钢筋砼双向受弯梁斜载面受剪承地力

本文在２１根双向受弯无腹筋钢筋砼矩形截面梁的试验研究基础上,推导了无腹筋双弯构件斜截面受剪承载力的计算表达式。采用将箍筋与砼分开单独考虑的离散化原则,进一步得出有腹筋双向受弯梁斜截面受剪承载力的计算表达式,理论计算与试验实测结果平均比值为０．９３。     

高延性混凝土加固RC梁抗剪性能试验研究

为利用高延性混凝土（HDC）良好的拉伸和剪切变形能力,提高无腹筋钢筋混凝土梁的受剪性能,该文通过对9根HDC加固梁、1根高性能复合砂浆加固梁及3根未加固梁进行静力试验,研究剪跨比、加固层厚度和加固层是否配置箍筋对梁破坏形态、受剪承载力及变形能力的影响。结果表明:采用HDC面层对无腹筋梁进行抗剪加固,可以显著提高梁的抗剪承载力和变形能力;HDC面层可代替部分箍筋的抗剪作用,改善无腹筋梁的剪切破坏形态,并提高梁的剪压比限值;HDC加固层越厚,其受剪承载力和变形能力提高越明显,但加固层厚度较大时,需采用措施防止HDC面层间发生剥离破坏;HDC面层配置附加箍筋,可进一步提高试件的受剪承载力和耐损伤能力。基于试验结果,该文提出了HDC加固试件的受剪承载力计算公式,其计算值与试验结果吻合较好。     

配置新型封闭缠绕式GFRP箍筋混凝土梁的受剪性能试验

对采用新型封闭缠绕式玻璃纤维增强树脂复合材料(GFRP)箍筋的混凝土梁进行了三点加载试验,考察了箍筋形式、纵筋配筋率、剪跨比、箍筋间距对配置新型封闭缠绕式GFRP箍筋混凝土梁受剪性能的影响规律。试验结果表明,新型封闭缠绕式GFRP箍筋的弯曲段强度与平直段受拉强度之比达到0.81,是拉挤成型箍筋的2.07倍。剪跨比和箍筋间距相同时,新型封闭缠绕式GFRP箍筋混凝土梁的受剪性能更好,其材料利用效率显著高于拉挤成型箍筋。梁的抗剪承载力随纵筋配筋率增加的提高幅度不大,但梁的延性有较明显改善。当箍筋间距为75 mm,新型封闭缠绕式GFRP箍筋的应变显著增大,同时对剪压区混凝土产生一定的约束作用,提升了受剪承载力。采用中国(GB 50608-2020)、美国(ACI 440.1R-15)、加拿大(CSA S806-12)、英国(BISE-1999)和日本(JSCE-1997)五种纤维增强树脂复合材料(FRP)筋混凝土结构设计规范计算的受剪承载力显著低于试验值,建议适当提高新型封闭缠绕式GFRP箍筋的断裂应变限值。     

高延性混凝土加固钢筋混凝土梁受剪性能试验研究及承载力计算

为研究高延性混凝土(HDC)加固钢筋混凝土梁的受剪性能,该文对7根HDC加固梁及4根未加固梁进行静力试验,研究剪跨比、配箍率、加固层厚度和加固层附加箍筋对钢筋混凝土梁破坏形态、荷载-挠度曲线、受剪承载力以及裂缝的影响。结果表明:采用HDC面层对钢筋混凝土梁进行受剪加固,可以显著提高梁的受剪承载力;HDC面层可以代替部分箍筋的受剪作用,改善钢筋混凝土梁的剪切破坏形态;加固试件在达到极限位移之后,试件的完整性较好,剩余承载力较高。基于试验结果,利用桁架-拱模型,提出了HDC加固钢筋混凝土梁的受剪承载力计算公式,计算值与试验值吻合较好。     

