 1-second period (S1) are

    given (as a percent of g), but these acceleration maps are only given in USA. The design response

    accelerations SDS and SD1 can be are calculated given formulas.

    GR-63-CORE 63 2002, / Annex 1/

    GR-63-CORE /6/ is a subset of family of documents for physical and environmental criteria for

    telephone facilities buildings and for equipment used in these facilities. The same requirements are also

    published in standard ANSI T1.329-1995 /13/. The GR-63-CORE can be also used for shear walls as a

    guideline for earthquake simulation test, but the response spectrum signal is, may be, too strong to be

    used in the tests.

    Zhao, Cyclic Performance of Cold-formed Steel Stud Shear Walls, /Annex 1/

    The report (thesis) describes the instructions of design standards in Northern America and in USA

    concerning the steel stud shear walls. The National Building Code of Canada (NBCC) does not define

    an R-value (force modification factor) for these walls. The report also contains a summary of previous

    cold-formed steel stud shear walls test programs in Northern America. A theoretical method to predict

    the shear capacity based on American Wood Design procedure is presented and results are comparedwith the peek loads obtained from tests. Force modification factor R has been suggested to be 2.0 cold-

    formed steel stud shear walls.

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    Bredel, Performance Capabilities of Light-Frame Shear Walls Sheathed with Long OSB Panels / Annex

    1/

    The report performs 34 test results of shear walls, width of 2.4 m and height of 2.4 to 3.0 m. The studs

    were wooden studs sheathing, oriented strand board (OBS) and anchoring system was Simpson HTT22

    device. The results include comparison between long and short panels when extra stud is needed

    between corner studs. The testing has also done with or without a mechanical hold down device

    attached to the base of the end stud.Salenikovich, The Racking Performance of Light-Frame Shear Walls Annex 1/

    The report describes 56 tests of light-frame timber shear walls which were sheathed with oriented

    strandboard (OSB) panels with aspect ratio of 4:1, 2:1, 1:1 and 2:3. The specimens were tested in

    horizontal position and no dead load was used in the tests. The anchoring system was either Simpson

    device, bolts or 16d nails. The test series includes also nail parameters, sheathing parameters and

    sheathing to framing connections.

    Fiorino, Seismic Behaviour of Sheathed Cold-Formed Steel Stud Shear Walls /Annex 1/

    The main objective of the research is to give a contribution to the evaluation of seismic performance of

    low-rise residential buildings with cold-formed steel members through the evaluation of seismic

    demand, capacity and their comparison.

    The strength of the sheathing is researched taking in account following failure modes: bearing failure in

    the steel frame, tilting failure of the screw, screw shear failure and bearing failure of the wood panel.

    Also the formulas of the strength of the frame (buckling) and strength of the anchoring bolts are shown

    in the paper.

    Kawai. Seismic Resistance and Design of Steel-Framed Houses /Annex 1/

    The paper describes the seismic design of steel framed houses in Japan. In January 1995 the great

    Hanshin Earthquake caused damage to houses and 50 000 temporary dwellings were build of which

    3000 units were imported steel-framed houses. After that Committee of steel Framed houses published

    standard of Design and Construction Specification and manuals for Steel Framed Houses. A hysteresis

    model under cyclic loading was developed and dynamic vibration tests of steel houses and shaking tabletests of steel framed walls were conducted.

    Serrette. Design Values for Vertical and Horizontal Lateral Load Systems/ Annex 1/

    The objective of the research is to provide a concise, basic design reference for LGS framed lateral load

    resisting systems and the tech note focus primary on codes UBC, IBC and IRC based design values and

    widely used standard design methodologies in the United States. The two basic lateral load resisting

    systems are shear walls and diagonal braced systems. The main factors that influence the performance

    of shear walls are the rate of loading, framing thickness, screw size, screw spacing, edge distance and

    material used in sheathing. The walls tested have been 2.4 m high and the ratio of height and length 4:1,

    2:2 and 1:1. The tests for the codes were done using cyclic signal and every step was repeated 3 times

    by same level and after that 3 decreasing steps were performed. The force modification factor R is

    defined as 4.5 for steel sheathed walls and 5.5 for plywood and OSB walls.Fulop. Performance of wall-stud cold-formed shear panels under monotonic and cyclic loading. Part I:

    Experimental research. /Annex 1/

    This research included a number of 15 full scale (24503600 mm) tests on steel framed walls. The

    sheathing configurations were: (i) X braced walls, (ii) corrugated sheath walls and (iii) OSB sheathed

    walls. Both fully sheathed walls and walls with openings were tested using the ECCS 45 cyclic loading

    protocol.

    Based on the test results a finite element methodology was developed for the evaluation of the load-

    bearing capacity, rigidity and ductility of different wall configurations sheathed with corrugated steel

    plates. The experimental results were also compared to available analytical formulas ECCS 45 for the

    calculation of capacity and rigidity. The conclusion of such comparison was that the formulas predict a

    very low capacity for the wall compared to the real capacity. However, large part of the capacity of the

    wall can not be regarded as elastic capacity since nonlinearities set in at an early stage of the

    deformation. Based on the experiments and analysis multi-level performance criteria was proposed.

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    In the final stage of the research non-linear time-history analysis was carried out using a tri-linear

    hysteretic model (i.e. modeling the behavior of the tested walls) and a set of historical earthquake

    records. The conclusion of the analysis was that the over strength contribute more to the performance of

    the walls in case of earthquake than the ductility.

    3.2.3 Discussion

    In recent years the use of steel stud shear wall structures seems to increase. Cold formed steel profilesare easy and fast to fabricate and also plenty of test have been done in order to find out the behavior and

    capacity against seismic forces. Most common testing method is cyclic testing with cyclic loading

    signal, but there are many signals available and each of them have some advantages. If one loading

    signal could be used the results could be comparable to each other and also the value of behavior factor

    of q could be given more accurate to steel stud shear wall panels.

    3.3 WP2 Seismic testing of joints

    3.3.1 Objectives of WP 2

    An assessment of the state of the art in seismic design and cold-formed steel structures indicates that

    concentric braced frames are a very effective means of providing the lateral stiffness, ductility and en-ergy dissipation required under seismic loads. Since these x-braced frames with diagonal steel straps are

    crucial in the seismic response of the whole building, the joint testing campaign focuses on their con-

    nections. The joints must be strong enough to allow the yielding of the diagonal straps.

    A careful planning of the testing campaign indicated that the bending tests initially envisaged were of

    little interest. For this reason, it was decided to concentrate in tensile tests of increasing complexity.

    Although not initially planned in the technical annex, it was also decided to close the joint testing cam-

    paign with small-scale tests of whole x-braced frames.

    The goals of this testing campaign are:

    To measure material properties of steel (yield stress and ultimate stress) To obtain relevant parameters of joints such as the initial stiffness, yielding load, ultimate load and

    maximum displacement To obtain complete force-displacement (F-d) curves, needed for the finite element modelling of x-

    braced frames

    To identify the various failure modes (bearing, net section failure,) To assess the suitability of various connection devices (screws, bolts, Rosette) for seismic design To check the dissipative capabilities of x-braced frames To compile guidelines for seismic testing of joints

    3.3.2 Activities and results obtained

    The joint testing campaign was divided into six phases (phase 0phase 5), described in detail in the

    corresponding technical annexes:

    Phase Description Technical report

    Planning of campaign WP2/BD001 Design of the joint testing campaign

    0 Material testing of steel

    1 Lap joints between straps

    2 Joints between strap and gusset

    WP2/BD002 Joint testing: phases 1 and 2

    3 Lower frame corners

    4 Upper frame corners

    WP2/BD003 and BD004 Joint testing: phases 3 and 4.

    Part I: Finnish specimens. Part II: Spanish specimens

    5 Small-scale x-braced frames WP2/BD005 Joint testing: phase 5

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    The main results obtained are as follows:

    Tensile testing of steel (phase 0)

    For all the specimens (two steels grades and four thicknesses) tested, the measured value of the yield

    and ultimate stress is significantly larger than the nominal value.

