Virtual hybrid simulation of beams with web openings in fire

Purpose: Perforated composite beams are an increasingly popular choice in the construction of buildings because they can provide a structurally and materially efficient design solution while also facilitating the passage of services. The purpose of this paper is to examine the behaviour of restrained perforated beams, which act compositely with a profiled slab and are exposed to fire. The effect of surrounding structure on the composite perforated beam is incorporated in this study using a virtual hybrid simulation framework. The developed framework could also be used to analyse other structural components in fire. Design/methodology/approach: A finite element model is developed using OpenSees and OpenFresco using a virtual hybrid simulation technique, and the accuracy of the model is validated using available fire test data. The validated model is used to investigate some of the most salient parameters such as the degree of axial and rotational restraint, arrangement of the openings and different types of fire on the overall fire behaviour of composite perforated beams. Findings: It is shown that both axial and rotational restraint have a considerable effect on time-displacement behaviour and the fire performance of the composite perforated beam. It is observed that the rate of heating and the consequent development of elevated temperature in the section have a significant effect on the fire behaviour of composite perforated beams. Originality/value: The paper will improve the knowledge of readers about modelling the whole system behaviour in structural fire engineering and the presented approach could also be used for analysing different types of structural components in fire conditions

Numerical modelling of composite floor slabs subject to large defections

This paper is concernedwith the ultimate behaviour of composite floor slabs. Steel/concrete composite structures are increasingly common in the UK and worldwide, particularly for multi-storey construction. The popularity of this construction formis mainly due to the excellent efficiency offered in terms of structural behaviour, construction time and material usage all of which are particularly attractive given the ever-increasing demands for improved sustainability in construction. In this context, the engineering research community has focused considerable effort in recent years towards understanding the response of composite structures during extreme events, such as fires. In particular, the contribution made by the floor slab system is of crucial importance as its ability to undergo secondary load-carrying mechanisms (e.g. membrane action) once conventional strength limits have been reached may prevent overall collapse of the structure. Researchers have focused on developing the fundamental understanding of the complex behaviour of floor slabs and also improving themethods of analysis. Building on thiswork, the current paper describes the development and validation of a finite element model which can simulate the response of floor slab systems until failure, both at ambient and elevated temperature. The model can represent the complexities of the behaviour including the temperature-dependent material and geometric nonlinearities. It is first developed at ambient temperature and validated using a series of experiments on isolated slab elements. The most salient parameters are identified and studied. Thereafter, the model is extended to include the effects of elevated temperature so it can be employed to investigate the behaviour under these conditions. Comparisons with current design procedures are assessed and discussed

Fire behaviour of concrete filled elliptical steel columns

In this work, a non-linear three-dimensional finite element model is presented in order to study the behaviour of axially loaded concrete filled elliptical hollow section (CFEHS) columns exposed to fire. This study builds on previous work carried out by the authors on concrete filled circular hollow section (CFCHS) columns both at room temperature and in fire. The numerical model is first validated at room temperature against a series of experiments on CFEHS stub columns available in the literature and subsequently extended to study the performance of slender columns at elevated temperatures. The aim of this work is to understand and represent the behaviour of axially loaded CFEHS columns in fire situations and to compare their effectiveness with that of the circular concrete filled tubular (CFT) columns. Parametric studies to explore the influence of variation in global member slenderness, load level, cross-section slenderness and section size are presented. Finally, guidance on the fire design of CFEHS columns is proposed: it is recommended to follow the guidelines of Clause 4.3.5.1 in EN 1994-1-2, but employing the flexural stiffness reduction coefficients established in the French National Annex with an equivalent EHS diameter equal to P/¿, where P is the perimeter of the ellipse.The authors would also like to acknowledge Universidad Politecnica de Valencia for providing fellowship funding for the first author's stay as a visiting academic at Imperial College London.Espinós Capilla, A.; Gardner, L.; Romero, ML.; Hospitaler Pérez, A. (2011). Fire behaviour of concrete filled elliptical steel columns. Thin-Walled Structures. 49(2):239-255. https://doi.org/10.1016/j.tws.2010.10.008S23925549

Fire design method for concrete filled tubular columns based on equivalent concrete core cross-section

In this work, a method for a realistic cross-sectional temperature prediction and a simplified fire design method for circular concrete filled tubular columns under axial load are presented. The generalized lack of simple proposals for computing the cross-sectional temperature field of CFT columns when their fire resistance is evaluated is evident. Even Eurocode 4 Part 1-2, which provides one of the most used fire design methods for composite columns, does not give any indications to the designers for computing the cross-sectional temperatures. Given the clear necessity of having an available method for that purpose, in this paper a set of equations for computing the temperature distribution of circular CFT columns filled with normal strength concrete is provided. First, a finite differences thermal model is presented and satisfactorily validated against experimental results for any type of concrete infill. This model consideres the gap at steel-concrete interface, the moisture content in concrete and the temperature dependent properties of both materials. Using this model, a thermal parametric analysis is executed and from the corresponding statistical analysis of the data generated, the practical expressions are derived. The second part of the paper deals with the development of a fire design method for axially loaded CFT columns based on the general rules stablished in EN 1994-1-1 and employing the concept of room temperature equivalent concrete core cross-section. In order to propose simple equations, a multiple nonlinear regression analysis is made with the numerical results generated through a thermo-mechanical parametric analysis. Once more, predicted results are compared to experimental values giving a reasonable accuracy and slightly safe results.The authors would like to express their sincere gratitude to the Spanish Ministry of Economy and Competitivity for the help provided through the project BIA2012-33144, and to the European Community for the FEDER funds.Ibáñez Usach, C.; Aguado, JV.; Romero, ML.; Espinós Capilla, A.; Hospitaler Pérez, A. (2015). Fire design method for concrete filled tubular columns based on equivalent concrete core cross-section. Fire Safety Journal. 78:10-23. https://doi.org/10.1016/j.firesaf.2015.07.009S10237

