采用剪切弯曲三角杆的对称冷弯型钢-混凝土组合梁的大比例试验

对对称冷弯型钢-混凝土组合梁进行静力受弯试验,介绍了基于剪切弯曲杆改进的剪切弯曲三角杆。冷弯型钢构件比热轧构件更薄,不允许焊接栓钉剪力连接件,剪切弯曲三角杆能解决这一问题。将两个冷弯型钢槽的背靠背连接成对称构件,它在静力作用下具有足够的强度和刚度。通过剪切弯曲三角杆的抗剪方程计算的抗弯承载值与试验数据很吻合。     

Test of shear transfer enhancement in symmetric cold-formed steel-concrete composite beams

An experimental programme was conducted to study the strength and behaviour of a bent-up tab shear transfer enhancement. Sixty eight push-out test specimens of cold-formed steel lipped channel sections (CFS) embedded in concrete planks which make use of the new proposed shear transfer enhancement called bent-up triangular tab shear transfer (BTTST) were tested in this programme. This paper summarises the results of the experimental study and develops an expression in order to predict the innovative shear transfer enhancement mechanism, BTTST in a new type of precast composite beam comprising CFS embedded in a precast concrete plank. The results show that specimens employed with shear transfer enhancements increase the shear capacities of the specimens as compared to those relying only on a natural bond between cold-formed steel and concrete. In this investigation, BTTST provided better performance in terms of strength. Furthermore the effects of different angles and sizes for BTTST, different thickness for CFS and different strengths for concrete are also discussed. It is concluded that the proposed shear transfer enhancement has sufficient strength and is also feasible.     

Experimental study of composite cold-formed steel C-section floor joists

Twelve large-scale slab specimens and twenty-two companion push-out specimens were tested to study the behavior and capacity of composite slab joists consisting of cold-formed steel C-sections and concrete. Four shear transfer mechanisms, including surface bond, pre-fabricated bent-up tabs, pre-drilled holes, and self-drilling screws, were employed on the surface of the flange embedded in the concrete to provide shear transfer capacity. Results indicated that specimens employed with shear transfer enhancements showed a marked increase in strength and reduced deflection compared with those relying only on a natural bond between steel and concrete to resist shear. Of the three shear transfer enhancements investigated, bent-up tabs provided the best performance at both the strength and serviceability limit states, followed by drilled holes in the embedded flanges. The use of self-drilling screws resulted in the lowest strength increase. The correlation of shear transfer capacity of push-out specimens with the ultimate capacity of large-scale specimens indicated that the average experimental flexural capacity of the slab specimens was approximately 1.16 times the average predicted value based on push-out test results.     

Inelastic behaviors of steel shear tab connections

Inelastic behaviors of shear tab connections commonly used in modern steel buildings are investigated in this work. Full‐scale steel shear tab connections with and without concrete slab physically tested by other researchers are closely simulated by non‐linear finite element (FE) method. Different nonlinear FE features (inelastic materials, surface‐based contacts and large geometric options) are included, and different solution strategies (Newton method and Explicit Dynamic method) are employed to balance computational effort and solution accuracy. The simulations extend our understandings on shear tab connections at micro levels, including stress distribution in the connection zone, movement of the neutral axis along the beam sections and normal stress distributions along steel shear tabs and concrete slabs. It is found that the shear tabs contribute to flexural strength of the beam‐to‐column connection and the elastic–plastic theory explains the observed behavior well only when concrete slab is not present. The composite steel shear tab connections have unsymmetrical behavior under negative and positive bending moments. The compressive concrete slabs significantly increase the flexural stiffness and strength of composite shear tab connections. It is also verified that the shear studs near steel columns play a key role for the composite connections. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance of a novel bent-up bars system not interacting with concrete

