Analysis of composite steel and concrete columns at high temperatures

The growing demand for knowledge about the effect of fire on structures has stimulated research worldwide. This article presents experimental results of short, composite columns made of steel and concrete when submitted to high temperatures in furnaces, with and without axial compression loading, as well as a numerical analysis of the temperature distribution in these columns. The columns were modeled as concrete‐filled tubes with three thicknesses and two diameters considered. In addition, standard fire temperature–time curves were obtained experimentally for use in the numerical calculations. Copyright © 2014 John Wiley & Sons, Ltd.     

Temperature distribution of steel columns protected by sprayed fire retardant coatings with three sides exposed to fire

Temperature gradient will occur when the steel framed column is heated from three sides in a fire. Current design codes provide the design equations to calculate the temperature elevation of the steel column unevenly heated in a fire. However, the design equation is based on the assumption that the temperature is uniformly distributed across the section. The temperature field of a steel column protected by sprayed fire retardant coating with three sided exposed to fire is analyzed using a verified finite element model. Parameters that affect the temperature distribution across the section are investigated, which include the section height, the web thickness, and the fire protection thickness. The coded equations based on the element factor approach are modified according to the finite element simulation results. Different temperature distribution profiles are proposed through using the heated flange temperature, the web temperature, and the protected flange temperature. Copyright © 2014 John Wiley & Sons, Ltd.     

方钢管混凝土柱-钢梁竖向加劲肋式节点非线性有限元分析

对方钢管混凝土柱-钢梁竖向加劲肋式节点建立了同时考虑几何非线性和材料非线性的有限元分析模型,模拟分析了单调加载下节点的受力性能,较为精确地分析了节点区应力分布.结果表明:由有限元模型所得的位移曲线与试验所得的低周反复荷载作用下的骨架曲线相符,由有限元模型所得的应变分布和发展规律与试验结果一致;竖向加劲肋式节点的梁端弯矩一部分通过竖向加劲肋传递给柱钢管腹板和核心混凝土,另一部分梁端弯矩由梁端翼缘直接传递给柱钢管翼缘和核心混凝土;节点的破坏模式为梁翼缘变截面最窄处形成塑性铰,最终梁受压翼缘出现严重的局部屈曲,而柱钢管和竖向加劲肋均在弹性范围内工作,很好地实现了强柱弱梁、强节点弱构件的抗震原则;节点核心区混凝土性能符合斜压杆受力机制.     

Experimental study of the fire resistance of walls and floors constructed with steel studs and steel joists

Steel‐framed houses using light‐gauge steel as a structural member have been developed and constructed since the early 2000s as a new construction pattern in the low‐rise construction market in Korea. Generally, the steel frames consist of two major load‐carrying elements such as load‐bearing wall and floor construction made up of approximately 1.0‐mm cold‐formed light‐gauge steel and light‐weight boards. Therefore, the steel frames are very simple to construct and make the construction period shorter than the ordinary construction type or concrete‐based construction. In Korea, regardless of the construction material types, the building regulation requires 1‐h fire rating for apartment buildings of four stories or under. To meet the fire resistance, new models of load‐bearing wall and floor should be developed. From the fire test results, two layer gypsum boards of 12.5 mm in thickness reinforced with glass fiber were proven satisfactory to provide 1‐h fire resistance with load‐bearing wall and floor. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental and numerical analysis of the thermal and mechanical behaviour of steel and recycled aggregate concrete composite elements exposed to fire

Using recycled aggregates in the production of concrete has been a viable alternative for sustainable development. Notwithstanding advanced information on this material at room temperature, its behavior when exposed to fire is still incipient. Thus, based on experimental analyses, the objective of this article is to evaluate the behavior of concrete produced with recycled aggregates for thermal insulation of steel elements, as well as to verify the physical and mechanical properties of these mixtures. For this purpose, eight prototypes, one made of steel and the others coated with different types of concrete, conventional and with recycled aggregates, were inserted in a horizontal oven and heated for 2 h. Based on experimental tests, numerical models were proposed and tested using the ABAQUS computational code, with consistent results when coherent thermal properties were adopted. The experimental results show that recycled aggregate concrete (RAC) has great thermal insulation potential and sustainable benefits, considering that the steel elements coated with this type of material, with the exception of those that underwent spalling, presented temperatures close to or below compared with concrete with natural aggregates. In this regard, it is observed that the thermal conductivity of RACs was inferior to conventional concrete, indicating that this material is a promising strategy for thermal insulation of steel structures.     

