ec3 design
TRANSCRIPT
1
Design of a steel frame according to Eurocode –SAP2000 Training Program
CSI Portugal & Spain
2CSI Portugal - Design of a Steel Frame
3. Portal frames
1. Architectural and environmental conditions
2. Architecture
7. Actions
4. Roof and walls sheeting
5. Purlins
8. Actions combinations
6. Bracing systems
Contents of Frame Design Example
Contents
9. Steel sheeting design
3CSI Portugal - Design of a Steel Frame
10. Modeling the structure
Contents of Frame Design Example
15. Members automatic ULS check
14. Members buckling lengths
11. Load assignments
16. Members automatic design
12. Frame buckling analyses
Contents (cont.)
13. Equivalent imperfection forces
17. SLS check
4CSI Portugal - Design of a Steel Frame
Objective: Design steel structure for indoor sports facility in the suburbs of the city of Évora (Portugal) with a covered area of 60 x 30 m2
Arquitectural requirements:
• Soil suitable for slallow foundations
• Materials: steel S275 for framework and S235 for roof and wall sheeting concrete C25/30 rebar reinforcement: S400
1. Architectural and Environmental Conditions
5CSI Portugal - Design of a Steel Frame
2. Architecture
1) Flat frame
imin = 0.5-1%
2) Duopitch or gable frame
Slope decreases moments in the middle region of the rafters
Roof shapes
for drainage
6CSI Portugal - Design of a Steel Frame
2. Architecture
3) Single slope, monopitch or shed frame 4) Parabolic or circular frame
5) Multispan frame
7CSI Portugal - Design of a Steel Frame
Chosen solution: 15 steep duo-pitch roof shape
2. Architecture
Portal frame components:
8CSI Portugal - Design of a Steel Frame
3. Portal Frames
Portal frames structural behaviour
Simply supported because of (i) support conditions or (ii) variable inertia
1) Simply supported beam
2) Articulated (pinned) frame
Isostatic
9CSI Portugal - Design of a Steel Frame
3. Portal Frames
3) Rigid connections frame
4) Cable stayed frame
Very slender rafters prone to up-lifting by wind
Hiperstatic
Plastic stress-resultant redistributions possible
10
1) Hot-rolled I- or H-section profiles 2) Welded beams (composed of unperforated plates)
3. Portal Frames
Support moments higher than span in rigid connections frameSolution: use knee joint
knee joint
CSI Portugal - Design of a Steel Frame
Rafter solutions
L < 30 ~ 35 m
3) Tapered beams: simply supported rafter Simply supported beam
For simply supported rafters or articulated frames
11CSI Portugal - Design of a Steel Frame
4) Perforated beams: honeycomb
3. Portal Frames
Increased bending resistance and stiffness maintaining shear resistance
Tubes can pass throught the beams
Higher costs (cuting and welding)
Usually pinned beams (may not resist bending + shear at supports)
5) Cellular beams: uniform or tapered
Tapered sectionUniform sectionFabricationL0/h = 15-30Similar to honeycomb + esthetics
12CSI Portugal - Design of a Steel Frame
6) Planar trusses Constant depth Variable depth
7) Spatial trusses
Cubes or tetrahedron shape
Complex connections
Hollow section profiles
Light solutions for long spans
Reduces bracing required
Boeing factory Olympic pool
3. Portal Frames
L0/h = 5-6L0/h = 10-12
20 < L < 100 m
13CSI Portugal - Design of a Steel Frame
Extreme rafter slenderness
8) Cable-stayed solutions
Additional column compression
Solution for large spans
Roof weight vs up-lifting forcesPossible up-lift due to wind forces
3. Portal Frames
14CSI Portugal - Design of a Steel Frame
Chosen solution:
Rafter: planar truss; RHS profiles; welded connections
Column:HEA or HEB
3. Portal Frames
Rigid connection(bolted)
Rigid connection(bolted)
15CSI Portugal - Design of a Steel Frame
• IPE, Z, U or channel purlins
3. Portal Frames
1) Regular (5-7 m)• Moderate actions
• Economical solution
2) Reduced (< 5 m) • Very high loads (wind, snow, insulation materials, soil)
3) Increased (> 7 m, < 12 m)
• Trussed purlins
• Interior constraints to column locations
• Roof sheeting suitable for long spans
Portal frames spacing
6 m
Chosen spacing:
16CSI Portugal - Design of a Steel Frame
Elements:
2) Trapezoidal steel sheeting: longer spans, lighter, thermal insulation possible, better esthetics, enough longitudinal strength for purlins bracing3) Corrugated aluminium sheeting: very light, corrosion resitant, expensive, too deformable (shorter spans), high noise in heavy rain
4) Translucid plastics (polycarbonate): low strength (shorter spans), sensitive to sunlight exposure (become brittle), combustible, very light
4. Roof and Walls Sheeting
