Bemessungshilfen und Konstruktion bei geneigten Querkräften

Design Methods and Detailing for RC Beams with Inclined Shear Forces The shear‐resistant design of reinforced concrete (RC) beams with rectangular cross sections and inclined shear forces (biaxial shear) is presented. Equations for the shear resistances provided by the tensile strut and by the compressive strut are derived according to the design concepts of DIN 1045‐1 and EC 2. They are verified to experimental data and elaborated to gain design charts. Examples show the practical applications. Existing detailing provisions for the anchorage of stirrups and the horizontal displacement in the tensile force of the bending reinforcement can directly be applied to cases of biaxial shear, if the rotations of the neutral axis and of the resultant strut‐and‐tie system are taken into account.     

Einheitliches Fachwerkmodell für Stahlbeton‐ und Spannbetonbauteile unter Querkraft‐ und Torsionsbeanspruchung

Uniform framework model for reinforced and prestressed concrete structural members under shear and torsion loading. Following the design provisions for shear and torsion according to DIN 1045‐1 the following two principle questions are raised: For a lot of situations in standard design praxis the allowable inclination of the concrete strut is determined to an angle as small as about 18° – while such a gentle strut angle in tests could only be proved in case of a high level additional compression force. Additionally, with the given two different design approaches a smooth transition between structures with and without required shear reinforcement is lacking. For the purpose of a general review experimental as well as theoretical investigations for beams under shear loading and torsion loading have been conducted. As consequence of the obtained results a uniform strut‐and‐tie model with simply application has been derived.     

基于修正软化拉-压杆模型的型钢#br# 混凝土深梁受剪承载力研究

为研究型钢混凝土深梁的受剪承载力,完成7组型钢混凝土深梁的静力试验和有限元分析,主要考虑剪跨比、型钢腹板高度及翼缘宽度等影响因素。试件的破坏模式为斜压破坏和剪切破坏。剪跨比对破坏形态有较大影响,较大的型钢腹板高度和翼缘宽度显著提高试件受剪承载力。在试验研究和有限元分析的基础上,考虑钢筋混凝土部分的软化效应、非软化混凝土与型钢翼缘的协调变形作用及腹板部分的受剪贡献,建立修正软化拉-压杆模型,并采用叠加原理推导型钢混凝土深梁受剪承载力实用计算方法。结果表明：修正软化拉-压杆模型能较好地反映型钢混凝土深梁的破坏特征和受力机制,文中提出的受剪承载力计算方法与试验数据吻合较好,对受剪影响因素考虑更加全面,能较好地预测型钢混凝土深梁的受剪承载力。     

Zur Mindestquerkraftbewehrung von Stahlbetonbalken

On minimum shear reinforcement amounts for reinforced concrete beams A ductile shear bearing behaviour of reinforced concrete beams is recently ensured by providing standardized amounts of minimum shear reinforcement in compliance with established detailing provisions. However, lower than minimum shear reinforcement amounts do not necessarily go along with a brittle mode of failure in all cases. Dependent on the individual layout and amount of stirrups, the contributions of other bearing capacities and the crack formation itself, the initial cracking force might be overtaken even along with further load gains and reasonable limited shear crack widths. Especially the latter one holds potential to rate the failure mode – brittle or ductile – on site. Experiments on lightly shear reinforced single span concrete beams are evaluated and rated with respect to minimum shear reinforcement amounts required. Thereby, special interest is set on the load‐deformation response obeying the critical shear crack and the structural design. Finally, the overall shear resistance as well as the stirrups' efficiency in the effective shear domain are analysed to derive suggestions for future practical application on‐site.     

Composite beam composed of steel and pre‐cast concrete. (Modularized Hybrid System,MHS) Part II: analytical investigation

This paper introduces the concept of a wide flange steel beam with the bottom flange encased in pre‐cast concrete. These composite beams utilize the merits of both steel and concrete materials. The effective interaction between the two materials can reduce the size of the steel beams. The reinforcement and the concrete are pre‐integrated with the bottom flange of the steel beam at a manufacturing plant. In this paper, the analytical investigation of the flexural moment strength of the composite beams at both the yield limit state and the maximum load limit state is performed and compared with the experimental results. The depth of the equivalent rectangular stress block of the beams is obtained using an equilibrium equation when both the compression steel reinforcements are present. The post‐yield behaviour of the composite beams is also investigated based on the normalized effective stiffness versus the normalized drift ratio . The stiffness of the composite beams degrades gradually with sufficient ductility and dissipating energy capability. A six‐step procedure provides a fast, effective and accurate way of investigating the post‐yield behaviour of the composite beams. Copyright © 2008 John Wiley & Sons, Ltd.     

