Seismic strengthening of reinforced concrete columns damaged by rebar corrosion using combined CFRP and steel jacket

In order to study the effectiveness of combined carbon fiber-reinforced polymer （CFRP） sheets and steel jacket in strengthening the seismic performance of corrosion-damaged reinforced concrete （RC） columns, twelve reinforced concrete columns are tested under combined lateral cyclic displacement excursions and constant axial load. The variables studied in this program include effects of corrosion degree of the rebars, level of axial load, the amount of CFRP sheets and steel jacket. The results indicate that the combined CFRP and steel jacket retrofitting technique is effective in improving load-carrying, ductility and energy absorption capacity of the columns. Compared with the corrosion-damaged RC column, the lateral load and the ductility factor of many strengthened columns increase more than 90% and 100%, respectively. The formulae for the calculation of the yielding load, the maximum lateral load and the displacement ductility factor of the strengthened columns under combined constant axial load and cyclically increasing lateral loading are developed. The test results are also compared with the results obtained from the proposed formulae. A good agreement between calculated values and experimental results is observed.

Dynamic performance of angle-steel concrete columns under low cyclic loading-II:parametric study

Tests of nine angle-steel concrete column （ASCC） specimens under low cyclic loading are described in a companion paper （Zheng and Ji, 2008）. In this paper, the skeleton curves from the numerical simulation are presented, and show good agreement with the test results. Furthermore, parametric studies are conducted to explore the influence of factors such as the axial compression ratio, shear steel plate ratio, steel ratio, prismatic concrete compression strength, yield strength of angle steel and shear span ratio, etc., on the monotonic load-displacement curves of the ASCCs. Based on a statistical analysis of the calculated results, hysteretic models for load-displacement and moment-curvature are proposed, which agree well with the test results. Finally, some suggestions concerning the conformation of ASCCs are proposed, which could be useful in engineering practice.

Experimental and analytical study on seismic behavior of steel-concrete multienergy dissipation composite shear walls

In this paper, a steel-concrete multi-energy dissipation composite shear wall, comprised of steel-reinforced concrete （SRC） columns, steel plate （SP） deep beams, a concrete wall and energy dissipation strips, is proposed. In order to study the multi-energy dissipation behavior and restorability after an earthquake, two stages of low cyclic loading tests were carded out on ten test specimens. In the first stage, test on five specimens with different number of SP deep beams was carried out, and the test lasted until the displacement drift reached 2%. In the second stage, thin SPs were welded to both sides of the five specimens tested in the first stage, and the same test was carried out on the repaired specimens （designated as new specimens）. The load-bearing capacity, stiffness, ductility, hysteretic behavior and failure characteristics were analyzed for both stages and the results are discussed herein. Extrapolating from these results, strength calculation models and formulas are proposed herein and simulations using ABAQUS carried out, they show good agreement with the test results. The study demonstrates that SRC columns, SP deep beams, concrete wall and energy dissipation strips cooperate well and play an important role in energy dissipation. In addition, this study shows that the shear wall has good recoverability after an earthquake, and that the welding of thin SP＇s to repair a deformed wall is a practicable technique.

Experimental study and analysis on fatigue stiffness of RC beams strengthened with CFRP and steel plate

The objective of this work is to investigate the fatigue behavior of reinforced concrete(RC) beams strengthened with externally bonded carbon fiber reinforced polymer(CFRP) and steel plate. An experimental investigation and theoretical analysis were made on the law of deflection development and stiffness degradation, as well as the influence of fatigue load ranges. Test results indicate that the law of three-stage change under fatigue loading is followed by both midspan deflection and permanent deflection, which also have positive correlation with fatigue load amplitude. Fatigue stiffness of composite strengthened beams degrades gradually with the increasing of number of cycles. Based on the experimental results, a theoretical model by effective moment of inertia method is developed for calculating the sectional stiffness of such composite strengthened beams under fatigue loading, and the calculated results are in good agreement with the experimental results.