1) Corrugated fibre-cement: economical, brittle, unesthetical, heavy, low insulation, asbestos fibres are unhealthy
Sheeting:
(i) Sheeting (iii) Drainage elements
(ii) Purlins (iv) Joint elements and purlins bracing
Steel sheeting with thermal insulation; 1.5 m spans
Adopted solution:
17CSI Portugal - Design of a Steel Frame
Main:• Transmit roof loads to the rafters• Brace the rafters upper chords or flanges
Purlin solutions:
- Hot rolled (IPE, UNP)1) Spans up to 9 m
- Cold-formed (Z-, channel or lipped channel section)
5. Purlins
2) Spans up to 15 m - planar or spatial truss beams - Planar beam with rods
- Planar beam with profiles
Functions:
Optional:• Brace the rafters lower chords (indirectely through the lower chords bracing rods)• Brace the portal frames for out-of-plane displacements• Transmit longitudinal horizontal endwall loads to the bracing system
UNP (channel) profiles
Chosen solution:
18CSI Portugal - Design of a Steel Frame
5. Purlins
Connection to the rafter:
Ovalisation: elongated bolt hole to function as a movement joint for thermal action
Types of connections to the rafters: (i) lower flange bolted, (ii) plate bolted to the web, (iii) use a channel
InclinedChosen configuration:
Purlin configurations:
Vertical Inclined
• For predominatly vertical loads (snow or life) • For predominatly normal loads (wind)• Easier to execute
19CSI Portugal - Design of a Steel Frame
5. Purlins
1) Simply supported
Supports and joints:
2) Gerber
3) Continuous beam
4) Two-span beam
Purlin connection:
Two-span beam in alternated configuration (see next slide)
Chosen solution:
20CSI Portugal - Design of a Steel Frame
5. Purlins
Two-span alternated configuration reactions:
Purlin
Rafter
Two-span non-alternated:One-span:
1.875/2 6.25/2 3.75/2 6.25/2 3.75/2
2.5/2 5/2 5/2 5/2 5/2
Two-span alternated:
• Distributes more uniformly the loads on the rafters
21CSI Portugal - Design of a Steel Frame
5. Purlins
• Determined by the sheeting span (1.2-2 m normally)
• Possibility of reduced spacing in localised zones (e.g., where wind loads are higher)
Spacing
1.5 m
Chosen spacing:
22CSI Portugal - Design of a Steel Frame
3) Purlins bracing
2) Rafter lower chords bracing
1) Frame longitudinal and transversal bracing
6. Bracing systems
23CSI Portugal - Design of a Steel Frame
Transversal bracing
6. Bracing systems
• resists longitudinal horizontal loads (e.g., wind loads in the enwalls)
• prevents global buckling
Longitudinal bracing
• resists transversal horizontal loads
• prevents global buckling
• only used in highly deformable frames• braces the rafters (absorbs their imperfection equiv. loads)
Central
• thermal action generates negligible axial forces• purlins under compression for wind loads (additional beams may be necessary)
Double-sided
• thermal action may result in high axial forces• purlins are not subjected to compression due to wind • No longitudinal bracing
Chosen bracing:
• Transversal double-sided
24CSI Portugal - Design of a Steel Frame
Rafter lower chord bracing
6. Bracing systems
• May be uniformly spaced or more concentrated on the most compressed zones
• Diagonal at 45
Chosen bracing:
Perpendicular
• works only in tension• must be fixed at both ends
endwall column
chord bracing rod
Diagonal
• normally at q=45• low q: less flexible but may not work in compression
• transfers the instability loads to the purlins
• high q: more flexible due to purlin bending
rafterpurlin
chord bracing rod
25CSI Portugal - Design of a Steel Frame
• Absobs the roof in-plane load component
• Limits purlin minor axis bending
• Reduces purlins lateral buckling length
6. Bracing systems
Bracing rod, tie rod or sag bar:
Bracing rod anchor:
a) Ridge (eave) purlins absorb the rod tension b) Diagonal rods transmit the tension to the rafters
Purlins bracing
• Connected using nuts and washers
26CSI Portugal - Design of a Steel Frame
2) Live
EN 1991: Part 1-1
3) Wind actions
4) Thermal actions
EN 1991: Part 1-4
EN 1991: Part 1-5
7. Actions
1) Dead
EN 1991: Part 1-1
27CSI Portugal - Design of a Steel Frame
Dead
377 mkNs Structural elements:
Note: members dead weight is automatically determined in SAP2000
Sheeting self-weight: 205.0 mkNqEd
Live
24.0 mkNqEd Roof:
kNQEd 1
(distributed)
(concentrated)EN 1991-1-1 Table 6.10
H category – roof not accessible except for normal maintenance and repair
EN 1991-1-1 Table A.4
7.1 Dead and Live Actions
28CSI Portugal - Design of a Steel Frame
7.2 Wind Action
222 /456.02725.121
21 mkNvq bb
Basic velocity pressure:
Wind force:
refppEkw AcqF .
