钢丝网复合砂浆加固混凝土受弯构件非线性分析

对用钢丝网复合砂浆加固的钢筋混凝土梁进行了正截面抗弯试验研究。试验包括16根用钢丝网加固的梁和两根未加固的对比梁,采用U形三面的加固方式(钢丝网复合砂浆包裹了梁的受拉面及两个侧面)。试验中对比了加固与未加固构件的裂缝开展情况、跨中挠度以及极限荷载。试验结果表明,钢丝网复合砂浆薄层可以明显地提高钢筋混凝土梁的抗弯承载力,提高抗裂性能,增强构件的抗弯刚度。理论部分采用非线性的方法得到加固构件的荷载-挠度曲线,与试验结果比较,有较好的吻合。     

Repair and strengthening of reinforced concrete square columns using ferrocement jackets

A series of 10 one-third scale square reinforced concrete column specimens were cast; preloaded under axial compression up to various fractions (0%, 60%, 80%, and 100%) of its ultimate load; repaired using ferrocement jackets containing two layers of Welded Wire Mesh (WWM) encapsulated in high strength mortar; and then retested to failure. The overall response of the specimens was investigated in terms of load carrying capacity, axial displacement, axial stress and strain, lateral displacement, and ductility. The test results indicated that jacketing reinforced concrete square columns with this form of ferrocement provided about 33% and 26% increases in axial load capacity and axial stiffness, respectively, compared to the control columns. The test results also indicated that repairing similar reinforced concrete columns (after preloading them to failure) with the same ferrocement jacket almost restored their original load capacity and stiffness. Furthermore, the repaired columns failed in a ductile manner compared to the brittle failure exhibited by the control columns.     

Strength and stiffness of post-heated columns repaired with ferrocement and fibre reinforced polymer jackets

This paper presents the results of an experimental study carried out to compare the effectiveness of ferrocement and fibre reinforced polymers (FRPs) jackets for the repair of post-heated square and circular reinforced concrete columns. The suite of test specimens comprised (a) non-heated and non-repaired; (b) post-heated and non-repaired and (c) post-heated and repaired, columns. Glass fibre reinforced polymer (GFRP), carbon fibre reinforced polymer (CFRP) and ferrocement jackets were used to repair the heated columns. All the columns were tested under axial compression. The test results covering the axial compressive strength, stiffness (secant stiffness), ductility, deformation and energy dissipation for the non-heated and non-repaired, and post-heated and non-repaired columns, were explored and compared with those of the post-heated columns repaired with FRP and ferrocement jackets. The test results showed that the FRP jackets increased the compressive strength, ductility, deformation ability and energy dissipation capacity of post-heated columns but did not increase the stiffness. However, the ferrocement jackets enhanced both the strength and stiffness of the post-heated columns. It is concluded that a possible combination of ferrocement and FRP jackets is the optimum solution to restore the required strength, stiffness and ductility following structural damage from a fire.     

BFRP筋钢纤维高强混凝土梁受弯承载力试验与理论

通过11根玄武岩纤维增强聚合物复合材料（BFRP）筋钢纤维高强混凝土梁的受弯性能试验,研究了钢纤维混凝土层厚度、钢纤维体积分数和BFRP筋配筋率对BFRP筋钢纤维高强混凝土梁受弯破坏形态及其承载力的影响。结果表明,BFRP筋钢纤维高强混凝土梁的破坏模式可分为受压破坏、受拉破坏和平衡破坏3种;钢纤维混凝土层厚度和钢纤维体积分数的变化对于BFRP筋钢纤维高强混凝土梁受弯承载力具有一定程度的影响,当BFRP筋配筋率为0.77%时,掺加体积分数为1.0%钢纤维的梁受弯承载力较无钢纤维梁提高了22.7%,在受拉区0.57倍截面高度内掺加1.0vol%钢纤维的梁受弯承载力达到全截面钢纤维混凝土梁受弯承载力的86.7%;增大BFRP筋配筋量可显著提高BFRP筋钢纤维高强混凝土梁的受弯承载力,BFRP筋配筋率为1.65%的试验梁受弯承载力较配筋率为0.56%的试验梁提高了39.4%。针对不同的破坏模式,提出了BFRP筋钢纤维高强混凝土梁受弯承载力和平衡配筋率的计算方法,并结合安全配筋率的概念对试验梁的破坏模式进行了预测,试验结果与分析结果吻合良好。     

