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.

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.

The Effects of Degradation Phenomena of the Steel-Concrete Interface in Reinforced Concrete Structures

Reinforced concrete (RC) constructions are the innovation of sustainable constructions replacing masonry constructions. Despite this, the use of concrete and steel to improve the performance of structural members in service is a recurring problem due to the immediate or overtime appearance of cracks. The objective of this work was therefore to assess the damage phenomena of the steel-concrete interface in order to assess the performance of an RC structure. Samples of approximately 30 cm of reinforcement attacked by rust were taken from broken reinforced concrete columns and beams in order to determine the impact of corrosion on high adhesion steel (HA) and therefore on its ability to resist. The experimental results have shown that the corrosion degradation rates of reinforcing bars of different diameters increase as the diameter of the reinforcing bars decreases: 5% for HA12;23.75% for HA8 and 50% for HA6. Using the approach proposed by Mangat and Elgalf on the bearing capacity as a function of the progress of the corrosion phenomenon, these rates made it possible to assess the new fracture limits of corroded HA steels. For HA6 respectively HA8 and HA12, their initial limit resistances will decrease by 4/4, 3/4 and 1/4. Based on the results of this study and in order to guarantee their durability, an RC structure can be dimensioned by taking into account the effects of reinforcement corrosion.

Fatigue properties of special kind of reinforced concrete composite beams

The special reinforced concrete composite beam consists of a steel fiber reinforced self-stressing concrete composite layer and a reinforced concrete T-beam, and constructional bars are set up at their bonding interface. Fatigue properties of the composite beam under the action of negative moment were experimentally studied. Through inverted loading mode the load-beating state of a composite beam was simulated under the action of negative moment. With the ratios of constructional bars being 0, 0.082% and 0.164% respectively as parameters, the effects of constructional bars on the properties of composite beam, such as fatigue life, crack propagation, rigidity loss as well as damage behavior of bonding interface, were studied. The mechanism of the constructional bars on the fatigue properties of the composite beams and the restriction mechanism of crack widths and rigidity loss were analyzed. The test results show that the constructional bars can enhance the shear resistance of the bonding interface between composite layer and old concrete beam and restrict expanding of steel fiber reinforced self-stressing concrete, which are beneficial to synergistic action of composite layer and old concrete beam, to reducing the stress amplitude of bars and the crack width of composite layer, and to increasing the durability and fatigue life of the composite beam.

钢板混凝土墙-钢筋混凝土楼板连接节点抗剪性能

模块化技术正在推动新一代核电厂的设计和发展,兼具优良工作性能和工业化施工性能的钢板混凝土(SC)结构在模块化结构具有广泛应用前景。SC墙-RC楼板连接节点作为SC模块结构与RC结构之间的典型传力构件,其结构设计必须既要保证荷载的有效传递,又要考虑模块化施工的可行性。为研究SC墙-RC楼板连接节点抗剪性能,设计并完成了2个“薄墙厚板型”SC墙-RC楼板连接节点循环加载试验,包括GB/T 51340—2018建议的钢筋连接器连接、附加抗剪键等两种连接方式。试验结果表明:在剪跨比1.50下试件均发生RC楼板弯剪破坏,节点主要传力破坏路径为加载端至楼板根部的斜压杆区域,说明节点结合面不配置抗剪键仍满足抗剪要求;试验过程中,直螺纹钢筋套筒无滑脱、未发生钢筋或焊缝拉断,延性系数均大于4,说明钢筋连接器连接的传力性能良好,可作为SC墙-RC楼板连接节点的有效连接方式;该节点核心区仍属于抗剪薄弱区域,若要满足“全强度连接”设计准则,核心区对拉筋体积含钢率应不低于0.59%。

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.

