Shear Transfer Capacity Research Articles

Shear-stress transfer across a crack in steel fibre-reinforced concrete

The ability of cracked reinforced concrete to transfer shear stresses is of major importance for concrete members designed to sustain high shear forces. Thereby, the maximum shear capacity is mainly affected by the aggregate interlock mechanism, the dowel action of longitudinal reinforcement, the restraining action of stressed reinforcement crossing the crack interface and the possible presence of stirrups. In case of steel fibre reinforced concrete (SFRC), where fibres are used to replace either completely or partially traditional stirrups, research has proven that the direct shear transfer capacity of cracked concrete is increased significantly by using fibres. By means of 69 direct shear tests, the shear-friction behaviour of SFRC with or without confining pressure has been studied further and existing empirical formulations have been checked. Since these models only provide a maximum shear strength, a more fundamental approach to model the direct shear behaviour of cracked SFRC is proposed in this paper. This model deals with the fibre-matrix interaction by means of fibre pull-out and aggregate interlock, as a function of the shear crack opening behaviour (i.e. combined opening and slipping).

Shear friction strength of monolithic concrete interfaces

This paper presents an integrated model for the shear friction strength of monolithic concrete interfaces derived from the upper-bound theorem of concrete plasticity. The model accounts for the effects of applied axial stresses and transverse reinforcement on the shear friction action at interfacial shear cracks. Simple equations are also developed to generalise the effectiveness factor for compression, the ratio of effective tensile to compressive strengths and the angle of concrete friction. The reliability of the proposed model is verified through comparisons with previous empirical equations and 103 push-off test specimens compiled from different sources in the literature. The previous equations considerably underestimate the concrete shear transfer capacity and the underestimation is notable for interfaces subjected to additional axial stresses. The proposed model provides superior accuracy in predicting the shear friction strength, resulting in a mean between experimental and predicted friction strengths of 0·97 and low scatter. Moreover, the proposed model shows consistent trends with the test results in evaluating the effects of various parameters on the shear friction strength.

Experimental investigation on the flexural behavior of steel-concrete composite beams with U-shaped steel girders and angle connectors

This paper focuses on a new type of steel-concrete composite beams consisting of U-shaped steel girders and angle connectors. Compared with conventional steel-concrete composite beams consisting of wide flange girders and headed shear stud connectors (or short channel connectors), the composite beams considered in this study have favorable flexural performance while reducing the excessive costs and potential construction challenges due to installation of the stud and/or channel shear connectors. Through four-point bending tests on five specimens, this research team experimentally investigated flexural behavior of the new composite beams. The five specimens were varied to have different angle connector intervals and installation locations. Test results show that composite beams with angle connectors welded to the webs of U-shaped steel girder fail in brittle failure modes while composite beam with angle connectors welded on the top flange of U-shaped steel girder fails in ductile failure mode. Based on the test results, it can be concluded that angle connectors welded on the top flange are more ductile than those welded to the webs. This paper also assesses adequacy of the existing formula for short channel connectors in quantifying the shear transfer capacity of angle connectors and the influence of installation location of angle connectors on the resulting beam response. Moreover, plastic moment resistance of the composite beam with full shear connection predicted by Eurocode 4 and AISC 360 and ultimate flexural strength of the partially composite beams predicted by the interpolation method in Eurocode 4 agree well with the experimental results. Besides, specifications in AS 2327.1 and provisions in AISC 360 neglecting the reduction factor could be used to estimate the initial stiffness of composite beams in this study by using cracked moment of inertia.

Shear Transfer Mechanism of Concrete Strengthened with External CFRP Strips

AbstractConcrete with reinforcing steel bars across a shear plane was strengthened using carbon fiber–reinforced polymer (CFRP) strips externally bonded to resist shear transfer. Specimens were designed and tested to give insight on shear transfer based on a component model. In this model, five components, i.e., the friction, aggregate interlock, adhesion, shear dilation, and dowel action, contributed to the overall shear resistance. Results indicated that the ultimate shear transfer capacities improved by 6 to 50% for specimens with steel reinforcement ratios varying from 0.46 to 1.20% and CFRP reinforcement ratios varying from 0.224 to 0.298%. The mechanism of shear resistance increase was due to the additional clamping force provided by CFRP strips, which led to a significant increase in the shear component of the adhesion. A best-fitting expression was presented to predict the ultimate shear transfer capacities of CFRP-strengthened concrete with satisfactory accuracy by comparing the calculated result...

