Bi-directional interaction of joint shear strength in non-seismically designed corner RC beam-column connections under seismic loading

Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the information on the seismic behavior of joints of space frames(3D joints)is insufficient.The 3D joints are subjected to bi-directional excitation,which results in an interaction between the shear strength obtained for the joint in the two orthogonal directions separately.The bi-directional seismic behavior of corner reinforced concrete(RC)joints is the focus of this study.First,a detailed finite element(FE)model using the FE software Abaqus,is developed and validated using the test results from the literature.The validated modeling procedure is used to conduct a parametric study to investigate the influence of different parameters such as concrete strength,dimensions of main and transverse beams framing into the joint,presence or absence of a slab,axial load ratio and loading direction on the seismic behavior of joints.By subjecting the models to different combinations of loads on the beams along perpendicular directions,the interaction of the joint shear strength in two orthogonal directions is studied.The comparison of the interaction curves of the joints obtained from the numerical study with a quadratic(circular)interaction curve indicates that in a majority of cases,the quadratic interaction model can represent the strength interaction diagrams of RC beam to column connections with governing joint shear failure reasonably well.

The Knee Joint Design and Control of Above-knee Intelligent Bionic Leg Based on Magneto-rheological Damper

The above-knee intelligent bionic leg is very helpful to amputees in the area of rehabilitation medicine. This paper first introduces the functional demand of the above-knee prosthesis design. Then, the advantages of the four-bar link mechanism and the magneto-rheological （MR） damper are analyzed in detail. The fixed position of the MR damper is optimized and a virtual prototype of knee joint is given. In the end, the system model of kinematics, dynamics, and controller are given and a control experiment is performed. The control experiment indicates that the intelligent bionic leg with multi-axis knee is able to realize gait tracking of the amputee＇s healthy leg based on semi-active control of the MR damper.

Pushover analysis of reinforced concrete frames considering shear failure at beam-column joints

Since most current seismic capacity evaluations of reinforced concrete （RC） frame structures are implemented by either static pushover analysis （PA） or dynamic time history analysis, with diverse settings of the plastic hinges （PHs） on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints （BCJs） during major earthquakes is commonly neglected. This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. To verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements. By considering shear failure at BCJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.

Seismic Behaviour of Beam-Column Joints of Precast and Partial Steel Reinforced Concrete

A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is located in the core joint region and the connections between concrete members. This paper presents an experimental study of a series of PPSRC specimens. These specimens are tested under low cyclic loading.Experimental results demonstrate that the bearing capacity of the PPSRC specimens is 3 times that of the ordinary reinforced concrete( RC) beam-column joints. The strength and stiffness degradation rates are slower compared with that of the RC beam-column joints. In addition,the strength of the core joint region and the connections is higher than other parts of the PPSRC specimens. Beam failure occurs firstly for the PPSRC specimens,followed by column failure and connections failure. The failure of the core joint region occurs finally.Test results show that the seismic performance of the PPSRC is better than that of the ordinary RC beam-column joints.

Finite Element Analysis (FEA) for the Beam-Column Joint Subjected to Cyclic Loading Was Performed Using ANSYS

This paper analyses the seismic performance of exterior beam-column joints strengthened with unconventional reinforcement detailing. The beam-column joint specimens were tested with reverse cyclic loading applied at the beam end. The samples were divided into two groups based on the joint reinforcement detailing. The first group (Group A) of three non-ductility specimens had joint detailing in accordance with the construction code of practice in India IS456-2000, and the second group (Group B) of three ductility specimens had joint reinforcement detailed as per IS13920-1993, with similar axial load cases as the first group. The experimental studies are proven with the analytical studies carried out by finite element models using ANSYS. The results show that the hysteresis simulation is satisfactory for both un-strengthened and ferrocement strengthened specimens. Furthermore, when ferrocement strengthening is employed, the strengthened beam-column joints exhibit better structural performance than the un-strengthened specimens of about 31.56% and 38.98 for DD-T1 and DD-T2 respectively. The analytical shear strength predictions were in line with the test results reported in the literature, thus adding confidence to the validity of the proposed models.

