Analytical investigation of the seismic performance of RC frames rehabilitated using different rehabilitation techniques

The objective of this study is to investigate analytically the effectiveness of different rehabilitation patterns in upgrading the seismic performance of existing non-ductile reinforced concrete (RC) frame structures. The study investigates the performance of two RC frames (with different heights representing low- and high-rise buildings) with or without masonry infill when rehabilitated and subjected to three types of ground motion records. The ground motion records represent earthquakes with low, medium and high frequency contents. Three models were considered for the RC frames; bare frame, masonry-infilled frame with soft infill, and masonry-infilled frame with stiff infill. Four rehabilitation patterns were studied, namely: (1) introducing a RC shear wall, (2) using steel bracing, (3) using diagonal FRP strips (FRP bracings) in the case of masonry-infilled frames, and (4) wrapping or partially wrapping the frame members (columns and beams) using FRP composites. Incremental Dynamic Analysis was conducted for the studied cases. The seismic performance enhancement of the studied frames is evaluated in terms of the maximum applied peak ground acceleration resisted by the frames, maximum inter-storey drift ratio, maximum storey shear-to-weight ratio and energy dissipation capacity.     

Evaluation of low-cycle fatigue damage in RC exterior beam-column subassemblages by acoustic emission

Since Acoustic Emission (AE) is effective in monitoring the initiation of cracks in materials and structures, it has been widely used as a real-time evaluation technique for damage in reinforced concrete (RC) elements such as beams or columns in moment-resisting frames. This paper investigates its applicability for assessing the low-cycle fatigue damage in RC exterior beam-column subassemblages, which are especially vulnerable parts of the RC frames when subjected to earthquakes. Two 3/5 scale specimens representing connections from the lower and upper part of a prototype building located in a moderate-seismicity area are tested under cyclic loading until collapse. Important differences between the two specimens are observed owing to the different size and amount of reinforcing steel. First, a significant increase in AE activity is observed when the steel reinforcement begins to undergo plastic deformations. Second, by means of the AE improved b-value method, it is clearly shown that the macroscopic fracture processes occur mainly during the loadings paths. Thus, on the basis of AE source location with four sensors situated around the beam-column joint, the AE is successfully correlated with the observed cracks. A strong correlation is also found between the accumulated plastic strain energy dissipated by the concrete and the accumulated AE energy. Based on this fact, a formula is proposed to predict the level of damage and the closeness to failure of an exterior beam-column subassemblage from the AE as recorded by sensors located near the joint.     

新型梁柱节点高层钢结构抗震性能研究

结构的抗震设计一般有两类途径:主动控制和被动控制。主动控制系统复杂且成本偏高,普通的被动控制抗震结构强震后修复困难。针对上述问题,本文提出了一种新型转动摩擦耗能梁-柱节点,并基于SAP2000对采用新型梁柱耗能节点的X形支撑钢框架体系和普通X形支撑钢框架体系进行了罕遇地震作用下的时程分析,结果表明采用了该新型梁-柱耗能节点的X形支撑钢框架体系具有更好的抗震性能。     

Study on load resisting mechanism of corroded RC frame structures against progressive collapse

为研究钢筋锈蚀对钢筋混凝土(RC)框架结构连续倒塌抗力机制的影响，对3个1/2缩尺RC梁-柱子结构开展了拟静力Pushdown试验，其中1个未锈蚀RC梁-柱子结构作为对照，另2个RC梁-柱子结构在节点区采用电化学加速锈蚀方法模拟钢筋锈蚀。试验结果表明：钢筋锈蚀会影响RC梁-柱子结构的裂缝开展顺序及钢筋断裂位置，同时钢筋锈蚀会削弱压拱机制及悬链线机制对RC结构抗连续倒塌能力的提升作用。在边节点锈蚀率为28.6%和中节点锈蚀率为5.2%的情况下，RC梁-柱子结构的第一峰值荷载和极限荷载分别降低了31.2%和57.4%。基于试验结果，通过对比分析验证不同压拱机制理论计算模型及悬链线机制理论计算模型评估锈蚀RC梁-柱子结构连续倒塌抗力机制的有效性。通过对比分析发现：Lu等提出的模型用于评估锈蚀RC梁-柱子结构压拱机制下的第一峰值荷载的准确性高且离散性低；Yu等所提模型对锈蚀RC梁-柱子结构悬链线机制下极限荷载的评估结果较为准确，但偏于保守。     

