An-Najah Staff

The current prescriptive approaches for evaluating fire resistance of reinforced concrete beams under standard fire exposure have a number of drawbacks and do not provide realistic performance assessment. As an alternative, time equivalent concept can relate the severity of design fire exposure to that of standard fire exposure. However, the current empirical formulae for evaluating such time equivalency are mainly derived for protected steel members and may not be applicable for reinforced concrete members.

This paper presents an energy-based time equivalency method for evaluating the fire resistance of reinforced concrete beams under design fire scenarios. The proposed method is based on the principle of equivalent energy, and estimates fire resistance based on the equivalency between standard and design fire exposures. The validity of the method is established by comparing the predictions from the proposed approach with those from existing methods (equivalent area method and empirical formulae) and with nonlinear finite element analysis. The applicability of the proposed approach to design situations is illustrated through a numerical example. It is shown that the proposed energy based method is capable of predicting equivalent fire resistance under design fire scenarios with an accuracy that is sufficient for practical purposes.

An approach for evaluating the fire resistance of reinforced concrete (RC) beams is presented in this paper. A macroscopic finite element model is applied to study the influence of various parameters on the fire resistance of RC beams. Data from parametric studies is utilized to develop a simplified expression for evaluating the fire resistance of an RC beam as a function of influencing parameters. The validity of the proposed approach is established by comparing the fire resistance predictions with those obtained from finite element studies as well as from fire resistance tests. Predictions from the proposed equation are also compared with fire resistance estimates from current codes of practice. The applicability of the approach to design situations is illustrated through a numerical example. The proposed rational approach expresses fire resistance in terms of conventional structural and material design parameters, and thus facilitates easy evaluation of fire resistance. The proposed approach provides better estimates than those from current codes of practice and thus can be used to evaluate the fire resistance of RC beams with an accuracy that is adequate for design purposes.

A numerical model, in the form of a computer program, for tracing the behavior of reinforced concrete (RC) beams exposed to fire is presented. The three stages associated with the numerical procedure for evaluating fire resistance of RC beams; namely, fire temperature calculation, thermal analysis and strength analysis, are explained. A simplified approach to account for spalling under fire conditions is incorporated into the model. The use of the computer program for tracing the response of RC beams from the initial pre-loading stage to collapse stage, due to the combined effect of fire and loading, is demonstrated. The validity of the numerical model is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. Through the results of numerical study, it is shown that the type of failure criterion has significant influence on predicting the fire resistance of RC beams.

In this paper, a model to predict the influence of fire induced restraints on the fire resistance of reinforced concrete (RC) beams is presented. The three stages, associated with the fire growth, thermal and structural analysis, for the calculation of fire resistance of the RC beams are explained. A simplified approach to account for spalling under fire conditions is incorporated into the model. The validity of the numerical model is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. The program is used to conduct two case studies to investigate the influence of both the rotational and the axial restraint on the fire response of the RC beams. Through these case studies, it is shown that the restraint, both rotational and axial, has significant influence on the fire resistance of the RC beams.