Beyond Alternate Load Path Method: Progressive Collapse Analysis Accounting Initial Condition and Damage
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Date
2024-05
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Addis Ababa University
Abstract
This thesis investigates progressive collapse analysis accounting initial conditions and damage. A method proposed by Shi et al., is considered with modification on the calculation of the residual axial load carrying capacity. The research aimed to demonstrate the overestimation of the potential for progressive collapse using the Alternate Load Path Method (APM) analysis. The methodology involved: conventional design of a 3-story moment-resisting frame, selection of a single charge weight, selection of 12 blast locations, calculation of reflected blast pressure at two points per column (center for flexure and end for direct shear), SDOF analysis of each column based on the angle of incidence, computation of residual axial load carrying capacity and initial displacement and velocity, and finally, progressive collapse analysis using these initial conditions. The key findings revealed that APM analysis overestimates the building's capacity. Compared to the benchmark analysis (blast-structure interaction), APM analysis either predicted partial collapse or no collapse at all. In contrast, APM with initial conditions and damage showed a similar trend to the benchmark analysis. However, for blast locations where no columns failed under direct blast loading, APM with initial conditions resulted in a progressive collapse occurring later than the benchmark analysis, with smaller transverse displacements, comparatively, over time. Nevertheless, progressive collapse was still triggered, with vertical displacement and velocity showing similar trends at the final stage. These findings suggest that using APM alone is inaccurate for investigating the potential for progressive collapse from blast loads. However, incorporating initial velocity and damage of all columns into the APM analysis yields results comparable to the blast-structure interaction method.
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Progressive Collapse Analysis, Load Path, Damage