Slide 1

Report
Analytical Evaluation of Precast Concrete Structures Resistance to
Disproportionate Collapse
Dr. Robert B. Fleischman, Dr. Zhang, Kaylene Boroski, Seyedreza Anvar
BACKGROUND
OVERVIEW
Progressive Collapse:

When a ”disproportionately” large portion of a structure fails successively following the failure of an
initial primary structural element
Oklahoma City Bombing Before and after: initial structural failure was lower
portion of three columns and some connecting slabs (4% of building). Final failure
included 42% of structure (Lew, 2002).

Since this occurrence and other famous failures, extensive work on disproportionate collapse has
been done; most studies investigate steel and reinforced concrete structures

Precast concrete may be particularly susceptible to progressive collapse due to:
→
Long spans between vertical support members
→
Variation on behavior of structure due to connections: concrete components interacting with
embedded or attached steel connectors
General Security Administration (GSA) Guidelines:

→
→

→
→
Linear procedure: “sequence-inversion” technique
Begin with unloaded structure, with initial failed elements removed
Design loads applied statically, amplified for dynamic effects, neglects path dependent effects
Nonlinear procedure: “load-history dependent” technique
Begin with static, intact structure
Remove failed elements after applying a gradually decreasing dynamic load
CANDIDATE STRUCTURES

A: 4-story building
B: 12-story building
C: 4-story parking
garage
SDC
LFRS
Diaphragm
B
C
D
C
D
B
C
D
Ext. precast walls
Hollow core
Structure A
Ext. precast walls
Hollow core
Ext. and Int. precast
walls
Double Tee
Objectives:
→ Confirm or provide new information on the performance
of the structures relative to the linear analyses
→ Provide guidelines on the strength and deformation requirements
for precast reinforcement for structural integrity
→ Investigate advanced tools for examining progressive collapse for
precast structure
Four-story residential structure  Plan 90x64 ft.
 Precast wall panels
 Exterior shear walls: 10 in. thick
 Hollowcore diaphragm: 16 4HC 12+2 panels
 Center precast support column: 30x30 in.
 Midspan support beam: 28IT48
Emphasis on connection modeling:
Failure Conditions and Distribution:
Add real-life capacity to connections via elements acting
as tensile and shear strengths of the connections.
Three failure conditions
considered -
Example: Horizontal wall joint
Structure C
Structure C
 E-W panel
 Corner panel
MODEL DEVELOPMENT
Initial development:
Progressive collapse models are
extended from previous shake table
seismic test models:
 Precast components modeled
individually throughout structure
 Discrete modeling of connections
allowing element separation
 Elements can be non-ductile
 Improvements include vertical
connection additions and vertical loading
Re-distribution of forces upon failure:
Representation in model:
Three spring
elements, one in
direction of each
Cartesian axis:
Z: tensile forces
X and Y: shear
forces
Connections
re-distribute
forces in
secondary load
paths using
non-traditional
connection
behaviors.
Preliminary results:
 Solid structure analyzed to static
load distributions
 “Collapsed” elements removed
 Static load equivalence added to
mimic intact structure
 Load equivalence removed over
0.02 seconds for re-distribution of
loads in structure
 Structure allowed 3 seconds of
free vibration for continued load
distribution and new structural
equilibrium
X-axis stress:
Shows shear connector
activation in tension
Y-axis stress:
Shows bending stress distribution
across 3D hollowcore panel element
Remaining limitations:
Realistic progressive collapse
behavior not entirely captured.
Desired additions:
Oklahoma City bombing images: http://911research.wtc7.net/non911/oklahoma/docs/britannica.jpg
Ghosh, S. K. (2009). Design and Progressive Collapse Analysis of a Four-Story Residential Building with Exterior Walls. PCI.
Lew. (2002). “Blast and Progressive Collapse.” http://www.arquitecturaenacero.org/attachments/article/21/AISC%20-%20FACTS%202%20-%20BLAST%20AND%20PROGRESSIVE%20COLLAPSE.pdf.
 N-S panel
Three-step process -
Lost Components Considered
for Analysis
- N/S wall panel
- E/W wall panel
- Corner wall panels
- E/W wall panel
- Corner wall panels
- N/S wall panel
- E/W wall panel
- Exterior column
Structure B
Structure A description:
Recently, PCI performed a linear static study on three typical precast structures
using the GSA linear procedure, which indicates high possibility of the precast
structures to progressive collapse. The objective of this project is to extending
this work using a progressive collapse evaluation for precast structures using
dynamic analysis following the GSA nonlinear procedures. The project will
make use of existing finite element models developed for seismic analyses of
precast structures, appropriately modified for progressive collapse.
Analysis Procedure:
Candidate structures analyzed for progressive collapse potential, due to the
loss of specified support components:
Structure
CASE STUDY: STRUCTURE A
 Vertical unseating of components
 3D elements for stress distribution
→ Prospective aid in readily
determining local element failure
and approximate locations
Structure oscillation
seeking new equilibrium

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