Nonlinear shear behavior of rock joints using a linearized implementation of the Barton-Bandis model

Experiments on rock joint behaviors have shown that joint surface roughness is mobilized under shearing,inducing dilation and resulting in nonlinear joint shear strength and shear stress vs.shear displacement behaviors.The Barton-Bandis(B-B) joint model provides the most realistic prediction for the nonlinear shear behavior of rock joints.The B-B model accounts for asperity roughness and strength through the joint roughness coefficient(JRC) and joint wall compressive strength(JCS) parameters.Nevertheless,many computer codes for rock engineering analysis still use the constant shear strength parameters from the linear Mohr-Coulomb(M-C) model,which is only appropriate for smooth and non-dilatant joints.This limitation prevents fractured rock models from capturing the nonlinearity of joint shear behavior.To bridge the B-B and the M C models,this paper aims to provide a linearized implementation of the B-B model using a tangential technique to obtain the equivalent M-C parameters that can satisfy the nonlinear shear behavior of rock joints.These equivalent parameters,namely the equivalent peak cohesion,friction angle,and dilation angle,are then converted into their mobilized forms to account for the mobilization and degradation of JRC under shearing.The conversion is done by expressing JRC in the equivalent peak parameters as functions of joint shear displacement using proposed hyperbolic and logarithmic functions at the pre-and post-peak regions of shear displacement,respectively.Likewise,the pre-and post-peak joint shear stiffnesses are derived so that a complete shear stress-shear displacement relationship can be established.Verifications of the linearized implementation of the B-B model show that the shear stress-shear displacement curves,the dilation behavior,and the shear strength envelopes of rock joints are consistent with available experimental and numerical results.

Macro and meso characteristics evolution on shear behavior of rock joints

Direct shear tests were conducted on the rock joints under constant normal load(CNL), while the acoustic emission(AE) signals generated during shear tests were monitored with PAC Micro-II system. Before and after shearing, the surfaces of rock joints were measured by the Talysurf CLI 2000. By correlating the AE events with the shear stress-shear displacement curve, one can observe four periods of the whole course of shearing of rock joints. By the contrast of AE location and actual damage zone, it is elucidated that the AE event is related to the morphology of the joint. With the increase of shearing times, the shear behavior of rock joints gradually presents from the response of brittle behavior to that of ductile behavior. By combining the results of topography measurement, four morphological parameters of joint surface, S p(the maximum height of joint surface), N(number of islands), A(projection area) and V(volume of joint) were introduced, which decrease with shearing. Both the joint roughness coefficient(JRC) and joint matching coefficient(JMC) drop with shearing, and the shear strength of rock joints can be predicted by the JRC-JMC model. It establishes the relationship between micro-topography and macroscopic strength, which have the same change rule with shearing.

Effect of rock joint roughness on its cyclic shear behavior

Rock joints are often subjected to dynamic loads induced by earthquake and blasting during mining and rock cutting. Hence, cyclic shear load can be induced along the joints and it is important to evaluate the shear behavior of rock joint under this condition. In the present study, synthetic rock joints were prepared with plaster of Paris(Po P). Regular joints were simulated by keeping regular asperity with asperity angles of 15°-15° and 30°-30°, and irregular rock joints which are closer to natural joints were replicated by keeping the asperity angles of 15°-30° and 15°-45°. The sample size and amplitude of roughness were kept the same for both regular and irregular joints which were 298 mm×298 mm×125 mm and 5 mm, respectively. Shear test was performed on these joints using a large-scale direct shear testing machine by keeping the frequency and amplitude of shear load under constant cyclic condition with different normal stress values. As expected, the shear strength of rock joints increased with the increases in the asperity angle and normal load during the first cycle of shearing or static load. With the increase of the number of shear cycles, the shear strength decreased for all the asperity angles but the rate of reduction was more in case of high asperity angles. Test results indicated that shear strength of irregular joints was higher than that of regular joints at different cycles of shearing at low normal stress. Shearing and degradation of joint asperities on regular joints were the same between loading and unloading, but different for irregular joints. Shear strength and joint degradation were more significant on the slope of asperity with higher angles on the irregular joint until two angles of asperities became equal during the cycle of shearing and it started behaving like regular joints for subsequent cycles.

Seismic behavior and mechanism analysis of innovative precast shear wall involving vertical joints

To study the seismic performance and load-transferring mechanism of an innovative precast shear wall(IPSW) involving vertical joints, an experimental investigation and theoretical analysis were successively conducted on two test walls. The test results confirm the feasibility of the novel joints as well as the favorable seismic performance of the walls, even though certain optimization measures should be taken to improve the ductility. The load-transferring mechanism subsequently is theoretically investigated based on the experimental study. The theoretical results show the load-transferring route of the novel joints is concise and definite. During the elastic stage, the vertical shear stress in the connecting steel frame(CSF) distributes uniformly; and each high-strength bolt(HSB)primarily delivers vertical shear force. However, the stress in the CSF redistributes when the walls develop into the elastic-plastic stage. At the ultimate state, the vertical shear stress and horizontal normal stress in the CSF distribute linearly; and the HSBs at both ends of the CSF transfer the maximum shear forces.

