Analysis of perforated beams in fire using a virtual hybrid simulation approach

Abstract

This thesis is concerned with the behaviour of composite perforated beams in fire conditions, and a new virtual hybrid simulation approach is proposed to facilitate the investigation. Composite perforated beams are an increasingly popular choice in the construction of long-span floor systems as they provide a structurally and materially efficient design solution and allow space for building services. Most of the relevant research conducted to date has been focussed on isolated beam elements, assuming simply-supported boundary conditions. These simplifying assumptions are largely due to the complexity of modelling the whole structure in high definition, as well as the significant associated computational expense. However, testing and analysing isolated components inherently ignores any load redistributions which take place in the structure and does not provide an insight into the thermomechanical interactions which develop during a fire. In this context, the two primary objectives of this work are to (i) develop a usable virtual hybrid simulation framework which assesses the response of individual structural elements subjected to fire, taking account of the surrounding structure and (ii) utilise this framework to investigate the behaviour of perforated beams exposed to fire including the effects from the surrounding structure in the form of axial and rotational restraint. In the virtual hybrid simulation method, the part of the structure which is exposed to fire is modelled in fine detail using shell and solid elements and the remaining surrounding structure is represented using simpler beam-column elements. The simulation is developed using a combination of the OpenSees, OpenFresco and Abaqus softwares and enables the user to investigate the behaviour of fire-exposed components while including the effect of the remaining structure without modelling the whole system in fine detail. The accuracy of the model is validated using available fire test data. The behaviour of composite perforated beams in fire is analysed using the developed framework and then compared with the predicted response obtained by modelling isolated simply-supported beams. The results highlight the importance of including the effects from the surrounding structure in the analysis. The virtual hybrid simulation framework is then utilised to investigate the influence of the most salient parameters including the type of fire, opening layout, restraint conditions as well as the material and geometric details. In the final part of the thesis, the current ambient temperature design standards for perforated beams are modified to account for the effects of fire. A series of analytical expressions are developed to estimate the fire resistance of composite perforated beams with different opening layouts, and these predictions are compared with the fire resistance obtained from the numerical simulations. It is shown that the proposed analytical approach provides a good estimation of the fire resistance for the majority of cases.