peak velocity pressure
differential pressure coeficient
reference areaNotes:• Fw.Ed is normal to the surface• friction force can be neglected when: A//4A∟
2
2//
2
3
aA
aA
e.g.:
Terrain category: III (regular cover of vegetation or buildings)
2/903.0456.098.1)15()15( mkNqmcmq bep
Peak velocity pressure:
smvccv bseasondirb /27270.10.10. Basic wind velocity:
season factor
directional factor
Évora county (Zone A): vb.0=27 m/s(National Annex, Table NA.I)
Peak velocity pressure (qp)
fundamental velocity
29CSI Portugal - Design of a Steel Frame
External pressure coeficient (cpe)
3.0,2.0 pic
(both should be considered)
Otherwise:
7.2 Wind Action
Internal pressure coeficient (cpi)
If area of opennings in each face is known:
openingsallofArea
0cwithopeningsofArea pe
Two wind directions are considered:
º0 º90
30CSI Portugal - Design of a Steel Frame
2 wind directions × 2 internal pressures = 4 wind loading cases
Differential pressure coeficient (cp):
7.2 Wind Action
Number of loading cases:
pipep ccc
31CSI Portugal - Design of a Steel Frame
Temperature in a element according to EN 1991-1-5:
neglected (elements are thin-walled)
7.3 Thermal Action
1) Uniform
2) Linearly varying
3) Nonlinear
neglected (elements are flexible for bending)
Uniform temperature variation of an element:
0TTTu
average temp. of an element in summer or winter considering a temp. profile
average temp. during construction
Example:
2outin TTT
32CSI Portugal - Design of a Steel Frame
(bright light surface)Location: Évora
CT
CT
º5
º45
min
max
03 T CT º200
7.3 Thermal Action
Évora county (Zone A) (National Annex, Tables NA.I and NA.II)
National Annex, Table NA.5.1
CT
CT
º18
º25
2
1
Inside temp.
Summer
Winter
Members temp.
CTTTT º355.0 13max
Temp. variation
CTTT
CTTT
º5.13
º15
0
0
Outside temp.
