Behaviour of earthquake damaged composite steel frame structures in fire

UoM administered thesis: Phd

  • Authors:
  • Riza Suwondo

Abstract

Post-earthquake fire events over the past few decades have become a major threat for buildings in seismic prone regions. Although post-earthquake fire events have caused many fatalities and high levels of damage, current building codes do not consider fire following an earthquake as a specific loading case. Furthermore, the current philosophies of seismic design permit a certain degree of damage to the structural elements which potentially makes structures more vulnerable when subjected to post-earthquake fire. This study is intended to address the fact that only limited research exists on the behaviour of earthquake damaged composite steel frames in a fire. The main objective is to improve the current understanding of post-earthquake fire behaviour of composite steel frames with a view to providing design recommendations. This study analysed a generic five-storey composite steel frame office building which is commonly used for modern buildings in seismic regions. For the first time, three-dimensional numerical models were developed to simulate the structural behaviour under fire following an earthquake. The finite element software ABAQUS v6.13 was used to model the structures. Steel beams and columns were modelled using two-node linear beam elements while concrete slabs were modelled using shell elements. A series of verification analyses were conducted to ensure that the results obtained from analysis give an acceptable level of accuracy. The finite element model was used to investigate the effect of earthquake damage on the fire resistance of composite steel frame buildings. A total of two types of earthquake damage; fire insulation delamination and residual lateral deformation, were investigated. Failure of the structure was defined using two measures, a beam deflection exceeding span/20 and column buckling. It was found that the earthquake damage can significantly reduce the fire resistance of the composite building. The reduction in fire resistance times results mainly from fire insulation delamination, particularly in the columns, rather than residual deformation. It was also found that fire insulation delamination on the protected beams, as might occur in an earthquake, considerably reduces the development of tensile membrane action. This has significant consequences for design because the benefits of tensile membrane action are often used for performance-based fire design of composite structures. Two methods of improvement are presented in this study to enhance the development of tensile membrane action concurrent with fire insulation delamination. Based on the results obtained, increasing slab thickness and improving fire protection rating can enhance the fire resistance of the whole building even with fire insulation delamination. The progressive collapse analysis of a 3D composite building under fire following an earthquake was also investigated. Several different locations of fire scenarios were first studied to investigate load redistribution path along two horizontal directions and the members’ interaction within the composite building frame. Then, the effect of residual deformation after an earthquake on the progressive collapse analysis of the composite building was investigated. It is found that neither the load redistribution path nor the fire resistance of the building is considerably affected by the residual deformation. A series of progressive collapse analyses subjected to travelling fire resulting from fire compartment damage was also performed. It is concluded that the survival of the building can be greatly affected by the spatial nature of the travelling fire as well as the inter-zone time delay. Therefore, a range of travelling fire scenarios must be considered based on the compartment condition to guarantee that the building can withstand the ‘worst case scenario’.

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Original languageEnglish
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Award date31 Dec 2019

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