Behavior of full-scale reinforced concrete beams retrofitted for shear and flexural with FRP laminates

Four full-scale reinforced concrete beams were replicated from an existing bridge. The original beams were substantially deficient in shear strength, particularly for projected increase of traffic loads. Of the four replicate beams, one served as a control and the remaining three were implemented with varying configurations of carbon fiber reinforced polymers (CFRP) and glass FRP (GFRP) composites to simulate the retrofit of the existing structure. CFRP unidirectional sheets were placed to increase flexural capacity and GFRP unidirectional sheets were utilized to mitigate shear failure. Four-point bending tests were conducted. Load, deflection and strain data were collected. Fiber optic gauges were utilized in high flexural and shear regions and conventional resistive gauges were placed in eighteen locations to provide behavioral understanding of the composite material strengthening. Fiber optic readings were compared to conventional gauges.Results from this study show that the use of fiber reinforced polymers (FRP) composites for structural strengthening provides significant static capacity increases approximately 150% when compared to unstrengthened sections. Load at first crack and post cracking stiffness of all beams was increased primarily due to flexural CFRP. Test results suggest that beams retrofit with both the designed GFRP and CFRP should well exceed the static demand of 658 kN m sustaining up to 868 kN m applied moment. The addition of GFRP alone for shear was sufficient to offset the lack of steel stirrups and allow conventional RC beam failure by yielding of the tension steel. This allowed ultimate deflections to be 200% higher than the pre-existing shear deficient beam. If bridge beams were retrofit with only the designed CFRP failure would still result from diagonal tension cracks, albeit at a 31% greater load. Beams retrofit with only the designed shear GFRP would fail in flexure at the mid-span at an equivalent 31% gain over the control specimen, failing mechanism in this case being yielding of the tension steel. Successful monitoring of strain using fiber optics was achieved. However, careful planning tempered by engineering judgement is necessary as the location and gauge length of the fiber optic gauge will determine the usefulness of the collected data.     

碳纤维布加固已承受荷载的钢筋混凝土梁抗弯性能试验研究及抗弯承载力计算

进行了6根碳纤维布加固已承受荷载的钢筋混凝土梁和2根对比混凝土梁的抗弯性能试验研究,分析了碳纤维布加固已承受荷载的钢筋混凝土梁的破坏机理,研究了荷载历史对加固梁极限荷载的影响。试验结果表明,粘贴碳纤维布可以有效地提高加固梁的抗弯承载能力。无论荷载历史如何,只要梁承受的初始荷载相同,梁破坏时的极限荷载基本相同。梁端锚固对加固梁的极限荷载影响不明显。根据不同的破坏模式,提出了碳纤维布加固已承受荷载的钢筋混凝土梁的承载力计算方法,给出了工程实用计算公式。     

Structural performance of corroded RC beams repaired with CFRP sheets

Corrosion of reinforcement is a serious problem and is the main cause of concrete structures deterioration costing millions of dollars even though the majority of such structures are at the early age of their expected service life. This paper presents the experimental results of damaged/repaired reinforced concrete beams. The experimental program consisted of reinforced concrete rectangular beam specimens exposed to accelerated corrosion. The corrosion rate was varied between 5% and 15% which represents loss in cross-sectional area of the steel reinforcement in the tension side. Corroded beams were repaired by bonding carbon fiber reinforced polymer (CFRP) sheets to the tension side to restore the strength loss due to corrosion. Different strengthening schemes were used to repair the damaged beams. Test results showed detrimental effect of corrosion on strength as well as the bond between steel reinforcement and the surrounding concrete. Corroded beams showed lower stiffness and strength than control (uncorroded) beams. However, strength of damaged beams due to corrosion was restored to the undamaged state when strengthened with CFRP sheets. On the other hand, the ultimate deflection of strengthened beams was less than ultimate deflection of un-strengthened beams.     

