Axial–flexural interaction in circular FRP-confined reinforced concrete columns

External confinement by fibre reinforced polymers (FRPs) is now a widely implemented technique to strengthen reinforced concrete (RC) columns. To date, the vast majority of experiments on FRP-confined concrete have considered short, unreinforced, small scale concrete cylinders, with aspect ratios of less than three and tested under concentric axial load. In practice, RC columns invariably have aspect ratios larger than three and are subjected to inadvertent load eccentricities or combined axial–flexural (P–M) loading. Limited available research suggests that the effectiveness of FRP confinement is reduced under P–M loading. This paper presents the results of a systematic test program on circular FRP-confined RC columns of realistic slenderness under eccentric axial loads to study the mechanics and performance of these types of members. Test data are compared against theoretical P–M interaction diagrams, as well as against recently published design guidelines for P–M interaction in FRP-confined RC columns.     

Fire safety design method of circular steel tube confined reinforced concrete columns

对于钢管约束钢筋混凝土柱抗火性能的研究,目前尚无抗火设计方法可供参考。实际工程中大多借鉴钢筋混凝土柱或钢管混凝土柱的抗火设计方法,但由于钢管约束钢筋混凝土柱的受力机理与二者不同,其耐火极限存在明显差异。为此,提出了火灾下圆钢管约束钢筋混凝土柱的耐火极限计算方法,分析了荷载比、长细比等因素对耐火极限的影响,并与钢筋混凝土柱和钢管混凝土柱进行了对比。研究表明：荷载比对圆钢管约束钢筋混凝土柱的耐火极限影响显著,荷载比越大,耐火极限越低;长细比、截面尺寸等因素对荷载比较小的构件影响显著。圆钢管约束钢筋混凝土柱的耐火极限为相同条件下钢筋混凝土柱的14.4%~66.0%,荷载比越大,两种构件的差异越大,按照钢筋混凝土柱的防火设计方法对圆钢管约束钢筋混凝土柱进行防火设计,结果偏于不安全;与钢管混凝土柱相比,钢管约束钢筋混凝土柱具有更高的耐火极限,是钢管混凝土柱的1.0~3.0倍。     

SRC和RC柱耐火性能和抗火设计的若干问题探讨

扼要介绍了影响型钢混凝土SRC和RC钢筋混凝土柱耐火极限的可能因素主要有截面尺寸、构件长细比、火灾荷载比、截面配筋率、截面含钢率、荷载偏心率、截面高宽比、钢材和混凝土强度等的几何参数、物理参数和荷载参数等对SRC和RC构件.构件耐火极限的影响规律,探讨了SRC和RC柱耐火性能和抗火设计中的若干问题。     

Reliability-based load factors for airblast and structural reliability of reinforced concrete columns for protective structures

Reliability-based design allows the decision-maker to select the level of reliability for a specific explosive blast loading scenario. Important to this is an understanding of airblast and resistance uncertainty. Reliability-based load factors are calculated and are dependent on the variability of model error, explosive mass and range. Reliability-based design load factors (RBDFs) are estimated for explosive ordnance, terrorism, weaponeering and other scenarios. The effect of RBDFs on structural reliabilities for reinforced concrete (RC) columns is then calculated where resistance and loading are random variables, and compared to target values. It was found, for realistic combinations of range and explosive mass variabilities, that RC columns designed to existing standards have a significant margin of safety with a probability of failure of 1?×?10^?3 to 1?×?10^?5. However, if there is large airblast variability, then the application of RBDFs is necessary to ensure that safety levels are acceptable according to international standards.     

不同受火方式下混凝土柱耐火性能的试验研究

通过5根高强混凝土柱和2根普通混凝土柱的足尺明火试验,考察了不同受火方式对混凝土柱破坏形态、轴向变形和耐火极限的影响。结果表明:(1)非四面受火柱的耐火极限较四面受火柱有很大提高,同时三面受火柱的耐火极限小于两面受火柱;(2)相同受火方式和相同轴压比下高强混凝土柱的耐火极限远低于普通混凝土柱;(3)相同受火方式下大轴压比普通混凝土柱的耐火极限可能小于中等轴压比的高强混凝土柱。在实际结构的抗火设计中,合理考虑受火方式、混凝土强度等级和轴压比的影响是十分必要的。     

Interaction diagram methodology for design of FRP-confined reinforced concrete columns

This paper presents a procedure that allows the construction of a simplified axial load – bending moment interaction diagram for FRP-wrapped Reinforced Concrete (RC) columns of circular and non-circular cross-sections for practical design applications. In the proposed methodology, the analysis of FRP-confined columns is carried out based on principles of equilibrium and strain compatibility equivalent to that of conventional RC columns, the primary difference being the use of the stress–strain model for FRP-confined concrete developed by Lam and Teng. Based on the consideration that the strength enhancement is of significance in members where compression is the controlling failure mode, only the portion of the interaction diagram corresponding to this type of failure is the focus of the methodology. Experimental evidence from RC specimens with a minimum side dimension of 300 mm (12 in.) and subjected to combined axial compression and flexure was collected and compared to the theoretical interaction diagrams. Even though limited experimentation has been conducted in the compression-controlled region for such type of members, data points appear to be consistent with the analytical predictions. A design method for RC members is therefore proposed following the principles of the ACI building code.     