Component model for shear transfer in reinforced concrete

A component model was developed from tests on 24 specimens with the purpose of understanding the shear resistance mechanism and predicting the ultimate shear transfer capacities of reinforced concrete (RC) with any length of crack. Targeted specimens were designed and tested, and analytical studies were performed. The results revealed that the shear resistance mechanism is primarily the development of shear components in a whole shear transfer process of initially uncracked RC after microcracking. Certain components weaken or vanish in completely or partly precracked RC. Expressions based on the component model were proposed to predict the ultimate shear transfer capacities of RC. Satisfactory agreement was achieved between the calculated results and the test data in this study and in the literature.

콘크리트의 전단마찰내력에 대한 시공줄눈의 영향

To evaluate the shear friction performance of concrete interfaces with construction joint, a total of 18 push-off specimens were tested under direct shear and constant axial compressive forces. The main parameters investigated were concrete unit weight, arrangement type of transverse reinforcement (V-type for perpendicular configuration to the shear plane and X-type for <TEX>$45^{\circ}$</TEX>-degree inclined configuration), and the magnitude of axial compressive stresses. The initial shear cracking stress and the slope at the ascending branch of the shear load-relative slip relationship were independent of the type of transverse reinforcement and concrete unit weight, whereas they tended to increase as the axial compressive stresses increases. The shear friction strength increased in proportion to the summation of the applied axial stresses and shear transfer capacity (<TEX>${\rho}_{vf}f_y$</TEX>) of transverse reinforcement. The X-type transverse reinforcement had higher shear transfer capacity than the V-type reinforcement. From the mechanical model derived using the upper bound theorem of concrete plasticity, the concrete cohesion and coefficient of friction at the interfaces with construction joint could be estimated to be 1.56 MPa and <TEX>$36.3^{\circ}$</TEX>, respectively.

저층형 철근콘크리트 전단벽의 전단강도 평가를 위한 스트럿-타이 모델

The previous strut-and-tie models (STMs) to evaluate the shear strength of squat shear walls with aspect ratio less than 2.0 do not consider the axial load transfer of concrete strut and individual shear transfer contribution of horizontal and vertical shear reinforcing bars in the web. To overcome the limitation of the existing models, a simple STM was established based on the crack band theory of concrete fracture mechanics. The equivalent effective width of concrete strut having a stress relief strip was determined from the neutral axis depth and effective factor of concrete strength. The shear transfer mechanism of shear reinforcement at the extended crack band zone was calculated from an internally statically indeterminate truss system. The shear transfer capacity of concrete strut and shear reinforcement was then driven using the energy equilibrium in the stress relief strip and crack band zone. The shear strength predictions of squat shear walls evaluated from the current models are in better agreement with 150 test results than those determined from STMs proposed by Siao and Hwang et al. Furthermore, the proposed STM gives consistent agreement with the observed trend of the shear strength of shear walls against different parameters.

Repair of prestressed concrete cylinder with localized delamination

For prestressed concrete cylindrical structures such as nuclear containments, tanks and silos, the curvature effect of the tendons introduces radial tensile stresses in the concrete shell which are generally neglected in the design of such structures. For example, many prestressed concrete nuclear containments in US, especially those which were not designed following radial reinforcement requirement of ACI-359, are reinforced only in the circumferential (hoop) and meridional (vertical) directions but not in the radial direction. This leaves these structures vulnerable to potential laminar cracking and delamination, especially during post-tensioning and/or detensioning process. Should delamination occur, the structure needs to be repaired by either replacing cracked concrete or by “pinning” the delaminated concrete layers together by post-installed anchors. The latter option of post-installed anchors is less invasive from construction stand point and generally suitable for repairing small or localized delamination only. A comprehensive study is undertaken to explore various aspects and design consideration of post-installed anchors for prestressed concrete cylinders. The radial tension demand is first established by combining a mechanical based model with a detailed finite element analysis. With such design demand for post-installed anchors established, the next step aims at developing the tightness requirement of existing delamination cracks for effective use of post-installed anchors. A comprehensive literature search and evaluation is carried out for shear transfer capacity across cracks of various widths. The findings are used to develop specific recommendations for acceptable crack widths to ensure adequate in-plane shear transfer capacity for various design load conditions. A design process for post-installed anchors is proposed for repairing a delaminated prestressed concrete cylindrical structure at the end of the paper, supplemented by an illustrative design example.