Notes:(construction during spring or automn)Temp. profile is deemed
linear (conservative)
CTTT º5.65.0 2min
Uniform temperature variation for the steel members:
33CSI Portugal - Design of a Steel Frame
DEAD
CB_LIVE ULS_STR/GEO-B1_0 1.35 1.5 0.9 ULS_STR/GEO-B1_1 1.35 1.5 0.9ULS_STR/GEO-B1_2 1 1.5 0.9ULS_STR/GEO-B1_3 1 1.5 0.9ULS_STR/GEO-B1_4 1.35 1.5ULS_STR/GEO-B1_5 1 1.5ULS_STR/GEO-B1_6 1.35 1.5 0.9ULS_STR/GEO-B1_7 1.35 1.5 0.9ULS_STR/GEO-B1_8 1.35 1.5 0.9ULS_STR/GEO-B1_9 1.35 1.5 0.9ULS_STR/GEO-B1_10 1.35 1.5 0.9ULS_STR/GEO-B1_11 1.35 1.5 0.9ULS_STR/GEO-B1_12 1.35 1.5 0.9ULS_STR/GEO-B1_13 1.35 1.5 0.9ULS_STR/GEO-B1_14 1 1.5 0.9ULS_STR/GEO-B1_15 1 1.5 0.9ULS_STR/GEO-B1_16 1 1.5 0.9ULS_STR/GEO-B1_17 1 1.5 0.9ULS_STR/GEO-B1_18 1 1.5 0.9ULS_STR/GEO-B1_19 1 1.5 0.9ULS_STR/GEO-B1_20 1 1.5 0.9ULS_STR/GEO-B1_21 1 1.5 0.9ULS_STR/GEO-B1_22 1.35 1.5ULS_STR/GEO-B1_23 1.35 1.5
Load pattern
LIVE WIND_2WIND_1 WIND_3 WIND_4 TEMP+ TEMP-
• 50 combinations• 7 are deemed the most unfavourable (green)
8. Actions Combinations
Actions combinations according to EN 1990:
34CSI Portugal - Design of a Steel Frame
Note: automatic load combinations obtained using CTM 1.0 software
CB_WIND3 ULS_STR/GEO-B1_24 1.35 1.5 CB_WIND4 ULS_STR/GEO-B1_25 1.35 1.5 CB_WIND1 ULS_STR/GEO-B1_26 1 1.5 CB_WIND2 ULS_STR/GEO-B1_27 1 1.5
ULS_STR/GEO-B1_28 1 1.5ULS_STR/GEO-B1_29 1 1.5ULS_STR/GEO-B1_30 1.35 0.9 1.5ULS_STR/GEO-B1_31 1.35 0.9 1.5ULS_STR/GEO-B1_32 1.35 0.9 1.5ULS_STR/GEO-B1_33 1.35 0.9 1.5ULS_STR/GEO-B1_34 1.35 0.9 1.5ULS_STR/GEO-B1_35 1.35 0.9 1.5ULS_STR/GEO-B1_36 1.35 0.9 1.5ULS_STR/GEO-B1_37 1.35 0.9 1.5ULS_STR/GEO-B1_38 1 0.9 1.5ULS_STR/GEO-B1_39 1 0.9 1.5ULS_STR/GEO-B1_40 1 0.9 1.5ULS_STR/GEO-B1_41 1 0.9 1.5ULS_STR/GEO-B1_42 1 0.9 1.5ULS_STR/GEO-B1_43 1 0.9 1.5ULS_STR/GEO-B1_44 1 0.9 1.5ULS_STR/GEO-B1_45 1 0.9 1.5
CB_TEMP1 ULS_STR/GEO-B1_46 1.35 1.5 CB_TEMP2 ULS_STR/GEO-B1_47 1.35 1.5
ULS_STR/GEO-B1_48 1 1.5ULS_STR/GEO-B1_49 1 1.5
DEAD
Load pattern
LIVE WIND_2WIND_1 WIND_3 WIND_4 TEMP+ TEMP-
8. Actions Combinations
35CSI Portugal - Design of a Steel Frame
2max.. /03.25.1903.05.1 mkNcqq ppQEdW Maximum wind load:
Permissable loads [kN/m2]
9. Steel Sheeting Design
Trapezoidal sheet sheeting:
• 0.5 mm
Chosen thickness:
2/41.2 mkNqRd
Thickness: 0.5 mmSpan: 1.5 mPermissable load:
03.241.2 . EdWRd qq
OK
(up-lifting)
36CSI Portugal - Design of a Steel Frame
Sheeting distributed self-weight:
6 m long sheets with 0.3 m overlaping5% of weight increase due to joint additional elements
23 /051.07.5681.9107.405.1 mkNpEd
sheet mass per sqr meter
9. Steel Sheeting Design
Actions on the purlins
Sheeting self-weight: mkNLpp EdEdG 077.05.1051.0.
Uniform life load: mkNLqp EdEdQ 58.0º15cos5.14.0cos.
Maximum wind load: mkNLqp EdWEdW 05.35.103.2..
