Shrinkage effects on the flexural stiffness of composite beams with solid concrete slabs: An experimental study

This paper describes the testing of three full-scale simply-supported composite steel-concrete beams. The specimens were representative of a typical secondary beam used in composite flooring systems and were designed in accordance with Australian guidelines with a degree of shear connection equal to 0.5. Two beams were cast unpropped while the third was prepared under propped conditions. The beams were loaded to failure 18 months from concrete casting by a point load applied at mid-span. During this period the specimens were monitored to collect information on their time-dependent behaviour. Extensive data was measured during the ultimate tests, i.e. deflection at quarter points, slip and strain readings. Standard coupon and cylinder tests provided the instantaneous material properties of the materials. Push-out tests were performed to obtain information on the response of the shear connectors. The measured ultimate strengths of the beams were greater than those calculated based on rigid-plastic analysis using the actual properties obtained from standard material tests. Although this information is very useful for the calibration of theoretical models and design recommendations, the main contribution of this paper is the recognition of the detrimental effects at service conditions of shrinkage in composite members incorporating a solid slab. This shrinkage was observed to cause the composite flexural stiffness to degenerate to the value calculated with no shear interaction for a certain range of loading.     

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.     

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.     

带体外力筋的预应力混凝土梁的极限强度和塑性

由于在减小梁腹厚度和维修可行性方面的优势,在当代的建筑趋势中带体外预应力的预浇拼接式桥梁已很普遍了。连续梁可以减少伸缩缝数量,改善行车路况,但这种梁的内在结构特性很难分析(尤其在极限状态下)。本丈通过实验来检验比较带体外应力和带复合应力的两种跨连续梁在非对称载荷下的伸缩特性     

Dynamic analysis of composite systems made of concrete slabs and steel beams

Structural engineers have long been trying to develop solutions using the full potential of its composing materials. At this point there is no doubt that the structural solution progress is directly related to an increase in materials science knowledge. These efforts in conjunction with up-to-date modern construction techniques have led to an extensive use of composite floors in large span structures. On the other hand, the competitive trends of the world market have long been forcing structural engineers to develop minimum weight and labour cost solutions. A direct consequence of this new design trend is a considerable increase in problems related to unwanted floor vibrations. For this reason, the structural floors systems become vulnerable to excessive vibrations produced by impacts such as human rhythmic activities. The main objective of this paper is to present an analysis methodology for the evaluation of the composite floors human comfort. This procedure takes into account a more realistic loading model developed to incorporate the dynamic effects induced by human walking. The investigated structural models were based on various composite floors, with main spans varying from 5 to 10 m. Based on an extensive parametric study the composite floors dynamic response, in terms of peak accelerations, was obtained and compared to the limiting values proposed by several authors and design standards. This strategy was adopted to provide a more realistic evaluation for this type of structure when subjected to vibration due to human walking.     

再生混凝土梁正截面开裂弯矩分析与试验研究

在基本假定的基础上,分析了再生混凝土梁正截面开裂弯矩理论计算模式。进行了27根再生混凝土梁和3根普通混凝土梁的正截面开裂弯矩试验。试验表明,相同条件下再生混凝土梁开裂弯矩比普通混凝土梁的小25%左右。根据试验结果分析了混凝土强度和纵筋配筋率对再生混凝土梁开裂弯矩的影响,回归出再生混凝土梁正截面抵抗矩塑性系数,从而建立了再生混凝土梁正截面开裂弯矩计算公式。应用其他研究者的试验结果对该公式进行了验证,结果表明,建立的再生混凝土梁正截面开裂弯矩计算公式具有较好的适用性。     

On the behavior of thin walled composite beams with stochastic properties under matrix cracking damage

Thin walled composite beam structures are prone to damage which results in change in the performance of these structures. The change in the performance due to damage may get confused with the variation in the performance due uncertainties in the properties of these structures. Here, the performances of the thin walled composite beam under matrix cracking damage having material uncertainties are studied. The cross-sectional stiffness properties are obtained using thin walled beam formulation, which is based on a mixed force and displacement method. The stochastic behaviors of material properties are obtained from previous experimental and analytical studies. The effects of matrix cracking are introduced through the changes in the extension, extension–bending and bending matrices of composites. The effects of matrix cracking on out-of-plane bending, inplane bending and torsion cross-sectional properties are studied at different crack densities for stochastic material properties. Further, the effects of matrix cracking and uncertainties on measurable properties such as deflections and frequencies are studied. Results show that the beam responses at different crack densities get mixed due to the material uncertainties. The estimates of variance obtained for observable system properties due to uncertainty can be used for developing more robust damage detection algorithms.     

