Dowel Effect Research Articles

Deformation and Plasticity of Reinforced Concrete

Statement of the problem.Development of the model of plasticity of reinforced concrete structures is based on the intensity of the "stress-strain" relation to project tensors using transitions, as well as the coefficients of the steps of forces and axes (principal angle and strain-strain, total shear strain, etc.). Results. The dependences of plasticity modulus of concrete, transverse coefficient have been obtained. Complex functions of generalized hypotheses of deplanation of linear and angular deformations and jumps for crack formation breakaway and stiffness are constructed. It includes force flows, i.e., blocks of compressed and tensile concrete for isotropic medium (the first object), "main cracks" from fracture mechanics, functional and two-cone element for the deformation effect of reinforced concrete. The resistance of the tensile concrete is transferred to the working reinforcement using the total average longitudinal and transverse forces for the transversal-isotropic environment, including the average modulus of reinforcement and the reduced tensile concrete coefficient of the second limit state group. The special dowel effect is derived from the second level model of structural mechanics for a rebar with two pinched ends, as well as crack opening (a development of the Thomas –– author hypothesis), crack-track bank shear, and buckling. The main vector of forces in the reinforcement is characterized by two values of longitudinal and transverse displacements and the width of opening and shear of the crack-track (the third object). Conclusions. The energetic theory on the surface of the sphere and the determination of the integral of the mean square value of the tangential stresses of plasticity theory allowed to develop an alternative to the ge-neral model in the form of a paraboloid by summing the volume sectors, radius-levels from the matrix of sliding planes (including octahedral and pure shear) in concrete medium from microcracks to macrocracks.

Dowel action of textile CFRP shear reinforcement in carbon reinforced concrete

Composite structures with textile CFRP (carbon fibre reinforced polymer) reinforcement are characterised by high compressive and tensile strength and have great potential for use in thin-walled structures such as shell structures or girder webs. However, the stress transfer mechanisms activated along cracks of carbon reinforced concrete (CRC) membranes have not been sufficiently investigated yet. Especially the potential of CFRP yarns to transfer shear across sliding crack surfaces has not been thoroughly understood.For steel reinforced concrete elements, dowel action has been studied for several decades and numerous constitutive laws for the shear contribution of dowel action have been developed. In contrast, the sensitivity to transverse pressure of CFRP reinforcement is expected to have a significant influence on the activation of dowel action in cracked CRC. Neither the damage and fracture of impregnated textiles due to transverse compression nor the shear-induced delamination of reinforcement in the vicinity of cracks have been investigated in detail. Therefore, suitable constitutive laws to describe the dowel effect of CFRP reinforcement are not available.This paper presents dowel tests with textile CFRP shear reinforcement and highlights the phenomenology of dowel behaviour in carbon reinforced concrete as well as the main factors influencing the dowel behaviour.

Numerical Investigation of the Effect of Longitudinal Fiberglass Dowels on Tunnel Face Support in Layered Soils

Tunnel face extrusion rigidity is an important factor for solving stress–strain problems in loose ground conditions. In previous studies, the effect of horizontal and vertical soil layering on tunnel excavation face stability in the presence of longitudinal fiberglass dowels has not been studied. Therefore, in this study, the effect of fiberglass dowels on the stability of the tunnel face in layered soil has been investigated. In this matter, the best dowel arrangement for minimizing the excavation face extrusion in the case of two-layer soil (horizontal or vertical) has been focused on. For this purpose, firstly, a 3D numerical model was validated based on field data provided previously, and then a 3D numerical tunnel was developed in FLAC3D, adopting the Mohr–Coulomb failure criterion. In continuation, the effect of tunnel diameter, initial pressure ranging from 0.5 to 1.5 MPa, and different placement angles of fiberglass dowels ranging from 0 to 9 degrees, with respect to the tunnel longitudinal axes on the tunnel face extrusion, have been investigated. In the case of horizontal layering, the results showed that the maximum extrusion rate is significantly increased where the elasticity modulus of the soil is reduced. In addition, comparing the maximum extrusion in vertical and horizontal layering, it was found that its value in the horizontal mode is much higher than in the vertical. Additionally, the extrusion of the tunnel face has changed significantly due to an alteration in the initial stress. Finally, it was discovered that tunnel face extrusion is not significantly affected by altering the angle of the fiberglass dowels.