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 stirIup 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.

Seismic performance and global ductility of RC frames rehabilitated with retrofi tted joints by CFRP laminates

This paper presents a new FRP retrofi tting scheme to strengthen local beam-column joints in reinforced concrete(RC) frames.The new retrofi tting scheme was proposed following a preliminary study of four different existing retrofi tting schemes.A numerical simulation was conducted to evaluate the effectiveness of FRP-strengthened reinforced concrete frames by bridging behavior of local joints to the whole structure.Local confi nement effects due to varying retrofi tting schemes in the joints were simulated in the frame model.The seismic behavior factor was used to evaluate the seismic performance of the strengthened RC frames.The results demonstrated that the new proposed retrofi tting scheme was robust and promising,and fi nite element analysis appropriately captured the strength and global ductility of the frame due to upgrading of the local joints.

基于转动摩擦铰阻尼器的干式装配梁-柱节点抗震性能试验

基于转动摩擦铰阻尼器(RFHD),提出了转动摩擦耗能干式装配梁-柱节点(DRFDBJ)。为了验证DRFDBJ结构对于实现预期力学性能的可行性和合理性,以施加在摩擦片表面的螺栓预紧力(P_(c))为变量,开展了2个工况下的DRFDBJ试件低周往复拟静力试验研究。结果表明:DRFDBJ结构的力学性能主要由RFHD提供并控制,试验中节点呈现了稳定的承载力和理想的变形、耗能能力,并实现了预期的损伤集中;2个不同P_(c)水准下节点承载力的试验值与理论值误差不超过5%,通过调整P_(c)可实现节点承载力的调控,为DRFDBJ结构承载力的可调控提供了支撑。

Study on Strengthening of RC Beam Column Joint Using Hybrid FRP Composites

Beam-Column joints are critical zones in reinforced concrete structures which are most vulnerable to earthquake forces. Hence strengthening beam-column joint is vital to save the structure and its inhabitants in case of seismic forces. Numerous retrofitting works using fibre reinforced polymer (FRP) composites are being undertaken worldwide. This work aims to investigate the effectiveness of strengthening beam-column joints using natural and artificial fibres. In this study, basalt (natural fibres) as monolithic composite (BFRP) and as hybrid composite along with glass (artificial fibres) were used for strengthening of beam-column joints. Totally six specimens were prepared and tested under monotonic loading. Specimen details used were: two control specimen, two specimens for monolithic wrapping and remaining two specimens for hybrid wrapping. The test results were compared with control and rehabilitated specimens. The performance of the treated joints was studied using the following parameters: initial and ultimate cracking loads, energy absorption, deflection ductility and stiffness at ultimate. From the test results, it was found that the hybrid combination of Basalt and Glass FRPs were found to be more effective in the treatment of beam-column joints. The strong column weak beam concept was achieved by failure in beam portion which helped in preventing the catastrophic failure of the entire structure.

增设角部阻尼器箍头榫木节点的抗震性能

为了给广府木结构的修复提供理论依据,采用菠萝格木材设计制作了5个箍头榫节点试件。考虑到榫卯构造尺寸的影响,首先进行了未加固无损节点的拟静力试验。然后,采用对原有外观影响较小的雀替型阻尼器对上述节点损坏试件进行加固,以尽可能保留建筑的原始风貌。最后,对加固节点进行拟静力试验,以研究节点的抗震性能变化以及阻尼器的加固效果。结果表明:采用阻尼器加固后的节点试件在加载至破坏时,榫卯处压痕明显,梁外榫外侧劈裂、脱榫现象明显,阻尼器脚部的橡胶与钢板有一定的脱离现象;对节点增设阻尼器能够弥补节点初期损伤导致的受力性能下降,为残损榫卯节点提供较好的后期刚度,提高节点的承载能力和耗能能力;与未加固试件相比,增设阻尼器后,试件的后期刚度、极限承载力、总滞回耗能均有所增加,分别提高18%、19%、20%以上。文中还在已有简化力学模型的基础上,结合OpenSees,提出了一种应用于箍头榫木结构的宏观模型建模方法。采用该方法得到的节点滞回曲线与试验结果吻合良好,可以有效模拟阻尼器加固的箍头榫木节点的滞回耗能特性。