37CSI Portugal - Design of a Steel Frame
Portal frame column
Sheeting equivalent beam
Lower chord bracing
Purlin
Transversal bracingEndwall column
Girt or wall purlin
Rafter truss
10. Modeling the Structure
Purlins bracing rod
Girts bracing rod
Modelled members:
38CSI Portugal - Design of a Steel Frame
10. Modeling the Structure
1) Stiffness model
• Longitudinal purlins and sheeting axially fixed
2) Strength model
• All purlins axially released (simply supported)
• Purlins connect the rafters to the transversal bracing contributing to their stability
• Purlins do not transmit thermal loads, since they are provided with movement joints (slotted connections)
Objective: perform buckling analyses
Objective: determine stress resultants for member design
Two frame models are used:
39CSI Portugal - Design of a Steel Frame
Local axes of roof and wall purlins:
1- axial2- major deflection3- minor deflection
Axis 3 (cyan) of UNP profile should be pointing upwards to avoid dirt or water accumulation in the profile
Axis 2 (green) should be pointing in-wards to make the application of wind loads easy
10. Modeling the Structure
40CSI Portugal - Design of a Steel Frame
Portal frame Rafter (planar truss)
Column
10. Modeling the Structure
Option 2: model members with the longest length possible
Option 1: model members with the shortest length possible
Advantages
Disadvantages
• buckling lengths are easily identified
• buckling lengths may be more difficult to determine
• it is necessary to determine the imperfection forces (and eventual P- effects) in all minor nodes
• it is only necessary to determine the imperfection forces and P- effects in the major nodes
Major node
Minor node
• only possible if the member is uniform (continuous) • Option 2
Chosen option:
41CSI Portugal - Design of a Steel Frame
10. Modeling the Structure
• Sheeting contributes to stabilize the rafters lower chords
Rafter lower chord P- instability:
Equivalent inertia beam:
(spaced 1 m)
1 m
Frame model: Purlin
Steel sheeting modeling
42CSI Portugal - Design of a Steel Frame
11. Load Assignments
Dead Live
43CSI Portugal - Design of a Steel Frame
11. Load Assignments
Wind 1 Wind 2
44CSI Portugal - Design of a Steel Frame
11. Load Assignments
Wind 3 Wind 4
45CSI Portugal - Design of a Steel Frame
11. Load Assignments
The thermal actions on the purlins can be ignored because they are provided with movement joints
Thermal
CT º0Purlins:
Rafters, columns and bracing:
CT º15
46CSI Portugal - Design of a Steel Frame
Frame buckling loads may be determined using equations (5.1) and (5.2) of EC3-1-1:
kNVEd 120
b) Transversal buckling
mH 0015.0max.
101.610015.011
1201
HEd
crh
VH
12. Frame Buckling Analysis
• Equation (5.2) is only valid for not significantly compressed and shallow (26) rafters
)2.5()1.5(HEd
crEd
crcr
hVH
FF
• Average compression force per column (LIVE load combination):• SAP2000 stiffness model is used and 1st order analyses are performed to determine H
a) Longitudinal buckling
104.760012.011
1201
HEd
crh
VH
mH 0012.0max.
No global 2nd order effects need to be considered
47CSI Portugal - Design of a Steel Frame
12. Frame Buckling Analysis
The lower chords buckling length may be verified using a buckling analysis:
• Only part of the structure needs to be analysed (decreases number of buckling modes to be checked)
• Additional restraints substitute the transversal bracing effect
• Useful to check if lower chord bracing has enough stiffness to function propertly
• Use stiffness model (purlins and sheeting axially fixed)
• Negative buckling loads are ignored
lower chord bracing
additional restraint
• Buckling length is the distance between inflection points of the buckled lower chord
Bracing system must resist the effect of member imperfections (eventually amplified by 2nd order effects) (EC3-1-1: 5.3.3) compressed
chordbraced point
48CSI Portugal - Design of a Steel Frame
12. Frame Buckling Analysis
a) LIVE load combinationBuckling mode 2:
37.72. b
lower chord buckling
bracing almost 100% effective
• Buckling length may be considered as the distance between bracing points
• Bracing must resist imperfection forces
58.114. b
• Sheeting shear stiffness likely to prevent this mode
Buckling mode 4:
upper chord buckling
Chord buckling modes
49CSI Portugal - Design of a Steel Frame
12. Frame Buckling Analysis
b) WIND3 load combination
51.134. b
• Sheeting shear stiffness likely to prevent this mode
Buckling mode 4:
upper chord buckling
Buckling mode 1:
08.71. b
lower chord buckling
bracing almost 100% effective
• Buckling length may be considered as the distance between bracing points
• Bracing must resist imperfection forces
Chord buckling modes
50CSI Portugal - Design of a Steel Frame
13. Equivalent Imperfection Forces
Lower chord bracing design
Member length: mL 54.1
One took advantage of bracing compressive stiffness therefore it must be checked for its buckling strength
Max. chord compressive force (LIVE comb):
kNNEd 310 Axial force (lower chord):
Braced pointLateral force: kNNEd 775.025.02
Imperfection: 005.0
Average comp. force: EdN25.0
Bracing axial force:
kNkNN Rdb 10.193.65.
kN10.1º45cos775.0
OKBracing buck. strength:
Comp.