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

A composite shear wall concept based on concrete filled steel tube （CFST） columns and steel plate （SP） deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements： CFST columns; SP deep beams; and reinforced concrete （RC） strips. The RC strips are intended to allow the core structural elements - the CFST columns and SP deep beams - to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

Experimental Investigation on the Properties of Recycled Concrete Using Hybrid Fibers

Due to the inherent property of concrete being very weak in tension, efforts have been made to overcome this deficiency by adding various type of fibers like carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), polypropylene fiber (PPF) and stainlesssteel fiber (SSF) smeared into the concrete mix. The present study involves experimental investigation on the use of GFRP, CFRP and SSF fibers alone or as combination to improve the mechanical properties of concrete. Furthermore, concrete cylinders were cast and tested for compression and tension using 10% fly ash as cement replacement in all specimens. Besides fiber material types, fiber reinforcement ratios of 1% and 1.5% were tested to investigate the mechanical properties of concrete. In all concrete cylinder tests, the fiber reinforcement ratio of 1% had a significant contribution in increasing the tensile strength as oppose to compressive strength. As a result, the tensile and compressive strengths were increased by 26% and 11%, respectively as compared to the control specimen. Increasing the fiber reinforcement ratio from 1% to 1.5%, resulted in diminishing the mechanical properties of concrete. However, reduction in concrete compressive strength was more prominent than the tensile strength. Furthermore, it was observed that, the crack propagation was decreased with the increase of fiber content when compared to the control specimen.

焊接多腔双钢板-混凝土组合剪力墙抗震性能分析

大多数双钢板-混凝土组合剪力墙采用螺栓连接或焊接肋的方式使钢板和混凝土协同工作。然而,这种连接方式可能导致整体性和塑性变形效率较低,且制作复杂,焊接多腔双钢板-混凝土组合剪力墙能够有效地避免这些问题。为了深入研究焊接多腔双钢板-混凝土组合剪力墙的抗震性能,基于约束混凝土真三轴塑性-损伤本构模型和钢材弹塑性混合强化-韧性损伤本构模型,建立了组合剪力墙的精细化三维实体-壳模型,将模拟所得的滞回曲线、骨架曲线、刚度退化曲线、弹性刚度、承载力、累积耗能、等效阻尼粘滞系数和延性系数与已有拟静力试验结果相比较,发现两者吻合较好。分析结果表明:轴压比对组合剪力墙模型算例刚度和承载力的影响较小,而随剪跨比增大,组合剪力墙模型算例的刚度和承载力呈线性降低;轴压比对组合剪力墙模型算例总塑性耗能的影响较小,而剪跨比的影响较大,剪力墙总塑性耗能随剪跨比增大而降低;轴压比和剪跨比都不会改变算例各部件的耗能分配机制,即组合剪力墙模型算例以外钢板和内隔板耗能为主。

薄壁钢板局部屈曲关键问题研究进展

钢结构以及钢-混凝土组合结构由于其强度高、耗能能力好、施工方便等优异性能,被广泛应用于工程结构中。然而,随着高强度钢材的应用,薄壁钢板呈现薄壁化、宽厚比随着构件截面尺寸的增大而不断增大的趋势,由于工程结构及荷载的复杂性等因素,钢板过早发生局部屈曲的风险不断加大,薄壁钢板的局部屈曲问题凸显,亟待开展系统性深入研究。对薄壁钢板局部屈曲研究的进展进行了概述,分析总结了现有试验研究和理论研究方面存在的局限性,详细介绍了笔者团队近年来聚焦于薄壁钢板局部屈曲关键问题开展的一系列研究工作及成果。

预应力螺栓连接钢板约束混凝土圆柱轴压性能研究

螺栓连接钢板(BST)约束混凝土圆柱,由于钢板可拆卸及更换,较钢管约束混凝土具有更好的可恢复性。以BST约束混凝土圆柱为研究对象,提出在两片拼装钢板间预留间隙,并拧紧螺栓而对其施加预压应力的方法。以施加的预压应力和径厚比为参数,对6根BST约束混凝土圆柱及1根无约束混凝土圆柱进行轴心受压试验。结果表明,预留间隙并拧紧螺栓的方法能对核心混凝土有效施加预压应力,使钢板在加载前即对核心混凝土形成有效约束。相较于无约束混凝土圆柱,同条件的施加预压应力的BST约束混凝土圆柱峰值应力最大提高74.5%,且残余强度最大能保持在峰值应力的92.3%。相较于未施加预压应力的BST约束混凝土圆柱,施加预压应力的BST约束混凝土圆柱预压应力越大,峰值应力越大,最大可提高18%;径厚比越小,BST约束混凝土圆柱峰值应力越大,但随着预压应力增大,峰值应力提高的幅度降低。

