使用预拱钢板对矩形预应力混凝土柱进行轴向加固

钢套常用于钢筋混凝土(RC)柱加固。之前的试验研究评估了钢套柱的延性和抗剪性能。然而,实践中常使用预压轴向荷载对RC柱进行加固。尚未对预应力引起的传统柱和新型套管之间的应力滞后效应进行研究。使用一种简单的新型卸载方法,利用预拱钢板提高预应力RC柱的轴向承载力,试验证明该方法能够有效提高RC柱的轴向承载力。提出相应理论模型来计算钢板加固柱的轴向承载力,将模型的预测结果与试验结果相比较,验证了该模型的准确性。     

Behavior and design of reinforced concrete frames retrofitted with steel bracing against progressive collapse

Steel bracing is able to improve progressive collapse resistance of reinforced concrete (RC) frames, but the bracing design is typically based on seismic retrofitting or lateral stability. There is no approach for design of steel bracing against progressive collapse. To this end, a retrofitting approach with steel braces is proposed based on analysis of macro finite element (FE) models with fiber beam elements. The FE models were initially validated through the experimental results of a braced frame and then used to investigate the effects of pertinent parameters on the progressive collapse resistance of planar frames. The results suggest the braces should be placed at the top story. Thereafter, macro FE models are built to investigate the dynamic responses of the three‐dimensional prototype RC frames under different column removal scenarios (CRS) and show the necessity of retrofitting. Accordingly, the design approach of steel bracing is proposed with incremental dynamic analysis (IDA) and assuming independent contribution of braces and frames to resistance. Finally, the fragility analysis of the frames under a corner‐penultimate‐exterior CRS is conducted through IDA and Monte Carlo simulation, and the results confirm the validity of the proposed design approach for retrofitting RC frames.     

消能支撑加固底部框架砌体房屋的弹塑性地震反应分析

本文采用弹塑性时程分析方法,对底部框架多层砌体房屋在不同烈度罕遇地震作用下进行了抗震性能评估;研究了在底部框架内增设消能外包混凝土无粘结钢支撑对房屋抗震性能的影响;对增设消能支撑加固方案和增设抗震墙加固方案进行了对比分析。分析结果表明,在底层框架砌体房屋的底层增设消能支撑可显著降低底层框架的最大层间位移,控制结构的塑性损伤,提高结构的抗震性能。增设消能支撑加固方案与增设抗震墙加固方案相比,结构加固更合理、更易实施。     

Behaviour of FRP-jacketed circular steel tubes and cylindrical shells under axial compression

Fibre-reinforced polymer (FRP) jackets have been widely used to confine reinforced concrete (RC) columns for enhancement in both strength and ductility. This paper presents the results of a recent study in which the benefit of FRP confinement of hollow steel tubes was explored. Axial compression tests on FRP-confined steel tubes are first described. Finite element modelling of these tests is next discussed. Both the test and the numerical results show that FRP jacketing is a very promising technique for the retrofit and strengthening of circular hollow steel tubes. In addition, finite element results for FRP-jacketed thin cylindrical shells under combined axial compression and internal pressure are presented to show that FRP jacketing is also an effective strengthening method for such shells failing by elephant’s foot collapse near the base.     

Performance-based prioritisation for seismic retrofitting of reinforced concrete bridge bent

In this study, a seismically deficient three-column reinforced concrete bridge bent has been considered which was designed in the pre-1965. Several retrofitting provisions, namely carbon-fibre-reinforced plastics jacketing, steel jacketing, concrete jacketing, and engineered cementitious composites jacketing, have been considered in this study to enhance the seismic resistance and the performance of a gravity load-designed bridge bent under seismic forces. Performance evaluation and optimal selection of retrofit techniques have multi-level and multi-factor features and, therefore, are regarded as multiple criteria decision-making (MCDM) problem. MCDM methods are decision-support procedures, which are used when there are multiple decision-makers involved in the evaluation and comparison of a set of alternatives involving different evaluation criteria. This paper shows the application of such methodological framework for a performance-based seismic retrofit selection of a multi-column bridge bent. Here, different seismic retrofit strategies, reflecting common as well as innovative approaches, are adopted, and their seismic performances are compared by using the technique for order preference by similarity to ideal solution MCDM algorithm. Through rigorous analyses, a decision-making tool has been developed to identify the most effective retrofitting scheme considering its seismic performance alone.     

