Investigating the Behaviour of Reinforced and Prestressed Concrete Beams Exposed to Fire

Abstract

This thesis presents investigating the behaviourof reinforced and prestressed concrete beams exposed to fire by using 3D finite element (FE) software. A two-step sequentially coupled thermal and mechanical stress analysis procedure was employed using finite element analy sis to trace the response of reinforced concrete beams. The first step simulates non-linear transient heat transfer analysis from ISO 834 time-temperature curve to the surface of con crete beam and through the length. The second step conducted nonlinear stress analysis to simulate the structural behaviour of the same beam subjected to mechanical load and nodal temperature (as nodal temperature time history) calculated from the first step. The FE mod els are validated with existing test data from literature to examine the accuracy of the simula tions. Values from the test and FE model are observed to be close to each other. Results from the analysis indicated that as fire exposure time increases the material behavior degrades since the nodal temperature distribution increases with an increase in exposure time. High temperature at bottom and both side of beam cause the tensile reinforcement to lose its flex ural strength as well as the concrete in the compression zone to lose its compressive strength. This reduction in the flexural strength of the beam will result in increasing deflections. Stress in RC beam increased at 30 and 60 minute, but after 60 minute exposure as time increases stress decreases. Stress in PC beam decreased as exposure time increased. It is hoped that this study can lay a basis for numerical analysis of fire effects in other structural elements, i.e., slabs, frames, and walls.