Performance of cellular composite floor beams at elevated temperatures

This paper describes an experimental and numerical study at both ambient and elevated temperatures on the behaviour of full-scale composite floor cellular steel beams. A total of four specimens, comprising two different steel geometries and loading conditions were tested under monotonic loading and at elevated temperatures. All beams were designed for a full shear connection between the steel beam and the concrete flange using headed shear studs. The beams were designed to fail by web-post buckling, which was observed in all the tests. Failure temperature observed in the fire tests indicated that failure by web-post buckling of cellular beams in fire cannot simply be estimated by applying temperature dependent reduction factors on stiffness, as given in codes. A finite element model is then established with both material and geometrical non-linearity using shell elements to compare against the experimental results. The comparison between the finite element prediction and actual test results are quite good in terms of failure modes, load deflection behaviour and ultimate loads.     

多孔钢梁在组合屈曲模态下的非线性分析

讨论了一般强度和高强度多孔钢梁在组合屈曲模态下的非线性分析。建立一个考虑腹板和翼缘初始几何缺陷、残余应力和材料非线性等情况的多孔钢梁的三维有限元模型。用具有不同长度,不同截面,不同荷载条件和不同失效模态的多孔梁的试验结果验证了此有限元模型。该模型能计算多孔梁的失效荷载,跨中荷载-挠度关系和失效模态。用120根多孔梁的有限元计算数据进行了参数分析,研究截面几何尺寸,梁长和钢材料强度对多孔梁强度和屈曲性能的影响。参数研究结果显示:由于组合腹板的扭转和腹板后屈曲引起的多孔梁失效对承载力有很大的影响。对于长细比较小的多孔梁,应用高强度钢材料将能显著提高失效荷载值。将有限元计算得到的失效荷载与利用澳洲规范计算的多孔梁平面外屈曲计算结果进行了对比,发现规范的计算结果对于平面外屈曲的一般强度多孔梁是不保守的,而对于组合腹板扭转和腹板后屈曲的高强度多孔梁的失效则非常保守。     

Nonlinear behaviour of unprotected composite slim floor steel beams exposed to different fire conditions

An efficient nonlinear 3D finite element model has been developed to investigate the structural performance of composite slim floor steel beams with deep profiled steel decking under fire conditions. The composite steel beams were unprotected simply supported with different cross-sectional dimensions, structural steel sections, load ratios during fire and were subjected to different fire scenarios. The nonlinear material properties of steel, composite slim concrete floor and reinforcement bars were incorporated in the model at ambient and elevated temperatures. The interface between the structural steel section and composite slim concrete floor was also considered, allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the composite beam. Furthermore the thermal properties of the interface were included in the finite element analysis. The finite element model has been validated against published fire tests on unprotected composite slim floor steel beams. The time–temperature relationships, deformed shapes at failure, time–vertical displacement relationships, failure modes and fire resistances of the composite steel beams were evaluated by the finite element model. Comparisons between predicted behaviour and that recorded in fire tests have shown that the finite element model can accurately predict the behaviour of the composite steel beams under fire conditions. Furthermore, the variables that influence the fire resistance and behaviour of the unprotected composite slim floor steel beams, comprising different load ratios during fire, cross-section geometries, beam length and fire scenarios, were investigated in parametric studies. It is shown that the failure of the composite beams under fire conditions occurred for the standard fire curve, but did not occur for the natural fires. The use of high strength structural steel considerably limited the vertical displacements after fire exposure. It is also shown that presence of additional top reinforcement mesh is necessary for composite beams exposed to short hot natural fires. The fire resistances of the composite beams obtained from the finite element analyses were compared with the design values obtained from the Eurocode 4 for composite beams at elevated temperatures. It is shown that the EC4 predictions are generally conservative for the design of composite slim floor steel beams heated using different fire scenarios.     

