Hysteretic energy dissipation capacity and the cyclic to monotonic drift ratio for rectangular RC columns in flexure

Predictions of energy dissipation capacity and of the deterioration of deformation capacity due to cumulative damage have been made by means of a non‐parametric empirical approach, called the conditional average estimator method, using empirical data on rectangular reinforced concrete columns that failed in flexure. Five input parameters were used: axial load index, index related to confinement, shear span index, concrete compressive strength, and longitudinal reinforcement index. The energy capacity was expressed in three different normalized forms and the deterioration of deformation capacity was defined as the ratio of the cyclic to the monotonic ultimate drift. The longitudinal reinforcement index, the index related to confinement, and the axial load index are the most influential input parameters in the case of energy capacity, whereas the latter two indices exhibit the most significant influence in the case of the drift ratio. Energy capacity decreases with an increasing axial load index, whereas it increases with increasing longitudinal reinforcement and with better confinement. In the case of the shear span index, the trend is more complex. Normal concrete has a higher energy dissipation capacity than high‐strength concrete. Similar trends are observed for the drift ratio, with the exception of the influence of the axial load index, where the trend is opposite. The dispersion of the results is high. Copyright © 2008 John Wiley & Sons, Ltd.     

Flexural deformation capacity of rectangular RC columns determined by the CAE method

A non‐parametric empirical approach, called the conditional average estimator (CAE) method, has been implemented for the estimation of the flexural deformation capacity of reinforced concrete rectangular columns expressed in terms of the ultimate (‘near collapse’) drift. Two databases (PEER and Fardis), which represent subsets of the original databases, were used. Four input parameters were employed in the basic model: axial load index, index related to confinement, shear span index, and concrete compressive strength. The results of analyses suggest that, in general, ultimate drift decreases with increasing axial load index, and increases with better confinement. An increase in the shear span‐to‐depth ratio has a beneficial effect until a turning point is reached. After that the opposite trend can be observed, i.e. a decrease in the ultimate drift with further increasing of the shear span‐to‐depth ratio. No clear trend is observed in the case of concrete compressive strength. The predictions, obtained by using the Fardis database are in general somewhat larger than the predictions from the PEER database, due to the difference in the definition of ultimate drift. The scatter of results is large. The local coefficient of variation, which is a measure for dispersion, amounts to about 0.2–0.5. The ultimate drifts obtained by using the two databases, were compared with the values predicted by the Eurocode 8 empirical formula. Copyright © 2006 John Wiley & Sons, Ltd.     

Seismic behavior and strength capacity of steel tube‐reinforced concrete composite columns

The steel tube‐reinforced concrete (ST‐RC) composite column is a novel type of composite column, which consists of a steel tube embedded in RC. In this paper, the seismic behavior of ST‐RC columns is examined through a series of experiments in which 10 one‐third scale column specimens were subjected to axial forces and lateral cyclic loading. The test variables include the axial force ratio applied to the columns and the amount of transverse reinforcement. All specimens failed in a flexural mode, showing stable hysteresis loops. Thanks to the steel tube and the high‐strength concrete it is filled with, the ST‐RC column specimens had approximately 30% lower axial force ratios and 22% higher maximum bending moments relative to the comparable RC columns when subjected to identical axial compressive loads. The amount of transverse reinforcement made only a small difference to the lateral load‐carrying capacity but significantly affected the deformation and energy dissipation capacity of the ST‐RC columns. The specimens that satisfied the requirements for transverse reinforcement adopted for medium ductile RC columns as specified by the Chinese Code for Seismic Design of Buildings (GB 50011‐2010) and EuroCode 8 achieved an ultimate drift ratio of around 0.03 and a displacement ductility ratio of approximately 5. The design formulas used to evaluate the strength capacity of the ST‐RC columns were developed on the basis of the superposition method. The predictions from the formulas showed good agreement with the test results, with errors no greater than 10%. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental investigation of damage behavior of RC frame members including non-seismically designed columns

Reinforced concrete (RC) frame structures are one of the mostly common used structural systems, and their seismic performance is largely determined by the performance of columns and beams. This paper describes horizontal cyclic loading tests often column and three beam specimens, some of which were designed according to the current seismic design code and others were designed according to the early non-seismic Chinese design code, aiming at reporting the behavior of the damaged or collapsed RC frame strctures observed during the Wenchuan earthquake. The effects of axial load ratio,shear span ratio, and transverse and longitudinal reinforcement ratio on hysteresis behavior, ductility and damage progress were incorporated in the experimental study. Test results indicate that the non-seismically designed columns show premature shear failure, and yield larger maximum residual crack widths and more concrete spalling than the seismically designed columns. In addition, longitudinal steel reinforcement rebars were severely buckled. The axial load ratio and shear span ratio proved to be the most important factors affecting the ductility, crack opening width and closing ability, while the longitudinal reinforcement ratio had only a minor effect on column ductility, but exhibited more influence on beam ductility. Finally, the transverse reinforcement ratio did not influence the maximum residual crack width and closing ability of the seismically designed columns.     

