Shear strength prediction of reinforced concrete walls

Most of existing codes ignore the effect of arch action on shear strength of reinforced concrete (RC) walls, and it leads to more conservative results. A new model considering the influence of the truss and arch on shear strength of RC walls is proposed in this paper. The shear strength provided by the truss is obtained by the modified compression field theory, and the shear strength provided by the arch is obtained by the shear deformation coordination between the truss and arch, which has an upper bound value. Experimental data of 78 RC walls failed in shear are collected to evaluate the adequacy of the proposed method by comparing with the models of Hwang and Lee, Wood, ACI 318‐11,, EC8, MCBC‐04, and JGJ 3‐2010, respectively. The results show that the average value and coefficient of variation of the experimental‐to‐calculated strength ratios obtained by the proposed model are 1.01 and 0.23, which shows better accuracy and reliability. Therefore, the proposed model can predict the shear strength of RC walls failed in shear accurately.     

Shear strength response of reinforced pond ash

Reinforced pond ash is a composite material, which can be used as an alternative construction material in the field of geotechnical engineering. To study the shear strength response of reinforced pond ash, a series of unconsolidated undrained (UU) triaxial test has been conducted on both unreinforced and reinforced pond ash. In the present investigation the effects of confining pressure (σ₃), number of geotextile layers (N), and types of geotextiles on shear strength response of pond ash are studied. The results demonstrate that normal stress at failure (σ_1f) increases with increase in confining pressure. The rate of increase of normal stress at failure (σ_1f) is maximum for three layers of reinforcement, while the corresponding percentage increase in σ_1f is around (103%), when the number of geotextile layers increases from two layers to three layers of reinforcement. With increase in confining pressure the increment in normal stress at failure, Δσ increases and attains a peak value at a certain confining pressure (threshold value) after that Δσ becomes more or less constant. The threshold value of confining pressure depends on N, dry unit weight (γ_d) of pond ash, type of geotextile, and also type of pond ash.     

Shear strength of reinforced concrete deep beams

An hypothesis is made for the shear mechanism of concrete deep beams based on the failure mode observed during testing. Using the hypothesis an equation is developed for predicting the ultimate strength of the beam. The equation is found to give reasonable values for the ultimate loads for beams with depth to span ratio as low as .     

Compressive strength of fiber reinforced highly compressible clay

Admixtures and geogrids are frequently used in practice to stabilize soils and to improve their load carrying capacity. In this study, polyester fibers were mixed with soft clay soil to investigate the relative strength gain in terms of unconfined compression. Samples were tested in unconfined compression with 0%, 0.5%, 1.0%, 1.5% and 2.0% plain and crimped polyester fibers. Verifications tests were also performed to investigate the repeatability of the test results. The results presented show that the degree of compaction affected the relative benefits of fiber reinforcement for the subject soil. Samples compacted after mixing various proportions of sand into clay (varying from 0% to 12% of clay) were also tested. It was observed that unconfined compressive strength of clay increases with the addition of fibers and it further increases when fibers are mixed in clay sand mixture. Verification tests performed revealed that even though the fibers were randomly oriented, tests results can be reproduced with reasonable accuracy.     

Shear strength characteristics of geosynthetic reinforced rubber-sand mixtures

Shear strength characteristics of the geosynthetic-reinforced rubber-sand mixture (RSM) has been investigated by conducting Unconsolidated Undrained (UU) triaxial test. In the first part, a series of UU triaxial tests have been carried out to know the size effect of granulated rubber/tyre chips from seven different rubber sizes. RSM sample that provides higher strength, energy absorption capacity and stiffness is considered as the optimal size and has been used in the investigation on geosynthetic-reinforced RSM. In the second part, shear strength characteristics of geosynthetic-reinforced RSM has been investigated by varying proportions of rubber content (50% and 75% rubber by volume), type of geosynthetic (geotextile, geogrid and geonets), number of geosynthetics (1–4) layers, geosynthetic arrangement and confining pressure. The results demonstrate that RSM reinforced with geosynthetic has enhanced peak strength, failure strength and corresponding axial strain at failure. Fifty percent RSM reinforced by geotextile and 75% RSM reinforced by geonets with 4 layers of reinforcement, led to a maximum increase in shear strength. The strength and energy absorption capacity are doubled for the reinforced RSM's, and reduced the brittleness index values as close to zero, which depends on the type, number of layers and arrangement of geosynthetic.     

