外文翻译--反复荷载作用下复合增强型钢筋混凝土框架结构的性能（中英文）

反复荷载作用下复合增强型钢筋混凝土框架结构的性能M.Nehdi和A.SaidDept,of Civil&Env.Eng.,西安大略大学,伦敦，安大略，加拿大 ,N6A 5B9 2004年5月5日投稿;2004年10月13日定稿摘要FRP作为增强混凝土结构的材料得到日益广泛的应用。FRP一个有待开发和研究的应用便是在钢筋混凝土框架结构中的应用。但是，由于FRP的弹性，使得FRP钢筋混凝土构件的韧性较差和耗能性也较差。复合增强型FRP钢筋的增强作用可以弥补缺乏韧性的FRP钢筋混凝土构件的不足。在构件横截面上布置两层，FRP钢筋放置于外层，钢筋置于内层，这样就远离了碳化及氯离子侵蚀的影响。结合FRP箍筋，这种方法可提高钢筋混凝土构件的耐腐蚀性能。但是，目前的设计标准，并没有叙述标准FRP钢筋混凝土结构详细的抗震设计规定。特别是在抗震设计中详细的梁柱节点设计是一个关键问题。在近期的地震中，许多结构性坍塌引发了梁柱节点的损坏。鉴于此，研究这一问题可更好地了解GFRP和FRP钢筋混凝土在地震荷载作用下的情况。在这项研究中，对分别配有钢筋、GFRP和复合增强型的GFRP钢筋的梁柱节点等尺寸模型进行了测试，并研究了他们的抗震性能。1.导言 钢筋的腐蚀一直是钢结构或钢筋混凝土结构恶化的主要原因，世界各地每年用于钢结构或钢筋混凝土结构的维修费用就是由于上述原因而大幅提高。此外例如在医院，现代没有这种用高分子材料来增强性能的磁性干扰设备，医院因此得不到一个无磁环境。这样人们对高分子材料（FRP）的应用就越来越感兴趣，因为这种高分子材料是天然无磁性的和耐腐蚀性的1。同时FRP的增强技术也能应用在选择容易嵌入光纤应变测量装置的结构中，以达到有效监测的目的。然而，与混凝土和传统钢筋的粘结性相比，FRP材料往往表现出较弱的粘结性。以FRP作为增强材料的混凝土可提高其性能，如表面变形和砂涂料性能，但其较弱的粘结性仍然是一个主要关注的问题，特别是在建筑物遭受地震或冲击载荷的作用下。Brown和Bartholomew2指出，FRP钢筋混凝土梁用强度设计方法可以预测钢筋混凝土梁的极限抗弯能力。然而，在设计过程中，挠度和延展性这两项标准不属于通常情况下钢筋设计中的问题。与钢筋（除一些新的碳纤维复合材料制品）相比，绝大多数的FRP材料通常都会显著降低FRP钢筋混凝土的弹性模量。因此FRP钢筋混凝土结构往往会产生较大的挠度，而且主要是在破坏之前弹塑性效果不大，通常是突然的和脆性破坏的。在设计中满足FRP钢筋混凝土结构挠度和粘结性的要求是一项挑战。因此，建议在FRP钢筋砖和梁设计中应着眼于钢筋路段的弯曲，以实现一个具体压缩损坏的塑性行为，这种做法往往使FRP钢筋混凝土具有抗折特性。 近年来，在复合型FRP钢筋和FRP钢筋混凝土结构中出现了越来越有兴趣的探讨。不过，这方面的研究工作普遍针对的是一些梁柱测试，大部分新近通过的FRP钢筋混凝土设计规格是不全面的，往往不包括详细的抗震设计规定，并不包括复合增强型的FRP钢筋混凝土结构系统。因此，需要进行研究，以探讨复合增强型的FRP混凝土框架结构在反复荷载作用下的状态，以此形成基础，为今后FRP钢筋混凝土在地震区设计的规范中进行规定。在这项研究中，分别对全增强的钢筋、没有增强的GFRP钢筋和复合增强型的GFRP钢筋梁柱节点在反复荷载作用下进行测试，对负载层位移包络线和耗能性进行了比较与讨论。2.研究的历史各类研究人员对FRP作为增强钢筋混凝土梁材料的应用作了调查。分别进行了各种各样的纵向和横向增强的研究。虽然横向增强通常是更接近于混凝土表面的实际情况，因此更容易受到腐蚀的FRP箍筋已经使用特殊的增强技术。在工业厂房中使用了的倒置箍筋已阻碍了其实际的可用性，即60的强度降低这样一个事实。此外，FRP钢筋弯曲作箍筋通常需要工厂生产的特殊设备。用FRP-NEFMAC（新纤维复合材料增强混凝土）网格可以提供一个解决这种问题的方法，四网格持续教育研究部门采取从新纤维复合材料增强混凝土网格提供了一个三分支箍筋图。Grira和Saatcioglu12研究了利用双钢网格和碳纤维网格作为隔离有纵向钢筋混凝土的箍筋。在反复荷载作用下对几个网格配置使用和标柱进行了测试。他们得出结论认为，双钢网格柱钢筋与碳纤维布置的箍筋效果相当。他们还争论，使用网格制成的钢筋或碳纤维复合材料是否提供了方便施工和即将开展的均匀分布的隔离压力沿栏无塞钢筋笼。他们认为，网格箍筋没有能在其节点发挥作用，这通常是与FRP箍筋具有相同的缺陷。已经对混合FRP-STEEL 钢筋混凝土做了有限的试验。Aiello和Ombres14测试了6组不同配置纵向钢筋的梁，包括只有钢，除了AFRP和混合AFRP-Steel梁，所有梁都配置了箍筋。相对于混合结构试件，钢的试件拥有很厚的保护层，以次来提供额外的保护来抵御腐蚀危害。实验结果表明，这种混合体系在失效时比AFRPSteel-Free体系有较低的挠度和叫高的延性。Leung和Balendran15在4点弯曲下测试了7组钢筋混凝土梁。STEEL和GFRP混凝土强度和加固率在增强加固和过度加固的截面被改变。相对与GFRP，钢筋被放在距混凝土表面30mm厚的地方。研究表明，对于混合梁，钢有助于有效地发挥整体作用性能。钢的刚度屈服大幅下降，GFRP钢筋对于抵御断裂开始发挥很大的作用。增大高强混凝土梁的抗弯能力，使扭转弯曲破坏转变为剪切破坏。3.实验方案 梁柱接头可以从平面框架单元中抽出。当柱是从一层至下一层的中间高度截断时，梁试验单元所采用的便是跨中至梁端的部分。3.1 钢筋增强研究实例3.2 GFRP增强研究实例3.3 复合增强型钢筋增强研究实例3.4 试验体系和程序 对上述梁柱节点进行了测试，适用于柱的恒定轴向载荷为600KN，并且在反复荷载（准静态）作用下适用于梁端。对柱不断施加轴向载荷，在应用液压千斤顶前，运用反向反复的负荷载，以模拟一个典型的应激状态下的负荷水平。该选定的加载模式适用于经常处于严重地震荷载下引起大形变的结构框架中。5.讨论用FRP作为增强混凝土结构的材料已在日益普及，但各种设计准则和规定，还需要制定其安全实施细则,才能大规模实地应用。例如，ACI440.1R-01找出各种各样与研究有关的问题，这些问题都需要解决，有一些如建立统计拉伸能力变化了的FRP钢筋是其中一个简单的问题。此外，对FRP横向钢筋起抗剪作用的钢筋混凝土构件必须妥为评估。在设计中，与混凝土相比钢筋加在较低强度的FRP中是困难的，例如在满足钢筋的伸缩长度情况下，梁的钢筋锚固在外墙接缝，而用FRP钢筋则需要额外的嵌入长度，而且很难在FRP钢筋制造弯角。所以在增强复杂结构的配置中很难采用这种材料，必须采取其它措施加以解决。6.结论根据实验观察和分析化验结果，可以得出以下结论：1 、强型的GFRP的梁柱节点测试时在扭转循环载荷作用下显示出非常低的可塑性特点，与钢和钢混试件相比其能量损耗大大降低。2 、复合增强型的GFRP钢筋的梁柱节点比传统加强型钢梁柱节点的刚度底，但比增强型的GFRP钢筋的梁柱节点的刚度高。3 、复合增强型的GFRP钢筋试件显示令人满意的位移量，延性RC框架建筑杂志上推举的假设最低位移要求的3% 24 。4 、混合型钢筋混凝土体系可以提供了一系列的性能要求，如耐用性，刚度，强度，韧性等，设计者可在混合体系和设计标准两者之间取得一个平衡。5 、本研究只集中于一级的亚带。更多全球性的观点应该在瞬间阻力结构设计中被采用。深入的动态分析和玻璃钢复合钢筋混凝土结构，以便更好地满足抗震要求。6 、为钢筋混凝土结构抗震延性设计制定的设计规范已经制定，有必要对FRP-RC结构重新加以评估。附件2：外文原文（复印件）Performance of RC frames with hybrid reinforcement under reversed cyclic loading M. Nehdi and A. Said Dept, of Civil & Env. Eng., The University of Western Ontario, London, Ontario, Canada, N6A 5B9 Received. 5 May 2004; accepted. 