A Study on the Distribution of Shear Forces Between Resisting Mechanisms in an RC Element Without Stirrups

This paper explores how the shear force distributes itself among the three main shear resistance mechanisms: shear resistance of the uncracked compressed chord, aggregate interlock, and dowel effect. Today’s dominating shear models, the critical crack theory (Muttoni et al. [1]) and the compression field theory (Collins et al. [2]) maintain that the main shear-resisting mechanism is aggregate interlock, while more recent studies (Marí et al. [3]), maintain that the main resistance mechanism is the shear resistance on the uncracked compression chord.
 In this paper FEM modelling is used to study a test carried out at the Universidad Politécnica de Madrid (UPM) to try to assign the shear force to the different shear mechanisms for different loading steps and elucidate what finally causes the failure of the structure. The results show that as load is increased the relative part of the shear force taken by the uncracked compressed chord increases until finally shear failure is reached when the principal tensile stress in the area located close to the load but towards the support reaches the tensile resistance of concrete, generating a crack that precipitates the failure of the beam.

Discontinuous bifurcation of FRCC with zero-thickness interface modeling

In this work, firstly a fracture-based interface constitutive theory, aimed at simulating the cracking mechanisms of Fiber Reinforced Cementitious Composites (FRCCs), is presented. The discontinuous formulation assumes a hyperbolic maximum strength criterion in terms of normal and shear joint stresses. The latter are evaluated on each crack front to simulate the failure behavior of plain and FRCC systems. A non-associated plastic flow rule, in conjunction with a post-cracking softening law, is defined to complete the modeling approach. On the other hand, the use of the most-classical Mixture Theory is followed for taking into account the actions of fibers in concrete matrix. The bridging mechanisms between fibers and active cracks are defined in terms of fiber-to-concrete bond–slip rule and dowel effects. Secondly, a normalized Cracking Indicator (CI) for discrete crack is proposed in the spirit of Hill’s indicator for loss of stability of inelastic continua, to effectively evaluate the most critical direction for further loading in terms of the resulting energy release and crack opening, while accounting for the fiber direction and content. After presenting the constitutive theory and, particularly, the novel concept of the CI, numerical analyses at constitutive level are performed to evaluate the evolution of the fracture energy, post-peak strength, and critical cracking directions under variable fiber contents. Different load scenarios are evaluated, and the numerical predictions are compared with experimental data.

A New Bond-Slip Model of Hybrid Bonded FRP-to-Concrete Joints

The dowel effect in hybrid bonded fiber reinforced plastic (HB-FRP) to concrete joints is difficult to quantify and make the anchoring joint instability. A new HB-FRP joint was built, which eliminates bonding between steel and FRP plates. Based on an empirical model of external bonding FRP (EB-FRP) to concrete joints and the new model of slip at debonding, the new unified bond-slip model of the HB-FRP joints is proposed. The parameters that affect the bond-slip model are analyzed. Pull-off tests are conducted for eight specimens with different numbers of mechanical fasteners, which has verified the proposed model. The load-slip relationship at the loaded end of the FRP plate was well predicted by the partial interaction numerical calculation and further verify the theoretical model.

Investigação dos mecanismos de resistência ao cisalhamento direto em peças de concreto com fibras de aço e PVA

Some mechanical properties of concrete can be improved with the addition of other materials, such as the incorporation of fibers, which results in increased tensile strength and toughness, presenting post-cracking behavior that significantly contributes to the transfer of shear stresses, especially in planes that are propitious to the formation of cracks. To evaluate the effects of the addition of fibers to concrete, in terms of the ultimate shear strength and the mechanisms that constitute it, such as cohesion between the component materials, aggregate interlock, friction and dowel action, an experimental program was carried out. Two mixtures were produced from a conventional concrete mix, with the addition of 0.5% steel fibers and 0.2% synthetic polyvinyl alcohol, PVA fibers. Specimens for direct shear testing, push-off type, were molded, with and without transverse shear reinforcement, and a steel-concrete bond condition was set as a variable. The results showed that the addition of steel fibers results in a significant increase in the shear strength of concrete, na effect not observed with PVA fibers. The aggregate interlock and cohesion mechanisms were responsible for approximately 70% of the ultimate shear strength in all the concrete tested, while the rest was attributed to friction and the dowel effect.

