Experimental Study on Fatigue Performance of Reinforced Concrete Beams in Corrosive Environment with Cyclic Loads

In marine environments,reinforced concrete bridge structures are sub-jected to cyclic loads and chloride ingress,which results in corrosion of the rein-forcing bars,early deterioration,durability loss,and a considerable reduction in the fatigue strength.Owing to the complexity of the problem and the difficulty of testing,there are few studies on the fatigue performance of concrete structures under the combined action of corrosion environment and cyclic load.Therefore,a coupling test device for corrosion and cyclic load is designed and fatigue tests of reinforced concrete beams in air environments and chlorine salt corrosive envir-onments are carried out.The fatigue corrosion process,damage mode,and corro-sion features of the test beams as well as chloride ion content in concrete are analyzed.The relationships of deflection,crack,and number of cycles in the dif-ferent environments are given.Results show that the fatigue life of the beam is.greatly reduced under coupled effects of the cyclic load and corrosive environ-ment,the failure fom of the beam is corrosion fatigue damage.The deflection and crack keeps growing with the increase in loading cycles.Under the coupling of cyclic load and corrosion env ironment,the content of chloride ion in concrete is low and there is less variety along the direction of penetration.

Post-fire cyclic behavior of reinforced concrete shear walls

The effects of fire exposure,reinforcement ratio and the presence of axial load under fire on the seismic behavior of reinforced concrete(RC) shear walls were investigated.Five RC shear walls were tested under low cyclic loading.Prior to the cyclic test,three specimens were exposed to fire and two of them were also subjected to a constant axial load.Test results indicate that the ultimate load of the specimen with lower reinforcement ratio is reduced by 15.8%after exposure to elevated temperatures.While the reductions in the energy dissipation and initial stiffness are 59.2%and 51.8%,respectively,which are much higher than those in the ultimate load.However,this deterioration can be slowed down by properly increasing reinforcement due to the strength and stiffness recovery of steel bars after cooling.In addition,the combined action of elevated temperatures and axial load results in more energy dissipation than the action of fire exposure alone.

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 behavior of multiple reinforcement,high-strength concrete columns:experimental and theoretical analysis

This study investigates the seismic performance of multiple reinforcement,high-strength concrete(MRHSC)columns that are characterized by multiple transverse and longitudinal reinforcements in core areas.Eight MRHSC columns were designed and subjected to a low cycle,reversed loading test.The response,including the failure modes,hysteretic behavior,lateral bearing capacity,and displacement ductility,was analyzed.The effects of the axial compression ratio,stirrup form,and stirrup spacing of the central reinforcement configuration on the seismic performance of the columns were studied.Furthermore,an analytical model was developed to predict the backbone force-displacement curves of the MRHSC columns.The test results showed that these columns experienced two failure modes:shear failure and flexure-shear failure.As the axial compression ratio increased,the bearing capacity increased significantly,whereas the deformation capacity and ductility decreased.A decrease in the spacing of central transverse reinforcements improved the ductility and delayed the degradation of load-bearing capacity.The proposed analytical model can accurately predict the lateral force and deformations of MRHSC columns.

带有新型SIP墙板的框架结构抗震性能研究

介绍了带有新型SIP墙板的钢筋混凝土框架结构的低周反复荷载试验,4个试件分别为一榀空框架试件、一榀未开洞的新型SIP墙板框架试件和两榀在不同位置开洞的新型SIP墙板框架试件,且4个试件的钢筋混凝土框架设计均相同,对比4个框架试件的抗震性能,得到了新型SIP墙板对框架结构抗震性能的影响。观察试验现象及分析试验结果表明,新型SIP墙板作为填充墙板对框架结构的延性、强度、耗能等抗震性能是有利的,同时新型墙板与框架结构之间的连接方式是可靠的。

用新型箍筋(S-Clip)的钢筋混凝土桥墩抗震性能试验研究

钢筋混凝土桥柱中,复合箍筋配筋方式非常复杂,施工难度大,用钢量多,且不易保证施工质量。针对该配筋方式存在的问题,提出一种新型的配筋方式,S-Clip筋。为了验证这种新型配筋方式的有效性,按照纵筋配筋率的不同,制作了两组大型桥墩柱的模型。通过两组模型的低周反复荷载试验,研究了分别采用普通复合箍筋和新型S-Clip筋的桥墩柱的抗震性能。试验结果表明,新型配筋方式能够充分发挥材料的力学性能,与原配筋方式具有相同的承载能力,而且在延性方面略有提高。在工程应用中,采用S-Clip筋提高了工程质量,加快了施工速度,节约钢材,具有广泛的应用前景。该应用技术的研究,对工程结构理论和应用技术的发展有着重要的作用。