Shear Transfer Mechanism and Design of Shear Connectors for Full-Depth Precast Deck Panel System

The development and implementation of full-depth, precast overhang panel systems has the potential to improve constructibility, productivity, and make bridges more economical. Recently, various shear connector systems have been proposed to provide shear-transfer resistance between girders and the precast overhang panels. There is, however, limited information and guidance on the design for shear-transfer capacities for full-depth, precast overhang panel systems. This research performed experiments and assessed the results to estimate the shear-transfer capacities of four types of shear connectors systems. The confinement system of the shear pocket was varied with the hopes of enhancing the sheartransfer capacity. Results indicate that five stages of shear-transfer and failure mechanisms occur during testing. These stages include initial adhesion loss, shear key action, shear key action failure, dowel action of the shear connectors at a sustained load, and final failure of the system. Results from this research indicate that steel reinforcing hoops placed in the shear pocket and shear reinforcing hoops placed in the overhang panel around the opening of the shear pocket provide limited or no improvement in capacity of the shear connector/coupler system. When comparing energy absorption capacities, however, the shear connector systems evaluated can provide improved performance when compared with the conventional R-bar system. A new equation is proposed based on this research.

휨 항복형 철근콘크리트 전단벽의 등가소성힌지길이 모델

본 연구의 목적은 경계요소를 갖는 철근콘크리트 전단벽의 잠재소성힌지길이를 합리적으로 평가할 수 있는 단순모델의 제시이다. 전단벽의 높이에 따른 이상화된 곡률분포로부터, 기본방정식은 항복모멘트와 최대모멘트 그리고 사인장균열에 의한 부가모멘트의 함수로 일반화되었다. 전단벽의 항복모멘트와 최대모멘트는 변형률 적합조건과 힘의 평형조건을 기반하여 산정하였다. 사인장균열 발생의 여부는 ACI 318-11에서 제시된 콘크리트의 전단력으로부터 검토되었으며, 부가모멘트는 Park and Paulay에 의해 제시된 트러스기구를 이용하여 산정하였다. 이들 모멘트식들은 다양한 변수범위에서 변수연구를 수행하였다. 결과적으로 등가소성힌지길이는 주철근 및 수직철근지수와 축력지수의 함수로 제시될 수 있었다. 제시된 등가소성힌지길이의 모델은 실험결과의 비교에서 평균 및 표준편차가 각각 1.019와 0.102로 실험 결과를 정확하게 예측하였다. The present study proposes a simple equation to straightforwardly determine the potential plastic hinge length in boundary element of reinforced concrete shear walls. From the idealized curvature distribution along the shear wall length, a basic formula was derived as a function of yielding moment, maximum moment, and additional moment owing to diagonal tensile crack. Yielding moment and maximum moment capacities of shear wall were calculated on the basis of compatability of strain and equilibrium equation of internal forces. The development of a diagonal tensile crack at web was examined from the shear transfer capacity of concrete specified in ACI 318-11 provision and then the additional moment was calculated using the truss mechanism along the crack proposed by Park and Paulay. The moment capacities were simplified from an extensive parametric study; as a result, the equivalent plastic hinge length of shear walls could be formulated using indices of longitudinal tensile reinforcement at the boundary element, vertical reinforcement at web, and applied axial load. The proposed equation predicted accurately the measured plastic hinge length, providing that the mean and standard deviation of ratios between predictions and experiments are 1.019 and 0.102, respectively.

Testing and Acceptance Criteria for Fiber-Reinforced Composite Grid Connectors Used in Concrete Sandwich Panels

Precast concrete sandwich panels have been used in building construction since the 1960s. These sandwich wall panels are constructed with two wythes of concrete separated by a layer of thermal foam plastic insulation and a shear connector mechanism between concrete wythes. Recently, more research is focused on fiber-reinforced composite grids as shear connectors due to their superior thermal performance compared to other connectors such as steel or solid concrete. However, while there are guidelines for design of concrete sandwich panels, there is no standardized guidance that provides testing and capacity determination for composite shear connectors. Therefore, testing and acceptance criteria were developed to evaluate the shear transfer capacities of fiber-reinforced composite grid connectors used in combination with rigid insulation in concrete sandwich panel construction. The criteria are intended to standardize testing and evaluation of the interaction between concrete and composite shear connectors so manufacturers can provide consistent results, and the data pool generated by standardized testing can support the formulation of design assumptions.

