A unified design approach for plate-reinforced 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 deformability. Shear studs are welded on the surfaces of the steel plate to transfer forces between the concrete and the steel plate. Extensive experimental studies and numerical simulation have demonstrated the effectiveness and efficiency of this new type of coupling beam in resisting high shear force and large rotational demand from large wind or seismic loading. In this paper, an original and comprehensive design procedure is proposed to aid engineers in designing this new type of beam and to ensure proper beam detailing for desirable performance. The proposed design procedure consists of four main parts, which are (1) estimation of ultimate shear capacity of beam, (2) design of RC component and steel plate, (3) shear stud arrangement in beam span, and (4) design of plate anchorage in wall piers. Using the proposed procedure, the load-carrying capacity of the PRC coupling beams which were previously tested and simulated was evaluated. The results were compared with those from non-linear finite element analyses and experimental studies for validating the design procedure. A worked example is given to illustrate the design of PRC coupling beams using the proposed procedure.     

Performance of shear connection in composite beams with profiled steel sheeting

This paper describes the structural performance of shear connection in composite beams with profiled steel sheeting. An accurate and efficient nonlinear finite element model was developed to study the behaviour of headed stud shear connectors welded through-deck. The profiled steel sheeting had transverse ribs perpendicular to the steel beam. The material nonlinearities of concrete, headed stud, profiled steel sheeting, reinforcement and steel beam were included in the finite element model. The capacity of shear connection, load-slip behaviour of the headed stud, and failure modes were predicted. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to study the effects on the capacity and behaviour of shear connection by changing the profiled steel sheeting geometries, the diameter and height of the headed stud, as well as the strength of concrete. The capacities of shear connection obtained from the finite element analysis were compared with the design strengths calculated using the American Specification, British Standard and European Code for headed stud shear connectors in composite slabs with profiled steel sheeting perpendicular to the steel beam. It is found that the design rules specified in the American and British specifications overestimated the capacity of shear connection, but the design rules specified in the European Code were generally conservative.     

Seismic behavior of code designed steel plate shear walls

The AISC Seismic Design Provisions now include capacity design requirements for steel plate shear walls, which consist of thin web plates that infill frames of steel beams, denoted horizontal boundary elements (HBEs), and columns, denoted vertical boundary elements (VBEs). The thin unstiffened web plates are expected to buckle in shear at low load levels and develop tension field action, providing ductility and energy dissipation through tension yielding of the web plate. HBEs are designed for stiffness and strength requirements and are expected to anchor the tension field formation in the web plates. VBEs are designed for yielding of web plates and plastic hinge formation at the ends of the HBEs.This paper assesses the behavior of code designed SPSWs. A series of walls are designed and their behavior is evaluated using nonlinear response history analysis for ground motions representing different hazard levels. It is found that designs meeting current code requirements satisfy maximum interstory drift requirements considering design level earthquakes and have maximum interstory drifts of less than 5% for maximum considered earthquakes. Web plate ductility demands are found to be significantly larger for low rise walls than for high rise walls where higher modes of vibrations impact the response. The percentage of story shear resisted by the web plate relative to the boundary frame is found to be between 60% and 80% and is relatively independent of panel aspect ratio, wall height, or hazard level, but is affected by transitions in plate thickness. Maximum demands in VBEs in design level shaking are found to be considerably less than those found from capacity design for SPSWs with 9 or more stories.     

Seismic performance parameters of RC beams retrofitted by CARDIFRC

A new high performance fibre-reinforced cementitious composite material (designated CARDIFRC^®), to be used for retrofitting concrete members, has been developed at Cardiff University. The material is compatible with concrete and possesses favourable strength and ductility properties desirable for seismic retrofit. It overcomes some of the problems associated with the current techniques based on externally bonded steel plates and fibre-reinforced polymer (FRP) laminates caused mainly by the mismatch of their tensile strength and stiffness with that of the concrete member being retrofitted.

This paper reports on the results of three-point and four-point flexure tests conducted on a number of non-ductile and ductile small scale RC beams retrofitted with externally bonded CARDIFRC^® strips. A number of different strip configurations and two strip thicknesses are investigated and their effect on the retrofitting process examined. Some strength and seismic performance parameters including toughness and ductility are evaluated for each retrofitted beam and compared with those of the corresponding control beams. It is shown that precast CARDIFRC^® strips, adhesively bonded to the surface of the RC beam can greatly increase the strength and ductility of the retrofitted beam; hence, they can be used successfully to enhance the seismic performance of both damaged and undamaged RC beams.     