锈蚀RC框架结构连续倒塌抗力机制研究

为研究钢筋锈蚀对钢筋混凝土(RC)框架结构连续倒塌抗力机制的影响,对3个1/2缩尺RC梁-柱子结构开展了拟静力Pushdown试验,其中1个未锈蚀RC梁-柱子结构作为对照,另2个RC梁-柱子结构在节点区采用电化学加速锈蚀方法模拟钢筋锈蚀。试验结果表明：钢筋锈蚀会影响RC梁-柱子结构的裂缝开展顺序及钢筋断裂位置,同时钢筋锈蚀会削弱压拱机制及悬链线机制对RC结构抗连续倒塌能力的提升作用。在边节点锈蚀率为28.6%和中节点锈蚀率为5.2%的情况下,RC梁-柱子结构的第一峰值荷载和极限荷载分别降低了31.2%和57.4%。基于试验结果,通过对比分析验证不同压拱机制理论计算模型及悬链线机制理论计算模型评估锈蚀RC梁-柱子结构连续倒塌抗力机制的有效性。通过对比分析发现：Lu等提出的模型用于评估锈蚀RC梁-柱子结构压拱机制下的第一峰值荷载的准确性高且离散性低;Yu等所提模型对锈蚀RC梁-柱子结构悬链线机制下极限荷载的评估结果较为准确,但偏于保守。     

Analytical investigation of response modification (behaviour) factor,R, for reinforced concrete frames rehabilitated by steel chevron bracing

Steel bracing of reinforced concrete (RC) frames has received noticeable attention in recent years as a retrofitting measure to increase the shear capacity of the existing RC buildings. In order to evaluate the seismic behaviour of steel-braced RC frames, some key response parameters, including the ductility and the overstrength factors, should first be determined. These two parameters are incorporated in structural design through a force reduction or a response modification factor. In this paper, the ductility and the overstrength factors as well as the response modification factor (or seismic behaviour factor) for steel chevron-braced RC frames have been evaluated by performing inelastic pushover analyses of brace-frame systems of different heights and configurations. The effects of some parameters influencing the value of behaviour factor, including the height of the frame and share of bracing system from the applied lateral load have been investigated. It is found that the latter parameter has a more localised effect on the R values and its influence does not warrant generalisation at this stage. However, the height of this type of lateral load-resisting system has a profound effect on the R factor, as it directly affects the ductility capacity of the dual system. Finally, based on the findings presented in the article, tentative R values have been proposed for steel chevron-braced moment-resisting RC frame dual systems for different ductility demands and compared with different type of bracing systems.     

钢筋混凝土中间层边节点模型化方法研究

钢筋混凝土梁柱节点区非弹性变形包括梁纵筋黏结滑移和节点核心区剪切变形,对钢筋混凝土梁柱组合体的受力性能影响较大,在有限元模型中合理地考虑节点区的这两种非弹性变形是数值计算的难点和关键。利用OpenSees结构分析平台中的梁柱节点单元,根据中间层边节点的受力特点和试验结果,通过对钢筋滑移分量和剪切块分量的计算模型、参数计算方法进行改进,提出了修正梁柱节点单元模型,并以多组试验结果为依据,校核了修正梁柱节点单元模型计算的准确性和适用性。分析结果表明：修正梁柱节点单元模型能有效模拟中间层边节点的整体受力性能和局部非弹性变形特性;改进的梁纵筋滑移模型能更合理地模拟贯穿节点梁纵筋的受力特性;改进的剪切块计算模型能准确模拟节点核心区的剪应力大小,以及两个不同加载方向的节点剪应力差异。     