锈蚀钢筋混凝土柱基于变形的性能指标研究

采用ABAQUS有限元软件,对按GB 50011-2010《建筑抗震设计规范》和GB 50010-2010《混凝土结构设计规范》设计的342个锈蚀钢筋混凝土柱进行有限元分析,研究钢筋的锈蚀率、轴压比、剪跨比、配箍率和纵向钢筋配筋率等参数对钢筋混凝土柱变形性能的影响。结果表明：当钢筋的锈蚀率较小时,构件的变形性能受锈蚀率影响不大;当钢筋的锈蚀率达到10%以后,构件的破坏形态发生改变,变形能力急剧退化;随着轴压比的增大,构件的变形能力降低;轴压比较小的构件变形性能受剪跨比影响比轴压比较大的构件明显;随着配箍率和纵向钢筋配筋率的增大,构件的变形能力有所提高;提出了锈蚀钢筋混凝土柱抗震性能等级和性能界限状态的划分方法,以塑性转角作为变形性能指标,对数值计算结果进行统计分析,得到了锈蚀钢筋混凝土柱各性能界限点的塑性转角统计特征值。研究成果可为钢筋混凝土结构全寿命的性能化抗震设计和抗震性能评估提供参考。     

Seismic behavior and shear strength of tubed RC short columns

Reinforced concrete (RC) short columns are vulnerable to brittle shear failure during an earthquake. The objective of this research is to evaluate the performance enhancement of RC short columns tubed with circular or square tubes. Eight short columns were tested under combined constant axial load and cyclic lateral load. The tested specimens included three circular tubed RC (CTRC) columns and three square tubed RC (STRC) columns. Two common RC short columns including one circular RC column and one square RC column were also tested as control specimens. The test results indicated that common RC short columns suffered brittle shear failure with little ductility, while the ductility of tubed RC short columns was excellent due to the effective confinement of the outer thin tube to the core concrete. The lateral load strength of CTRC short columns increases with the increasing of axial load ratio, while the axial load ratio has little effect on the plastic deformation capacity of CTRC short columns. The shear strength increases with increasing of axial load ratio, while the plastic deformation capacity decreases with increasing of axial load ratio for STRC short columns. A circular tube prevents the core concrete from shear failure more effectively than a square tube for the tubed RC short columns. A modified ACI design method is adopted to calculate the nominal shear strength of STRC columns as well as CTRC columns based on the test and analysis results.     

柱失效方程中荷载相关特性对承载力抗震设计可靠度的影响

以竖向荷载和水平地震作用组合下的钢筋混凝土柱和钢柱为对象,研究了失效方程中荷载相关特性对柱承载力抗震可靠性的影响。根据现行《混凝土结构设计规范》和《钢结构设计规范》分析了不同柱弯矩轴力相关曲线的特性。结合多个框架结构实例,对比了柱失效方程中荷载相关曲线与规范考虑情形的异同。实例分析表明:水平地震和竖向荷载组合作用下,小偏压RC柱和工字型钢柱的荷载相关曲线与规范考虑的情形较为符合,均近似为负相关的直线;水平地震和竖向荷载组合作用下,大偏压RC柱的荷载相关曲线则与规范考虑的情形有较大出入,存在明显的正相关段部分。在此基础上,考虑失效方程复杂特性,依据已有的荷载和抗力变量概率模型,采用Monte Carlo法分析了水平地震和竖向荷载组合作用下柱的可靠性。结果表明:钢柱和小偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化幅度较小,与规范模式计算结果较接近;大偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化会有较大幅度波动,与规范模式计算结果差异较大;当轴压力荷载效应比值为负时,大偏压RC柱的承载力抗震可靠度会低于规范计算值较多,现行柱可靠性设计方法会偏于不安全。     