    Lap joints in straps (phase 1)

    In screwed joints, two main failure modes are identified: tilting (and bearing) + net section failure

    (T+NSF) and tilting + bearing + pull out (T+B+PO), see Fig. WP2.1. The thickness of the straps and

    the number of screws determine the mode of collapse. For straps of the same thickness (t 1 = t2), tilting

    always occurs from the beginning. The final failure mode is pull-out (4 columns of screws or less) or

    net section failure (6 columns of screws). For straps of different thickness (t1 < t2), bearing of the thinner

    sheet may be as significant as tilting at the beginning. The final mode of failure also depends on the

    number of screws.

    In bolted joints, the two main failure modes are tilting + bearing + tearing of the sheet (T+B+TS) and

    tilting + bearing + net section failure (T+B+NSF). All the joints with one column of bolts fail due to

    bearing. For the joints with two columns, it depends on the diameter of the bolts and the thickness of thestraps. Net section failure is observed in joints with two columns of 10 mm diameter bolts and in joints

    with two columns of 8 mm diameter bolts connecting straps of different thickness. Joints connecting

    straps of the same thickness by means of two columns of 8 mm diameter bolts fail due to bearing.

    (a) (b)Fig. WP2.1. Failure modes in screwed joints:

    (a) tilting + bearing + net section failure; (b) tilting + pull-out

    The original Rosette joint is based on a single-collar connector. One of the outputs of this project is an

    improved, double-collar design. The general tendency of the experimental results is that the double-

    collar connector has a higher ductility and, hence, is more suitable for seismic design.

    Joints between diagonal strap and gusset (phase 2)

    The failure modes are in good agreement with the results for screwed joints of phase 1. The specimens

    have a reduced number of screws (less than 6 columns), so they fail due to tilting and pull-out when

    t1=t2 (strap and gusset of same thickness) and due to tilting, bearing and tensile failure of the sheet when

    t1

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    (a) (b)Fig. WP2.2. Test set-ups for frame corners: (a) lower corners (anchor-bolted);

    (b) upper corners (note the extra fastening device)

    In thermo-slotted lower corners, two primary modes of failure were identified: punching of the track-

    stud connection and tensile failure of the diagonal strap. These failure modes were typically preceded

    by other phenomena such as local buckling of the track and distortional buckling of the outer stud. As

    for upper corners, the first tests with the grips resulted in undesired failure modes, affecting the stud and

    track rather than the strap. Low values of the peak load were obtained. For this reason, it was decided to

    reinforce the track and stud of the remaining specimens. The reinforced specimens had a much better

    performance, both in terms of failure mode and peak load.

    In solid lower corners, two different joint configurations (with and without eccentricity) were analyzed.

    As designed, all specimens failed due to net section failure of the straps. As for upper corners, speci-

    mens with narrow straps failed in the expected net section failure mode. With wide straps, on the con-

    trary, failure was due to local buckling of track and stud.Whole x-braced frames (phase 5)

    As expected, diagonal straps buckled out of plane under very low compression loads, see Fig. WP2.3

    Diagonal straps under tension, on the other hand, underwent large plastic deformation. Other

    phenomena were also detected: local buckling of the upper corner gussets and of the flanges of the

    studs. However, these local phenomena only occurred at the late stages of the loading process, so they

    did not affect the intended yielding of diagonal straps. The tests were monitored in detail and video-

    recorded. The main output of the test is the force-displacement curves. The wide hysteretic loops

    amount to large energy dissipation.

    (a) (b)Fig. WP2.3. Cyclic tests of x-braced frames: (a) buckling of compressed straps;

    (b) hysteretic force-displacement cycles

    -50000

    -40000

    -30000

    -20000

    -10000

    0

    10000

    20000

    30000

    40000

    50000

    -80 -60 -40 -20 0 20 40 60 80

    d (mm)

    F

    (N)

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    3.3.3 Discussion

    The goals of the joint testing campaign have been successfully achieved. On the one hand, it has pro-

    vided as direct output some relevant parameters of joints and useful guidelines for proper seismic de-

    sign. The knowledge and experience gained in each phase was applied in the design of the specimens of

    the next phase and also in the shear walls (see WP 3). On the other hand, joint testing has provided, af-

    ter the analysis of WP 4, with valuable information regarding the seismic suitability of the various con-

    nection devices and joint configurations, in terms of strength and ductility.

    The current campaign has focused on straps of constant width. An interesting extension would be to

    consider also straps of variable width (e.g. bone-shaped straps).

    3.4 WP3 Seismic testing of shear walls

    3.4.1 Objectives of WP 3

    In standards, guidelines and literature there is not sufficient satisfying formulas to design shear walls for

    seismic loads and therefore the testing is very important phase in seismic design. Eurocode 8 does not

    give exact values for behaviour factor q concerning the steel stud shear walls.

    Seismic loading during an earthquake is a dynamic loading by nature and therefore the test loading can

    also be dynamic. Dynamic loading can be achieved by using vibration table (shaker table), but there isalso some difficulties in testing. Mostly the houses to be tested are so big and heavy the testing cannot

    be performed and therefore only parts e.g. part of wall can be tested. Also the dynamic testing depends

    largely of the seismic signal and natural frequency of the house and therefore the results obtained can-

    not be generalized. On the other hand dynamic testing is useful when comparing test results and theo-

    retical formulation or mathematical methods. By dynamic testing (e.g. impact hammer or sine sweep

    test) can be used to measure the damping and natural frequency of the shear wall element. The dynamic

    test will also show the effects of impacts if the joints have been loosen or diagonals stretched.

    Cyclic test method is generally used method for shear walls. The pushing test only in one direction will

    not give reliable results especially when holes of screws in sheathing have been grown up or if the di-

    agonals have been stretched and in the middle position the rigidity of the wall has decreased. In earlier

    research reports there are many suggestions for cyclic signal to be used in cyclic tests and most of them

    have some advantages. One common cyclic test signal and method is introduced in the report and also

    the method to define seismic parameters (e.g. ductility, over strength, pinching and hardening). The

    same cyclic signal and methods to define parameters are developed to be suitable for all kinds of steel

    stud shear walls.

    The goals of this testing campaign are:

    To measure material properties of steel (yield stress and ultimate stress) used in studs, tracks, di-agonals and sheathings

    To select the proper seismic method and cyclic method to test shear walls To construct the testing facility to perform seismic and cyclic tests

    To design shear wall including all details like joints, stiffening system and anchoring equipments To perform a cyclic and seismic tests for shear wall elements To obtain relevant parameters of shear walls such as the initial stiffness, ductility, over strength,

    pinching and hardening by using measured cyclic and backbone curves of the elements.

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    3.4.2 Activities and results obtained

    The shear wall testing campaign was divided into 6 phases (phase 1 phase 6), described in detail in the

    corresponding technical reports and Annexes shown in Table WP3.1:

    Table WP3.1. Test series and technical reports of WP 3.

    Phase Description Technical report

    1

    Seismic test series 1

    (small scale elements)

    WP3/E005 Seismic tests of shear walls, Part 1

    2Seismic test series 2

    (small scale elements)

    WP3/E012 Seismic tests of shear walls, Part 2

    3Cyclic test series 1

    (full scale elements)

    WP3/E007 Cyclic tests of shear walls, Part 1

    4Cyclic test series 2

    (full scale elements)

    WP3/E0010 Cyclic tests of shear walls, Part 2

    5Cyclic test series 3

    (full scale elements)

    WP3/E0015 Cyclic tests of shear walls, Part 3

    6 Test summaryWP3/E0016 Test summary and guidelines for

    seismic testing

    The main results obtained are as follows:

    Seismic test series (Phases 1 and 2)

    The seismic test series consist of four steps, where the small scale shear wall element was tested on vi-

    bration table using cyclic test method, impact hammer test, sine sweep test and earthquake simulation

    test. The tests were done using extra weights at the top of the element in order to simulate the weight of

    the upper floor and roof of the house. This series was repeated and the seismic signal was increased all

    the time according to Table below. The maximum cyclic deflection was selected same as the maximum

    deflection during earthquake simulation test. The height of the small scale elements was 1.3 m and

    width 0.6 m. The seismic tests were done using plywood, gypsum board or steel plate sheathings or di-

    agonals to stiffen the wall. The seismic test facility is shown in Fig. WP3.1 (left). In the Phase 1(Seismic test series 1) the shear wall elements were broken during earthquake simulation test according

    to Zone 4 and final cyclic test were not performed. In the Phase 2 (Seismic test series 2) the shear wall

    elements were also tested, at the end, using cyclic signal until the specimens were broken.