钢波纹板-模袋混凝土支护结构及其在圆形竖井中的应用研究

为探究钢波纹板-模袋混凝土支护结构的施工工艺及其应用效果,通过室内单轴压缩试验研究加压排水工艺对不同养护龄期模袋混凝土强度的影响规律;然后,建立三维有限元数值模拟,开展钢波纹板-模袋混凝土支护结构第2阶段现场工艺试验,验证其结构和工艺的可行性及工程效果。结果表明:1)加压排水工艺可以显著提升模袋混凝土的早期抗压强度,轻质量模袋在加压排水中对模袋混凝土抗压强度的提升效果最佳;2)模袋混凝土能够有效地填充钢波纹板与开挖面间的空隙,模袋有助于混凝土气体与水分的排出,从而缩短凝固成型时间;3)混凝土灌注过程对钢波纹板受力影响轻微,各块波纹钢构件在工作状态下均匀受力;4)类似工程中推荐应用轻质量的涤纶长丝纺粘针刺非织造土工布模袋。

大跨度公铁合建斜拉桥钢混板-桁组合梁关键节点空间受力特性

针对大跨度公铁合建斜拉桥—主跨808 m洪奇沥特大桥新型钢混板-桁组合梁的关键节点—辅助墩顶钢混节点,采用ANSYS软件建立钢桁-混凝土板组合梁部分节段细化的全桥多尺度有限元模型,分析边跨组合梁节点在受力最不利工况下的受力规律及传力特性,并讨论下弦杆等杆件截面等结构参数变化对节点受力、传力的影响规律。结果表明:最不利组合工况下,边跨组合梁辅助墩顶钢混节点处钢结构最不利Mises应力为265.9 MPa,混凝土局部最大名义拉应力为9.2 MPa,导致局部开裂而受力转移至钢结构;在辅助墩顶局部负弯矩影响下,内外节点板处应力总体呈“倒V”形分布,混凝土顶面及底面分别呈“鞍形”及“倒鞍”形分布;节点处下弦杆(含管内混凝土)、竖杆分别传递77.86%和40.15%荷载,为纵向、竖向主要传力构件;混凝土桥面厚度变化对自身应力影响明显,其厚度和下弦杆截面面积对纵向传力比影响大,竖杆截面面积对自身竖向传力影响相对明显;混凝土厚度及下弦杆、斜腹杆、竖杆截面为节点受力、传力的主要影响因素,其系数在0.8~1.1时,组合梁关键节点各构件应力及传力比均较为合理。

带PBL剪力键的钢芯板混凝土组合剪力墙低周往复加载试验研究

为研究带PBL剪力键的钢芯板混凝土组合剪力墙的抗震性能,对1个型钢混凝土组合剪力墙和4个钢芯板混凝土组合剪力墙进行了循环往复加载试验;观察带PBL剪力键的钢芯板混凝土组合剪力墙在水平循环荷载下的破坏全过程,并分析该类剪力墙的滞回特征、变形能力、承载能力、耗能性能、刚度和强度退化能力。结果表明:钢芯板混凝土组合剪力墙的破坏模式主要为弯曲型破坏,滞回曲线较为饱满;配置钢芯板的剪力墙承载力、延性性能和耗能能力较优;PBL剪力键的构造方式可保证钢芯板与混凝土之间的黏结性能完好,PBL剪力键平放会导致剪力墙出现沿PBL剪力键的水平通缝,影响剪力墙承载能力的发挥,建议采用PBL剪力键竖放的构造形式。