基于主动超声激励的岩石节理刚度分布测量研究

Goodman提出采用节理刚度表征复杂岩石节理面的拓扑行为并为其提供定量值,而无需对节理面的粗糙度、接触面积等参数进行详细测量分析。然而目前对岩石节理刚度的测量仍存在局限,因此,在试验室环境下采用压电陶瓷换能器对完整平板试件和含节理平板试件进行弹性波激励,同时采用三维扫描激光多普测振仪监测平板内弹性波的传播数据。将采集的波场信号数据进行滤波、插值、积分等一系列处理,并基于Schoenberg线性滑移模型计算节理刚度分布,实现岩石节理接触行为的全局参数表征,同时进一步验证了岩石节理全场超声表征的可行性。全场波形数据清晰地揭示了岩石节理界面接触行为,为后续深入探索岩石节理几何形状、孔径、界面性质及其地震特征之间的相互关系奠定了基础。

型钢混合连接装配式混凝土剪力墙结构受力机理研究

结合钢筋混凝土结构和钢结构的优势,设计一种型钢-螺栓-后浇混凝土装配式剪力墙型钢混合连接。基于ABAQUS有限元软件建立混合连接的剪力墙模型,探究低周往复荷载作用下该混合连接预制剪力墙的受力性能,主要分析模型的破坏形态、受力机制、变形曲线、特征承载力等,并扩展分析了材料强度、轴压比、连接件数量、型钢截面高度等参数对模型受力性能影响。结果表明:装配式剪力墙破坏形态为压弯破坏,破坏时钢连接件仍保持完整,符合“强连接,弱墙肢”的基本设计理念;装配式剪力墙具有较好的承载力、延性和刚度;轴压比对结构承载力影响显著,型钢混合连接间距的增大能有效提升剪力墙延性。建立了型钢混合连接抗剪需求承载力计算模型和公式,并与国内外规范计算值对比分析,公式计算值和BS EN 1992欧洲规范计算值分别与模拟值的误差在15%和20%以内,均可用于型钢混合连接剪力墙竖缝受剪承载力设计参考。

New criterion for rock joints based on three-dimensional roughness parameters

The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.

贯通型锯齿状节理岩体的剪切力学行为

为探究一阶起伏角和法向应力对贯通型锯齿状节理岩体剪切强度及变形的影响规律,在不同法向应力作用下对含不同一阶起伏角的锯齿节理试样进行室内直剪试验,建立一个贯通型锯齿状节理岩体剪切强度估算公式并进行验证。结果表明:相同法向应力作用下,根据其形态特征的不同,剪切应力-位移曲线分为滑动型曲线、滑动-峰值型曲线和峰值型曲线3类,滑动型曲线和滑动-峰值型曲线可分为非线性缓慢上升阶段、线性陡升阶段“、上凸形”缓慢上升阶段、近似平直阶段和平直阶段,峰值型曲线可分为非线性缓慢上升阶段、线性陡升阶段、“微凸型”上升阶段、脆性跌落阶段和波动缓降阶段;根据起伏角的不同,锯齿节理岩体的破坏模式可概化为滑移破坏、爬坡破坏和爬坡啃断破坏,每种破坏模式下节理损伤演化过程均可分为3个阶段,即滑移破坏模式可分为压密阶段、克服摩擦阶段和滑移阶段,爬坡破坏模式可分为压密阶段、爬坡滑移阶段和塑性流动阶段,爬坡啃断破坏模式可分为压密爬坡阶段、爬坡啃断阶段和啃断滑移阶段;含不同一阶起伏角的锯齿节理岩体剪切强度均随法向应力和起伏角的增加而增大,其计算表达式仍然遵循M-C准则。