Repair of shear-deficient normal weight concrete beams damaged by thermal shock using advanced composite materials

The use of advanced composite materials such as Fiber Reinforced Polymers (FRPs) in repairing and strengthening reinforced concrete structural elements has been increased in the last two decades. Repairing and strengthening damage structures is a relatively new technique. The aims of this study was to investigate the efficiency and effectiveness of using Carbon Fiber Reinforced Polymer (CFRP) to regain shear capacity of shear-deficient normal weight high strength RC beams after being damaged by thermal shock. Sixteen high strength normal weight RC beams (100 × 150 × 1400 mm) were cast, heated at 500 °C for 2 h and then cooled rapidly by immersion in water, repaired, and then tested under four-point loading until failure. The composite materials used are carbon fiber reinforced polymer plates and sheets. The experimental results indicated that upon heating then cooling rapidly, the reinforced concrete (RC) beams exhibited extensive map cracking without spalling. Load carrying capacity and stiffness of RC beams decreased about 68% and 64%, respectively, as compared with reference beams. Repairing the thermal damaged RC beams allowed recovering the original load carrying without achieving the original stiffness. Repaired beams with CFRP plates with 90° and 45° regained from 90% to 99% of the original load capacity with a corresponding stiffness from 79% to 95%, whereas those repaired with CFRP sheet on the web sides and a combination of CFRP plates and sheet regained from 102% to 107% of the original load capacity with a corresponding stiffness from 81% to 93%, respectively. Finally, finite element analysis model is developed and validated with the experimental results. The finite element analysis showed good agreement as compared with the experimental results in terms of load–deflection and load–CFRP strain curves.     

Effect of steel and synthetic fibers on flexural behavior of high-strength concrete beams reinforced with FRP bars

Six high-strength concrete beam specimens reinforced with fiber-reinforced polymer (FRP) bars were constructed and tested. Three of the beams were reinforced with carbon FRP (CFRP) bars and the other three beams were reinforced with glass FRP (GFRP) bars as flexural reinforcements. Steel fibers and polyolefin synthetic fibers were used as reinforcing discrete fibers. An investigation was performed on the influence of the addition of fibers on load-carrying capacity, cracking response, and ductility. In addition, the test results were compared with the predictions for the ultimate flexural moment. The addition of fibers increased the first-cracking load, ultimate flexural strength, and ductility, and also mitigated the large crack width of the FRP bar-reinforced concrete beams.     

混杂纤维布加固钢筋混凝土梁抗弯性能试验及理论研究

该文提出了碳/芳纶/玻璃三种纤维混杂思路,高强、高弹模碳纤维提高承载能力,高延伸率玻璃纤维改善延性,而芳纶纤维使应力从碳纤维向玻璃纤维平稳转移。通过对11根钢筋混凝土梁的抗弯试验,研究了不同混杂方式、混杂结构、纤维布层数对梁抗弯性能的影响。结果表明:如果应力转移不平稳,混杂纤维布将与混凝土发生局部剥离,导致混杂纤维布加固效果降低;在相同纤维布层数条件下,与单一碳纤维布加固梁相比,碳/芳纶/玻璃层间混杂纤维布加固梁的初裂、屈服、峰值和极限荷载分别降低了22%、12%、12%和16%,而位移延性系数提高了20%,表明碳/芳纶/玻璃层间混杂纤维布能够显著降低单一碳纤维布的脆性。在试验研究的基础上,采用弹塑性截面分析法计算了混杂纤维布加固梁的承载力,理论计算值与试验值吻合良好。     

Structural behaviour of RC beams with external flexural and flexural–shear strengthening by FRP sheets

This paper presents experimental research on reinforced concrete (RC) beams with external flexural and flexural–shear strengthening by fibre reinforced polymer (FRP) sheets consisting of carbon FRP (CFRP) and glass FRP (GFRP). The work carried out has examined both the flexural and flexural–shear strengthening capacities of retrofitted RC beams and has indicated how different strengthening arrangements of CFRP and GFRP sheets affect behaviour of the RC beams strengthened. Research output shows that the flexural–shear strengthening arrangement is much more effective than the flexural one in enhancing the stiffness, the ultimate strength and hardening behaviour of the RC beam. In addition theoretical calculations are developed to estimate the bending and shear capacities of the beams tested, which are compared with the corresponding experimental results.     