    Table WP3.2. Test sequence in seismic testing.

    Testing sequence* Dynamic test sequence Series

    Dyn1 & Dyn2

    Step 1 Cyclic test (very small amplitude)

    Step 2 Impact hammer test

    Step 3 Sine sweep test (GR-CORE-63)

    Step 4 Earthquake simulation test according

    to Zone 1,2, 3 or 4 (GR-CORE-63)

    Step N Final cyclic test (VTT cyclic signal)

    The seismic test series were done in order to be able to measure actual natural frequency (impact ham-

    mer test and sine sweep test) and damping value (impact hammer test) of the shear wall elements. Also

    the tests were done in order to get information of the dynamic behaviour of the elements (e.g. impacts,

    loosening of the elements) and to compare theoretical calculation methods to dynamic test results. Extra

    weights installed at the top of the shear wall was selected so the natural frequency of the specimen is 7

    to 10 Hz as in real small house and the amplifying of the earthquake signal occurs with the correct natu-

    ral frequency value.

    The measured relative damping ratios support the use of 5% damping for the analysis of steel-framed

    house structures. Based on the dynamic (i.e. earthquake) testing of walls it can be concluded that the

    failure modes under dynamic loading were essentially the same as in case of cyclic loading.

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    Fig. WP3.1. Seismic testing facility (seismic testing of small scale elements) and cyclic testing facility

    (cyclic testing of full scale elements)

    Cyclic test series (Phases 3, 4 and 5)

    The cyclic test series were done using full scale shear wall elements and cyclic loading signal. The

    cyclic test facility is shown inFig. WP3.1 (right) and system allows only the movement of the wall inthe wall direction. All the tests were done using only side force at the top of the specimen and no

    vertical force or extra weights were used in the tests. The side force and horizontal and vertical

    deflections were measured in the tests. The shear wall elements were fixed to the base using anchoring

    bolts and the anchoring forces were also measured by force transducers.

    The height of the shear wall elements was 2.75 m and width 2.4 m, but also two narrow specimens the

    width of 1.2 m was used. The cyclic tests were done using plywood, gypsum board or steel plate

    sheathings or diagonals to stiffen the wall. In some tests diagonals or steel plate was used under gypsum

    board to see the effect of the two combined stiffening system. The studs and tracks were cold formed C

    (or C with lips) profiles and diagonals were perforated steel straps or threaded steel rods.

    The test results show the steel plate can be used to stiffen the shear wall and the fixing of the steel plate

    behaves inelastic and the steel plate itself is not yielding. This is acceptable because the number of

    screws is large and the breaking is starting at the corners not being the sudden phenomena. In some

    cases the anchoring bolt or the clip angle in the corner was broken before the maximum capacity of the

    wall was achieved.

    The cyclic test series provided information concerning basic design properties (ex. capacity, strength) of

    different real wall configuration. Sometimes the results have to be treated with caution because the wall

    panel failure was unexpected (ex. anchor bolt failure) and clearly pointed to fault of the design concept.

    A continuous improvement of the wall detailing has been an important outcome of the tests.

    All the results are performed in technical reports shown in Table WP3.1 and in Annex 3.

    Test summary and guidelines of testing (Phase 6)

    The test results of seismic and cyclic tests were gathered and analyzed in phase 3. The recommended

    cyclic signal developed for the cyclic tests is shown in Fig. WP3.2 (left). The signal is designed to be

    proper for various kinds of steel stud shear walls and is can be used without knowing beforehand the

    actual yield limit of the shear wall. The method to define the basic parameters (e.g. yield limit, ductility,

    over strength, pinching and hardening) is shown in Fig. WP3.2 (right) and has been developed to be

    suitable for various kinds of steel stud shear walls. The maximum shear force measured has been 77 kN

    when steel plate or diagonals under gypsum board was used. The maximum over strength factor has

    been 0.52 when gypsum board was used on both sides of element.

    The experimental results obtained in this testing campaign here stand at the basis of the calculation of q

    factor in Annex 4, as well as at the proposals for ductility and over strength values for different wall

    configurations in Annex 6.

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    -4

    4

    0

    Time

    Displacement

    -Dmax

    Dmax

    0.4xFmax

    iniK

    D

    F

    maxF

    eF

    ini0.75xK

    yF

    HxKini

    Dmax

    Fig. WP3.2. Cyclic testing signal used in the tests and method to define basic design parameter of the

    shear wall.

    3.4.3 Discussion

    The tests of WP3 have been performed according to test plan. The cyclic tests show, all the details have

    to be carefully designed in order to get the desired failure mode. In some tests the anchoring bolt or clip

    angle in corner was broken before the lowering part in deflection-load curve was achieved. The test also

    show the steel plate can be used to stiffen the shear wall, because the structure has good ductility and

    the breaking will occur gradually without sudden break. In earlier research of shear walls many differ-ent kinds of cyclic curves has suggested and many of them has some advantages in some cases. The

    cyclic signal recommended to use in the tests is selected to be quite simple and the deflection steps are

    selected to be same through the test in order to avoid pre-tests of the specimen. The number of cycles is

    selected to be quite low to avoid low cycle fatigue phenomenon. In earlier research many methods have

    been performed for the defining of seismic parameters of shear walls. The method recommended in this

    research is selected to be quite simple and suitable for many kinds (different shape) of backbone curves.

    As many researchers have pointed out, one cyclic loading method and one method to define seismic

    parameters is desirable to select in the future in order to be able to compare the test results. The research

    in the project show, the behaviour factor q is depended on the seismic parameters and therefore q factor,

    seismic parameters and design limit are related to each other.

    3.5 WP4 Analysing of the test results

    3.5.1 Objectives of WP 4

    The broad objective of WP 4 is to process the results of the testing campaign for joints (WP 2) and

    shear walls (WP 3) in order to improve the design and calculation methods (either by means of simpli-

    fied formulas or more advanced approaches). To reach that general goal, the main specific objectives

    are as follows:

    WP4.1 Analysing the results of joint tests

    Classify the various failure modes in terms of their seismic suitability (strength and ductility)

    Determine the relation between parameters in joint design (steel grade, strap thicknesses, numberand diameter of connectors,...) and failure mode Compare experimental ultimate loads of the joints to the strengths calculated by means of the Euro-

    code 3 Part 1.3 design formulas

    Identify, with the combination of experiments and FE analysis, good design rules for joints (e.g.avoid eccentricity, reinforce tracks and studs to avoid local instabilities,)

    WP4.2 Analysing the results of shear wall tests

    Develop simplified formulas for the design of shear walls Develop models for the hysteretic response of shear walls under cyclic loads Validate and fit the parameters of these models with the experimental results Use the calibrated models to perform a parametric study and obtain the q-factor of shear walls

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    3.5.2 Activities and results obtained

    The analysis of the test results is described in detail in the corresponding technical annexes:

    Description Technical report

    WP 4.1 Joint tests

    Preliminary analysis of effect of eccen-

    tricity in jointsWP4/B001 WP4: Analysing the results of joint tests

    Analysis of phase 1 lap joints with

    screws

    WP4/B004 Experimental testing of joints for seismicdesign of lightweight structures. Part I: Screwed joints

    in straps

    Analysis of phase 1 lap joints with bolts

    WP4/B005 Experimental testing of joints for seismic

    design of lightweight structures. Part II: Bolted joints in

    straps

    WP 4.2 Shear wall tests

    Finite element models of shear walls WP4/B002 Modelling of shear walls

    Hysteretic SDOF models of shear wallsWP4/B003 Hysteretic modelling of x-braced shear

    walls

    Determination of q-factor WP4/BE001 Analysis of shear walls

    The main results obtained are as follows:

    WP 4.1 Analysing the results of joint tests

    Many different phenomena have been observed in the tests: bearing, tilting, pull-out, pull-through,net section failure, punching, tearing, local buckling, For x-braced frames with straps of constant

    width, the preferred mode for seismic design is net section failure, because i) it is the most ductile

    and ii) it is the only mode that allows the dissipative action (i.e. yielding) of diagonal straps to take

    place.