基于Pushover方法的耗能自复位铰节点框架结构抗震性能分析

基于Pushover分析方法研究设置耗能自复位铰节点(EDSC-HJ)的钢筋混凝土框架结构的抗震性能.首先介绍EDSC-HJ框架的结构形式,并建立了EDSC-HJ框架结构的有限元模型,通过与振动台试验结果对比验证数值模拟的正确性;其次使用Pushover方法计算EDSC-HJ框架有控结构与无控结构的抗震性能并设计节点弹性恢复装置和耗能装置的力学参数.结果表明:EDSC-HJ框架结构节点相对转动刚度比的合理取值区间为0.05~0.5;设置节点阻尼器的EDSC-HJ有控结构的层间位移响应下降了76%,且满足限值要求;由于节点阻尼器的设置提高了结构的附加抗侧刚度,有控结构的基底剪力响应提高了23%.EDSC-HJ框架结构的抗震性能明显优于钢筋混凝土框架(RCF)结构,具有良好的韧性结构特征.

双阶受力干式装配梁-柱节点抗震性能试验研究

研究提出了一种双阶受力干式装配梁-柱节点(DADBJ)。该节点的关键组件是摩擦铰(RFH)和预设缝防屈曲钢板(SBRSP),具备2个受力工作阶段和损伤集中易修复的特性。为了验证DADBJ构造的合理性,揭示其双阶段受力工作机理,设计加工了DADBJ试件,以SBRSP的预设缝隙宽度作为试验变量,进行了2个工况的低周往复拟静力试验。结果表明:提出的DADBJ构造实现了预期的双阶段受力特性,第一阶段由RFH提供节点的力学性能,第二阶段由RFH和SBRSP共同提供节点的力学性能;DADBJ的损伤集中于芯板,通过更换SBRSP芯板对节点快速修复,节点的性能可恢复到初始状态;SBRSP的预设缝隙宽度可直接决定DADBJ第二阶段的启动位移;提出的DADBJ双阶屈服荷载理论公式和二阶启动位移理论公式精确度好。该研究可为装配式框架结构和多阶受力型结构的设计和研究提供参考。

剪切型阻尼器增强大头榫节点模型试验研究

中国传统木结构建筑破坏主要由榫卯节点松动、变形及拔榫引起.为解决榫卯节点容易松动、变形及拔榫破坏问题,引入节点阻尼器技术,在传统木结构建筑榫卯节点处安装扇形剪切型阻尼器.为研究传统木结构典型节点大头榫安装阻尼器后的抗震性能及增强效果,设计制作了6个大头榫足尺节点模型,其中3个榫卯节点未装阻尼器,3个榫卯节点安装阻尼器.通过低周反复加载试验研究6个试验模型的滞回特性、骨架曲线、刚度退化曲线及等效黏滞阻尼系数变化规律.研究结果表明:安装阻尼器可以有效控制节点的拔榫破坏;同时有效增强节点耗能、强度及刚度;安装阻尼器节点模型的极限承载力是未安装节点模型的1.5~3.5倍.