后加交叉钢支撑对RC框架结构的影响研究

为揭示后加交叉钢支撑对RC框架结构的影响规律,考虑结构层数、支撑截面尺寸及支撑与框架结构的连接方式三种影响因素,采用ETABS建立结构模型,对加钢支撑后RC框架结构的周期、刚度及基础反力及梁柱内力进行了定量分析。结果表明,后加交叉钢支撑对不同结构层数的RC框架的影响规律基本相同,支撑截面尺寸对支撑所在的结构单元的构件内力有较大影响,支撑与框架结构刚接或铰接连接的计算结果基本相同。此外,后加钢支撑承担了大部分的水平剪力,钢支撑对重力荷载或地震作用下的基础反力、地震作用下的柱轴力、梁弯矩及剪力,以及重力荷载作用下的梁轴力均有较大的影响。     

混凝土楼板对钢框架梁柱节点抗震性能影响的试验研究

为了研究节点区混凝土楼板对钢框架梁柱节点抗震性能的影响,完成了4个不同构造形式的节点试件在低周循环荷载下的破坏试验,分析了节点构造与混凝土楼板配筋率等因素对节点承载力、转动刚度、极限转动能力、耗能能力、延性和极限破坏状态的影响。对节点破坏模式和滞回曲线的分析表明,保证焊接质量是避免节点脆性破坏的重要措施。采用长焊接孔的节点,使钢梁发生了局部屈曲破坏,既可减少局部应力集中,又可提高节点的延性,提高配筋率可以显著增强节点的抗弯承载力。另外,混凝土楼板的存在使节点在构造上存在不对称性,应该在节点设计中给予考虑。     

Research on seismic behavior of GFRP-reinforced concrete beam-column joints

为提高RC框架结构震后可恢复性，采用GFRP筋替代钢筋应用于混凝土梁柱结构中。以配箍率、轴压比、混凝土强度为变量对梁柱组合体开展了拟静力试验研究。试验中共对8个GFRP筋混凝土梁柱组合体、1个RC梁柱组合体进行了测试，比较了GFRP筋与普通钢筋混凝土梁柱组合体的变形和破坏过程，对比分析了各梁柱组合体的滞回曲线、承载能力、残余位移、能量耗散以及钢筋的应变分布等。试验结果表明：GFRP梁柱顶点残余位移显著下降，较RC柱顶残余位移降低60%左右，但其耗能能力低于RC梁柱节点的；在往复荷载作用下，GFRP筋混凝土梁柱框架破坏符合“强柱弱梁”特征，能够承受较大侧向位移，其在达到5.5%位移角时仍未表现出脆性破坏特征；GFRP筋梁柱组合体承载能力、耗能能力和纵筋利用率随着配箍率、混凝土强度的增加而增大。此外，综合考虑配箍率、轴压比、混凝土强度对GFRP筋梁柱节点核心区受剪性能的影响，提出了该种节点核心区受剪承载力计算方法，并基于国内外相关试验数据对其进行了验证。结果表明，提出的计算式能有效计算GFRP筋梁柱节点核心区受剪承载力。     

GFRP筋混凝土梁柱组合体抗震性能试验研究

为提高RC框架结构震后可恢复性,采用GFRP筋替代钢筋应用于混凝土梁柱结构中。以配箍率、轴压比、混凝土强度为变量对梁柱组合体开展了拟静力试验研究。试验中共对8个GFRP筋混凝土梁柱组合体、1个RC梁柱组合体进行了测试,比较了GFRP筋与普通钢筋混凝土梁柱组合体的变形和破坏过程,对比分析了各梁柱组合体的滞回曲线、承载能力、残余位移、能量耗散以及钢筋的应变分布等。试验结果表明：GFRP梁柱顶点残余位移显著下降,较RC柱顶残余位移降低60%左右,但其耗能能力低于RC梁柱节点的;在往复荷载作用下,GFRP筋混凝土梁柱框架破坏符合“强柱弱梁”特征,能够承受较大侧向位移,其在达到5.5%位移角时仍未表现出脆性破坏特征;GFRP筋梁柱组合体承载能力、耗能能力和纵筋利用率随着配箍率、混凝土强度的增加而增大。此外,综合考虑配箍率、轴压比、混凝土强度对GFRP筋梁柱节点核心区受剪性能的影响,提出了该种节点核心区受剪承载力计算方法,并基于国内外相关试验数据对其进行了验证。结果表明,提出的计算式能有效计算GFRP筋梁柱节点核心区受剪承载力。     

