REINFORCED CONCRETE ELEMENTS SUBJECTED TO FIRE ATTACK

D. Reshmasri, B. Dheera Lessa, N. Murali Krishna

Abstract: In these days of rapid urbanization the frequency of accidents due to fire are high. Structural sustenance thereafter is always doubtful. Non availability of technical literature on concrete behavior at elevated temperatures is the reason for this shortcoming. Even if such information is available, it is too inadequate to predict the longevity of the structure and its utility for occupation. In this backdrop the present study using FEM approach is taken up to evaluate the extent of damage due to fire attack making use of MSC Nastran. The accidents due to fire are more frequently caused by electric short circuiting in the control panel rooms in high raised buildings. The damage caused to column elements is often considered more critical as the columns are the principal load carrying members transferring loads from the superstructure to footings. In the present study heat propagation in a portion of a column member subjected to heat of 10000C acting for duration of two hours is evaluated using MSC Nastran. The temperature variation across the thickness of concrete is studied considering the variation of thermal conductivity with temperature and porosity. The propagation of heat and the corresponding distress to concrete is determined from surface to the central core of the column along the shorter dimension. The output results obtained from the transient thermal analysis module of Nastran are fed as inputs to the structural analysis module to obtain the stresses and strains caused by fire. A large data of such information with varying parameters of temperature, duration of fire attack and concrete properties is proposed to be generated to be used later as set of training patterns to train a BOPN based neural net paradigm. The information from the neural net output would be used for working out the sizes of equivalent structural elements in the distressed structure. The revised structural configuration with the distressed RC element replaced by equivalent elements should facilitate the structural assessment

Keywords: Temperature, Thermal Stress, Thermal Strain, Thermal Conductivity, Porosity, Neural Network

DOI: https://doi.org/10.15623/ijret.2015.0413020