NASCC 2007 - AISC 13th Edition Specification

8/18/2019 NASCC 2007 - AISC 13th Edition Specification

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Josh Plummer, S.E.Josh Plummer, S.E.

Director of Training & SupportDirector of Training & SupportFoothill Ranch, CA Foothill Ranch, CA


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Electronic Automation of theElectronic Automation of the

AISC 13 AISC 13thth EditionEdition

Analysis Methods of Chapter CAnalysis Methods of Chapter C

Direct Analysis MethodDirect Analysis Method(Appendix 7)(Appendix 7)


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Summary of New RequirementsSummary of New Requirements

•• Must Account for GeometricMust Account for GeometricImperfections (Out ofImperfections (Out of PlumbnessPlumbness))

•• Must Account for 2Must Account for 2ndnd Order EffectsOrder Effects

(P(P-- ∆ ∆ & P& P--δδ))•• Must Include Member StiffnessMust Include Member Stiffness

Reductions Due to Residual StressesReductions Due to Residual Stresses

•• Use of KUse of K--Values Can Be Eliminated inValues Can Be Eliminated in

Most CasesMost Cases

Analysis MethodsAnalysis Methods

Of Chapter COf Chapter C


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Methods Meeting RequirementsMethods Meeting Requirements

11stst Order AnalysisOrder Analysis

Amplified 1Amplified 1stst Order AnalysisOrder Analysis

General 2General 2ndnd Order AnalysisOrder Analysis

Direct Analysis Method (Appendix 7)Direct Analysis Method (Appendix 7)




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11stst Order AnalysisOrder Analysis (Section C2.2b)(Section C2.2b)

•• Only Allowed WhenOnly Allowed When•• PPr r ≤≤ 0.5P0.5Pyy (LRFD)(LRFD)

•• PPr r ≤≤ 0.3125P0.3125Pyy (ASD)(ASD)

•• Must Include Minimum Notional Load inMust Include Minimum Notional Load in ALL ALL Load CombinationsLoad Combinations

•• NNii = 2.1(= 2.1(ΔΔ // L)YL)Yii ≥≥ 0.0042Y0.0042Yii

•• Must Apply BMust Apply B11 Amplifier to all Member Amplifier to all Member

MomentsMoments

•• BB11 = C= Cmm/(1/(1-- αα

PPr r /P/Pe1e1))≥≥

11




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Amplified 1Amplified 1stst Order Analysis (C2.1b)Order Analysis (C2.1b)

•• Qualifies as a 2Qualifies as a 2ndnd Order AnalysisOrder Analysis

•• MMr r = B= B11MMntnt + B+ B22MMltlt•• PPr r = P= Pntnt + B+ B22PPltlt

BB11 = C= Cmm/(1/(1-- ααPPr r /P/Pe1e1)) ≥≥ 11

BB22 = 1/(1= 1/(1--((αΣαΣPPntnt//ΣΣPPe2e2)))) ≥≥ 11

++ The Additional Requirements ofThe Additional Requirements ofGeneral 2General 2ndnd Order AnalysisOrder Analysis




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General 2General 2ndnd Order AnalysisOrder Analysis

Any Method That Accounts for Any Method That Accounts for PP--ΔΔ & P& P--δδ

Additional Requirements: Additional Requirements:

1.1. ASD Analysis Shall Be Carried Out Under 1.6 ASD Analysis Shall Be Carried Out Under 1.6x Load Combinations (Results Divided by 1.6)x Load Combinations (Results Divided by 1.6)

2.2. Must Include Minimum Notional Load in AllMust Include Minimum Notional Load in AllGravity Load CombinationsGravity Load Combinations

3.3. Must Use KMust Use K--Factors for Moment FrameFactors for Moment FrameColumns If (2Columns If (2ndnd Drift / 1Drift / 1stst Drift) > 1.1Drift) > 1.1




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Direct Analysis MethodDirect Analysis Method (Appendix 7)(Appendix 7)

•• Preferred Method in AISC SpecificationPreferred Method in AISC Specification

•• No Restrictions on UseNo Restrictions on Use

•• Must Be Used if (2Must Be Used if (2ndnd Drift / 1Drift / 1stst Drift) > 1.5Drift) > 1.5

Direct AnalysisDirect Analysis

MethodMethod


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Geometric ImperfectionsGeometric Imperfections

•• Apply Notional Loads = 0.002Y Apply Notional Loads = 0.002Yii(Assumes Imperfection = L / 500)(Assumes Imperfection = L / 500)

•• Notional Loads May Be Reduced WhenNotional Loads May Be Reduced When

Imperfections Are Smaller Imperfections Are Smaller

•• If (2If (2ndnd Drift / 1Drift / 1stst Drift) < 1.5, Notional LoadsDrift) < 1.5, Notional Loads

