SEISMIC PERFORMANCE OF FIRE AFFECTED BUILDINGS

Abstract

Considerable amount of work has been done on properties of materials at high temperature. Past research has looked at effect of fire on individual structural element when subjected to heating from standard fire test. While it is important to understand the performance of individual concrete members during a fire, the behaviour of the same structural elements within the context of a complete structure can vary widely from their independent responses. There is need of development of model which should consider effect of fire on the whole structure under realistic fire. Once fire breakout in the structure, it results in loss in strength of structure and it may not possible to use structure safely, especially during earthquake. There will be need of retrofitting of the structure. In severe cases of fire retrofitting may also prove to be an uneconomical solution. Hence to check this feasibility of structure for retrofitting level of damage after fire should be found out. In the present study, 2-D portal frame with four stories and four bays is analysed at post fire stage and capacity curves are drawn for different possible cases of fire occurrences. The building is assumed to be subjected to ISO fire of duration 1 hour and 2 hour. Analysis of different sections used in the frame has been done for Thermal effects and thermal profiles are plotted. Results of thermal analysis using ANSYS software are compared with experimental results by V.K.R. Kodur and Asian Concrete Model Code, (ACMC) guidelines. Also effect of area of steel on thermal profiles across the section is discussed. Cross section is idealised into a compound section of made up of strips of different material properties. These idealised sections are analysed to find moment curvature relationship and PM interactions using XTRACT. To study effect of different parameters on moment curvature and PM interaction, parametric study has been done. The moment curvature and PM interactions are used to define plastic behavior of a section i.e. hinge properties in SAP2000. Residual behaviour of the structure in form of `Capacity Curve' is obtained.