Perforated shear connectors on composite girders under monotonic loading: An experimental approach

This paper presents the results of sixteen push-out tests performed at the Civil Engineering Department of the University of Coimbra, Portugal, on perforated steel shear connectors with varying geometries. Eight tests using the previously studied Perfobond and T-Perfobond geometries were initially performed and were followed by another eight tests on two innovative geometries, the I-Perfobond and 2T-Perfobond. The investigated variables included the shear connector geometry and the provision of transverse reinforcement within a shear connector’s holes. The results are presented and discussed with a focus on the shear connectors’ structural responses in terms of their shear transfer capacity, ductility, stress distribution and collapse modes. Finally, a comparison of the experimental results with existing analytical models of the Perfobond and T shear connectors is also presented to establish their accuracy and applicability.

Assessment of shear transfer capacity of non-cracked concrete strengthened with external GFRP strips

To investigate the interaction of internal steel reinforcement and external fiber reinforced polymer (FRP) composites on the behavior of shear transfer, 16 non-cracked push-off specimens were tested. Specimens were internally reinforced with steel reinforcement ratios between zero and 1.54% and externally strengthened with different widths of Glass FRP layers. In strengthened specimens, shear transfer capacity increased from 3% to 38% compared to plain specimens. The contribution of FRP reinforcement in shear transfer capacity, as the percentage of cylindrical concrete strength (fc′), was between 0.6%fc′ and 3.7%fc′. Based on the results, the characteristic behavior of strengthened specimens is described.

Pre-Cracked Concrete Shear Strengthened with External CFRP Strips

In reinforced concrete design, there are situations where transfer of shear across a specific plane needs to be considered. Examples of such situation include corbels, bearing shoes, ledger beam bearing, and a host of connection between precast concrete elements. In this study, the shear transfer behavior of reinforced concrete is investigated experimentally by conducting test on 6 precracked push-off specimens. The major parameters considered are the amount of reinforcement and externally bonded fiber reinforced polymer fabrics through the shear plane. External strengthening with Fiber Reinforced Polymer (FRP) fabrics is an effective technique for improving the structural performance and life span of the existing reinforced concrete structures. This paper illustrates the result of shear transfer capacity and modes of failure of the precracked reinforced concrete push-off specimens bonded externally with FRP. An experimental investigation was conducted to study the effectiveness of FRP as an external reinforcement. Based on experimental results, the external FRP reinforcement controls the shear slip along the shear plane and crack width. In the unstrengthened push-off specimens, the pre-existing crack along the shear plane will reduce the ultimate shear transfer capacity and increase of shear slip at all load levels. However in strengthened specimens, the external FRP reinforcement will control the increase of slip and increase the ultimate shear stress transfer capacity along the shear plane.

In-plane seismic performance of unreinforced masonry walls strengthened with unbonded prestressed wire rope units

This study proposes a practical strengthening technique for enhancing the in-plane shear strength and ductility of unreinforced masonry (URM) walls using the unbonded prestressed wire rope units. Six full-scale strengthened URM walls and an unstrengthened URM wall were tested under constant axial load and cyclic lateral loads to explore the significance and limitations of the developed seismic strengthening procedure. The main variables investigated were the aspect ratio of walls, and the spacing and configuration of the prestressed wire ropes. The ductility of the walls tested was evaluated using the work damage indicator calculated at each loading step from the hysteretic loops. In addition, shear transfer capacities of masonry and wire ropes were identified based on the statistical fitting of test data for URM walls compiled from the literature and 45° truss analogy, respectively, in order to propose simple equations for shear strength of the URM walls strengthened with the developed wire rope units. Test results showed that the proposed strengthening procedure was highly effective in enhancing the in-plane shear strength and ductility of URM walls and controlling crack propagation along head and bed mortar joints. The shear strength and work damage indicator increased with the decrease of the spacing of wire ropes, showing that the inclined wire ropes were more capable of enhancing ductility than vertical wire ropes. The crack resistance capacity and stiffness of URM walls were also improved due to the additional axial compression force provided from the prestressing force applied to the wire ropes. The shear capacities obtained from the proposed simple equations were in good agreement with the test results, indicating that the mean and standard deviation of the ratios between measured and predicted shear capacities were 1.14 and 0.13, respectively.

