Date of Award

Summer 7-1-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Aboutaha, Riyad S.

Keywords

CFRP jacketing, High strength concrete, Post-fire behavior, Rehabilitation, Residual axial capacity, Steel jacketing

Subject Categories

Civil and Environmental Engineering | Civil Engineering | Engineering

Abstract

In recent decades, the post-fire behavior of reinforced concrete (RC) columns with normal and high-strength concrete has become an important research topic. Numerous studies have demonstrated that RC columns exhibit good fire resistance owing to the thermal properties of concrete. Therefore, reinforced concrete structures rarely collapse within a finite fire duration and can be successfully repaired. Along with the increasing number of skyscrapers, high-strength concrete (HSC) has played an equally important role as normal-strength concrete (NSC) in the industry. In this study, the thermal behavior of RC columns with NSC and HSC exposed to ISO 834 standard fire for various durations was studied experimentally and numerically. The mechanical behaviors of post-fire RC columns and columns retrofitted with carbon fiber-reinforced polymer (CFRP)/steel jackets were investigated. The effectiveness of each strengthening scheme was evaluated, and analytical models were proposed to estimate the axial strengths of post-fire RC columns and retrofitted RC columns.In the experimental phase of the study, the thermal behavior of circular RC columns exposed to ISO 834 standard fire was determined experimentally and discussed. The major variables considered were fire exposure time and concrete compressive strength at room temperature. The fire exposure times were set as 60, 90, and 120 mins to investigate the effect of fire duration on the temperature distribution inside the columns. The concrete strength of the RC columns ranged from 50 MPa to 90 MPa to investigate the different thermal behaviors of RC columns with different concrete strengths. In addition, post-fire columns were retrofitted with CFRP and steel jackets to evaluate the effectiveness of the retrofitting system on strength, stiffness, ductility, and energy dissipation. In the numerical phase of the study, finite element modelling (FEM) was performed to simulate the heat transfer process and compressive structural behavior of post-fire RC columns and retrofitted columns. Two 3-D finite element models – one to simulate the temperature field development and one to simulate the structural behavior – were developed and verified against experimental results. There was good agreement between the finite element results and experimental results in terms of the axial strength, load-displacement response, and failure mode. Furthermore, a parametric study was performed on the finite element (FE) models to further study the fire exposure time up to 240 min, and the number of CFRP layers up to three. In the last phase of this research, analytical models to estimate the axial strength of post-fire RC columns, post-fire RC columns retrofitted with CFRP jackets, and post-fire RC columns retrofitted with steel tubes were proposed based on experimental data and parametric studies.

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Open Access

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