Luís Laím

Influence of web stiffeners on cold-formed steel beams subjected to fire

Purpose This paper aims to present the results of a study on the behaviour of cold-formed galvanized steel beams subjected to fire, using the results of a large programme of experimental tests. Design/methodology/approach The research investigated the influence of web stiffeners in the sections and the stiffness of the surrounding structure, including the axial and rotational restraining to the thermal elongation, on the flexural behaviour of the beams in case of fire. In other words, the structural response of different open cold-formed steel beams, with and without web stiffeners, was compared in case of fire. Findings The results showed that a good choice between using cold-formed steel beams, with and without web stiffeners, may depend on the section shape and the internal forces generated in these members during a fire. Originality/value Temperatures in the furnace and at several points of the beams, as well as deformations and restraining forces and moments, were measured to achieve those goals and consequently to assess the critical time and temperature of these beams.

Flexural Behaviour of Cold-Formed Steel Beams

This paper reports a series of flexural tests at ambient temperature focused on cold-formed steel beams composed especially by two or more CFS profiles which are often used in floors and roofs of warehouses and industrial buildings. The main objective of this research was to assess the failure loads and modes of the studied beams and also to compare the structural response of these different kinds of beams. Finally, the results showed above all that the failure loads of the open cross-section beams corresponded to the lateral-torsional buckling modes, whereas the distortional buckling was the responsible buckling mode for the failure loads of the hollow cross-section beams.

Experimental and numerical study on the fire response of cold-formed steel beams with elastically restrained thermal elongation

Purpose This paper is mainly aimed at the structural performance of compound cold-formed galvanised steel beams under fire conditions based on the results of a large programme of experimental tests and numerical simulations. The main objective of this research was to assess the critical temperature and time of the studied beams. Other important goals of this research work were to investigate the influence of the cross-sections (C, lipped-I, R and 2R beams) and, above all, of the axial restraint (0, 0.45, 3, 7.5, 15, 30, ∞ kN/mm) to the thermal elongation of the beam and the rotational restraint at beam supports (0, 15, 80, 150, 300, 1,200 and ∞ kN.m/rad) on the fire resistance of this kind of beams. Design/methodology/approach This paper still provides details of the simulation methodology for achieving numerical stability and faithful representation of detailed structural behaviour and compares the simulation and experimental results, including beam failure modes, measured beam axial forces and beam mid-span deflections. Findings Good agreement between Abaqus simulations and experimental observations confirms that the finite element models developed with the Abaqus/standard solver are suitable for predicting the structural fire behaviour of restrained cold-formed steel beams. Originality/value The results showed above all that the effect of the stiffness of the surrounding structure seems to decrease with the increasing slenderness of the beams.

Cold-formed steel columns at both ambient and fire conditions

Purpose The use of cold-formed steel members has increased significantly in the past few years; however, its design is only briefly addressed in the current design codes, such as the EN 1993-1-3. To evaluate the compressive behavior of single and built-up cold-formed steel members, at ambient and simulated fire conditions with restrained thermal elongation, experimental and numerical tests were undertaken. Design/methodology/approach Four cross-section shapes were tested, namely, one single (lipped channel), one open built-up (I) and two closed built-up (R and 2R), considering two end support conditions, pinned and fixed. Two test set-ups were specifically developed for these tests. Based on the experimental results finite element models were developed and calibrated to allow future parametric studies. Findings This paper showed that increasing the level of restraint to thermal elongation and the initially applied load led to lower critical temperatures. Increasing the level of restraint to thermal elongation, the failure is governed by the generated axial restraining forces, whereas for lower levels of restraint to thermal elongation, the failure is controlled by the temperature increasing. Originality/value This paper is a contribution to the knowledge on the behavior of cold-formed steel columns subjected to fire, especially on the ones with a built-up cross-section, where results on thermal restrained ones are still scarce. It presented a set of experimental and numerical results useful for the development of numerical and analytical analysis concerning the development of new simplified calculation methods.