    To allow the dissipative action of diagonal straps (of constant or non-constant width) or otherbracing systems (such as steel plates), it is important to avoid other failure modes such as punching

    of the connection of the lower corners to the foundation or the instability of tracks and studs (local,

    distortional or global buckling).

    The hierarchy between dissipative and non-dissipative parts of the structure can be more easilyenforced if a steel of lower grade is used for dissipative parts (e.g. diagonal straps) than for non-dissipative parts (e.g. tracks and studs).

    Self-drilling screws should be the preferred means of connection is seismic design. The main reasonis that their diameter is smaller and, consequently, there is more net section area available.

    Bearing of screwed connections between straps of constant width should be avoided (for instance,by placing enough screw columns in the joint or by connecting two steel sheets of different

    thickness).

    Bolts are less adequate than screws for the seismic design of joints, see Fig. WP4.1. If, for somespecific reason, bolts are chosen (not recommended), acceptable performance may be achieved by

    i) using only one row of bolts; ii) using washers; iii) drilling the minimum feasible hole; iv)

    choosing the steel with the largest ratio of ultimate to yield strength; v) widening the straps in the

    perforated areas, if manufacturing constraints of x-braced frames allow. When Rosette connections are used, the improved double-collar type is recommended due to its

    larger ductility.

    The Eurocode 3 Part 1.3 formulas for the calculation of the net section strength of screwed andbolted joints give acceptable results. On the contrary, the formulas for the bearing mode of failure

    significantly underpredict the ultimate load of joint. The two main drawbacks of these bearing

    formulas are that they i) do not appropriately take into account the thickness of the thicker strap,

    and ii) they are defined for the 3 mm displacement maximum load. In fact, a better agreement

    between experiments and predictions is obtained by using an equivalent thickness (mean average of

    the two straps) and using the formula proposed by Eurocode for straps thicker than 1 mm for all the

    straps.

    Test set-ups should be carefully designed to ensure a correct grip of the test specimens and to avoid

    spurious failure modes. The joint behaviour is barely affected by a cyclic loading-unloading-reloading process. The modes

    of failure, force-displacement curves, ultimate loads, stiffness, do not change. For this reason, a

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    seismic joint testing campaign may consist largely of monotonic tests, with only a very small

    number of loading-unloading tests (for verification purposes).

    The level of geometrical detail provided by finite element model is a valuable tool for the design ofjoints.

    WP 4.2 Analysing the results of shear wall tests

    Unsheathed x-braced or sheathed (e.g. with steel sheets) shear walls are a very effective means of

    dissipating seismic energy in a controlled manner, provided that joints and members (studs andtracks) are strong enough to allow yielding of straps or sheets.

    The global seismic response of shear walls can be efficiently modelled by means of single-degree-of-freedom (SDOF) hysteretic models, which lead to results similar to that of a nonlinear finite

    element model at a much lower computational cost.

    Two SDOF hysteretic models for shear walls have been developed in the framework of this project:i) a bilinear slip model for x-braced frames, with extreme pinching caused by behaviour of diagonal

    straps (negligible load-carrying capacity under compression, yielding under tension) and ii) a

    multilinear model with additional features (mainly variable amount of pinching and over-strength).

    The parameters of the multilinear model can be calibrated in a straightforward manner, a a goodagreement between numerical and experimental cycles is obtained for both x-braced and sheathed

    shear walls, see Fig. WP4.2.

    The multilinear model has been used to carry out an extensive parametrical analysis, covering awide range of natural and artificial earthquake records, period of vibration, ductility, pinching and

    over-strength.

    On the basis of this parametrical analysis, a new formulation of the q-factor of shear walls isdeveloped in this project. The q-factor is obtained as

    ep p oq q c c?

    where qep is the base value of the q-factor given by Eurocode 8, gp is a correction factor due to

    pinching and go is a correction factor due to over-strength. This is a significant improvement,

    because the EC 8 base value qep is designed for elastic-perfectly-plastic cycles (i.e. no pinching and

    no over-strength).

    A design method for flat thin-steel sheathed walls is proposed. Whole buildings can be modelled by combining the multilinear SDOF model for each shear wall. In

    this manner, the hysteretic response of the whole building, including torsional effects caused by

    asymmetry, can be predicted.

    0

    0,2

    0,4

    0,6

    0,8

    1

    1,2

    1,4

    0 20000 40000 60000 80000

    Put (N)

    r fT+NSF

    T+B+PO

    (a) (b)Fig. WP4.1 Strength ductility ratio vs. ultimate load for joints between straps of constant width:

    (a) screws; (b) bolts. Only screwed joints with NSF mode are above 1.

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    (a) (b)Fig. WP4.2. Fitting of the multilinear model for cyclic tests of shear walls: (a) x-braced; (b)

    sheathed

    3.5.3 Discussion

    The goals of this WP have been successfully achieved. In close interaction with WP 2 (joint testing) and

    WP 3 (shear wall testing), the analysis carried out in this WP has led to better designs and calculation

    methods. One important contribution of this project is a new formulation for the q-factor of shear walls.

    The current formulas in Eurocode 8 do not take into account pinching and over-strength, two salient

    features of the hysteretic loops of lightweight steel shear walls.

    The analysis of screwed joints have highlighted the limitations of Eurocode 3 Part 1.3 formulas for

    bearing resistance, especially for two members of different thickness. A preliminary proposal to im-

    prove these formulas is made in this project. Further experimental and analytical work would be neces-

    sary to make a more detailed proposal.

    3.6 WP5 Recommendations for practical design

    3.6.1 Objectives of WP5

    The development, using the results of work packages 1 to 4, of guidance for the design of light gauge

    steel buildings in earthquake areas. The task included: (i) the proposal of a design methodology and

    associated design equations for use in manual design of light gauge steel buildings in such a way that

    (ii) it is suitable for adoption by code drafters to facilitate future coverage of seismic design of light

    gauge steel buildings in Standards, particularly the Eurocodes (EN 1998-1).

    The method had to contain:

    Guidance on analysis methods (including FE analysis) of light gauge steel buildings subjectedto earthquake loading.

    Guidance on detailing based on the lessons learnt from the test programme (WP 3), distilledinto recommendations for the detailing of joints, lateral bracing, shear walls and other details.

    3.6.2. Activities and obtained results

    The results obtained in WP5 are synthesised in the document Design Guide for Seismic Design of

    Light-Gauge Steel Framed Buildings (PR-377/Guide), and is presented in shorter form in Annex 6 of

    this report. The structure of the work undertaken essentially follows the stated goals of WP5. The ac-tivities were divided five phases, and the obtained results also reflect this division:

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    Phase Description Technical report

    1 Study of existing provisions of

    EN1998-1

    PR-377 Design Guide for Seismic Design of Light-Gauge

    Steel Framed Buildings

    2 Improvements for existing

    code(EN1998-1) provisions

    PR-377 Design Guide for Seismic Design of Light-Gauge

    Steel Framed Buildings

    PR377/WP4/BE001 Analysis of shear walls

    3 Recommendation for design

    and detailing

    PR-377/Guide Design Guide for Seismic Design of Light-

    Gauge Steel Framed Buildings

    5 Design example I PR-377/Guide Design Guide for Seismic Design of Light-

    Gauge Steel Framed Buildings

    6 Design example II (Only in the

    Design Guide)

    PR-377/Guide Design Guide for Seismic Design of Light-

    Gauge Steel Framed Buildings

    The main results are as follows:

    Study of existing provisions of EN1998-1

    Even if general provisions from EN 1998-1 can be applied, many of the rules stated are not specific

    enough to be directly used for the design of light-gauge steel houses.

