Shear behavior of continuous reinforced concrete T-beams using wire rope as internal shear reinforcement

The use of wire ropes with high-strength and high flexibility as internal shear reinforcement can solve the difficulties encountered in bending higher strength steel bar and can provide a better shear behavior to concrete beams. Three two-span reinforced concrete T-beams were tested to failure in order to examine the possibility of the practical application of wire ropes as shear reinforcement. The measured shear capacities of beams were compared with predictions obtained from equations specified in ACI 318-08 and the mechanism analysis based on the upper-bound theorem of concrete plasticity. Test results showed that using spiral-type wire rope as shear reinforcement is highly favourable for controlling the diagonal crack width and enhancing the ductility of beams failing in shear. In particular, the high-strength of the wire ropes significantly promoted the shear capacity of concrete beams. When a limit stress of 420 MPa for wire ropes is employed, ACI 318-08 is highly conservative in beams with spiral-type wire ropes compared with the control beams with closed stirrups. In addition, ACI 318-08 is still conservative when using the equivalent yield strength of wire ropes. On the other hand, the predictions obtained from the mechanism analysis are in good agreement with test results, regardless of the type of shear reinforcement.     

预应力高强钢丝绳抗弯加固钢筋混凝土梁的试验研究

提出一种预应力高强钢丝绳抗弯加固混凝土结构的新方法(简称P-SWR加固技术)。介绍这种新技术的提出思想及实现工艺,对预应力高强钢丝绳抗弯加固混凝土梁进行试验研究,重点讨论直接加载、先损伤后加载、钢丝绳层数、钢丝绳与混凝土黏结性能、锚固方式等参数对加固性能的影响,并与粘贴CFRP和钢板加固混凝土梁性能作了比较。试验结果表明,预应力高强钢丝绳加固能同时显著提高混凝土梁的开裂荷载、截面刚度、屈服荷载、最大承载力,加固后的梁发生钢筋屈服、受压区混凝土压坏、钢丝绳断裂的延性破坏,能有效限制混凝土裂缝宽度,钢丝绳能达到极限拉伸应变而充分发挥作用。P-SWR加固技术可较好地解决现有加固方法中的诸多缺点,是一种高效主动式的加固技术。另外,该技术还具有易施工、耐火、耐老化、成本低等优点,值得在实际工程中大力推广应用。     

Aggregate interlock in lightweight concrete continuous deep beams

There are very few, if any, available experimental investigations on aggregate interlock capacity along diagonal cracks in lightweight concrete deep beams. As a result, the shear design provisions including the modification factor of ACI 318-08 and EC 2 for lightweight concrete continuous deep beams are generally developed and validated using normal weight simple deep beam specimens. This paper presents the testing of 12 continuous beams made of all-lightweight, sand-lightweight and normal weight concrete having maximum aggregate sizes of 4, 8, 13 and 19 mm. The load capacities of beams tested are compared with the predictions of strut-and-tie models recommended in ACI 318-08 and EC 2 provisions including the modification factor for lightweight concrete. The beam load capacity increased with the increase of maximum aggregate size, though the aggregate interlock contribution to the load capacity of lightweight concrete deep beams was less than that of normal weight concrete deep beams. It was also shown that the lightweight concrete modification factor in EC 2 is generally unconservative, while that in ACI 318-08 is conservative for all-lightweight concrete but turns to be unconservative for sand-lightweight concrete with a maximum aggregate size above 13 mm. The conservatism of the strut-and-tie models specified in ACI 318-08 and EC 2 decreased with the decrease of maximum aggregate size, and was less in lightweight concrete deep beams than in normal weight concrete deep beams.     

