Simplified Modeling of Bonded Prestressed High Strength Concrete Girders during Fire Exposure
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.