Steel Moment Frame Connection Performance Limits for Disproportionate Collapse Analysis (SEI 2012)

STEEL MOMENT FRAME CONNECTION PERFORMANCE LIMITS FOR

DISPROPORTIONATE COLLAPSE

Caroline Field, P.E., CEng MICE Andy Coughlin, P.E. Steven Wopschall, P.E.

Hinman Consulting Engineers, Inc.

San Francisco, CA

Copyright © 2012 Hinman Consulting Engineers, Inc. 1

Overview

• Definitions • Analysis Process • Criteria

Introduction

• 1960’s high rise building

• Partially restrained moment connections

Case Study • Connection

Strength • Material Strength • Rotation Limits

Key Findings


STEEL MOMENT FRAME CONNECTION PERFORMANCE LIMITS FOR DISPROPORTIONATE COLLAPSE

Definitions

• Disproportionate Collapse – “A collapse that is characterized by a

pronounced disproportion between a relatively minor event and the ensuing collapse of a major part or whole of a structure”

• Progressive Collapse – “A collapse that commences with the failure

of one or a few structural components and then progresses over successively affected other components”



ASCE Terminology and Procedures Subcommittee

Design and Performance

Phenomenon and Mechanism

A likely scenario…

Federal Building • Occupied by

DoD • Major

Investment

UFC 3-023-03 • Occupancy III

Bldg • Alternate Path

Method

ASCE 41-06 • Nonlinear

Method • Connection

Backbones • Rotation Limits



How valid is the use of modeling parameters created for seismic time-history analysis?

Case Study • 1960’s era steel

high rise • 30 stories • WF30 to WF16

girders • Double Split-T

Connections • UFC 3-023-03,

Alternate Path Method



Source: Chicago Tribune

Analysis Assumptions • LS-DYNA Nonlinear Time History

Analysis (LSTC 2007)

• *MAT_SEISMIC_BEAM with nonlinear backbones from ASCE41-06

• Belytschko-Schwer resultant beam elements

• Instantaneous column removal

• 2% damping



Column Removal Locations



9 Bays @ 28’-0” = 252’-0”

5 B

ays

@ 2

8’-0

” =

140’

-0”

3 plan locations x 13 elevations x 4 lateral load directions = 156 total runs 3 plan locations x 9 elevations x 1 lateral load direction = 39 total runs

Steel Connections



Source: ASCE 41-06

Source: FEMA 274 (2000)

Source: UFC 3-023-03

Steel Connections • Limit State 1: Shear in Bolt • Limit State 2: Tension in Bolt • Limit State 3: Tension in Tee • Limit State 4: Flexure in

Tee



Source: ASCE 41-06

ASCE 41-06

FEMA 274

vs.

≈30% of Beam Moment Capacity

≈70% of Beam Moment Capacity Source: AISC Steel Manual, 13th Ed.

vs.

FEMA 355D ≈50% of Beam Moment Capacity

(Empirical)

ANALYSIS RESULTS Per ASCE 41-06 Connections (≈30% of Beam Moment Capacity)





SENSITIVITY RESULTS Per FEMA 355D Connections (≈50% of Beam Moment Capacity)





SENSITIVITY RESULTS Per FEMA 274 Connections (≈70% of Beam Moment Capacity)





Discussion-Connection Strength



Source: ASCE 41-06 Source: AISC Steel Manual, 13th Ed.

Huge difference in outcomes.

ASCE 41-06 vs.

FEMA 355D vs.

FEMA 274

Discussion-Material Strength • Default Properties



Material ASTM Lower Bound Yield Strength

(ksi)

Expected Strength Translation Factor

Expected Yield Strength

(ksi) Steel WF A36 37 1.1 40.7

Steel Column A36 37 1.1 40.7 Steel Column A441 42 1.1 46.2

H.S. Bolts A325 15 (shear);

40 (tension) 1.1 (tension) 44.0

• Coupon Testing Coupon Location

(Steel WF Girders)

Yield Strength (ksi)

Ultimate Strength (ksi)

2nd 49 73.8 13th 42.8 68.5 31st 51.9 77.6

Mean 47.9 73.3 Std. Deviation 4.7 4.6

Discussion-Material Strength • Comparison



Method Lower Bound Yield Strength

(ksi)

Expected Yield Strength

(ksi)

ASCE 41-06 36 40.7 FEMA 273 36 54

Coupon Testing 43.3 47.9

Discussion-Rotation Limits “The test results show that the rotational capacities of both the WUF-B and RBS connections under monotonic column displacement are about tw ice as large as those based on seismic test data.” [emphasis added]

-NIST Technical Note 1669 “An Experimental and Computational Study of Steel

Moment Connections under a Column Removal Scenario,” Sept 2010, pp. xvi.



Key Findings



Seismic Criteria for Disproportionate Collapse

Analysis?

Rotation Limits

Material Properties

Connection Strength

Coupon Testing Preferred for Both

Could affect whether costly retrofit is required.

Conservative?

Highly Sensitive for Disp. Collapse

Analysis

Questions?



www.hce.com/blog

@hinmanpulse

Andy: [email protected] Caroline: [email protected]

Contact Info:

Source: Chicago Tribune

Documents

Steel Moment Frame Connection Performance Limits for Disproportionate Collapse Analysis (SEI 2012)