Interaction of buckling modes in castellated steel beams

This paper investigates the behaviour of normal and high strength castellated steel beams under combined lateral torsional and distortional buckling modes. An efficient nonlinear 3D finite element model has been developed for the analysis of the beams. The initial geometric imperfection and material nonlinearities were carefully considered in the analysis. The nonlinear finite element model was verified against tests on castellated beams having different lengths and different cross-sections. Failure loads and interaction of buckling modes as well as load-lateral deflection curves of castellated steel beams were investigated in this study. An extensive parametric study was carried out using the finite element model to study the effects of the change in cross-section geometries, beam length and steel strength on the strength and buckling behaviour of castellated steel beams. The parametric study has shown that the presence of web distortional buckling causes a considerable decrease in the failure load of slender castellated steel beams. It is also shown that the use of high strength steel offers a considerable increase in the failure loads of less slender castellated steel beams. The failure loads predicted from the finite element model were compared with that predicted from Australian Standards for steel beams under lateral torsional buckling. It is shown that the Specification predictions are generally conservative for normal strength castellated steel beams failing by lateral torsional buckling, unconservative for castellated steel beams failing by web distortional buckling and quite conservative for high strength castellated steel beams failing by lateral torsional buckling.     

轻钢-混凝土组合梁的试验研究及非线性有限元分析

针对轻钢-混凝土组合梁这种新的结构形式,本文进行了六个试件的试验研究,分析了构件的破坏形式、荷载-位移曲线、荷载-应变曲线、钢材和混凝土的应变分布及板宽度方向应变分布等。通过试验研究,初步了解了轻钢-混凝土组合梁的特点和各种截面的粘结性能。采用组合梁单元模型,对轻钢-混凝土组合梁进行了非线性有限元分析,理论计算结果与试验结果吻合较好。     

Finite element modeling of block shear failure in coped steel beams

Block shear is a potential failure mode that is encountered in the connection regions of coped steel beams. Limited experimental studies completed so far have shown that the block shear failure in coped steel beams is a complex phenomenon, which is highly dependent on the number of bolt lines. In this paper, the use of the finite element method in predicting the block shear failure load was studied by making comparisons with experimental findings. The effects of numerical modeling details on load capacity predictions were investigated. In light of these investigations, a finite element analysis methodology has been developed and used to conduct a parametric study. Simplified load capacity prediction equations were developed based on the results of the parametric study and are presented herein.     

Behaviour of headed stud shear connectors for composite steel-concrete beams at elevated temperatures

The behaviour of composite steel-concrete beams at elevated temperatures is an important problem. A three-dimensional push test model is developed herein with a two-dimensional temperature distribution field based on the finite element method (FEM) and which may be applied to steel-concrete composite beams. The motivation for this paper is to increase the awareness of the structural engineering community to the concepts behind composite steel-concrete structural design for fire exposure. The behaviour of reinforced concrete slabs under fire conditions strongly depends on the interaction of the slabs with the surrounding elements which include the structural steel beam, steel reinforcing and shear connectors. This study was carried out to consider the effects of elevated temperatures on the behaviour of composite steel-concrete beams for both solid and profiled steel sheeting slabs. This investigation considers the load-slip relationship and ultimate load behaviour for push tests with a three-dimensional non-linear finite element program ABAQUS. As a result of elevated temperatures, the material properties change with temperature. The studies were compared with experimental tests under both ambient and elevated temperatures. Furthermore, for the elevated temperature study, the models were loaded progressively up to the ultimate load to illustrate the capability of the structure to withstand load during a fire. It is concluded that finite element analysis showed that the shear connector strength under fire exposure was very sensitive. It is also shown that profiled steel sheeting slabs exhibit greater fire resistance when compared with that of a solid slab as a function of their ambient temperature strength.     

