Ove Pettersson

Rational Design Methodology for Fire Exposed Load Bearing Structures

The state-of-art of reliability studies in the area of fire-exposed structures or structural members is illustrated, taking examples from published papers concerning load-bearing building structures of steel, reinforced concrete, and wood. In parallel, trends are described in the present development of rational structural fire design methods, principally adapted to modern loading and safety philosophy for the non-fire state. Statistically derived results are presented for fire-exposed, insulated steel structures in office buildings, giving the breakdown of the total variance in maximum steel temperature and load-bearing capacity into component variances as a function of the insulation characteristics. The safety index and probability of failure are compared numerically for different fire design procedures. The data presented are examples of the information which is required as input in a qualified systems analysis of fire exposed load-bearing structures.

On the Fire Resistance of Structural Steel Elements Derived from Standard Fire Tests or by Calculation

Abstract Due to high costs, a fire resistance test of a load-bearing structural element is usually limited to one test specimen — in a few countries, to two test specimens. Accordingly, there are no possibilities of evaluating the test results statistically. For a single test specimen, the actual quality of the structural material represents a random sample from a wide variety. This applies also to the initial imperfections of the structural elements. In consequence of this, a standard fire resistance test is generally carried out on a test specimen with a load-bearing capacity which is greater — most often significantly greater — than the load-bearing capacity related to the characteristic values of the mechanical material strength and of the imperfections of the structural member. In current practice, no corrections of the test results with respect to this are made. In a conventional analytical design, a determination of the load-bearing capacity of a structure at room temperature conditions is based on the characteristics values of the strength and imperfections. Extended to a structural fire engineering design, this procedure will give an analytically determined fire resistance of a load-bearing structural element which is lower — normally essentially lower — than the corresponding value derived from a standard fire resistance test. Available methods for a simplified calculation of the temperature of fire exposed steel structures are, as a rule, based on the assumption of a uniformly distributed temperature structure at each time of fire exposure. The ECCS Recommendations for an analytical design of steel structures exposed to a standard fire follow this kind of approach. For certain types of steel structures, for example, beams with a slab on the upper flange, a considerable temperature variation arises over the cross section as well as in the longitudinal direction during a fire resistance test. A simplified, analytical method, which neglects this influence, gives a further underestimation of the fire resistance in relation to the corresponding result obtained in a standard fire resistance test. The described discrepancies between an analytical and an experimental determination of the fire resistance are further discussed and analysed in Sections 2 and 3, with particular reference to different types of steel structures. The discussion is focussed on the loading and restraint conditions, the scatter of material properties and geometrical imperfections, and the temperature variation over the structure or structural element. The discussion is summarized in Section 4 and alternative methods of correction are outlined briefly for obtaining an improved consistency between the analytical and the experimental approaches. In Section 5, one of these methods is further developed to a design basis which can be applied easily in practice. Principally, the method is characterized by a correction of the analytically determined load-bearing capacity, based on the characteristic value of the structural material properties, the characteristic value of the imperfections of the structure, and a uniformly distributed steel temperature across and along the structure. Two different sequences of the design procedure are dealt with, defined according to Figs. 10 and 11. The resultant correction factors, ƒ and κ, belonging to the respective sequences, are given by Figs. 8 and 12 for columns, isostatic beams, and hyperstatic beams. The straight line curves in Figs. 9 and 13 show corresponding, simplified relationships for the ƒ and κ factors. The derived method of correction must be characterized as an approximate approach. This is in consequence of the present state of knowledge, which does not allow a solution of high accuracy. The task to develop a correction procedure which leads to improved consistency between an analytically and an experimentally determined fire resistance, should also be seen in the context of the inadequate reproducibility of the standard fire resistance test.

Practical need of scientific material models for structural fire design — General review

Abstract More and more countries are now permitting a classification of structural elements with respect to fire exposure to be formulated analytically as an alternative to the internationally prevalent method of classification, based on results of standard fire resistance tests. In some countries, the authorities also have taken the next step to approve a general practical application of a direct analytical design procedure, based on the natural compartment fire concept. The process of an analytical structural fire design comprises three main components — the determination of the fire exposure, the thermal analysis and the mechanical behaviour analysis. The components require access to well-defined input information on: (a) material properties for describing the characteristics of the fire load and the compartment fire; (b) material properties for determining the transient temperature state of the fire-exposed structure; and (c) material properties for determining the related mechanical behaviour and load-bearing capacity. With a summary presentation of the development and characteristics of the analytical structural fire design as a background, the paper is focusing on the mechanical material properties at elevated temperatures. A systematic scheme of classification of available tests is referred to and the importance is stressed of using such functionally well-defined tests which give material properties, stringently connected to material behaviour models being independent of the type of load-bearing structure.

University training of senior fire brigade officers. The new approach in Sweden

In Sweden a fundamental development has recently taken place in the training of future senior fire brigade officers. There are two main changes: the training period has been substantially increased and the theoretical part upgraded to university curriculum level with final requirements corresponding to a university undergraduate degree. The new educational system reflects the changing and expanding role of fire brigades and the need for a professionally improved leadership. To put the new training system into a proper context, the varied and dissimilar responsibilities of a Swedish fire brigade officer should be touched upon. Four main sectors are identified: business administration, fire prevention, training of employed staff and rescue service operations. The main structure of the training system and the university curriculum are discussed. (Less)

University Training of Senior Fire Brigade Officers. The New Approach in Sweden

GORAN HOLMSTEDT, ROBERT JÖNSSON, SVEN-ERIK MAGNUSSON AND OVE PETTERSSON The Forum is intended to provide for dialogue and discussion among fire experts, scientists and consultants. Contributions to The Forum will not be refereed in the conventional sense, but will be subject to review by the Journal’s Editorial Board relative to appropriateness, clarity, timeliness, and scope of interest. The Editorial Board will be the sole judge of those contributions to be published. Opinions expressed, however, are those of the authors and not of the Editors or Technomic Publishing Com-