Thermal and mechanical transient behaviour of steel doors installed in non‐load‐bearing partition wall assemblies during exposure to the standard fire test

In this paper, the authors present experimental results and observations of four full‐scale standard fire tests on single‐leaf steel doors and steel frames installed in 3 × 3 m non‐load‐bearing partition walls. Three full‐scale fire tests were performed on steel doors installed in lightweight partition walls constructed by using steel C‐section studs with gypsum boards fixed on both sides. Two lightweight walls incorporated Rockwool cavity insulation, while the third lightweight wall was constructed without cavity insulation. The fourth fire test involved a steel door installed in a masonry partition wall. While the steel door leaf and door frames were identical in all four full‐scale tests, only the steel door installed in the masonry wall achieved the desired fire resistance rating of 30 min. The integrity criterion for fire resistance was determined for the scenario when the door opened away from the furnace. The duration of fire resistance according to the integrity criterion was found to be 38, 25 and 19 min for the same door when installed in masonry wall, uninsulated lightweight wall and insulated lightweight wall respectively. For the thermal insulation criterion of fire resistance, the scenario of the door opening into the fire was found to be the most onerous. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental fire analysis of steel‐to‐timber connections using dowels and nails

The paper describes and discusses the results of an extensive testing programme on the structural behaviour of timber connections under ISO‐fire. The results of reference tests performed at normal temperature are also presented. From the variety of timber connections multiple shear steel‐to‐timber connections with dowels and slotted‐in steel plates and connections with steel side plates and annular ringed shank nails were experimentally studied. Particular attention was given to the analysis of the efficiency of different strategies in order to increase the fire resistance of the timber connections. The test results showed that unprotected multiple shear steel‐to‐timber connections with dowels designed for normal temperature reached a fire resistance of about 30 min. A reduction of the load level applied during the fire did not lead to a significant increase of the fire resistance. By increasing the side timber members as well as the end distance of the dowels by 40 mm the connections reached a fire resistance of more than 70 min. Connections protected by timber boards or gypsum plasterboards showed a fire resistance of around 60 min. Thus, from a fire design point of view these strategies were favourable in order to increase the fire resistance of the connections significantly. Unprotected connections with steel side plates and annular ringed shank nails failed already after about 12 min due to large deformations of the nails and the steel side plates directly exposed to fire. By protecting the steel side plates using an intumescent paint the fire resistance of the connections was increased to around 30 min. The test results enlarged the experimental background of timber connections in fire significantly. Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental and numerical study on compressive performance of perforated brick masonry after fire exposure

This paper discusses the compressive performance of perforated brick masonry after fire exposure. Compressive strength tests of the mortar, clay perforated brick, and perforated brick masonry specimens were performed in accordance with ISO834 fire tests of different durations. The temperature distribution of the masonry materials and specimens was simulated using the finite element software ABAQUS, with the thermal parameters of masonry materials recommended by European standard Eurocode 6 and related literature. The compressive strength reduction factors of mortar and clay perforated brick exposed to different fire durations were calculated via the layered method suggested by European standard Eurocode 1. In addition, the compressive strength reduction factors after cooldown were obtained from the experimental data of the masonry materials, and by considering further reductions in the compressive strength after cooling from high temperatures. Experimental data of the masonry specimens were compared with the numerical results obtained using the reduction factors proposed in this work. The comparison revealed an overall acceptable approximation. Thus, the method presented in this paper can be used to evaluate the residual capacity of masonry structures after fire.     

Experimental and numerical investigation of fire development in a real fire in a five‐storey apartment building

A fire in a five‐storey apartment building was investigated experimentally and numerically. The room of origin of the fire was a living room in the second floor and the fire was started by a candle on a television set. The fire spread externally over the building faccade and internally along the staircase and affected all the flats above leading to two fatalities. It is estimated that the fire was discovered minutes after ignition and the fire service was called very shortly after the detection and was at the scene 9 min after the call. By this time large sections of the façade were on fire already. The rapid fire that spread over the façade and the staircase necessitated detailed investigations. Compliance of building products with the building regulations was investigated. One conclusion of the investigations was that the person who caused the fire by leaving the candle on the TV set unattended should not be held responsible for the two fatalities in the upper floors. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental study of tenability during a full‐scale motorcoach tire fire

Full‐scale fire experiments were conducted at the National Institute of Standards and Technology (NIST) to investigate tire fire interactions with the passenger compartment of a motorcoach. A single full‐scale experiment with a partially furnished interior was conducted to investigate tire fire growth within the passenger compartment and the onset of untenable conditions. A tire fire was initiated using a burner designed to imitate the frictional heating of hub and wheel metal caused by failed axle bearings, locked brakes, or dragged blown tires. Measurements of interior and exterior temperatures, interior heat flux, heat release rate, toxic gases, and visibility were performed. Standard and infrared videos and still photographs were also recorded. The results of this single experiment showed that after fire penetration into the passenger compartment, the tenability limits were reached within 8 minutes near the fire and within 11 minutes throughout the passenger compartment.     