Increasing the bending and shear capacities of reinforced concrete members is an interesting issue in structural engineering. In recent years, many studies have been carried out to improve capacities of reinforced concrete members such as using post and pre-tensioning, Fiber Reinforced Polymer and other techniques. This paper proposes a novel and significant technique to increase the flexural capacity of simply supported reinforced concrete beams. The proposed method uses a new reinforcement bar system having bent-up bars, covered with rubber tubes. This technique will avoid interaction of bent-up bars with concrete. They are located in the zone where compressive and tensile forces act against one another. The compressive force in the upper point of the bent-up bars is exerted to the end point of these bars located under neutral axis. Moreover, the tensile stress is decreased in reinforcements located under the neutral axis. This will cause the Reinforced Concrete (RC) beam to endure extra loading before reaching yield stress. These factors may well be considered as reasons to increase bending capacity in the new system. The laboratory work together with finite element method analysis were carried out in this investigation. Furthermore, bending capacity, ductility, strength, and cracking zone were assessed for the new proposed system and compared with the conventional model. Both the FEM simulation and the experimental test results revealed that the proposed system has significant impact in increasing the load bearing capacity and the stiffness of the RC beams. In the present study, an equation is formulated to calculate bending capacity of a new reinforcement bar system beam.     

Seismic behavior of steel beams and CFT column moment-resisting connections with floor slabs

This research investigates the seismic performance of four steel beams to concrete filled steel tube (CFT) column connections with floor slabs, including two interior and two exterior joints. The objective of this research is to evaluate firstly the composite effect of the steel beam and floor slab commonly used in Taiwan in practice. Secondly, the seismic behavior of new connection details such as the taper flange or larger shear tab in the beam-end is investigated to prevent complete joint penetration welds (CJP) of the girder flanges from the unexpected brittle failure found in the latter after the Northridge earthquake. In addition to the experimental investigation, the development and validation of analytical models for the assessment of the force-deformation behavior of the joint components are also conducted. The slab effect on the shear transfer in the panel zone is investigated as well.     

部分混凝土外包波形钢腹板组合工字梁的抗剪性能试验研究

针对提高负弯矩作用下连续梁的结构特性提出了一种新型的部分混凝土外包波形钢腹板组合工字梁。对这种混凝土外包组合工字梁在对抗荷载下的抗剪性能进行试验分析研究。试验结果显示与普通的工字梁相比,混凝土外包组合工字梁的剪切屈曲因受外包混凝土的限制而有了更好的抗剪强度。由于组合截面的抗剪刚度是基于波形钢腹板和破裂前外包混凝土平均厚度的总和,且其抗剪强度决定了由钢腹板和外包混凝土共享的抗剪强度比。此外,根据试验中的破坏模式和应变分布,提出部分混凝土外包波形钢腹板组合工字梁的预估抗剪强度。试验结果验证了之前分析得出的弹性阶段的抗剪刚度和抗剪比。且之前计算得出的钢腹板与组合梁的抗剪强度也与试验结果一致。通过对比可知文中提到的分析方法可以应用到部分混凝土外包波形钢腹板组合工字梁结构的抗剪刚度预估和抗剪强度设计中去。     

Reinforcement schemes for cold-formed steel joists with a large web opening in shear zone—An experimental investigation

The floor joists of cold-formed steel (CFS) structures often require large web openings. Reinforcement of such openings may mitigate the detrimental effects arising from such web openings. This paper is based on an experimental investigation conducted to establish reinforcement schemes for CFS joists with a large web opening located in high shear zones. The investigation considered a large web opening cut out in the middle of the web of a lipped channel section. Circular and square large web openings of about 65% web depth were considered. The shear tests involved short span specimens, simply supported at the ends, and subjected to a mid-span point load. This paper presents the experimental set-up, and the test results associated with 27 individual tests consisting of nine sets of three identical tests. These test sets consist of cold-formed steel joists sections with (a) no web opening, (b) webs having circular or square openings, (c) webs having reinforced openings. Three different reinforcement schemes were investigated, however, the test results indicated that the proposed “Vierendeel truss type reinforcement scheme” can restore the original shear strength of such sections having circular or square openings. Overall, this study establishes a cost-effective reinforcement scheme for cold-formed steel joists having a large web opening in high shear zone.     