马鞍山长江公铁大桥Z3号桥塔施工关键技术

巢马城际铁路马鞍山长江公铁大桥主航道桥为(112+392+2×1120+392+112)m三塔钢桁梁斜拉桥,Z3号桥塔为超高多肢钢-混组合塔,高308 m。上塔柱钢结构高87.5 m,分13个吊装节段,最重505 t;中、下塔柱混凝土结构高217.5 m,分38个节段液压爬模施工;钢-混结合段高3 m,内部采用PBL键+剪力钉+高强度钢锚杆+高强度混凝土结构形式。在中塔柱设置钢管临时横撑控制塔柱线形及应力;下横梁采用落地支架法分层施工,与对应塔柱同步浇筑;钢-混结合段混凝土采用C60细石补偿收缩混凝土+高强度灌浆料,保证了混凝土施工质量;采用工厂“2+1”立体匹配制造、“提升站+运输栈桥”钢塔节段转运等技术,并研制15000 t•m超大型塔吊,实现了钢塔柱大节段的制造、整体滩地运输和吊装;钢塔节段间采用栓焊组合连接形式,通过设置工艺隔板、双面坡口等措施控制了钢塔焊接变形;利用定位桁架临时锁定钢塔合龙段实现了钢塔的精确合龙,定位桁架受力及变形均满足要求。

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。

预应力混凝土梁-型钢混凝土柱新型框架节点受剪承载力计算方法

梁柱节点受剪承载力计算是混凝土框架结构节点抗震设计的关键点之一,由于节点剪力传递机理与构造的复杂性,目前尚未形成完善的节点受剪承载力计算理论。该文阐述了预应力混凝土梁-型钢混凝土柱新型框架节点的受力机理,并基于桁架模型和斜压杆模型,提出了一种同时考虑预应力筋与型钢贡献的节点受剪承载力计算方法。开展了新型节点受力性能拟静力试验,分别选取了梁端破坏与节点剪切破坏两种破坏形式的节点试验数据,对所建立的新型节点受剪承载力计算方法进行了验证评估,结果表明,该文提出的预应力混凝土梁-型钢混凝土柱框架节点承载力计算方法具有较好的精度。

环口板加强带脱空缺陷的钢管混凝土T型节点滞回性能试验研究

为研究环口板加强带脱空缺陷的钢管混凝土T型节点的抗震性能,完成了12根节点试件在主管受恒定轴拉力与支管受轴向往复荷载作用下的滞回试验,基于试件破坏模式、荷载-位移滞回关系和应变发展考察了采用环口板加强带脱空缺陷T型节点试件的效果,并对比分析支主管直径比和主管径厚比对试件加强效果的影响。试验结果表明:采用环口板加强T型节点有效抑制了脱空缺陷导致的主管塑性变形,并实现带缺陷T型节点承载力、刚度、延性和耗能能力的完全恢复,甚至优于相应的无脱空试件,其中加强试件的承载力较带脱空缺陷试件提升12.6%以上,较无脱空试件提升6.5%以上,表明经合理设计的环口板加强措施能够弥补脱空缺陷对节点抗震性能的不利影响。

某超高层项目钢管混凝土组合柱应用

某超高层项目荷载较大,导致框架柱截面较大,严重影响建筑空间使用。采用钢管混凝土组合柱,和型钢混凝土柱相比,标准层每根柱节约建筑有效使用面积1.5~1.8m^(2),结构主体成本节约近1000万元。提出了对钢管进行开孔的梁柱节点做法并分析五种不同节点方案,采用大型通用有限元软件ABAQUS进行仿真分析,充分考虑框架梁对节点的约束作用,得到五种节点方案的极限承载力及钢管的最大应力,结果表明采用钢管开孔的梁柱节点做法可行,并得到最合理的开孔形式;分别对7种不同箍筋形式进行受力性能分析,并考虑实际施工因素,得到最为合理的箍筋设置形式。

基于软化效应的型钢混凝土节点抗剪承载力计算

根据现有试验资料,对规范YB 9082—2006《钢骨混凝土结构技术规程》和JGJ 138—2016《组合结构设计规范》中型钢混凝土节点抗剪承载力计算公式进行计算,结果表明,规范计算结果偏于保守,且离散性较大,主要原因在于混凝土项取值过于简化,导致计算结果离散性大。基于软化效应,考虑主拉方向对主压方向强度的弱化影响,对混凝土强度、配箍率、型钢约束强度、轴压比等因素的影响进行量化分析,并提出抗剪承载力计算公式中混凝土项的修正公式,结果表明,所提公式可以合理考虑各因素的影响,提高计算结果的准确性并降低离散性。

