Влияние динамического эффекта на несущую способность железобетонных колонн, работающих в условиях огневых воздействий

Abstract

This article provides an example of the calculation of eccentrically compressed reinforced concrete elements exposed to dynamic loads and fire effects. The dynamic factor for the concrete under regular conditions is available, and it exceeds one in any case. However, in case of a fire exposure, the value of this factor varies from 0,4 to 0,8, depending on the loading rate and temperature. The value of the dynamic factor was identified in the course of an experiment; thereafter, the pattern of influence of the dynamic effect caused by the progressive collapse of buildings and produced onto the bearing capacity and fire resistance of compressed elements of the pylon and the column was identified. ANSYS 12.1 software package was employed to perform the fire resistance analysis of the pylon on the 1st floor of a 59-storey building. The problem was modeled in the 3D formulation. It represented a pylon exposed to static loading and standard fire conditions. For comparison purposes, bearing capacity values were calculated for different values of the thermal load. The calculation of temperature fields was based on the resolution of boundary value problems of transient heat conduction in capillary-porous bodies. The solution to the problem of the four-sided fire exposure at standard fire temperature values was obtained in characteristic points of the support structure to assess the change in its load-bearing capacity. It is proven that dynamic effects of a fire reduce the bearing capacity of columns by 40 %. Therefore, the analysis of the bearing capacity of structures in terms of their fire resistance should take account of the possibility of progressive collapse of buildings.