Shear-friction Theory Research Articles

The influence of shear surface quality on the mechanical properties of long-span prestressed continuous rigid-frame bridge

PurposeThe long-span continuous rigid-frame bridges are commonly constructed by the section-by-section symmetrical balance suspension casting method. The deflection of these bridges is increasing over time. Wet joints are a typical construction feature of continuous rigid-frame bridges and will affect their integrity. To investigate the sensitivity of shear surface quality on the mechanical properties of long-span prestressed continuous rigid-frame bridges, a large serviced bridge is selected for analysis.Design/methodology/approachIts shear surface is examined and classified using the damage measuring method, and four levels are determined statistically based on the core sample integrity, cracking length and cracking depth. Based on the shear-friction theory of the shear surface, a 3D solid element-based finite element model of the selected bridge is established, taking into account factors such as damage location, damage number and damage of the shear surface. The simulated results on the stress distribution of the local segment, the shear surface opening and the beam deflection are extracted and analyzed.FindingsThe findings indicate that the main factors affecting the ultimate shear stress and shear strength of the shear surface are size, shear reinforcements, normal stress and friction performance of the shear surface. The connection strength of a single or a few shear surfaces decreases but with little effect on the local stress. Cracking and opening mainly occur at the 1/4 span. Compared with the rigid “Tie” connection, the mid-span deflection of the main span increases by 25.03% and the relative deflection of the section near the shear surface increases by 99.89%. However, when there are penetrating cracks and openings in the shear surface at the 1/2 span, compared with the 1/4 span position, the mid-span deflection of the main span and the relative deflection of the cross-section increase by 4.50%. The deflection of the main span increases with the failure of the shear surface.Originality/valueThese conclusions can guide the analysis of deflection development in long-span prestressed continuous rigid-frame bridges.

Experimental and finite element analysis on mechanical performance of prefabricated assembly inverted arch to lining joints of large section highway tunnel under direct shear loding

To investigate the mechanical properties of the prefabricated inverted arch to cast-in-place lining joints, 21 "Z"-shaped shear specimens for direct shear testing were designed and manufactured, with the interface planted steel bars ratio, interface size, and interface treatment method as variable parameters. The whole failure process of the joint under a direct shear stress state was observed and recorded during the test, the shear-slip curve of the specimen was obtained, failure mechanism and variation law of the joint's direct shear mechanical characteristics were carefully examined. The results reveal that the specimen's shear performance improves following the interface chiselling treatment. The specimens fail in three ways: simple concrete failure, simple planted steel bars failure, and assimilative failure of the concrete and the planted steel bars. The ultimate shear capacity, ductile failure capacity, resistance to damage evolution, and energy dissipation capacity of the specimens rise as the planted steel bars ratio increases. When the planted steel bars ratio increases from 0.7% to 1.1%, the improvement is the most significant, reaching 66.3%. When the planted steel bars ratio is the same, the shear bearing capacity improves as the interface size grows. The finite element model of the “Z”-shaped shear specimen of the prefabricated inverted arch and the cast-in-place lining joint is established, and the parameter extension analysis is performed. Based on the test results and the Extended Shear-Friction Theory, a high-accuracy calculation model of shear capacity of precast inverted arch and lining joint is presented.

Friction and Cohesion Interface Shear Factors of Ultra-High-Performance Concrete (UHPC) Cast on Hardened Conventional Concrete

In composite structures, interface shear resistance is a critical design criterion for transferring forces between interconnected elements at the contact surface. Recently, Ultra-High-Performance Concrete (UHPC) applications in construction have been growing rapidly due to superior mechanical and durability properties; however, there is no guidance on how to predict the interface shear resistance of UHPC cast on hardened conventional concrete (CC). This paper presents the experimental and analytical investigations conducted to develop friction and cohesion factors of the shear friction theory for UHPC cast on hardened CC in composite sections. Push-off shear tests and slant shear tests were conducted to evaluate and validate the effect of interface surface texture, interface reinforcement ratio, CC and UHPC compressive strength, and fiber presence. A friction factor of 1.0 was adopted—as in the current code provisions—while a cohesion factor of 3.45 MPa (0.5 ksi) between UHPC cast on intentionally roughened hardened CC was proposed, which is significantly higher than that in the current code provisions of CC. Also, increasing the interface shear reinforcement ratio increased the interface shear resistance significantly and resulted in a more ductile failure. Neither UHPC compressive strength nor the presence of steel fibers had a significant effect on the interface shear resistance of UHPC cast on hardened CC.