锈蚀钢筋混凝土梁的抗剪承载力分析模型

锈蚀钢筋混凝土梁的传统抗剪承载力模型大多属于经验模型,考虑的影响因素不全面且缺乏严密的理论推导,导致计算精度有限。基于修正压力场理论,建立了可以综合考虑钢筋锈蚀对临界斜裂缝倾角、梁有效抗剪截面积、配筋率、配箍率等关键因素影响的锈蚀钢筋混凝土梁的抗剪承载力模型,通过与85组试验数据和现有模型的对比分析,验证了模型的适用性和计算精度。结果表明,该模型具有严密的理论基础,考虑的影响因素全面,计算精度较高、离散性较小。     

Shear strength of alluvial soils reinforced with PP fibers

Bulletin of Engineering Geology and the Environment - Alluvial soils can be defined as sediments that have not completed their geological formation have high void ratios, low bearing capacity, and...     

Shear strength and failure mechanism of needle-punched geosynthetic clay liner

The internal shear strength of a geosynthetic clay liner (GCL) within composite liner systems is crucial for the stability of landfills and should be carefully considered in the design. To explore the shear strength and failure mechanism of the extensively used needle-punched GCL, a series of displacement-controlled direct shear tests with five normal stress levels (250–1000 kPa) and eight displacement rates (1–200 mm/min) were conducted. The shear stress to horizontal displacement relationships exhibit well-defined peak shear strengths and significant post-peak strength reductions. The monitoring results of the thickness change indicate that the degree of volumetric contraction is related to the reorientation of fibers and dissipation of pore water pressure. Furthermore, the peak and residual shear strengths both depend on the displacement rate because of the rate-dependent tensile stiffness of needle-punched fibers and shear strength of the soil/geosynthetic interface. Through additional tests and lateral comparison, it was discovered that the shear behavior of sodium bentonite, degree of hydration, and pore water pressures all affect the shear mechanisms of the NP GCL. In particular, the failure mode transfers from fiber pullout to fiber rupture with the increase in water content as the hydrated bentonite particles facilitate the stretching of needle-punched fibers.     

Shear strength prediction for steel reinforced concrete deep beams

This study proposes an analytical method for determining the shear strengths of steel reinforced concrete deep beams under the failure mode of concrete crushing originally based on the softened strut-and-tie model. The proposed method is a good physical model that can correlate well with the observed failure phenomenon of steel reinforced concrete deep beams. By comparing the predictions of the proposed method with the available test results from the literature, it was found that the proposed method is capable of predicting the shear strengths for steel reinforced concrete deep beams with sufficient accuracy. The shear-carrying behavior of steel reinforced concrete deep beams is highly influenced by the ratios of flange width to gross width, the shear span-to-depth ratios, and the concrete strengths. When the ratio of flange width to gross width is low, the shear-carrying capacities of steel reinforced concrete deep beams increase with the increasing ratio. However, if the ratio of the flange width to gross width is higher than a critical value, then the failure mode of steel reinforced concrete deep beams will be converted from diagonal compression failure into bearing failure.     

基于修正压力场理论的型钢超高强混凝土柱受剪承载力研究

为分析型钢超高强混凝土柱受剪机理,并准确计算其受剪承载力,基于修正压力场理论提出型钢超高强混凝土柱的受剪承载力计算模型。该模型通过柱端部截面中心正应变ε0来考虑轴力、弯矩和剪力的相互作用,并通过关键参数混凝土主压应力角θ和平均纵向应变εx来反映剪跨比、轴力以及配箍对柱受剪承载力的影响。推导出型钢超高强混凝土柱受剪承载力的计算式,并分析其两种剪切破坏形式。通过两组型钢超高强（高强）混凝土柱的低周反复试验结果对该受剪模型进行验证。研究表明：模型能合理考虑轴力、弯矩和剪力的相互作用,反映剪跨比、轴力和箍筋对受剪承载力的影响;模型计算所得受剪承载力与试验值吻合较好。     

棕榈丝加筋红黏土的无侧限抗压强度研究

红黏土是一种典型的特殊土,土体性质极不稳定,特别是遇水强度快速衰减,容易引发地基沉降或边坡坍塌等工程地质灾害。通过开展棕榈丝改良红黏土的无侧限抗压强度试验,研究不同棕榈丝掺量及长度对红黏土无侧限抗压强度的影响。结果表明,随棕榈丝掺量的增大,棕榈丝加筋土的无侧限抗压强度相应增加;随棕榈丝长度的增大,棕榈丝加筋土的无侧限抗压强度先增大后减小,棕榈丝加筋土的最优棕榈丝长度为20mm。棕榈丝可有效控制土体的变形,提高土体的残余强度。     