    One particularity is that light-gauge steel profiles are Class 4 sections. As such EN 1998-1 (clause6.5.3) recommends such elements not to be used in earthquake resistant buildings ifthe dissipative ele-

    ments are to be formed in compression or bending. The dissipative elements in light-gauge steel houses

    are formed in tension (X braced walls) or in connections (sheathed walls).

    A second particularity of light-gauge steel structures is that the first period of vibration (T1) of such

    structures is relatively low (under the corner period TC of the design spectrum). In this range of periods

    the non-linear behaviour of the structures strongly depends on the period. This is incorporated in section

    4.3.4 of EN 1998-1 when calculating the non-linear displacement (d s), but it is not generally used in the

    code elsewhere. It became obvious that optimally, at every level of the design, the period of vibration

    should be taken into account.

    Improvements for existing code(EN 1998-1) provisions

    There are two points where, based on the results of the project, proposals are made to EN 1988-1.Firstly it is proposed that it is more strongly emphasised in the code that Class 4 profiles can, in certain

    conditions, be used in earthquake zones. Namely, structures resisting earthquake loads by shear walls

    have satisfactory non-linear behaviour and ductility in order to be accepted. Secondly, it is proposed

    that for light-gauge steel houses (and generally for structures with low period of vibration), the q factor

    in the design takes into account the effect of the first period and of the hysteretic properties of the shear

    walls. In this sense it is proposed that the q factor is evaluated by:

    OPepqq cc ? Eq. WP5.1Where gP a correction factor due to pinching (see Annex 6 ch. 6.4)

    gO a correction factor due to overstrength (see Annex 6 ch. 6.4)

    qep is the base value of q:

    @

    /-?

    C;

    ;)1(1

    TT

    TTTT

    qC

    Cep

    o

    Eq. WP5.2

    Where T fundamental period of vibration of the structure

    ductility of the structure

    TC corner period

    The above formulation is consistent with the existing proposals of the code, but it extends to the possi-

    bility that overstrength and pinching characteristics of the hysteretic behaviour of the walls are taken

    into account.

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    Recommendation for design and detailing

    Based on the extensive experimental program a proposal is made concerning the hysteretic characteris-

    tics to be used in the design of different shear typologies (Table WP5.1). The parameters to be taken into account are: ductility (=Dp/De), structural overstrength factor (OvS=Fy/Fd) and pinching factor (P=

    1Fp/Fd, see. Fig. WP5.1).

    Table WP5.1. Recommended characteristics for shear walls

    Shear wall skeleton - Stiffening system P OvS H

    Thin walled C profiles Stiffening: Thin steel plate 1 1.2 3 0

    Thin walled C profiles Stiffening: Diagonal stiffening 1 1 4 0

    Thin walled C profiles Stiffening: Thin steel plate combined with gyp-

    sum board

    0.95 1.4 3 0.25

    Thin walled C profiles Stiffening: Wood based panels 0.95 1.5 3 0.35

    pDeDD

    hK

    pF

    dF

    K

    y

    FF

    Fig. WP5.1. Cases of hysteretic models for analysis

    Concerning detailing of light-gauge steel structures required checks are given in order to enforce a hier-

    archy of dissipative and non-dissipative parts. The hierarchy depends on the typology of the shear-wall

    sheathing and the most advantageous (i.e. ductile) failure mode should be enforced.

    The rules of the guide intend to enforce plastic deformations in: (i) the diagonal strap (X-braced walls)

    or in (ii) sheathing to skeleton connections (sheathed walls). All other failure modes are deemed to be

    undesirable including: (i) compressive failure of studs, (ii) bending failure of studs and tracks, (iii) fail-

    ure of other connection elements that seathing-to-skeleton connections. Overstrength (usually 20%) is

    imposed on the load capacity corresponding to non-desired failure modes. In case of connections usu-

    ally bearing failure is enforced over any other failure mode. One exception is the case of constant cross

    section straps used in X braced walls, when net section failure is imposed for end connections of the

    braces in order to ensure sufficient ductility for the walls.

    As it was a special field of interest, an analytical method was developed in order to predict the loadbearing capacity and the rigidity of wall panels sheathed with flat steel plates. The method is based on

    the equivalency of steel-plate sheathing with a series of steel straps developing yielding obliquely in the

    direction of the principal stress (see. Annex 6. Ch. 6.7.7).

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    Design example I

    In this calculation the design procedure for a usual house structure is exemplified (Fig. WP5.2).

    Fig. WP5.2. Plan, section and axonometric view of example house

    The design checks are made, on one hand using the simplified method recommended as a result of this

    project, which incorporates elements from EN 1998-1 but also the special detailing rules and calculation

    improvements proposed in the project. In the example special care has been taken to enforce the desired

    hierarchy of elements and to exemplify all checks that are needed for the proper design of the building.

    On the other hand advanced design method, using specially developed hysteretic models, was used to

    prove the validity of the simplified design and to present a more advanced alternative to the simple de-

    sign method.

    The conclusion of the design example is that the presented two storey structure can withstand an earth-quake of large peak ground acceleration (PGA=0.32g).

    Design example II (available only in Technical report: PR-377/Guide Design Guide for Seismic De-

    sign of Light-Gauge Steel Framed Buildings)

    The second design example (Fig. WP5.3) proved that one storey light-gauge buildings located in rela-

    tively strong wind areas (vref=22m/s) do not require special attention from the point of view of earth-

    quake design if: (i) they are in weak earthquake zones (PGA0.08g), (ii) they have a regular configura-

    tion, (iii) they are properly designed for wind loads and (iv) the stiffening system used for wind is prop-

    erly detailed to ensure ductile behaviour of the building. This result is encouraging since in many loca-

    tions in Europe the earthquake loads are small.

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    Fig. WP5.3. Dimensions of the building (6 walls in y-direction and 4 in x-direction)

    3.6.3 Discussion

    Experimental and analytical results generated by the research project were combined with existing pre-

    scriptions in EN1998-1 in order to develop more specific and more advanced design rules for light-

    gauge steel structures in earthquake regions. The design method was presented in a format compatiblewith EN1998-1 (and many times linked with existing prescriptions) but specific/supplementary rules

    were emphasised.

    The design method proposals were used in two calculation examples, which proved that (i) light-gauge

    steel house structures of up to two storeys can be designed to fulfil conditions in very strong earthquake

    zones and that (ii) in weak earthquake zones wind design is sufficient to in case of, properly configured,

    light one-storey structures.

    4. Conclusions

    The objective of the project was to develop guidance for codified design rules, guidance on analysismethods and guidance on detailing for seismic design of light-gauge steel framed buildings. In current

    European seismic design standards, there are no specific rules available for light-gauge steel buildings.

    The scope of the project was limited to one or two storey buildings with load bearing stud walls made

    of cold-formed steel profiles. In LGS-buildings shear walls are the elements which have to provide

    sufficient ductility before failure during seismic actions. Typical bracing methods that are also covered

    in this research are X-bracings with diagonal steel straps, sheeting of plane steel sheets or gypsum or

    wood based wallboards. Main strategy in the shear wall design of LGS-buildings is to design the

    bracing system as dissipative elements and design studs and tracks and other load bearing elements to

    behave elastically with adequate overstrength avoiding local bucklings.

    The project was divided into a number of Work Packages that involved laboratory tests and numerical

    analyses in order to develop design methods and practical applications for LGS-houses in seismic areas.

    In WP1, review to current design standards was complied. WP2 consisted of a comprehensive

    connection test series for steel plate connections used in diagonal X-braces and test series for sub-

    assemblies for different shear wall corner configurations. Test results were utilised in the design of

    X

    Y

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    shear wall details in full scale tests in WP3. Test results also indicated that the current design formula in

    prEN1993-1-3 for bearing failure of screw connections underestimates considerable the capacity.

    In WP3, several shear wall tests were performed by using different bracing methods in order to find out

    hysteretic behaviour and main parameters such as resistance, ductility, pinching and overstrength

    needed in seismic design. During the test program, several improvements and new innovations were

    made to the shear wall configurations and details.