Behaviour of thin steel plate shear walls regarding frame members

Steel plate shear walls in buildings are known to be an effective and strong means for resisting lateral forces. The view of some structural designers is to use heavy stiffeners to reinforce and increase the buckling capacity of shear walls; whereas, if the walls are left unstiffened and allowed to buckle, their energy absorption will increase significantly due to the post-buckling capacity. On the other hand, the optimal design of thin steel plate shear walls (TSPSWs), which are categorized as thin-walled structures, involves the proper prediction of their buckling strength. In turn, this prediction is a function of the status of their assumed boundary conditions. Many design rules conservatively suggest simply supported boundary conditions for elastic member restraints. In this paper, the effects of surrounding members (i.e. beams and columns) on the overall behaviour of TSPSWs are studied. The results show that, unlike the present view, the flexural stiffness of surrounding members has no significant effects, either on elastic shear buckling or on the post-buckling behaviour of shear walls. The torsional rigidity has a significant effect only on the elastic buckling load, and the extensional stiffness slightly affects the post-buckling capacity.     

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.     

Shear strength of the connection between a steel coupling beam and a reinforced concrete shear wall in a hybrid wall system

No specific guidelines are available for computing the shear strength of the connection between a steel coupling beam and a reinforced concrete shear wall in a hybrid wall system. There were carried out analytical and experimental studies on the connection between a steel coupling beam and a concrete shear wall in a hybrid wall system. The bearing stress at failure in the concrete below the embedded steel coupling beam section is related to the concrete compressive strength and the ratio of the width of the embedded steel coupling beam section to the thickness of the shear walls. Experiments were carried out to determine the factors influencing the shear strength of the connection between a steel coupling beam and a reinforced concrete shear wall. The test variables included the reinforcement details that confer a ductile behaviour in the connection between a steel coupling beam and a shear wall, i.e., the auxiliary stud bolts attached to the steel beam flanges and the transverse ties at the top and the bottom steel beam flanges. In addition, additional test were conducted to verify the strength equations of the connection between a steel coupling beam and a reinforced concrete shear wall. The proposed equations in this study were in good agreement with both our test results and other test data from the literature.     

Flexural behavior of GFRP-reinforced concrete encased steel composite beams

To improve the ductility and meanwhile ensure satisfactory corrosion-resistant performance, a new type of FRP-reinforced concrete encased steel (FRP-RCS) composite beams comprised of ductile structural steel shapes in combination with corrosion-resistant FRP-reinforced concrete was proposed and studied. An experimental investigation on flexural behavior of the proposed FRP-RCS beams was conducted by testing a total of seven simply supported beam specimens subjected to four-point bending loads. The test specimens included one FRP-reinforced concrete (FRP-RC) beam reinforced with GFRP bars only and six FRP-RCS beams reinforced with both GFRP bars and encased structural steel shapes. The main parameters considered in this study were concrete compressive strength, amounts of GFRP reinforcement as well as ratio and configuration of encased structural steel shapes. The test results indicate that using encased steel shapes can provide a significant enhancement in load carrying capacity, stiffness, ductility and energy absorption capacity of tested beams. The tested FRP-RC beam suffered a brittle failure caused by the sudden fracture of tensile GFRP bars whereas the proposed FRP-RCS beams behaved in a ductile manner mainly due to the beneficial residual strength of encased steel shapes following concrete crushing. In addition, an analytical method was suggested to predict the load carrying capacity of the proposed FRP-RCS beams.     

Long-term deflection of cracked composite beams with nonlinear partial shear interaction: I — Finite element modeling

In this paper, a uniaxial nonlinear finite element procedure for modeling the long-term behavior of composite beams at the serviceability limit state is presented. The finite element procedure follows a displacement-based approach. The nonlinear load-slip relationship of shear connectors as well as the creep, shrinkage, and cracking of concrete slab are accounted for in the proposed finite element procedure. The effects of creep and shrinkage of the concrete slab are considered only for uncracked concrete. The nonlinear iterative procedure adopted for tracking the nonlinear behavior of the composite beam implemented the total nodal deformations, not the incremental deformations, as the independent variables of any iteration. The results of the proposed finite element procedure were compared with the experimental results of four composite beams reported in the literature. The proposed finite element procedure was capable of predicting the deflections and stresses of the four beams with an acceptable degree of accuracy. A parametric study was conducted to study the effect of the nonlinearity of load-slip relationship of shear connectors and the cracking of the concrete deck on the long-term behavior of simply-supported composite beams.     