Nonlinear finite element analysis of bond-slip performance of recycled aggregate concrete filled circular steel tube

The aim of this paper is to solve the problem of extremely difficult, low work efficiency and low accuracy of finite element analysis (FEA) when considering the bond-slip performance of recycled aggregate concrete filled circular steel tube (RACFCST). Toward this end, spring elements generation software for RACFCST V1.0, parametric modeling software for push-out test of RACFCST V1.0, and the Nodes selection program for RACFCST were developed. The FEA model of the RACFCST push-out test was established with the software and the model was calculated in ABAQUS, the calculated results were compared with the existing test results. The results show that: (1) The FEA model of RACFCST components considering bond-slip can be efficiently, accurately and simply established by spring elements generation software for RACFCST V1.0; (2) The results of FEA were found to be in good agreement with the experimental data, and spring elements generation software can solve the problem of FEA of RACFCST considering bond-slip performance; (3) The modeling efficiency and accuracy of RACFCST components can be greatly improved by Parametric modeling software for push-out test of RACFCST V1.0; (4) The efficiency and flexibility of selecting nodes during post-processing is greatly improved by Nodes selection program for RACFCST V1.0.     

Performance of a light timber‐framed compartment in natural fire subjected to lateral load

A common approach for designing buildings for lateral stability during and post‐fire in New Zealand is to ensure that a fire‐rated structure does not collapse when subjected to a nominal horizontal force. For external walls of residential buildings, which are required to resist a lateral load of 0.5 kPa, it is hypothesised that the adjacent unrated construction could provide sufficient support. A natural fire experiment has been conducted to evaluate the fire performance of a laterally loaded light timber‐framed compartment, with external dimensions of 4.33 m × 3.35 m and a stud height of 2.4 m constructed with a timber truss roof and plasterboard ceiling. During the experiment, the ceiling collapsed at 12 to 13 minutes, and the bottom chord of the roof truss failed in tension after 28 minutes which resulted in the fire‐rated wall losing its lateral stability at 28 minutes. The fire severity experienced in the compartment has been estimated to correspond to an equivalent time of 33‐minute exposure to a standard furnace time‐temperature. It is concluded that there is no need to provide nominal (additional) moment‐resisting fixity at the base of the fire‐rated wall when exposed to the standard fire for no more than 30 minutes.     

Thermal performance of load‐bearing walls made of cold‐formed hollow flange channel sections in fire

Typical load‐bearing light gauge steel frame (LSF) walls are made of conventional lipped channel section studs and gypsum plasterboards. Current research at the Queensland University of Technology is investigating the effects of using new thin‐walled stud sections on the fire‐resistant rating of LSF walls, in particular, the use of hollow flange channel (HFC) sections. A sound knowledge on the thermal performance of these LSF walls is essential, but expensive and time‐consuming nature of fire tests has acted as a barrier. In this study, finite element models were developed to predict the thermal performance of load‐bearing LSF walls made of HFC section studs exposed to fire on one side. The developed models were validated using the results of five full‐scale standard fire tests of LSF walls. They were then extended to perform a parametric study where the effects of stud dimensions, geometries, spacings and wall configuration were evaluated. The hot and cold flange time‐temperature profiles of HFC studs were developed as a function of the aforementioned parameters, which can be used to predict the fire resistance ratings of LSF walls. This paper presents the fire tests, and the details of the developed finite element models and the thermal performance results of LSF walls made of HFC studs. Copyright © 2015 John Wiley & Sons, Ltd.     

Development of a creep‐free stress‐strain law for fire analysis of steel structures

This paper presents a practical procedure for obtaining creep‐free stress‐strain laws for steel exposed to fire, on the basis of codified stress‐strain laws that consider creep implicitly. The applicability of the proposed procedure has been tested on two commonly used stress‐strain laws for steel at elevated temperature, the Eurocode 3 law and a Ramberg–Osgood model, both of which have implicit consideration of creep. The simulation of two published steel coupon experiments on steel of grades S275 and S355 shows that both the Eurocode and Ramberg–Osgood stress‐strain laws produce inaccurate predictions of creep in fire at elevated temperatures. The proposed procedure was thereby used to extract the implicit creep according to the heating rates of the transient coupon tests and to derive the creep‐free stress‐strain laws. It has been shown that, by combining the creep‐free stress strain law obtained by the proposed methodology with an explicit creep model, a more realistic prediction of steel behaviour in the selected coupon test studies can be achieved. Copyright © 2015 John Wiley & Sons, Ltd.     

