Progressive Collapse 23

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GSA Progressive Collapse Design

Guidelines Applied to

Concrete Moment-Resisting

Frame Buildings

David N. Bilow, P.E., S.E. and Mahmoud E. Kamara, PhD

Portland Cement Association

Tri-Service Infrastructure Systems

Conference & Exposition

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Topics

Definition

Comparison of DOD & GSA requirements

Purpose of PCA study

Study procedure

Results

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3

Ronan Point

(1968)

Explosion on 18 Explosion on 18thth floor floor

Wall panel blown

out

22 floors collapse

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Ronan Point

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Prevent

Progressive

Collapse

Explosion at ground Explosion at ground floor floor

Local damage only

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GSA and DOD Criteria Comparison

Middle of long side, middle of short side, & corner column, at each Middle of long side,

middle of short side, & corner column, at

Column Removal

Req’d for Low LOP w/o vertical tie, Medium LOP, & High LOP

Required for nonexempt Alternate Path

Analysis

Vertical and/or horizontal tie forces, and ductility Redundancy, ductility

& continuity Tie

Requirements

Very Low, Low, Medium, and High Exempt or nonexempt Level of Protection (LOP) DOD GSA Requirement

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Comparison

Linear static, nonlinear static, or nonlinear dynamic Linear static preferred Method of Analysis 1.0DL + 0.5LL Recommended Upward Loads on Floor Slabs 1.2DL + 0.5LL + 0.2W DL + 0.25LL Loads for Dynamic Analysis 2.0(1.2DL + 0.5LL) + 0.2W Adjacent bays & floor above 1.2 DL + 0.5LL for rest of structure

2(DL +0.25LL) all bays and floors Loads for Static Analysis DOD GSA Requirement

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Comparison

Exterior: 1500 ft2 or 15% Interior: 3000 ft2 or 30% Exterior: 1800 ft2 Interior: 3600 ft2 Maximum Extent of Floor Collapse

Allow plastic hinges & moment redistribution DCR 6 2.0 for typical structures Acceptance Criteria specified in ACI 318 1 Strength Reduction Factor, 1.25 1.25 Material Strength Increase Factor DOD GSA Requirement

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PCA Study Objectives

1. Determine how to apply the GSA progressive collapse guidelines.

2. Determine additional reinforcement needed to meet requirements for

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References

General Services Administration

Progressive Collapse

Analysis and Design Guidelines for

New Federal Office Buildings and

Major Modernization Projects

June 2003

2000 International Building Code

ACI 318

ACI 318--99 Building Code Requirements for99 Building Code Requirements for Structural Concrete

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Study Procedure

1. Design 3 building structures for live, dead, wind, and seismic loads

2. Instantaneously remove selected first floor columns

3. Calculate the alternate path loads per GSA criteria

4. Apply the GSA loads to the structure 5. Determine moments and forces

6. Determine ultimate unfactored member capacity

7. Calculate Demand Capacity Ratios 8. Calculate additional reinforcement

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Building Plan

Number of stories: 12

Bay size in each direction: 24’ Typical story height: 12’

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Loads

Floor Live Load = 50 psf

Superimposed Dead Load = 30 psf

Dead Load

Wind Load for 70 MPH

Seismic Load

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Three Reinforced Cast-in-Place Concrete

Moment Frame Buildings

Special moment frame .61g D Intermediate moment frame .094g C Ordinary moment frame .024g A Type of Detailing Short Period Acceleration Seismic Design Class

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Load Combinations

Normal Loading U = 1.4D + 1.7L U = 0.75(1.4D + 1.7L+ 1.7W) U = 0.75(1.4D +1.7L +1.1 E)

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Analysis and Design

Select preliminary member sizes

Model in 3 dimensions

Static linear elastic analysis

Beam and column reinforcement calculated

ETABS software version 8.11

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Remove 1

stst

_{Story Columns}

Interior column removed for

parking and public space

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Alternate Load Path Analysis

Four new models of each of 3 buildings

First story columns removed

Progressive Collapse Alternate Load Path

Gravity Load = 2(DL+0.25LL)

Determine forces and moments (ETABS)

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Bending Moments

After Removing Long Side Center Column After Removing

Corner Column

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Shear Forces

After Removing Long Side Center Column

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Calculate Demand Capacity Ratios

DCR = Q

UD

/Q

CE

QUD: Acting force from alternate load path

QCE: Ultimate unfactored component

capacity with strength increased 25% Limits:

DCR < 2.0 for typical structures DCR < 1.5 for atypical structures

NEHRP Guidelines for Seismic Rehabilitation of

Buildings

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Remove 1

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DCRs Flexure - Corner Column Eliminated - B1

0 2 1 2 3 4 5 6 7 8 9 10 11 12 St o ry DCR SDC D SDC C SDC A

Study Results

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DCRs Flexure Long Side Column Eliminated -B2 0 2 1 2 3 4 5 6 7 8 9 10 11 12 St o ry SDC D SDC C SDC A

Results

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25 DCRs Flexure Long Side Column Eliminated

-B27 0.00 2.00 1 2 3 4 5 6 7 8 9 10 11 12 St or y DCR SDC D SDC C SDC A

Results

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DCR for Shear in Beams

1.04 1.04 1.46 1.46 1 1 1.01 1.01 1.39 1.39 3 3 .94 .94 1.32 1.32 5 5 .86 .86 1.23 1.23 7 7 .81 .81 1.19 1.19 9 9 .79 .79 1.17 1.17 11 11 B27 B27 B2 B2 Story Story

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Remove 1

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DCR for 1

st

Story Columns

_{Story Columns}

.44 .44 .65 .65 .84 .84 C12 C12 .59 .59 .76 .76 1.02 1.02 C11 C11 .73 .73 .88 .88 1.23 1.23 C10 C10 X X X X X X C9 C9 Seismic Seismic Class D Class D Seismic Seismic Class C Class C Seismic Seismic Class A Class A Column Column

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Summary of Results

235 of 456 55 of 456 All All All Number Add Rebar > 2.0 Beams, Class A Add Rebar > 2.0 Beams, Class C None < 2.0 Beams, Class D None < 2.0 Columns None < 2.0 Shear Action DCR Value Item

Additional rebar for “A” Structures Cost = $12,000

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Applying the GSA criteria to prevent progressive collapse for concrete buildings can be accomplished by the