The effect of semi-rigid joints and an elastic bracing system on the buckling load of simple rectangular steel frames

A linear stability analysis for establishing the combined effect of joint flexibility and an elastic bracing system on the buckling load of steel plane frames is presented herein. Based on the beam-to-column model of Eurocode 3, the subsequent study shows that joint flexibility is a very important parameter that needs to be incorporated into the stability analysis of frames with semi-rigid connections. It was found that assuming flexible connections in such frames always leads to a reduction of their buckling load, which is proven to be significant in many characteristic cases. Numerical results for simple elastically braced or unbraced frames with semi-rigid connections, in tabular and graphical form, reveal the pronounced effect of joint flexibility and elastic bracing on their buckling load. The results presented herein can be readily used for the design of simple frames against buckling, while the flexible connection concept can be applied to all types of steel frames.     

半刚性连接钢框架的弹性屈曲荷载计算

以单层多跨框架结构为研究对象,通过对各梁柱构件建立失稳状态的控制微分方程并引入相应的连续性条件和边界条件,建立了半刚性连接平面钢框架结构整体弹性失稳的临界荷载计算模型,并研制了相应的计算程序。计算结果表明,框架结构的半刚性连接特性和水平支撑对其整体稳定性的影响极为显著,而且结构失稳的整体效应需引起高度重视。分析结果还表明,作用于多跨框架结构竖向荷载的分布特征对整体框架结构的弹性屈曲荷载有不可忽视的影响,而这一点在目前钢框架的设计理论中并未充分考虑。另外,半刚性连接特性及结构的支撑刚度对钢框架结构稳定性的影响具有明显的界限性和区间性,即当连接刚度或支撑刚度超过一定数值时,其变化对框架结构弹性屈曲荷载的影响将无需再考虑。     

Seismic behaviour of infilled and pilotis RC frame structures with beam-column joint degradation effect

The influence of the exterior joints capacity deterioration on the local and global failure mechanisms of reinforced concrete structures with infills is investigated. Exterior beam-column joints with reduced capacity is the common case for the majority of RC structures designed according to older design standards. Nevertheless in common practise the response of these regions is typically assumed as rigid. A key parameter of this investigation is the inclusion of the joints strength and stiffness degradation in the study of the seismic performance of the structures. In this direction, a special-purpose rotational spring element that incorporates a special behaviour model is employed for the simulation of the exterior joints’ local response. The spring element has been incorporated in a well-established general program for nonlinear static and dynamic analysis. The effectiveness of the used joint element model has been demonstrated in a previous paper through comparisons with experimental data reported in literature. In this paper an attempt is presented for the investigation of the influence of the exterior joint damage on the seismic behaviour of bare and infilled RC frame structures. Two types of masonry infilled structures are considered: (a) infilled frame and (b) infilled frame without infills at the base storey (pilotis frame). A parametrical study of the overall seismic response using push over analyses and step-by-step analyses is performed. Results in terms of interstorey drifts, base shear, failure mode, ductility requirements and joints rotational requirements demonstrate that neglecting the possible local damage of the exterior joints may lead to erroneous conclusions and unsafe design or seismic behaviour evaluation that subsequently may become critical in some cases. Furthermore the influence of exterior joints degradation has been proven of vital importance for the overall behaviour of pilotis frames.     