基于软化拉-压杆模型的钢筋混凝土框架节点受剪分析

软化拉.压杆模型是基于经典桁架模型理论而发展起来的一种模型,主要用于混凝土结构中应力紊乱区的受剪设计.以包含钢筋混凝土变梁中节点在内的各类框架节点为研究对象,建立框架节点等效核心区在剪、压复合荷载作用下的计算模型,应用软化拉.压杆模型对节点等效核心区进行受力分析,推导框架节点的受剪承载力计算公式,并通过国内外110个钢...     

Shear strength model of the reinforced concrete beams with embedded through-section strengthening bars

In this study, finite element (FE) analysis is utilized to investigate the shear capacity of reinforced concrete (RC) beams strengthened with embedded through-section (ETS) bars. Effects of critical variables on the beam shear strength, including the compressive strength of concrete, stiffness ratio between ETS bars and steel stirrups, and use of ETS strengthening system alone, are parametrically investigated. A promising method based on the bond mechanism between ETS strengthening and concrete is then proposed for predicting the shear resistance forces of the strengthened beams. An expression for the maximum bond stress of the ETS bars to concrete is developed. This new expression eliminates the difficulty in the search and selection of appropriate bond parameters from adhesion tests. The results obtained from the FE models and analytical models are validated by comparison with those measured from the experiments. Consequently, the model proposed in this study demonstrates better performance and more accuracy for prediction of the beam shear-carrying capacity than those of existing models. The results obtained from this study can also serve researchers and engineers in selection of the proper shear strength models for design of ETS-strengthened RC beams.     

法向循环荷载下筋土界面的剪切应力规律及预测

为了研究法向动荷载作用下筋土界面的剪切应力变化规律,采用大型动态直剪仪,对相对密实度为75%的砾石和土工格栅的界面进行了剪切试验,研究了4种法向初始应力（20,40,60,80 kPa）和4种法向荷载振动幅值（10,20,30,40 kPa）对筋土界面循环剪切特性的影响。在试验的基础上,建立了法向循环荷载作用下筋土界面在峰值前和残余阶段的剪切应力-法向应力表达式。同时,结合应力时间差规律,并考虑法向初始应力和荷载振幅等的影响,提出了界面剪切应力-剪切位移的表达式。将两种预测表达式与试验结果进行了对比,均具有较好的吻合度,验证了方法的正确性。     

Shear strength and behavior of tubed reinforced and steel reinforced concrete (TRC and TSRC) short columns

Tubed RC and SRC short columns are special kinds of concrete filled tubular columns but the steel tube does not pass through the beam–column connection and is shorter than concrete core. In areas that suffered earthquakes, the short columns are vulnerable to brittle shear failure. TRC and TSRC short columns are widely used in bridges, high-rise buildings and large factories. So it is important to investigate the behaviors and approaches to improve the ductility of these kind of columns. The aim of this study is to develop a nonlinear finite element model (FEM) for TRC and TSRC short columns and to compare the results with those experimentally captured. Depending on the FEM results, the elastic–plastic method was used to analyze the stress status of the steel tube. A modified ACI design method is adopted to calculate the nominal shear strength of TRC and TSRC short columns based on the FEM and analysis results.     

Shear failure analysis on ultra-high performance concrete beams reinforced with high strength steel

A new deck system for moveable bridges was developed that makes use of ultra-high performance concrete (UHPC) reinforced with high strength steel (HSS) rebar to achieve the light weight and high strength requirements in moveable bridge applications. However, the typical deck strips of this deck system failed predominantly due to shear cracks in simply supported beam proof tests. This paper investigates the mechanism of the deck strip shear failure experimentally and analytically. Experimental studies were performed at several scales, including material characterization, bond strength tests, small-scale prism tests, and full-scale beam tests. Specimens with traditional shear strengthening techniques were also tested. Several existing formulas were utilized to predict the shear strength, and the results were compared to the experimental results. The accuracy and limitations of these formulas are discussed. The shear failure of UHPC-HSS beams is not characterized by brittle response or catastrophic load reduction as with normal reinforced concrete. Therefore, this particular shear failure mode is regarded as acceptable. However, the additional shear resistance caused by the localized deformation of the longitudinal reinforcement is not recommended to be considered for design capacity formulas.     

