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

:

50-063CSIA 7831

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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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b

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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

1-2 50-063 CSIA : SBATE 50-063CSIA

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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ezaS.www808moc. ezaS www808moc

:abatjom808moc.oohay@

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moc.ezasnarI.www

DSA DFRL 5002 CSIA 7831 :

: 98 -