A coupled adhesive-frictional model tailored for interfacial behaviors between UHPC and NC materials

In this paper, a coupled adhesive-frictional is proposed and implemented within an implicit finite element (FE) solver, targeting interfacial behaviors between ultrahigh-performance concrete (UHPC) and normal concrete (NC) materials. The model couples the adhesive force and frictional force, which is consistent with the mainstream shear-friction theory. The proposed model is realized by the zero-thickness cohesive element, thorough user-defined element (UEL) subroutine provided by the general FE software Abaqus/Standard. The model satisfactorily predicts the bond strength between UHPC and NC materials subject to various statuses, i.e., the tensile force (direct-tensile test), and combined compressive and shear forces (slant shear test). In addition, the interfacial model works fully compatible with the concrete damaged plasticity model, which is adopted for the UHPC and NC materials. The combination of these two models yields agreed with simulation results, which effectively predicts various cracking propagation and failure patterns of UHPC-NC composite specimens. The specimens in literatures are selected for comparisons and the numerical simulations clearly illustrate the complex interactions between the matrix cracking and interfacial debonding.

Shear slip post-cracking behaviour of polyolefin and steel fibre reinforced concrete

The most significant structural concrete codes consider the shear contribution of fibres in structural design when using fibre reinforced concrete (FRC) if certain requirements are met. However, instead of obtaining such a contribution based on the results of shear tests, the structural codes establish that the parameters used in the structural design be obtained from bending tests. In order to assess the accuracy of such an approach, this study analyses the shear contributions of fibres in FRC by means of shear push-off tests. The influence of two of the most common structural fibres is examined: hooked-end steel and polyolefin fibres. The paper includes the description of the experimental campaign and the push-off tests. In addition, the analysis of the cracking patterns by means of digital image correlation (DIC) is also included. The experimental results are compared with a shear crack opening behaviour model. The significance of the research relies in the comparison of the shear residual capacity of the concrete reinforced with two main types of structural fibres, the cracking patterns and suitability of the shear-friction theory for reproducing the opening-sliding of the crack under push-off testing of FRC.

Experimental investigation of perfobond hoop shear connector’s bearing capacity and slip

Perfobond hoop (PBH) is a type of shear connector specifically promoted from perforated steel plate connectors (PBL) with relatively higher bearing capacity and ductility. However, there is limited information on the effect of the parameters on PBH’s bearing capacity and slip, such as concrete compressive strength, opening diameter on perfobond plate and hoop diameter. To investigate the mechanical behavior of PBH, push-out tests were conducted under static loading. Corresponding failure modes, bearing capacity and load-slip relationship were obtained. In this paper, the shear-friction theory and the method of multivariate linear regression analysis are employed to analyze the experimental results and a simplified formula for PBH bearing capacity is proposed based on the test results of eighteen specimens. By fitting the normalized results of specimens, an empirical equation for the load-slip relationship of PBH within the whole loading process is obtained, which is in an exponential form. The proposed formulae are both validated with the verification results and can provide good references for the design and applications of PBH.

An optimum indeterminate strut-and-tie model for reinforced concrete corbels

The failure behavior of a reinforced concrete corbel is complicated due to the shear span-to-effective depth ratio, reinforcement patterns, load conditions, and material properties. In this study, an optimum first-order indeterminate strut-and-tie model that reflects all characteristics of the failure behavior is proposed for the rational design of reinforced concrete corbels with a shear span-to-effective depth ratio of less than 1.0. A load distribution ratio that transforms the indeterminate strut-and-tie model into a determinate model is also developed to help structural designers design reinforced concrete corbels using the strut-and-tie model methods of current design codes. For the development of the load distribution ratio, a material nonlinear finite element analysis of the proposed first-order indeterminate strut-and-tie model was conducted repeatedly by changing the combination of primary design variables of the corbels. To examine the validity of our results, the ultimate strengths of 294 reinforced concrete corbels tested to failure by other investigators were predicted using the proposed strut-and-tie model with the load distribution ratio, the existing determinate strut-and-tie models representing arch and truss load transfer mechanisms, and the American Concrete Institute 318 conventional design method based on a shear friction theory. The ultimate strengths predicted by the proposed strut-and-tie model agreed fairly well with the experimental results. The ratio of the experimental strength to the predicted strength (and coefficient of variation) was 1.09 (28.0%), implying that the proposed strut-and-tie model can represent the load transfer mechanisms of corbels most appropriately.