Modelling and analysis of retrofitted and un-retrofitted masonry-infilled RC frames under in-plane lateral loading

In the context of various developing countries where many old structures require retrofitting or strengthening work to mitigate earthquake hazards, a cost-effective method is the retrofitting of damaged masonry-infilled reinforced concrete (RC) frames using ferrocement overlays, and the strengthening of existing infilled RC frames with ferrocement. However, no reliable mathematical or computational tool is accessible in the open literature to estimate the effect of such a retrofitting technique quantitatively. The present study is a numerical investigation of the retrofitting effect of masonry-infilled RC frames using ferrocement. A finite element technique has been used effectively to develop a computational model for analysing bare RC frames, together with un-retrofitted and retrofitted masonry-infilled RC frames. The proposed model accounts for the material nonlinearities of both concrete and masonry, and the yielding of reinforcing steel. It is shown that the proposed model can be used effectively in predicting the load carrying capacity of existing RC frames, as well as the required degree of strengthening when ferrocement overlays are applied as a retrofitting scheme. A parametric study was performed using the proposed model on bare and infilled frames to quantify the effects of different parameters. This enabled the development of a simplified equation for predicting the ultimate load carrying capacity of masonry-infilled RC frames, which proved to be reasonably accurate and which was validated by both experimental and numerical results.     

Seismic retrofitting of nonductile beam-column sub-assemblage using FRP wrapping and steel plate jacketing

The paper discusses the aspects of repair and retrofitting technique adopted for a damaged reinforced concrete beam-column joint specimen under cyclic loading. A specimen designed based on Indian Standard specifications with consideration of seismic load but without adopting ductile detailing (NonDuctile) was investigated under reverse cyclic loading. Then, the damaged nonductile specimen was repaired with epoxy mortar and grouted using low viscous polymer, and retrofitted using fiber reinforced plastic (FRP) wrapping in beam and column components and steel plate jacketing in joint region. The experimental results showed that the retrofitted specimen not only regained its original strength and stiffness but also has overcome the deficiencies of nonductile detailing. The present study shows that a proper repair and adequate retrofitting technique can be used for strengthening and improvement of damaged regions in reinforced concrete structures.     

外套钢管混凝土加固RC柱技术研究进展

外套钢管混凝土加固法兼具了增大截面加固法和外包(粘)钢加固法的优点,并利用钢管混凝土组合结构的优良受力特性,可显著改善结构柱的受力性能。近年来,该加固方法得到了大量研究,且该技术在实际工程中亦有诸多应用,表现出了很好的使用前景。为更好地促进该加固技术的理论研究与工程应用,对近年来有关外套钢管混凝土加固RC短柱的轴压、偏压和抗震性能及相应复合加固中长柱轴压性能的研究进展进行综述,分析已有的研究成果,并对后续的研究方向给出建议。研究表明:该复合加固法可以大幅提高被加固RC柱在各种受力工况下的承载力和刚度,并能显著改善其延性;但有关外套钢管混凝土加固柱的力学性能和设计方法等有待深入研究,应进一步通过试验和数值模拟等手段,研究截面形状、二次受力、原柱受损、加固材料和界面等因素对复合加固柱受力性能的影响;加固材料的设计强度取值、加固柱长期力学性能和外套钢管混凝土加固柱的抗震设计方法等应是理论研究及工程应用的关注重点。     

Experimental study on multi-panel retrofitted steel transmission towers

Due to the increasing demands on power supply and telecommunication services, existing transmission towers are frequently being required to carry extra loads above their initial design limits. A range of methods have therefore been used to increase the capacity of existing towers by retrofitting them in some way. This paper addresses steel lattice transmission towers with main leg members retrofitted by steel angles through bolted double steel angle connectors, a method that is widely used in practice but to date with little experimental research to support it. Three unreinforced tower models and four groups of retrofitted tower models with and without preloading have been tested in the structural laboratories at the University of South Australia. The experimental results verify the effectiveness of the retrofitting method. Load sharing analysis shows that axial loads can be effectively transferred between original tower members and reinforcing members through the bolted-splice system. Preloading reduces the load sharing in reinforcing members in the early loading stage but does not have significant influence on the ultimate strength of the whole structure.     