民大广场A楼结构抗震设计

民大广场A楼为带转换层的型钢框架-剪力墙结构体系,因建筑功能的需要,结构外框架不设框架梁,外框架柱为纺锤状斜柱,转换层采用新型组合结构转换梁。所采用的结构通过基于性能的抗震分析、拟静力试验和振动台试验等验证是可行的,其破坏机制遵循"强柱、弱梁、更强转换梁、最强节点区"的原则。双型钢混凝土转换梁具有较强承载能力和较好耗能性能。     

带楼板的钢梁和CFT柱抗弯连接的抗震分析

对4个带楼板的钢管混凝土柱连接进行抗震性能分析,包括2个内部和2个外部节点。研究目的主要是对台湾地区广泛采用的钢梁组合楼板的性能进行分析。其次对梁末端楔形翼缘或者较大剪切键等连接处的抗震性能也进行了研究,以避免如Northridge地震后出现的那种不可预料的脆性破坏导致的梁翼缘焊缝完全熔透。     

Numerical investigation of longitudinally stiffened web channels predominantly in shear

In practice, there is a wide variety of commercially available channel sections with complex shapes where the web is stiffened by adding longitudinal intermediate stiffeners. These stiffeners may improve the shear capacity of the channels. Recently, the Direct Strength Method (DSM) of design of cold-formed sections has been extended in the North American Specification for Cold-Formed Steel Structural Members (NAS S100:2012) to include shear based on research by the authors. The prequalified sections include flat webs and webs with small intermediate longitudinal stiffeners. To extend the range to larger intermediate stiffeners as occurs in practice, a series of predominantly shear tests of lipped channel sections with one web stiffener of different shapes and various sizes has been performed at the University of Sydney. Six different types of stiffened web channel sections were tested along with an additional reference plain section. All tests were conducted with straps screwed on the top flanges adjacent to the loading points. These straps provide torsion/distortion restraints which may enhance the shear capacities of the sections. The test failures were observed mainly in the combined bending and shear modes. Numerical simulations based on the Finite Element Method (FEM) using the software package ABAQUS/Standard are also performed to compare with and calibrate against the tests. The accurate results from the FEM models allow extension of the test data. Based on the reliable FEM models, a series of FEM modelling of predominantly shear tests for stiffened web channels has been performed without straps attached to the top flanges adjacent to loading points. The test and FEM results are subsequently plotted against the DSM interaction curves between bending and shear where the interaction is found to be significant. An extended range of DSM prequalified sections with longitudinally stiffened web channels in shear is proposed in this paper.     

夹芯墙板覆面冷弯薄壁型钢承重复合墙体受剪试验

为满足多层冷弯薄壁型钢房屋建筑的抗震及防火要求,同时兼顾施工便捷性,提出了夹心墙板覆面的新型冷弯薄壁型钢复合墙体,并完成了11片足尺模型水平加载试验。试验表明： 1） 复合墙体的受剪破坏主要由墙板周边的螺钉连接失效引起,即螺钉将墙板撕裂或螺钉剪断引起,墙板与自攻螺钉之间的连接力学性能成为影响复合墙体受剪性能的主要因素;增大墙板厚度或者采用玻镁板代替石膏板可提高复合墙体抗剪性能,而龙骨立柱的截面尺寸对复合墙体受剪性能影响不明显; 2） 同侧墙板层数的增加对复合墙体受剪承载力及刚度虽有明显提高,但未达到线性叠加程度;夹心墙板的使用有利于墙体蒙皮效应的发挥,相应的墙体受剪性能优于墙体同侧双层墙板覆面时的受剪性能; 3） 蒸压加气混凝土（ALC）板周边与自攻螺钉的连接区域在较低水平荷载作用下出现板材开裂现象,故不宜采取ALC板参与墙体受力的连接方式。研究给出了新型冷弯薄壁型钢复合墙体的受剪承载力及抗剪刚度设计指标,供工程设计参考。     

