Numerical investigation on dynamic characteristics changes of RC columns and frames under elevated temperature

Abstract

Fire hazard is a high impact threat to human life and engineering structures, which may result in significant loss of strength and huge damage to building components. In order to determine the strength and durability of structural elements after the fire and consequently to clarify the serviceability status for planning the necessary maintenance strategies, the structural behaviours of building elements under elevated temperature is to be precisely evaluated. Therefore, this work generates the accurate structural assessment data for fire performance assessment of reinforce concrete columns and frames by performing heat transfer and modal analyses along with numerical methods using special finite element software. Moreover, the results are compared with both analytical and numerical methods in order to validate the software results. On this basis, the results are first compared with Eurocode 2) as well as Wickstrom and Hertz methods and then the resulted data are further validated numerically using different software. In other words, this study evaluates the performance of structural elements under fire load, while conducting a comprehensive and detailed performance assessment on dynamic characteristics named as natural frequencies, mode shapes and damping ratios. Moreover, the effects of varying cross-sectional dimensions, concrete grades, exposure durations and different exposure scenarios of reinforce concrete elements are precisely evaluated using parametric analyses, and the resulted data set is presented as set of formulas, nomographs and tables. The parametric study points out the influence of elevated temperatures on natural frequency values and mode shapes. Consequently, the rise in temperature resulted in significant decrease in natural frequency values. However, no specific pattern has been observed for the changes in resulted mode shapes. The outputs are generally based on the natural frequency values and the amount of change in these values for various situations. It is hoped that the results will actively contribute to the further development of existing fire regulations in the area of structural health monitoring at elevated temperatures.