Half a century of reinforced concrete electric poles maintenance: inspection,field-testing,and performance assessment

Application of reinforced concrete (RC) poles as overhead electrical transmission line supports has become of great interest during recent years worldwide. The higher strength, longer life, and the potential to span longer distances than steel poles are the key reasons behind this tendency. A great variety of architectural shapes, relatively low maintenance costs, and high electrical resistance make RC a prominent alternative to steel. The drawbacks related to the application of RC poles include the high self-weight and vulnerability to damage. Self-weight might be reduced by prestressing the reinforcement and/or forming a tubular structure for the poles. However, both of these options might increase the vulnerability of the supports. Moreover, long-term processes (deterioration of concrete and corrosion of steel reinforcement) complicate the prediction of structural properties. This paper presents results of the everlasting inspection of the overhead electric power distribution system in Lithuania: technical state of more than 500 RC supports was assessed; selected poles were tested until failure. A specific point of this research is that most of the inspected supports were under maintenance since the middle of last century. The inspection results were used for developing the technical condition of RC pole evaluation scale proposed in this paper.     

U形预应力钢板箍加固T形截面钢筋混凝土梁受剪性能试验研究

为改进T形截面钢筋混凝土(RC)梁的受剪加固工艺,提出了一种采用U形预应力钢板箍对T形截面RC梁进行受剪加固的技术。采用简支梁跨中集中力加载的方法,完成了1个足尺未加固RC梁和5个足尺加固RC梁的单调静载试验,研究U形钢板箍间距和预应力水平对加固RC梁受剪性能的影响。通过试验得到了试件的损伤发展过程、破坏形态、荷载-变形曲线以及钢板箍、钢筋和混凝土的应变曲线。研究表明：采用U形预应力钢板箍可有效提高既有T形截面RC梁的斜截面受剪承载力,试件受剪承载力随钢板箍间距的减小而提高,最大提高幅度可达46.1%。当钢板箍间距小于400mm时,加密钢板箍对试件受剪承载力的提高作用逐渐减弱。钢板箍预应力水平在0.35以上时,进一步提高预应力水平对试件受剪承载力无明显影响。提出了U形预应力钢板箍加固T形截面RC梁受剪承载力的计算式,计算结果与试验结果吻合良好,可为既有T形截面RC梁的加固设计提供参考。     

Analytical investigation of response modification (behaviour) factor,R, for reinforced concrete frames rehabilitated by steel chevron bracing

Steel bracing of reinforced concrete (RC) frames has received noticeable attention in recent years as a retrofitting measure to increase the shear capacity of the existing RC buildings. In order to evaluate the seismic behaviour of steel-braced RC frames, some key response parameters, including the ductility and the overstrength factors, should first be determined. These two parameters are incorporated in structural design through a force reduction or a response modification factor. In this paper, the ductility and the overstrength factors as well as the response modification factor (or seismic behaviour factor) for steel chevron-braced RC frames have been evaluated by performing inelastic pushover analyses of brace-frame systems of different heights and configurations. The effects of some parameters influencing the value of behaviour factor, including the height of the frame and share of bracing system from the applied lateral load have been investigated. It is found that the latter parameter has a more localised effect on the R values and its influence does not warrant generalisation at this stage. However, the height of this type of lateral load-resisting system has a profound effect on the R factor, as it directly affects the ductility capacity of the dual system. Finally, based on the findings presented in the article, tentative R values have been proposed for steel chevron-braced moment-resisting RC frame dual systems for different ductility demands and compared with different type of bracing systems.     

