Analytical Evaluation of Precast Concrete Structures Resistance to Disproportionate Collapse

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Nov 26, 2013 (3 years and 8 months ago)

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Analytical Evaluation of Precast Concrete Structures Resistance to
Disproportionate Collapse











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).


Candidate structures analyzed for progressive collapse potential, due to the

loss of specified support components:


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


Preliminary results:

Dr. Robert B. Fleischman, Dr. Zhang, Kaylene Boroski, Seyedreza Anvar

Structure

SDC

LFRS

Diaphragm

Lost Components Considered
for Analysis

A:

4
-
story building

B

C

D

Ext. precast walls

Hollow core

-

N/S

wall panel

-

E/W wall panel

-

Corner wall panels

B:

12
-
story building

C

D

Ext. precast

walls

Hollow core

-

E/W

wall panel

-

Corner wall panels

C:
4
-
story parking

garage

B

C

D

Ext. and Int. precast
walls

Double

Tee

-

N/S wall panel

-

E/W wall panel

-

Exterior column

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
.


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

OVERVIEW

BACKGROUND

CASE STUDY: STRUCTURE A

MODEL DEVELOPMENT


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

Structure C

Structure C

Structure B

Structure A

Re
-
distribution of forces upon failure:

Three spring
elements, one in
direction of each
Cartesian axis:


Z: tensile forces


X and Y: shear
forces



Example:

Horizontal wall joint

Representation in model:

Analysis Procedure:

Three
-
step process
-



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


Remaining limitations:

Realistic progressive collapse
behavior not entirely captured.
Desired additions:


Vertical unseating of components


3D elements for stress distribution


Prospective aid in readily
determining local element failure
and approximate locations


Structure A description:

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:

Add real
-
life capacity to connections via elements acting
as tensile and shear strengths of the connections.


Failure Conditions and Distribution:

Three failure conditions
considered
-



N
-
S panel



E
-
W panel



Corner panel




Connections
re
-
distribute
forces in
secondary load
paths using
non
-
traditional
connection
behaviors.



X
-
axis stress:

Shows shear connector
activation in tension


Y
-
axis stress:

Shows bending stress distribution
across 3D hollowcore panel element


Structure oscillation
seeking new equilibrium


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.