预制节段UHPC梁接缝抗剪性能的有限元模拟

该文采用有限元软件ABAQUS对预制节段超高性能混凝土(UHPC)梁剪力键接缝的抗剪性能进行了三维精细有限元模拟。模型中同时考虑了材料非线性、几何非线性以及UHPC材料的塑性损伤,模拟得到的荷载-滑移曲线和破坏模态等均与试验结果吻合良好。采用经过验证的有限元模型对剪力键接缝的抗剪性能进行了数值参数分析,结果表明:接缝的抗剪承载力及其对应的滑移随着所施加的侧向应力或UHPC强度的增大而增大,但UHPC抗压强度对抗剪承载力的影响大于UHPC抗拉强度,而且UHPC的抗拉压强度之间无固定的相关规律,因此对于UHPC接缝抗剪承载力的计算应分别考虑抗拉强度与抗压强度的影响;由于剪应力分布的不均匀性,抗剪承载力的计算还应考虑多键块的强度折减效应。此外,对剪力键接缝构造的参数分析结果表明:当键块的宽度和总高度相同时,接缝抗剪承载力随着键块相对高度的减小而增大,但当键块相对高度小于1/2时,接缝的抗剪承载力基本保持不变;当键块总面积以及键块数量相同时,多个键块之间的协同工作能力随键块竖向间距的增大而变强;键块深度对接缝抗剪承载力的影响不大。与目前被广泛采用的普通混凝土接缝抗剪承载力的计算公式对比,有限元的预测值明显小于计算公式的预测值,且偏差随着侧向应力的增大而增大,因此有必要针对UHPC剪力键接缝提出新的抗剪承载力计算式。

失效铝合金平底无铆连接接头的原位固相修复方法

为了修复失效平底无铆连接接头并提高其力学性能,提出一种原位固相修复方法。通过对比研究平底无铆连接接头和修复接头的显微组织、力学性能和断裂失效行为,验证修复方法的可行性和有效性。结果表明,失效平底无铆连接接头的断裂颈部被成功地原位修复。焊核的显微组织被充分细化,使得修复接头的力学性能得到提升。转速和持续加热时间对修复接头的力学性能起着至关重要的作用。与平底无铆连接接头相比,冶金结合使修复接头的力学性能得到加强。修复接头的最大拉剪强度提高了409.90%,最大断裂伸长量提高了68.92%。断裂失效行为表明,修复接头的强度明显高于原始平底无铆连接接头,这说明失效平底无铆连接接头的修复方法是可行有效的。

外肋板式钢板混凝土组合剪力墙与钢梁节点抗震性能试验研究

外肋板式钢板混凝土组合剪力墙与钢梁节点是一种新型墙梁节点,设计并制作了四个足尺的外肋板式钢板混凝土剪力墙与钢梁节点模型试件进行低周往复加载试验,研究钢梁跨高比、外肋板宽厚比以及设置栓钉对试件的滞回性能、延性、耗能和刚度退化等抗震性能的影响。结果表明该节点具有良好的延性和耗能能力,外肋板对节点承载力有较大提升,跨高比较小的试件在弹塑性阶段具有更好的耗能能力,改变外肋板宽厚比和在墙侧设置栓钉对该节点初始刚度无明显影响,该节点荷载有两种传递方式,一种由外伸梁传至外肋板,再由外肋板传至剪力墙;另一种直接由外伸梁传递至剪力墙,前者占比更高。

带钢接头的装配式钢筋混凝土梁抗剪性能研究

为研究现有两种带钢接头的装配式钢筋混凝土梁抗剪性能,设计制作了6个钢筋混凝土梁试件进行足尺试验研究,其中包括4个带钢接头的钢筋混凝土梁和2个用于对比的普通钢筋混凝土梁。通过记录各试件的试验现象及破坏形态,测量各试件的抗剪承载力、位移和应变等参数,对试件的抗剪性能与剪切延性进行分析。结果表明:与普通钢筋混凝土梁相比,使用钢接头且下部设置受拉钢板、无纵向受力钢筋的试件极限抗剪承载力有所降低,下部设置纵向受力钢筋的试件极限抗剪承载力提高18.5%~24.5%,剪切延性均有所提高。通过对目前各国现行钢筋混凝土梁抗剪承载力计算方法的适用性评价发现,我国现行规范可较好地预测带钢接头的装配式钢筋混凝土梁的抗剪承载力。

节段预制桥梁胶接缝剪切性能试验研究

接缝是预制节段桥梁的重要部位,也是薄弱环节,为了研究节段式预应力桥梁胶接缝在直剪状态下力学性能,采用剪力键齿深、齿距作为影响因素进行了节段式胶接缝体外预应力混凝土桥梁剪力键抗剪试验,通过对加载后发生的竖向位移和破坏荷载进行对比来分析上述两个因素对胶接缝抗剪承载能力的影响。结果表明:各试件的竖向变形主要分为线性变形和错动滑移两个阶段,变形曲线相近;剪力键直剪承载力与直剪破坏面面积成正比关系,与齿深、齿距无直接关联;试件开裂后不久即达到破坏荷载,且无明显稳定的屈服段,属于脆性破坏。