Detailing of concrete-to-concrete interfaces for improved ductility

Recent research has shown that reinforced concrete (RC) beams with concrete-to-concrete casting interfaces where plastic hinges are likely to develop, may experience reduced ductility in comparison to similar structural elements casted at once, due to a potential shear slippage along the casting interfaces. Although of relevant importance for both precast and cast in situ RC structures, this problem is still not addressed in current codes and standards, which limit the safety check of casting interfaces to the verification of their strength based on improved expressions of the “shear friction theory”, the latter proposed in the 60’s. However, recent research has shown that friction strength of casting interfaces depends on interface width opening, and it is significantly reduced after the yield of the bending reinforcement. During the formation of plastic hinges, shear stresses run preferentially across the compressed zones of the interfaces, reducing their strength, and ultimately the specimens’ ductility.In this paper, different and alternative details for interfaces are proposed to improve global behaviour, and in particular, ductility of RC beams with casting interfaces located on plastic hinges regions. An experimental campaign was carried out to study the effect of: (i) epoxy and latex based adhesion promoters’ usage between castings; (ii) web reinforcement; (iii) geometry of interfaces; (iv) and shear level.Results show that both epoxy and latex based adhesion promoters, currently used in construction, hardly improve the tensile strength of casting interfaces, to a point that the interface presence has negligible impact on the cracking pattern. A much better result was observed from the use of a web reinforcement crossing the interface perpendicularly. Although this solution revealed itself also incapable to avoid preferential cracking along the interfaces, it proved to be efficient in limiting shear slippages. The adoption of inclined interfaces either perpendicular or parallel to the expected direction of shear cracks proved also to be an efficient solution. Finally, the likelihood of experiencing a shear slippage along the interface is strongly dependent on the existing shear level after the formation of a plastic hinge.

Strut-and-tie model for shear strength of reinforced concrete ‘push-off’ specimens

An analytical formulation based on the truss analogy has been used for prediction of shear capacity in uncracked ‘push-off’ specimens made with natural concrete and with recycled aggregate concrete. The analytical model shows that shear capacity is a function of tie force across the shear plane. This tie force is reckoned to consist of the tensile capacity of concrete in the shear plane and the tensile force resisted by the clamping reinforcement bridging the shear plane. It is shown that if the ‘concrete contribution’ to this tie force can be estimated, then the amount of clamping reinforcement required to furnish the balance of the force in the tie can be determined for the condition of yielding of this reinforcement. The proposed methodology has been validated by comparing the predicted amounts of clamping reinforcement required to resist reported shear capacities in the literature with the provided values. Based on the shear friction theory, design for push-off shear capacity using strut-and-tie models has been proposed.

Experimental research on the behaviour of concrete-to-concrete interfaces subjected to a combination of shear and bending moment

The shear strength of concrete-to-concrete interfaces subjected to either shear or normal forces perpendicular to the interface, or to a combination of both, has been predicted using the “shear-friction theory” developed in the 60’s for connections for the precast construction. The “shear-friction theory” has been developed considering shear failure as pure slippage, and not in combination with a tension crack, and it has been adopted in most design codes worldwide. Although several improvements have been made to the original theory in the last 50years, few have addressed the behaviour of interfaces subjected to a combination of shear and bending moment, where a shear slippage may occur along a tension crack and a compression zone. This is a relevant issue for the design of both cast-in-place and precast reinforced concrete structures.This paper, presents an experimental work addressed to the study of the behaviour of concrete-to-concrete interfaces subjected to a combination of shear and bending moment. The influence of the interface on the global behaviour and shear and bending strengths of a beam specimen are addressed, as well as the application of the design expressions.Results show that the load transfer capacity across the interface is reduced due to the bending moment crack opening, but it has no influence on the shear and the bending strengths of the beam specimen. However, the bending ductility of the latter is partially reduced due to a shear slippage occurred after the formation of a plastic hinge, and the collapse of the compression zone. It was not possible to evaluate the accuracy of the design expressions to predict the interface maximum friction strength. However, the general application of these expressions to this situation is doubtful, as they are incapable to predict the strength deterioration occurred after the yielding of the longitudinal reinforcement.

Extracting Size-Dependent Stress–Strain Relationships from FRP-Confined Concrete Cylinders for Varying Diameters and Heights

AbstractSince most of the available data regarding fiber-reinforced polymer (FRP)-confined columns has been generated from tests on small-scale cylinders, it is important to ensure that the proposed equations are truly representative of the actual behavior of large-scale columns. In this paper, mechanics solutions have been developed to show the influence of specimen size, that is both diameter and height, on the stress–strain relationship of axially loaded FRP-confined concrete cylindrical specimens using shear-friction theory. Two distinct cylinder failure modes have been examined: that of the circumferential wedge that is common in standard cylinders with aspect ratios of 2∶1; and that of the single sliding plane that occurs at higher aspect ratios. It is often quite difficult, if not impossible, due to the capacities of the testing machines, to test large or large-scale FRP-wrapped specimens under pure compression to extract their axial-stress/axial-strain relationships. It is shown in this paper thro...

