对减轻钢结构逐步破坏的改造方法的效应评估

根据GSA和DoD为预防结构逐步破坏而制订的规范中所推荐的APM方法,对提高重力荷载下,钢结构抗弯能力的三种改造方法的有效性进行了分析。主要采用的是三维非线性动力分析法。分析模型为6×3跨的18层钢结构,这个结构曾由于底层突然移除一根柱而遭受到破坏。对跨长为5,6,7·5,9m的4个建筑进行了分析。分别采用三种方法改造结构并对其进行了评估,即增加梁的强度、增加梁的刚度以及同时增加梁的强度与刚度。通过分析改造后梁的转角、约束力和位移延性这三个性能指标的增强效应,来评估相应改造方法的有效性。     

Seismic performance parameters of RC beams retrofitted by CARDIFRC

A new high performance fibre-reinforced cementitious composite material (designated CARDIFRC^®), to be used for retrofitting concrete members, has been developed at Cardiff University. The material is compatible with concrete and possesses favourable strength and ductility properties desirable for seismic retrofit. It overcomes some of the problems associated with the current techniques based on externally bonded steel plates and fibre-reinforced polymer (FRP) laminates caused mainly by the mismatch of their tensile strength and stiffness with that of the concrete member being retrofitted.

This paper reports on the results of three-point and four-point flexure tests conducted on a number of non-ductile and ductile small scale RC beams retrofitted with externally bonded CARDIFRC^® strips. A number of different strip configurations and two strip thicknesses are investigated and their effect on the retrofitting process examined. Some strength and seismic performance parameters including toughness and ductility are evaluated for each retrofitted beam and compared with those of the corresponding control beams. It is shown that precast CARDIFRC^® strips, adhesively bonded to the surface of the RC beam can greatly increase the strength and ductility of the retrofitted beam; hence, they can be used successfully to enhance the seismic performance of both damaged and undamaged RC beams.     

扇形铅黏弹性阻尼器加固RC框架的抗震性能试验研究

针对钢筋混凝土框架结构梁柱节点震害严重的抗震问题,提出采用扇形铅黏弹性阻尼器加固框架结构的 方法,结合扇形阻尼器型式提出外包箱形钢板和外包U形钢板两种不同的加固连接方式。为研究扇形铅黏弹性阻 尼器加固框架的抗震性能,设计并制作了3榀框架试件,分别为空框架和两榀不同连接的扇形铅黏弹性阻尼器加 固框架,通过低周反复加载试验分析了其滞回性能、承载能力、刚度退化、耗能能力等参数。试验结果表明：采 用扇形铅黏弹性阻尼器加固的框架滞回曲线饱满、耗能能力强、加固效果良好;扇形铅黏弹性阻尼器为框架提供 了一定的抗侧刚度,提高了框架的水平承载能力,延缓了框架塑性铰的产生,使框架具有良好的耗能能力;外包 U形钢板和外包箱形钢板用于扇形铅黏弹性阻尼器与主体结构的连接都是有效的,这两种不同的连接方式对加固 框架的整体抗震性能影响不大。     

Effect of different size of joint enlargement on seismic behavior of gravity load designed RC beam‐column connections

Effect of different size of planer joint enlargement as a noninvasive and practical strategy for seismic retrofit of gravity load designed external reinforced concrete beam‐column connections was experimentally investigated. The joint region was enlarged using steel angles that are mounted using prestressed cross‐ties. Reverse cyclic load tests on five half‐scale control and retrofitted external RC beam‐column connections were conducted. Three different size of planer joint enlargement being 180, 140, and 90 mm were considered for retrofitted specimens. The performance of the retrofitted specimens is compared with that of the control gravity load designed beam‐column connections, in terms of load–displacement hysteresis curve, energy dissipation and ductility capacities, and global strength and stiffness degradation behavior. The experimental results showed that increasing the size of planer joint enlargement significantly enhances the seismic capacity of the retrofitted connections, in terms of strength, stiffness, energy dissipation, and ductility capacity and also planer joint enlargement can relocate beam plastic hinges to outside the joint panel.     