A force-based model for composite steel-concrete beams with partial interaction

This paper presents a new force-based beam-column element for the nonlinear analysis of composite steel-concrete beams with partial interaction. The element is made up of three components: (a) a fiber beam-column element that models the behavior of the steel girder, (b) a fiber beam-column element that models the behavior of the concrete deck, and (c) a bond element that models the transfer of forces between the steel and concrete elements through shear connectors. The model neglects uplift and frictional effects. The fiber beam-columns are force-based elements that depend on force interpolation functions. A linear bending moment and a constant axial force serve as the interpolation functions. An important factor that favors the use of force-based elements in modeling composite structures is their ability to treat any type of distributed element loads. Distributed element loads are applied internally in a continuous manner by force superposition at the control sections. The state determination of these elements is based on an iterative solution that determines the element resisting forces and stiffness matrix. The bond element is a spring-type element that assumes a linear bond stress variation along the length. The nonlinear behavior of the composite element derives entirely from the constitutive laws of the steel, the concrete and the shear connectors. The paper concludes with a correlation study to investigate the validity of the model. Good agreement between analysis and experimental results was observed.     

聚丙烯纤维混凝土梁抗剪性能试验研究

分析了聚丙烯纤维掺量、配箍率、混凝土强度等级、剪跨比四个参数对混凝土梁斜截面初裂剪力和抗剪承载力的影响。提出了聚丙烯纤维混凝土梁斜截面受剪承载力计算方法,为工程实践提供理论依据。     

高强钢组合梁研究概述

近年来,钢—混凝土组合梁结构发展很快,在建筑和桥梁领域已经得到了越来越多的应用.在材料科学取得长足进步以及组合梁理论不断完善的背景下,把高强高性能材料引入到普通的钢—混凝土组合梁中,将取得显著的经济效益和社会效益.高强材料组合梁是新材料和新结构的有机结合.本文主要介绍了高强钢组合梁在国内以及在澳大利亚、欧洲、美国等发达地区的研究现状,并指出其优点和在设计中存在的问题.文中对高强钢与高强混凝土相结合的组合梁亦有所提及.     

Experimental study on straight composite beams subjected to combined flexure and torsion

Acceptable methods of ultimate load analysis and design for composite steel-concrete beams are nowadays readily available. However, in the case when a composite beam is curved in plan under vertical loading or an edge beam, the beam is subjected to a state of combined flexure and torsion. Previous studies have shown that current methods of using flexure-torsion interaction equations for reinforced concrete beams cannot be directly applied to composite steel-concrete construction. Moreover, partial shear connection which has been commonly used in composite steel-concrete construction has not been previously addressed in studies on flexure-torsion interaction. Therefore, this paper provides results from several test programmes to support the view that in the presence of flexure, there will be an increase in the torsional moment capacity but the flexural capacity does not increase in the presence of torsion. In addition to these experimental results, a model has been provided to allow for the design of combined flexure and torsion.     

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.     

Nonlinear analysis of composite beams subjected to combined flexure and torsion

There are situations in which a composite steel-concrete beam is subjected to torsion, such as members that are curved in plan or straight edge beams in buildings or bridges. The composite action of the steel beam and concrete slab in torsion is usually ignored in design codes of practice. Therefore, a three-dimensional (3D) finite element model is introduced in this paper to simulate composite steel-concrete beams subjected to combined flexure and torsion with the influence of partial shear connection using a commercial software ABAQUS. Brick and truss elements were used with the incorporation of nonlinear material characteristics and geometric behaviour in the model. This is coupled with an extensive parametric study using the validated finite element model using different parameters such as the span length and the level of shear connection. From the analytical study, a new phenomenon has been uncovered, which was validated by the test observation. This phenomenon called torsion induced vertical slip is an important issue, which would make the assumption plane sections remain plane invalid. In addition, difference in span length greatly affected the flexure-torsion interaction relationship of the composite steel-concrete beams, whilst the partial shear connection did not affect the relationship. Design models for readers to take away at the end of this paper are also proposed.     

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.     

预应力钢-混凝土连续组合梁的变形分析

对预应力钢-混凝土连续组合梁在正常使用极限状态下的变形计算进行分析。分析考虑钢与混凝土之间的滑移效应,建立简化计算模型,并在此基础上,提出混凝土支座开裂区长度以及预应力筋内力增量的计算公式,给出两跨预应力连续组合梁跨中挠度的计算图表。分析结果表明,两跨预应力连续组合梁变形计算公式计算正常使用极限状态预应力筋的内力值精度较高,不考虑预应力筋内力增量的变形计算值较试验值偏大,考虑预应力筋内力增量的变形计算值精度有明显提高,与试验结果吻合较好,可供工程设计参考。最后在两跨预应力连续组合梁变形计算公式的基础上提出预应力连续组合梁变形计算的通用方法。     

Full-scale long-term and ultimate experiments of simply-supported composite beams with steel deck

This paper presents the details of an experimental study carried out on two full-scale simply-supported composite steel-concrete beams to investigate their long-term behaviour and how this affects their ultimate response. The specimens were formed by a steel joist and a concrete slab with steel deck, and possessed identical spans and cross-sections. The ribs of the steel deck were orthogonal to the longitudinal axis of the steel joist, representing a secondary beam of a typical composite building flooring system. The beams were designed based on Australian guidelines with a degree of shear connection equal to 0.79. The samples were cast using unpropped construction. One specimen was kept unloaded for the entire duration of the tests. The second one was subjected to a sustained uniformly distributed load for about four months, after which it was loaded to failure. Particular attention was placed in this study on the occurrence of non-uniform shrinkage through the concrete thickness due to the presence of the profiled sheeting which prevented moisture egress to occur from the underside of the slab. Short- and long-term push-out tests were carried out to measure the response of the shear connectors over time. An analytical model was recommended to predict the long-term behaviour of composite beams with steel deck and its adequacy was validated against the reported experiments. For its simplicity, the proposed approach lends itself for design applications.     