소성 이론에 의한 강섬유 보강 초고성능콘크리트의 전단 마찰 강도식 제안

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is distinguished from the normal concrete by outstanding compressive and tensile strength. Cracked normal concrete resists shear by aggregate interlocking while clamped by transverse reinforcement, which is called as shear friction theory. Cracked UHPFRC is expected to have a different shear transfer mechanism due to rather smooth crack face and post-cracking behavior under tensile force. Twenty-four push-off specimens with transverse reinforcement are tested for four different fiber volume ratio and three different ratio of reinforcement along the shear plane. The shear friction strength for monolithic concrete are suggested by limit analysis of plasticity and verified by test results. Plastic analysis gives a conservative, but reasonable estimate. The suggested shear friction factor and effectiveness factor of UHPFRC can be applied for interface shear transfer design of high-strength concrete and fiber reinforced concrete with post-cracking tensile strength.

Simulating the Behavior of FRP-Confined Cylinders Using the Shear-Friction Mechanism

The axial compressive behavior of concrete confined with fiber reinforced polymer (FRP) has received much attention over the past two and a half decades, with over 90 empirical and semiempirical models developed to predict the compressive stress strain behavior. While there is no doubt that in general these models show a good correlation to the dataset from which they were derived, when applied to a global dataset, accuracy is reduced. In response to the largely empirical analysis approaches, which should only be applied within the bounds from which they were developed, a new, mechanics-based approach for predicting the axial and lateral stress-strain relationships of concentrically loaded FRP-confined cylinders is presented. The approach uses shear-friction theory to simulate the formation and displacement of sliding planes as concrete softens. It is shown that cylinders can fail through two shear-friction mechanisms, namely, through either the formation of a circumferential wedge, or, a single sliding plane. Importantly, from this is shown that although each mechanism is defined by the same shear-friction material properties different stress-strain relationships result and this may explain some of the scatter of test results. In this paper, the mechanism of a single sliding plane is derived and compared with that of a circumferential wedge.

Tension Stiffening Analysis for Cyclically Loaded RC Beams

Ductility is an important aspect of cyclically loaded reinforced concrete (RC) structures. One of the method that can be used to measure the ductility of an RC structure is the moment-curvature approach. However, due to it being a strain-based approach it cannot be used to directly simulate behaviour associated with interface displacement that occur when an RC member is cracked. This leads to dependency on empirical values, which imposes limitations on how the moment-curvature approach can be used. In recent years a new displacement based method for measuring ductility has been developed, and can simulate the interface displacement behaviours through the use of partial-interaction theory and shear friction theory. This paper aims to extend the general tension stiffening analysis of the displacement-based approach to allow for cyclic loading. The tension-stiffening analysis was then validated against experimental results and the results were found to agree fairly.

Optimisation of shear strengthened reinforced concrete beams

External prestressed carbon fibre reinforced polymer straps can be used to strengthen shear-deficient reinforced concrete structures. For an efficient shear retrofitting system, the optimum combinations of parameters such as the number of straps, strap locations, strap stiffness and initial strap prestress need to be identified. The modified compression field theory and the shear friction theory have previously been applied to carbon fibre reinforced polymer strap strengthened beams. As implemented, both of these methods are iterative. Particle swarm optimisation and genetic algorithm stochastic optimisation methods were used to reduce the computational cost associated with the shear strength evaluation and also to search the design space for carbon fibre reinforced polymer strap strengthened beams. An initial comparison across several test functions showed that the preferred optimisation algorithm depended on the characteristics of the design space. When applied to a reinforced concrete case study, the genetic algorithm was better for searching the shear friction theory shear strength design space that was characterised by several peaks. However, for the smoother modified compression field theory shear strength evaluation space, and for the design space for the carbon fibre reinforced polymer strengthened beams calculated using either the modified compression field theory or the shear friction theory, the particle swarm optimisation converged more quickly and accurately. The optimised solutions reflect the assumptions within the underlying evaluation methods.