钢筋混凝土水池壁板水平施工缝抗渗性能试验研究

钢筋混凝土水池壁板因混凝土浇筑施工间断形成水平施工缝,造成新旧混凝土无法形成良好连接,在高水压作用下易出现渗漏。本文对不同混凝土材料及模拟水平施工缝试块进行了抗渗试验,对比分析了其抗渗性能,试验结果表明,添加聚丙烯纤维和内掺水泥基渗透结晶防水材料均能一定程度提高混凝土抗渗性能,而施工缝处的抗渗性能远低于混凝土自防水性能,对水平施工缝迎水面涂抹水泥基渗透结晶防水材料能有效提高该处的抗渗性能。对2片比例为1∶2的缩尺钢筋混凝土水池壁板进行了一次成型和考虑施工缝的二次成型局部渗透性能试验,试验结果表明,施工缝处混凝土因浇筑、振捣和养护不充分,池壁容易形成贯通裂缝,难以达到混凝土自防水目标要求。采用改性混凝土材料及在相关部位进行表面处理,能有效提高关键部位抗渗性能,进而提高整体抗渗性能。采用BP神经网络,建立了混凝土抗渗性能与其材料参数和施工工艺之间的非线性预测模型。

轴压比和面承板厚度对混合节点抗震性能的影响

为了研究新型柱全截面隔板式钢筋混凝土柱-钢梁(RCS)混合框架节点形式的抗震性能,考虑不同轴压比和面承板厚度的影响,对2组共6个3/4比例的梁柱节点进行低周往复加载试验研究.试验中所有试件均发生设计预期的节点剪切破坏,滞回曲线呈弓型,表明节点具有良好的抗震性能.试件最终因节点区的混凝土开裂剥落而丧失承载力.试验结果表明,当轴压比为0~0.25时,随着轴压比的增大,RCS节点开裂荷载有所增大,峰值荷载前斜裂缝数量减少、宽度减小,试件的承载力、刚度和耗能能力均有所提高.节点域柱纵筋黏结应力随轴压比增大而减小,表明节点域内黏结状况有明显改善.相较于单向面承板试件,双向面承板试件在承载能力、延性和耗能能力方面均表现出显著提高;当双向面承板厚度由6 mm增加至10 mm时,试件峰值承载力和刚度的提升幅度相对有限.

考虑节点域影响的钢管约束钢筋混凝土柱框架结构抗震性能研究

近年来,钢管约束钢筋混凝土(STRC)柱结构已成为组合结构研究热点之一。约束钢管在柱端断开能够充分发挥其对混凝土的约束效果,增强柱体承载力及抗震性能。然而,节点区域将变得相对薄弱,传统结构体系性能分析中多以节点为刚性域,不考虑节点本身的变形及受损对结构的影响,这将导致STRC柱结构分析及设计存在一定的安全隐患。本文在STRC框架结构中引入节点单元Joint2D来模拟节点的受荷变形全过程,对比分析了节点单元对抗震性能模拟结果的影响,评价了不同强节点系数结构的地震易损性和抗倒塌性能。结果表明,不考虑节点性能的分析结果过高地估计了结构性能,造成不满足规范限值要求的性能指标被分析为满足要求。《钢管约束混凝土结构技术标准》中一级抗震的强节点系数1.5在罕遇地震时将偏于不安全,为满足结构使用安全及抗倒塌能力,建议取强节点系数为1.7。