Experimental analysis of steel fiber reinforced concrete beams in shear

Abstract Some normative recommendations are conservative in relation to the shear strength of reinforced concrete beams, not directly considering the longitudinal reinforcement rate. An experimental program containing 8 beams of (100 x 250) mm2 and a length of 1,200 mm was carried out. The concrete compression strength was 20 MPa with and without 1.00% of steel fiber addition, without stirrups and varying the longitudinal reinforcement ratio. Comparisons between experimental failure loads and main design codes estimates were assessed. The results showed that the increase of the longitudinal reinforcement ratio from 0.87% to 2.14% in beams without steel fiber led to an improvement of 59% in shear strength caused by the dowel effect, while the corresponding improvement was of only 22% in fibered concrete beams. A maximum gain of 109% in shear strength was observed with the addition of 1% of steel fibers comparing beams with the same longitudinal reinforcement ratio (1.2%). A significant amount of shear strength was provided by the inclusion of the steel fibers and allowed controlling the propagation of cracks by the effect of stress transfer bridges, transforming the brittle shear mechanism into a ductile flexural one. From this, it is clear the shear benefit of the steel fiber addition when associated to the longitudinal reinforcement and optimal values for this relationship would improve results.

Numerical investigation for strengthened RC footings with square concrete jacketing

Strengthening of existing isolated footings using concrete jacketing is a traditional method to increase the load-carrying capacity and to enhance the performance of isolated footings. This paper presents a parametric study and a numerical validation for full-scale square footings strengthened with concrete jacketing, using either dowels and bonding agent or bonding agent only, to connect the existing and new concrete surfaces. A nonlinear finite element program “ABAQUS” was used for the numerical validation and the parametric investigation for various parameter's effect on the load-carrying capacity and contact stress redistribution underneath the strengthened footings. The parameters used in the parametric analysis include the ratio of the concrete jacket depth to the concrete footing depth, concrete compressive strength, spacing between dowels, and the ratio of the concrete jacket width to the concrete footing width. The effect of dowels on load carrying capacity of footings strengthened using a full concrete jacket is insignificant for jacket width smaller than the footing width. In footing strengthened using a full concrete jacket, the load carrying capacity increases by 9% compared to the non-strengthened footing.

Experimental study on bonding behaviour of interface between UHPC and concrete substrate

The aim of this study is to investigate the effect of substrate surface roughness, fibre type, and water-to-binder ratio on the bond behaviour between ultra-high-performance concrete (UHPC) and normal-strength concrete (NSC). In addition, the suitability of different methods for evaluating the surface roughness using a sand-filling method, the height, number, and area of exposed coarse aggregates, and capillary absorption was verified. The results indicated that surface roughness was the most critical factor, followed by the water-to-binder ratio, and finally, the steel fibre type on influencing the bond strength. These methods for evaluating the surface roughness showed good consistency. The bond strength enhancement was mainly attributed to the compact transition zone of UHPC–NSC and the dowel effect of the steel fibres on the substrate surface recess. Based on the experimental bond strength values, an UHPC–NSC shear strength equation was derived, considering the repair surface roughness, and other research data verified the applicability of the proposed equation. Moreover, the NSC area fraction on the UHPC overlay side and the damage index of the composite specimen after debonding had a good linear relationship with the interface performance.

