Model-based analysis of a concrete building subjected to fire

Abstract

A case study is presented of the Windsor Tower fire in Madrid, a mainly concrete-framed office block, which was involved in a major, multiple floor fire in February 2005. The performance of the structure is documented and examined using all available methods, including analysis of data on the fire and computer modelling of the fire and structure.

Holistic structural performance during a fire is more complex than the effects of fire upon individual members which make up the structure. In concrete structures, fire conditions can have a variety of structural effects, both positive and negative, beyond the deterioration of the mechanical properties of the material. In order to properly understand the performance of concrete buildings, comprehensive models, which account for all relevant factors, are required. One of the key challenges is the limited data available from well-instrumented full-scale tests on whole concrete structures, compared to the large amount of data on the behaviour of individual concrete members and the large number of experiments carried out on steel and composite steel/concrete structures.

Here, a systematic approach is adopted for modelling, building up from fundamental, but simplified, analyses. The fire conditions have been computed using simplified analyses and Computational Fluid Dynamic (CFD) modelling. Similarly, the thermal and mechanical response of the structure is assessed using simplified analyses and Finite Element Method (FEM) modelling.

The CFD simulations provide the fire exposure histories of the structural members. The FEM calculations have examined the structural effects of changes to the concrete properties due to increased temperature. Extrapolation of results can examine redundancies within a building and their mobilisation to prevent collapse of the structure in the case of fire.

The paper gives an introduction to the Windsor Tower structure, the fire itself and further details of the methods used in modelling the fire and structural response. Model sizing, structural properties and failure modes are discussed along with initial analysis.