IDRC14-MehrdadSasani

5th International Disaster and Risk Conference IDRC 2014
‘Integrative Risk Management - The role of science, technology & practice‘ • 24-28 August 2014 • Davos • Switzerland
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A Multihazard View of
Progressive Collapse Resistance
for Enhancing Resilience of Society
Mehrdad Sasani
Department of Civil and Environmental Engineering
Northeastern University
Boston, MA, USA

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Engineering Community Resilience
Resilience is defined as ability to prepare and plan for, absorb, recover
from, or adapt to actual or potential adverse events within and across
built environment, social, economic, and ecological domains (NAS,
2012)
We touch on both engineering aspects of resilience and decision
making approach for achieving community resilience
• Engineering resilience, as it relates to evaluating performance of
structures and infrastructures, comprises a subset of issues relevant
to community resilience
• Identifying strategies to improve community resilience is largely
driven by engineering, economic and environmental sciences
• Social agreement, however, will likely differ for different
communities and it is important to have an adaptable framework
for achieving resilient communities

From Performance to Resilience Based Design
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Time to recovery
(Consequence in terms of extent of damage and repair costs)
Hazard
Years ≡
No Collapse
(Extreme)
Months
(High)
Weeks
(Medium)
Days
(Low)
Extreme
High
Medium
Low

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Why is collapse resistance important?
• There is a continuing effort to use risk-based (as opposed to
uniform hazard-based) approaches in building codes (e.g.
ASCE 7-10, 2010)
• In seismic design, a uniform risk of collapse is now used as
basis of new risk-targeted ground motion maps
• Trauma caused by collapse of buildings is primary cause of
deaths and injuries in most earthquakes (Coburn and
Spencer, 2002)
• Similarly for response to blasts, majority of 168 fatalities
during 1995 bombing of Murrah Federal building were due to
partial collapse of structure and not to direct blast effects
(Unified Facilities Criteria, 2009)

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Multihazard View (e.g. Seismic vs Blast)
Important structural characteristics for collapse resistance
• For seismic ground motions, structural deformation capacity
and ductility are primary characteristics of importance
(Sozen, 1981)
• For a structure designed as ductile (special), lateral loads are
3/8th of those for an ordinary structure
• In order to resist collapse following loss of columns (say due
to blasts), however, the strength of the structure to
redistribute gravity loads can become very important



m
F
m
F
Gravity Load
P
Gravity Load


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P
Equivalent SDOF system
Front view of 3D structure
Equivalent SDOF system
Front view of 3D structure
Sasani, M. and Sagiroglu, S., "Progressive collapse of RC structures: A multihazard perspective," Structural
Journal, ACI, Vol. 105, No. 1, pp. 96-103, 2008.

Strain Hardening
Coefficient
40
30
20
10
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0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Yield Force / Column Axial Force
0
Displacement Ductility Demand
=0.03
=0.05
=0.1
=0.2
=0.4

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Enhancing Resilience
In order to evaluate current state of resilience and identify
strategies for improving community resilience there is a need to
consider:
a. individual structures and infrastructures
b. systems , such as transportation, communication, Water
supply and distribution, health, and financial
c. System of systems (i.e. community)

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For each level of multiple hazards,
1. Evaluate risks to individual components of each system (for
instance a bridge within the transportation system or a
power plant within the electric grid).
2. Express risks in terms of time to recovery, and percent
functional, which should be conducted more importantly at
system level, considering systems interaction
3. Identify and quantify other resilience metrics such as
collapse likelihood, cost of repairs, as well as social and
environmental impacts (as continuous or for simplicity as a
discrete quantity)
4. Final and most important step is decision making

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• One approach to evaluate resilience is to consolidate its
metrics so that community resilience can be measured and
compared quantitatively, even by a single measure, such as
cost.
• Another approach is to avoid directly combining resilience
metrics and instead categorizing and providing data about
different metrics of resilience (including both quantitative,
such as economic cost and time to recovery, and qualitative,
such as social and environmental impacts data) to facilitate
decision making by communities.

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Other Metrics

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Conclusions
• Representative engineering aspects of resilience is discussed
in context of multiple hazards (e.g. seismic vs blast effects)
• Importance of structural strength to redistribute gravity loads
and resist collapse following severe hazards is demonstrated
• While risk assessment based on sound engineering principles
is required, it is not sufficient for decision making and social
agreement
• An approach is presented to help decision making process
and achieving resilience goals considering communities’
resources and priorities

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Relation to Post 2015 Framework for
Disaster Risk Reduction
This study can be considered in context of disaster risk reduction at 2 levels:
1. From specific structural engineering point of view, important structural
characteristics relevant to resilience under multiple hazards must better
understood to optimize use of limited resources in enhancing resilience.
2. From a general point of view, it is an effort to emphasize that resilience
goals and objectives must be adaptable to societal priorities as opposed to
being uniquely and strictly defined for all, leaving communities with the sense
that: “We cannot achieve resilience.” Instead, provide them with an
adaptable framework and options they can choose from.
• Needs for Post 2015 Framework for Disaster Risk Reduction
– Research is needed at both levels
From an engineering point of view structural characteristics in context of
multiple hazards must identified
From a general point of view, research is neede3d to make resilience an
achievable and relative goal

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Acknowledgement
Inputs and comments made by Professor Matthias Ruth is
greatly appreciated.

IDRC14-MehrdadSasani

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