The Assessment and Response of Concrete Structures Subject to Fire

Abstract

Over the last 20 to 30 years, the field of structural fire design has shifted from relying on single element fire resistance testing to the consideration of the effects of full-frame behaviour. The change has been driven by the desire to build more advanced structures and reduce costs. It has been facilitated in part due to structural testing, and in part due to development of complex modelling techniques. This thesis considers the modelling of concrete structures, and presents new techniques and methodologies for analysing the performance of structures in fire. The first part of this work traces modelling techniques from fundamental constitutive behaviour through to sectional capacity calculation. Load induced thermal strain and constitutive modelling approaches are investigated and their impact on structural behaviour is considered. A new, general, technique for conducting sectional analysis on concrete elements is also created. The method relies on analysis of the sectional tangent stiffness to efficiently calculate the biaxial bending capacity of a concrete section subject to any heating regime. This approach is more accurate and conservative than current methods and has the potential to be used as a design tool. This work develops a series of new approaches for the design of large structures subject to fire. A rational and quantifiable methodology is developed for assessing the performance of a structure when subject to fire; this new approach addresses the mismatch in complexity between current vi modelling techniques and measures of structural performance. It allows a more precise approach to be taken to the definition of failure; and can be easily used to compare the structure’s response to different design fires. Finally, a new technique for the definition of design fires founded on fundamental fire dynamics is presented. The approach challenges the assumptions typically made when applying temperature-time curves and is based around the observed phenomenon of travelling fires. A concrete framed structure is subject to a number of travelling fires and the response is assessed using both conventional techniques and the new, in depth analysis.