Analytical prediction of ultimate moment and curvature of RC rectangular sections in compression

This paper presents closed form expressions linking the ultimate bearing capacity to the ultimate curvature of rectangular RC sections subjected to axial load and bending moment acting in one of the two symmetry planes of the section. With respect to possible simplified formulations the following effects are also considered: confinement of the concrete, hardening of the longitudinal reinforcement, and presence of reinforcing bars distributed orthogonally to the neutral axis. The formulation is proposed in dimensional terms after a preliminary definition of the geometrical and mechanical parameters governing the structural response of the class of sections considered. The analytical expressions derived using the proposed approach also allow one to determine the compression level that makes the ultimate bending moment maximum as well as to evaluate the curvature corresponding to the first yielding of the principal reinforcement in tension. Comparing this value of curvature with the ultimate one, an approximate estimation of the available ductility of curvature of the section can be made. The analytical procedure is validated by comparing the results with those obtained using a typical numerical approach. Some experimental results are also considered.     

钢管自应力混凝土柱抗震性能试验研究

本文通过对水平反复荷载作用下4根钢管自应力混凝土柱和2根普通钢管混凝土柱的抗震性能试验研究,分析了两种钢管混凝土的荷载-挠度(P-Δ)滞回曲线和骨架曲线特点,从而进一步阐述了轴压比、自应力大小和混凝土强度等因素对钢管混凝土抗震性能的影响。试验结果表明,影响柱抗震性能的最主要因素是轴压比和自应力。随着轴压比的增加,钢管自应力混凝土位移延性系数下降;而自应力的存在不仅提高了反复荷载作用下钢管混凝土的极限水平承载力,同时也使其延性系数得到显著的增加。     

Experimental study of hollow rectangular bridge column performance under vertical and cyclically bilateral loads

To investigate the seismic performance of hollow reinforced concrete(RC) bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending,five specimens were tested.A parametric study is carried out for different axial load ratios,longitudinal reinforcement ratios and lateral reinforcement ratios.The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity,which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns.Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations,and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance.However,the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design.The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations,and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges(JTG/T B02-01-2008).The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns,and it was much less than those specified in the current JTG/T.Thus,the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.     

Seismic strengthening of RC columns using external steel cage

Steel caging technique is commonly used for the seismic strengthening of reinforced concrete (RC) columns of rectangular cross‐section. The steel cage consists of angle sections placed at corners and held together by battens at intervals along the height. In the present study, a rational design method is developed to proportion the steel cage considering its confinement effect on the column concrete. An experimental study was carried out to verify the effectiveness of the proposed design method and detailing of steel cage battens within potential plastic hinge regions. One ordinary RC column and two strengthened columns were investigated experimentally under constant axial compressive load and gradually increasing reversed cyclic lateral displacements. Both strengthened columns showed excellent behavior in terms of flexural strength, lateral stiffness, energy dissipation and ductility due to the external confinement of the column concrete. The proposed model for confinement effect due to steel cage reasonably predicted moment capacities of the strengthened sections, which matched with the observed experimental values. Copyright © 2009 John Wiley & Sons, Ltd.     