预应力混凝土叠合空心楼板的受剪性能试验研究

结合现浇空心楼盖与叠合楼盖的优点,提出在一种新型预应力叠合楼板中布置筒芯内模以形成叠合空心楼板。进行了3组共10块模型板带的板端抗剪试验,根据实测试件的荷载位移曲线、受剪承载力及板中箍筋应变变化情况,研究了筒芯内模布置方式、预制底板形式、抗剪箍筋、肋梁及顺筒肋对叠合空心板受剪性能和自然粗糙叠合面粘结强度的影响。研究结果表明:顺筒布置的叠合空心板抗剪承载力高于横筒布置的对比试件;预制带肋底板的预制纵肋能有效提高叠合空心试件的抗剪性能和叠合面水平抗剪强度;无论筒芯布置方式和预制底板形式如何变化,叠合层混凝土与预制底板的叠合面粘结强度均满足水平抗剪要求;依据试验结果,提出了考虑不同混凝土强度等级、叠合面高度、肋梁和顺筒肋影响的叠合空心板受剪承载力计算方法。     

钢筋混凝土双向受弯梁次生扭矩的分析研究

探讨了次生扭矩对钢筋混凝土双向受弯梁抗剪承载力的影响。提出逐级加载、待定系数的方法计算钢筋混凝土双向受弯梁的次生扭矩,编制了钢筋混凝土双向受弯梁次生扭矩的全过程分析计算机程序。计算值与试验结果的对比分析表明,该方法合理可行。通过对次生扭矩影响抗剪承载力的主要因素的分析,获得一些有参考价值的结论,并提出在工程实践中,计算承受集中荷载的有腹筋双向受弯梁的抗剪强度时,次生扭矩影响应予以考虑。     

HRB600级钢筋高强混凝土无腹筋梁受剪试验研究

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。     

预应力型钢超高强混凝土梁受剪承载力试验研究

基于12榀预应力型钢超高强混凝土简支梁和2榀预应力型钢普通强度混凝土简支梁的受剪试验,揭示了影响试验梁受剪性能的主要因素,探讨了剪跨比、箍筋间距、腹板厚度、混凝土强度和预应力度对试验梁的破坏形态、荷载-挠度曲线、斜截面开裂荷载和受剪承载力的影响规律。试验结果表明:预应力型钢超高强混凝土梁具有更好的受剪承载力和剪切延性,以及更大的刚度;基于试验结果建立了预应力型钢超高强混凝土梁的受剪承载力建议计算公式,计算结果与试验结果吻合较好,表明了该文提出的计算公式具有较高的精度。研究成果将为预应力型钢超高强混凝土梁的设计计算和工程应用提供理论依据。     

双向受弯混凝土梁斜截面受剪承载力的试验研究

本文介绍了六根承受集中荷载的双向受弯无腹筋钢筋混凝土矩截面简支梁的试验,指出了荷载斜弯角是梁斜栽面受剪承载力的重要影响因素,当受拉纵筋位于梁底面时,斜截面受剪承载力承荷载斜弯角的增大而降低。     

纤维增强混凝土梁柱节点受剪承载力计算

将纤维增强混凝土(FRC)梁柱节点在地震作用下的抗剪机制简化为约束斜压杆机制和桁架机制的综合作用,约束斜压杆机制由节点核心区FRC和箍筋共同作用形成的约束FRC抵抗,桁架机制由节点核心区梁、柱纵筋与周围FRC之间的粘结力承担。考虑这两种机制在受剪承载力机制中的比例,推导出FRC梁柱节点受剪承载力计算公式。将所收集到的28个FRC梁柱节点试件受剪承载力试验值与计算值进行比较,二者之比的平均值为1.04,变异系数为0.08,验证了受剪承载力计算模型的合理性。     