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.     

Seismic behaviour of coupling beams in a hybrid coupled shear walls

Steel coupling beams in a hybrid coupled shear wall provide a viable alternative for concrete coupling beams coupling individual reinforced concrete wall piers. Due to the lack of information, current design methods for calculating embedment lengths are silent about cases in which hybrid coupled walls have connection details of stud bolts and horizontal ties. In this work, an analytical study was carried out to develop a model for calculating the embedment lengths of embedded steel sections. Five models for calculating embedment lengths in a hybrid coupled wall are developed as variations of the Prestressed Concrete Institute guidelines for steel brackets attached to reinforced concrete columns. In addition, experimental studies on the hybrid coupled shear wall were carried out. The main test variables were the ratios of the coupling beam strength to the connection strength. The test results indicate that it is more advantageous to design the coupling beams as shear yielding members since the shear-critical coupling beam exhibits a more desirable mode of energy dissipation than the flexure-critical coupling beam.     

Elastic lateral stability of I-shaped cellular steel beams

In this paper, the lateral stability of cellular steel beams is numerically investigated. The study is carried out using three-dimensional finite element modeling of simply supported I-shaped cellular steel beams with a broad spectrum of cross-sectional dimensions, span lengths and web perforation configurations. Stability analyses are carried out for beams subjected to equal end moments, mid-span concentrated loads and uniformly distributed loads. Finite element results reveal that, unlike the case of conventional beams with solid webs, the moment-gradient coefficient C_b is significantly influenced by the beam geometry and slenderness. In addition, the C_b coefficient of cellular beams depends on the web perforation configuration. Moment-gradient coefficient values that fluctuate closely to those values recommended by design codes are associated with pure elastic lateral torsional buckling (LTB) deformations. As the beam slenderness decreases, the web distortion increases, leading to the lateral distortional buckling (LDB) mode, which is associated with lower C_b values than code-recommended ones. Severe reduction in the C_b coefficient to values less than 1.1 is noticed for shorter-span beams where the response is dominated by non-lateral local buckling modes.A simplified approach is developed to enable accurate prediction of a moment modification factor κ_LB for cellular beams. The proposed κ_LB factor is provided by an empirical formula that is derived based on the best fit of the finite element results related to lateral buckling (LTB and LDB) modes only. The proposed approach allows for accurate and conservative evaluation of the critical moment associated with the lateral torsional/distortional buckling of cellular beams. Several numerical examples are worked out to illustrate the application of the proposed procedure.     

Shear strength of trapezoidal corrugated steel webs

Corrugated webs are used to increase the shear stability of the steel webs of beams and girders and to eliminate the need for transverse stiffeners. This paper focuses on the shear strength of corrugated steel webs with trapezoidal corrugations. Previously developed formulas for predicting the shear strength of steel trapezoidal corrugated webs, along with the corresponding theory, are summarized. A new formula is developed, which considers interaction among the various shear failure modes. More than 100 test results from previous research are organized and evaluated according to relevant test specimen parameters. The conditions of many of these tests are found to be inconsistent with the theoretical conditions assumed in deriving the shear strength formulas. The various formulas for predicting shear strength are then compared with selected test results. The new formula is shown to be more accurate than previous formulas for estimating the shear strength of corrugated steel webs.     

Stiffness analysis of concrete filled steel plate composite coupling beams

联肢剪力墙弹性阶段的内力分布、抗侧刚度等工作性能主要受墙肢与连梁刚度的影响。为了准确分析外包钢板-混凝土联肢组合剪力墙的受力性能,对外包钢板-混凝土组合连梁的刚度进行了分析。基于钢板与混凝土无相对变形和忽略混凝土抗拉强度的基本假定,建立了组合连梁钢与混凝土无滑移的截面内力与变形之间的关系,并推导了截面刚度的计算公式。对于常用工程设计参数范围内的组合连梁,考虑滑移后得到的抗侧刚度相比无滑移情况减小了10%~24%。通过对无滑移组合连梁刚度公式中的混凝土部分贡献的折减(折减系数为0.5),得到了无特殊界面构造的外包钢板 混凝土组合连梁的刚度计算公式。通过与有限元分析和试验结果的对比,验证了公式的准确性。     

