部分外包混凝土简支组合梁受弯性能试验研究

为了研究部分外包混凝土组合梁在正弯矩作用下的受力性能,考察钢梁腹部钢筋混凝土对组合梁承载力及刚度的影响,对4根简支梁试件进行了试验研究,其中包括1根普通钢-混凝土组合梁试件和3根钢梁腹板与腹部混凝土界面采用不同连接方式的部分外包组合梁试件。试验结果表明：钢梁腹板与腹部混凝土界面采用不同连接方式对部分外包组合梁的受弯承载力和刚度没有显著的影响;与普通钢－混凝土组合梁相比,由于钢梁腹部钢筋混凝土的贡献,部分外包组合梁的受弯承载力和抵抗变形的能力均有较大的提高;承载力极限状态时部分外包组合梁中钢梁与腹部混凝土之间的相对滑移值较小,其滑移效应对组合梁截面受弯承载力的影响可以忽略不计。在试验研究的基础上,推导了部分外包组合梁塑性受弯承载力的计算公式,计算结果表明,简化塑性理论可以较准确地预测该类组合梁的受弯承载力。     

受负弯矩和压缩作用的组合梁的性能和设计

调查了受负弯矩和轴向压缩共同作用下钢-混凝土组合梁结构的性能。在这项研究中,对6个承受负弯矩作用的足尺寸的组合梁同时进行压缩。轴向压缩的等级由低到高变化。根据试验,构建并标定一个非线性有限元模型来对试验结果进行验证。该模型能够对试验所用梁的非线性响应和最终破坏模式做出预测。所构建的有限元模型对一些常在实际中使用的组合梁可进行一系列参数分析。分析发现,当压缩荷载作用于组合截面时,组合梁的负弯矩承载能力明显降低,钢梁的局部屈曲更显著,影响了截面的延展性。基于截面平衡的刚塑性分析可以合理地预测组合截面的复合强度,因此可适当地使用于设计原理中。在负弯矩区钢梁腹板处使用纵向加劲肋可消除腹板屈曲,并增加组合截面的转动能力。根据试验结果和有限元分析提出一个可应用于工程实践中的简化设计模型。     

Behaviour and design of composite beams subjected to negative bending and compression

This paper investigates the behaviour of steel–concrete composite beams subjected to the combined effects of negative bending and axial compression. For this study, six full-scale tests were conducted on composite beams subjected to negative moment while compression was applied simultaneously. The level of the applied axial compression varied from low to high. Following the tests, a nonlinear finite element model was developed and calibrated against the experimental results. The model was found to be capable of predicting the nonlinear response and the ultimate failure modes of the tested beams. The developed finite element model was further used to carry out a series of parametric analyses on a range of composite sections commonly used in practice. It was found that, when a compressive load acts in the composite section, the negative moment capacity of a composite beam is significantly reduced and local buckling in the steel beam is more pronounced, compromising the ductility of the section. Rigid plastic analysis based on sectional equilibrium can reasonably predict the combined strength of a composite section and, thus, can be used conservatively in the design practice. Detailing with longitudinal stiffeners in the web of the steel beam in the regions of negative bending eliminate web buckling and increase the rotational capacity of the composite section. Based on the experimental outcomes and the finite element analyses a simplified design model is proposed for use in engineering practice.     

侧向扭转屈曲时冷成型钢梁的特性及设计

建筑物中越来越多地使用冷成型钢梁作为楼板的辅助及受力构件,其在没有足够侧向约束时的性能和瞬时承载力将受到侧向扭转屈曲的影响。以往对侧向扭转屈曲的研究主要针对热成型卷边钢梁,因此需要对简单支撑下相同弯曲度冷成型卷边槽钢梁的特性进行数值模拟。采用业内广泛认可的有限元分析软件ABAQUS进行建模,对不同条件下冷成型钢梁微单元的侧向扭转屈曲性能和承载力进行分析和模拟。将瞬时承载力结果与冷成型钢结构规范中当前设计准则的预测结果进行比较并对其进行适当的修正。欧洲的设计规范较为保守,而澳大利亚、新西兰和北美的设计规范则较为宽泛。基于有限元分析结果,对规范中的瞬时承载力设计公式进行修正。阐述了参数分析的细节问题,修正了当前设计规范,提出了侧向扭转屈曲时冷成型卷边槽钢梁的新设计准则。     

Experimental and numerical analysis on the structural behaviour of cold-formed steel beams

A research study on the structural behaviour of cold formed steel beams with C-, I-, R- and 2R-shaped cross-sections at ambient temperature is presented, based on the results of a large programme of experimental tests and numerical simulations. Firstly, several four-point bending tests were carried out in order to assess mainly the failure loads and failure modes of the beams. Secondly, a suitable finite element model was developed to compare with the experimental results, and finally, a parametric study was undertaken in order to investigate the influence of the thickness, height and length of the beams on its structural behaviour.     