钢筋混凝土梁循环加载时Kaiser点的确定方法

对常用的几种Kaiser点确定方法进行了比较分析,从参数的选用、判断方法等方面指出了各方法的优点及不足之处。通过对钢筋混凝土梁进行循环加载试验,分析各级荷载下的AE累积计数N与荷载F关联曲线的特点,发现在ln N-F半对数坐标上,关联曲线的拐点坐标具有明显的变化规律,可作为钢筋混凝土梁循环加载时的Kaiser点;提出了用求解曲线拐点来确定Kaiser点的方法,并利用该方法对钢筋混凝土梁受荷过程的Felicity效应进行了分析。

火灾后SRC柱-RC梁框架结构性能反复加载试验研究

对一个SRC柱-RC梁框架在火灾后与另一个对照框架在常温下进行了低周反复加载试验,研究了该框架的火灾后性能,评价了框架的承载力、刚度退化、延性、耗能能力、累积损伤,同时对P-Δ效应进行了分析。试验结果表明,与未暴露在火灾的SRC柱-RC梁框架相比,火灾后SRC柱-RC梁框架的承载力降低、刚度减小、延性系数下降、累积损伤增大,且P-Δ效应更为明显。由于框架柱截面中有核心钢的存在,SRC柱-RC梁框架在火灾后的滞回曲线仍保持饱满,破坏前的承载力可以保持在较高的水平,依然表现出良好的耗能能力。其塑性极限转动超过0.04rad,可以满足中国抗震设计规范的要求。

单轴循环加载海水腐蚀下的SMA加固钢筋混凝土柱轴压性能研究

采用单向循环加载对钢筋混凝土柱受人工海水盐溶液腐蚀后进行形状记忆合金(SMA)加固,研究其受力性能。试验结果表明:试件经盐溶液腐蚀后,SMA加固试件的刚度、延性得到了较大的提升,而承载力提升不大,且随着盐溶液浓度的增加,其刚度、延性以及承载力提升幅度在减小甚至无明显变化,说明SMA丝加固对试件遭受一定浓度盐溶液腐蚀具有抵抗作用。盐溶液浓度的增加会降低钢筋混凝土柱的承载力、刚度和延性,随着盐溶液浓度的增加,承载力降低幅度增大,耗能性能降低幅度变小。盐溶液浓度为15%时,SMA加固试件的耗能性能比未腐蚀未加固试件高约4倍,表明SMA加固能很好地改善试件的耗能性能。

预制U型截面腹板PSRC梁抗震性能研究

对三根U型截面腹板预制装配式型钢混凝土梁进行低周反复荷载试验.分析其滞回曲线、骨架曲线、延性、强度衰减规律、刚度退化规律及耗能,研究不同剪跨比和不同现浇部分混凝土强度对PSRC梁抗震性能的影响。试验结果表明,剪跨比对PSRC梁的破坏特征影响较大;现浇部分混凝土强度能够提高试件的承载力及初始刚度,对变形能力及耗能性能影响较小;通过理论分析建立了PSRC梁屈服承载力计算公式。

单轴循环受拉条件下SP-HFRC力学性能试验研究

通过对21个钢-聚丙烯混杂纤维混凝土(SP-HFRC)试件进行单轴循环受拉试验,研究SP-HFRC在循环受拉条件下的力学行为变化规律。重点分析混杂纤维体积掺量及长径比对应力-应变全曲线、累积塑性应变、刚度退化、应力退化的影响。结果表明:混杂纤维具有逐级阻裂作用使得SP-HFRC试件呈现明显延性破坏特征;应力-应变全曲线卸载点应变与塑性应变呈线性关系;SP-HFRC刚度退化过程随钢纤维体积掺量和长径比增加而减缓,受聚丙烯纤维体积掺量的影响不明显;纤维对应力退化率的影响不明显。在试验结果和相关文献试验数据的基础上,建立了SP-HFRC单轴循环受拉应力-应变全曲线方程,可用于结构非线性和滞回性能等的分析。

Mechanical compression release device in steel bracing system for retrofitting RC frames

The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can release the compressive force in the bracing members is developed, and its performance is evaluated. For comparison, four steel braced RC frames were constructed and tested under reverse cyclic loads. Two of them had different amounts of bracing and the other two had the same amount of bracing but incorporated different type of device, called compression release device, which is developed and described in this paper. It can be concluded from the test results that the newly developed device can effectively be used in steel braced systems to prevent buckling failure of the bracing members. Therefore, the device enhances the ductility of brace-framed systems by allowing an adequate capacity for energy dissipation.

