Fundamental principles of structural behaviour under thermal effects

Abstract

This paper presents theoretical descriptions of the key phenomena that govern the behaviour of composite framed structures in fire. These descriptions have been developed in parallel with large scale computational work undertaken as a part of a research project (The DETR-PIT Project, Behaviour of steel framed structures under fire conditions) to model the full-scale fire tests on a composite steel framed structure at Cardington (UK). Behaviour of composite structures in fire has long been understood to be dominated by the effects of strength loss caused by thermal degradation, and that large deflections and runaway resulting from the action of imposed loading on a 'weakened' structure. Thus 'strength' and 'loads' are quite generally believed to be the key factors determining structural response (fundamentally no different from ambient behaviour). The new understanding produced from the aforementioned project is that, composite framed structures of the type tested at Cardington possess enormous reserves of strength through adopting large displacement configurations. Furthermore, it is the thermally induced forces and displacements, and not material degradation that govern the structural response in fire. Degradation (such as steel yielding and buckling) can even be helpful in developing the large displacement load carrying modes safely. This, of course, is only true until just before failure when material degradation and loads begin to dominate the behaviour once again. However, because no clear failures of composite structures such as the Cardington frame have been seen, it is not clear how far these structures are from failure in a given fire. This paper attempts to lay down some of the most important and fundamental principles that govern the behaviour of composite frame structures in fire in a simple and comprehensible manner. This is based upon the analysis of the response of single structural elements under a combination of thermal actions and end restraints representing the surrounding structure. r

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“…A clean stability failure mechanism is clearly indicated by a simple computational analysis. Not only this, the analysis is entirely consistent with the fundamental principles developed during the Cardington work [2]. The following sections report in reasonable detail the various steps of the analysis undertaken…”

“…Computational modelling and analytical studies [1,2] at Edinburgh University have shown that of these two competing effects in large frame structures, the former dominates the behaviour of the structure in the early stages while the latter becomes important near failure. In this paper structural behaviour is interpreted by analysing the typical structural responses to loading, namely, strains and stresses and more importantly their resultants (integrals), i.e.…”

“…The load capacity is further enhanced by thermally induced pre-stressing in laterally restrained slabs and composite floor systems Local buckling (this is a misnomer as this is in fact 'local yielding' [8]) of the lower flanges of steel beams (acting compositely with the slab) occurs at relatively low steel temperatures (between 100 ¡ C to 200 ¡ C) but this was not found to be a detrimental mechanism A number of generally applicable fundamental principles of structural behaviour in fire were identified to be important as part of the modelling and analysis exercise [2] and proved invaluable in making sense of the complex computational results. These are:…”

Fire Insulation of Aluminum Glazed Partitions Depending on the Infill Solution of Framework Profiles

“…The metal profiles are composed of aluminium or steel elements connected with thermal separator (three-chamber profiles) [30]. In case of metal profiles, it is essential to proper fill in their section in order to ensure insulation of the profiles and reduce the adverse impacts of the thermal stress [31]. Inside the profiles there are placed special insulating inserts usually made of gypsum plasterboards, silicate -cement boards, silicate -calcium boards or mineral wool plates, although on the market are also present solutions with timber infill [32], [33].…”

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“…Two of them are from connections of group one and the two others are related to the connections of group two. Characteristics of the specimens are presented in Table 4 for every specimen [7,8].…”