Shear strength of reinforced concrete beams with stirrups

This study presents alternative shear strength prediction equations for reinforced concrete (RC) beams with stirrups. The shear strength is composed of the contribution of the nominal shear strength provided by stirrups and the nominal shear strength provided by concrete. For the concrete contribution, cracking shear strength values estimated by Arslan’s equations are almost same those obtained with ACI 318 simplified equation in terms of coefficient of variation (COV). However, mean values estimated by ACI 318 tend to be more conservative comparing to the mean values obtained with Arslan’s equations. Thus, for the consideration of concrete contribution to shear strength, Arslan’s equations are used. To obtain the shear strength of RC beams, shear strength provided by stirrups is added to the concrete shear strength estimated by Arslan’s equations. Results of existing 339 beam shear tests are used to investigate how accurate proposed equation estimates the shear strength of RC beams. Furthermore, ACI 318 and TS500 provisions are also compared to the aforementioned test results. It is found that proposed equations for beams with shear span to depth ratios (a/d) between 1.5 and 2.5 are also conservative with a lower COV than ACI 318 and TS500. However, when a/d ratios exceed 2.5 (both normal and high strength concrete beams), ACI 318, TS500 and proposed equations give similar COV value.     

钢筋混凝土构件在压、拉弯剪共同作用下的强度包络图研究

试验表明,钢筋混凝土构件在压(拉)弯剪共同作用下,各种受力状态下的强度是相关的。为了反应构件在压弯剪和拉弯剪共同作用下各强度之间的相关性,该文以压(拉)弯相关性为基础,通过引入剪力项,推导出钢筋混凝土构件在压(拉)弯剪复合受力下的强度相关性公式,公式同时能够分别体现各种两两受力状态的强度相关性,并且与试验数据拟合良好,能够较真实地反映构件的受力状态。同时,以强度相关性公式为基础,绘制出了压(拉)弯剪强度包络图,并以该强度相关性公式和包络图为基础制定钢筋混凝土构件在压(拉)弯剪作用下的损伤标准,最终为结构抗倒塌研究中的构件抽离提供依据。     

钢筋钢纤维混凝土梁斜截面抗剪强度的理论模式

本文结合对试验结果的分析，以平衡方程为基础研究钢筋混凝土梁和钢筋钢纤维混凝土梁斜截面抗剪强度的理论模式。该模式考虑了剪压区混凝土高度及其应力分布、裂缝投影长度、骨料咬合、纵筋销栓作用及钢纤维的增强作用，概念明确、易于理解，与试验结果符合性好。     

型钢高强混凝土短柱的抗剪机理与抗剪承载力

通过若干个型钢高强混凝土短柱的低周反复加载试验,对轴力和水平剪力共同作用下型钢高强混凝土短柱的受力性能进行了研究。由粘贴在箍筋和型钢表面的应变片和应变花,测到了柱中箍筋的应力-应变、型钢的剪应力-剪应变在不同受荷阶段的发展变化状况,分析了箍筋、型钢腹板以及混凝土在构件中的抗剪作用以及轴力在型钢与混凝土之间的分配关系,揭示了型钢高强混凝土短柱的抗剪机理,提出了型钢高强混凝土短柱不同破坏形态下的抗剪承载力计算公式,公式的计算结果与试验结果符合较好。     

钢板-混凝土组合板抗剪承载性能的试验研究与数值分析

主要通过试验研究与数值模拟,分析钢板-混凝土组合板在受剪状态下的承载力、变形、裂缝发展情况以及钢板与混凝土参与抗剪程度等。进行了3块钢板-混凝土组合板试件和1块无钢板混凝土试件的抗剪承载力试验。结果表明:钢板-混凝土组合板试件的剪切破坏形式主要是斜拉破坏;钢板承担了约50%以上总剪力,由于钢板的协同作用,混凝土承担的剪力与按照规范计算的混凝土抗剪承载力相比有较大幅度的提高;随着栓钉间距的增大,构件的抗剪承载力减小。基于修正压力场理论对ABAQUS进行了材料层面的二次开发,建立了适合钢板-混凝土组合板抗剪分析的数值仿真模型,模拟结果与试验结果吻合较好。     

剪跨比对CFRP加固无腹筋混凝土梁剪切破坏及尺寸效应的影响研究

剪跨比对FRP抗剪加固梁的裂缝开展和破坏模式有重要影响,但对FRP加固梁抗剪强度及尺寸效应的影响研究较少.采用三维细观数值模拟方法,考虑混凝土细观组成的非均质性及碳纤维布(CFRP)与混凝土之间的相互作用,建立了CFRP加固无腹筋钢筋混凝土梁剪切破坏力学分析模型.在验证细观模拟方法合理性的基础上,拓展模拟与分析了剪跨比...     