锚杆预紧力对节理岩体抗剪性能影响的试验研究

利用配置的混凝土块体模拟围岩,采用节理直剪的方式,研究了40,80 kN两种预紧力下锚杆对节理岩体抗剪性能的影响。研究结果表明:随着预紧力的提高,锚固节理岩体的初期剪切刚度提高,对于抑制围岩的初期变形,提升锚杆支护效能有重要作用;随着预紧力提高,锚固节理岩体的变形呈阶段性特征,表现为急增阻、缓增阻和降阻3个阶段;井下试验结果表明,提高预紧力,锚杆的工作阻力得到提升,高预紧力全长锚固锚杆支护系统对于节理裂隙围岩的加固效果良好。

预制装配式混凝土墙板螺栓连接抗剪性能试验研究

为研究预制装配式混凝土墙板螺栓连接的抗剪性能,通过对4个采用装配式螺栓连接的预制墙板结构试件进行单向反复加载试验,获得试件的滞回曲线、骨架曲线、特征荷载与位移;在此基础上对装配式螺栓连接的刚度退化情况以及延性指标进行计算和分析。研究结果表明:装配式螺栓连接具有良好的承载力、刚度及耗能能力,是一种可靠的干连接方式;通过对薄弱部位进行箍筋加密和增加螺栓的个数,能显著提高装配式螺栓连接的抗剪性能。

基于MCFT理论的RC框架节点受剪性能研究

根据10个梁高不等的钢筋混凝土框架中节点试件在低周反复荷载作用下的试验结果,重点分析该类框架节点的破坏过程和破坏特点。在试验研究的基础上,建立框架节点等效核心区在剪、压复合作用下的计算模型,应用改进斜压场理论(MCFT)对等效核心区进行受力分析,并通过国内外83个无扭矩作用框架节点试件(包括常规中节点、边节点、变梁中节点等)峰值剪应力的试验结果与该模型计算得到的理论结果进行对比,二者吻合良好。

聚合物砂浆嵌缝加固石墙灰缝抗剪性能研究

根据条石砌筑石墙的砌筑和构造特点,提出了采用聚合物砂浆对石墙进行嵌缝抗震加固的方法。通过对12片聚合物砂浆嵌缝加固的双剪试件和12片有垫片干砌甩浆砌筑的对比试件进行抗剪性能试验研究,探讨采用聚合物砂浆嵌缝加固对石墙通缝抗剪承载能力的提高效果,分析不同砂浆强度、不同压应力水平下的嵌缝加固情况。试验结果表明,聚合物砂浆嵌缝加固能有效提高石墙灰缝的抗剪承载能力和剪切变形能力。在低砂浆强度、低压应力水平的情况下,其加固效果更明显。在试验的基础上,提出了聚合物砂浆嵌缝加固后石墙通缝的抗剪强度计算公式,计算值与试验值吻合良好。本文提供的内容可供石墙抗震加固研究和工程应用借鉴参考。

大尺度RC梁柱节点抗震性能及尺寸效应试验研究

基于对一个大尺度RC梁柱节点在低周反复荷载下的加载试验,研究节点的破坏形态、承载能力、滞回特性和耗能能力等抗震性能。并与已有的两个中小尺度梁柱节点的试验数据进行对比,分析尺寸效应对其的影响。结果表明:这些节点都经历了核芯区开裂、梁端屈服、核芯区通裂、剪切极限直至破坏的过程。但是,随着尺寸的增加,节点核芯区斜裂缝的数量明显增多,斜裂缝带中间宽两端细的趋势更加明显。特别在加载后期,大构件节点核芯区的变形和抗剪承载能力下降,刚度衰减加快,耗能能力和延性明显下降。由此看来,在混凝土结构的抗震设计中应该对构件尺寸效应给予更多的注意。

核心区剪切破坏的RC变梁中节点受力模型研究

根据10个梁高不等钢筋混凝土框架中节点试件在低周反复荷载作用下的试验结果,分析了该类非规则节点的破坏过程和破坏特点.在试验研究的基础上,根据节点区梁柱传来外力的平衡条件,建议了核心区发生剪切破坏的钢筋混凝土中节点受力分析的数学模型,并应用该模型对变梁节点受力性能进行参数分析.研究结果表明:对于核心区发生剪切破坏的节点试件,节点剪力和层间剪力二者并非线性比例关系;梁筋与核心区混凝土二者间的粘结锚固是影响节点抗剪强度的关键参数.

玻璃纤维片材加固混凝土梁柱节点的抗震性能研究

进行了 6个玻璃纤维 (GFRP)片材加固混凝土梁柱节点在低周反复荷载作用下的试验研究 ,结果表明GFRP片材加固节点是一个有效的加固方法 ,节点的抗剪强度和延性比加固前有较大的提高。基于试验结果提出了考虑混凝土、箍筋、GFRP片材共同作用的节点抗剪承载力计算方法。