13 October 2004 ABSTRACT The use of FRP as reinforcement in concrete structures has been growing rapidly. A potential application of FRP reinforcement is in reinforced concrete (RC) frames. However, due to FRPs predominantly elastic behaviour, FRP-RC members exhibit low ductility and energy dissipation. Hybrid steel-FRP reinforcement can be a viable solution to the lack of ductility of FRP-RC members. Using two layers of reinforcement in a section, FRP rebars can be placed in the outer layer and steel rebars in the inner layer away from the effects of carbonation and chloride intrusion. Combined with the use of FRP stirrups, this approach can enhance the corrosion resistance of RC members. However, current design standards and detailing criteria for FRP-RC structures do not provide detailed seismic provisions. In particular, the design and detailing of beam-column joints is a key issue in seismic design. During recent earthquakes, many structural collapses were initiated or caused by beam-column joint failures. Thus, research is needed to gain a better understanding of the behaviour of FRP and hybrid FRP-steel-RC under seismic loading. In this study, three full-scale beam-column joint specimens reinforced with steel, GFRP and a hybrid GFRP-steel configuration, respectively were tested in order to investigate their performance in the event of an earthquake. 1.INTRODUCTION Corrosion of reinforcing steel has been the primary cause of deterioration of reinforced (RC) structures, requiring substantial annual repair costs around the world. Furthermore, modem equipments that employ magnetic interferometers, such as in hospitals, require a nonmagnetic environment with no metallic reinforcement. This has led to an increasing interest in fibrereinforced polymers (FRP) reinforcement, which is inherently nonmagnetic and resistant to corrosion 1. Measurement devices for structural health monitoring purposes. However, FRP materials often exhibit weaker bond to concrete and lower ductility compared to that of conventional steel reinforcement. The bond of FRP to concrete can be improved by means of mechanical anchorages such as surface deformations and sand coating, but its lower ductility remains a major concern, especially in structures subjected to seismic and/or impact loading.Brown and Bartholomew 2 observed that FRP-RC beams behaved in a similar manner to that of steel-RC beams. However, in the design process, two criteria that are not usually problematic in the case of steel reinforcement can govern the design in the case of FRP reinforcement: deflection and ductility. Most FRP materials usually have a significantly lower modulus of elasticity compared to that of steel (except for some new CFRP products) and thus, often generate higher deflections, Furthermore, the predominantly elastic behaviour of FRP results in little warning before a usually sudden and brittle failure. Satisfying deflection and ductility requirements is a challenge in designing FRP-RC structures. Thus, it is recommended that flexural design of FRP-reinforced slabs and beams should aim at over-reinforced sections in order to achieve a concrete compression failure, which usually allows FRP-RC flexural members to exhibit some plastic behaviour before failure 3, 4.In recent years, there has been a growing interest to investigate the performance of mixed steel-FRP as well as steel-free FRP-RC structures. However, research in this area has been generally limited to some beam and column testing.Most of the newly adopted specifications for the design of FRP-reinforced concrete 4-8 are not comprehensive, often do not include detailed seismic provisions, and do not cover hybrid FRP-steel RC systems. Therefore, research is needed to investigate the performance of FlIP and hybrid FRP-steelreinforced concrete frames under reversed cyclic loading in order to form the basis for future design code provisions for FRP-reinforced concrete in seismic zones. In this study, fullscale steel-reinforced, steel-free GFRP-reinforced, and hybrid GFRP-steel-reinforced beam-column joints were tested under reversed cyclic loading; Their behaviour including load-storey drift envelope relationship and energy dissipation were compared and