Experimental discussion on the mechanisms behind the fire spalling of concrete

The behaviour of six concretes at high temperature (600 °C) and in particular the risk of fire spalling is studied. Tests are performed with two sizes of samples: small samples (300 × 300 × 120 mm³) and small slabs (700 × 600 × 150 mm³). Different storage conditions (pre‐drying at 80 °C, air and water storing) are used to highlight the effect of the initial water content. Thanks to different scenarios of heating, the influence of the heating curve is studied. Results enabled to identify parameters that highly influence the risk of fire spalling: initial water content and concrete permeability during heating. The permeability of concrete can increase during heating due to the melting of the polypropylene fibres or by thermal damage. This thermal damage is important when heating is violent (ISO 834 or increased hydrocarbon fire), or when concrete is made with silico‐calcareous aggregates (flint). Fire spalling cannot be explained by either the only thermo‐mechanical behaviour of concrete, or only by the appearance of high pore gas pressure. Based on the recent hypothesis of the critical zone, the formation of a saturated layer of liquid water is consistent with the results obtained. Copyright © 2014 John Wiley & Sons, Ltd.     

Flammability of oil‐based painted gypsum wallboard subjected to fire heat fluxes

The flammability of painted gypsum wallboard (GWB) exposed to fire heat fluxes is investigated. GWB samples coated with multiple layers of alkyd/oil‐based paint are subjected to constant incident heat fluxes of 35, 50 and 75 kW/m² in the Cone Calorimeter for periods of 5, 10 and 15 min. A number of coats of alkyd/oil‐based interior semi‐gloss enamel paint, including 1, 2, 4, 6 and 8 coats, are applied over a single coat of oil‐based primer to the exposed surface of 16 mm (5/8 in.) thick type X GWB. Unpainted type X GWB is also evaluated under the same exposure conditions. The potential for upward flame spread based on the Cone Calorimeter results is evaluated. The occurrence of paint ‘blistering’ is observed to have a significant effect on the time to ignition and consequently on the potential for upward flame spread. Further work is needed to evaluate the conditions under which ‘blistering’ will occur and its effects on the potential for surface flame spread on painted gypsum wallboard. Copyright © 2004 John Wiley & Sons, Ltd.     

危险废物检测常见误差分析及应对措施

随着工业的不断发展,工业生产过程中产生的危险废物也日益增多,危险废物处置的需求也不断扩大。危险废物不处理或不规范处理处置所带来的大气、水源、土壤等的污染也将会成为制约可持续发展的瓶颈。危险废物处置行业已经成为当前蓬勃发展的行业,如何提高危险废物检测的准确性、避免危险废物检测过程中产生误差也成了各危险废物处置单位重点关注的事情。本文对危险废物检测各个流程可能产生系统误差的点进行了梳理,并给出了问题的解决手段。     

高强型钢混凝土柱承载力计算的研究现状

目前型钢混凝土柱中的型钢与混凝土越来越多地采用高强材料,形成了三类高强型钢混凝土柱：采用高强型钢的类型、采用高强混凝土的类型、同时采用高强型钢与高强混凝土的类型。目前有关高强型钢混凝土柱承载力的研究可分为两大类：国内外主要规范（规程）中的计算方法,规范（规程）以外的研究及方法。基于对这两大类研究的介绍与对比分析,从正截面偏压承载力、正截面轴压承载力和斜截面受剪承载力三方面分别给出了相应的推荐计算方法或者指明了待完善的研究方向。     

Experimental and numerical analysis of the influence of cable tray arrangements on the resulting mass loss rate and fire spreading

In the context of industrial buildings and power plants, electrical installations and cable trays represent a main fuel load and a potential initial fire source due to possible short circuits or comparable malfunction. Furthermore, a fire can spread from one tray to additional trays mounted above and/or horizontally on one tray. Because of the high significance of cable fires, several research projects have been carried out, investigating the fire behaviour of cables from small‐scale tests, eg, the cone calorimeter, up to large‐scale tests, analysing complete cable tray constructions. The goal of the work presented in this paper is the extension of the knowledge regarding the influence of geometrical parameters like the packing density and tray distance on the burning behaviour and fire spread of cable tray installations. The results are considered, together with test results from the literature, to quantify the main physical parameters describing the burning behaviour. In a next step, the general applicability of these parameters as input data for the parametrization of the source term of numerical simulations is shown. The test results show that the burning behaviour and the fire spreading highly depend on the cable arrangement of the cables on the cable tray, in combination with other boundary conditions. By applying the results as input for a fire simulation, the mass loss rate is considered appropriately.