腹筋对轻骨料混凝土深受弯构件受剪性能及尺寸效应影响的试验研究

完成对称集中荷载作用下的8根轻骨料混凝土深受弯构件及2根普通混凝土深受弯构件受剪性能试验,分析了腹筋配筋率及截面高度对破坏过程及形态、荷载 跨中挠度曲线、特征荷载、斜裂缝发展趋势、纵筋及腹筋应变等的影响机制与规律,重点明确了腹筋对深受弯构件抗剪承载力及尺寸效应影响的作用机理。为合理量化腹筋在传力机制中的贡献,建立以腹筋作为竖向拉杆的改进拉-压杆模型(STM),结合对典型压杆有效系数模型的分析和评价,验证了改进STM的有效性。试验结果表明：试件主要发生剪压破坏,其破坏形态与截面高度无关,腹筋可有效约束混凝土剥落;随腹筋配筋率增大,名义开裂/极限强度呈增大趋势,而最大斜裂缝宽度随之降低;腹筋可在抵抗斜截面内部分拉应力的同时对压杆形成有效侧向约束,削弱尺寸效应影响。计算结果表明：与简化STM相比,改进STM能够合理反映腹筋配筋率对受剪承载力的影响,基于ACI 318.19压杆有效系数的改进STM的预测值与试验值吻合良好。     

Flexural and shear capacities of concrete beams reinforced with GFRP bars

This paper reports test results of 12 concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars subjected to a four point loading system. All test specimens had no transverse shear nor compression reinforcement and were classified into two groups according to the concrete compressive strength. The main parameters investigated in each group were the beam depth and amount of GFRP reinforcement. Two modes of failure were observed, namely flexural and shear. The flexural failure is mainly occurred due to tensile rupture of GFRP bars either within the mid-span region or under the applied point load. The shear failure is initiated by a major diagonal crack within the beam shear span. This diagonal crack extended horizontally at the level of the GFRP bars indicating bond failure.Simplified methods for estimating the flexural and shear capacities of beams tested are presented. The flexural capacity is estimated based on the compatibility of strains and equilibrium of forces. Comparisons between the flexural capacity obtained from the theoretical analysis and that experimentally measured in the current investigation and elsewhere show good agreement. To predict the shear capacity of the beams tested, four methods recently proposed in the literature for GFRP-reinforced concrete beams are used. These methods have been developed by modifying the ACI 318-99 shear capacity formula for steel-reinforced concrete beams to account for the difference in the axial stiffness of GFRP and steel bars. It has been shown that the theoretical predictions of the shear capacity obtained from these methods are inconsistent and further research needs to be carried out in order to establish a rational method for the shear capacity calculation of GFRP-reinforced concrete beams.     

Experimental and analytical investigation of CFRP flexural and shear strengthening efficiencies of RC beams

This paper studies the CFRP flexure and shear strengthening efficiencies of concrete beams. Half-scale beams, with different flexure and shear internal steel ratios, were tested in three-point bending. Flexure or shear-critical beams were provided with CFRP longitudinal sheets or U-wraps, respectively. Flexure–shear-critical beams were provided with shear or combined systems. At high flexural damage, 38.3% reduction in shear strengthening efficiency was noted at higher ductility, while the flexural strengthening efficiency reduced by 65.7% at high shear damage, both from capacity perspectives. The U-wraps were 22% activated, while full sheet activation occurred and reduced by dowel rupture by 30.8% at high shear damage. While single failures were accurately predicted by ACI 318M-05 and ACI 440.2R-08, combined ones were not.     

轻骨料混凝土无腹筋梁受剪性能试验研究

为研究骨料种类对无腹筋梁受剪性能的影响,以剪跨比和纵筋配筋率为变量,进行了16根集中荷载作用下的无腹筋混凝土简支梁受剪性能试验,其中8根采用普通碎石混凝土,8根梁采用页岩陶粒（轻骨料）混凝土,对轻骨料和普通混凝土梁的裂缝发展、破坏形态、斜向开裂荷载、受剪承载力、跨中挠度、裂缝面相对位移等进行了观察和测量。对比分析表明：轻骨料混凝土梁的斜向开裂荷载和受剪承载力均低于普通混凝土梁,其裂缝面较普通混凝土的更加光滑;将轻骨料混凝土梁受剪承载力试验值与采用我国JGJ 12-2006《轻骨料混凝土结构技术规程》和美国规范ACI 318-11、加拿大规范CSA 23.3-04、欧洲规范EC 2方法的计算值进行对比分析,结合此次试验结果和从国内外文献中搜集的126组已有试验数据,对我国JGJ 12-2006的受剪承载力公式的准确性和安全性进行探讨,提出了无腹筋轻骨料混凝土梁受剪承载力计算的建议公式。     

