Experimental study on separating reinforced concrete infill walls from steel moment frames

In a multistory building frame, stiff reinforced concrete (RC) infill walls may be terminated above the first story for architectural purposes, which may create a soft-first-story structure. To eliminate this detrimental situation, this paper proposes to separate the RC infill wall from the steel moment frame by slits. An experimental program of four one-bay-by-one-story steel moment frame specimens along with pushover analyses of multistory frame models were presented to validate the proposed idea. This study conducted cyclic loading tests on a total of four moment-resisting-frame specimens, which included one bare frame; one with ordinary RC infill wall; and two with side slits between RC wall and frame members. Furthermore, pushover analyses of multistory frame models with soft first story configurations were also conducted to illustrate the effect of RC infill walls with or without slit separation. Both experimental and analytical results showed that the stiff RC infill wall dominated the lateral resistance and drift capacity of the test specimens, and that by adding slit-separated features at the edges of infill walls improved the drift capacity. It is concluded that the slit-separated features can be a viable option to eliminate the soft-story problem caused by vertically irregular configuration of RC infill walls.     

考虑全填充墙作用的钢筋混凝土框架抗连续倒塌性能分析

为探究钢筋混凝土(RC)全填充墙框架在边中柱失效情况下的抗连续倒塌性能及其承载力计算方法,基于已有试验和有限元程序OpenSees建立宏观有限元数值模型展开研究。数值模型中的梁柱采用基于力的纤维梁单元模拟,填充墙则转化为等效斜撑并用桁架单元进行表征。填充墙宏观模型涉及等效斜撑的宽度、数量和相应材料属性的确定,为此对比了不同等效斜撑模型的适用性,确定了一种连续倒塌工况下全填充墙的宏观模拟方案。进而利用验证的数值模型,揭示全填充墙框架防倒塌的荷载传递机制,并研究了层数和填充墙砌体抗压强度对抗倒塌性能的影响。结果表明：全填充墙框架荷载主要通过墙体对角传递且全填充墙会与周围框架形成一种桁架机制;随填充墙砌体抗压强度降低,结构抗力峰值呈下降趋势。最后,以填充墙和周边框架竖向承载刚度比为基本参数,建立了通过求得填充墙和框架刚度以及纯框架理论弯曲承载力,便可快速评估规则RC填充墙框架防倒塌能力的回归模型。     

Cyclic behavior of prefabricated reinforced concrete frame with infill slit shear walls

A composite structural system consisting of prefabricated reinforced concrete frame with infill slit shear walls (PRCFW), with good ductility, is a new type of earthquake resistant structure. Pseudo-static tests were performed to evaluate the seismic behavior of the PRCFW system. Two one-bay, two-story PRCFW specimens were both built at onehalf scale. Additional computational research is also conducted to enhance the nonlinear analytical capabilities for this system. Combined with the concrete damaged plastic (CDP) model provided by finite element program ABAQUS and the constitutive model of concrete proposed by Chinese code, the damage process of the PRCFW structure under cyclic load is simulated. The simulated results show a good agreement with the test data, the dynamic behavior of the PRCFW system can be simulated sufficiently accurate and efficient to provide useful design information. The experimental and numerical study show that this system has the potential to offer good ductility and energy absorption capacity to dissipate input energy, and stiffness adequate for controlling drift for buildings located in earthquake-prone regions.     

Behavior and design of reinforced concrete frames retrofitted with steel bracing against progressive collapse

Steel bracing is able to improve progressive collapse resistance of reinforced concrete (RC) frames, but the bracing design is typically based on seismic retrofitting or lateral stability. There is no approach for design of steel bracing against progressive collapse. To this end, a retrofitting approach with steel braces is proposed based on analysis of macro finite element (FE) models with fiber beam elements. The FE models were initially validated through the experimental results of a braced frame and then used to investigate the effects of pertinent parameters on the progressive collapse resistance of planar frames. The results suggest the braces should be placed at the top story. Thereafter, macro FE models are built to investigate the dynamic responses of the three‐dimensional prototype RC frames under different column removal scenarios (CRS) and show the necessity of retrofitting. Accordingly, the design approach of steel bracing is proposed with incremental dynamic analysis (IDA) and assuming independent contribution of braces and frames to resistance. Finally, the fragility analysis of the frames under a corner‐penultimate‐exterior CRS is conducted through IDA and Monte Carlo simulation, and the results confirm the validity of the proposed design approach for retrofitting RC frames.     