泸定M_(S)6.8级地震大岗山拱坝横缝及阻尼器工作性态分析

横缝作为高拱坝强度的薄弱部位,在地震作用下的工作性态至关重要。泸定M_(S)6.8级(面波震级)地震中,大岗山拱坝坝顶顺河向峰值加速度PGA达到586.63 cm/s^(2),坝址烈度达Ⅷ度,是唯一经历近场强震考验及设置阻尼器抗震措施的200m级高拱坝。依据震后大坝横缝及阻尼器宏观现象和监测原观数据,对横缝及阻尼器工作性态进行了分析,结果表明地震过程中大坝横缝存在开合过程,震后部分横缝存在残余张开,开度增量在-0.05~0.43mm之间,总体表现为下游侧略大于上游侧,左岸大于右岸,初步分析主要由于横缝高频开合导致灌浆材料部分剥离测缝计无法复位,拱坝仍处于弹性工作状态;拱坝坝顶3组阻尼器在地震前后两端位移增量在0.32~1.06 mm之间,表现为拉伸,其中靠近拱冠梁的16#横缝位移增量最大。结合测缝计监测成果初步分析,阻尼器在强震作用下对降低局部区域横缝开度有一定作用,在主震后的历次余震中阻尼器未见明显动作痕迹。相关成果可为震后大坝安全评估、高拱坝抗震设计及研究提供参考。

新型雀替式黏弹性阻尼器增强传统木结构节点试验研究

为提高中国传统木结构房屋的抗震性能,本工作采用新型雀替式黏弹性阻尼器对榫卯节点进行加固,制作了两个足尺台阶透榫节点模型,采用新型雀替式黏弹性阻尼器对其中一个节点进行加固。通过低周反复荷载试验,分析台阶透榫节点加固前后的滞回曲线、骨架曲线、刚度退化和耗能能力等抗震性能指标。结果表明:使用新型雀替式黏弹性阻尼器加固台阶透榫节点是可行的,加固后节点滞回曲线的滑移和捏缩现象大幅减轻,滞回环面积增大,耗能能力提升204.5%;加固后试件的骨架曲线斜率和极限承载力均得到大幅提升,正向承载力最大提升173.8%,负向承载力最大提升162.2%;新型雀替式黏弹性阻尼器可以极大提高台阶透榫节点的刚度储备,加固后节点的初始刚度提升216.1%;新型雀替式黏弹性阻尼器加固台阶透榫节点有利于防止节点拔榫破坏,加固后节点的残余拔榫量正负向分别减少33.35 mm和22.2 mm。这些结果可为传统木结构的加固工程提供参考。

扇型雀替式黏弹性阻尼器增强传统木结构半榫节点试验研究

为探究云南典型穿斗式木结构榫卯节点的加固方法,本工作使用云南本地松木制作了两个半榫节点,采用扇形雀替式黏弹性阻尼器加固半榫节点,通过低周往复荷载试验对比研究加固前后节点的力学性能。结果表明,加固后半榫节点在30 mm的加载幅值内滞回曲线的滑移和捏缩现象减轻,滞回环面积增大。加固半榫节点(RHT)的最大弯矩为4.9 kN·m,约为未加固半榫节点(HT)的3.92倍;承载力大幅提升,正向承载力最大提升233.6%,负向承载力最大提升375.7%;刚度储备增大,RHT的平均刚度为96.28 kN·m/rad,较未加固节点刚度提升137.8%;耗能能力增强,加固后半榫节点的耗能能力提高50.52%。

增效转动摩擦阻尼器的工作机理及力学性能分析

该文提出了一种新型增效转动摩擦阻尼器(ERFD),由杠杆原理放大其转动角度,进而提高其耗能能力,适用于梁柱节点。为验证ERFD工作机理的可行性,采用ABAQUS软件建立其有限元数值模型,以相同摩擦工况的扇形摩擦阻尼器(SFD)和未放大的转动摩擦阻尼器(RFD)作为对照模型进行力学性能分析,进而探究ERFD耗能增效机制。研究结果表明:ERFD的承载力、刚度和耗能均得到明显提高,较于SFD分别增大了17.63%、12.54%、14.53%;其他三个改变摩擦片布置方式的试件的刚度和耗能比ERFD分别减少29.38%、58.67%、70.76%和29.55%、58.96%、70.58%;ERFD的承载能力和耗能能力相较于RFD放大了92.38%、85.49%。这说明ERFD耗能能力良好,且三个点均布置摩擦面的整体力学性能较好,且增效效果显著。