北京市既有农村住宅砖木结构加固前后振动台试验研究

以北京市既有农村住宅广泛采用的单层砖木结构房屋为研究对象,通过加固前后2个大比例尺模型的振动台试验,研究抗震加固方法的有效性。试验结果表明：未加固房屋由于前后纵墙抗侧刚度相差大,纵向地震作用下前纵墙侧移大,砖柱损伤严重;山墙平面外变形大,形成贯穿的斜向裂缝;8度小震作用下墙体开裂,中震作用下墙体损伤严重,大震作用下模型结构濒于倒塌。根据试验结果,提出了抗震加固方法,包括加设钢门窗框及钢板圈梁,采用钢筋网砂浆面层加固山墙和砖柱。振动台试验表明,上述加固方法显著提高了此类砖木结构房屋的抗震能力,加固后结构达到“小震不坏、中震可修、大震不倒”的抗震设防目标。     

Experimental study for seismic retrofit of non‐seismic designed reinforced concrete structures

An evaluation of seismic performance was conducted for a reinforced concrete (RC) structure designed without seismic considerations. The seismic performances of many existing structures are often inadequate based on the current seismic design codes, and it is sure that this is the general tendency in most countries. Six specimens were designed and constructed to simulate RC frames built in the 1980s, before the introduction of earthquake‐resistance design provisions in South Korea. The specimens were composed of one control specimen without any retrofit and five specimens retrofitted using wire‐bracing, brick infill wall, steel bracing (X‐ and K‐type) and corner gusset plate. All retrofitted specimens show significant increase in strength and ductility. The behaviours of each specimen are compared in the view of maximum strength, maximum moment, stiffness and energy dissipation capacity. Overall, efficiency analysis was also demonstrated in this study. Copyright © 2010 John Wiley & Sons, Ltd.     

预应力碳纤维加固钢筋混凝土梁的二次受力性能研究

预应力CFRP加固技术是近年来得到重视的新型加固方法,但目前国内外关于预应力碳纤维CFRP加固混凝土受弯构件的二次受力性能方面的研究较少.通过2根长7.2m的大型钢筋混凝土梁试件预应力CFRP二次受力加固的试验研究,考察预先加载至钢筋屈服后再采用预应力CFRP加固的钢筋混凝土梁的力学性能,比较非预应力CFRP加固构件的...     

钢框架抗震改造的支撑系统研究

评估了不同支撑系统改造的抗弯钢框架的抗震性能。采用3种结构形式:中心支撑框架、防屈曲支撑框架和巨型支撑框架。设计了一横向刚度不足的9层钢框架,满足规范对高地震灾害区域结构的侧移要求。用中心支撑、防屈曲支撑和巨型支撑改造框架,进行非弹性时程分析,评估地震作用下的结构性能。以局部变形(杆件转角)和整体变形(层间及屋顶侧移)为参数,比较改造框架非弹性性能的不同。结果表明:巨型支撑框架是最有效率的支撑系统,其最大层间侧移比抗弯框架低70%,比中心支撑框架低50%。侧移的减小量与地震特性有关,尤其是频率。防屈曲支撑的抗震性能仅稍优于巨型支撑框架,但其总质量更大。巨型支撑框架的杆件和节点用钢量比中心支撑框架低20%,既降低了费用又体现了抗震优势。     

钢框架抗震改造的支撑系统研究

评估了采用不同支撑系统改造的抗弯钢框架的抗震性能。共采用3种结构形式:中心支撑框架、防屈曲支撑框架、巨型支撑框架。设计了一横向刚度不足的9层钢框架,满足规范对高地震灾害区域结构的侧移要求。用中心支撑、防屈曲支撑和巨型支撑改造框架。进行非弹性时程分析,评估地震作用下的结构性能。以局部变形(杆件转角)和整体变形(层间及屋顶侧移)为参数,比较改造框架非弹性性能的不同。结果表明:巨型支撑框架是最有效率的支撑系统,其最大层间侧移比抗弯框架低70%,比中心支撑框架低50%。侧移的减小量与地震特性有关,尤其是频率。防屈曲支撑的抗震性能仅稍优于巨型支撑框架,但其总质量更大。巨型支撑框架的杆件和节点用钢量比同心支撑框架低20%,既可降低费用又具有抗震优势。     

Retrofitting of reinforced concrete beams using composite laminates

This paper presents the results of an experimental study to investigate the behaviour of structurally damaged full-scale reinforced concrete beams retrofitted with CFRP laminates in shear or in flexure. The main variables considered were the internal reinforcement ratio, position of retrofitting and the length of CFRP. The experimental results, generally, indicate that beams retrofitted in shear and flexure by using CFRP laminates are structurally efficient and are restored to stiffness and strength values nearly equal to or greater than those of the control beams. It was found that the efficiency of the strengthening technique by CFRP in flexure varied depending on the length. The main failure mode in the experimental work was plate debonding in retrofitted beams.     

Displacement-restraint bracing for seismic retrofit of steel moment frames

This paper presents a seismic retrofit method using wire rope (cable) bracing for steel moment-resisting frames. The retrofitted frame using the proposed bracing system exhibits ductile behavior and maintains seismic energy dissipation capacity to the same extent as the original bare frame. The bracing member does not act for small and medium vibration amplitudes. For large vibration amplitudes, the bracing member acts and restrains unacceptably large story drift. This retrofit method prevents an increase in the column compression force resulting from the brace action. Cyclic loading test results of the portal frames reveal fundamental characteristics of the proposed bracing system. Seismic response analyses are also conducted for the three-story moment-resisting frames. The effectiveness of the retrofit method is discussed in light of these test and analysis results.     