新型开洞圆钢管混凝土柱-混凝土梁连接节点受力性能研究

传统的钢-混凝土混合结构的圆钢管混凝土柱-混凝土梁连接节点存在钢筋交错、纵横向需与钢构件避让或开孔等情况,节点构造复杂,施工难度较大,连接节点成为钢-混凝土混合结构的设计及施工难点。对此提出了新型开洞圆钢管混凝土柱-混凝土梁连接节点,并结合近年来采用钢-混凝土混合结构的项目经验,对该类节点进行有限元分析,研究了柱顶轴压力和柱端水平力对节点各部分构件受力性能的影响,结果表明,柱顶轴压力的变化显著影响了圆钢管混凝土柱钢管开洞位置各构件的应力,且偏心力对圆钢管混凝土柱承载力有一定的折减。最后考虑到钢管壁开洞对圆钢管混凝土柱存在一定程度的削弱,采用了四种加强措施,分析了四种加强措施下钢管荷载-应力曲线,结果表明,开洞位置钢管壁加厚效果最为显著,设置内环板对缓解应力集中效应也有一定的效果,设置竖向断开加劲肋与设置竖向连续加劲肋荷载-应力曲线基本一致,考虑到设置竖向断开加劲肋所需钢材更少,认为设置竖向断开加劲肋具有较为显著的优越性。

现浇钢筋混凝土框架结构节点施工质量控制分析

随着社会经济的不断发展,我国建筑工程数量逐渐增多,框架结构作为建筑工程的重要部分,对于保障建筑质量具有重要意义。而在现浇钢筋混凝土框架结构中,节点属于施工重要位置,能够起到承受板、柱、梁的作用,节点施工质量对于整体结构的稳定性、安全性和耐久性具有重要影响。然而,由于多种因素的影响,节点施工质量控制存在一定的难度。基于此,本文主要结合具体工程案例,分析现浇钢筋混凝土框架结构在节点施工质量控制方面的不足与控制要点,以期保证梁柱节点的施工质量,促进建筑行业的长久以及稳定发展。

过活断层倒虹吸地面压力管结构型式比较研究

以往对过活断层倒虹吸地面压力管道研究,往往只单独研究钢衬钢筋混凝土管和明钢管两种结构型式,具体哪种管型更为合适尚无比较。采用有限元方法,通过建立地面钢衬钢筋混凝土管和明钢管两种管道有限元模型,对比分析了两种管道型式过活断层倒虹吸在断层蠕滑变形、黏滑变形以及地震作用下的位移和应力。研究结果表明:①钢衬钢筋混凝土管和明钢管管线中布置多个波纹管伸缩节后,均能较好适应断层蠕滑变形;②两种管道结构位于主断层范围的波纹管伸缩节在断层黏滑变形作用下变形均在100 mm以上,设计难度大;③地震作用下,在主断层范围内的钢衬钢筋混凝土管虽然位移大,但地震引起的应力较小,而明钢管在固定支座处的受力情况明显恶化;④综合多种工况的计算结果,钢衬钢筋混凝土管的受力情况比明钢管更优秀,但明钢管具备运行期检修复位的条件,两种管道方案各有优劣,应根据工程具体需求合理选择管道结构型式。

型钢混凝土组合结构梁板柱施工质量控制要点分析

型钢混凝土组合结构梁板柱是一种目前应用广泛的新型建筑结构,具有高刚度、高强度和抗震性能好等优点。但施工中也会存在一些质量问题,如型钢混凝土梁板柱的连接、型钢混凝土界面黏结等,型钢混凝土梁板柱施工质量控制对结构性能和整体稳定性具有较大影响。通过对型钢混凝土组合结构梁板柱的施工质量控制要点的分析,从型钢与混凝土界面的黏结性能、型钢混凝土梁板柱连接的方式等方面进行了论述,为型钢混凝土组合结构梁板柱的施工质量控制提供了一定的理论参考。

城镇老旧小区加固设计方法及施工关键技术研究

本研究以呼北高速公路沿线木结构建筑为例,提出了城镇老旧小区加固设计方法及施工关键技术。首先,针对该项目研究设计了4种加固节点形式;其次,形成了脚手架和钢结构改造房的关键技术;最后,分析了4种加固节点形式加固前后构件的力学性能。本研究实现了“加固设计—施工—分析”的集成化方法,所提出的节点形式可以有效提高结构的抗震性能。