Fire performance of bolted connections in laminated veneer lumber

This paper describes an investigation into the fire performance of bolted tensile connections in laminated veneer lumber (LVL) made from radiata pine. The capacity of the bolted connections depends on the embedment strength of the wood and on the yield moment of the bolts. The purpose of the research was to develop a prediction method for the time to failure of the connections when exposed to fire. An experimental investigation was carried out on the axial tensile strength of three types of bolted connections that utilized either wood or steel splice plates. Some specimens were tested at ambient temperatures while similar specimens were tested in fire conditions with a constant applied load. In addition, single‐bolted connections were tested under constant elevated temperature conditions to determine the embedment strength of the LVL. Connections with no steel plates, or with steel plates slotted between the timber members, performed better than those with exposed steel. A simplified design approach is proposed, using an extension of the Johansen formulae, such that the embedment strength of the LVL depends on the temperature in the bolt. Copyright © 2009 John Wiley & Sons, Ltd.     

Model fire tests on a beam‐to‐leg connection in an offshore platform topside

Beam‐to‐column connections are of great significance as they noticeably influence the mechanical behavior of structures at ambient and elevated temperatures. Observations from full‐scale fire tests confirm that connections play an important role on the resistance time of structural components in fire. Because of the high cost of elevated temperature tests, adequate experimental data on a broad range of connections are not available. One type of such connections is the I‐beam‐to‐circular tubular leg connections in offshore oil/gas platform topsides. Considering the high risk of fire events in offshore oil/gas platforms, our study focuses on the structural behavior of this type of connection at elevated temperatures. Eleven small‐scale experimental tests were conducted on a uniplanar welded steel I‐beam‐to‐tubular chord connection with external diaphragms to investigate their fire resistance capacity. Local strengthening and partial thermal insulating were separately introduced to the connection components. The results show that the external diaphragms play a considerably more important role on the connection fire response as compared with that for the vertical stiffeners. It is also found that the degradations in the connections' stiffness at elevated temperature might be closely correlated with the classical thermomechanical data on steel material. Copyright © 2013 John Wiley & Sons, Ltd.     

The modified spring‐stiffness model for welded simple connection at elevated temperature

The outbreak of fire events in high‐rise buildings in recent years and the vulnerability of steel structure buildings, which leads to partial or complete failure of structures, clearly illustrate the need for designing such buildings against fire. The first step in fire design of structures is to have access to simplified equations for analyzing structural components against fire. Regarding this issue, to provide moment‐rotation relationships for designing welded seated angle connections, a modified spring stiffness model is presented in this article. In this method, the effective connection components are represented as springs with certain strength and stiffness properties that change as the temperature changes. Considering the special effect of welds on the behavior of these types of connections, separate springs for each section of the welds are considered and the effects of temperature on welds and base metal are taken into account. Comparing the results obtained from the proposed formulas with those of the tests, as well as the numerical analysis results, shows that the results in this method can be provided fast and accurately.     

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.     

Predicting the fire resistance of timber members loaded in tension

The paper presents a numerical model for predicting the fire resistance of timber members. Fire resistance is evaluated in a two‐step process implemented in the Abaqus finite element code: first, a time‐dependent thermal analysis of the member exposed to fire and then a structural analysis under a constant load are performed. The structural analysis considers the reduction in mechanical properties (modulus of elasticity and strength) of timber with temperature. The analysis terminates when the member can no longer redistribute stresses from the hottest to the coldest parts, leading to structural failure. The model was used to simulate fire tests carried out on specimens made from laminated veneer lumber loaded in tension. Experimental data in terms of temperature, charring depth, displacement and failure time were compared with the numerical results obtained by assuming the thermal properties and degradation of mechanical properties with temperature as suggested by Eurocode 5, showing an overall acceptable approximation. The fire resistance of the timber member was then predicted depending upon the applied tensile loads using the numerical model and analytical formulas. The proposed finite element model can be used to predict the fire resistance of timber structures as an alternative to expensive and complicated experimental tests. Copyright © 2012 John Wiley & Sons, Ltd.     