碳纤维复合材料(CFRP)约束矩形截面混凝土柱应力-应变关系研究

现有对于CFRP约束混凝土圆柱的应力-应变关系的研究已经开展得较为广泛，但对于实际中存在更多的矩形柱而言，其相关研究却非常有限。本文对14根碳纤维（CFRP）约束矩形截面混凝土柱进行了轴压试验，分析了试验现象和受力机理，研究了圆角半径，截面长宽比、外包纤维量对承载性能的影响，给出了试验结果，并基于试验数据验证了Lamand Teng（2003）提出的面向设计的纤维约束混凝土矩形柱应力-应变模型，所得的计算值与试验结果基本吻合，证明了该模型的可靠性，能够满足设计要求。     

外壳预制核心现浇装配整体式钢筋混凝土柱的抗弯性能试验研究

制作了2根外壳预制核心现浇装配整体式钢筋混凝土柱(以下简称RC柱)和1根现浇对比RC柱试件,进行新型装配整体式RC柱的抗弯承载力试验研究,分析比较两类RC柱的破坏过程、破坏模式、荷载-位移特性、主筋应变发展特点及开裂荷载和极限承载力。研究表明:新型装配整体式RC柱与现浇RC柱具有相同的抗弯承载力特性;基于试验研究,进一步探讨新型。装配整体式RC柱极限承载力的计算理论,为该类RC柱的设计提供参考。     

Large deflection behavior effect in reinforced concrete columns exposed to extreme dynamic loads

Reinforced concretes (RC) have been widely used in constructions. In construction, one of the critical elements carrying a high percentage of the weight is columns which were not used to design to absorb large dynamic load like surface bursts. This study focuses on investigating blast load parameters to design of RC columns to withstand blast detonation. The numerical model is based on finite element analysis using LS-DYNA. Numerical results are validated against blast field tests available in the literature. Couples of simulations are performed with changing blast parameters to study effects of various scaled distances on the nonlinear behavior of RC columns. According to simulation results, the scaled distance has a substantial influence on the blast response of RC columns. With lower scaled distance, higher peak pressure and larger pressure impulse are applied on the RC column. Eventually, keeping the scaled distance unchanged, increasing the charge weight or shorter standoff distance cause more damage to the RC column. Intensive studies are carried out to investigate the effects of scaled distance and charge weight on the damage degree and residual axial load carrying capacity of RC columns with various column width, longitudinal reinforcement ratio and concrete strength. Results of this research will be used to assessment the effect of an explosion on the dynamic behavior of RC columns.     

高轴压比CFRP约束钢筋混凝土圆柱抗震性能试验与有限元分析

为研究高轴压比下FRP约束钢筋混凝土圆柱的抗震性能,对6根碳纤维约束钢筋混凝土圆柱及2根对比柱进行伪静力试验。结果表明:塑性铰区包裹碳纤维可显著改善高轴压比柱的抗震性能,轴压比较高时不应忽略箍筋对核心混凝土的约束贡献。基于OpenSees中的纤维模型,对柱水平力-位移滞回曲线进行有限元模拟。轴压比小于0.45时,数值模拟与试验结果吻合较好;轴压比大于0.45时,考虑核心混凝土受箍筋及FRP双重约束的计算结果与试验结果更为接近。分析轴压比、FRP包裹长度等参数对约束柱抗震性能的影响,轴压比大于0.6时,FRP约束混凝土圆柱的水平承载力开始降低;FRP在塑性铰区的包裹长度为1.2倍柱直径时,可达到与全柱包裹相当的效果。     

Seismic behavior and strength of tubed steel reinforced concrete (SRC) short columns

The seismic behavior of tubed SRC short columns has been investigated by testing eight specimens subjected to combined constant axial compression and lateral cyclic load. Three circular tubed SRC columns (CTSRC) and three square tubed SRC (STSRC) columns were tested in this research with two common SRC columns for comparison. Different axial load ratios (n₀=0.3, 0.4 and 0.5) have been adopted for the constant axial load. The test results indicate that the shear strength, plastic deformation capacity, ductility index, and energy dissipating capacity of the tubed SRC short columns were much higher than those of the SRC columns with the same steel ratio and axial compressive load. The lateral load strength of CTSRC and STSRC short columns increased with an increment in axial load level, while the axial load ratio has no obvious effect on the plastic deformation capacity of CTSRC and STSRC short columns. The steel tubes prevented the shear failure of the concrete more effectively in the circular columns than in the square ones. Shear connector studs should be used in CTSRC and STSRC short columns to prevent bond failure between concrete and flanges of the steel section. A modified ACI design method was adopted to calculate the nominal shear strength of STSRC columns as well as CTSRC columns.     