Simplified elasto-plastic analysis of composite beams and cellular beams to Eurocode 4

The elasto-plastic analysis of composite beams is important when considering the increase in bending resistance of the beam and the end slip between the steel and concrete at higher strains. This paper provides a simplified method of elasto-plastic analysis by considering equilibrium of the composite cross-section as a function of its strain profile. A parabolic-rectangular stress block for concrete is used in this model with a declining concrete strength at strains exceeding 0.0035. The bending resistance of the composite beam is expressed as a function of the bottom flange strain, and is compared to fully plastic design to EN 1994-1-1: Eurocode 4 and the AISC LRFD Code.The effect of various parameters on the development of the plastic bending resistance of composite beams is investigated, such as asymmetry of the section, the steel strength, the influence of propped or un-propped construction, strain hardening in the steel and reducing concrete strength at high strains, interface slip, and the effect of openings in the web of the beams. It was found that a moment of 95% of the plastic bending resistance of a composite beam (0.95M_p?) is reached at a flange strain of 2 to 4 × yield strain for propped beams and 5 to 10 × yield strain for un-propped beams. When strain hardening in the steel is included in the analysis, bottom flange strains at a moment of 0.95M_p? are reduced by up to 30% relative to the case without strain hardening.     

Plastic mechanisms database for thin-walled cold-formed steel members in compression and bending

Short members of thin-walled cold-formed (TWCF) steel sections, in compression and bending, fail by forming local plastic mechanisms. Taking into account the localised buckling pattern, the collapse of slender members, due to the interaction between local and overall buckling modes, is always characterised by local plastic mechanism failure mode. Based on these two observations, the ultimate strength in interactive buckling of these members can be regarded as an interaction between localised plastic mode and overall elastic one.The yield line mechanism method has been widely used to predict the sectional strength (e.g. local) of thin-walled cold-formed steel members that involve failure mode characterized by local collapse mechanisms. This method can be also used to study post-collapse behaviour and to evaluate the load-carrying capacity, ductility and energy absorption.This paper is based on previous studies and some latest investigations of authors, as well as the literature collected data. It represents an attempt to make an inventory, classify and range geometrical and analytical models for the local-plastic mechanisms aiming to characterize the ultimate capacity of some of the most used cold-formed steel sections in structural applications.     

Glass fibre reinforced plastic (GFRP) rebars for concrete structures

The study described is a part of a large-scale experimental and theoretical programme on the application of fibre reinforced plastic ( ) reinforcement for concrete structures initiated at the Université de Sherbrooke (Sherbrooke, Canada). The programme is being carried out to gain an insight into the flexural behaviour of concrete beams reinforced with glass fibre reinforced plastic ( ) rebars. Results of experimental study on 3.3 m long beams reinforced with two different types of rebars are presented and compared to that of conventional steel reinforced concrete beams. Three series of reinforced concrete beams were tested in flexure. The beams were 200 mm wide and respectively 300, 450 and 550 mm high. The paper also attempts to present the properties of and its components and to give an oversight of relevant research activities involving rebars as reinforcement for concrete units.     

Post-failure behaviour of box section beams under pure bending (an experimental study)

The results of a program of experiments set up to explore the post-failure behaviour of box section beams subjected to pure bending are presented. Rectangular and trapezoidal cross-section beams were loaded up to and beyond collapse in a four-point bending configuration. Load–deflection graphs were recorded and the details of the observed plastic collapse mechanisms were noted. Experimental collapse curves are compared with those derived from theoretical models of plastic collapse mechanisms based upon rigid–plastic theory.     

Numerical simulation of the nonlinear bending response of fibre-reinforced cementitious matrix beams and comparison with experimental results

The aim of this work is the efficient numerical simulation of the bending behaviour of fibre reinforced cementitious matrix (FRCM) beams. For the production of the FRCM specimens, a high-strength cementitious matrix with hooked-end steel fibres is used. Two types of FRCM beams are considered. The first type has no conventional steel reinforcement, while the second one includes longitudinal and transverse reinforcement steel bars. For comparison reasons, conventional reinforced concrete (RC) beams are also studied. The beams are tested under static and cyclic loading. The response of the tested beams is simulated by means of effective two-dimensional finite element models, in which the contribution of the FRCM is taken into account by means of two different layers of finite elements. The first one represents the cementitious matrix while the second one accounts for the contribution of the steel fibres in a homogenized manner. The presented models are able to follow the nonlinearities that appear in the corresponding physical models. The validity of the proposed methodology is established by comparing the numerical results with the corresponding experimental results.     