Shear-flexural strength mechanical model for the design and assessment of reinforced concrete beams

A conceptual model for the prediction of the shear-flexural strength of slender reinforced concrete beams with and without transverse reinforcement is presented. The model incorporates the shear transferred by the un-cracked concrete chord, along the crack's length, by the stirrups, if they are, and, in that case by the longitudinal reinforcement. After the development of the first branch of the critical shear crack, failure is considered to occur when the stresses at any point of the concrete compression chord reach the assumed biaxial stress failure envelope. A physical explanation is provided for the evolution of the shear transfer mechanisms, and the contribution of each one at ultimate limit state is formulated accordingly. Simple equations are derived for shear strength verification and for designing transverse reinforcement. The method is validated by comparing its predictions with the results of 1131 shear tests, obtaining very good results in terms of mean value and coefficient of variation. Because of its accuracy, simplicity and theoretical consistency, the proposed method is considered to be very useful for the practical design and assessment of concrete structures subjected to combined shear and bending.     

开裂混凝土梁长期挠曲变形研究

开裂混凝土构件的长期挠曲变形难以预测,配筋率、荷载大小及徐变收缩效应均是影响构件长期挠曲变形的重要因素.以钢筋混凝土梁近700d的收缩徐变试验为基础,运用双线性法预测开裂钢筋混凝土梁的长期挠曲变形,编制了分析计算程序,与试验实测结果吻合较好,并对影响构件长期挠曲变形的因素进行了参数分析,本文方法便于工程实际应用.     

Two-dimensional FE model for evaluation of composite beams, I: Formulation and validation

This paper develops a two-dimensional finite element model for composite beams, based on the use of the commercial package ANSYS. Different degrees of continuity can be taken into account, permitting the investigation of systems ranging from simply-supported to fully-continuous. Beams with either full or partial shear connection can be considered, as well as different slab typologies. The model represents the behaviour of all components of the composite arrangement, based on the best available current understanding, including the reinforcing bars (considering the tension-stiffening effect), the load-slip characteristic of the shear connectors, and the key components of the beam to column connection. In addition, material nonlinearity for all components is taken into account. The model has been fully verified by extensive comparisons against experimental and numerical results and it has been demonstrated that it is suitable for comprehensive parametric studies of the behaviour of composite beams. A sensitivity study focusing on both the required and the available rotation capacities and their importance for moment redistribution in semi-continuous composite beams is presented in the companion paper.     

A contribution to understanding the influence of concrete cracking on timber concrete composite bridge beams

Despite of widely implemented advances in TCC bridge technology, there are still no satisfying design recommendations that consider the influence of concrete cracking on the distribution of forces and deformation. A research project at Universidad Austral de Chile studied several aspects of concrete cracking in TCC bridges with timber beams of greater depth than width using elastic dowel‐type shear connectors. One of the results of concrete cracking is a reduction of the slip modulus of the connectors. This weakening was simulated in shear tests by a small gap between the timber and the concrete. A test calibrated FEM model was used for a parametric study of 120 different cases, most of which did not show concrete cracking. Where concrete cracking occurred, it caused an increase in the timber tensile stresses and beam deflection of up to 20 %. We conclude that concrete cracking occurs when the timber‐concrete depth ratio is less than four times the cubic root of the effective flange width of the concrete slab. Beitrag zur Berücksichtigung des Einflusses der Rissbildung im Beton in Holz‐Beton‐Verbundbrücken Trotz des hohen Entwicklungsstands der Holzverbundbrückentechnologie, fehlen ausreichende Entwurfsgrundlagen für die Berücksichtigung des Einflusses der Rissbildung auf die Schnittkraft‐ und Verformungsverteilung. Im Rahmen eines Forschungsprojekts an der Universidad Austral de Chile werden verschieden Aspekte der Rissbildung in Holzverbundbrücken mit Holzbalken mit größerer Höhe als Breite und elastischen stiftförmigen Verbindungsmitteln untersucht. Dabei wurde festgestellt, dass sich die Rissbildung auf den Schubmodul del Verbindungsmittel auswirkt. Dieser Einfluss wurde in Scherversuchen durch einen kleinen Spalt zwischen Holz und Beton simuliert. Anhand eines mit Versuchen kalibrierten FEM‐Modells wurden eine Parameterstudie mit 120 verschieden Fälle durchgeführt. In den meisten Fällen tritt keine Rissbildung auf. Wenn es zu Rissbildung kommt, vergrössern sich die Holzzugspannungen und die Durchbiegung um bis zu 20 %. Wir stellen fest, dass Rissbildung auftritt, wenn das Bauhöhenverhältniss von Holz und Beton kleiner als die vierfache Kubikwurzel der mitwirkenden Plattenbreite der Betonplatte ist.