CFRP筋增强ECC梁弯曲性能试验研究

为研究碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)筋/超高韧性纤维增强水泥基复合材料(Engineered cementitious composite,ECC)梁的抗弯性能,对3根CFRP筋/ECC梁、1根玻璃纤维增强树脂复合材料(Glass fiber reinforced polymer,GFRP)筋/梁和1根CFRP筋混凝土梁进行了四点弯曲试验,分析了配筋率、纤维增强树脂复合材料(Fiber reinforced polymer,FRP)筋类型和基体类型对梁抗弯性能的影响。试验结果表明:CFRP筋/ECC梁与GFRP筋/ECC梁和CFRP筋混凝土梁类似,均经历了弹性阶段、带裂缝工作阶段和破坏阶段;配筋率对CFRP筋/ECC梁的受弯性能影响较大。随着配筋率的增加,CFRP筋/ECC梁的承载能力不断提高,延性性能逐渐减弱;ECC材料优异的应变硬化能力和受压延性,使得CFRP筋/ECC梁的极限承载能力和变形能力均优于CFRP筋混凝土梁;由于ECC材料多裂缝开裂能力,CFRP筋/ECC梁开裂后,纵筋表面应变分布比CFRP筋混凝土梁更均匀; 由于聚乙烯醇(Polyvinyl alcohol,PVA)纤维的桥联作用,CFRP筋/ECC梁破坏时,其表面出现了大量的细密裂缝,且能保持较好的完整性和自复位能力;正常使用阶段,CFRP筋/ECC梁的最大弯曲裂缝宽度均小于CFRP筋混凝土梁。最后,根据试验结果,建立了基于等效应力图的CFRP筋/ECC梁弯曲承载力简化计算模型,确定模型中的相关系数。由简化模型计算的极限承载力与试验结果具有较好的相关性。      

Use of permanent ferrocement forms for concrete beam construction

The results of an experimental investigation to examine the feasibility and effectiveness of using precast U-shaped ferrocement laminates as permanent forms for construction of reinforced concrete beams are presented in this paper. The precast permanent ferrocement forms are proposed as a viable alternative to the commonly used wooden and/or steel temporary forms. The experimental program comprised casting and testing of three control reinforced concrete beams of dimensions 300?×?150?×?2000?mm and eighteen beams of total dimensions of 300?×?150?×?2000?mm consisting of a reinforced concrete core cast in a precast U-shaped permanent ferrocement form of thickness 25?mm. Each control beam was reinforced with two steel bars of 12?mm diameter at the top and bottom of the beam and stirrups of 10?mm diameter placed at 200?mm intervals. The concrete core of the beams incorporating permanent ferrocement forms was reinforced with two steel bars of 12?mm diameter placed at the tension side of the beam without any stirrups. Three types of steel mesh were used to reinforce the ferrocement laminate. These types are: woven wire mesh, ×8 expanded wire mesh, and EX156 expanded wire mesh. Single layer and double layers of each type of the steel mesh were employed. All specimens were tested under three-point flexural loadings. The performance of the test beams in terms of strength, stiffness, cracking behavior and energy absorption was investigated. The results showed that high serviceability and ultimate loads, crack resistance control, and good energy absorption properties could be achieved by using the proposed ferrocement forms.     