Post tensioned tendons for seismic retrofitting of weak bolted T-stub connections

Current design philosophy for conventional steel moment resisting frames (MRFs) in high seismic regions is that the frames should not collapse for major earthquakes. However, significant structural damage and residual drift due to inelastic deformations in beams and columns may cause loss of building occupancy or operation after major earthquakes. On the other hand, Selecting the optimum technique for rehabilitation of existing structures with weak connections has been a challenge for engineers in the recent years. In this study, the authors proposed using post-tensioned tendons for rehabilitation of bolted Tstub connections with weak bolts or weak T-stub flange as well as a technique for changing pinned connections to moment connections. Six corner connection specimens are made and tested under SAC cyclic loading protocol. The results of this study show that this rehabilitation technique not only modifies the cyclic behavior of weak rigid connections and changes simple bolted connections into moment connections, but also it improves the behavior of the rehabilitated connections in a way that their behavior is more desirable than that of the reference rigid connection designed according to AISC. For example, flexural capacity and rotational stiffness of the retrofitted connections are higher than those of the reference connection by 18 and 26% in average respectively. Besides, rehabilitation using post tensioned tendons add self-centering ability to the retrofitted connection that has a major role in preventing permanent deformations in frame and thus, the possibility of using frictional dampers in self-centering frames for increasing the energy absorption capacity is provided. This rehabilitation technique in bolted connection with weak T-stub flange has better cyclic behavior compared to that of a connection with weak bolts, since the T-stub participates in energy absorption and higher energy absorption is reached.     

预制自保温钢筋混凝土墙板加固震损框架试验研究

为了达到震后快速加固修复和建筑节能改造等综合加固改造目的,提出采用三明治式预制自保温钢筋混凝土墙板（PISW）对震损钢筋混凝土框架进行快速加固的方法。开展了4榀采用预制自保温钢筋混凝土墙板加固震损框架模型的低周往复加载试验,研究了预制自保温钢筋混凝土墙板与损伤框架之间的连接构造以及墙板配筋率对加固效果的影响,分析了试件的破坏特征、滞回性能、骨架曲线、耗能能力等。结果表明：采用预制自保温钢筋混凝土墙板加固方法可大幅度提高震损框架的承载能力;预制自保温钢筋混凝土墙板与损伤框架之间的界面强度是影响加固试件承载能力的主要因素;由于墙板破坏不充分,墙板配筋率的变化并未对承载力产生明显影响。基于试验研究结果提出了预制自保温钢筋混凝土墙板加固震损框架受剪承载力计算方法。     

附加减震钢框架的加固混凝土框架结构抗震性能试验研究

为提高既有混凝土框架抗震性能,在不显著增加既有结构构件受力的同时,在混凝土框架外部增设钢框架并设置屈曲约束支撑。设计并制作1榀纯混凝土框架和2榀设置附加减震钢框架的混凝土框架,通过低周往复加载试验,研究其开裂和破坏状态、滞回曲线、骨架曲线、刚度退化、等效阻尼比以及钢筋混凝土梁、附加钢框架的应变发展等。试验结果表明：增设附加减震框架后,结构破坏机制更加合理,屈曲约束支撑耗能性能稳定,加固后结构的滞回曲线饱满;采用外部附加钢框架加固钢筋混凝土框架,可提高既有混凝土框架结构的受剪承载能力至3倍以上,既有结构、外部附加钢框架和屈曲约束支撑可协同工作,在设防目标下可避免混凝土柱发生压剪脆性破坏;最后对附加减震框架改进连接构造设计提出了建议。     

An innovative scheme for retrofitting masonry-infilled non-ductile reinforced concrete frames

An innovative retrofit scheme is proposed for masonry-infilled non-ductile reinforced concrete frames to remedy the brittle shear failure caused by the huge strut force exerted by the un-reinforced masonry (URM) panel on the columns following corner crushing of the panel. The URM panel is separated from the columns, and steel brackets are provided to transfer the strut forces from the panel to the beam, thereby totally eliminating transfer of large strut force to the columns. This scheme has a beneficial effect of increasing the shear capacity of the beam due to the large compression induced in it to resist theshear component caused by the strut force. Cyclic load test on a 3/4 scale specimen of a single-bay, single-story frame assembly retrofitted with the proposed scheme has revealed much enhanced performance over the un-retrofitted one, with the drift capacity increased five folds while retaining most of the strength and stiffness.     