Behavior of steel-concrete composite cantilever beams with web openings under negative moment

The effect of web openings on the mechanical behavior of composite beams under negative moment was studied through monotonically loading tests. Nonlinear finite element method based analysis was also conducted for cantilever composite beams. The test and the finite element analysis results indicated that the initial cracking loads of composite beams with web opening are lower than that without web opening. The first crack initiated from the concrete slab on the top of the opening. The beams with web opening failed due to shear failure of concrete slab upon the opening. It was also found that the load carrying capacity of beam decreases with the increase of the moment-to-shear ratio at the central line of the opening and the mechanical behavior of beam can be improved significantly by applying stiffening steel plates around the opening. To quantify the reduction of load carrying capacity, a method for calculating the load carrying capacity of beams with web openings under negative moment was derived with consideration of the interaction between moment and shear. Good consistency was obtained between the proposed method, the finite element method and the test results.     

Behaviour of embedded steel plate in composite coupling beams

Plate-reinforced composite (PRC) coupling beam is fabricated by embedding a vertical steel plate into a conventional-reinforced concrete coupling beam to enhance its strength and ductility. Shear studs are welded on the steel plate surfaces to allow for proper load transfer between the concrete and steel plate. The present study focuses on the evaluation of internal load distributions and load sharing on the embedded steel plate as well as at the shear studs in composite coupling beams using the nonlinear finite element package ATENA. The proposed two-dimensional finite element model is able to simulate the overall load-deflection behaviour and internal load distributions of coupling beams subjected to bending and shear forces. The reliability of the model is demonstrated by comparisons with the available experimental results. This is followed by an extensive and carefully planned parametric study using the calibrated finite element model. Numerical results on the effects of steel plate geometry, span-depth ratio of beams and steel reinforcement ratios at beam spans and in wall regions are presented and discussed in this paper. The finite element model provides a better understanding of the behaviour of shear studs as well as plate anchorage in the wall regions and embedded beam region. Based on the numerical results, equations for quantifying the shear stud forces are established and a set of non-dimensional design charts for determining the internal forces of the embedded steel plates is constructed. Both of them are useful for engineers to design PRC coupling beams.     

基于神经网络的蜂窝钢梁的承载力研究

对腹板易发生后屈曲的简支蜂窝钢梁的承载力进行研究,讨论分析梁承载力和失效模型的非线性有限元法的准确性。由于非线性有限元计算量很大,故基于有限元进行参数研究,提出蜂窝钢梁腹板的后屈曲临界荷载的经验公式。另采用传统的反向传播神经网路和自适应神经模糊推理系统方法进行求解,并对比传统有限元分析结果,验证经验公式、反向传播神经网络法、自适应神经模糊推理系统法的准确性。结果表明:反向传播神经网络法和自适应神经模糊推理系统法比经验方程更准确。     

Finite element studies on profiled steel composite beams

This article is concerned with finite element studies on profiled steel composite beams to investigate their elastic and ultimate load behaviour. Finite element code LUSAS is used to carry out the non-linear analyses to determine the load carrying capacity of the beams. Results from the experimental studies reported by other researchers are first used to assess the accuracy of the finite element modelling. Analyses are carried out thereafter to study different shapes, arrangements and number of steel sheeting ribs. Effects of the parameters such as concrete compressive strength f _c, yield stress f _yp of the profiled steel sheeting, and thickness of the steel sheeting on the ultimate load capacity of the profiled steel composite beams are examined. The results are presented in the form of load-deflection plots and ultimate load values. It is concluded that the ultimate load capacity of the profiled steel composite beams can be predicted with an acceptable accuracy by the proposed finite element modelling. Results show that the load carrying capacity of the beams are influenced by shapes, arrangements and number of ribs. It is also found that compressive strength f _c of the concrete, and yield stress f _yp and thickness of profiled steel sheeting have significant influences on the performance of these beams.     

Resistance and thermal insulation of a composite FRP–steel beam

For an optimal design of roof-elements for long spans one has to consider both load-carrying capacity and heat conductivity. In this paper three different alternative web configurations for joining web to flange in a roof-element are investigated. A composite web in combination with fibre reinforced plastics (FRP) is proposed as a solution to achieve an optimised performance. The connection is designed as a mechanical pin-type fastener with a general purpose polyester matrix FRP. Full-scale beam tests and small-scale properties test were carried out. Where connection failure took place, the derived connection capacity load matches fairly. A predicted span length of a roof element is in the order of 8–10 m in a design situation should be possible using the FRP–steel web. The load-carrying and thermal insulation performance of FRP–steel, expanded metal and slotted steel beams are compared by finite element analysis.     

