Slender reinforced concrete shear walls with high-strength concrete boundary elements

Reinforced concrete structural walls are commonly used for resisting lateral forces in buildings. Owing to the advancements in the field of concrete materials over the past few decades, concrete mixes of high compressive strength, commonly referred to as high-strength concrete (HSC), have been developed. In this study, the effects of strategic placement of HSC on the performance of slender walls were examined. The finite-element model of a conventional normal-strength concrete (NSC) prototype wall was validated using test data available in extant studies. HSC was incorporated in the boundary elements of the wall to compare its performance with that of the conventional wall at different axial loads. Potential reductions in the reinforcement area and size of the boundary elements were investigated. The HSC wall exhibited improved strength and stiffness, and thereby, allowed reduction in the longitudinal reinforcement area and size of the boundary elements for the same strength of the conventional wall. Cold joints resulting from dissimilar concrete pours in the web and boundary elements of the HSC wall were modeled and their impact on behavior of the wall was examined.     

钢筋混凝土空腹桁架屋架设计

本文通过一个大跨度钢筋混凝土空腹桁架屋架在实际工程的应用实例,着重介绍了钢筋混凝土空腹桁架屋架的结构设计及构造措施;为这种钢筋混凝土空腹桁架屋架的工程应用提供参考。     

Torsional behavior of steel fiber reinforced concrete beams

Torsion of structural members and the behavior of steel fiber reinforced concrete became the area of interest of many researchers in the past and it is still newsworthy. In this study, 12 reinforced concrete (R/C) beams with Steel Fiber Reinforced Concrete (SFRC) were tested to observe the failure under torsional moments. The volumetric steel fiber content, fiber aspect ratio, and the longitudinal reinforcement were the variables of the investigation. Unit torsional angle of twist versus torsional moment (torque) response of each specimen was monitored during the experiments, and the effect of above variables on this response was critically investigated. It was observed that not only the torque capacity of R/C beam is modified by the addition of Steel Fiber Reinforcement (SFR) but also the energy absorption capacity is significantly affected by the SFR addition. Besides, an empirical equation relating the torque to twist for SFRC beams is proposed and tested against the test data.     

Shear strength prediction of reinforced concrete walls

Most of existing codes ignore the effect of arch action on shear strength of reinforced concrete (RC) walls, and it leads to more conservative results. A new model considering the influence of the truss and arch on shear strength of RC walls is proposed in this paper. The shear strength provided by the truss is obtained by the modified compression field theory, and the shear strength provided by the arch is obtained by the shear deformation coordination between the truss and arch, which has an upper bound value. Experimental data of 78 RC walls failed in shear are collected to evaluate the adequacy of the proposed method by comparing with the models of Hwang and Lee, Wood, ACI 318‐11,, EC8, MCBC‐04, and JGJ 3‐2010, respectively. The results show that the average value and coefficient of variation of the experimental‐to‐calculated strength ratios obtained by the proposed model are 1.01 and 0.23, which shows better accuracy and reliability. Therefore, the proposed model can predict the shear strength of RC walls failed in shear accurately.     

钢筋混凝土填充墙抗爆分析

主要对爆炸冲击荷载作用下钢筋混凝土填充墙与框架柱进行整体动力响应数值模拟,得到墙体与框架柱的最大变形随时间响应变化过程,分析表明墙体主要表现为单向板受力。     

钢筋混凝土和钢纤维混凝土杂散电流腐蚀实验研究

依据地铁杂散电流对地下金属物质发生阳极氧化的电化学腐蚀机理,模拟了钢筋混凝土和钢纤维混凝土试件的杂散电流腐蚀实验。通过两种不同材料在相同的杂散电流环境中进行模拟腐蚀比较,分析了钢筋混凝土和钢纤维混凝土在抵制杂散电流腐蚀的耐久性和破坏形式方面的异同。结果表明,两种材料的耐久性能差异较大,破坏形式也不同,相同条件下,钢纤维混凝土的耐久性能显著降低。     

