Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Youssef, Maged

Abstract

To evaluate the behavior of structures exposed to fire and estimate their structural fire resistance, engineers need design tools to overcome the complexities associated with structural analysis during fire exposure. These complexities include the uneven distribution of temperature within the structural elements and the deterioration in material properties. The current study introduces a simplified numerical model to evaluate the flexural behavior of bonded prestressed high-strength concrete sections exposed to fire. The model starts by predicting the temperature distribution within a structural element using 2-D finite difference analysis. It then uses one-dimensional sectional analysis to estimate the section behavior. The numerical model is validated using experimental work by others. The model was developed based on standard fire exposure. To generalize the model and make it valid for natural fire exposure, Equations were developed to transfer any natural fire to a standard fire with an equivalent duration. The equivalent standard fire will produce a similar internal temperature distribution within an HSC prestressed section as that by the natural fire. The equivalent duration analysis is the first to consider different cross-section shapes and account for the explosive spalling phenomenon. A parametric analysis was then conducted on prestressed concrete sections of different shapes. For each section, the structural performance was evaluated in terms of the moment-curvature diagram. Simplified equations were then developed, using non-linear regression analysis, to estimate the moment-curvature diagram of the considered sections when they are exposed to a standard fire of a specific duration.

Summary for Lay Audience

Concrete as a construction material, is performing well on load bearing and fire resisting, but when a fire event lasts more than a few hours, high temperature would decompose part of concrete exposed to fire and the concrete would lose most of its strength. Structural engineers have responsibilities to design a concrete structure to withstand the fire long enough for people to escape and provide support for the rescue effort. A reliable method is using computer software to simulate the structure behavior under fire attack, so that engineers can estimate how much load a structure can support and how long the structure can survive when it is under fire exposure. This research is focusing on prestressed high strength concrete girder, which is normally used as a critical structural member for heavy loads and long span locations, how well it can resist fire is crucial for the fire safety of the whole structure system. This thesis provides a theoretical analysis for the prestressed concrete girder exposed to fire and provides a method with computer program to calculate the girder’s behavior and capacity during fire incident. This research fills in some blanks of current structural analysis/design practice, and provides a tool to estimate the performance of prestress girders under fire exposure.

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