预应力高强钢丝绳抗弯加固钢筋混凝土梁的理论分析

预应力高强钢丝绳加固是一种新型高效加固方法(简称P-SWR加固技术)。首先对试验用钢丝绳抗拉强度、拉伸极限应变和松弛等力学性能进行试验研究;然后给出预应力高强钢丝绳加固后混凝土梁开裂荷载、最大承载力计算方法;结合预应力高强钢丝绳加固混凝土梁的荷载-挠度关系曲线,分析了预应力度、配筋率、钢丝绳与混凝土黏结性能等各种参数对P-SWR加固梁截面短期刚度的影响,提出了相应的计算公式;基于高强钢丝绳抗弯加固对混凝土梁裂缝平均间距和钢筋应力影响的分析,建议了计算P-SWR加固后混凝土梁最大裂缝宽度的修正规范方法、名义拉应力方法和实用简化方法。建议的各计算方法简单,与相应试验值的比较表明具有较高的精度,可用于P-SWR抗弯加固混凝土结构的理论分析和简化设计。     

Flexural strengthening of RC beams using distributed prestressed high strength steel wire rope: theoretical analysis

Various strengthening techniques for structural elements using different materials have been investigated. Recently, a new, reliable and cost-effective strengthening technique with distributed prestressed high strength steel wire rope (P-SWR technique) was proposed. This paper mainly focuses on theoretical analysis of the flexural behaviour of reinforced concrete (RC) beams strengthened with the P-SWR strengthening technique. First, mechanical properties of steel wire rope such as ultimate strength, ultimate tensile strain and relaxation were tested. Second, an evaluation method, including the prediction of cracking load and flexural capacity of RC beams strengthened with P-SWR, was proposed. Third, prestressed level of P-SWR, ratio of reinforcement, and bond strength of P-SWR and concrete responsible for short-term cross-sectional stiffness were studied and associated calculation equations are suggested. Finally, according to parametric studies, an entire evaluation system, including a modified Rao & Dilger code calculation method and hypothetical tension method, as well as a simplified method for predicting the maximum crack width, is proposed. All of these analytical procedures are based on experimental studies. A great similarity between the experimental and analytic results suggests that the proposed methods are highly accurate.     

混锚预应力U形碳纤维条带抗剪加固混凝土梁试验研究

研发钢筋混凝土梁抗剪加固用U形纤维增强复材（FRP）条带的预应力系统,提出一种预应力U形条带端锚与黏贴并用（简称混锚）的抗剪加固方法。完成了1根未加固、7根采用U形碳纤维（CFRP）条带进行抗剪加固的矩形截面梁剪切试验,加固梁中1根为纯黏贴、6根为混锚预应力。结果表明：混锚预应力加固在抑制主斜裂缝开展、延缓箍筋屈服和提高箍筋塑性利用率等方面的表现均优于纯黏贴加固,能够防止FRP端部剥离并实现拉断破坏,大幅度提高纤维强度利用率,显著提高梁的抗剪承载力,最大提升率达92%。预应力和配纤率的大小对抗剪加固效果有较明显影响,其他条件相同时,预应力越大或配纤率越高,加固梁综合性能越好。建议了混锚预应力U形CFRP有效应变的计算公式,用于预测剪切破坏时CFRP的贡献和加固梁的承载能力,与试验结果符合良好,可供工程应用参考。     

考虑混凝土贡献的修正变角桁架模型

为提高有腹筋RC（钢筋混凝土）浅梁抗剪承载力的预测准确性和稳定性,提出一种考虑混凝土贡献的修正变角桁架模型。首先,基于变角桁架模型得到箍筋的抗剪贡献值计算公式,并结合塑性下限定理确定斜裂缝倾角的取值|其次,通过混凝土浅梁受压区的劈裂破坏模式得到混凝土项的抗剪贡献值计算公式,并利用尺寸效应系数考虑了混凝土项的脆性破坏特征|最后,将箍筋项和混凝土项提供的抗剪承载力进行叠加,建立有腹筋RC浅梁抗剪承载力计算公式。基于有腹筋RC浅梁抗剪承载力试验数据库ACI-DAfStb对本文、GB50010、ACI及AASHTO规范中抗剪计算公式的预测准确性进行对比评估,结果表明：文中抗剪承载力公式不仅能够体现配筋率、剪跨比和混凝土强度等主要抗剪参数的影响规律,还能考虑尺寸效应和斜裂缝倾角对抗剪承载力的修正|同时,在抗剪承载力预测准确性和稳定性方面,相对规范方法有所较高。     

