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Most railway masonry arch bridges were designed according to codes that predate the 1950s; therefore, assessing their load-carrying capacity to comply with current codes is of the utmost importance. Nonetheless, acquiring the necessary information to conduct in-depth analyses is expensive and time consuming. In this article, we propose an expeditious procedure to conservatively assess the Load Rating Factor of masonry arch railway bridges based on a minimal set of information: the span, rise-to-span ratio, and design code. This method consists in applying the Static Theorem to determine the most conservative arch geometry compatible with the original design code; assuming this conservative geometrical configuration, the load rating factor, with respect to a different design load, is estimated. Using this algorithm, a parametric analysis was carried out to evaluate the Load Rating Factor of old arch bridges in respect of the modern freight load of the Trans-European Conventional Rail System, for different spans, rise-to-span ratios, and original design codes. The results are reported in easy-to-use charts, and summarized in simple, practical rules, which can help railway operators to rank their bridges based on capacity deficit.

Purpose: 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.Design/methodology/approach: 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).Findings: 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.Originality/value: 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.

In this paper, fire safety engineering principles were applied to a steel-framed office building. The case study consisted of a 15-storey steel moment-resisting frame designed in Japan. Once the performance criteria had been defined, two severe fire scenarios for the unprotected structure, implying a different degree of building collapse, were identified and modelled in zone models, OZone and consolidated fire and smoke transport (CFast), as well as in the computational fluid dynamics software Fire Dynamics Simulator (FDS). Based on the results of the fire development simulation, several finite-element thermo-mechanical analyses were performed with SAFIR. OZone and CFast models, which are much less computationally demanding, provided comparable failure mode and time with respect to FDS. Since the steel frame was seismically designed as a moment-resisting frame in the two main horizontal building directions, the columns were particularly stocky. Moreover, they were only partially heated because they were located on the compartment edges. For these reasons, columns did not exhibit failure, in contrast to the assumptions taken in the risk-ranking process in relation to the evaluation of the consequences, suggesting a revision of such estimations and a possible iterative procedure for the definition of critical fire scenarios for the structure.

The paper presents the development of a three-dimensional (3D) beam element for the analysis of steel structures in fire that properly accounts for the degradation of the torsional strength and stiffness owing to thermal exposure. The element is well-suited for the analysis of members that are subjected to significant torsional effects, as steel members with open cross-sections subjected to torsion, lateral-torsional buckling, and torsional buckling. The element is based on a corotational formulation and small strains assumption, while the local formulation was developed according to both the Timoshenko and Bernoulli beam theories. The stress-strain relationship and thermal expansion of steel were implemented according to Eurocode EN 1993-1-2 (CEN 2005). A comprehensive numerical analysis was performed and results for several case studies are presented in the paper to assess the performance of the 3D beam element. The outcomes indicated very good agreement when compared with shell-based models, highlighting promising capabilities of modeling steel structures in fire. Moreover, the proposed element showed more accurate results with respect to beam elements included into two commercial software, i.e., ABAQUS and SAFIR.

In the analysis of structures in fire, numerical models must account for the effects of increasing temperatures. Although different finite elements capable of effectively tackling the problem are available, 3D beam elements employed in many commercial software do not properly account for the degradation of the torsional properties with temperature. In this context, an enhanced 3D beam element based on a co-rotational formulation is proposed. The element was specifically developed for steel elements and is well suited for the analysis of structures that exhibit a significant torsional behavior. The Timoshenko beam theory was employed and the steel stress-strain law and thermal expansion were implemented according to EN1993-1-2. Two different case studies are presented in this paper. Numerical analyses by means of two different software (ABAQUS and SAFIR) were performed and compared to the results. The outcomes confirmed the effectiveness of the proposed element.