温度影响下不同轴压比双钢板混凝土组合剪力墙抗震性能

研究不同温度环境下不同轴压比双钢板混凝土组合剪力墙的抗震性能,以温度(40、20、-40℃)和轴压比(n=0.3、0.4、0.5、0.6)为控制参数,设计了12片剪力墙。利用ABAQUS对双钢板组合剪力墙试验进行对比验证,验证有限元结果的准确性。通过对12个剪力墙的承载能力、塑性变形能力、耗能能力、延性对比分析,探究其在代表性温度环境下轴压比对试件的抗震性能变化规律。结果表明,在相同的温度环境下,随着轴压比的增加,剪力墙的承载能力增加,延性降低。轴压比对于刚度退化的影响不明显。在20℃环境下,剪力墙的延性好于40和-40℃环境下延性。-40℃环境下,剪力墙的承载能力高于40和20℃环境。

近场爆炸下波纹双钢板混凝土组合墙板的损伤破坏及抗爆性能

相对于传统的钢筋混凝土墙板和平面双钢板-混凝土组合墙板(profiled double-skin composite wall,PDSCW),波纹双钢板-混凝土组合墙板(concrete-infilled double steel corrugatedplate wall,CDSCW)具有更高的轴向抗压承载力、更大的侧向抗弯刚度以及良好的抗冲击和抗震性能,在船舶和军事领域有广阔的应用前景。制作2种CDSCW试件,通过近场爆炸试验对比分析了2种试件的损伤模式及动态响应;采用ANSYS/LS-DYNA软件建立了CDSCW和PDSCW的有限元模型,研究了近场爆炸下2种混凝土组合墙板的损伤机理和爆炸响应,并与试验结果进行对比分析;分析了混凝土厚度、钢板厚度、药量对CDSCW抗爆性能的影响。结果表明:近场爆炸作用下,相较于PDSCW,相同混凝土方量和尺寸(长、宽)的CDSCW具有更大的抗弯刚度、更强的抗变形能力以及更优的抗爆性能;增加波纹深度能有效提高CDSCW的抗爆性能,可为抗爆构件设计和相关工程研究提供参考。

波纹钢形状与拱效应对加固盖板涵承载力的影响

为了探索波纹钢形状对加固盖板涵承载力的影响及填充混凝土的拱效应形成机制,采用室内试验与数值分析相结合的研究方法,以一个室内模型试验结果为基准,建立了72个箱形、圆弧及其之间的过渡形状的波纹钢加固盖板涵的数值模型,探明了加固体系承载力随波纹钢形状参数的变化规律;基于合理拱轴的概念,探明了填充混凝土的拱效应形成机理,并采用5个数值模型进行了验证。结果表明:拱腋半径保持不变时,加固体系的承载力随着拱顶、侧墙半径的增加而减小;拱顶、侧墙半径不变时,加固体系的承载力随着拱腋半径的增加而增大;提升加固体系承载力最有效的方式是增加拱腋半径,其次是减小拱顶和侧墙半径;填充混凝土的拱效应与荷载类型有关,当波纹钢的形状能保持拱轴连续并且在素混凝土刚性角以内时,加固体系的承载力最高。在设计波纹钢加固盖板涵结构时,应根据实际工程需要综合考虑波纹钢形状与填充混凝土的拱效应,尽量避免紧贴原盖板涵的加固设计。

双层带钢板暗支撑装配整体式混凝土剪力墙抗震性能研究

为研究带钢板暗支撑装配整体式混凝土剪力墙的抗震性能,设计制作1片双层带钢板暗支撑装配整体式混凝土剪力墙和1片双层带钢板暗支撑现浇混凝土剪力墙,其中装配整体式剪力墙内置钢板暗支撑在墙身与基础梁和上下墙身水平连接节点处采用双面角焊缝连接以适应施工时的安装尺寸冗余度要求。对试件进行低周反复加载试验,结果表明:采用双面角焊缝连接预制墙身内置钢板暗支撑可以适应较大的施工冗余度,并且保证暗支撑传力的可靠性;装配整体式剪力墙具有和现浇剪力墙等同的水平承载力、刚度退化水平和耗能能力;2个构件均为弯曲破坏,但装配整体式剪力墙在一层墙体后浇带与预制墙身接缝处也产生塑性铰。