自密实混凝土无腹筋梁抗剪性能

为研究自密实混凝土无腹筋梁的抗剪性能和裂缝开展形态,进行了集中荷载作用下12根无腹筋钢筋混凝土简支梁(8根自密实混凝土和4根普通混凝土)的剪切破坏试验,变量为混凝土强度和剪跨比。探讨了《混凝土结构设计规范》(GB 50010―2010)、Zsutty拟合公式、美国规范(ACI318-11)抗剪承载力计算公式对自密实混凝土无腹筋梁抗剪承载力计算的适用性和准确性。收集了在集中荷载作用下的130根自密实混凝土和798根普通混凝土矩形截面无腹筋梁剪切破坏试验数据,将自密实混凝土和普通混凝土无腹筋梁抗剪承载力进行了对比。结果表明:自密实混凝土梁和普通混凝土梁的裂缝发展、破坏形态大致相同,自密实混凝土梁斜裂缝断面更为光滑;Zsutty拟合式计算结果与本文试验结果最接近;GB 50010—2010计算结果与本文试验结果也比较吻合,但偏于不安全;美国规范ACI 318-11计算公式偏差较大;自密实混凝土梁受剪承载力略低于普通混凝土梁。     

Flexural strengthening of reinforced lightweight polystyrene aggregate concrete beams with near-surface mounted GFRP bars

Application of near-surface mounted (NSM) fibre reinforced polymer (FRP) bars is emerging as a promising technology for increasing flexural and shear strength of deficient reinforced concrete (RC) members. In order for this technique to perform effectively, the structural behaviour of RC elements strengthened with NSM FRP bars needs to be fully characterized. This paper focuses on the characterization of flexural behaviour of RC members strengthened with NSM glass-FRP bars. Totally, 10 beams were tested using symmetrical two-point loads test. The parameters examined under the beam tests were type of concretes (lightweight polystyrene aggregate concrete and normal concrete), type of reinforcing bars (GFRP and steel), and type of adhesives. Flexural performance of the tested beams including modes of failure, moment–deflection response and ultimate moment capacity are presented and discussed in this paper. Results of this investigation showed that beams with NSM GFRP bars showed a reduction in ultimate deflection and an improvement in flexural stiffness and bending capacity, depending on the PA content of the beams. In general, beams strengthened with NSM GFRP bars overall showed a significant increase in ultimate moment ranging from 23% to 53% over the corresponding beams without NSM GFRP bars. The influence of epoxy type was found conspicuously dominated the moment–deflection response up to the peak moment. Besides, the ultimate moment of concrete beams reinforced with GFRP bars could be predicted satisfactorily using the equation provided in ACI 318-95 Building Code.     

钢筋钢丝网砂浆加固RC梁的抗剪试验

进行了钢筋混凝土(RC)原梁、钢筋钢丝网砂浆(SWM)加固RC梁和钢筋网砂浆(SM)加固RC梁的抗剪试验研究.结果表明:相对于SM加固法,SWM加固法能大幅度提高加固梁的抗剪承载力;即使在钢丝网用量很少的情况下(施工方便),加固梁仍具有良好的裂缝控制能力和相对较大的变形能力.同时,给出了加固梁的抗剪承载力和斜裂缝宽度的计算公式,其计算结果与试验结果基本吻合.     

基于试验数据的高强混凝土梁抗剪承载力计算方法Ⅱ.有腹筋梁

收集了国内外学者所做的281根高强混凝土有腹筋梁剪切破坏的试验数据,建立了高强混凝土有腹筋梁剪切破坏的数据库。将数据库中所有梁的试验结果与中国《混凝土结构设计规范》（GB 50010—2010）、美国混凝土结构设计规范ACI 318 14中的公式以及Zsutty公式所预测的结果进行比较,研究各公式对于高强混凝土梁的适用性,再将GB 50010—2010公式中的系数进行修正,得到一个新的公式。结果表明:Zsutty公式的预测结果最精确,美国ACI 318 14规范中公式的预测结果最为保守;新公式较原规范公式更加适用于高强混凝土有腹筋梁。     