(L50x5)
51CSI Portugal - Design of a Steel Frame
13. Equivalent Imperfection Forces
2) Columns initial geometric imperfection
76.06115.0115.0 mm(EC3-1-1: 5.3.3)
mmLe m 175001176.05000
number of members to brace
Slotted hole ovalisation of +/- 4 mm every 12 m
md 24
mm812244
1) Bolt hole ovalisation (slotted connection) effect
• The purlins only work axially for displacements higher than the ovalisation
Purlin
m11
3) The effect of the ovalisation must be added to the imperfection
mmee equiv 258170.0
Instability loads on the transversal bracing
52CSI Portugal - Design of a Steel Frame
13. Equivalent Imperfection Forces
4) Bracing force
kNVEd 120 (LIVE load comb.)
Compressive force per column:
Supported by right bracingSupported by left bracing
Bracing force applied in each bracing system corner:
kN
LeVF equivEdEd
64.11110251206
63
.0
Neglectable (less than 1% of the wind load)
5) Effect of ovalisation displacement in columns
kNmH /0072.0
kN
HH
11.10072.0108 3
(from SAP2000 strength model)
to be applied on top of each column
53CSI Portugal - Design of a Steel Frame
13. Equivalent Imperfection Forces
Columns equivalent geometric imperfections
866.02115.0115.0 mm
mh 0
Imperfection equivalent forces
mm 115.0
132with2 hh h
32h
Portal frame in-plane imperfection
mh 15
kNNEd 35.012000289.0
00289.0866.032
2001
20010
54CSI Portugal - Design of a Steel Frame
14. Members Buckling Lengths
In SAP2000 the buckling lengths of members are determined by:
Buckl. length = K factor × L factor × Member length
There are 3 types of L factors:• major axis L factor• minor axis L factor• lateral torsional L factor
Related to the rotational stiffenesses at the member ends
Related to the intermediate bracing
There are 5 types of K factors:
• K1.z – minor plane in braced mode
• K1.y – major plane in braced mode• K2.y – major plane in sway mode
• K2.z – minor plane in sway mode
• KLT – lateral torsional mode
- K2 (sway mode) values are used by default
Note:
55CSI Portugal - Design of a Steel Frame
14. Members Buckling Lengths
Determination of K factors according to Annex E of old EC3:
),(KfactorK 21
22212
12111
KKKKKKKK
cc
cc
• In SAP2000 the K factors are determined from the components of the beams stiffenesses in the considered plane:
iiicc KKK cos11
iiicc KKK cos22
Note: - If ‘P-Delta done’ is checked, K2.y= K2.z= KLT=1
Unbraced
Braced
56CSI Portugal - Design of a Steel Frame
14. Members Buckling Lengths
L factor automatic determination
• In SAP2000 the effect of intermediate bracing due to other bars intersecting the member is incorporated by the L factor:
(i) Only members with 60 w.r.t. the buckling plane are considered as bracing elements
(ii) Stiffness or strength requirements for bracing members are not checked
(iii) L factor is equal in minor axis buckling and lateral torsional buckling
º307.0º301
(minor)factor L
º607.0º601
(major)factor L
ifif
ifif
57CSI Portugal - Design of a Steel Frame
14. Members Buckling Lengths
1st Overwrite – Lateral Bracing
Overwriting K factors and L factors
• For L factors for minor plane and lateral torsional buckling• Point bracing and/or uniform bracing on top and/or bottom flange are possible• Top or bottom always braces minor plane buckling• Top or bottom only braces lateral buckling if the respective flange is under compression
2nd Overwrite – Direct Overwrite
• For all K factors and L factors• Overwrites the lateral bracing overwrite if L factors are specified
• L factor = maximum unbraced length
58CSI Portugal - Design of a Steel Frame
14. Members Buckling Lengths
Lower chord buckling lengths
m5.1
m5.4
Member length:
Diagonal nodes spacing:
Bracing spacing:
Manually determined factors:
305.0752.145.4LTB)(FactorL305.0752.145.4Minor)(FactorL102.0752.145.1Major)(FactorL
Automatically determined factors:
OK
mL 752.14
59CSI Portugal - Design of a Steel Frame
14. Members Buckling Lengths
Upper chord buckling lengths
m5.1
m5.1
Member length:
Diagonal nodes spacing:
Purlins spacing:
Manually determined factors:
098.0261.155.1LTB)(FactorL098.0261.155.1Minor)(FactorL098.0261.155.1Major)(FactorL
mL 261.15
Automatically determined factors:
OK
60CSI Portugal - Design of a Steel Frame
14. Members Buckling Lengths
Purlins buckling lengths
m1Member length: Equiv. Sheeting bars spacing:
Manually determined factors:
5.063LTB5.063Minor
166MajorFactor L
1LTB1Minor1Major
sway)-(nonFactorK
mL 6
Automatically determined factors:
Not OKOK
Overwrites:
• Equiv. sheeting rods don’t provide lateral bracing. L Factor Minor and LTB are 0.5 due to the bracing rods
Braced nodes spacing: m3
OK
Factors after overwrite:
OK
61CSI Portugal - Design of a Steel Frame
Automatically determined factors:
OKNot OK
14. Members Buckling Lengths
Portal frame columns
m932.0
m5.1Member length:
Chord nodes spacing:
Girts spacing:
Manually determined factors:
136.0115.1LTB136.0115.1Minor
915.011932.011MajorFactor L
1LTB1Minor
7.0~5.0Major
sway)-(nonFactorK
mL 11
OK
Factors after overwrite:
OK
Overwrites:
• Column has a K Factor Major between 0.5 (fixed-fixed) or 0.7 (fixed-pinned). The latter value is adopted conservatively
62CSI Portugal - Design of a Steel Frame
14. Members Buckling Lengths
Endwall columns
m5.1Member length: Girts spacing:mL 14
OK
Factors after overwrite:
OK
Automatically determined factors:
OKNot OK
Overwrites:
• Column has a major K Factor of 0.7 (fixed-pinned).
Manually determined factors:
107.0145.1LTB107.0145.1Minor
11414MajorFactor L
1LTB1Minor
7.0Major
sway)-(nonFactorK
63CSI Portugal - Design of a Steel Frame
15. Members Automatic ULS Check
• Use SAP2000 frame strength model
Check members for collapse ULS
Steel frame design preferences:
• Interaction factors method (EC3-1-1: Annex A and B)
• Check ‘P-Delta done’ if 2nd order effects at the nodes are already determined (Sway K Factors become unitary)
• Set design code and coutry
• Ignore seismic code (EC8)
• Demand/Capacity ratio limit should be 1 for ULS but may be user specified
64CSI Portugal - Design of a Steel Frame
16. Members Automatic Design
2) Select design groups
Design -> Steel Frame Design -> Select Design Groups
3) Start design of structureDesign -> Steel Frame Design -> Start Design/Check of Structure
• If optimised member sections are significantly smaller than the original ones, it may be necessary to run the buckling analyses again with the new sections
Note:
1) Assign Auto select section properties to the groupsDefine -> Section Properties -> Frame Sections
Add New Property -> Auto Select List
65CSI Portugal - Design of a Steel Frame
Action combinations for SLS:
Serviceability limit state (SLS): Limitation of vertical and horizontal displacements (National Annex EN 1993-1-1)
DEAD LIVE WIND2 TEMPSLS_CARAC_0 1 1 0.6SLS_CARAC_1 1 1SLS_CARAC_2 1 1 0.6SLS_CARAC_3 1 1SLS_CARAC_4 1 0.6 1SLS_CARAC_5 1 1
17. SLS Check
Note: automatic load combinations obtained using CTM 1.0 software
2) Horizontal displacements:(on columns top)
(frames without lift equipment)150limit h
mm 073.015011009.0 limitmax Column (HE400A):
1) Vertical displacements:(of every beam)
200limit L (general roof cathegory)
mm 030.02006025.0 limitmax Purlins (UPN 140):mm 150.020030027.0 limitmax Rafter:
Endwall column span (HE300A): mm 070.020014015.0 limitmax