Size effect in uncracked and pre-cracked reinforced concrete beams shear-strengthened with composite jackets

The paper deals with the size effect on shear behaviour of reinforced concrete beams strengthened with fiber reinforced polymer jackets. Continuous U-jackets were made of glass or carbon fiber fabrics and epoxy composite materials. Twelve uncracked or pre-cracked strengthened reinforced concrete beams and six beams without strengthening, all of them in 6 different sizes, were tested. The results indicate that fabric-epoxy continuous U-jackets have reduced the brittleness of the shear failure of beams, tensile strains in stirrups, and, in a significant way, also the width of shear cracks at the failure state. Although similar strengthening was used for both, uncracked and pre-cracked beams, activation of jackets significantly differed. While jacket strains and their strengthening effectiveness were affected by the sizes of uncracked, retrofitted beams, they remained almost constant in pre-cracked, repaired beams of varying sizes. In contrast to repaired beams, stirrups in retrofitted beams did not yield at failure. Degree of strengthening, defined as the ratio of strengthened-to-unstrengthened beam shear capacities, was studied. It was found out that consideration of the degree of strengthening would provide relations reflecting real behaviour of reinforced concrete beams strengthened with fiber reinforced polymer U-jackets or U-jacketed strips.     

Experimental and analytical investigation of reinforced high strength concrete continuous beams strengthened with fiber reinforced polymer

Carbon and glass fiber reinforced polymer (CFRP and GFRP) are two materials suitable for strengthening the reinforced concrete (RC) beams. Although many in situ RC beams are of continuous constructions, there has been very limited research on the behavior of such beams with externally applied FRP laminate. In addition, most design guidelines were developed for simply supported beams with external FRP laminates. This paper presents an experimental program conducted to study the flexural behavior and redistribution in moment of reinforced high strength concrete (RHSC) continuous beams strengthened with CFRP and GFRP sheets. Test results showed that with increasing the number of CFRP sheet layers, the ultimate strength increases, while the ductility, moment redistribution, and ultimate strain of CFRP sheet decrease. Also, by using the GFRP sheet in strengthening the continuous beam reduced loss in ductility and moment redistribution but it did not significantly increase ultimate strength of beam. The moment enhancement ratio of the strengthened continuous beams was significantly higher than the ultimate load enhancement ratio in the same beam. An analytical model for moment–curvature and load capacity are developed and used for the tested continuous beams in current and other similar studies. The stress–strain curves of concrete, steel and FRP were considered as integrity model. Stress–strain model of concrete is extended from Oztekin et al.’s model by modifying the ultimate strain. Also, new parameters of equivalent stress block are obtained for flexural calculation of RHSC beams. Good agreement between experiment and prediction values is achieved.     

Effect of damaged concrete cover on the behavior of corroded concrete beams repaired with CFRP sheets

Fiber reinforced polymer matrix composites are being increasingly considered for use in civil infrastructure. These materials have found the maximum current use as materials for rapid and cost-effective rehabilitation (retrofit, repair and strengthening) of deteriorating and under-strength structural concrete components. This paper presents the experimental results of damaged/repaired reinforced concrete (RC) beams. The experimental program consisted of RC rectangular beam specimens exposed to accelerated corrosion. The corrosion rate was varied from 5% to 15% which represents loss in cross-sectional area of the steel reinforcement in the tension side. Half of the damaged beams were repaired by bonding Carbon Fiber Reinforced Polymer (CFRP) sheets to the tension side to restore the strength loss due to corrosion. The other half of the beams was first cleaned by removing spalled concrete cover and rusted bars were thoroughly cleaned. A new layer of concrete was cast to replace the removed spalled concrete cover. Then the CFRP sheets were attached to the new concrete layer. Corroded beams showed lower stiffness and strength than control (uncorroded) beams. Strength of damaged beams due to corrosion was restored to the undamaged state when repaired with CFRP sheets for all repaired beams, but the stiffness was almost unchanged. However, the repaired beams with replaced concrete cover layer resisted higher loads on average of 13% compared to damaged beams repaired without replacing the concrete cover layer.     