钢筋混凝土简支深梁压杆-拉杆模型试验对比分析

深受弯构件的拉压杆模型已经得到了广泛的认可。为研究混凝土深梁设计中采用的压杆-拉杆模型,进行了简支深梁集中荷载下的模型静载试验。试验设计依据为《混凝土结构设计规范》(GB 50010—2010)中深梁的相关规定及美国《混凝土结构建筑规范》(ACI318M-05)中压杆-拉杆模型设计的相关规定,试验参数为剪跨比、配筋方式等。试验结果表明,深梁混凝土抗压强度软化系数β与剪跨比和分布钢筋配筋率有关;水平分布筋对于承载力的贡献大于竖向分布钢筋。根据试验结果比较,中国规范对于小剪跨比(λ≤1)深梁的设计有较大的安全储备,美国规范深梁设计中所采用的压杆-拉杆模型较为经济合理。     

Seismic behavior of high strength concrete beams

Experimental and analytical studies on the seismic performance of high strength concrete beams in moment resisting frame structures are described. Two large-scale high strength concrete and two counterpart normal strength concrete model beams with a length-to-depth ratio of 6·0 (i.e. shear span ratio of 3·0) have been tested under cyclic shear and double bending. The beams were heavily reinforced in the longitudinal direction to study beam performance under high seismic shear demand. Transverse reinforcement was designed following the seismic design provisions of current ACI 318–95 code. Both high and normal strength concrete beams developed ductile flexural responses. High strength concrete beams exhibited increased capacity and improved hysteretic performance compared to normal strength concrete beams. A simple analytical approach based on the moment curvature characteristics of critical sections has also been developed to predict the flexural behavior of structural beams. Comparison of analytical and test results indicates that behavior of high strength concrete beams can be satisfactorily predicted. © 1998 John Wiley & Sons, Ltd.     

铁尾矿砂混凝土梁受剪性能试验研究

为研究铁尾矿砂混凝土简支梁与普通混凝土简支梁受剪性能的差异,完成了12根铁尾矿砂混凝土梁和3根普通河砂混凝土梁的受剪承载力试验,试验梁变化参数为混凝土强度等级（C30、C40和C50）、剪跨比（2.0和2.5）和配箍率（0.14%、0.19%和0.28%）;分析了铁尾矿砂混凝土梁受剪破坏形态和斜截面受力特点,探讨了ACI 318-08和GB 50010—2010《混凝土结构设计规范》普通混凝土梁受剪承载力计算式对铁尾矿砂混凝土梁受剪承载力的适用性。结果表明：铁尾矿砂混凝土梁与普通混凝土梁的受剪破坏形态相同;相同混凝土强度等级下铁尾矿砂混凝土梁受剪承载力比普通混凝土梁受剪承载力高;在相同荷载作用下,铁尾矿砂混凝土梁的箍筋应变大于普通混凝土梁;普通混凝土梁受剪承载力计算式适用于铁尾矿砂混凝土梁,具有一定安全储备;提出的适用于集中荷载作用下剪压破坏的铁尾矿砂混凝土梁受剪承载力计算算式,其精度高于GB 50010—2010的计算结果。     

持载混凝土梁端锚无黏结预应力U形碳纤维带受剪加固试验研究

利用已研发的适用于U形纤维增强复材(FRP)的端锚无黏结预应力系统,对1根未加固梁及6根预应力碳纤维(CFRP)条带加固的不同持载水平钢筋混凝土梁进行受剪性能试验,探究端锚无黏结预应力加固法的有效性。研究结果表明：该方法能够对不同持载水平混凝土梁进行有效加固,可避免条带的端部剥离破坏并实现拉断破坏,提高纤维强度利用率,延缓箍筋屈服,抑制梁刚度的退化和斜裂缝的开展,提升构件受剪承载力,最大提升率约75%;预应力加固效果易受持载水平和配纤率影响,其他加固参数相同时,较高持载水平和配纤率的加固梁受剪性能更好,受剪承载力提高幅度更大。端锚无黏结预应力U形CFRP条带加固梁受剪承载力计算结果与实测结果吻合较好,可为加固设计提供参考。