碳纤维布粘贴加固BFRP筋-ECC-混凝土组合梁受弯性能研究

工程结构服役期间经常由于使用功能改变或使用荷载增加而需要对结构进行加固改造。为研究经碳纤维布粘贴加固后的玄武岩纤维增强塑料（BFRP）筋-工程用水泥基复合材料（ECC）-混凝土组合梁的受弯性能,对3组共12根不同ECC高度替换率（0、0.29和0.58）的BFRP筋-ECC-混凝土组合梁底分别粘贴1、2和3层碳纤维布的加固构件及未加固构件进行静力受弯性能试验。研究碳纤维布粘贴层数和ECC高度替换率对组合梁受弯承载力和破坏形态的影响。试验结果表明：采用受拉性能优异的ECC替代受拉区部分混凝土形成的ECC-混凝土组合梁不仅可提高构件承载力,还可有效改善构件抵抗开裂和变形的能力;组合梁底粘贴3层碳纤维布,裂缝宽度可降至未加固试件的10%,受弯承载力提高20%,挠度降低50%。借鉴钢筋混凝土理论,基于合理的基本假定和简化的材料本构模型,提出粘贴碳纤维布加固的组合梁受弯承载力计算式,并给出碳纤维布强度折减系数,理论预测值与试验实测值吻合良好。     

具有初始应力和变形的薄壁组合梁的自由振动

研究了由静力外荷载而导致的结构初始平面内变形和剪切弹性对双向对称的薄壁组合梁动力特性的影响。分析采用了基于大位移和转角的几何非线性理论。采用里兹法(Ritzmethod)对控制方程进行离散,并采用一种分析法来获得结构的自振频率。研究中梁被施加以均衡的初始弯矩、分布荷载和集中荷载。数字结果表明:当短轴的弯曲刚度与长轴的弯曲刚度的比值较大时,由于初始位移的影响,传统的振动分析方法可能会导致不准确的预测。此外,对不同的层状叠合材料结构,对跨长和影响荷载作用点高度也进行了研究。     

长期荷载作用后钢-竹界面黏结性能分析

为研究钢-竹组合构件长期荷载作用后的整体工作性能,针对纯胶结型界面与复合胶结型界面共27个钢-竹界面试件进行了长期荷载作用后的推出试验,以界面形式、长期持荷水平以及持荷时间为基本参数,对钢-竹界面的承载力、黏结应力及相对滑移进行了分析。研究表明：钢-竹界面构造形式合理,具有较高的承载能力,长期荷载作用后试件界面完整性良好,复合胶结型界面试件的破坏具有显著的延性特征;2组纯胶结型界面试件在长期荷载作用后承载力发生衰减,衰减系数分别为0.91与0.81;纯胶结型界面的剪应力与相对滑移分布具有“两端大、中间小”的特征,2组试件界面最大剪应力分别为1.41MPa和1.25MPa,与短期荷载作用后试件相比,约衰减10%和20%,界面的相对滑移则略有增长;长期荷载作用后复合胶结型界面的承载力、黏结应力及相对滑移与短期荷载作用后试件相比,未发生显著变化,自攻螺钉可有效提高界面抗剪能力,按间距80mm加设自攻螺钉后,界面最大剪应力可达到1.7MPa。提出了长期荷载作用后的钢-竹界面黏结承载力计算方法,其计算结果与试验结果吻合较好。     

Effect of roughness on the shear behavior of rock joints subjected to impact loading