Stahlbetonträger mit zweiachsiger Querkraftbeanspruchung

Reinforced Concrete Beams subject to biaxial Shear Forces: strut‐and‐tie models, experiment and design approach Spatial strut‐and‐tie models are developed for the design of reinforced concrete beams subject to biaxial shear forces. They are derived from a resolution of the vector of the resultant shear force and valid for beams with rectangular cross sections. The models consist of tensile struts of stirrups and longitudinal bars, compressive concrete struts directed to each separate area of the longitudinal reinforcement in the cracked part of the cross section as well as compressive struts stiffening the stirrups. They are qualitatively verified by experiments and further elaborated to derive design charts for the design of the stirrups. An example shows the practical application of the charts.     

Ein Bemessungsansatz für zweiachsig durch Querkräfte beanspruchte Stahlbetonbalken mit Rechteckquerschnitt

Design of Reinforced Concrete Beams with rectangular Cross Sections against biaxial Shear Forces An approach is presented to design reinforced concrete beams with rectangular cross sections and usual stirrups against shear forces that act inclined to the principal axes of the cross sections. It basis on the “truss model with crack friction” and adds supplementary terms to the equations of the shear resistances acc. to DIN 1045‐1 to take account for shear force inclinations. Verifications to experimental as well as numerical data are given. An example shows that resistances evidently decrease – or higher amounts of stirrup reinforcement become necessary –, if shear forces deviate from principal axes.     

提高约束钢筋混凝土短梁抗震性能的设计方法研究

本文利用71根约束钢筋混凝土短梁在反复荷载下的试验研究结果，综合分析了剪跨比（跨高比）、梁端上部配筋特征、附加交叉腹筋、垂直与水平分布腹筋、钢纤维、以及剪压比诸参数对短梁的破坏形态、抗弯与抗剪承载力、延性、耗能的影响；同时对提高短梁抗震性能的设计方法进行了研究。最后提出了延性约束钢筋混凝土短梁的抗震设计方法建议。     

Experimental study on shear behavior of reinforced concrete beams with web horizontal reinforcement

In determining the shear capacity of reinforced concrete beams, current codes do not provide any calculation method to evaluate the influence of web horizontal reinforcement, although they exist as structural reinforcements (or skin reinforcement). The present paper comprises results of 11 reinforced concrete beams in an effort to investigate the influence of web horizontal reinforcement on the shear behavior of reinforced concrete beams. The primary design variables are the shear-span-depth ratio, different reinforcement ratio of stirrups and web horizontal reinforcement. Influence of web horizontal reinforcement on crack patterns and failure mode was studied. It was found that web horizontal reinforcement can increase the shear capacity of the beams and restrain growth of inclined cracks effectively. Test results are very valuable, as very few references of shear tests can be found focusing on the effect of web horizontal reinforcement on the shear capacity of the beams.     

基于纤维梁柱单元的RC带翼缘剪力墙抗震性能分析

为高效准确地模拟钢筋混凝土构件在复杂荷载作用下非线性行为,采用OpenSees中基于刚度法的纤维梁柱单元,建立一种考虑弯曲和剪切共同作用的RC带翼缘剪力墙非线性分析模型,并对已完成的4个不同边缘构件和截面形式的RC带翼缘剪力墙的拟静力试验进行数值模拟;通过比较数值模拟结果与试验结果,验证有限元模型的准确性;通过有限元分析,研究轴压比(0.1~0.3)、剪跨比(1.8~3.0)、翼缘宽度与腹板高度比(0.5~1.1)、混凝土强度(C30~C45)、纵筋配筋率(0.73%~2.22%)以及箍筋配箍率(0.74%~5.19%)对RC带翼缘剪力墙抗震性能的影响。研究表明：随着轴压比、翼缘宽度与腹板高度比、混凝土强度以及纵筋配筋率的增大,带翼缘剪力墙的承载力逐渐增大,其极限变形能力在翼缘受拉方向也相应增大,而在翼缘受压方向不断减小。剪跨比的增大使得带翼缘剪力墙的承载力明显减小,但是变形能力大幅提高。箍筋配箍率的提高可以有效延缓带翼缘剪力墙翼缘受拉方向的破坏。     