Apply To Gravity Load Combinations Only Apply To Gravity Load Combinations Only


MethodMethod


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22ndnd Order AnalysisOrder Analysis

•• PP-- ∆ ∆ (Big Delta) Analysis(Big Delta) Analysis Always Required Always Required

•• PP--δδ (little delta) Analysis(little delta) AnalysisCan Be Ignored IfCan Be Ignored If ααPPr r < 0.15P< 0.15PeLeL

Example: W12x65 Column (L = 15Example: W12x65 Column (L = 15’’))

PPeLeL = 4708 kips= 4708 kips PPyy = 955 kips= 955 kips

ΦΦPPnn = 746 kips= 746 kips →→ 0.16P0.16PeLeL


MethodMethod


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AISCAISC ““BenchmarkBenchmark”” ProblemsProblemsDirect AnalysisDirect AnalysisMethodMethod

Case 1Case 1

Case 2Case 2


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BenchmarkBenchmark – – Case 1Case 1Direct AnalysisDirect AnalysisMethodMethod



Zero JointsZero Joints

One JointOne Joint

Three JointsThree Joints


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BenchmarkBenchmark – – Case 1Case 1Direct AnalysisDirect AnalysisMethodMethod Case 1: Deflection Amplification

1.00

1.50

2.00

2.50

3.00

3.50

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Axial Force Normalized by Euler Buckling Load, P/Pe

A

m p l i f i c a t i o n F a c t o r , Y m

RISA (1 Node) RISA (3 Nodes) RISA (10 Nodes) AISC Benchmark




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BenchmarkBenchmark – – Case 1Case 1Direct AnalysisDirect AnalysisMethodMethod Case 1: Moment Amplification

1.00

1.50

2.00

2.50

3.00

3.50

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7


A

m p l i f i c a t i o n F a c t o r ,

M m





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BenchmarkBenchmark – – Case 2Case 2Direct AnalysisDirect AnalysisMethodMethod Case 2: Deflection Amplification

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

0 0.05 0.1 0.15 0.2


A m p l i f i c a t i o n F a c t o r , Y m





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BenchmarkBenchmark – – Case 2Case 2Direct AnalysisDirect AnalysisMethodMethod Case 2: Moment Amplification

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

0 0.05 0.1 0.15 0.2

Axial Force Normalized by Euler Buckling, P/Pe

A m p l i f i c a t i o n F a c t o r , M m





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Material NonMaterial Non--Linearity EffectsLinearity Effects

Axial Stiffness ReductionAxial Stiffness Reduction•• 0.8EA0.8EA – – For Members Whose AxialFor Members Whose Axial

Stiffness Contributes To Lateral Stability ofStiffness Contributes To Lateral Stability of

StructureStructure – – Columns That Are Part of LFRSColumns That Are Part of LFRS

– – Braces That Are Part of LFRSBraces That Are Part of LFRS


MethodMethod


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Material NonMaterial Non--Linearity EffectsLinearity Effects

Flexural Stiffness ReductionFlexural Stiffness Reduction•• 0.80.8ττbbEIEI – – For Members Whose FlexuralFor Members Whose Flexural

Stiffness Contributes To Lateral Stability ofStiffness Contributes To Lateral Stability of

StructureStructure – – Beams That Are Part of Moment FramesBeams That Are Part of Moment Frames

– – Columns That Are Part of Moment FramesColumns That Are Part of Moment Frames

– – TauTau ((ττbb) Is Based on Axial Load) Is Based on Axial Load

•• TauTau May Be Set toMay Be Set to ‘‘1.01.0’’ If AnIf An Additional Additional

Notional Load (0.001YNotional Load (0.001Yii) Is Included) Is Included


MethodMethod


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Analysis Methods of Chapter CAnalysis Methods of Chapter C

•• 11

stst

Order AnalysisOrder Analysis•• Amplified 1Amplified 1stst Order AnalysisOrder Analysis

•• General 2General 2ndnd Order AnalysisOrder Analysis

Direct Analysis MethodDirect Analysis Method (Appendix 7)(Appendix 7)•• Geometric Imperfections (Notional Loads)Geometric Imperfections (Notional Loads)

•• 22ndnd Order EffectsOrder Effects

•• Material NonMaterial Non--LinearityLinearity


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RISARISA’’s Implementation of D.A.M.s Implementation of D.A.M.

Notional LoadsNotional Loads

PP--∆∆ (Big Delta)(Big Delta)

PP--δδ (little delta)(little delta) Automated StiffnessAutomated Stiffness

AdjustmentsAdjustments


MethodMethod


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Josh Plummer, S.E.Josh Plummer, S.E.

Foothill Ranch, CAFoothill Ranch, CA

(800) 332(800) 332--RISARISA

[email protected] [email protected]

Documents

NASCC 2007 - AISC 13th Edition Specification