Flexural capacity of bi-directional GFRP strengthened RC beams with end anchorages: experimental and theoretical studies

This paper presents the results of experimental and theoretical studies on the flexural capacity of reinforced concrete (RC) beams strengthened using externally bonded bi-directional glass fibre reinforced polymer (GFRP) composites and different end anchorage systems. A series of nine RC beams with a length of 1600mm and a cross-section of 200mm depth and 100mm width were prepared and externally strengthened in flexure with bi-directional GFRP composites. These strengthened beams were anchored with three different end anchorage systems namely closed GFRP wraps, GFRP U-wraps, and mechanical anchors. All these beams were tested with four-point bending system up to failure. The experimental results are compared with the theoretical results obtained using the relevant design guidelines. The experimental results demonstrate a significant increase in the flexural performance of the GFRP strengthened beams with regard to the ultimate load carrying capacity and stiffness. The results also show that GFRP strengthened beams without end anchorages experienced intermediate concrete (IC) debonding failure at the GFRP plate end, whereas, all the GFRP Strengthened beams with different end anchorage systems failed in rupture of GFRP with concrete crushing. The theoretical results revealed no significant difference among the relevant design guidelines with regard to the predicted ultimate moment capacities of the bi-directional GFRP strengthened RC beams. However, the results show that ACI Committee 440 (2008) design recommendation provides reasonably acceptable predictions for the ultimate moment capacities of the tested beams strengthened externally with bi-directional GFRP reinforcement followed by FIB Bulletin 14 (2001) and eventually JSCE (1997). The research work presented in this manuscript is authentic and could contribute to the understanding of the overall behaviour of RC beams strengthened with FRP and different end anchorage systems under flexural loading

Behaviour of Composite Beams Made Using High Strength Steel

BRIE

Elevated temperature material properties of stainless steel reinforcing bar

Corrosion of carbon steel reinforcing bar can lead to deterioration of concrete structures, especially in regions where road salt is heavily used or in areas close to sea water. Although stainless steel reinforcing bar costs more than carbon steel, its selective use for high risk elements is cost-effective when the whole life costs of the structure are taken into account. Considerations for specifying stainless steel reinforcing bars and a review of applications are presented herein. Attention is then given to the elevated temperature properties of stainless steel reinforcing bars, which are needed for structural fire design, but have been unexplored to date. A programme of isothermal and anisothermal tensile tests on four types of stainless steel reinforcing bar is described: 1.4307 (304L), 1.4311 (304LN), 1.4162 (LDX 2101®) and 1.4362 (2304). Bars of diameter 12 mm and 16 mm were studied, plain round and ribbed. Reduction factors were calculated for the key strength, stiffness and ductility properties and compared to equivalent factors for stainless steel plate and strip, as well as those for carbon steel reinforcement. The test results demonstrate that the reduction factors for 0.2% proof strength, strength at 2% strain and ultimate strength derived for stainless steel plate and strip can also be applied to stainless steel reinforcing bar. Revised reduction factors for ultimate strain and fracture strain at elevated temperatures have been proposed. The ability of two-stage Ramberg-Osgood expressions to capture accurately the stress-strain response of stainless steel reinforcement at both room temperature and elevated temperatures is also demonstrated

Modelling the influence of age of steel fibre reinforced self-compacting concrete on its compressive behaviour

Steel fibre reinforced self-compacting concrete (SFRSCC) can combine the benefits of self-consolidating concrete technology with those derived from adding steel fibres to quasi-brittle cement based materials. In a recent applied research project joining pre-casting industry, private and public research institutions, a method was developed to design cost-competitive SFRSCC of rheological and mechanical properties required for the prefabrication of SFRSCC fac¸ade panels. To assure safe demoulding process of the panels, the influence of the concrete age on the compression behaviour of the SFRSCC should be known. For this purpose, series of tests with specimens of 12 h to 28 days were tested in order to analyze the age influence on the compressive strength, strain at peak stress, Young’s modulus, and compressive volumetric fracture energy. The experimental program was divided in two groups of test series, one with SFRSCC of a volumetric fibre percentage of 0.38% and the other with 0.57%. To apply the obtained data in the design and numerical analysis framework, the influence of the age on these SFRSCC properties was modelled. This work describes the carried out experimental program, presents and analyzes the obtained results, and provides the derived analytical expressions

Analysis of Strain State and Cracking of Cocnrete Sleepers

Prestressed concrete sleepers are the most common type of the sleepers used on the railroad. They serve as rail supports and absorb loads induced by trains. Sleepers are important for the durability and safety of the railroad and are exposed to various loads and an agressive environment during exploitation. Therefore, different types of appearing damage can determine their reliability. The article briefly discusses possible causes of damage and the deterioration of prestressed concrete sleepers. End cracking and damage at the rail seat was determined during the inspection of used sleepers. Therefore, the strain state and cracking of the rail seat of the sleeper was analysed under static and dynamic loads. The paper provides the obtained results of experimental research of used and new sleepers

Research note: Describing average illuminance for P-class roads

Design criteria for lighting in subsidiary roads usually include a minimum average horizontal illuminance, widely assumed to be the arithmetic mean illuminance. Analyses of the illuminance distributions over thirty road sections shows that the distributions are not normal and hence the median is more appropriate than the arithmetic mean as a measure of central tendency: the medians are significantly lower than the arithmetic means but the two are highly correlated. Design recommendations should state whether it is the arithmetic mean or median and not just the ‘average’ that is required