    One main goal of the project was to determine the q-factor for LGS-structures. q-factor makes itpossible to apply elastic design method for seismic actions. This term takes into account non-linear

    behaviour of the structure. Two hysteretic modeling alternatives for shear walls have been developed in

    the WP4. These models were used in parametric study resulting analytical formulas to calculate the q-

    factor as a function of above mentioned parameters resulted from shear wall tests and also the period of

    vibration.

    Finally in WP5, design recommendations for seismic design of light-gauge steel framed buildings were

    given for practical design. It is provided that it is possible to design dissipative systems with thin-walled

    structures belonging to cross-section class 4. In the design example, it was shown that LGS-house can

    withstand even severe earthquakes without failure.

    5. Future works

    The restrictions of this research are mainly based on the lack of experimental experience of the whole

    building behaviour during the earthquake loading. Its very costly to test whole buildings under seismic

    loadings, but information of that kind of behaviour would be in the interest. Non-structural elements

    may have influence on the seismic response of the building. Current understanding is that by neglecting

    the effect of cladding leads design on the safe side. However, it would be interesting to study in detail

    the performance of these non-structural elements.

    The increase of asymmetry of the building causes a decrease of the q-factor. It would be very interest-

    ing to quantify the dependency of the q-factor carrying out an extensive analysis, with several earth-

    quakes, different configurations of shear walls or eccentricity in two main horizontal directions.

    Plain steel sheathed structures showed good potential in this research. Some extra testing with thicker

    plate thicknesses could be useful. Further experimental and analytical work would also be necessary in

    order to make a more detailed proposal to the screw connection static strength in the case of different

    thicknesses, because it seems that the current EN1993-1-3 standard gives very conservative results.

    Because light-weight steel structures might be quite new solutions in many countries on seismic areas,

    its quite clear that dissemination activities are needed in order to convince the designers of benefits of

    LGS-structures.

    6. Assessment of exploitation and impact of the research results6.1 Technical and economic potential for the use of results

    New, proposed seismic design methods for light-gauge steel buildings open the way to design LGS-

    structures effectively by using simplified elastic design, but still utilising non-linear and ductile behav-

    iour of the structure. Analytical calculation methods are given to calculate q-factor of the buildings with

    X-braced or steel sheet sheathed shear walls. Recommendations to 1) carry out cyclic shear wall tests

    and 2) define parameters from the test results for determining q-factor, help in the development of new

    types of shear walls.

    An improved Rosette joining system with increased ductility and load capacity has been developed dur-

    ing the project to meet high ductility requirements in seismic regions. (i.e. double collar joint). This newjoint can be used in LGS frames for several purposes; in the diagonals of X-braced walls, frame-

    integrated stud diagonals, open-web headers and generally enabling better wall panels with more value-

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    added in them. A new family of roof trusses has become feasible as well as longer span open web joists.

    A modular space frame structure has also been developed based on the research results.

    An U.S. patent has been applied for for the new Rosette Joint and will be followed with PCT process

    and national patents.

    Structural detailing for Ruukki, Rosette and Teccon products have been developed to ensure ductile be-

    havior of frames. The whole lateral stiffening system of a LGS building has been considered, the mostimportant details are:

    -details of X-braced and steel sheet sheathed shear walls

    -anchoring of the shear wall

    -joining of shear wall to the intermediate floor and the roof

    Steel sheet sheathed wall panels have been used earlier in Ruukkis structures for other purposes, but

    now the load bearing capacity can be utilised. Furthermore, the details developed here for seismic ac-

    tions can be utilised also for other loading cases such as wind loadings.

    A deeper knowledge has been achieved concerning to proper seismic design of LGS-buildings by all

    industrial partners. Rosette Systems is now better prepared to assist its customers (i.e. LGS frame fabri-

    cators) in the production of more competitive and structurally safe solutions to earthquake prone re-

    gions. Ruukki and Teccon as LGS frame fabricators are able to provide their customers cost effective

    LGS-solutions from low to severe seismic areas.

    6.2 List of publications

    Journal papers

    Pastor N. and Rodrguez-Ferran A., Hysteretic modelling of x-braced shear walls. Thin-Walled Struc-

    tures43 (10) 1567-1588.(2005)

    Pastor N. and Rodrguez-Ferran A Hysteretic modelling of lightweight steel framed buildings, sub-

    mitted toEarthquake Engineering and Structural Dynamics (2006).

    Casafont M., Arnedo A., Roure, F. & Rodrguez-Ferran, A. Experimental testing of joints for seismicdesign of lightweight structures. Part 1: screwed joints in straps. Thin-Walled Structures, in press.

    (2006).

    Casafont M., Arnedo A., Roure, F. & Rodrguez-Ferran, A. Experimental testing of joints for seismic

    design of lightweight structures. Part 2: bolted joints in straps submitted to Thin-Walled Structures

    (2006).

    Conference papers

    Pastor N. and Rodrguez-Ferran A, Hysteretic behaviour of light gauge steel framed buildings, pre-

    sented in Congreso de Mtodos Numricos en Ingeniera. Granada, Spain, on July 4-7 2005.

    Workshops

    Pastor N. and Rodrguez-Ferran A., Modelling of Light Gauge Steel Structures, 2nd

    Workshop in Ap-

    plied Science and Engineering. Vall de Nria, Spain, on January 20-22. 2003

    Pastor N. and Rodrguez-Ferran A., Hysteretic behaviour of x-braced shear walls, 3rd

    Workshop in

    Applied Science and Engineering. Vall de Nria, Spain, on January 19-21. 2004

    Pastor N. and Rodrguez-Ferran A., Hysteretic behaviour of light gauge steel framed buildings, 4th

    Workshop in Applied Science and Engineering (NMASE 05). Vall de Nria, Spain, on 18-21.Jan. 2004.

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    6.3 List of technical reports produced in the project

    PR377/WP1/B001 Modelling of light-gauge structures (2003)

    PR377/WP4/B002 Modelling of shear walls (2004)

    PR377/WP4/B003 Hysteretic modelling of X-braced frames (2004)

    PR377/WP4/B004 Experimental testing of joints for seismic design of lightweight structures - Part I:

    Screwed joints in straps (2005)

    PR377/WP4/B005 Experimental testing of joints for seismic design of lightweight structures - PartII: Bolted joints in straps (2005)

    PR377/WP2/BD001 Design of the joint testing campaign (2003)

    PR377/WP2/BD002 Joint testing: phases 1 and 2 (2004)

    PR377/WP2/BD003 Joint testing: phases 3 and 4, Part I Finnish specimens (2004)

    PR377/WP2/BD004 Joint testing: phases 3 and 4, Part II Spanish specimens (2005)

    PR377/WP2/BD005 Joint testing: phase 5 (2005)

    PR377/WP1/E001 Bibliographic review of scientific journals and standards of light gauge steel con-

    structions (2002)

    PR377/WP3/E005 Seismic tests of shear walls Part I (2004)

    PR377/WP3/E007 Cyclic tests of shear walls Part I (2004)

    PR377/WP3/E009 Test results of different Rosette Joints (2004)

    PR377/WP3/E010 Cyclic tests of shear walls Part II (2005)PR377/WP3/E015 Cyclic tests of shear walls Part III (2005)

    PR377/WP3/E016 Test summary and guidelines for seismic testing (2005)

    PR377/WP3/E018 Design formulas for steel sheeted shear walls (2005)

    PR377/WP3/BE001 Analysis of shear walls (2005)

    PR377/WP1/F001 Design of Structures (2003)

    PR/377/Guide Design Guide for seismic design of light-gauge steel framed buildings

    7. List of most relevant figures and tables

    (The first number after Fig. or Table indicates to the corresponding Annex number)

    WP1

    Fig.1.1 (a) Steel skeleton of light-weight steel house (b) stud and track profile with thermal perforation

    Fig.1.2 Horizontal design response spectrum for simplified analysis

    WP 2

    Fig. 2.1 Screwed lap joint between straps

    Table 2.2 Results of monotonic tests on screw joints

    Table 2.8 Results of Rosette joints

    Table 2.9 Results of corner tests

    WP 3Fig.3.2 Vibration table and shear wall element with weights at the top

    Fig.3.24 Interpretation used in this study

    Fig. 3.27 Test specimens of cyclic test series Cyc 2

    Table 3.5 Dynamic test results for specimen Dyn1-2 (plywood sheathing)

    Table 3.6 Natural frequencies and damping values of test series Dyn1-3 (gypsum board sheeting)

    Table 3.8 Maximum and minimum values of sensors in seismic test series Dyn2 (final cycle tests)

    Table 3.12 Elastic- yield- and ultimate state strength in cyclic tests of Cyc1

    Table 3.14 Elastic- yield- and ultimate state strength in cyclic tests of Cyc2

    Table 3.16 Elastic- yield- and ultimate state strength in cyclic tests of Cyc3.