Fire characteristics of steel members coated with nano‐enhanced polymers

Polymeric coatings applied to masonry infill walls have been demonstrated to provide protection against blast. Steel frames may be embedded in these walls to improve the structural characteristics of the building. During the process of retrofitting the walls with blast protection polymeric coatings, the steel frame may be fully or partially coated with these materials to provide adequate anchorage of the retrofit system to the frame and to avoid global failure of walls subjected to blast loading. The development of a blast‐resistant coating for masonry walls that safeguards all structural elements in a fire would provide buildings with protection against explosions and a fire following the blast, as well as against ordinary building fires. This paper uses a numerical tool based on the particle finite element method to evaluate the melting and dripping of nano‐enhanced polymeric coatings applied on steel members embedded within masonry walls. Viscosity measurements were performed to obtain needed parameters for the simulations. Polyurea nanocomposite residues showed a minimum in viscosity with temperature, possibly caused by cross‐linking and charring. Model results for the polyurea residue with the lowest value of minimum viscosity showed that the coating remained attached, although there was some flow that caused a chunk of material to break off from an overhang. Copyright © 2013 John Wiley & Sons, Ltd.     

基于FEM的承受附加载荷的法兰连接安全评价

在考虑垫片力学性能的非线性和非保守的基础上,建立了承受附加载荷高温螺栓法兰连接结构的有限元分析方法.运用APDL和UIDL开发了基于ANSYS环境的法兰连接结构强度和紧密性分析模块,实现了连接系统的参数化建模及程序化计算.提出了基于紧密性的承受附加载荷螺栓法兰连接的安全评价方法,并以某铂重整装置接管法兰连接为对象,验证了有限元分析和安全评价方法的可行性,确定了该连接的安全操作条件.研究结果为承受附加载荷的螺栓法兰连接系统的安全评价和结构设计提供了借鉴.     

Eurocode method for calculating the external steelwork temperature in fire; comparative studies

To design a steel structure in fire is necessary to know its temperature. Using the data from many experimental fire tests, Margaret Law estimated the maximum temperature in a compartment (natural fire), the external heat transfer to steel elements and the maximum temperature value for steel. The Eurocode adopted her method, with minor adjustments. The method is very calculation intensive—it involves about 60 equations—too many for a quick hand calculation. Besides, while a distinction is made between steel members engulfed and not engulfed in flame, the method is not clear about partially engulfed members. The authors developed the software ExteelFire to determine the maximum temperature of external steel structures for buildings in fire based on the Eurocode method including the determination of the temperature of the partially engulfed elements. Aiming to ascertain the level of safety of the Eurocode method, the results from ExteelFire and a numerical analysis performed using Smartfire (CFD software for the fire model) and Super Tempcalc (finite element method, FEM, software for the thermal analysis) were compared. Furthermore, results from ExteelFire and from two full‐scale experimental tests (Dalmarnock and Ostrava) were contrasted. Based on the comparisons, the Eurocode method is conservative. Copyright © 2015 John Wiley & Sons, Ltd.     

Fire structural modelling and testing of welded aluminium plate

The structural response of welded aluminium in fire is computationally and experimentally analysed. A finite element (FE) model is developed to compute the deformation and failure of gas metal arc welded (GMAW) aluminium plate under combined loading and one‐sided unsteady‐state heating representative of fire. The FE model predicts the deformation of the weld, heat‐affected zone and parent plate based on the combined effects of elastic softening, plastic softening and creep. The effects of residual stresses in the weld and thermal expansion on the deformation response are also analysed. The numerical accuracy of the model is rigorously evaluated using a large amount of deformation and failure stress data obtained from fire structural tests performed with welded AA5083–AA5083, AA5083–AA6061 and AA6061–AA6061 plates. Good agreement is found between results computed with the FE model and experimental testing. The results reveal that GMAW welds do not reduce the structural performance of aluminium in fire unless the maximum temperature remains below the recrystallisation temperature. Copyright © 2014 John Wiley & Sons, Ltd.     

Overall stability analysis of oversized steel‐framed buildings in a fire

Our present paper summarizes the shortcomings in the current fire‐resistant design of oversized steel structures and proposes a method for overall stability analysis of steel structures in the event of fire. The Fire Dynamics Simulator (FDS) software platform–based large‐eddy simulation technology can accurately reflect the environment in a fire scenario and correctly predict the spatial–temporal change in the smoke temperature field within an oversized space. Adopting the FDS software and finite element structural analysis (ANSYS) coupling can fundamentally overcome the natural defect of adopting the International Organization for Standardization (ISO) standard curve (or other indoor homogeneous temperature increase curves) that substitutes a point for the overview of a field. They reflect the structural additional internal force and internal force redistribution incurred by the gradient temperature difference of the spatial–temporal changing nonhomogeneous temperature field and both theoretically and technically realize the analysis of structural heat transfer and mechanical properties in a natural fire. Furthermore, a modified model to predict the steel temperature curve in localized fire is also proposed. The localized fire in large spaces can be treated as a point fire source to evaluate the flame thermal radiation to steel members in the modified model. Copyright © 2014 John Wiley & Sons, Ltd.     