Random Forest versus Support Vector Machine Models’ Applicability for Predicting Beam Shear Strength

The shear and bending are the actions that are experienced in the beam owing to the fact that the beam is a flexural member due to the load in the transverse direction to their longitudinal axis. The shear strength (Vs) computation of reinforced concrete (RC) beams has been a major topic in the field of structural engineering. There have been several methodologies introduced for the Vs prediction; however, the modeling accuracy is relatively low owing to the complex characteristic of the resistance mechanism involving dowel effect of longitudinal reinforcement, concrete in the compression zone, contribution of the stirrups if existed, and the aggregate interlock. Hence, the current research proposed a new soft computing model called random forest (RF) to predict Vs. Experimental datasets were collected from the open-source literature including the related geometric properties and concrete characteristics of beam specimens. Nine input combinations were constructed based on the statistical correlation to be supplied for the proposed predictive model. The prediction accuracy of the RF model was validated against the Support Vector Machine (SVM), and several other empirical formulations have been adopted in the literature. The proposed RF model revealed better prediction accuracy in addition the model structure emphasis in the incorporation of seven predictors by excluding (beam flange thickness and coefficient). In the quantitative term, the minimal root mean square error value was attained (RMSE = 89.68 kN).

Investigation on structural performance of perfobond strip connector group in steel-concrete joints

The use of an innovative type of perfobond rib (PBL) shear connector in steel–concrete joints of hybrid girder bridges has gained wide popularity among bridge engineers. For a PBL group with multi-row PBLs in tandem arrays, comprehensive interactions exist among the connectors. However, the current design approaches assume that the force transferred by each row of PBL is uniform, resulting in an overestimated shear resistance of the connector group. The main objective of this paper is to introduce a mathematical approach, which accounts for the bonding-friction effects (BF) at the perforated steel plate/concrete slab interfaces and the reinforced concrete dowel (RD) effects by the perfobond hole, to assess the ultimate resistance of PBL group under the RD fracture failure mode. In this study, six push-out specimens for different PBL groups, with varying connectors’ quantity, were evaluated experimentally to determine the key parameters for the proposed analytical model. The experimental results revealed the significant reduction in average resistance of single PBL in a connector group as connector number increased. The proposed approach is validated by an experimental database that includes push-out test results obtained from the previously published studies and afterwards converted to the design load level, which can be extensively applied to the PBL group using normal concrete and ultra-high performance concrete (UHPC). The proposed analytical approach provides an efficient tool for analyzing and designing of PBL group in steel–concrete joints of hybrid girder bridges.

Triplet Tests and Numerical Validations of Stone Masonry with Dowels Under Shear

Dowels are connected to two masonry units in the vertical direction for the continuity and integrity of walls. According to the national and international literature, studies investigating the effectiveness of dowels on masonry walls are rare. This paper presents a preliminary experimental study performed on tuff stone masonry specimens with dowels to assess the effects of dowels on the shear capacity of masonry walls. For this aim, 54 masonry specimens, nine being controls without dowels and 45 with different dowel diameters and axial load levels, were tested under triplet test procedures, according to TS EN 1052-3 regulations. Numerical validations were performed using the LUSAS finite element software package. The experimental results were compared with numerical simulations. The present study reveals that dowels significantly improve the shear capacity of masonry walls. Furthermore, recommendations regarding suitable dowel ratios are made.

Calibration of Concrete Damaged Plasticity Model parameters for shear walls

ABSTRACT Reinforced concrete structures are relatively complex to analyze, with nonlinear effects like cracking, crushing, steel yielding, aggregate interlock, dowel effect, concrete-rebar interaction and so on. The concrete damaged plasticity CDP model is a consolidated smeared-crack model which accounts for multiaxial behavior with good agreement to experimental results. One particular relevant application which benefits greatly from such feature is the shear wall, as shear stress significantly influences its overall behavior, therefore multiaxial constitutive models and three-dimensional finite elements usage consist in a fitting modeling approach. Reinforced concrete shear walls are structures especially useful for lateral force-resisting systems, as they provide ductility, stiffness and strength. Albeit CDP is widely applied, its parameters are not consensus in the literature, which represents a relevant research gap. The present work considers and compares CDP parameters from relevant literature, in order to calibrate those parameters for the case of reinforced concrete shear walls. To this purpose, four wall experiments related in the bibliography are modeled using solid finite elements for concrete and trusses for rebars using commercial package ABAQUS. All walls are flexure-controlled with aspect ratio greater than 2.0. By varying those parameters and comparing obtained force vs. displacement curves and interesting values attained, like yield lateral force and displacement, stiffness and maximum lateral force, it is settled a set of parameters with acceptable response focusing in the post-peak response based on the lower estimated error of displacement capacity. Those parameters agree reasonably with literature, although it is possible that obtained calibration is restricted to flexure controlled shear walls scope. It is possible that usage of trusses to represent reinforcement does not consider dowel effect, so a suggestion for future studies is to change trusses for elements with transverse stiffness, like beams or solids.