2축-응력장 이론을 이용한 철근콘크리트 부재의 전단마찰 해석

직접 전단력이 작용하는 철근콘크리트 부재는 콘크리트 계면의 전단전달에 의해 외력에 저항한다. 현행 구조설계기준의 전단마찰 관련식은 과거 연구자들의 실험 결과를 바탕으로 유도되었으며, 전단마찰강도는 콘크리트 계면을 가로지르는 철근 단면적의 크기에 비례한다. 이러한 경험식을 통해 구해진 전단마찰강도는 철근비가 큰 콘크리트 부재의 경우 실측값과 비교해서 매우 낮은 값을 나타낸다. 이 연구에서는 2축-응력장 이론을 이용하여 종방향 철근의 항복 이후 콘크리트 경사스트럿의 압축파쇄로 이어지는 일련의 극한 한계상태를 정의하고자 하였다. 2축 응력 상태의 콘크리트 최대 압축강도의 변화를 고려하기 위하여 수정압축장이론, 연화트러스모델의 구성방정식을 사용한 각각의 경우에 대하여 전단마찰 강도를 평가하였다. 타당성 검증을 위하여 과거 연구자들에 의해 수행된 직접 전단강도 실험값들과 2축-응력장 이론을 이용하여 구한 값들을 현행 구조설계기준의 전단마찰식과 함께 비교하였으며, 보통강도 콘크리트로 제작된 비균열 직접 전단 시험체의 경우 산정값과 실측치가 대체적으로 일치함을 확인하였다.

Durability of SG-laminated reinforced glass beams: Effects of temperature, thermal cycling, humidity and load-duration

This paper investigates the durability of structural glass beams that are composed of annealed glass, stainless steel reinforcement and SG (SentryGlas®) interlayer sheets. To do so, a series of pull-out tests (to investigate the shear transfer capacity of the SG) and a series of bending tests (to investigate the structural response of the beams) have been performed at different temperatures, after thermal cycling, after humidity exposure, and for long-duration loading. From the results it is concluded that the beams are highly redundant and durable, but that the effects of humidity are not yet sufficiently understood to apply them in humid environments.

Evaluating the shear-friction resistance across sliding planes in concrete

Shear friction or aggregate interlock behaviour across sliding planes in concrete is now a well-established area of research. Two separate shear-friction approaches have been developed previously where these separate approaches either quantify the shear transfer capacity for a given crack displacement, normal stress and crack separation (Walraven Approach) or quantify the maximum shear transfer for a given crack confinement (Mattock Approach). In this paper, these two seemingly disparate approaches are combined to provide sufficient information to simulate all aspects of shear friction in initially cracked planes including a quantifiable failure limit for various crack separations and displacements. The shear friction components of initially uncracked sliding planes are also derived from the analysis of actively confined concrete cylinders and a failure envelope for initially uncracked sliding planes is developed. Hence, this paper provides the technique for determining the shear friction properties not only for initially cracked sliding planes, which have previously been available, but also for initially uncracked sliding planes which were not previously available so that shear-friction theory can now be used for all aspects of concrete.

A STUDY ON STRESS TRANSFER CHARACTERISTICS AT CONNECTIONS OF HYBRID STRUCTURES

Shield-driven tunneling has been playing a significant role recently as a standard method in urban tunnel construction. As the main road tunnels have to be connected with ramp tunnels efficiently, engineers have sought to develop steel-concrete composite structures using the longitudinal ribs of the steel segment as shear connectors. However, the shear connector at the connection between different types of members has hardly been studied and its stress transfer mechanism is not well understood. The authors carried out fracture experiments with scale down models for this connection, and examined the stress transfer mechanism and the shear transfer capacity carried by shear connectors and studs. A stress-transfer model for easily calculating shear transfer capacity was developed and verified through the comparison with experimental results and analytical results based on the nonlinear finite element method.

EVALUATION OF IN-PLANE SHEAR TRANSFER IN DEVELOPED PCA FLOOR SLAB SYSTEM FOR UNBONDED PRESTRESSED CONCRETE FRAME STRUCTURE

In this study, a new PCa floor system for an unbonded prestressed concrete (PC) frame structure was developed. Deformation of unbonded PC frame structure is expected to concentrate in the joint between beam and column and, as a result, damage such as cracks to beams and columns can be reduced during an earthquake. Floor slab applied to these structures is needed to be provided with not only sufficient in-plane shear transfer capacity but also system to avoid confinement of movement of beam-column joint. For this purpose, a new PCa slab-beam joint system was proposed and loading tests of full scale specimens were carried out. From the experimental results, it was shown that shear stiffness and strength in the new joint system with shear cotter were almost same with those in conventional half PCa floor slab. Moreover, an evaluation method of in-plane shear of floor slab between the frames with different stiffness and shear capacity was examined based on equilibrium of shear force in frames and floor slabs. Static push-over and seismic response analyses of prototype frame structures were carried out to discuss the requirement for in-plane shear capacity of floor slab and design shear for slab-beam joint. Significant difference was not found between the seismic responses of frame structures with rigid floor and those with the new floor slab system, provided that the slab-beam joint was designed accordance with the proposed evaluation method of in-plane shear.