循环荷载作用下钢筋混凝土框格单元结构受力机理试验研究

为研究密肋复合墙板内钢筋混凝土框格单元结构的力学性能退化机理,对3个不同相对刚度比的框格单元及3个空框格结构进行了1/2比例模型循环加载试验。分析钢筋混凝土框格单元结构的破坏发展过程,探讨了外围框格构件对结构承载能力与变形能力的影响。研究结果表明框格单元结构的破坏顺序与结构相对刚度有关。随着结构相对强度的变化,框内填充砌体表现出不同的破坏模式。压缩变形越大,框格单元结构变形滞后现象越明显。界面缝隙对框格单元结构的初始刚度影响显著,但对峰值承载能力影响较小。经多次加卸载循环后,框格单元结构的峰值承载能力仍远高于对应的空框格结构。当外围框格构件与填充砌体在刚度与强度两方面均匹配时,填充砌体刚度退化较慢。     

角钢桁架型钢混凝土梁纯扭性能试验研究

为了研究角钢桁架型钢混凝土梁在扭矩作用下的受力性能,进行了6根角钢桁架型钢混凝土梁和1根钢筋混凝土对照梁纯扭试验。通过试验研究,揭示了角钢桁架型钢混凝土梁在纯扭作用下的受力机理与破坏形态,分析了角钢桁架型钢混凝土梁受扭性能的影响因素。试验结果表明,角钢桁架型钢混凝土梁比普通钢筋混凝土梁的抗扭性能有很大的提高,大体上随着腹杆体积配钢率的提高而增大,其中增加斜腹杆试件的抗扭性能最好。     

钢管混凝土叠合柱轴压性能研究

为研究钢管混凝土叠合柱轴压性能,基于合理的钢材和混凝土本构关系模型,采用纤维模型法和有限元法分析方法计算叠合柱轴压荷载-变形关系曲线。将理论计算结果与试验结果进行对比,验证了理论分析模型的正确性。在此基础上,对叠合柱的破坏模态、轴向荷载分配以及组成钢管混凝土叠合柱的外围钢筋混凝土、钢管和钢管内部混凝土之间相互作用等进行分析,提出了叠合柱的轴压承载力简化计算式,简化计算结果与试验结果吻合较好。为保证外围钢筋混凝土和内部钢管混凝土较好地协同工作,建议外围钢筋混凝土中箍筋的约束指标与内部钢管混凝土的约束效应系数比值不应小于0.188。     

单调荷载作用下高强混凝土梁受弯性能尺寸效应研究

进行了不同截面尺寸高强混凝土梁的弯曲试验,研究了梁高对其受弯性能的影响。试件采用C70高强混凝土,纵向受力钢筋采用HRB400级钢筋。试件截面尺寸不同,截面长宽比、剪跨比和配筋率等参数保持一致。分析了不同截面尺寸对高强混凝土梁的名义开裂弯矩、名义屈服弯矩、名义极限弯矩、延性以及塑性转动能力的影响。研究结果表明,高强混凝土梁的名义开裂弯矩、名义屈服弯矩和名义极限弯矩无明显尺寸效应,而试件的位移延性系数和塑性铰区的塑性转动能力则表现出明显的尺寸效应,随截面尺寸的增大梁的位移延性系数和塑性铰区塑性转动能力有所降低。     