Seismic performances of reinforced concrete frames with wall-like columns

In regions of low to moderate seismic risk, such as Singapore and Malaysia, buildings with relatively weak lateral structural resisting systems are likely to be common. Although ground motions because of long distance earthquakes centred in Sumatra have occurred, there has been no record of earthquake damage in this region. This article compares the results obtained from pushover analyses of six-storey reinforced concrete (RC) frames with experimental observations. The experimental observations of four internal beam-column joints, which were designed according to BS 8110, were summarised. From this, we address the performance of some typical RC frame structures under low seismic loading. By adding about 0.075% of hoop reinforcement in the beam-column joints, one can improve the seismic performance of the frame in the weak direction more significantly than in the strong direction. Also, relatively large joint shear input during low to moderate earthquakes can result in diagonal tension cracking and the building may likely be governed by joint shear failure.     

框架节点梁柱端部碳纤维布加固的受力分析和设计方法研究

针对各种原因造成的与钢筋混凝土节点(柱脚)相连的梁或柱抗弯性能不足,设计了一种用碳纤维布提高梁柱抗弯能力的加固方法,并用试验进行了验证。本文用ANSYS有限元程序建立了梁柱端部用碳纤维布加固的钢筋混凝土框架中部梁-柱-节点试件的三维有限元模型,用弹簧单元模拟胶层的粘结滑移,分析了应力在混凝土、碳纤维布和铝角钢之间的传递和发展过程。在与试验结果的对比分析和对有关参数的有限元分析基础上,提出了该加固技术的设计方法。     

复式钢管混凝土外钢管不连通环梁节点抗震性能试验研究

设计一种用于复式钢管混凝土结构的新型外钢管不连通环梁节点,介绍该新型节点的构造和制作过程,进行四个梁柱组合体低周反复荷载试验,研究新型节点的抗震性能。试验结果表明:新型节点具有较好延性和变形能力,增加环梁配筋率和柱内钢管尺寸可提高节点的承载力。通过合理的构造措施,外钢管不连通环梁节点中内钢管混凝土、竖向插筋和密排环箍以及周边环梁一起保持了钢管混凝土柱的连续性,节点整体性强,满足结构设计"强柱弱梁"及"强节点弱构件"的设计原则,具有较好的抗震性能。     

钢筋混凝土框架结构基于时变的抗震性能研究

钢筋混凝土结构在使用过程中由于钢筋锈蚀抗震性能退化。为了研究钢筋混凝土框架结构在正常使用环境下随使用时间的增加其抗震性能的退化规律,采用通用有限元分析软件ABAQUS对锈蚀钢筋混凝土框架进行多尺度建模以提高计算精度并保证计算效率。基于锈蚀钢筋混凝土构件及单榀框架的试验数据,验证了多尺度建模方法的正确性。采用多尺度模型对4层钢筋混凝土框架结构进行了静力推覆分析及弹塑性时程分析,对比不同使用时间的钢筋混凝土框架结构的地震反应和损伤情况。结果表明：当使用时间为25a时,结构的抗震性能与新建结构接近;当使用时间超过50a时,随着使用时间的增加,结构的承载能力及刚度退化明显,在地震作用下的位移响应逐渐增大,地震损伤范围不断扩大;相比新建结构,当使用时间为50、75a和100a时,结构的抗侧承载力分别降低了6.2%、14.1%及18.1%,罕遇地震作用下的最大层间位移角分别增大了9.2%、19.8%及25.1%。     

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.     

装配式新型梁-柱钢连接节点抗震性能研究

与传统建筑业相比,装配式建筑具有能耗低、施工周期短、施工现场环境好等优点.本文基于现有的装配式RC结构梁-柱节点连接方式,提出了一种用于装配式RC结构的新型梁-柱钢连接节点,以期克服现浇混凝土连接节点施工效率低的缺点,同时保证节点的强度和稳定性,进而确保结构具有良好的整体性.通过有限元分析软件ABAQUS对现浇与新型梁...