HPC端部加强双钢板组合剪力墙的抗震性能

为研究高性能混凝土端部加强双钢板组合剪力墙受力机理及破坏形态,以轴压比、腹部普通混凝土强度等级为关键参数,设计了4片普通试件,7片HPC端部加强试件,运用ABAQUS构建其有限元模型,研究其抗震性能。结果表明:同轴压比下,HPC端部加强试件相比普通试件屈服荷载提高16.30%,峰值荷载提升13.40%;随着轴压比提高,HPC端部加强试件峰值荷载和屈服荷载分别提高7.22%和2.72%,随着轴压比减小,HPC端部加强试件延性提升22.26%;提高腹部腔体混凝土强度等级,HPC端部加强试件的屈服荷载和峰值荷载分别提高13.01%和11.14%,延性提升16.91%。

功能可恢复RCS混合框架结构研究进展

钢筋混凝土柱-钢梁(RCS)混合框架结构以其结合了混凝土优异的抗压性能及钢材优异的抗弯性能而受到广泛关注,而可恢复功能结构以其震后快速恢复使用功能的能力,也成为地震工程界研究的新热点。功能可恢复RCS混合框架结构可以在弯矩较大的梁端和柱脚部位设置可更换构件,实现结构的功能可恢复能力。文中简述了近年来功能可恢复RCS混合框架结构研究进展,重点关注各类型功能可恢复钢梁、功能可恢复摇摆柱脚的构造研究,介绍了功能可恢复RCS混合框架结构性能分析研究进展。最后,对功能可恢复RCS混合框架结构仍需深入研究的问题进行了展望。

铁路混合梁钢-混结合段受力及理论计算

为研究铁路混合梁钢-混结合段结构的受力及其理论计算公式,在既有公路桥梁钢-混结合段计算公式的基础上,提出铁路混合梁钢-混结合段截面应力、顶底板剪力连接件、承压板传力验算公式;并以主跨335 m汉巴南铁路嘉陵江特大桥为研究背景,采用有限元分析的方法探究结合段受力特性及应力纵、横向分布规律,进而开展结合段受力理论与数值计算对比分析。数值计算结果表明,结合段混凝土均处于受压状态,不同截面位置处结合段钢、混应力横向分布均存在一定的不均匀性。公式验算结果表明:结合段混凝土应力均受压,满足截面应力验算要求;剪力连接件的抗力系数介于1.30~4.49,结合段剪力连接件具有良好的安全储备;承压板抗力系数介于3.18~10.08,表明前后承压板抗力远大于计算传力荷载,并具有优化的空间。理论公式计算的结合段顶底板混凝土应力、剪力钉应力与有限元计算结果总体相近,在修正后可用于钢-混结合段的防开裂/脱离、抗剪受力计算。

装配式带夹芯保温槽型玻璃钢-钢板-槽钢-混凝土组合剪力墙轴压性能研究

提出一种装配式带夹芯保温槽型玻璃钢-钢板-槽钢-混凝土组合剪力墙,设计3个具有不同配筋形式和混凝土种类的墙板试件进行轴心受压试验,获得墙板在轴压作用下的破坏模式、荷载-位移曲线、荷载-应变曲线、承载力储备系数、延性系数、材料利用率等性能指标。通过ABAQUS有限元分析软件对墙板进行参数化分析,研究内嵌钢板强度和厚度对其轴压性能的影响。结果表明,墙板具有良好的承载力储备能力和延性性能;混凝土中掺入1%体积比的钢纤维可显著提高墙板内混凝土的抗拉性能,使混凝土强度得到更加充分的利用,布置钢筋可以显著提高墙板延性;墙板的承载力和延性随内嵌钢板厚度和强度的增加而增大,强度为Q355、厚度为4、6mm时,墙板材料利用率更高。提出适用于该类墙板的轴压承载力设计公式,考虑钢板屈曲和截面组合效应的墙板轴心受压承载力设计公式计算结果较精确。