无腹筋钢筋混凝土受弯构件基于修正压力场理论的受剪计算

为解释无腹筋钢筋混凝土受弯构件的受剪破坏机理,并反映尺寸效应对无腹筋受弯构件受剪强度的影响,在修正压力场理论基础上,对钢筋混凝土构件受剪破坏做了进一步研究,提出沿受弯构件斜裂缝表面平均剪应力的计算公式,并考虑混凝土构件的尺寸效应提出抗剪强度简化计算公式。与国内外无腹筋梁的512个试验结果比较表明,采用提出的斜裂缝表面平均剪应力公式按修正压力场理论计算的受剪承载力及按文中简化公式计算的受剪承载力与试验结果比值的变异性很小,可用于无腹筋钢筋混凝土梁的受剪分析和设计。     

Modeling of the cyclic behavior of shallow foundations resting on geomesh and grid-anchor reinforced sand

Storage tank foundations with frequent discharges and filling or road embankments under repeated traffic loads are examples of foundations subjected to the cyclic loading with the amplitude well below their allowable bearing capacity. The concern exists for the amount of uniform and non-uniform settlement of such structures. The soil under such foundations may be reinforced with geosynthetics to improve their engineering properties.This paper deals with the effects of using the new generation of reinforcement, grid-anchor, for the purpose of reducing the permanent settlement of these foundations under the influence of proportion of the ultimate load. Unloading-reloading field tests were performed to investigate the behavior of a square footing on the sand reinforced with this system under such loads. The effects of footing size and reinforcement types on the cyclic behavior of the reinforced sand were studied experimentally and numerically by the aid of computer code. The large-scale results show that by using the grid-anchors, the amount of permanent settlement decreases to 30%, as compared with the unreinforced condition. Furthermore, the number of loading cycles reaching the constant dimensionless settlement value decreases to 31%, compared with the unreinforced condition. Another goal of this paper is to present the equations for reinforced soil under cyclic loading to prevent such complicated calculation involved in deformation analysis. According to these equations, calculation of the permanent settlement and the number of load cycles to reach this amount for each foundation with a given size on the geomesh and grid-anchor reinforced sand, without further need to carry out the large-scale test, is supposed to perform easily.     

Shear strength of a fibre-reinforced clay at large shear displacement when subjected to different stress histories

The topic of fibre-reinforced soil has been introduced and studied increasingly in the past few decades. However, the shear strength response of fibre-reinforced clay soils with different initial void ratio values when subjected to large shear displacement has not been explored in the literature. The purpose of this study is to evaluate the shear strength responses of fibre-reinforced clay soils when remoulded with relatively small and large initial void ratio and subjected to large shear displacement. In order to exclude the composition variability of the fibre-reinforced samples when subjected to various normal effective stresses, a series of multi-stage reverse drained direct shear test was undertaken with four reverse cycles of ±7 mm, ±7 mm, ±7 mm and +14 mm to achieve an accumulative horizontal shear displacement up to 56 mm that is 93% of the sample dimension. The first stage of the testing programme was carried out on soil samples consolidated at normal effective stress of 600 kPa and unloaded to 50 kPa, followed by 4 shear cycles at normal effective stresses of 50, 100 and 200 kPa, respectively. The results of these tests confirmed significant effective stress ratio improvement with fibre reinforcement, even at large shear displacement to the fourth cycle. However, the rate of improvement decreased with normal effective stress and initial void ratio. Based on the experiments carried out in this study, the optimum fibre content to increase the shear strength of the clay soil with initial void ratio of 0.64 was found to be 0.25% with 140%, 81% and 23% increase in the stress ratio over that of the unreinforced soil at normal effective stresses of 50, 100 and 200 kPa, respectively. The second stage of the testing programme was conducted on a set of samples consolidated and sheared at normal effective stresses of 50, 100 and 200 kPa, respectively. The optimum fibre content was found to be related only to the initial void ratio of the soil, irrespective of the stress history of the soil and the applied normal effective stress. The shear stress ratio of the fibre-reinforced clay soils at large shear displacement was found to be relatively independent of the stress history of the soil. For all soil samples tested in this study, the stress ratio at 200 kPa normal effective stress was found to remain between 0.45 and 0.60.