Assessment of effective slab widths in composite beams

This paper deals with the behaviour of composite beams with particular focus on the effective slab width, which is required for simplified structural analysis and design. Current design codes propose values for the effective width which are mostly a function of the beam span ignoring in this way the influence of other important parameters. Several 3D numerical simulations are conducted in this paper in order to illustrate these parameters and accordingly a new methodology is suggested for evaluating the effective width. The proposed approach is easier to apply in comparison with other existing methods based on stress integration, and provides effective width values which result in a more reliable representation of the actual beam state when simplified analysis is carried out. The application of the new method indicates that the effective width is mostly related to the actual slab width and, in many cases, the values obtained can significantly differ from those proposed in design codes. Validation of the new approach is carried out through comparison of simplified 2D models with the results obtained from a recent experimental investigation as well as from more complex 3D numerical simulations.     

Nonlinear finite element analysis of concrete filled steel plate composite coupling beams: force and deformation mechanics

在外包钢板-混凝土组合连梁试验研究的基础上,对组合连梁试件和不同参数取值的补充模型进行了非线性有限元分析。有限元分析得到的滞回曲线与试验曲线吻合良好,能较好地模拟组合连梁的受力行为。通过应力分析,发现内填混凝土的工作机制类似于斜压杆,其压力沿着连梁对角线方向从一端的受压侧传递到另一端的受压侧。外包钢板承担的剪力比例和弯矩比例的范围分别为0.36~0.76和0.57~0.82;混凝土的剪力与轴压力之比和连梁的高跨比近似相等。连梁的侧向位移由节点区变形引起的梁端转角、连梁的弯曲变形与剪切变形产生;在常用的跨高比范围内,剪切变形产生的侧向位移在总位移中占有较大比例,且受跨高比的影响很大。     

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.     

Full-scale tests on composite steel-concrete beams with steel trapezoidal decking

This paper describes the detailed testing of two full-scale steel-concrete composite beams comprised of composite slabs with deep trapezoidal decking connected to universal beams by welded stud shear connectors. The ribs of the decking were orthogonal to the longitudinal axes of the steel beams. This situation exists in secondary beams in flooring systems of steel framed buildings, and beams with deep trapezoidal slabs of this type are economic since they are able to span large distances, with or without propping. Despite the popularity of these decks and many useful research contributions over several decades, there are some concerns related to the strength and ductility of the shear connection because of the large voids in the slab and the need to place the studs off-centre to circumvent welding them through the longitudinal stiffener in the rib. There is also significant disquiet as to the applicability of push test results on much smaller specimens to the design of full-scale beams. The experimental work in this paper therefore intends to provide benchmark data for the calibration of theoretical models and of design recommendations. The beams were 8 m long with low degrees of shear connection. The tests showed that both beams behaved in a very ductile fashion with the ultimate moment capacities being above those predicted from the Eurocode 4 guidelines.     

钢—混凝土组合梁单调静力性能有限元分析

利用ANSYS软件建立了钢—混凝土组合梁的有限元模型,并对其进行了非线性分析,通过与试验结果的对比验证了建模方法的正确性,在此基础上,分析了栓钉间距、有效预应力等参数对钢—混凝土组合梁静力性能的影响,以期为钢—混凝土组合梁的设计计算提供指导。     

Behaviour of flush end plate joints to concrete-filled steel tubular columns

This paper presents the results of an experimental program for bolted moment connection joints of circular or square concrete filled steel tubular (CFST) columns, and H-shaped steel beams using high-strength blind bolts. In order to investigate the static performance and failure modes of the blind bolted connection, an experimental program was conducted involving four sub-assemblages of cruciform beam-to-column joints subjected to monotonic loading. Moment-rotation relationships of the tested connections were obtained and their performance was evaluated in terms of their stiffness, moment capacities and ductility. The test parameters varied were the column section type and the thickness of the end plate. The results showed that the proposed blind bolted connection, which behaves in a semi-rigid and partial strength manner according to the EC3 specification, displays reasonable strength and stiffness. The rotation capacity of this type of connection to square or circular CFST columns exceeds 70 mrad and this satisfies the ductility requirements for earthquake-resistance in most aseismic regions. The blind bolted connection is shown to be a reliable and effective solution for moment-resisting composite frame structures.