    WP 4Fig. 2.12 Ratio of experimental over predicted ultimate strengths, Put/Pud, for screwed joints between

    straps of different thickness (t1

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    Fig. 2.39 FE analysis of bottom corner joints

    Fig. 4.26 Scheme of proposed design procedure for shear walls

    WP 5

    Fig. 6.1 Design procedure of typical shear walls

    Fig. 6.4 Lower and upper corner details of X-braced shear walls

    Fig. 6.8 Intermediate floor to shear wall joint

    8. List of references

    WP1

    EN1998-1 (2004), Eurocode 8, Design of structures for earthquake resistance. Part 1: General rules,

    seismic actions and rules for buildings.

    Salenikovich A.J. (2000) The Racking Performance of Light-Frame Shear walls, Doctor of Philosophy

    Dissertation, Virginia Polytechnic Institute and State University, August 8, 2000

    Fiorono L. (2003) Seismic Behaviour of Sheathed Cold-Formed Steel Stud Shear Walls: An

    Experimental Investigation, PhD Thesis, Universit degli Studi di Napoli Federico II, 2003

    Kawai Y., Kanno R., Uno N., Sakumoto Y. (1999) Seismic resistance and design of steel-framed

    houses, Nippon Steel Technical Report No. 79 January 1999

    Fulop L.A. & Dubina D. (2004) Performance of wall-stud cold-formed shear panels under monotonic

    and cyclic loading. Part I: Experimental research, Thin-Walled Structures, Vol. 42, No. 2., 321.

    WP2

    Casafont M., Arnedo A., Roure, F. & Rodrguez-Ferran, A. (2006). Experimental testing of joints for

    seismic design of lightweight structures. Part 1:screwed joints in straps. Thin-Walled Structures, in

    press.

    Casafont M, Arnedo A., Roure, F. & Rodrguez-Ferran, A.(2006). Experimental testing of joints forseismic design of lightweight structures. Part 2: bolted joints in straps. Thin-Walled Structures, submit-

    ted.

    WP3

    Cola/UCI (2001) Report of a testing program of light-framed walls with wood-sheathed shear panels,

    Light frame test committee A subcommittee of the research committee. December 2001.

    K. Gatto, C.M. Uang(2003) Effects of loading protocol on the cyclic response of woodframe shear

    walls, Journal of structural engineering, Oct. 2003, p. 1384-1392

    GR-63-CORE (2002), Telecordia Technologies. NEBS requirements: Physical protection. Issue 2.

    WP 4

    Pastor N & Rodrguez-Ferran, A. (2005). Hysteretic modelling of x-braced frames. Thin-Walled Struc-

    tures, 43(10), 1567-1588.

    Pastor N & Rodrguez-Ferran, A. (2006). Hysteretic modelling of lightweight steel framed buildings.

    Earthquake Engineering and Structural Dynamics, submitted.

    Mostaghel N. (1999) Analytical Description of Pinching, Degrading Hysteretic Systems, Journal of

    Engineering Mechanics, Volume 125, Number (2).

    WP 5

    EN 1998:2004 (E), Eurocode 8: Design of structures for earthquake resistance. Part 1: General rules,

    seismic actions and rules for buildings, 2004

    EN 1993-1-3, Eurocode 3: Design of steel structures, Part 1-3: General rules. Supplementary rules for

    cold-formed members and sheeting, 04 July 2004

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    ANNEX 1:

    Available design methods and new technologies for seismic design(WP1)

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    TABLE OF CONTENTS

    1. ANNEX 1 - Available design methods and new technologies for seismic design ......................... 291.1. Historical development of steel-framed houses ..................................................................... 29

    1.2. Structural solutions in steel framed houses............................................................................ 29

    1.3. Main characteristics that influence earthquake behaviour ..................................................... 30

    1.4. General concepts of earthquake design.................................................................................. 31

    1.5. Standards and research overview........................................................................................... 31

    1.5.1. Eurocode 8 (EN1998-1 2004) ....................................................................................... 31

    1.5.2. GR-63-CORE and ANSI T1.329-1995 ......................................................................... 32

    1.5.3. International Building Code, IBC-2003 (2004)............................................................. 34

    1.5.4. Uniform Building code UBC (1997)............................................................................. 36

    1.6. Research overview ................................................................................................................. 37

    1.6.1. Zhao (2002): Cyclic Performance of Cold-formed Steel Stud Shear Walls.................. 37

    1.6.2. COLA-UCI (2001): Report of a Testing Program of Light-Framed Walls with Wood-

    Sheathed Shear Panels ................................................................................................... 38

    1.6.3. Bredel (2003): Performance Capabilities of Light-Frame Shear Walls Sheathed with

    Long OSB Panels........................................................................................................... 38

    1.6.4. Salenikovich (2000): The Racking Performance of Light-Frame Shear Walls............. 39

    1.6.5. Fiorino (2003): Seismic Behaviour of Sheathed Cold-Formed Steel Stud Shear Walls39

    1.6.6. Kawai et al. (1999): Seismic Resistance and Design of Steel-Framed Houses ............ 40

    1.6.7. Cecotti (2002): Validation of seismic design parameters for wood-frame shear-wall

    systems........................................................................................................................... 41

    1.6.8. Serrette (2002) Design Values for Vertical and Horizontal Lateral Load Systems ...... 41

    1.6.9. Fulop & Dubina (2004): Performance of wall-stud cold-formed shear panels under

    monotonic and cyclic loading......................................................................................................... 42

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    1. ANNEX 1 - Available design methods and new technologies for seismicdesign

    1.1. Histor ical development of steel-framed houses

    House structures based on skeleton structure covered with sheeting and finishing material were based

    first on wood elements.

    Later, as steel became largely available, the same concept of skeleton+sheeting and finishing has been

    applied but using steel instead of wood skeleton. However, traditional hot rolled steel profiles were not

    the best choice for the manufacturing of the skeleton. The diversity of shape and size of houses made it

    impossible to properly adapt the few available hot-rolled steel profiles to the diversified applications in

    a house. Hence, early steel framed house solutions remained at the stage of prototypes or isolated pre-

    fabrication attempts, but never acquired a significant share on the market.

    An important breakthrough was the introduction to the market of cold-formed steel profiles. The most

    important advantage these profiles brought was adaptability of the shape to different applications. The

    range of few available hot-rolled profiles diversified. The development of connection techniques whichrequired lighter equipment in order to replace traditional welds has helped the market acceptance of

    houses with cold-formed steel skeleton.

    The houses using cold-formed profiles in the skeleton utilise the concept of load bearing wall studs

    which imply the use if a network, of relatively small, load bearing elements instead of a few strong

    columns and beams.

    In the early stage cold-formed steel framed houses have gained significant market share on the markets

    where these two pre-requisites existed, namely in Japan, USA, Australia, UK and Northern European

    countries. In a later stage, companies have started to expand to other regions where the introduction of

    cold-formed steel houses was done via conscientious expansion strategy.

