GSA Progressive Collapse Design Guidelines for Concrete Frame Buildings
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This document summarizes a study on applying progressive collapse design guidelines from the General Services Administration (GSA) to concrete moment frame buildings. The study involved designing 3 buildings with different seismic design classifications and removing first floor columns to analyze the load paths. Demand-capacity ratios were calculated for members. Results showed beams in the lowest seismic class needed minor reinforcement additions, while other members met criteria without additions, demonstrating GSA guidelines can be applied at low cost.
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GSA Progressive Collapse Design Guidelines for Concrete Frame Buildings
- 1. 1 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 St. Louis, MO - August 2005
- 2. 2 Topics Topics Definition Definition Comparison of DOD & GSA requirements Comparison of DOD & GSA requirements Purpose of PCA study Purpose of PCA study Study procedure Study procedure Results Results
- 3. 3 Ronan Point Ronan Point (1968) (1968) Explosion on 18 Explosion on 18th th floor floor Wall panel blown Wall panel blown out out 22 floors collapse 22 floors collapse
- 5. 5 Prevent Prevent Progressive Progressive Collapse Collapse Explosion at ground Explosion at ground floor floor Local damage only Local damage only
- 6. 6 GSA and DOD Criteria Comparison Middle of long side, middle of short side, & corner column, at each floor one at a time Middle of long side, middle of short side, & corner column, at ground level only 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
- 7. 7 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
- 8. 8 Comparison Exterior: 1500 ft 2 or 15% Interior: 3000 ft 2 or 30% Exterior: 1800 ft 2 Interior: 3600 ft 2 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
- 9. 9 PCA Study Objectives PCA Study Objectives 1. Determine how to apply the GSA progressive collapse guidelines. 2. Determine additional reinforcement needed to meet requirements for reinforced concrete frame buildings.
- 10. 10 References References General Services Administration General Services Administration Progressive Collapse Progressive Collapse Analysis and Design Guidelines for Analysis and Design Guidelines for New Federal Office Buildings and New Federal Office Buildings and Major Modernization Projects Major Modernization Projects June 2003 June 2003 2000 International Building Code 2000 International Building Code ACI 318 ACI 318- -99 Building Code Requirements for 99 Building Code Requirements for Structural Concrete Structural Concrete
- 11. 11 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
- 12. 12 Building Plan Building Plan Number of stories: 12 Bay size in each direction: 24’ Typical story height: 12’ First story height: 15’
- 13. 13 Loads Loads Floor Live Load = 50 psf Floor Live Load = 50 psf Superimposed Dead Load = 30 psf Superimposed Dead Load = 30 psf Dead Load Dead Load Wind Load for 70 MPH Wind Load for 70 MPH Seismic Load Seismic Load - - 3 Locations 3 Locations
- 14. 14 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
- 15. 15 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)
- 16. 16 Analysis and Design Analysis and Design Select preliminary member sizes Select preliminary member sizes Model in 3 dimensions Model in 3 dimensions Static linear elastic analysis Static linear elastic analysis Beam and column reinforcement calculated Beam and column reinforcement calculated ETABS software version 8.11 ETABS software version 8.11
- 17. 17 Remove 1 Remove 1st st Story Columns Story Columns Interior column removed for parking and public space
- 18. 18 Alternate Load Path Analysis Alternate Load Path Analysis Four new models of each of 3 buildings Four new models of each of 3 buildings First story columns removed First story columns removed Progressive Collapse Alternate Load Path Gravity Load = 2(DL+0.25LL) Determine forces and moments (ETABS) Determine forces and moments (ETABS)
- 19. 19 Bending Moments After Removing Long Side Center Column After Removing Corner Column X X
- 20. 20 Shear Forces Shear Forces After Removing Long Side Center Column X
- 21. 21 Calculate Demand Capacity Ratios DCR = QUD/QCE 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 NEHRP Guidelines for Seismic Rehabilitation of Buildings Buildings- - FEMA 1997 FEMA 1997
- 22. 22 Remove 1 Remove 1st st Story Columns Story Columns
- 23. 23 DCRs Flexure - Corner Column Eliminated - B1 0 2 1 2 3 4 5 6 7 8 9 10 11 12 Story DCR SDC D SDC C SDC A Study Results Study Results
- 24. 24 DCRs Flexure - Long Side Column Eliminated - B2 0 2 1 2 3 4 5 6 7 8 9 10 11 12 Story DCR SDCD SDCC SDCA Results Results
- 25. 25 DCRs Flexure - Long Side Column Eliminated - B27 0.00 2.00 1 2 3 4 5 6 7 8 9 10 11 12 Story DCR SDC D SDC C SDC A Results Results
- 26. 26 DCR for Shear in Beams 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
- 27. 27 Remove 1 Remove 1st st Story Columns Story Columns
- 28. 28 DCR for 1 DCR for 1st 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
- 29. 29 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
- 30. 30 Applying the GSA criteria to prevent progressive collapse for concrete buildings can be accomplished by the structural engineer using readily available software and for little additional construction cost. Conclusion Conclusion
- 31. 31 Contact Information Contact Information David N. Bilow, P.E., S.E. David N. Bilow, P.E., S.E. Portland Cement Association Portland Cement Association dbilow@cement.org dbilow@cement.org 847 847- -972 972- -9064 9064 847 847- -972 972- -9065 Fax 9065 Fax 5420 Old Orchard Road 5420 Old Orchard Road Skokie, IL 60077 Skokie, IL 60077