Compressive and cyclic flexural response of double-hooked-end steel fiber reinforced concrete

Recent developments on high-performance double-hooked-end steel fibers have enhanced the wide applications of steel fiber reinforced concrete(SFRC).This study presents the compressive properties and the cyclic flexural performance of the SFRC that were experimentally examined.Three different double-hooked-end steel fibers at 0.25%,0.5%,0.75%,and 1%volume fractions were considered.All fiber types had similar length to diameter ratios,while the first two fiber types had similar anchorage mechanisms(4D)and tensile strength and the third type had different anchorage mechanism(5D)and a higher tensile strength.The increased volumetric ratio of the fibers increased the post-peak compressive strain(ductility),the tensile strength,and the cyclic flexural strength and cumulative energy dissipation characteristics of the SFRC.Among the 4D fibers,the mixtures with the larger steel fibers showed higher flexural strength and more energy dissipation compared to the SFRCs with smaller size fibers.For 1%steel fiber dosage,4D and 5D specimens showed similar cyclic flexural responses.Finally,a 3D finite element model that can predict the monotonic and cyclic flexural responses of the double-hooked-end SFRC was developed.The calibration process considered the results obtained from the inverse analysis to determine the tensile behavior of the SFRC.

纤维织物增强高延性混凝土加固RC短柱抗剪性能试验研究

为研究纤维织物增强高延性混凝土(TR-HDC)加固钢筋混凝土短柱的抗剪性能,设计了6根钢筋混凝土柱,包括2个对比柱和4个TR-HDC加固柱.通过低周反复荷载试验,对比分析剪跨比、纤维织物层数对试件破坏形态、变形、承载力和耗能能力的影响.结果表明:采用TR-HDC加固钢筋混凝土短柱,可显著提高其抗剪承载力;TR-HDC与原混凝土柱协同工作性能良好,加固后的混凝土柱的变形、承载力和耗能能力明显提高;增加纤维织物的层数对钢筋混凝土短柱的抗剪承载力提高幅度较小,但可大幅增强柱的耗能和变形能力;剪跨比较大时,更有利于发挥TR-HDC加固材料的力学性能.基于桁架-拱模型,提出TR-HDC加固钢筋混凝土短柱的抗剪承载力计算方法,计算结果较准确.

低周反复荷载下PSRC梁的抗剪性能

通过对4根低周反复荷载作用下的PSRC梁和1根单调加载的PSRC梁的对比试验,研究了剪跨比、加载方式及现浇混凝土强度对PSRC梁裂缝发展、破坏形态及受剪承载力的影响,并在JGJ 138—2016《组合结构设计规范》基础上建立了适用于PSRC梁斜截面受剪承载力公式。研究结果表明:反复荷载作用下PSRC梁的斜截面受剪承载力比单调加载低,且循环次数越多,受剪承载力降低越多;剪跨比为2试件的极限承载力和斜截面受剪承载力比剪跨比为1的试件低;现浇混凝土强度等级对正向加载时的受剪承载力有一定影响。

预应力混凝土梁-型钢混凝土柱框架节点抗震性能试验研究

预应力混凝土框架结构具有较好的抗裂性能和较高的承载能力,但在实际工程中,裂缝控制要求较为严格,容易出现预应力混凝土框架梁端配筋过多,进而导致梁端承载力过剩,难以实现“强柱弱梁”的抗震设计原则。针对这一问题,提出3种不同连接形式的预应力混凝土梁-型钢混凝土柱节点,通过6个预应力混凝土梁-型钢混凝土柱框架节点试件的低周反复加载试验,研究抗裂等级(影响梁预应力筋数量)、梁柱节点形式对节点破坏形态、滞回曲线、延性、刚度退化等影响规律。研究结果表明:3种不同连接形式的6个试件均发生了“梁端弯剪破坏”,而节点和柱破坏轻微,预应力混凝土框架节点通过使用型钢混凝土柱实现了“强柱弱梁”的抗震设计目标,试件延性和耗能能力较好;二级抗裂的节点试件强度退化、割线刚度退化较三级抗裂更快,抗震性能稍差;三种形式的节点中,形式2节点的强度退化、刚度退化较慢,抗震性能较好,且施工方便。