钢筋混凝土砖砌体组合墙抗震性能

以往的研究表明,钢筋混凝土-砖砌体组合墙是一种抗震性能好、造价低的优良结构形式。本研究通过22片不同高宽比、不同竖向压应力、不同竖向配筋率和不同水平配筋率的钢筋混凝土-砖砌体组合墙的抗震性能研究,并通过国内其它65片类似墙体的分析,对这种墙体在竖向和水平荷载作用下的破坏特征、墙体的正截面承载力、斜截面承载力及抗震性能进行了分析研究,给出了墙体抗震承载力计算公式,可为该类房屋的设计提供参考。     

Cyclic behaviour of hinged steel frames enhanced by masonry columns and/or infill walls with/without CFRP

Abstract

This paper investigates the in-plane seismic behaviour of hinged steel frames that are enhanced with masonry columns and/or infilled walls. First, eight half-scaled hinged steel frame specimens were constructed according to the realistic structural system of Bund 18, which is a historical building in Shanghai, China. Then, cyclic loads were exerted on these frames. The test results indicated that the seismic behaviours of the hinged steel frames can be significantly improved with the use of masonry columns and/or infilled masonry walls as well as with proper strengthening due to carbon fibre-reinforced polymer (CFRP) sheets. A simplified model was developed to simulate the seismic behaviours of these frames. In this model, infilled walls and CFRP sheets were replaced by diagonal struts, and the steel members and their surrounding elements were treated as composite members. Finally, this model was verified by experimental results.     

Cyclic behavior of steel frame structures with composite reinforced concrete infill walls and partially-restrained connections

This paper presents an experimental study of the cyclic behavior of a composite structural system consisting of partially-restrained (PR) steel frames with reinforced concrete infill walls. The composite interaction is achieved through the use of the headed stud connectors along the steel frame-infill interfaces so that the two main components of the system share in the resistance of lateral shear and overturning moment. Having the relatively light steel frame constructed using PR connections maximizes the economy of the system, while still ensuring system integrity in the post-peak range of deformation. The one-bay, two-story test specimen was built at one-third scale. The study shows that this system has the potential to offer strength appropriate for resisting the forces from earthquakes and stiffness adequate for controlling drift for low- to moderate-rise buildings located in earthquake-prone regions. Redundancy is also exhibited in this system through alternate load paths occurring at different levels of loading, including shear stud-infill interaction, steel frame-infill strut interaction, and deformation of the steel frame. Improvement is needed for reducing the post-peak strength degradation observed in the present study.     

附加减震钢框架的加固混凝土框架结构抗震性能试验研究

为提高既有混凝土框架抗震性能,在不显著增加既有结构构件受力的同时,在混凝土框架外部增设钢框架并设置屈曲约束支撑。设计并制作1榀纯混凝土框架和2榀设置附加减震钢框架的混凝土框架,通过低周往复加载试验,研究其开裂和破坏状态、滞回曲线、骨架曲线、刚度退化、等效阻尼比以及钢筋混凝土梁、附加钢框架的应变发展等。试验结果表明：增设附加减震框架后,结构破坏机制更加合理,屈曲约束支撑耗能性能稳定,加固后结构的滞回曲线饱满;采用外部附加钢框架加固钢筋混凝土框架,可提高既有混凝土框架结构的受剪承载能力至3倍以上,既有结构、外部附加钢框架和屈曲约束支撑可协同工作,在设防目标下可避免混凝土柱发生压剪脆性破坏;最后对附加减震框架改进连接构造设计提出了建议。     

混凝土空心砖施工方法

介绍了混凝土空心砖施工的材料,从砂浆拌制、组砌方法及砖墙砌筑几方面对混凝土空心砖的施工方法进行了论述,重点对混凝土空心砖墙的砌筑进行了说明,提出了混凝土空心砖施工的质量标准,从而积累混凝土空心砖施工经验.     

Nonlinear 3D finite element simulation of reinforced concrete flat plates retrofitted with externally bonded CFRP strips

In this study, a comprehensive 3D non-linear finite element modelling procedure is presented for the simulation of reinforced concrete flat plates, retrofitted with externally bonded carbon fibre-reinforced polymer (CFRP) strips and subjected to punching shear loads. The presented modelling procedure may be used to conduct parametric numerical analyses on the response of reinforced concrete elements similar to considered in this study. The modelling procedure is applied on: (i) a solid, un-retrofitted flat plate and (ii) eight flat plates with openings and retrofitted with externally bonded CFRP strips. In the procedure, debonding of CFRP strips from concrete surfaces is accounted for by defining appropriate bilinear shear stress–slip and normal stress–gap relationships. In the model, the corner lift-offs observed at the corners of the flat plates are also considered by defining appropriate restrains and frictional support conditions. Results obtained from the proposed modelling procedure are verified using experimental data available in the literature. From the verification, accuracy of the proposed modelling procedure is confirmed in terms of structural responses such as load displacement relationships and crack propagations of the test specimens.     