    1.2. Structur al solutions in steel framed houses

    The typical structural solution for cold-formed steel houses is based on the concept of many, relatively

    thin, load bearing beams and studs. The entire structure is a spatial mesh of cold-formed steel profiles

    (Fig. 1.1.a). Wall studs are usually made of galvanised steel of 12 mm thickness. In Nordic countries,

    the web of wall stud is usually perforated in order to minimise cold bridge effect on the wall structure

    (Fig. 1.1.b). The connection technique is most commonly based on self drilling screws, but other

    systems like clinching, Rosette joining and gluing is also used. In the structure, vertical forces are

    transmitted to beams and roof rafters, which then connect to the wall studs and transmit the forces

    through the studs to the foundation. It is usual that beams and roof rafters are placed to the same

    intervals as steel studs, so that transmission of the forces is by direct contact (i.e. avoiding if possible

    bending effects). Typical steel skeleton of light-weight steel house is shown inFig. 1.1.a.

    (a) (b)

    Fig. 1.1. (a) Steel skeleton of light-weight steel house (b) stud and track profile with thermal perforation

    In transmission of horizontal forces (i.e. wind and earthquake) the primary role is played by the

    horizontal planes (i.e. floor plane, or roof plane). In these horizontal planes a diaphragm behaviour has

    to be imposed (ex. floors have to be stiff in their own plane) in order to ensure uniform distribution of

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    forces in the supporting walls. By good diaphragm behaviour it is assured that the plane of the floor

    displaces and rotates as a solid plane element during horizontal loading conditions.

    In LWS-houses, due to the reduced mass of the structure, diaphragm behaviour can be ensured by light

    elements like: (i) corrugated sheathing connected to the floor joists or (ii) wood based plates connected

    to floor joists. Providing over concreting of the floors would greatly enhance the diaphragm behaviour

    of the floor. However, overall this method is not advantageous because it introduces large masses intothe otherwise light structure.

    The next important elements are the wall-panels themselves which are transmitting the horizontal forces

    from the plane of the upper floor towards the foundations. From the horizontal loads the walls are

    loaded preponderantly in shear. Normally there is also some axial force present in the walls due to the

    vertical loads.

    Shear walls are combination of a steel skeleton, made of C and U cold-formed profiles, and some type

    of sheathing which covers one or both sides of the skeleton. The connections between cold-formed

    profiles are usually made with self-drilling screws and their behaviour is close to hinged. Hence, the

    skeleton without the sheathing is not capable to transmit horizontal forces. The transmitting of

    horizontal forces takes place trough the interaction of the skeleton with the sheathing. Therefore, formthe point of view of lateral load bearing capacity both the type of the skeleton and the type and

    distribution of the sheathing-to-skeleton connections is critical.

    Shear walls can be constructed to resist horizontal loads in many alternative ways using: (i) X-bracing

    system with flat straps; (ii) X-bracing system with diagonal rods; (iii) stiffening with flat of corrugated

    steel sheaths; (iv) stiffening with gypsum board or (v) combinations of the previous.

    Once the strength and stiffness of the shear walls is ensured by the use of sheathings, it becomes

    important to properly connect the wall to the foundation. This is achieved by anchoring devices in the

    corners of the wall and intermediate fixings in midfield. Horizontal loads generate shear forces in these

    connections, but also uplift forces in the corners. In order to transmit both types of forces, the design of

    anchoring devices requires special attention.

    1.3. Main char acteristics that influence earthquake behaviour

    One exceptional loading condition of cold-formed steel houses is the earthquake loading situation. This

    loading is different form other actions because: (i) it is an action that is very rarely applied but when it

    appears (ii) its intensity can be very high and largely unpredictable.

    In order to ensure good earthquake behaviour for a structure some fundamental rules concerning the

    structure should be respected: (i) the structure has to have regularity of stiffness and geometry both in

    plan and elevation, (ii) horizontal planes have to ensure diaphragm behaviour, (iii) the structure has to

    have redundancy and (iv) eventual failure has to be as ductile as possible.

    While the regularity (and to some extent the redundancy) condition have to be fulfilled by properlyarranging the shape of the building, the other conditions are related to the choice of the structural

    system and the detailing used. Therefore, proper choice of structural elements and of connection details

    has to ensure good overall ductility for the structure.

    The problematic of horizontal diaphragm action is usually deemed to be fulfilled if certain

    constructional details are met. If floor openings are of normal size and the structure of the floor is build

    of materials with sufficient in plane rigidity (i.e. OSB plate, plywood plate, corrugated sheath, concrete)

    connected to the structure with a normal screw schedule (i.e. self drilling screw spacing recommended

    by the supplier of the sheathing plate) it is normally supposed that floor diaphragm action is sufficient

    to satisfy in earthquake conditions. If more throughout analysis is to be carried out than existing

    standards (ex. ECCS-88 1995) can be used.

    In the final stage the failure of the structure is produced by the walls. Therefore, the walls (or as they

    are called wall-panels) are the elements which have to provide sufficient ductility before failure. Also,

    the sequence of failure of the walls have to ensure overall ductile and redundant behaviour of the

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    structure. For these reasons, the study of the behaviour of wall panels is often in the focus of research

    concerning earthquake behaviour of steel-framed houses.

    1.4. General concepts of ear thquake design

    In the basic case of simple and regular structures the effect of the seismic action, and other effects of

    other actions included in the seismic design, can be determined using linear-elastic analysis of the

    structure. Because the horizontal force (Fb) generated by the earthquake is inertial in nature, it can be

    generically expressed as:

    mSF db ? 1.1

    Where Sd factor expressing the effect of the mass which is usually accepted to be a

    function of the period of vibration of the structure T1, (in a very simplified approach it is

    the ordinate of the design spectrum corresponding to the period of the building T1)

    m the mass of the building (i.e. including mass due to the fraction of variable

    load) above the foundation or above the rigid basement

    So it can be observed immediately that the loading side is influenced by a property of the structure,

    namely by its rigidity.

    An other key element in calculating the seismic load (Sd) according to all modern standards is that, if

    elastic design is adopted, than the elastic earthquake load depends on the non-linear behaviour of the

    structure (i.e. practically on its ductility). This relationship is incorporated in the codes by the so called

    q-factor that is used for reduction of forces obtained from linear analysis. The ability of the structure to

    withstand plastic deformations without loosing load bearing capacity is of high significance for

    earthquake reliability. If structure is fully elastic until failure then q=1, otherwise q>1.

    There are three important characteristics which define the non-linear behaviour of light-gauge steel

    structures and the value of the corresponding q factor:

    Cold-formed steel profiles belong to Class 4 cross section according to the Eurocode 3 (EN 1993-1-1 2005) classification. According to the Ec3 this leads to reduced ductility of the structures

    using such profiles. However, what is not mentioned is that the ductility also depends on the

    failure mode of the member. It is true that Class 4 members can not sustain plastic deformation in

    bending or compression, but they can by plastic bearing deformations in the connections (ex. in

    case of steel or wood plate sheathed walls) or by tension yielding (ex. in case of cross-braced

    walls). Therefore the ductility of shear walls made of cold-formed steel members is significant

    (i.e. 4-5).

    The non-linear behaviour of the walls is often characterised by significant strength reserve. Aftersome non-linearity is activated in the wall (ex. some connections start to deform beyond the

    elastic limit) the structure is capable to redistribute the loads and resist further increase of theload. The overstrength can be (i.e. especially in walls sheathed with rigid plates) as large as 50-

    60%. The overstrength has a beneficial effect on the q factor.

    Steel houses are light structures. The reduced mass often leads to natural periods of vibrationbeing as low as 0.15-0.2s. In this range of periods the effect of structural ductility is not, but the

    effect of overstrength is significant. The combined effect of ductility, overstrength and the natural

    period of vibration determine the q factor of the structures.

    1.5. Standar ds and research overview

    1.5.1. Eurocode 8 (EN1998-1 2004)

    In Eurocode 8 (EN1998-1 2004) no-collapse requirement is defined so that the structure shall be

    designed and constructed to withstand seismic actions without local or global collapse and must retain

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    its structural integrity and a residual load bearing capacity after seismic action. Usually the reference

    probability of exceedence is 10% in 50 years or the reference return period is 475 years.

    Damage limitation requirement means that the structure shall withstand a