Transcript
Structure 808 Webinar with Associated of Kerman University (Bahonar ) Of IRANy ( )
Methods of Stability Analysis
for the Design of Steel Frames((Evaluation of the ELM and the DAM Method according to AISC Evaluation of the ELM and the DAM Method according to AISC 360360--20052005))
Mojtaba Asghari
.com808www.SazeIRAN Kerman December 2010IRAN,Kerman-December 2010
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50-063CSIA 7831
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SBATE 50-063 CSIA DFRL
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Stability Analysis in Design of Steel BuildingIn ETABS v.9.5 withAISC 360-05 StandardAISC 360 05 Standard
Design Analysis Method Second
O d M th d Order Method :
Direct Analysis
Design Analysis Method
Effective Length
Limited 1st Order
Stability Analysis in
ETABS General 2nd OrderP
Second Order Method
Amplified 1st Order
P
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AISC 2005 :
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It is a state-of-the-art methodology for the structural engineering profession for the 21st century.
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Design Analysis Method :
Specification2005 AISC
C2 2 D i R i tC2.2 Design Requirements
Effective Length Method (C2.2a) Limited applicationpp
uses K>1.0
First-order analysis (C2.2b) Limited application
Simplest approach
Direct Analysis Method (Appendix 7)Direct Analysis Method (Appendix 7) Applies to all buildings (K=1.0)
Preferred method
Effective Length Method ELM Effective Length Method ELM
Applies when 5.1/ 122 = stndBpp Notional Loads, Ni = 0.002Yi (gravity load combinations) Second-Order Analysis
Nominal Geometry
Nominal Stiffness
K from a sidesway buckling analysis K from a sidesway buckling analysisthen K=1.01.1/ 12 stnd
AISC360-05 ) ( .
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50-063 CSIA 6-1-7-2-01 50-063 CSIA
B5.1 2 . B5 1 2 .
Direct Analysis Method DAM Direct Analysis Method DAM9Applies to all structures9 K=1 0
5.1,5.1 22 < BB9 K=1.09 Straight-forward Analysis and Design9 Improved Results & Less potential for error9Applies to all lateral systems or combination of systems w/o distinction9Most accurate determination of internal forces when combined with rigoroussecond-order analysis
: . 5.1,5.1 22 < BB . K
1 . Effective Length
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8 0 0 1b
b . 8.0 0.1
Stiffness Reduction
Reduced flexural stiffness, 0.8 EI
Generally = 1.0 for the following :
Beams
bb
Beamsmoment frames (low axial load)
Braced frames (flexural stiffness does not contribute)
Braces (flexural stiffness does not contribute) Columns in braced frames (flexural stiffness does not contribute)
Can take = 1.0 for all members if :
apply additional notional load Ni = 0.001Yib
Eliminates iteration! 0.002
3 0.003 . 1 50% .
Procedure Summary
Model the structure (no change)Apply Notional LoadsPerform second-order analysis on nominal geometry with reduced stiffnessPerform second order analysis on nominal geometry with reduced stiffnessDesign all members for resulting forcesDesign compression members with K=1.0
Updates Stability Design Requirements
New requirements for analysisRecognizes current analysis optionsAddresses shortcomings of previous methods (K = ?)Addresses shortcomings of previous methods (K ?)Provides straight-forward methods
DAM is most general and accurate approachDAM is most general and accurate approach
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Second Order Analysis in ASD - AISC 360-05 :
Carried out under 1.6 times ASD load combinationResults divided by 1.6 to obtain required strengths
In Direct second order analysis , the method already includes 1.6 factor
Initial imperfections, either
Notional Loads at each level, or Notional Loads at each level
Ni = 0.002Yi
Yi = total gravity load on a levelYi total gravity load on a level
Applied to all load combinations
Applied only in Gravity Combos, except for 5.12 BGravity load combinations:
Two orthogonal directionsPositive and negative senseSame direction at all levels
Model with assumed out-of-plumbness
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S d O d A l iSecond Order Analysis:
General 2nd Order P Second Order Method
P
Amplified 1st Order
) ( General 2nd Order P P
P
General Second-Order Analysis
Free of limitations of amplified first-order methodMore accurate determination of internal forces and strength level deformations
Complex geometryirregular lateral framing
Structure Analyzed for Load Combinations (ASD with a 1.6 factor) Stable model required
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::RefrencesRefrences :: RefrencesRefrences - 10 1387
- AISC-360-2005
- AISC 2010-Draft
-ETABS AISC360-05 Manual-Jason R Ericksen, CSC ,How To Guide for the Direct Analysis Method, 2010
-Christopher m. Hewitt ,Stability Analysis Its not as Hard as You Think,2008p , y y ,
-CSI DAM Guide Manual
This presentation Published for this Virtual Internet Forum:
- Persian Civil Forum:www Iransaze comwww.Iransaze.com
- Latin Civil International Forum:www.forum.civilea.com
And My Structural Websait:www Saze808 comwww.Saze808.com
Email for contact with Publisher:mojtaba808@yahoo.comj @y
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DSA DFRL 5002 CSIA 7831 :
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