混杂纤维HPC深梁的剪切变形性能

采用正交设计法对18组混杂纤维高性能混凝土(HPC)深梁和2组普通高性能混凝土深梁进行受剪试验,分析了深梁的变形性能。结果表明,普通HPC深梁剪切破坏时均发生劈裂破坏,而混杂纤维HPC深梁则有劈裂破坏和斜压破坏两种形态,但仍达不到延性破坏的要求。混杂纤维(钢纤维和聚丙烯纤维)的掺入,延缓了HPC深梁斜裂缝的出现时间,减小了水平及竖向分布钢筋的应变,深梁开裂时斜截面混凝土应变的突变明显变小。     

钢-ECC组合梁负弯矩区受弯性能试验研究

纤维增强水泥基复合材料（Engineered Cementitious Composite,ECC）具有高延展性以及受拉刚化特点,应用于组合梁桥的负弯矩区时可有效减少桥面板的受拉开裂。完成了2根钢-ECC组合梁和1根钢-混凝土组合梁对比构件在负弯矩作用下的静力加载试验,通过试验研究了不同配筋率的ECC对结构受力性能特别是抗裂性的影响。试验研究表明：在负弯矩作用下,钢-ECC组合梁的刚度较钢-混凝土组合梁明显提高|由于ECC翼板的抗拉作用导致截面中和轴上升,钢梁受压区增大,构件延性有所降低|钢-ECC组合梁可有效提高结构的开裂荷载并减小裂缝宽度,提高配筋率有利于进一步减少ECC翼板的裂缝宽度。提出了钢-ECC组合梁的承载力与开裂荷载的计算方法,提供了挠度分析的方法和裂缝宽度的基本模型。     

Mit Schrauben Bewehren – Neue Ergebnisse

Self‐tapping screws as reinforcement – new results. Self‐tapping continuously threaded screws can be used as elements for reinforcement or joints in timber construction because of their high axial strength and excellent bonding properties. The layout of the reinforcing or joining screws can be derived from strut‐and‐tiemodels which are common in concrete design and follow the internal flow of forces. Several series of tests in 2007 already showed the high potential of this construction method on various joint details and reinforced timber elements. Based on this success in 2008 further tests were taken out on joints and timber beams with altered and more sophisticated screw configurations. Hereby the load‐bearing capacity of timber beams reinforced with steel lamellas and rigid frame corners connected with self‐tapping screws was extraordinary and demonstrated once more the high potential of this design method.     

Teilfertigdecken nach DIN 1045‐1. Wichtige Punkte der Bemessung und Konstruktion

Partly pre‐fabricated reinforced concrete Floors/Ceilings according to DIN 1045‐1. Important Points of Design and Construction There are invasive changes in design and construction of partly pre‐fabricated reinforced concrete floors/ceilings connected with the application of DIN 1045‐1, July 2001 issue. This applies specifically to the verification of acceptance of thrust force in the joint between pre‐cast slab and the on‐site concrete. The basic elements will be gathered for this extensive verification and an example is given. Regulations for the arrangement of lattice girders as bond/shear force reinforcement as well as concrete covers will be shown in detail. Structures of support are easier to implement in the future.     

Shear strength prediction for steel reinforced concrete deep beams

This study proposes an analytical method for determining the shear strengths of steel reinforced concrete deep beams under the failure mode of concrete crushing originally based on the softened strut-and-tie model. The proposed method is a good physical model that can correlate well with the observed failure phenomenon of steel reinforced concrete deep beams. By comparing the predictions of the proposed method with the available test results from the literature, it was found that the proposed method is capable of predicting the shear strengths for steel reinforced concrete deep beams with sufficient accuracy. The shear-carrying behavior of steel reinforced concrete deep beams is highly influenced by the ratios of flange width to gross width, the shear span-to-depth ratios, and the concrete strengths. When the ratio of flange width to gross width is low, the shear-carrying capacities of steel reinforced concrete deep beams increase with the increasing ratio. However, if the ratio of the flange width to gross width is higher than a critical value, then the failure mode of steel reinforced concrete deep beams will be converted from diagonal compression failure into bearing failure.     