考虑弯剪耦合作用的RC剪力墙拟静力试验研究

剪力墙结构在水平地震作用下受力与框架柱有很大的不同,无反弯点,弯矩与剪力的耦合作用贯穿整个墙体。为了探究弯矩和轴压比对剪力墙破坏的影响,取某11层高层建筑的底部两层剪力墙,按照1:2缩尺,设计了三个两层剪力墙试件并进行低周往复加载拟静力试验。与传统拟静力试验相比,该试验竖直方向加载通过两个作动器实现弯矩与水平剪力保持固定比例关系。试验结果表明,考虑弯剪耦合作用、轴压比为0.25的试件SW1破坏时有大量水平裂缝及斜裂缝,试件最终发生弯曲破坏型侧向倒塌。考虑弯剪耦合作用、轴压比为0.5的试件SW2破坏时为贯通水平裂缝,试件最终发生脆性竖向倒塌。不考虑弯矩作用、轴压比为0.25试件SW3破坏时有大量斜裂缝,试件最终发生弯剪破坏型侧向倒塌。该文对其破坏形态、滞回特性、变形能力、耗能能力、截面应变等进行了研究,研究结果表明弯矩作用对剪力墙的破坏模式以及屈服、峰值、极限荷载、延性等参数都有重大影响,建议剪力墙在分析和设计中应考虑弯剪耦合作用。     

Steel–concrete composite shear walls using precast high performance fiber reinforced concrete panels

In this research, seismic performance of composite steel plate shear walls (CSPSWs) using high performance fiber reinforced concrete (HPFRC) panels is experimentally and numerically investigated. Three one‐story one‐bay CSPSW specimens using precast HPFRC panels were designed and fabricated for cyclic quasi‐static experiments. The HPFRC panels of composite shear wall specimens did not have any steel rebars. The main purpose of the study was to understand the effects of rigid and semirigid HPFRC panels on the seismic behavior of the system. Shear capacity, ultimate shear strength, lateral stiffness, energy dissipation, and ductility ratios of the specimens are evaluated. The experimental results demonstrate that specimens were able to resist lateral load up to at least interstory drift of 6%. Using HPFRC panels, CSPSW specimens becomes stiffer in the elastic region, and the yield displacement of the shear wall is decreased; therefore, the ductility ratio of the system is increased. It should be noted that ultimate shear strength, initial elastic stiffness, and energy absorption of specimens with an HPFRC panel on one side or both sides of the infill steel plate were approximately the same. However, using two HPFRC panels is not economical in comparison with CSPSW with an HPFRC panel on one side. Additionally, the second panel increases the seismic mass of the structure.     

Modelling shear–flexure interaction in equivalent frame models of slender reinforced concrete walls

Quasi‐static cyclic tests on reinforced concrete (RC) walls have shown that shear deformations can constitute a significant ratio of the total deformations when the wall is loaded beyond the elastic regime. For slender RC walls that form a stable flexural mechanism, the ratio of shear to flexural deformations remains approximately constant over the entire range of imposed displacement ductilities. This paper proposes a method for incorporating shear‐flexure interaction effects in equivalent frame models of slender RC walls by coupling the shear force‐shear strain relationship to the curvature and axial strain in the member. The suggested methodology is incorporated in a finite element consisting of two interacting spread inelasticity sub‐elements representing flexural and shear response, respectively. The element is implemented in the general finite element code IDARC and validated against experimental results of RC cantilever walls. In a second step, it is applied in inelastic static and dynamic analyses of tall wall and wall‐frame systems. It is shown that ignoring shear‐flexure interaction may lead to erroneous predictions in particular of local ductility and storey drift demands. Copyright © 2013 John Wiley & Sons, Ltd.     

无粘结预应力混凝土框架火灾下的温度反应分析

火灾中影响无粘结预应力结构反应的因素较多，其中结构在火灾时对温度的反应是研究结构抗火性能的重要方面。本文通过模拟真实火灾环境，对4榀无粘结预应力混凝土框架进行了火灾试验，测出了在火环境下结构的温度场分布情况，并用计算机模拟温度场，从而为结构理论分析提供了温度数据。     

Probabilistic model for failure initiation of reinforced concrete interior beam-column connections subjected to seismic loading