钢板阻尼连接的装配式边柱减震节点滞回性能试验研究

为研究不同耗能机制的钢板阻尼连接对装配式钢框架梁柱节点力学性能的影响,本文对两个钢板阻尼连接的装配式边柱减震节点试件进行拟静力试验研究,获得试件的破坏模态、滞回曲线、骨架曲线、滑移曲线和应变发展情况,分析试件的承载力、延性、耗能能力、弯矩–转角等性能指标。研究结果表明:钢板阻尼连接的装配式边柱减震节点具有较好的承载性能和耗能性能,在试验过程中未发现梁、柱主体构件及节点核心区破坏现象,可将损伤集中控制于钢板阻尼连接处。耗能钢板圆形开孔的承压型钢板阻尼连接的装配式边柱减震节点(试件BSDC)主要为耗能钢板发生受拉破坏,长圆形开孔的摩擦型钢板阻尼连接的装配式边柱减震节点(试件FSDC)出现明显的滑移行为,在钢板阻尼连接处产生明显的弯曲残余变形。试件FSDC的承载力略低于试件BSDC,且由于往复荷载下的摩擦系数和预紧力损伤,加载后期试件FSDC承载力出现轻微下降,但其滞回曲线较为饱满,滞回行为稳定,而试件BSDC由于耗能钢板断裂导致承载力急剧下降。试件FSDC的耗能能力和延性均优于试件BSDC,摩擦型钢板阻尼连接耗能占比为88%,承压型钢板阻尼连接为67%,实现了集中耗能,钢板阻尼连接处的滑移行为可改善试件的耗能性能和变形能力。

黏弹性阻尼器加固穿斗式平面外木排架的抗震性能

为研究穿斗式木结构的抗震性能及其加固方法,选取杉木和松木两种木材,设计并制作四榀穿斗式木结构平面外框架,采用黏弹性阻尼器加固试件,对加固和未加固的木框架分别进行低周往复荷载试验,研究结构的抗震性能及阻尼器的加固效果.研究结果表明:加固后木排架滞回曲线的滑移和捏缩现象大幅减轻,滞回环面积增大,等效黏滞阻尼比增加,耗能能力增强,杉木和松木排架耗能能力分别提高83.31%和286.34%;加固后试件的骨架曲线斜率和极限承载力均得到大幅提升,斜率大致随加载幅值增大而增大,极限承载力杉木排架最大提升218.32%,松木排架最大提升458.89%;加固后木结构框架的刚度储备增高,初始刚度杉木试件提升46.9%,松木试件提升264.1%;杉木试件在安装阻尼器后节点的残余拔榫量减少15.06 mm,松木试件减少31.96 mm.

SMA绞线预制梁-柱自复位耗能节点数值研究与参数优化

为了提高预制混凝土框架的抗震能力并控制震后残余变形,提出了一种新型的混合自复位预制混凝土梁柱节点(self-centring precast concrete beam-column connection,SC-PCBCC),其中采用了旋转摩擦阻尼器(rotational friction hinge damper,RFHD)和形状记忆合金(shape memory alloy,SMA)并联的结构。重点探讨了使用SMA绞线控制的自复位装置对SC-PCBCC进行改进。首先,介绍了SC-PCBCC的结构和工作原理;其次验证对比了1.0%、1.5%、2%和2.0%预应变下的超弹性1×7 SMA绞线、RFHD和SC-PCBCC的有限元模型,并进行了初步验证。研究结果表明,该节点具有较高的刚度、承载力、耗能能力以及较好的复位性能;最后对SC-PCBCC中SMA绞线的关键参数:SMA绞线预应变、直径和长度进行了参数分析,以优化其抗震性能。建议SC-PCBCC使用的SMA绞线初始预应变、直径和长度范围分别为1.5%~2.0%、15~18 mm和175~205 mm,以实现SC-PCBCC的优异承载性能、能量耗散和自复位性能。此外,节点中的SMA绞线和RFHD可在震后快速更换,实现高效灾后修复。总体而言,所提出的SC-PCBCC表现出了卓越的减震能力、自复位能力和可修复性。