Ultimate punching shear strength analysis of slab–column connections

A simple analytical model is presented to predict the ultimate punching shear strength of slab–column connections. The model is based on the physical behavior of the connections under load, and is therefore applicable to both lightweight and normal weight concrete. The model assumes that punching is a form of combined shearing and splitting, occurring without concrete crushing, but under complex three dimensional stresses. Failure is then assumed to occur when the tensile splitting strength of the concrete is exceeded. The theory is applied to predict the ultimate punching shear strength of 60 slab–column connections reported recently in literature, and designed to fail in shear, involving a large number of variables, such as type of concrete, concrete strength, tension steel ratio, compression reinforcement and loaded area. The results show very good agreement between the predicted and experimental values. The uniqueness of the model is that it incorporates many physical characteristics of the slabs and their failure behavior, and this is reflected by its ability to predict extremely well the results of tests conducted by researchers other than the authors.     

Strength of shear keys used in pre-cast prestressed composite beams

This work investigates the shear strength of shear keys used in slab–web connections in pre-cast bridge systems. In pre-cast systems where the slab is also a pre-cast element, the slab–web connection is discontinuous and usually made by casting concrete plugs (shear keys) through holes left over on the line of connection with the web at prescribed spacing. The contribution of the slab to the flexural strength of the composite beam is highly dependent on the individual shear strength of the keys and the spacing between them. In this work a test program was developed to estimate the shear strength of full scale shear keys used in practice to combine pre-cast reinforced concrete slab bridge deck to pre-cast prestressed pretentioned concrete girders, as a function of the amount and type of connection steel. On the basis of test results and the shear-friction model, an equation for the estimation of the shear strength of the shear keys is here proposed.     

Recycled aggregate concrete as structural material

The use of recycled aggregates in concrete opens a whole new range of possibilities in the reuse of materials in the building industry. The utilisation of recycled aggregates is a good solution to the problem of an excess of waste material, provided that the desired final product quality is reached. The studies on the use of recycled aggregates have been going on for 50 years. In fact, none of the results showed that recycled aggregates are unsuitable for structural use. However, some hypothetical problems related to durability aspects resulted in recycled aggregates being employed practically only as base filler for road construction. This paper focuses on the possibility of the use of recycled aggregate concrete as a structural material. For that purpose an experimental study of the shear behaviour and strength of beams made with recycled aggregate concrete was studied. Twelve beam specimens with the same compression strength, four concrete mixtures using different percentages of recycled coarse aggregates (0%, 25%, 50% and 100%) and three different transverse reinforcement arrangements were cast and tested up to failure. Analytical predictions of the experimental results were carried out using a numerical model based on the modified compression field theory and simplified models such as those proposed by Cladera & Mari, the Canadian standard CSA and the Eurocode-2. The results obtained indicate that a substitution of less than 25% of coarse aggregate, scarcely affects the shear capacity of RC beams, provided that all measures related to dosage and durability aspects have been adopted.     

Punching shear strength of interior concrete slab–column connections reinforced with steel fibers

A theoretical study was performed to investigate the punching shear strength of interior slab–column connections made of steel fiber reinforced concrete (FRC). In the steel FRC slab–column connection, the shear force applied to the critical section is resisted by both the compression zone and the tension zone at the critical section. The shear capacity of the compression zone was defined by considering the interaction between the shear and the normal stresses developed at the critical section. The shear capacity of the tension zone was defined by considering the post-cracking tensile strength of FRC. By using the shear capacity, a new strength model for the punching shear strength of steel FRC slab–column connections was developed. The proposed strength model was verified using existing test results and showed very good accuracy. For convenience in design, a simplified design equation was also developed.