反复荷载下方钢管型钢再生混凝土组合柱抗震性能试验研究

为研究方钢管型钢再生混凝土组合柱的抗震性能,通过对9个组合柱试件进行低周反复荷载试验,对其地震破坏特征进行分析,并详细探究再生粗骨料取代率、型钢配钢率、方钢管宽厚比和轴压比等影响参数对组合柱承载力、延性及耗能能力等抗震性能指标的影响。研究结果表明:在反复水平荷载作用下组合柱呈现典型的压弯塑性铰破坏模式。组合柱的荷载-位移滞回曲线呈饱满“纺梭形”,具有较好的耗能能力。再生粗骨料取代率对组合柱的承载力的影响较小,随着再生粗骨料取代率的增加,组合柱的延性和耗能能力逐渐下降,延性和耗能能力最大分别下降7.83%和7.6%,组合柱试件承载力先升高后下降,承载力最大变化幅值为1.98%,影响幅值较小。随着方钢管宽厚比的减小或型钢配钢率的提高,组合柱的承载力和延性均得到提高,宽厚比从100降至33,承载力提高了57.44%,而型钢配钢率从4.2%增长至6.3%,承载力和延性则分别提高了21.45%和20.44%,说明方钢管宽厚比和型钢配钢率对组合柱抗震性能影响较大。另外,增大轴压比对组合柱试件的抗震性能不利,随着轴压比的增大,组合柱的滞回曲线饱满度下降,延性降低,轴压比从0.2提高到0.6,延性降低了11.11%。研究结论可为方钢管型钢再生混凝土组合柱的抗震设计提供参考。

火灾后装配式钢筋混凝土梁疲劳性能试验研究

开展火灾后装配式钢筋混凝土结构承载性能研究,对于其抗灾能力提升具有重要的理论和现实意义。为模拟装配式钢筋混凝土梁装配连接节点性能,设计了4根两端为预制部分、钢筋采用灌浆套筒连接的对接连接足尺装配式钢筋混凝土简支梁试件,对1根试件进行火灾作用后的静力加载试验,对另外3根试件进行火灾作用后循环加载下的耐疲劳性能试验。结果表明:经历火灾作用后的试验梁,静载破坏呈现延性破坏特征,而疲劳破坏则呈现明显的脆性破坏特征;循环荷载下限值相同时,随着循环荷载上限值的增加,试验梁实测疲劳寿命明显降低,循环荷载幅值为150和120 kN时的实测疲劳寿命比幅值为90 kN时分别降低55.07%和34.78%,说明循环荷载幅值对火灾后装配式钢筋混凝土梁的耐疲劳性能影响显著。

成型钢筋混凝土柱抗震性能非线性有限元分析

成型钢筋是采用机械加工成型的钢筋制品,能有效提高钢筋加工质量与效率,降低加工成本,减少废料损耗,具有广阔的应用前景。目前,有关成型钢筋混凝土构件的研究主要集中在楼板和剪力墙方面,对柱的研究则相对较少。基于有限元软件ABAQUS,建立了成型钢筋混凝土柱的滞回分析模型。基于完成的3根成型钢筋混凝土柱抗震试验研究结果,验证了该模型合理性。在此基础上,开展了有限元参数分析,主要参数包括成型方式(穿箍、绕箍)、轴压比(0.2,0.4,0.6,0.8)、混凝土强度等级(C30,C40,C50,C60)、纵筋配筋率(0.78%,1.1%,1.5%,3.0%)、配箍率(0.45%,0.7%,1.0%)及箍筋构造(体积配箍率相同,双肢或三肢)等。分析结果表明:穿箍成型、绕箍成型和绑扎对比试件的承载力相近,相差≤5%;当轴压比从0.2增加到0.8时,试件的承载力提高22%,而延性系数下降42%;当纵筋配筋率从0.78%增加到1.5%时,试件的承载力提高31%,延性系数提高11%,而当配筋率从1.5%增加到3.1%时,试件的承载力提高39%,延性系数则降低52%;当纵筋配筋率从0.78%增加到1.5%时,双肢箍试件比三肢箍试件的延性系数高约20%,而当配筋率从1.5%增加到3.1%时,双肢箍试件的延性系数较三肢箍试件低约25%,这主要是由于在高配筋率情况下三肢箍对截面约束效果更好所致。

矿渣基地聚物混凝土柱抗震性能研究

为了研究不同强度等级的矿渣基地聚物混凝土柱的抗震性能,设计了3个普通混凝土悬臂柱试件和3个矿渣基地聚物混凝土悬臂柱试件,通过低周反复荷载试验,对地聚物混凝土柱的破坏模式、裂缝发展、滞回性能、位移延性、耗能性能、刚度与强度退化和承载力等进行了评估,分析了混凝土种类、混凝土强度对试件抗震性能的影响。结果表明,在低周反复荷载作用下,与普通混凝土试件相比,矿渣基地聚物混凝土柱的抗震性能并未明显改善;提高地聚物混凝土强度会改变地聚物混凝土柱的破坏模式,从而对部分抗震性能(延性、耗能能力)产生不利的影响;验证表明《混凝土结构设计规范》(GB 50010—2010)中受弯承载力计算公式对于地聚物混凝土构件的计算结果偏小,拓展到工程应用中偏安全。