钢筋混凝土矩形截面受扭最小配筋率构件的钢筋受力分析

以 9根钢筋混凝土矩形截面配筋率较小受扭构件的实验为基础 ,用有限元分析软件Ansys对构件进行了全过程静力模拟受力分析 ,计算结果与实验数据吻合较好 .讨论了构件截面变形随荷载的变化情况 ,纵筋和箍筋在屈服前后的变形、受力情况等 .     

Assessment of load carrying capacity of castellated steel beams by neural networks

In this paper, load carrying capacity of simply supported castellated steel beams, susceptible to web-post buckling, is studied. The accuracy of the nonlinear finite element (FE) method to evaluate the load carrying capacity and failure mode of the beams is discussed. In view of the high computational burden of the nonlinear finite element analysis, a parametric study is achieved based on FE and an empirical equation is proposed to estimate the web-posts’ buckling critical load of the castellated steel beams. Also as other alternatives to achieve this task, the traditional back-propagation (BP) neural network and adaptive neuro-fuzzy inference system (ANFIS) are employed. In this case, the accuracy of the proposed empirical equation, BP network and ANFIS are examined by comparing their provided results with those of conventional FE analysis. The numerical results indicate that the best accuracy associates with the ANFIS and the neural network models provide better accuracy than the proposed equations.     

Behaviour of composite cellular steel — Concrete beams at elevated temperatures

The behaviour of composite cellular floor beams is becoming important as such members are increasingly used in multistorey buildings. In the event of fire, this issue becomes increasingly critical, particularly for exposed steelwork. In a fire situation, a composite beam has a much higher perimeter area exposed to fire in its lower web-flange section than in the upper web-flange section, and so the temperature distribution across a composite beam is usually non-uniform. The reduction in fire of the strength and stiffness of the material properties of the perforated steel beam, as well as differential thermal expansion, therefore becomes an important influence on the overall behaviour of the composite beam. The objective of this research is to enhance the level of understanding of the generic behaviour of composite cellular floor beams in fire conditions. In this paper, three-dimensional nonlinear finite element models of composite cellular floor beams have been developed, taking into consideration the influence of the changes in material properties with temperature. Experimental data from furnace tests on cellular composite floor beams obtained from previous research work has been used to validate the FE models. An analytical model based on existing design guides is also presented in this paper. It is concluded that finite element analysis results are in good agreement with the experimental data, and all the failure modes have been accurately predicted. The proposed simplified analytical methods show reasonable agreement with the test and FE results, and are always conservative.     

Full-scale long-term experiments of simply supported composite beams with solid slabs

This paper presents an experimental study aimed at the evaluation of the long-term behaviour of composite steel-concrete beams designed with partial shear connection formed by a steel joist and a solid concrete slab. Three full-scale simply supported beams with identical spans and cross-sections were prepared and tested. These specimens were designed as secondary beams of a typical composite flooring system based on Australian guidelines with the lowest permitted level of degree of shear connection of 0.5. They were cast simultaneously to enable comparisons with respect to pouring and loading conditions. One beam was cast un-propped and was kept unloaded for the whole duration of the long-term tests to measure shrinkage effects. The remaining two beams, cast under un-propped and propped conditions, respectively, were subjected to a sustained uniformly distributed load. Standard short-term and long-term tests were carried out to obtain the relevant material properties of both the steel and the concrete. Short-term and long-term push-out tests were carried out to obtain information on the response of the shear connectors. The experimental results were modelled by means of the finite element method. The time-dependent behaviour was depicted using a step-by-step procedure, while the steel joist and reinforcement were assumed to remain linear elastic. Two constitutive relationships were adopted for the shear connection, i.e., a linear-elastic one, and a new time-dependent one, to account for the long-term effects produced in the complex stress state of the concrete surrounding the shear connectors. The latter representation is intended to fall within the framework of simplified approaches suitable for design applications. Considerations of the accuracy of the numerical predictions are presented based on the two shear connection models.     