锈蚀钢筋混凝土圆柱抗震性能的试验研究

对不同锈蚀程度的钢筋混凝土圆柱进行低周反复试验,研究了不同轴压比下的钢筋锈蚀率对钢筋混凝土圆柱滞回曲线、骨架曲线、刚度、延性及耗能能力的影响;给出了试件累积耗能、屈服荷载、极限荷载、荷载最大值和位移延性系数与钢筋锈蚀率和轴压比的关系。研究表明,随着钢筋锈蚀率和轴压比的增大,试件的滞回曲线趋于干瘪,骨架曲线下降段变陡,试件的刚度、延性和耗能能力减小。     

反复荷载下型钢混凝土柱受扭损伤试验研究

为研究型钢混凝土柱在反复荷载下的受扭损伤,完成了11根型钢混凝土柱和1根钢筋混凝土柱复合受扭试验。通过试验观察了构件的受力过程和破坏特征,研究两种不同型钢混凝土柱的裂缝开展与分布规律。基于能量守恒定律,考察了柱截面配钢形式、扭弯比、轴压比、混凝土强度等级、配箍率以及配钢率对累积损伤的影响。研究结果表明:型钢混凝土柱的损伤演变分为3个阶段:弹性阶段、弹塑性阶段和破坏阶段;配钢形式、扭弯比和配箍率是影响型钢混凝土柱损伤程度的重要因素;配型钢,降低扭弯比和提高配箍率对于损伤指标分别最大降低了22.1%、14.3%和14.0%;损伤指标受轴压比、配钢率和混凝土强度等级影响程度较小。     

RC梁与柱在不同地震作用下的变形限值分析

分析钢筋混凝土(RC)梁与柱基于不同地震作用下的变形限值,对钢筋混凝土梁与柱进行低周往复循环加载拟静力试验.然后对试验进行仿真模拟,将试验结果与仿真模拟结果进行对比分析,发现二者结果相近,从而验证仿真模拟的可行性.在构件的荷载-位移曲线上获取屈服点、峰值点和极限点,分别计算这3个状态点对应的侧向位移值与构件计算长度的比...     

高强钢筋混凝土柱轴心受压承载力可靠度研究

课题组搜集186根高强钢筋混凝土轴压柱的试验数据,得到相关统计参数,选用JC法并利用MATLAB软件编制计算程序迭代求解高强钢筋混凝土柱轴压承载力可靠指标。分析不同荷载组合、钢筋强度、混凝土强度以及配筋率等参数对混凝土柱轴压承载力可靠指标的影响。研究结果表明:高强钢筋混凝土柱轴压承载力可靠指标随计算模式不确定性系数的增大而增大;随着荷载效应比的增大,可靠指标呈现出先增大后减小的趋势;可靠指标随钢筋强度的提高而减小,随混凝土强度提高而增大;随着配筋率的增大,可靠指标逐渐减小,高配筋率对轴压构件不利。     

Assessment indices for the seismic vulnerability of existing R.C. buildings

The seismic vulnerability of old multi‐storey reinforced concrete (R.C.) buildings reinforced with substandard details is assessed as a function of interstorey drift demand imposed by the design earthquake while considering brittle termination of elastic response of the critical members of the structure due to a premature shear failure. Interstorey drift demand is related to column and wall translational stiffnesses which are expressed through analytical derivations in terms of the floor area ratios of gravity and lateral load bearing members in the critical floor. Interstorey drift capacity is related to the available transverse reinforcement and the axial load ratio of the vertical members. The significance of the area ratio of vertical members in the typical floor as an index of vulnerability is explored with reference to the limitations in the value of axial load ratio used in R.C. design in order to secure ductile flexural behavior, and also with reference to the stability index of gravity load bearing members. Interstorey Drift Spectra are derived for the existing R.C. buildings suitable for rapid seismic vulnerability screening but also as a guide for rehabilitation of the existing structures. Lightly reinforced or substandard reinforced concrete buildings that reportedly collapsed during previous earthquakes are used as example case studies in order to calibrate the proposed methodology. Copyright © 2010 John Wiley & Sons, Ltd.     

高强钢筋增强UHPC-NC组合柱抗震性能研究

为探讨高强钢筋增强UHPC-NC组合柱抗震性能,基于大型有限元程序ABAQUS,结合UHPC、NC和高强钢筋材料本构关系,校准损伤塑性模型中相关参数,建立高强钢筋增强UHPC-NC组合柱抗震有限元模型。通过与3个NC柱和3个UHPC柱拟静力试验结果对比,验证分析模型的有效性。在此基础上,进一步探讨轴压比、纵筋直径、纵筋强度、箍筋间距和UHPC高度等敏感参数对高强钢筋增强UHPC-NC组合柱抗震性能的影响。结果表明,高强钢筋增强UHPC-NC组合柱位移延性系数随轴压比、纵筋直径和箍筋间距的增大而降低,随纵筋强度和UHPC高度的增加表现出先增大后逐渐平缓的趋势,合适的UHPC替换高度能充分发挥高强钢筋和UHPC材料特性并取得良好的经济性。     