Bond strength between concrete substrate and repair mortar: Effect of fibre stiffness and substrate surface roughness

This study investigated the effects of fibre stiffness, substrate surface roughness, and surface angle on the bond strength between concrete substrate and repair mortar. The substrate surface was repeatedly treated with high-pressure water to obtain various roughness values. Steel and carbon fibres played the role of rigid and flexible fibres, respectively, in the repair mortar. The bond strength (including both adhesion and friction components) was evaluated via slant shear tests with various slant shear angles. Adhesion was examined using the Mohr–Coulomb approach to reflect pure bond behaviour. The results indicate that bond strength (σ0,av, fibre type 0) increased as the roughness increased; further, removing the floating pulp layer can improve adhesion. However, after removal and with increasing substrate surface roughness (fibre type 0), there was no significant change in adhesion. As the roughness increased, the number and length of exposed steel fibres increased. The steel fibres maintained their original shape in the mixture and significantly enhanced adhesion because of the dowel and second-order dowel effects. In contrast, carbon fibres were severely deformed in the mixture and showed decreased adhesion owing to pores existing at the interface. The synergy between steel and carbon fibres can enhance the ultimate load capacity of steel fibres under axial compression. This enhances the dowel effect, thereby improving adhesion.

Experimental Laboratory Testing on Behavior of Dowels in Concrete Pavements.

This paper describes the testing of effectiveness and behavior of dowels placed in transversal joints of concrete pavements, while focusing on dimensions and quality of commonly used materials. The analysis uses experimental tests in laboratory conditions which were performed independently in the Czech Republic and Slovak Republic. The comparison of quality as well as potential use of alternative materials of dowels is made with the use of developed tests focusing on main requirements, such as longitudinal displacement in cement concrete, resistance of coating to damage, and reduced potential to concrete damage. Furthermore, the paper describes and compares loading results of the relative concrete deformations around dowels by strain gauges that were analyzed. Results of deformations on beams with an inserted dowel and the findings that were observed during the measurement are presented.

Coupling model of jointed rock mass and rock bolt in offshore LPG underground storage

AbstractMost of the surrounding rocks of offshore liquefied petroleum gas (LPG) reservoirs occur in jointed rock mass. This paper is aimed at the reinforcement of the layered composite rock masses. First, the structural mechanical model of the elastic deformation and completely plastic deformation for the bolt was constructed. Then, the equations of axial force, shear force, and bending moment in the cross section of the bolt were obtained by the force‐method canonical equation. The shear‐slip resistance effect of the bolt was decomposed into the friction effect and the dowel effect. In addition, the quantitative relationship between shear resistance and the characteristic angles (anchoring angle, friction angle, dilatancy angle, and deflection angle) and the geometrical and physical parameters of the bolt were derived. Finally, the influence of each characteristic angle on the mechanical properties of the bolt was analyzed in details and the model was verified. The analysis results showed that the laterally constrained load of the rock stratum on the bolt can be characterized by a power function, but the optimal power should be no less than 10. The dominant position of either the friction effect or the dowel effect was changed with the matching of different characteristic angles. The increase of the friction angle and dilatancy angle of the joint surface of the rock is beneficial to improve the lateral shear resistance of the bolt. The effect of the deflection angle on the lateral shear resistance of the bolt was affected by the anchoring angle. The optimal anchoring angle of the bolt should be in the range of 50°‐60°. The results in this study have important theoretical significance to guide the offshore anchoring engineering of layered composite rock masses.