discussed.2. SCOPE OF PREVIOUS WORKThe use of FRP as reinforcement in RC beams was investigated by various researchers. Different permutations of FlIP and steel as longitudinal and transverse reinforcement,respectively were studied 9-11. Although transverse reinforcement is usually closer to the concrete surface and is therefore more vulnerable to corrosion, limited investigations have been performed on the use of FRP stirrups. The use of FlIP stirrups has been hindered by their limited availability and the fact that a 60% strength reduction factor at bends for various types of FRP is recommended 6. Also, bending FRP bars to make stirrups typically needs to be performed in production plants with special care and equipment. The use of FRP NEFMAC (New Fiber Composite Material for Reinforcing Concrete) grids can provide a solution to such a problem; a four-ceU unit taken from a NEFMAC grid provides a three-branched stirrup as shown in Fig. Grira and Saatcioglu 12 investigated the use of both steel grids and CFRP grids as stirrups for confinement of concrete columns having longitudinal steel reinforcement. Several grid configurations were used and column specimens were tested under cyclic loading. They concluded that the performance of columns reinforced with CFRP stirrups was comparable to that of columns reinforced with steel stirrups. They also argued that the use of grids whether made of steel or CFRP provides ease of construction and a near-uniform distribution of the confinement pressure along the column, without congesting the reinforcement cage. They reported that the NEFMAC gridbased stirrups failed at their nodes, which is usually the common weakness of FRP stirrups. Fukuyama et al. 13 tested a half-scale three-storey AFRP-reinforced concrete frame under quasi-static loading. RA11S aramid-bars were used for the longitudinal reinforcement of columns, RA7S bars were used as flexural reinforcement for beams and slabs, while RA5 bars were used as shear reinforcement. RA11S, RA7S and RA5 are braided bars with cross-sectional areas of 90, 45 and 23 mm 2, respectively. It was argued that frame deformations governed the design. The frame remained elastic up to a drift angle of 1/50 rad, and no substantial decrease in strength took place after rupture of some main beam rebars owing to the high degree of structural indeterminacy of the frame. It was also noted that the rehabilitation of such a frame was easier than that of conventional RC flames since residual deformations were smaller. However, the flame was not tested to collapse and its behaviour under excessive deformations was not reported. Limited research has been performed on hybrid FRP-steel reinforced concrete. Aiello and Ombres 14 tested 6 beams with different configurations of longitudinal reinforcement including steel only, AFRP only, and hybrid AFRP-steel beams, all with steel stirrups. For some of the hybrid specimens, steel was placed with a larger concrete cover to provide extra protection against corrosion. Experimental results showed that such a hybrid system can have lower service deflection and higher ductility at failure than that of the AFRP steel-flee system. Leung and Balendran 15 tested seven RC beams under four point bending. Concrete strength and reinforcement ratios for both steel and GFRP were varied to produce under-reinforced and over-reinforced sections. Steel rebars were placed at 30 mm higher concrete cover compared to that for GFRP rebars. The study showed that for hybrid beams, steel contributed more effectively to the overall behaviour up to yield. Afterwards, the stiffness of yielded steel dropped drastically and the GFRP rebars started to contribute more efficiently to the section resistance. For high strength concrete beams, the increased flexural capacity resulted in shifting the flexural failure