碳纤维布改善高强混凝土柱延性的试验研究

本文进行了8根高强混凝土柱在低周反复荷载作用下的试验，研究了使用碳纤维布横向包裹的高强混凝土柱来提高其延性这种加固方法的有效性。本文研究了碳纤维布横向包裹高强混凝土柱的受力特性，分析了加荷角度，碳纤维布拉伸强度以及碳纤维布的包裹层数等因素对构件抗震加效果的影响，并对碳纤维布加固高强混凝土柱使其延性提高的机理进行了探讨，试验结果表明，横向缠裹碳纤维布可显著提高高强混凝土柱的延性。     

Seismic performance of steel reinforced ultra high-strength concrete composite frame joints

To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete (SRUHSC) columns and steel reinforced concrete (SRC) beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirrup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete (SRC) frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.     

Research on the influencing factors for residual displacements of RC bridge columns subjected to earthquake loading

Following the 1995 Kobe earthquake, many RC bridge columns were demolished due to a residual drift ratio of more than 1.75 % even though they did not collapse. The residual drift ratio is a quantitative index for the performance objective of reparability in the bridge seismic design. Numerical models of the columns are built to study the factors that influence the residual displacement of RC bridge columns. In these models, both column bending and bar pulling out deformation are considered using the fiber column-beam element and zero-length section element, respectively. Then, nonlinear time history analyses are performed. The factors that influence column residual displacement, such as the characteristics of ground motion, the structural responses (the maximum lateral drift ratio and the displacement ductility factor), and the structural characteristics (the aspect ratio and the longitudinal reinforcement ratio) are investigated. It is found that the near-fault ground motion induces a larger residual drift ratio than the far-fault ground motion. The residual drift ratio becomes larger due to the increase of the maximum lateral drift ratio, the displacement ductility factor, and the aspect ratio. Further, a larger longitudinal reinforcement ratio can induce a larger residual drift ratio due to the contribution of the bar pulling out deformation.     

薄壁方钢管混凝土柱劲化设计及轴压性能探讨

对于薄壁方形钢管混凝土柱,有效且经济地提高柱的承载力、刚度和延性,增强其抵抗局部屈曲的能力是目前的一项重要研究课题。据此,进行8个薄壁方形钢管混凝土轴压试件的研究,比较普通薄壁钢管混凝土柱与劲化薄壁钢管混凝土柱的轴压极限承载力、延性性能、局部屈曲模态及相应耗钢量,研究表明:劲化设置在增加较少用钢量的情况下,使钢管壁对核心混凝土的约束作用相对于普通钢管混凝土柱和单纯加设约束拉杆的钢管混凝土柱更趋均匀,提高了整体约束效应,混凝土强度得以提高,本构关系明显改善。从而增加了钢管混凝土柱的轴压承载力和延性,改变了钢管的局部屈曲变形状态,其实用效益与经济效益极其可观,具有良好推广价值。     

关于日本框架柱受剪承载力公式的讨论

通过对日本抗震设计规范中有关钢筋混凝土框架柱受剪承载力代表性公式的研究，凸现了由经验公式到基于桁架一拱模型建立的发展趋势。对各公式中所包括的影响框架柱受剪承载力的主要因素(如剪跨比、轴压比、配箍率、混凝土强度、纵筋率等)进行了深入讨论，并采用框架柱受剪承载力试验数据考察了各个公式的有效性。     

CFRP布约束增强高强混凝土柱抗震性能数值分析

采用地震工程开源模拟软件OpenSees（Open System for Earthquake Engineering Simulation）对CFRP（Carbon Fiber Reinforced Polymer,碳纤维增强复合材料）布加固高强钢筋混凝土方柱的抗震性能进行了数值分析。采用Steel02Material和Concrete02Material材料本构模型模拟了CFRP布加固高强混凝土方柱的抗震性能;在此基础上,进一步研究了轴压比和剪跨比这2个因素对试件抗震性能的影响。将所得数值分析结果与相同条件下的试验结果对比后发现：基于Steel02 Material和Concrete02 Material材料本构,利用OpenSees,可以较好地模拟CFRP布加固高强混凝土方柱的抗震性能,并且与试验结果（滞回曲线、骨架曲线、水平承载力和位移延性系数）能够较好地吻合,从而说明该数值分析方法还可以准确地反映出轴压比和剪跨比对高强混凝土柱抗震性能的影响规律。