Numerical and experimental investigation on the shear resistance of functionally graded concrete (FGC) beams

Functionally graded concrete (FGC) is one of the most innovative materials combining two or more different concrete strength in building elements to optimise the construction cost. Studies focussing on the behaviour of graded concrete in flexural strength have been conducted by several researchers, whilst the research on the shear behaviour of FGC beam has not been initiated yet. Investigation on the shear behaviour of RC graded concrete beam is necessary due to the fabrication process could create a cold-joint that lower the load-carrying capacity of the element. Delamination possibly presents on the casted concrete layer during the loading and turns the beam behaviour more brittle in action. To further investigate these hypotheses, a laboratory testing and a numerical analysis are conducted in this research. Three pieces of RC beams with an identical dimension of 120 x 240 x 2200 mm are prepared with the concrete strength of 20 MPa, 30 MPa, and 20-30 MPa. The specimens are then tested using a four-point bending method in the age of 28 days. A set of strain gauge is mounted in stirrups surface to record the strain response on each incremental load. To validate the result, the specimens are also modelled in three-dimension using Abaqus. The results show that there is a significant difference in the stress-strain curve resulted from the experimental works and the model simulation. It is due to the limitation of programme to model the real interaction between the rebars and the concrete. In reality, the presence of aggregate interlocking, concrete contribution in withstanding compression stress, dowel effect improves the shear resistance of beams. Additionally, the interfacial failure did not present during the testing owing to the support of stirrups that confine the transition zone of concrete layers.

Anchor Design of a Ring Joint Based on Reliability in a Precast Shear Wall Structure

Precast buildings have been widely used owing to its outstanding features. As these buildings consist of a combination of various components, the mechanical properties of the connections play a critical role in the overall performance of the structure, particularly the vertical connections in shear wall members. A new connection called ring joint is proposed for precast buildings, and test pieces were designed to analyze the anchor performance. The damage phenomena and test data were observed and recorded. The displacement, force, and strain were analyzed, and the results indicated that the anchor length was a key factor and the connection was safe and reliable under reasonable design. Numerical analysis was conducted to explore the mechanical mechanism, and a bearing capacity model was proposed combining the bond and dowel effects simultaneously. Anchor length was determined based on reliability analysis under various conditions, and other suggestions were proposed. All these could guarantee the mechanical properties of the connection, as well as safety and reliability, and promote the popularization and application.

Assessment of a force–displacement based multiple-vertical-line element to simulate the non-linear axial–shear–flexure interaction behaviour of reinforced concrete walls

A comprehensive assessment of a new version of the macroscopic force–displacement based multiple-vertical-line element (SFI-MVLEM-FD), which can be used to simulate non-linear axial–shear–flexure interaction in RC walls, is presented. The element models the shear response taking into account all the basic physical mechanisms that transfer shear forces over cracks: (a) the dowel effect of vertical bars, (b) the axial resistance of horizontal/shear bars, and (c) the interlocking of aggregate particles in cracks. In order to provide a wide range of its use, and to enable the analysis of various types of buildings, the SFI-MVLEM-FD element was included in the local version of the OpenSees program system. The element was assessed with respect to already performed quasi-static cyclic experiments of various RC shear walls. In this paper, the results of numerical analyses of two representative rectangular walls, where the influence of shear on the overall response was of particularly significance, are presented and compared with those obtained in the experiments. In order to estimate the efficiency of the new element in more general cases, it was also assessed by means of a large-scale shake-table test of a typical non-planar lightly reinforced RC coupled wall. The test examples showed that the SFI-MVLEM-FD model can capture all the important mechanisms of the response, as well as being able to efficiently describe the axial–shear–flexure interaction in various types of RC walls: (a) rectangular and non-planar, (b) cantilever and coupled, and (c) subjected to different types of excitation, uni-axial or bi-axial. It was found that the model is capable of clearly identifying the three fundamental mechanisms, which contribute to shear resistance. This is one of the few models, which are able to describe the significant deterioration of the (shear) strength of RC walls that are near to collapse for different reasons: e.g. the buckling of their longitudinal bars, rupture of the horizontal reinforcement, and other significant degradation of different types of shear mechanism. This makes it suitable for the analysis of different types of RC walls, which are subjected to different levels of seismic excitations. It is even able to simulate the near collapse response influenced by very different collapse mechanisms.