Developing OpenSees software framework for modelling structures in fire

Abstract

Fire following an earthquake (FFE) is a hazard that is not usually accounted for in either earthquake or fire resistant design of structures. There have however been many instances in the past of FFE events causing even greater damage and even loss of life than the original earthquake. The potential damage associate with this hazard is increasing considerably with increasing urbanisation in seismically vulnerable regions. It is reasonable for users to expect that structures should maintain their integrity for a long enough period in an FFE event allowing emergency crews to assist the most vulnerable occupants to evacuate the building safely. Because of the lack of regulatory requirements there is naturally very little research on the response of structural frames under FFE events so far, but given the reasons discussed earlier, it is clearly a matter of increasing importance that engineers should develop a better understanding of the behaviour of seismically damaged structural frames in fire. This thesis project was fortunate to have occurred at a time when a set of full-scale fire tests were taking place at IIT Roorkee in India, in collaboration with the University of Edinburgh to address exactly this topic. This thesis research was undertaken to model these experiments (to determine the fire resistance of a reinforced concrete frame first subjected to simulated seismic damage). The open source software framework OpenSees was chosen for the modelling work as it was considered to be the best software tool for modelling structures under earthquake loading. The first part of this thesis reports the development work done on OpenSees for adding thermomechanical analysis modules to enable the modelling of FFE events using this software framework. The code developed for OpenSees has been allowed the introduction of features not available in commercial software such as ABAQUS. Many new classes were developed, such as ThermalAction, ThermalElement, ThermalSeciton, TheramalMaterial, etc. The newly developed code was tested using a number of benchmark problems and modelling of real fire experiments on steel and composite framed structures. The results from these tests showed that the new developments were successful. The second part of the thesis describes the modelling of the reinforced concrete (RC) frame tested at IIT Roorkee, which was first subjected to cyclic displacement loading (to introduce damage in the frame similar to that of a seismic event) and then to a one hour kerosene fire. The modelling was first used to provide predictions of the performance of the test frame under the proposed loading, to fine tune the design of the experiment. The modelling subsequent to the tests was gradually improved to achieve better comparisons with the test results and to develop a detailed understanding of the behaviour of seismically damaged RC frames in fire, which was also compared to the behaviour in fire of undamaged frames.