基于钢筋分离模式优化的RC深梁静力试验研究

钢筋应力渐进结构优化以钢筋单元应力为灵敏度,针对钢筋分布演化出接近钢筋满应力目标的最优拓扑,为钢筋混凝土(RC)深梁的工程配筋设计提供新方法.按照该方法完成RC简支深梁的优化配筋设计,并开展静力试验.试验过程中发现,随着荷载的增大,深梁表面弯曲裂缝充分开展,剪切裂缝得到有效控制,在达到峰值荷载后存在明显的持荷且变形大幅...     

Torsion und Querbiegung in Plattenbrücken,gegebenenfalls mit einbetonierten Stahlträgern (WIB‐Bauweise)

Torsion und transverse bending in plate bridges, also those containing cast‐in steel beams (WIB‐construction). In usual reinforced‐concrete plate bridges, torsion and transverse bending are superfluous for equilibrium. These secondary moments depend on the assumed stiffness and will be unnecessarily overestimated in a homogeneous elastic analysis without consideration of cracking. This results in excessive transvers reinforcement, particularly for railroad bridges containing cast‐in steel beams. Apparently paradoxical aspects of the plate twisting moment are clarified. This facilitates insight into modeling plates by gridworks. Procedures to determine the strain‐induced stress in the transverse reinforcement are described.     

纵筋率对无腹筋约束梁抗剪性能影响的研究

各国规范在以往的对钢筋混凝土梁斜截面抗剪承载力性能的试验研究中,研究都是按较高纵筋率来进行,建立在这种纵筋率较高的梁的受剪性能试验数据基础上的规范抗剪设计方法可能偏差较大。而本文按较低纵筋率来研究梁的抗剪性能。试验表明,不同纵筋率对梁的抗剪性能和裂缝发展状况有重要影响,规范公式用于小纵筋率无腹筋约束梁受剪设计时可能偏不安全。     

循环荷载作用下型钢高强高性能混凝土短柱抗剪承载力研究

基于循环荷载作用下的型钢高强高性能混凝土短柱的试验结果,对影响型钢高强高性能混凝土柱剪切破坏的剪跨比、轴压比、混凝土强度、含钢率以及配箍率等主要因素进行分析。通过单独考虑钢筋混凝土部分、型钢部分、轴压力部分对柱抗剪承载力的贡献,根据叠加原理,并考虑位移延性需求的影响,分别给出型钢高强高性能混凝土短柱剪切黏结破坏以及剪切斜压破坏两种情况下的抗剪承载力计算公式。通过与试验结果的对比发现,所建立的公式能较好地反映型钢高强高性能混凝土短柱的抗剪承载力,研究结果可为型钢组合结构规范的修订以及工程设计提供理论依据和参考。     

Strengthening of RC beams in shear using GFRP inclined strips – An experimental study

Though there have been a number of studies on shear strengthening of RC beams using externally bonded fiber reinforced polymer sheets, the behaviour of FRP strengthened beams in shear is not fully understood. This is partly due to various reinforcement configurations of sheets that can be used for shear strengthening and partly due to different failure modes a strengthened beam undergoes at ultimate state. Furthermore, the experimental data bank for shear strengthening of concrete beams using FRP remains relatively sparse due to which the design algorithms for computing the shear contribution of FRP are not yet clear. The objective of this study is to clarify the role of glass fiber reinforced polymer inclined strips epoxy bonded to the beam web for shear strengthening of reinforced concrete beams. Included in the study are effectiveness in terms of width and spacing of inclined GFRP strips, spacing of internal steel stirrups, and longitudinal steel rebar section on shear capacity of the RC beam. The study also aims to understand the shear contribution of concrete, shear strength due to steel bars and steel stirrups and the additional shear capacity due to glass fiber reinforced polymer strips in a RC beam. And also to study the failure modes, shear strengthening effect on ultimate force and load deflection behaviour of RC beams bonded externally with GFRP inclined strips on the shear region of the beam.