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Buckling should be carefully considered in steel assemblies with members subjected to compressive stresses, such as bracing systems and truss structures, in which angles and built-up steel sections are widely employed. These type of steel members are affected by torsional and flexural-torsional buckling, but the European (EN 1993-1-2) and the American (AISC 360-16) design norms do not explicitly treat these phenomena in fire situation. In this work, improved buckling curves based on the EN 1993-1-2 were extended by exploiting a previous work of the authors. Moreover, new buckling curves of AISC 360-16 were proposed.

The buckling curves provided in the norms and the proposed ones were compared with the results of numerical investigation. Compressed angles, tee and cruciform steel members at elevated temperature were studied. More than 41,000 GMNIA analyses were performed on profiles with different lengths with sections of class 1 to 3, and they were subjected to five uniform temperature distributions (400–800 C) and with three steel grades (S235, S275, S355).

It was observed that the actual buckling curves provide unconservative or overconservative predictions for various range of slenderness of practical interest. The proposed curves allow for safer and more accurate predictions, as confirmed by statistical investigation.

This paper provides new design buckling curves for torsional and flexural-torsional buckling at elevated temperature since there is a lack of studies in the field and the design standards do not appropriately consider these phenomena.

The purpose of this paper is to propose a method for hybrid fire testing (HFT) which is unconditionally stable, ensures equilibrium and compatibility at the interface and captures the global behavior of the analyzed structure. HFT is a technique that allows assessing experimentally the fire performance of a structural element under real boundary conditions that capture the effect of the surrounding structure.

The paper starts with the analysis of the method used in the few previous HFT. Based on the analytical study of a simple one degree-of-freedom elastic system, it is shown that this previous method is fundamentally unstable in certain configurations that cannot be easily predicted in advance. Therefore, a new method is introduced to overcome the stability problem. The method is applied in a virtual hybrid test on a 2D reinforced concrete beam part of a moment-resisting frame.

It is shown through analytical developments and applicative examples that the stability of the method used in previous HFT depends on the stiffness ratio between the two substructures. The method is unstable when implemented in force control on a physical substructure that is less stiff than the surrounding structure. Conversely, the method is unstable when implemented in displacement control on a physical substructure stiffer than the remainder. In multi-degrees-of-freedom tests where the temperature will affect the stiffness of the elements, it is generally not possible to ensure continuous stability throughout the test using this former method. Therefore, a new method is proposed where the stability is not dependent on the stiffness ratio between the two substructures. Application of the new method in a virtual HFT proved to be stable, to ensure compatibility and equilibrium at the interface and to reproduce accurately the global structural behavior.

The paper provides a method to perform hybrid fire tests which overcomes the stability problem lying in the former method. The efficiency of the new method is demonstrated in a virtual HFT with three degrees-of-freedom at the interface, the next step being its implementation in a real (laboratory) hybrid test.

This paper aims to present the assumptions and the issues that arise when developing an integrated modelling methodology between a computational fluid dynamics (CFD) software applied to compartment fires and a finite element (FE) software applied to structural systems.

Particular emphasis is given to the weak coupling approach developed between the CFD code fire dynamics simulator (FDS) and the FE software SAFIR. Then, to show the potential benefits of such a methodology, a multi-storey steel-concrete composite open car park was considered.

Results show that the FDS–SAFIR coupling allows overcoming shortcomings of simplified models by performing the thermal analysis in the structural elements based on a more advanced modelling of the fire development, whereas it appears that the Hasemi model is more conservative in terms of thermal action.

A typical design approach using the Hasemi model is compared with a more advanced analysis that relies on the proposed FDS–SAFIR coupling.

This study aims to evaluate the feasibility of a hybrid fire testing by real-time subdivision of physical and numerical substructures (NSs) on simplified structures as a milestone in the development of the method.

An interface where the data was exchanged between a finite element software and a hydraulic jack regulator using text files has been developed and applied to perform two experimental campaigns of nine tests on simple steel frame structures with different thermal loading conditions. In the first experimental campaign, the physical substructure (PS) was assumedly protected by insulating material, while the NS was uniformly exposed to ISO 834 fire on all sides. The difference of the second experimental campaign from the first one was that the PS was heated on one side.

The experimental results showed how a gap between the determined equilibrium position and the “real” position caused by the time lag, as well as an overshoot phenomenon due to the non-synchronized action of both substructures, may occur. From the identification of the overshoot, two paths of development spring to mind to reduce the delay of the NS.

In the context that the number of proposal theoretical algorithms continues to increase with the absence of real experimental adjustments, such experimental results and the associated analysis constitute additional understandings to identify possible paths of improvements that might have been missed or could not be accessed through previous studies.