The shear behavior is regarded as the dominant property of rock joints and is dramatically affected by the joint surface roughness. To date, the effect of surface roughness on the shear behavior of rock joints under static or cyclic loading conditions has been extensively studied, but such effect under impact loading conditions keeps unclear. To address this issue, a series of impact shear tests was performed using a novel-designed dynamic experimental system combined with the digital image correlation (DIC) technique. The dynamic shear strength, deformability and failure mode of the jointed specimens with various joint roughness coefficients (JRC) are comprehensively analyzed. Results show that the shear strength and shear displacement characteristics of the rock joint under the impact loading keep consistent with those under static loading conditions. However, the temporal variations of shear stress, slip displacement and normal displacement under the impact loading conditions show obviously different behaviors. An elastic rebound of the slip displacement occurs during the impact shearing and its value increases with increasing joint roughness. Two identifiable stages (i.e. compression and dilation) are observed in the normal displacement curves for the rougher rock joints, whereas the joints with small roughness only manifest normal compression displacement. Besides, as the roughness increases, the maximum compression tends to decrease, while the maximum dilation gradually increases. Moreover, the microstructural analysis based on scanning electron microscope (SEM) suggests that the roughness significantly affects the characteristics of the shear fractured zone enclosing the joint surface.     

碳纤维布加固混凝土柱的斜截面受剪承载力计算

碳纤维布加固混凝土结构是一种新型结构加固方法。本文进行了６个碳纤维布加固混凝土柱和一个对比混凝土柱的受剪试验研究,分析了碳纤维布的受剪加固机理及其影响碳纤维布受剪加固效果的因素。试验研究表明,碳纤维布受剪系数ν与碳纤维配箍特征值λ_（ＣＦＳ）、剪跨比和轴压比等因素有关。根据试验结果分析,提出了碳纤维布受剪系数ν的计算方法和碳纤维布加固混凝土柱受剪承载力计算公式,计算值与试验值吻合较好。     

Detailing recommendations for 1.83 m wide cold-formed steel shear walls with steel sheathing

The paper presents an experimental investigation on 1.83 m wide, 2.44 m high cold-formed steel (CFS) stud framed shear walls using steel sheet sheathing. Four wall configurations were studied through monotonic and cyclic tests. The test results indicated that besides the sheet buckling and screw pull out, the buckling of interior studs might occur for the 1.83 m CFS walls. To prevent the failure in the studs, special detailing was developed in this research. It was discovered that the special detailing could increase both the shear strength and the ductility of the shear walls. The research also found that the codified nominal shear strengths can be conservatively used for walls with an aspect ratio of 3:2. Based on the test results, the nominal seismic shear strength for 1.83 m wide CFS shear walls was established for design purposes.     

Headed steel stud anchors in composite structures, Part I: Shear

The formula in the 2005 American Institute of Steel Construction Specification to compute the strength of headed steel stud anchors (shear connectors) in composite steel/concrete structures has been used in the United States since 1993, after being proposed based primarily on the results of push-out tests. In the past several decades, the range of members used in composite structures has increased significantly, as has the number of tests in the literature on the monotonic and cyclic behavior of headed studs in composite construction. This paper reviews 391 monotonic and cyclic tests from the literature on experiments of headed stud anchors and proposes formulas for the limit states of steel failure and concrete failure of headed stud anchors subjected to shear force without the use of a metal deck. Detailing provisions to prevent premature pryout failure are also discussed. This paper also reviews proposals from several authors and provides recommended shear strength values for the seismic behavior of headed studs. The limit state formulas are proposed within the context of the 2005 AISC Specification, and comparisons are made to the provisions in the ACI 318-08 Building Code, the PCI Handbook, 6th Edition, and Eurocode 4. The scope of this research includes composite beam-columns [typically concrete-encased steel shapes (SRCs) or concrete-filled steel tubes (CFTs)], concrete-encased and concrete-filled beams, boundary elements of composite wall systems, composite connections, composite column base conditions, and related forms of composite construction.     

内填砌体短肢墙的抗震性能试验研究

通过对1榀4层单跨内填砌体短肢墙结构在低周反复荷载作用下的拟静力试验研究,分析了这类结构的延性、滞回特性、骨架曲线及刚度退化等问题。研究表明:砌体的存在大幅提高了结构的初始刚度和极限承载力。内填砌体短肢墙结构具有双功能结构的优点,是一种新型抗震控制剪力墙。根据试验中发现的问题,为工程设计提出了建议。