Analytical Investigation and Monitoring of End-Zone Reinforcement of the Alaskan Way Viaduct Super Girders

In this paper, the authors present findings from nonlinear finite element analysis of end zone cracking of deep pretensioned concrete I-girders. They investigate the end zone reinforcement of eight 210 foot long, 100 inch deep super girders used in the construction of the Alaskan Way viaduct replacement in downtown Seattle, Washington. Field observations revealed a similar response by the super girders to the release of pretensioning to that of other commonly-used I-girders. End zone cracking occurred immediately after release, and it included a typical network of splitting cracks along the web height and the web and bottom flange interface. The authors propose a closed-form solution based on shear friction theory that could serve as an alternative for estimating tensile stress in end zone reinforcement along the web and bottom flange interface.

Interface Shear Transfer on Composite Concrete Members

The shear-friction theory was adopted in design codes to predict the longitudinal shear strength between parts of concrete members cast at different times. This is a relevant subject for different situations, such as the connection between precast members with cast-in-place parts and strengthening of existing reinforced concrete (RC) members with a new concrete layer. The bond strength of the interface is controlled by parameters such as the substrate roughness, curing conditions, and the material strength and stiffness of both concrete layers, among others. Some of these for example, differential shrinkage due to different curing conditions, and differential stiffness due to the difference in the Young's modulus of each layer are not addressed in codes. This paper presents recommendations and proposes an alternative design approach for concrete-to-concrete interfaces that can be adopted in future revisions of ACI 318 and Eurocode 2. A comparison between ACI 318 and Eurocode 2 is presented.

격자형 강합성 바닥판 이음부의 전단내력 평가

본 논문에서는 프리캐스트 방식으로 제작 가능한 격자형 강합성 바닥판의 이음부에 기계식 연결방식을 적용하고자 콘크리트 전단키와 고장력볼트로 구성되는 이음부에 대해 Push-out 시험으로 전단내력을 구하였으며, 이를 전단마찰 이론에 근거한 이론식 및 설계식과 비교함으로써 전단내력을 평가하였다. 분석결과에 따르면, 이음부 접합면을 에폭시로 부착한 경우가 전단키를 강판으로 보강한 경우 보다 약 10% 정도 더 큰 전단내력을 갖는 것으로 나타났으나, 실험체간 전단내력의 편차는 전단키를 강판으로 보강한 경우가 더 작게 나타났다. 실험결과를 계산식 및 설계식과 비교한 결과, 기존 설계식으로 안전하게 설계될 수 있음을 알 수 있었다. 그러나, ACI-318에 의할 경우 이음부 전단내력이 과소평가되기 때문에 LRFD에서 제시된 설계식의 적용이 더 적당한 것으로 분석되었다. In order to apply a mechanical deck joint to the prefabricated steel grid composite decks, shear resistance of a joint composed of concrete shear key and high-tension bolt is experimentally evaluated by the push-out test. Shear resistance evaluated by the test is compared with resistance estimated by empirical and design equations based on the shear friction theory. Test results show that joint specimens bonded by epoxy have about 10% more shear resistance than specimens with strengthened shear key by steel plates, but in the case of specimens with strengthened shear key there is smaller resistance deviation than specimens bonded by epoxy. In comparison with resistances estimated by empirical and design equations, the deck joint can be safely designed. But because the existed shear resistance of deck joint is underestimated by the ACI-318, application of the LRFD design equation could be more reasonable.

Design recommendations for interface shear transfer in fib Model Code 2010

AbstractInterface shear transfer between differently aged concretes is a topic that crops up frequently and in different situations in structural design. In the fib Model Code for Concrete Structures 2010 the fundamental basics of concrete‐to‐concrete load transfer are given in section 6.3 and the corresponding design rules in 7.3.3.6. The different potential mechanisms contributing to the shear resistance along the interface, i.e. adhesive bond, aggregate interlock, friction and dowel action, are thus combined and their relationship taken into account by interaction factors. This article summarizes the most important results from past and ongoing studies and presents the background to the theory forming the design basis of fib Model Code 2010, the “extended shear friction theory” (ESF).

Mechanics-Based Hinge Analysis for Reinforced Concrete Columns

AbstractThe lateral deformation behavior of a RC column is particularly important because it not only magnifies the moment but also affects the ability of the column—and, subsequently, the frame—to sway and absorb energy at all stages of loading. The lateral deformation is affected by disturbed regions, such as tensile cracks or compression wedges, which are often simulated with the help of hinges whose properties are derived empirically. Being empirical, these hinges can only be used within the bounds of the tests from which they were derived, and in this respect are of limited use. In this paper, a mechanics-based hinge is developed that can be used at all stages of loading (that is, at serviceability through to ultimate) and also during failure. The mechanics-based model is based on the principle of plane sections remaining plane, shear-friction theory that quantifies the behavior of RC across sliding planes, and partial-interaction theory that allows for slip between the reinforcement and the encasing...