PhD Oral Exam - Omar El-Kafrawy, Civil Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

This thesis presents a comprehensive investigation into the progressive collapse resistance of reinforced concrete (RC) framed structures using the Alternate Path Method (APM), a widely used threat-independent design approach aimed at ensuring building stability after localized structural damage. Progressive collapse, characterized by disproportionate failure of a structure following the loss of one or more critical components, is often triggered by extreme events like explosions, impacts, or material degradation. The primary objective of this research is to evaluate the ability of RC framed structures to withstand progressive collapse under various column loss scenarios, while also examining the effects of structural simplifications and modeling reductions on analysis accuracy.

The study investigates the behavior of both full-frame and bare-frame models under the sudden removal of interior and corner columns. Nonlinear static and dynamic analyses are conducted using finite element modeling to simulate progressive collapse behavior. The research begins with a detailed calibration of analytical models against experimental data to ensure the reliability of the numerical results. A key focus is on the calculation of the Dynamic Increase Factor (DIF), a multiplier used to account for increased demands on structural elements during dynamic events. DIF values derived from pushdown and pseudo-static curves are compared with those prescribed in the General Services Administration (GSA) and Unified Facilities Criteria (UFC) guidelines. The influence of floor slabs on the structure's robustness and response is thoroughly examined and quantified, revealing a significant enhancement in progressive collapse resistance when slabs are included. Moreover, model reduction techniques are explored to achieve computational efficiency without sacrificing analysis accuracy in scenarios involving interior column loss.

In addition, this research develops a simplified approximate method for evaluating progressive collapse, which offers a practical and efficient tool for engineers to assess the vulnerability of RC framed structures. This method is validated through experimental results and could serve as a practical tool for early-stage design evaluations, offering a balance between accuracy and efficiency in progressive collapse assessment.