Structural Behavior of Steel Tube and Coupler Scaffolds with Stability Strengthening Details

The multi-span steel tube and coupler scaffold is one of the main temporary structural forms in building and bridge construction. Given the insufficient research on their bearing capacity and design method, steel tube and coupler scaffolds have frequently collapsed in recent years and have caused serious casualties and economic losses. Through six prototype tests and a numerical analysis, this study investigated the effect of stability strengthening measures, such as vertical X-bracing, horizontal X-bracing, surrounding non-loading area, and lateral wall-tied constraints, on the ultimate bearing capacity and failure mode of multi-span steel tube and coupler scaffolds under a uniformly distributed line load of upper horizontal tubes. Using the finite element numerical analysis verified by the test data, the influence of height-width ratio, structure height, story height, spacing of vertical tubes, X-bracing layout, lateral wall-tied constraints, and surrounding non-loading area on the ultimate bearing capacity of multi-span steel tube and coupler scaffolds was analyzed. Design methods for multi-span steel tube and coupler scaffolds under a uniformly distributed line load of upper horizontal tubes were proposed based on the results of the prototype test and finite element numerical analysis. The reasonability of the design method was verified by the test data and finite element analysis results.     

腹板开矩形孔复杂卷边冷弯槽钢梁局部屈曲性能及直接强度法研究

为了研究腹板开孔复杂卷边冷弯槽钢梁的局部屈曲性能，以及探究北美冷弯型钢结构设计规范(AISI S100-2016)中腹板开孔冷弯槽钢梁局部屈曲直接强度法计算公式的可靠性，对孔高比(孔洞高度与腹板高度的比值)分别为0、0.2、0.4、0.6和0.8的10个腹板开矩形孔复杂卷边冷弯槽钢梁纯弯试件进行了静力试验研究。试验结果表明，开孔和不开孔试件均发生以局部屈曲为主的屈曲破坏模式，与不开孔试件相比，开孔试件的受弯承载力下降，且下降幅度随孔高比的增大而增大。利用ANSYS有限元程序对试验进行了模拟分析，分析结果与试验结果吻合良好；在此基础上，采用经试验验证的有限元模型，通过变换腹板高度、板厚和孔高比开展了有限元参数分析，并根据有限元参数分析结果对已有腹板开孔冷弯槽钢梁的弹性局部屈曲临界应力近似计算公式进行了修正。基于试验结果、有限元参数分析结果以及修正的弹性局部屈曲临界应力近似计算公式，对AISI S100-2016中开孔冷弯槽钢梁发生以局部屈曲为主破坏时的直接强度法计算公式进行了修正。     

Notional load method for industrial steel storage racks

The discussion in this paper is on the stability analysis and design of industrial steel storage racks. Studies were carried out to evaluate the current Effective Length Method, and to examine the Notional Load Method as an alternative design procedure. Presently, the design of industrial steel storage racks in the United States is carried out according to the Rack Manufacturers Institute (RMI) specification using the effective length method. The notional load method is a new method for stability analysis and design of structural steel systems introduced in the AISC Specification for Structural Steel Buildings (ANSI/AISC 360-05). The difference between these two methods is that in the effective length method the beam-column member within the frame is designed based on effective member length while in the notional load method it is designed based on actual member length and the analysis is based on a reduced stiffness in the structure. The finite element method, which considers both geometric and material nonlinearities, was used as the basis for evaluating the accuracy of these two design methods. The study was carried out for numerous cold-formed steel industrial storage rack configurations. The application to cold-formed steel structures had to include the frequently encountered torsional–flexural buckling and semi-rigid joints. Results showed that the effective length method is more conservative than the notional load method and the notional load method agrees better with the finite element results than the effective length method does. It is, therefore, recommended that the notional load method be considered as an alternative means for industrial steel storage rack design.