Bracing systems for seismic retrofitting of steel frames

The present study assesses the seismic performance of steel moment resisting frames (MRFs) retrofitted with different bracing systems. Three structural configurations were utilized: special concentrically braces (SCBFs), buckling-restrained braces (BRBFs) and mega-braces (MBFs). A 9-storey steel perimeter MRF was designed with lateral stiffness insufficient to satisfy code drift limitations in zones with high seismic hazard. The frame was then retrofitted with SCBFs, BRBFs and MBFs. Inelastic time-history analyses were carried out to assess the structural performance under earthquake ground motions. Local (member rotations) and global (interstorey and roof drifts) deformations were employed to compare the inelastic response of the retrofitted frames. It is shown that MBFs are the most cost-effective bracing systems. Maximum storey drifts of MBFs are 70% lower than MRFs and about 50% lower than SCBFs. The lateral drift reductions are, however, function of the characteristics of earthquake ground motions, especially frequency content. Configurations with buckling-restrained mega-braces possess seismic performance marginally superior to MBFs despite their greater weight. The amount of steel for structural elements and their connections in configurations with mega-braces is 20% lower than in SCBFs. This reduces the cost of construction and renders MBFs attractive for seismic retrofitting applications.     

Empirical hysteretic energy with strength,strength and drift,and SCWB designs using steel moment‐resisting frames

This paper represents the hysteretic energy performance of twelve steel moment‐resisting frames intentionally designed by three different design procedures. The three types of design procedure were: (1) strength controlled design; (2) strength and drift controlled design; and (3) strong‐column/weak‐beam controlled design. The energy performances of the so‐designed frames were discussed in view of the effects of strength variations, stiffness variations, and plastic mechanism variations, on the hysteretic energy input and its distribution in multiple storey frames. An empirical mean hysteretic energy formula has been proposed based on this study. Copyright © 2001 John Wiley & Sons, Ltd.     

A comparative study on fatigue behaviour of steel beams retrofitted with welding,pultruded CFRP plates and wet layup CFRP sheets

This paper investigates the fatigue behaviour of defected steel beams retrofitted with three different methods, i.e., welding, welding and bonding with CFRP plates or CFRP woven sheets laminated via a wet lay-up process. Two different types of CFRP materials and two types of epoxies were selected in this study. An initial cut was made on the tensile flange in the mid span of each beam. Different failure modes were observed for beams retrofitted with CFRP plates and CFRP sheets. It was found that one layer of CFRP plate and epoxy strengthening system can extend the fatigue life of steel beams about 7 times comparing with beams repaired with solely welding method, while the fatigue life was extended abound 3 times for beams strengthened with 4 layers of CFRP woven sheets. Mean S–N curves were obtained based on the test data, that can be used to predict the fatigue life of steel beams retrofitted with similar CFRP materials. The crack propagation rate was measured using strip strain gauges. The CFRP plates showed better performance in resisting crack propagation than CFRP sheets under fatigue loading conditions. The relationship between the maximum stress and the crack propagation rate could be used to predict the crack length of beams retrofitted with similar CFRP strengthening systems.     

Y型偏心钢支撑加固震损混凝土框架的滞回性能试验

为研究Y型偏心钢支撑加固震损混凝土框架结构的抗震性能,通过对2榀1/3缩尺、单层、单跨损伤的混凝土框架采用Y型偏心钢支撑加固后的低周往复加载试验,系统研究Y型偏心支撑加固震损混凝土框架的滞回性能、刚度退化、延性性能、耗能能力及耗能梁段的剪切变形等。结果表明:Y型偏心钢支撑加固震损混凝土框架具有较高的水平承载力和抗侧刚度,并具有较强的耗能能力。随着耗能梁段腹板高度的增加,加固后试件的水平承载力有所提高,但试件的位移延性和耗能等性能略有劣化。     

Monotonic and cyclic loading tests for cold-formed steel wall frames sheathed with calcium silicate board

This research is concentrated on the structural strength and behavior of cold-formed steel wall frame sheathed with calcium silicate board under shear load. Test specimens with two different thicknesses of sheathing were assembled, 9 mm and 12 mm, with one-side or two-side of attachment. Monotonic shear and cyclic loading tests are conducted on wall specimens utilizing two C sections connected back-to-back to be as chord studs and calcium silicate board sheathing on the exterior. Based on the test results, detailed discussions on the strength, stiffness, energy absorption, ductility ratio, and failure mode of cold-formed steel wall specimens are given. It is noted that the failure mostly occurred at the bottom track of wall specimens due to the large deformation or tearing failure of track. The wall strength is not affected by the change of sheathing's thickness significantly, but wall frames attached with two-side calcium silicate board sheathing provide higher resisting strength and stiffness than those attached with one-side sheathing. In this study, test results are also used to compare with the previous study that single chord stud was used in the assembly of wall frame. In addition, the suggested response modification factor of the wall sheathed with calcium silicate board is proposed for design purpose.