Numerical modelling of carbon fibre‐reinforced polymer and hybrid reinforced concrete beams in fire

Investigation on the fire resistance of fibre‐reinforced polymer (FRP) reinforced concrete (RC) is essential for increased application of FRP bars in the construction industry. Experimental tests for determining the fire resistance of RC elements tend to be expensive and time‐consuming. Although numerical models provide an effective alternative to these tests, their use in case of FRP RC structures is hindered because of the insufficient constitutive laws for FRP bars at elevated temperatures. This paper presents the details of a numerical modelling work that was carried out for simply supported carbon FRP (CFRP) and hybrid (steel‐FRP) bar RC beams at elevated temperatures. Constitutive laws for determining temperature‐dependent strength and stiffness properties of CFRP bars are proposed. Numerical models based on finite element modelling were employed for the rational analysis of beams using the proposed constitutive laws. The behaviour of concrete was simulated by means of a smeared crack model based on the tangent stiffness solution algorithm. The employed numerical models were validated against previous experimental results. The theoretical rebar stresses were calculated in both the FRP and steel bars, and the differences are discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

A numerical model for the behaviour of masonry under elevated temperatures

A thermo‐structural finite element model for the behaviour of masonry panels exposed to fire conditions has been developed. The model has been specifically designed to simulate the behaviour of both loaded and unloaded brickwork panels in plane stress, which are subject to various types of temperature distribution associated with typical fire situations. The current model has been evaluated using experimental results from fire tests on half‐ and full‐scale masonry walls exposed to elevated temperature on one face. Analytical and experimental results for the fire tests were basically in good agreement, indicating that reliable results can be achieved provided that accurate material properties and test boundary conditions are known, and that reliable temperature distribution data through the thickness of the wall is available. Copyright © 2003 John Wiley & Sons, Ltd.     

Heat transfer model for a cementitious‐based insulation with moisture

The lack of actual thermal properties of fire insulation materials lead to erroneous temperature prediction of protected structural steel members. For cementitious‐based fire insulations, moisture held in the pores significantly alters the thermal response of the material. In this study, a heat transfer model is proposed to accurately predict the thermal response of cementitious‐based fire insulations. The effects of the moisture and the decomposition of calcium hydroxide are incorporated in the thermal properties of the selected insulation material. The model was validated against the thermal response of the material obtained experimentally using the finite element programme abaqus (LAF Group, Sydney, NSW, Australia). Copyright © 2013 John Wiley & Sons, Ltd.     

Hollow‐core concrete slabs exposed to fire

The aim of this paper is to provide recommendations to designers and to propose a simple method for designers to model the structural behaviour of hollow‐core concrete (HC) floor slabs in fire. The proposed finite element model incorporates a grillage system using beam elements to capture the thermal expansion of the precast units in both directions, with the topping concrete over several precast units modelled by shell elements. The research reported herein compares the proposed model with various fire test results of HC slabs. The simulation outcomes show good agreement with the experimental results. Several HC slab flooring systems tested previously at the University of Canterbury for seismic purposes were simulated using this modelling scheme. Various supporting schemes have been considered, and the results show that different arrangements of axial and rotational restraint at the supports can significantly influence the fire performance of the concrete slab floors. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of different cord pitch on the pullout force of steel cord conveyor belt splice