高强钢-混凝土组合梁受弯性能试验研究

为研究高强钢-混凝土组合梁在静载作用下的受弯性能,共进行了8根简支梁在跨中两点对称荷载作用下的试验。8根试件均为完全剪力连接,主要变化参数为混凝土强度等级和钢梁强度等级。加载方式为单调静力加载,试验测量内容主要为竖向加载荷载、挠度、截面应变等。试验结果表明,所有试件均发生典型的弯曲破坏,高强钢与混凝土通过栓钉连接表现出良好的整体工作性能。现行规范中的简化塑性计算方法可以较准确地预测该类型梁的极限受弯承载力。根据该塑性理论方法,对组合梁进行了参数分析,主要变化参数为混凝土强度等级和钢梁强度等级。分析表明,其他条件相同时,相比混凝土强度,钢梁强度是影响组合梁受弯承载力的主要因素。研究为高强钢在组合梁中的应用提供了试验依据。     

Experimental bending tests of partially encased beams at elevated temperatures

This paper presents the result of an experimental research about the lateral torsional buckling instability during bending tests of Partially Encased Beams (PEB) at elevated temperature. A set of twenty seven four-point bending tests, grouped in ten series, were carried out to analyse the influence of relative slenderness, beam temperature and the shear bond conditions between concrete and steel in bending. In addition, this study compares the behaviour of PEB and bare steel beam under bending at room temperature.PEB specimens are based on IPE100 steel profiles, with two different lengths 2.4 m (medium series) and 3.9 m (large series), tested in bending using simple supporting conditions and exposed to different temperatures levels of 200 °C, 400 °C, and 600 °C.Two different shear bond conditions, between steel profile and lateral concrete, were analysed at 400 °C: one series with connectors formed by welded stirrups to the web and another series with natural adherence between steel and concrete, not welded stirrups.PEB attained lateral torsional buckling as deformed failure mode at the ultimate limit state, except for the case of PEB tested at 600 °C that results in a plastic hinge failure. The bending resistance was determined for the maximum load event (F_u) and for the displacement limit corresponding to L/30 (F_L/30) and compared with the results of the Eurocode 3 part 1–2 simple calculation method, considering an adaptation of its formulae to PEB. The expected reduction in bending resistance at elevated temperature is in good agreement with the experimental reduction factor, when the deformation criterion is used.     

工形对称截面不锈钢梁变形性能的试验研究

为研究国产不锈钢梁的非线性变形性能,对4根焊接不锈钢梁进行静力加载试验,并采用有限元软件ANSYS进行数值模拟。试验材料为国产奥氏体不锈钢316,加载类型包括单点加载和两点加载。试验结果表明:由于不锈钢材料非线性的影响,在荷载水平较大时,不锈钢梁的变形性能具有明显的非线性;当材料屈服时,塑性挠度占总挠度的50%左右;出现较大的平面外位移时,塑性挠度增加更加显著。该试验结果可为国产不锈钢梁的挠度计算提供依据。     

The effects of axial tension on the sagging-moment regions of composite beams

This paper studies the effects of axial tension on the sagging moment regions of steel–concrete composite beams. The study comprised an extensive experimental programme and nonlinear finite element analyses. Six composite beams were designed and tested under the combined effects of axial tension and positive bending moment. The beams were loaded to their ultimate capacity and the experimental moment-axial tension interaction diagram was constructed. Following the tests, a finite element model was used to simulate the nonlinear response of the composite beams. The validity of the model was thoroughly assessed against the available experimental data and a parametric study was conducted to study different beam sizes and the effect of partial shear connection on the interaction diagram. It was found that the moment capacity of a composite beam is reduced under the presence of an axial tensile force acting in the steel beam section. In addition, the use of partial shear connection does not affect significantly the shape of the interaction diagram. The tensile capacity of the composite section, however, is limited by the axial capacity of the steel beam alone. Based on the experimental results and the finite element analyses, a simplified equation is proposed for the design of composite beams subjected to positive bending and axial tension.     

Zur plastischen Bemessung hochfester kammerbetonierter Verbundträger

Plastic design method for high‐strength partially concrete encased composite beams. Partially concrete encased composite beams offer numerous advantages compared to conventional composite beams consisting of a steel beam and a concrete slab. In many cases these advantages are not used because of missing practicable design models. In the current paper the load bearing behaviour and the rotation capacity of partially concrete encased composite beams made of high strength steel and concrete is investigated using experimental tests and parametric studies. At first the influence of high strength concrete encasement and high strength structural steel on the cross section capacity is described. Taking into account the stress‐strain distribution of high strength concrete and steel a new plastic design method for partially concrete encased composite beams was affiliated. The experimental and theoretical results are documented in the research report [1] and the dissertation [2].     