into a shear failure.Some research focused on providing ductility to FRP rebars that are manufactured by filament winding or pultrusion. For instance, Tamuzs and Tepfers 16 investigated the properties of a hybrid FRP rod. They used multiple fibre types along with braiding fibre strands around a soft porous core to achieve a more ductile behaviour. The hybrid rods they produced could provide a ductile behaviour, but the difference between the moduli of different fibre strands seemed to cause uneven load transfer, while the compression of the core material caused a reduction of cross-section. A similar study was performed by Bakis et al. 17 who developed pseudo- ductile FRP rods using different types of fibres. The rods behaved in a pseudo-ductile manner when tested under tension, but premature failure took place due to local stress concentrations. Another study performed by Harris et al. 18 developed a ductile hybrid FRP rebar through braiding of various fibres followed by a pultrusion process. Belarbi et al. 19 were also successful in developing composite reinforcing rebars with a relatively more stable stress-strain behaviour in tension and better load-deflection behaviour under four-point bending. However, such rebars are still in early experimental stages and there is not enough data on their field performance, especially under seismic loading. 3. EXPERIMENTAL PROGRAM Beam-column joints can be isolated from plane frames at the points of contraflexure. The beam of the current test unit is taken to the mid-span of the bay, while the column is taken from the mid-height of one storey to the mid-height of the next storey. 3.1 Steel-reinforced specimen (J1) 3.2 GFRP-reinforced specimen (J4) 3.3 Hybrid-reinforced specimen (J5)3.4 Test setup and procedure5. DISCUSSION The use of FRP as reinforcement in concrete structures has been increasing in popularity, yet various design guidelines and provisions still need to be developed for its safe implementation in large-scale field applications. For instance, the ACI 440.1R-01 identified a wide variety of research issues pertaining to FRP that need to be addressed, some of which are as simple as establishing the statistical variation of the tensile capacity of FRP rebars. Moreover, the contribution of FRP transverse reinforcement to the shear capacity of RC elements needs to be properly evaluated. The lower bond strength of FRP to concrete compared to that of steel imposes difficulties in design, for instance in satisfying rebar development length such as in the case of beam reinforcement anchorage in exterior joints, for which using FRP would require additional embedded length compared to when steel rebars are used. Also the difficulty of manufacturing bends in FRP makes it difficult to adopt this material in reinforcing structurally complicated configurations and needs to be addressed. A major drawback of steel-free FRP-RC systems is their low energy dissipation under earthquake loading, as demonstrated by the performance of the tested FRP-reinforced joint specimen (J4). The energy input from ground motion is equal to the sum of potential, kinematic, damping and hysteretic energy components 22. The potential and kinematic energy components vanish after the static equilibrium of the structure is reached, while the damping and hysteretic energy components are responsible for energy dissipation. The hysteretic component becomes the major contributor to energy dissipation when significant inelastic deformations take place. Hence, an FRP-reinforced frame may have to be designed with a high damping component so that when added to its relatively limited hysteretic Component, it can dissipate the energy input during an earthquake. Design guidelines for framed RC buildings by the Architecture Institute of Japan, as outlined by Kobayashi et al. 23, entail