The results of previous experimental tests indicate that reinforced concrete interior beam column joints may exhibit significant strength and stiffness loss under earthquake loading, and the results of post-earthquake reconnaissance indicate that joint failure may result in structural collapse. Thus seismic evaluation and design of reinforced concrete frames requires accurate prediction of the potential for joint failure. This paper presents a binomial logit model, developed using data from 110 experimental tests, which define the probability that a reinforced concrete interior beam-column building connection, with a specific set of design parameters, will exhibit either a non-ductile joint shear failure prior to beam yielding or a ductile failure that initiates with beam yielding. The calibrated model identifies the relative importance of various design parameters in determining the connection’s response mechanism. The model can be used by an engineer designing a new connection, constructed of normal or high-strength materials, to estimate the likelihood of joint failure initiation. The model can also be used by an engineer evaluating an existing structure to estimate the likelihood of joint failure, determine the factors that most significantly affect this likelihood, and, thereby, develop a suitable and efficient retrofit strategy.     

某公路改建工程钢筋混凝土悬臂式挡土墙设计

结合上海六奉公路改建工程的工程实例,对悬臂式挡土墙支护结构进行了各项计算与验算,包括土压力计算、滑动稳定性验算、地基应力及偏心距验算等,通过计算总结得出钢筋混凝土悬臂式挡土墙占地少、美观、工期快,值得推广。     

Behavior of steel-sheathed shear walls subjected to seismic and fire loads

A series of tests was conducted on six 2.7 m×3.7 m shear wall specimens consisting of cold-formed steel framing sheathed on one side with sheet steel adhered to gypsum board and on the opposite side with plain gypsum board. The specimens were subjected to various sequences of simulated seismic shear deformation and fire exposure to study the influence of multi-hazard interactions on the lateral load resistance of the walls. The test program was designed to complement a parallel effort at the University of California, San Diego to investigate a six-story building subjected to earthquakes and fires. The test results reported here indicate that the fire exposure caused a shift in the failure mode of the walls from local buckling of the sheet steel in cases without fire exposure, to global buckling of the sheet steel with an accompanying 35% reduction in lateral load capacity after the wall had been exposed to fire. This behavior appears to be predictable, which is encouraging from the standpoint of residual lateral load capacity under these severe multi-hazard actions.     

An experimental and numerical study of the effect of thickness and length of CFRP on performance of repaired reinforced concrete beams

Experimental and numerical analyses are performed to predict the loading carrying capacity of reinforced concrete beams strengthened with carbon fibre reinforced plastics (CFRP) composites. The effect of CFRP thickness and length on the failure load and ductility is studied and curves of initial cracking load, ultimate load, stiffness, ductility and fibre stresses are presented. The results of tests and simulations show a good agreement and indicate that, in contrast with a control beam, initial cracking loads of strengthened beams increase slightly, whilst stiffness and ductility increase more and the ultimate loads increase considerably. Stresses in the carbon fibre decrease with the increase of fibre sheet thickness. Cracking patterns of strengthened beams are improved. Crack propagation varies with the change of fibre length and results in the variation of failure mode of beams. Variation of the length of CFRP sheet is the main reason of variation of the stress of interface. Therefore, debonding failure, unless adequately considered in the design process, may significantly decrease the effectiveness of the strengthening.     

Proportioning of reinforced concrete column sections

Relatively simplistic recommendations are widely available for the preliminary sizing of reinforced concrete columns. A simple, more precise approach is developed herein. The neutral axis depth and reinforcement required to provide a desired resistance to axial load and moment was determined analytically for the common case of symmetrically distributed reinforcement. Readily available solver routines are used to determine section dimensions required to provide the desired axial and flexural strength, for a desired reinforcement ratio. The approach is illustrated for two examples, including a case in which independent load combinations cause bending about each principal axis of the section.     

砖混结构中钢筋混凝土构造柱、圈梁对抗震的作用

本文对砖混结构构造柱和圈梁从规范规定出发,通过构造柱和圈梁在砖混结构中的不同作用,结合“5．12”汶川大地震对构造柱和圈梁不规范的设计或施工造成砖混结构房屋的不同损坏情况,进行粗略分析构造柱和圈梁对砖混结构抗震所起到的主要关键作用,供今后的砖混结构的设计、施工有所参考。