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。     

日本结构抗震加固的工程实例

本文由株式会社日建设计的结构设计部工程师具体介绍了一些地震加固工程实例。由于日本是多地震国家,不仅在结构设计时要求建筑物在地震后易于加固,而且在结构加固时也要求加固得足以抵抗将来可能发生的更强烈的地震,以保证建筑物的耐久性能。在日本,抗震理论和技术年复一年地提高,这里,主要介绍两种地震加固的方法—制振和隔震。实例1是采用含低屈服点钢材的吸能支撑(Energy Absorption Bracing,EAB)来进行地震加固的例子。该建筑建造于1970年,是一个64m高的型钢骨混凝土结构(Steel framed Re-inforced Concrete,SRC)。实例2是建于1920年的一所大学的小礼拜堂。这个2层的建筑高12.6m,由砖建成。在经过多方调查后,提出了三种方案来对其进行地震加固,最终选用了基底隔震技术来使得建筑上部的钢筋用量最小。实例3是一个国际儿童文献图书馆的改造工程,该图书馆成功地保留了原来建筑的历史价值,并且又增加了很多当代图书馆的新功能。在该工程中采用了基底隔震技术。     

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.     

磁流变阻尼智能加固体系的试验研究

提出利用磁流变阻尼器(MRD)对有损伤结构进行智能加固。根据MRD的特点,结合我国抗震设计规范,给出MRD智能加固的三个等级性能目标,对其进行量化,并确定MRD智能加固的设计要点。利用MRD对一有损伤钢筋混凝土框-剪偏心结构进行抗震加固,并进行振动台试验。结果表明,采用MRD智能加固后的结构抗震性能大大提高,优于用被动控制方法加固的结构。     

A novel lifetime cost-benefit analysis method for seismic retrofitting of low-rise reinforced concrete buildings

This article presents a novel simplified method for assessing seismic damage to low-rise reinforced concrete (RC) buildings by using the hazard curve of response spectral acceleration. Moreover, the occurrence of an earthquake is assumed to follow a Poisson process when analysing the occurrence probability of a specified damage state in the remaining service life and expected losses induced by seismic damage. Then, a novel procedure for estimating lifetime costs and benefits of seismic retrofitting is proposed. In the case study, 16 practical design projects for seismic retrofitting of RC school buildings in Taipei are subjected to lifetime cost-benefit analysis using the proposed method. It can be found that not only lifetime cost-benefit ratios but also the financial return period for each dollar invested seismic retrofitting can be identified conveniently. Additionally, they are useful information for making decisions about whether to retrofit a building or not.     

CFRP增强钢筋混凝土矩形中空桥墩的非线性模型

钢筋混凝土中空桥墩承受了较大弯矩和剪力,为减轻自重,提高基础的承载力,进行强度-质量比及强度-刚度比的结构优化,进而在高地震作用下以及边界要求抬高基础时,减少柱的自重,降低地震响应。近十年来,对采用纤维增强复合材料加固的实心柱进行了广泛研究,然而缺乏对纤维增强复合材料加固空心柱的研究。基于脆性破坏机制下的强度和延性,所提出的约束模型和计算公式能够预测纤维增强复合材料加固空心柱的基本性能,即混凝土保护层的破裂和钢筋屈曲(空心构件的一般破坏模式)。根据混凝土以及约束外壳的应力-应变关系,可以对各级荷载下多轴应力状态以及混凝土或外裹FRP的破坏形式进行评估。根据曲率和延性,所提模型对构件变形进行了评估。研究表明:理论分析结果与试验结果吻合较好。     

国内外建筑隔震改造加固概述

本文总结了国外利用隔震技术对既有的房屋进行抗震加固的工程应用情况,其特点是:1.隔震改造的多为多层房屋;2.仅美国和日本在高层房屋的改造中应用了隔震技术;3.隔震改造的结构形式有钢筋混凝土结构、钢结构、砖石砌体结构、木结构等各种形式;4.以基底隔震为主,也有中间层隔震的应用实例.     

钢混框架梁端负弯矩区加固技术现状分析及建议

加固方法的快捷性、高效性对于加固改造工程尤为重要.然而钢筋混凝土框架梁端负弯矩区受弯承载力不足的加固一直缺乏好的方法.文章对钢筋混凝土框架粱端负弯矩区加固技术现状进行了分析,作为示例探讨了P-SWR技术应用的可行性,并针对框架结构加固研究提出了若干建议.