The splice is the weakest part of the entire steel cord conveyor belt. And it occurs steel cord twitch fault frequently. If this fault cannot be dealt with timely and accurately, broken belt accidents would be occurred that affecting the safety of production seriously. In this paper, we investigated the different cord pitch pullout of the steel cord conveyor belt splice by using ABAQUS. The finite element model of the ST630 type steel cord conveyor belt was established, same as to the standard of the experimental sample. The pullout force of length 50.0, 70.0, 80.0 and 100.0 mm single steel cord impacted at steel cord conveyor belt splice was numerically computed respectively. The finite element model consists of rubber, steel cord and failure unit. Failure unit is used to simulate the bonding relationship between steel cord and rubber. Mooney-Rivlin hyper-elastic model for rubber was employed in the numerical simulations. Typical results obtained have been validated by experimental result and the relative error between simulation results and experimental results is within 10%. Simulations were also done for cord pitch of 4.0, 4.5, 6.0, 7.0 and 8.0 mm to study its effect on the pullout force of steel cord conveyor belt splice. The variation of cord pitch at normal impact was found to have influence as long as the cord pitch was different. It provides us the numeric value of the pullout force with the different cord pitch, and conducts us selecting the correct steel cord configuration spacing for the steel cord conveyor belt splice, as well for the steel cord conveyor belt. This is an efficient way for avoiding the steel cord twitch fault and the broken belt accident, while ensuring their high reliability and service life.     

Fire performance of non-load-bearing double-stud light steel frame walls: Experimental tests,numerical simulation,and simplified method

Double-stud light steel frame (LSF) walls provide an enhanced insulation performance when exposed to fire conditions. However, the behavior of different configurations of such assemblies under fire is not well understood. Thus, this study aimed to assess the fire resistance of non-load-bearing double-stud LSF walls subjected to ISO834 standard fire. The walls were lined with one or two type F gypsum plasterboards on each side, using cavity uninsulated or insulated with ceramic fiber. The experimental tests revealed that a wider cavity slows the heat transfer through the cross-section, delaying the temperature rise on the unexposed surfaces. The use of ceramic fiber insulation substantially increases the fire resistance of the wall and when the cavity is partially filled with this material, if the blanket is placed towards the exposed side, enhanced insulation fire resistance is achieved. Based on the finite element method, a numerical validation was conducted using a special hybrid approach that used experimental temperature values inside the cavities or insulation blankets. This approximation was essential to improve the numerical results. Also, the employment of an air layer, located at specific regions of the models, helped to improve the numerical results, introducing an extra thermal resistance. A new simplified approach was proposed based on the improved design model available in the literature, and the results obtained are consistent with the experimental results. The predicted insulation fire resistance of the numerical and simplified methods agreed well with the experimental results and useful information is supplied to support further numerical and experimental studies.     

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 and numerical study on the performance of hollow and concrete‐filled elliptical steel columns subjected to severe fire

This paper presents the results of an experimental and validated theoretical study to investigate the performance of steel columns with hollow and concrete‐filled elliptical sections subjected to hydrocarbon fire. The test programme involved 18 columns with 200 × 100 × 8‐mm, 300 × 150 × 8‐mm and 400 × 200 × 8‐mm elliptical sections representing slenderness of 50, 33 and 24, respectively. The 1800‐mm columns were subjected to the severe hydrocarbon fire curve and tested under loadings ratios of 20%, 40% and 60% of the EC3 ultimate strength. The paper presents the obtained experimental results including measured axial and lateral displacements, failure temperatures and failure time. A three‐dimensional model was built using the finite element method (FEM) and was validated using the obtained tests results. The finite element model showed an excellent agreement with tests results of failure temperatures, failure modes, and axial and lateral displacements. However, because of restrictions in the software capabilities, the mechanical–thermal behaviour of concrete including spalling was not considered in the model. The verified finite element model was used to conduct a parametric analysis involving a range of parameters of loading level and slenderness. The study has shown that the concrete‐filled sections have demonstrated an improved fire resistance when compared with the hollow sections under the low loading ratios. The FEM model has successfully predicted the unique thermal profile of elliptical section under fire, which was observed during the tests. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Effect of insulation on the fire behaviour of steel floor trusses

This paper describes a study into the fire behaviour of open‐web steel trusses supporting concrete floor slabs, exposed to a range of realistic design fires. This study is intended to give some insight into the possible structural behaviour of the floor trusses in the World Trade Center (WTC) towers. The analysis was carried out using a non‐linear finite element program SAFIR. The trusses were analysed with and without protective insulation for several different fires, each with three types of connections; pinned at both ends, simply supported, and simply supported with an axial spring. This paper shows that the likely failure mode of the floor truss depends on the connection strength, and emphasizes the importance of ensuring that the insulation remains intact. Unlike the actual event in the WTC with multiple floors exposed to fire, this analysis only considers a single floor, hence the results from this analysis do not confirm the actual behaviour of the buildings while they collapsed. Copyright © 2004 John Wiley & Sons, Ltd.