Date of Award

12-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Committee Chair

Amit H. Varma

Committee Member 1

Mark D. Bowman

Committee Member 2

Robert J. Connor

Committee Member 3

Erica C. Fischer

Committee Member 4

Judy Liu

Abstract

Multi-hazard analyses can be used to create more sustainable and resilient structural designs by considering cascading hazards and the overall system performance of structures exposed to multiple hazard types. This dissertation develops a methodology to assess building resilience for seismic, wind, fire, and post-earthquake fire scenarios. Special emphasis is placed on understanding the interdependencies and relationships between earthquake and fire damage in the assessment of structures for post-earthquake fire. The proposed methodology includes designing a building structure according to the latest building codes, developing a three-dimensional (3D) finite element method (FEM) computer model to represent building behavior, and conducting incremental dynamic and incremental fire analyses as a means to assess building performance to multiple cascading hazards. The approach is articulated by analyzing two 10-story steel structures. These structures were designed for hazard levels in Chicago, IL and Los Angeles, CA. The buildings have the same geometry and gravity framing, but vary in the design of the perimeter moment resisting frames (MRFs). Detailed 3D FEM building models were developed in ABAQUS in order to more adequately simulate real-building behavior. The framing members are modeled using beam elements and the composite floor slabs are modeled as shell elements. This model provides building level response to earthquakes, wind, fires, and fires following earthquakes. It permits redistribution of loading through catenary action during column failure in a fire event and can simulate connection and member failures. In order to simulate seismic hazards, nonlinear time history ground displacement records were applied to the base of the building and Rayleigh damping was implemented. Because ABAQUS is not traditionally used to simulate seismic building behavior, the seismic response was validated using another computer program. Fire loads were modeled using parametric time-temperature curves from Eurocode to simulate compartment fires at the first, fifth and ninth stories of the buildings. Damage from the seismic structural model was imported into the fire structural model in order to capture post-earthquake fire behavior. The level of modeling within each model varied as necessary in order to adequately capture building behavior for each hazard, while maintaining computational efficiency. The findings of this study show that post-earthquake fire resilience for structures in high and low seismic areas are the same regardless of seismic damage, as long as moment frame connections have not fractured. For compartment fires where there is no seismic damage (no plastic hinging or fracture of members), the system responds the same as a fire-only scenario. Gravity columns are the most vulnerable components because of their high utilization ratio. Buckling of gravity columns can cause column, bay or system failures in the corner, edge and interior compartments, respectively. The perimeter moment frame system can help to prevent system collapse due to gravity column failure, but it cannot prevent the gravity column failure from occurring. In some cases, moment frame connection fractures may result in additional, subsequent failure modes (such as system collapse) that occur after gravity column failure initiates. Pilot studies show that increasing gravity column sizes or its fireproofing can increase the multi-hazard resilience of the system. These modifications can prevent gravity column failure from occurring and, in turn, any subsequent failures that may occur in response. In addition, implementing a rebar mat within the composite slab can help to redistribute loads and prevent progressive collapse in interior compartments. Studies were also performed to examine the effect of fireproofing damage on the fire resilience of the structure.

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