钢框架内填预制带竖缝钢筋混凝土剪力墙抗震性能试验研究

为改进钢框架内填预制带竖缝钢筋混凝土剪力墙的抗震性能,将耳板引入钢框剪与内填墙的连接中。通过2个两层单跨缩尺比为1∶3的钢框架内填预制带竖缝钢筋混凝土剪力墙模型试件的拟静力试验研究,考察了耳板连接的可靠性和内填墙裂缝的开展与结构变形能力,分析了结构的破坏机理、滞回性能、刚度退化、变形及延性和耗能能力等。试验结果表明：抗剪连接件(U形筋)在梁柱节点上下耳板的连接处未发生破坏,耳板连接具有可靠的工作性能;钢框架带竖缝剪力墙结构具有良好的延性,平均位移延性系数大于3;内填墙的承载力由竖缝根部的剪切破坏控制。     

碳纤维加固钢筋混凝土施工技术

阐述了采用碳纤维布加固的优点、材料特性及其构造做法,详细介绍了碳纤维布加固钢筋混凝土的施工工艺,指出该技术是一种经济、适用、新型的结构方法,且具有轻质高强、施工便捷、耐腐蚀性和耐久性强等优点,值得推广使用。     

Sound insulation of fibre reinforced mud brick walls

The aim of this paper is to find a better alternative for the insulation of industrial noise and to improve the mechanical properties of fibre reinforced mud bricks. It was observed that the fibre reinforced mud bricks fulfill the compressive strength and sound insulation requirements of the ASTM and Turkish Standards. Basaltic pumice as an ingredient was found to improve the sound insulation performance of fibre reinforced mud bricks. The experimental results showed that fibre reinforced mud brick, with basaltic pumice as ingredient, can be used in industrial buildings for walls to improve sound insulation.     

预应力碳纤维加固钢筋混凝土梁试验研究

通过试验研究了预应力碳纤维加固钢筋混凝土梁对其承载力、变形等方面的影响，论证了预应力碳纤维加固法的可行性，指明了这种方法尤其适用于大跨度的受弯构件。     

Capacity design for composite partially restrained steel frame‐reinforced concrete infill walls with concealed vertical slits

This paper presents an innovative capacity‐based design procedure that aims to achieve the ideal seismic performance for the composite partially restrained (PR) steel frame‐reinforced concrete (RC) infill wall with concealed vertical slits (PSRCW‐CVS). The proposed method adopts the direct capacity design principles and preselected preferred plastic mechanism such that the RC infill wall undergoes ductile failure prior to the other steel components in the event of a rare‐level earthquake (i.e., earthquake with a 2% probability of exceedance in 50 years). Based on the ultimate resisting capacity of RC infill walls, the free‐body diagrams and simplified design formulae for the surrounding steel components, including the vertical boundary element (VBE), horizontal boundary element (HBE), PR connection, and shear connectors, were proposed. To demonstrate the reasonability of the capacity‐based design procedure, a five‐story PSRCW‐CVS structure was designed according to the proposed design method, followed by a series of nonlinear time history analyses. The overall seismic response of this example was evaluated in terms of story displacement, interstory drift ratio, residual story displacement, and residual interstory drift ratio. The proposed method yielded a more uniform interstory drift ratio distribution along the height of the five‐story PSRCW‐CVS structure. Structural damage was controlled by achieving the preselected preferred plastic mechanism.     

框架结构非承重混凝土多孔砖填充墙裂缝的防治

从原材料检验、设计构造措施、砌体及抹灰工程施工操作工艺和重点防裂部位加强措施等环节,介绍了框架结构非承重混凝土多孔砖填充墙裂缝的防治。提出应认真做好防治裂缝的专项方案、施工技术交底、过程检查控制的每一项具体工作。     

填充墙和现浇板对钢筋混凝土框架结构整体超强的影响研究

为充分实现框架结构的“强柱弱梁”耗能机制,需要考虑填充墙、现浇T形截面梁及其翼缘现浇板内与梁肋平行配置的钢筋对结构整体超强系数的影响。考虑抗震设防烈度、结构层数等因素,严格按我国抗震规范设计了15个典型钢筋混凝土框架结构,对结构进行Pushover 分析,得到了各种结构在非弹性阶段由于内力重分布而形成的超强性能。结果表明：结构设计考虑填充墙、现浇楼板的影响,会提高结构的整体超强能力,结构整体超强系数均随着抗震设防烈度的增高而减小,且先随结构层数的增大而减小,结构层数大于8层后,又随结构的层数的增大而增大。可以保守地认为,分别按抗震设防烈度6,7,8度设计的结构,同时考虑填充墙和现浇板影响时,结构整体超强系数分别至少要达到5.0,3.0,2.0。     

A multi-objective design method for seismic retrofitting of existing reinforced concrete frames using pin-supported rocking walls

Over the past several decades, a variety of technical ways have been developed in seismic retrofitting of existing reinforced concrete frames (RFs). Among them, pin-supported rocking walls (PWs) have received much attentions to researchers recently. However, it is still a challenge that how to determine the stiffness demand of PWs and assign the value of the drift concentration factor (DCF) for entire systems rationally and efficiently. In this paper, a design method has been exploited for seismic retrofitting of existing RFs using PWs (RF-PWs) via a multi-objective evolutionary algorithm. Then, the method has been investigated and verified through a practical project. Finally, a parametric analysis was executed to exhibit the strengths and working mechanism of the multi-objective design method. To sum up, the findings of this investigation show that the method furnished in this paper is feasible, functional and can provide adequate information for determining the stiffness demand and the value of the DCFfor PWs. Furthermore, it can be applied for the preliminary design of these kinds of structures.