外贴碳纤维布钢筋混凝土偏压柱强度和延性的影响因素分析

基于2 3根外贴碳纤维布(CFRP)钢筋混凝土偏压柱及对比柱在单调荷载作用下的试验结果,比较分析了在其他条件相同的情况下CFRP粘贴方式、混凝土强度、柱纵向配筋率和荷载偏心值这4个因素对柱的承载力和延性的影响,得出了对外贴碳纤维布加固钢筋混凝土偏压柱有重要意义的结论。     

Cm factor for non-uniform moment diagram in RC columns

Generally, reinforced concrete columns are subjected to a non-uniform moment diagram due to unequal eccentricities at the two ends of the columns or to transverse loads along the columns. Most building codes and material specific codes allow the design of columns with the factor C_m, in order to simplify the general analysis of the column to approximate a column with equivalent uniform moment diagram.This paper presents expressions for C_m according to the type of load that is applied along the column. Two C_m expressions are proposed: the first one approaches the solution using a differential equation based on the elastic behavior of the columns; the second one is based on results obtained through a numerical simulation. This study is valid for hinged reinforced high and normal strength concrete columns, subjected to a sustained and short time load with compression and uniaxial bending.The proposed method can be used both to design and analyze RC columns with enough accuracy for engineering practice and involves higher precision and safety factor in comparison with current codes (Eurocode-2 (2004) [European Committee for Standardization. Eurocode 2: Design of concrete structures—Part 1: General rules and rules for buildings. EN 1992-1-1:2004] ACI-318 (08) [ACI Committee 318. Building code requirements for structural concrete (ACI 318–08). Detroit: American Concrete Institute; 2008]).     

碳纤维布加固钢筋混凝土短柱的抗震性能试验研究

本文对碳纤维布加固的钢筋混凝土短柱的抗震性能进行了试验研究。探讨了轴压比、碳纤维布用量、配箍率和加载顺序等对碳纤维布加固的钢筋混凝土短柱的破坏机理、受力性能及抗震性能的影响。试验结果表明,碳纤维布加固的钢筋混凝土短柱具有很好的延性,能有效提高钢筋混凝土短柱的抗震性能;先施加轴力后进行碳纤维布加固的加载顺序,会降低碳纤维布对柱的约束作用,一定程度上影响对柱的抗剪能力的提高。在此基础上,提出了碳纤维布加固钢筋混凝土短柱的受剪承载力计算公式,可供工程设计和进一步研究参考。     

再生混合钢筋混凝土短柱的轴压性能试验

开展了8根再生混合钢筋混凝土短柱的轴压试验,考察了废弃混凝土类型和混合比对试件荷载-变形曲线及抗压承载力的影响趋势,探讨了现行规范有关短柱抗压承载力的计算方法对于再生混合钢筋混凝土短柱的适用性。研究结果表明:(1)混合比相近时,节段型再生混合短柱的抗压承载力大于块体型再生混合短柱;(2)现浇混凝土抗压强度大于废弃混凝土相应强度时,再生混合短柱的抗压承载力随混合比增大而降低;(3)节段型再生混合短柱的抗压承载力可直接采用现行规范计算,块体型再生混合短柱则需再乘以0.9左右的折减系数。     

使用预拱钢板对矩形预应力混凝土柱进行轴向加固

钢套常用于钢筋混凝土(RC)柱加固。之前的试验研究评估了钢套柱的延性和抗剪性能。然而,实践中常使用预压轴向荷载对RC柱进行加固。尚未对预应力引起的传统柱和新型套管之间的应力滞后效应进行研究。使用一种简单的新型卸载方法,利用预拱钢板提高预应力RC柱的轴向承载力,试验证明该方法能够有效提高RC柱的轴向承载力。提出相应理论模型来计算钢板加固柱的轴向承载力,将模型的预测结果与试验结果相比较,验证了该模型的准确性。     

A new look at reliability of reinforced concrete columns

This paper presents an investigation on reliability of reinforced concrete columns. For short columns, the fiber model is used for generating failure surfaces and strain and stress histories of both steel and concrete fibers under proportional and sequential loads. Two failure criteria, one based on the collection of peak-load points, the other based on prescribed maximum concrete strains are presented. For slender columns, failure surfaces are generated using a method proposed in 1991 by Ba ant et al. (ACI Structural Journal, 1991, 88, 391–401). The reliability estimation of short and slender columns under random loads is formulated by Monte Carlo simulation in the load space. In this space, isoreliability contours for both deterministic and nondeterministic columns under different load paths and load correlations are plotted. It is demonstrated that these factors may have substantial effects on the reliability of reinforced concrete columns. Therefore, the results of this study can be used to support the consideration of load path and load correlation in the development of improved evaluation and design specifications for reinforced concrete columns.