progressive collapse 23
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GSA Progressive Collapse Design
Guidelines Applied to
Concrete Moment-ResistingFrame Buildings
David N. Bilow, P.E., S.E. andMahmoud E. Kamara, PhDPortland Cement Association
Tri-Service Infrastructure SystemsConference & ExpositionSt. Louis, MO - August 2005
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TopicsTopics
DefinitionDefinition
Comparison of DOD & GSA requirementsComparison of DOD & GSA requirements
Purpose of PCA studyPurpose of PCA study
Study procedureStudy procedureResultsResults
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Ronan PointRonan Point(1968)(1968)
Explosion on 18Explosion on 18thth
floorfloor Wall panel blownWall panel blown
outout
22 floors collapse22 floors collapse
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Ronan PointRonan Point
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PreventPrevent
ProgressiveProgressiveCollapseCollapse
Explosion at groundExplosion at ground
floorfloor
Local damage onlyLocal damage only
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GSA and DOD Criteria Comparison
Middle of long side,
middle of short side, &
corner column, at eachfloor one at a time
Middle of long side,
middle of short side, &
corner column, atground 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 horizontaltie forces, and ductilityRedundancy, ductility& continuityTieRequirements
Very Low, Low, Medium,and High
Exempt or nonexemptLevel of Protection
(LOP)
DODGSARequirement
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Comparison
Linear static, nonlinear static,
or nonlinear dynamic
Linear static
preferred
Method of
Analysis
1.0DL + 0.5LLRecommendedUpward Loads onFloor Slabs
1.2DL + 0.5LL + 0.2WDL + 0.25LLLoads forDynamic 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 andfloors
Loads forStatic Analysis
DODGSARequirement
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Comparison
Exterior: 1500 ft2
or 15%Interior: 3000 ft
2or 30%
Exterior: 1800 ft2
Interior: 3600 ft2
Maximum Extent of Floor Collapse
Allow plastic hinges & moment redistribution
DCR 6 2.0 fortypical structures
Acceptance Criteria
specified in ACI 3181Strength ReductionFactor,
1.251.25Material StrengthIncrease Factor
DODGSARequirement
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PCA Study ObjectivesPCA Study Objectives
1. Determine how to apply the GSA progressive collapse guidelines.
2. Determine additional reinforcement
needed to meet requirements forreinforced concrete frame buildings.
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ReferencesReferences
General Services AdministrationGeneral Services Administration
Progressive CollapseProgressive Collapse
Analysis and Design Guidelines for Analysis and Design Guidelines for
New Federal Office Buildings andNew Federal Office Buildings andMajor Modernization ProjectsMajor Modernization Projects
June 2003June 2003
2000 International Building Code2000 International Building Code
ACI 318 ACI 318--99 Building Code Requirements for99 Building Code Requirements for
Structural ConcreteStructural Concrete
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Study Procedure
1. Design 3 building structures for live,
dead, wind, and seismic loads2. Instantaneously remove selected firstfloor columns
3. Calculate the alternate path loads perGSA criteria
4. Apply the GSA loads to the structure5. Determine moments and forces
6. Determine ultimate unfactored membercapacity
7. Calculate Demand Capacity Ratios
8. Calculate additional reinforcement
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Building PlanBuilding Plan
Number of stories: 12
Bay size in each direction: 24’
Typical story height: 12’
First story height: 15’
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LoadsLoads
Floor Live Load = 50 psf Floor Live Load = 50 psf
Superimposed Dead Load = 30 psf Superimposed Dead Load = 30 psf
Dead LoadDead Load
Wind Load for 70 MPHWind Load for 70 MPHSeismic LoadSeismic Load -- 3 Locations3 Locations
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Three Reinforced Cast-in-Place Concrete
Moment Frame Buildings
Special momentframe
.61gD
Intermediate
moment frame
.094gC
Ordinary momentframe
.024g A
Type of DetailingShort Period Acceleration
SeismicDesign 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 Analysis and Design Select preliminary member sizesSelect preliminary member sizes
Model in 3 dimensionsModel in 3 dimensions
Static linear elastic analysisStatic linear elastic analysis
Beam and column reinforcement calculatedBeam and column reinforcement calculated
ETABS software version 8.11ETABS software version 8.11
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Remove 1Remove 1stst Story ColumnsStory Columns
Interior columnremoved for
parking and publicspace
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Alternate Load Path Analysis Alternate Load Path Analysis
Four new models of each of 3 buildingsFour new models of each of 3 buildingsFirst story columns removedFirst story columns removed
Progressive Collapse Alternate Load Path
Gravity Load = 2(DL+0.25LL)
Determine forces and moments (ETABS)Determine forces and moments (ETABS)
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Bending Moments
After Removing Long
Side Center Column
After Removing
Corner Column
X X
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Shear ForcesShear Forces
After Removing LongSide Center Column
X
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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
BuildingsBuildings-- FEMA 1997FEMA 1997
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Remove 1Remove 1stst Story ColumnsStory Columns
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DC Rs Flexure - Co rner C olumn Eliminated - B 1
0 2
1
2
3
4
5
6
7
8
9
10
11
12
S t o r
y
D C R
SDC D
SDC C
SDC A
Study ResultsStudy Results
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DCRs Flexure - Long Side Column Eliminated -
B2
0 2
123
45678
9101112
S t o r y
DCR
SDC D
SDC C
SDC A
ResultsResults
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DCRs Flexure - Long Side Column Eliminated -
B27
0.00 2.00
1
234
56
78
91011
12
S t o r y
DCR
SDC D
SDC C
SDC A
ResultsResults
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DCR for Shear in BeamsDCR for Shear in Beams
1.041.041.461.4611
1.011.011.391.3933
.94.941.321.3255
.86.861.231.2377
.81.811.191.1999
.79.791.171.171111B27B27B2B2StoryStory
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Remove 1Remove 1stst Story ColumnsStory Columns
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DCR for 1DCR for 1stst
Story ColumnsStory Columns
.44.44.65.65.84.84C12C12
.59.59.76.761.021.02C11C11
.73.73.88.881.231.23C10C10
XXXXXXC9C9
SeismicSeismicClass DClass DSeismicSeismic
Class CClass CSeismicSeismicClass A Class A ColumnColumn
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Summary of Results
235 of 456
55 of 456
All
All
All
Number
Add Rebar> 2.0Beams, Class A Add Rebar> 2.0Beams, Class C
None< 2.0Beams, Class D
None< 2.0Columns
None< 2.0Shear
ActionDCR ValueItem
Additional rebar for “A” Structures
Cost = $12,000
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Applying the GSA criteria to preventprogressive collapse for concrete
buildings can be accomplished by thestructural engineer using readily
available software and for little additional
construction cost.
ConclusionConclusion
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Contact InformationContact InformationDavid N. Bilow, P.E., S.E.David N. Bilow, P.E., S.E.
Portland Cement AssociationPortland Cement Association
dbilow@cement.orgdbilow@cement.org
847847--972972--90649064847847--972972--9065 Fax9065 Fax
5420 Old Orchard Road5420 Old Orchard Road
Skokie, IL 60077Skokie, IL 60077
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