Slenderness limits for cold-formed channel sections in bending by experimental methods

Inelastic design methods allow for larger application of loads on sections than elastic design methods, due to the redistribution of yield stress through the depth of the section. Sections that can reach the full plastic capacity and maintain it for sufficient rotation are considered applicable for plastic mechanism design, resulting in more economical structural solutions. Cold-formed steel channel sections are used extensively in portal frame structures in agricultural and light industrial/commercial applications, structures well suited to plastic design, however may currently only be designed elastically. To address this limitation in design standards, experimental and numerical analyses on the inelastic bending capacity of cold-formed channel sections are performed, and design rules to account for such behaviour are developed. Design rules are prepared using the hot-rolled steel specification methodology of classifying a section as compact, non-compact or slender (according to the Australian Standards) and Classes 1, 2, 3 and 4 (according to the European Standards). Proposals for the Australian standard are shown to provide accurate and reliable capacity predictions for cold-formed steel channel sections whose bending capacity exceeds the elastic limit.     

冷弯槽钢受弯时长细比限值试验研究

非弹性设计方法与弹性设计方法相比,其截面的允许荷载值较大,这是由于屈服应力沿截面高度进行了重新分布。塑性设计方法使得截面的塑性能力和塑性铰的转动特性得到充分发挥,从而使结构设计更为经济合理。冷弯槽钢在农业和轻工/商业中广泛用于门式刚架结构,塑性设计方法对这类结构非常适用,然而目前仅采用弹性设计方法对其进行设计。为突破设计规范的限制,对冷弯槽钢的非弹性弯曲能力进行了试验研究和数值分析,以建立相应的设计准则。设计准则采用热轧钢分类方法,将截面分为紧凑型、非紧凑型及细长型(根据澳大利亚规范),或1,2,3,4级(根据欧洲规范)。澳大利亚规范所预测的超过弹性极限范围的冷弯槽钢弯曲能力精确可靠。     

加筋增强玻璃梁受弯性能试验研究

为实现玻璃梁延性化破坏的目标，借鉴钢筋混凝土结构的思路，通过在玻璃梁底部受拉区配置不锈钢的方式制成加筋增强玻璃梁。玻璃开裂后通过不锈钢传递拉力，以形成开裂后承载机制。文章对加筋增强玻璃梁的受弯性能展开试验研究，通过试验，研究试件受弯的受力行为，识别不同破坏形态；通过对试验现象、荷载位移曲线、荷载应变曲线和裂缝发展过程的分析，研究构件在开裂前和开裂后的受力机理；通过定义6个力学性能指标，定量描述加筋增强玻璃梁受弯的力学性能；通过对不同玻璃种类、配筋率、截面高度的加筋增强玻璃梁试件力学性能指标进行对比，识别对加筋增强玻璃梁力学性能有显著影响的因素及其影响规律。研究结果为加筋增强玻璃梁的分析和设计提供试验基础。     

钢-高强混凝土组合梁的试验研究

为了研究钢-高强混凝土组合梁在静载作用下的抗弯性能,本文完成了8根钢-高强混凝土组合梁在跨中两点对称荷载作用下的试验,对其受力性能进行了分析,并探讨了翼缘板混凝土强度、钢梁屈服强度和翼缘板宽度对组合梁正截面受弯承载力、延性的影响。结合试验结果和理论分析,对现行规范中组合梁正截面受弯承载力计算公式进行了补充修正,以拓宽计算公式中翼缘板混凝土强度的适用范围,为高强混凝土在钢-混凝土组合梁中的应用提供设计依据。     

Simplified nonlinear simulation of steel–concrete composite beams

A computationally efficient macro-model approach is proposed for investigating the nonlinear response of steel–concrete composite beams. The methodology accounts for material nonlinearity and interface slip between the concrete slab and the steel beam. The validity of the technique is evaluated through comparison of the macro-model-based simulations with results obtained from experimental testing of composite beams. Four full scale composite beams are tested under monotonic positive and negative bending. The results show that the proposed macro-element-model can capture the essential characteristics of the nonlinear load–deformation response of composite beams. Such an approach is a compromise between simplicity and accuracy and a viable alternative to detailed finite elements analysis. Additionally, a parametric study, including the compressive strength of slab concrete, the yield strength of the steel flanges and web, and the shear connection degree, of the steel–concrete composite beams subjected to positive moment is conducted utilizing the numerical macro-model proposed. The slips and their influences on the behaviors of composite beams during loading process have been analyzed.