ensuring seismic performance by overcoming the ductility deficiency of FRP-RC frames. The study recommended the use of the capacity spectrum method. Performance demand and capacity spectra were evaluated and a performance point, where the demand and capacity spectra meet and members are still below their flexural capacity, was defined as the safety limit. This performance-based design approach was successfully applied to the analysis of a 9-floor FRP-RC frame. The study also pointed out the cruciality of damping in FRP-RC structures and recommended the use of vibration control devices. The use of hybrid steel-FRP RC systems could address many of the drawbacks of steel-free RC systems. Steel reinforcement can be used in lateral load resisting structural members, which are not usually exposed to aggressive media, while FRP reinforcement can be used in the envelope of the structure to enhance durability. Alternatively, a hybrid reinforcement configuration can make use of the corrodible steel at a thick concrete cover, while the more durable FRP stays at a minimum cover. Thus, the structure can benefit from using such a hybrid reinforcement system to provide both durability (using FRP) and post-peak reserve strength (using steel). The present study focussed only on comparing the behaviour of FRP, hybrid steel-FRP, and steel-reinforced beam-column joints. Full-scale tests on entire FRP and hybrid-reinforced frames need to be performed to assess the progress of failure globally. The results can be used to calibrate numerical models that can be used to simulate the behaviour of multi-storey FRP and hybrid-reinforced frames with high degrees of redundancy, and accordingly predict the progress of failure. Moreover, passive energy dissipation devices can provide a source of energy dissipation for FRP-reinforced frames, which needs further focussed research. Overall, research efforts are still needed to address many questions and uncertainties, and to develop adequate design provisions dedicated to steel-free and hybrid RC systems, before their widespread use in demanding large-scale structural applications becomes feasible and safe in seismic areas. 6. CONCLUSIONS An effort was made to investigate the performance of GFRP and hybrid steel-GFRP-reinforced beam-column joints and to compare their behaviour to that of standard steel-reinforced beam-column joints under reversed quasi- static (cyclic) loading.,the following conclusions can be drawn: The GFRP-reinforced beam-column joint showed very low plasticity features when tested under reversed cyclic loading. This resulted in lower energy dissipation compared to that of the steel and hybrid reinforced specimens. The hybrid GFRP-steel-reinforced beam-colunm joint showed lower stiffness than that of the conventional steel- reinforced beam-column joint, but exhibited higher stiffness than that of the GFRP-reinforced specimen. The GFRP and hybrid-reinforced specimens showed satisfactory drift capacity, assuming a minimum drift requirement of 3% (0.03 rad) as recommended in the literature for ductile RC flame buildings 24. A hybrid RC system could be tailored to provide a range of performance requirements such as durability, stiffness, strength, ductility, etc. A designer may adapt the reinforcement configuration of the hybrid system to accommodate a balance between such design criteria. This study was only focussed on the level of the subassemblage. A more global concept should be adopted in the design of moment-resisting frames. Thorough dynamic analysis of GFRP and hybrid-RC structures should be performed to better assess their capacity in meeting seismic resistance requirements. Design code provisions for the seismic design of RC structures, which have been developed for ductile steel reinforcement, need to be re-evaluated for FRP-RC structures.