HRBF500钢筋C100混凝土梁抗剪性能试验研究

为了解配置HRB600级纵筋的高强混凝土梁受剪性能,以纵筋配筋率、混凝土钢纤维掺量为变化参数,对5根配置HRB600级纵筋的无腹筋梁进行了受剪试验,对比分析了各试验梁的斜截面承载力、荷载-挠度曲线、裂缝宽度和破坏特征。研究结果表明：随着纵筋配筋率的提高,HRB600级钢筋高强混凝土梁的开裂荷载和斜截面极限荷载增大,斜裂缝宽度减小;钢纤维可以有效地提高高强混凝土梁的斜截面开裂荷载,限制斜裂缝的产生与发展;随着钢纤维掺量的增加,高强混凝土梁的受剪承载力增大;使用现行混凝土结构设计规范和纤维混凝土结构技术规程对配置HRB600级纵筋的高强混凝土梁和钢纤维高强混凝土梁的斜截面受剪承载力进行设计计算,其结果是偏于安全的。     

Seismic strengthening of shear critical post-heated circular concrete columns wrapped with FRP composite jackets

An experimental study was carried out to investigate the seismic performance of post-heated circular reinforced concrete columns wrapped with glass or carbon fibre reinforced polymer jackets. Eight shear critical reinforced circular columns with a shear span-to-depth ratio of 2.5 were tested under a combined constant axial and cyclic lateral displacement history, simulating earthquake loading. The columns were tested in three groups, unheated, post-heated and post-heated repaired with either glass fibre reinforced polymer (GFRP) or carbon fibre reinforced polymer (CFRP). In terms of seismic performance the test results indicated that using GFRP or CFRP jackets significantly increased the shear capacity, ductility and energy dissipation of the post-heated damaged columns. However, the GFRP or CFRP did not increase the stiffness of the post-heated damaged columns. It was found that the unheated and post-heated damaged columns failed in a brittle shear mode while the mode of failure of posted-heated columns repaired with GFRP or CFRP was successfully shifted from a shear to a ductile flexural failure.     

混合配筋钢纤维增强混凝土梁受弯承载力试验及理论计算

为研究玻璃纤维增强聚合物复合材料(GFRP)筋与普通钢筋混合配筋钢纤维增强混凝土(SF/混凝土)梁的受弯性能及其受弯承载力计算方法,在考虑受拉区混凝土抗拉强度的基础上,给出混合配筋SF/混凝土梁的界限配筋率及受弯承载力计算公式;在此基础上设计制作了三种配筋方式的SF/混凝土梁,重点探讨了混合配筋率及筋材面积比(A_f/A_s)对试验梁失效模式和受弯承载力的影响;同时,借助已有相关试验结果,对比分析了混凝土强度对混合配筋SF/混凝土梁受弯性能的影响。试验和对比分析结果表明:混合配筋SF/混凝土梁正截面应变仍符合平截面假定;相同配筋形式下,混合配筋SF/混凝土梁的受弯承载力和跨中挠度随筋材面积比A_f/A_s的增加而增大;单层配筋梁的受弯承载力比双层配筋梁大;合理提高混凝土强度可在充分发挥GFRP筋抗拉作用的同时进一步提高混合配筋SF/混凝土梁的受弯承载力;采用本文给出的界限配筋率公式能有效预测混合配筋SF/混凝土梁的失效模式;梁受弯承载力建议公式的预测值与试验值吻合较好,具有良好的适用性。      

Mechanical performance of composite-strengthened concrete structures

The interest of using fibre reinforced plastic (FRP) materials in rehabilitating damaged concrete structures respectively has been increased rapidly in recent years. In this paper, the structural behaviours of the glass–fibre composite strengthened concrete structures subjected to uni-axial compression and three point bending tests are discussed through experimental studies. Two types of concrete structure are used in present study, they are concrete cylinder and rectangular concrete beam. Discussion on the environmental effects of composite strengthened reinforced concrete (RC) structures is also addressed. Experimental results show that the use of glass–fibre composite wrap can increase the load carrying capacity of the plain concrete cylinders with and without notch formation. The flexural load capacity of the concrete beam increases to more than 50% by bonding 3 layers of glass–fibre composite laminate on the beam tension surface. Direct hand lay up method gives better strengthening characteristic in term of the ultimate flexural load compared with pre-cured plate bonding technique. The flexural strengths of composite strengthened RC beams submerged into different chemicals solution for six months are increased compared with the RC beams without strengthening. The strength of the concrete structure is seriously attacked by strong acids.