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Due to design using older codes, material degradation and increased traffic loads, numerous reinforced concrete bridge members, such as beams and slabs, have insufficient shear capacity and need shear strengthening. An efficient shear strengthening technique consists of adding drilled-in vertical reinforcing bars within the existing concrete member and to bond these bars to the concrete with high-strength epoxy adhesive. However, the shear design method prescribed by the Canadian Highway Bridge Design Code for members with stirrups may overestimate the shear capacity of shear strengthened members with epoxy-bonded bars. This paper presents the effect of bonded shear reinforcement on shear resistance mechanisms and summarizes a proposed shear design method developed for reinforced concrete members with epoxy-bonded shear reinforcement.

Alkali-silica reaction (ASR) is one of the most damaging mechanisms affecting concrete structures worldwide. ASR effects on the durability and serviceability of damaged concrete are widely known and fairly well understood. However, the structural implications are still unclear, and a number of contradictory data are found in the literature, especially regarding shear behavior. The influence of ASR distressed reinforced concrete on aggregate interlock is presented in this paper. Push-off specimens having different transverse reinforcement ratios were fabricated with ASR reactive coarse aggregates. The specimens were monitored over time and displayed different levels of expansion. Results indicated that ASR-induced expansion and damage were affected by the transverse reinforcement ratio. However, little to no aggregate interlock reduction was observed on ASR-affected specimens up to moderate expansion levels (about 0.12%). It was found that there were two controlling and competing mechanisms that affected aggregate interlock for ASR-affected specimens: the beneficial effects of chemical prestressing and the detrimental ASR-induced damage.

A large proportion of concrete bridges in North America are reaching the end of their service life. An important factor that accelerates deterioration is the amount of salts used during winter months. The chloride ions from the salt enter the concrete and destroy the passive-oxide layer that protects the reinforcing steel from corrosion. The TransChlor® software is used to simulate the time history of chloride ion ingress into a typical concrete bridge. A climate model is used to simulate the exposure of the structure to winter conditions. A probabilistic method is used to propagate the uncertainty on material properties in the model and to obtain the distribution of chloride ion concentrations. A procedure for updating the distribution is proposed using data from core samples at two depths (25/50 mm) and for the two types of exposure (splash/direct). The procedure is shown to be very efficient in reducing bias and variance from model predictions.

Post-installed epoxy-bonded shear reinforcement is a promising technique to increase shear capacity of reinforced concrete (RC) structures. However, the behavior of epoxy-bonded bars largely affects the shear strengthening efficiency. To better predict the behavior of epoxy-bonded bars, a bond model is developed in this paper. This model appears to adequately predict the behavior of epoxy-bonded bars observed in experimental pullout tests and beam loading tests. Based on numerical results, a simplified model is proposed to predict the epoxy-bonded bars’ stress according to the crack width. It appears that the behavior of long embedded bars is similar to stirrups in terms of crack width and bar stress. However, a large diagonal crack is required to reach the bar yielding strength when the bar embedment length is below a transition length, which differs from stirrups. Embedment length below the epoxy-bonded bar development length leads to pullout failure and bar capacity lower than the bar yielding strength.

In order to investigate the effect of the serviceshear load at the time of strengthening a thick slab using bonded transverse reinforcing bars, an experimental study has been carried out.Five (5)beams representing slices of a thick slab were tested to induce different shear load levels in the beamsat the time of strengthening then loaded up to shear failure. Tests were conducted on a slab without shear reinforcement and the others on slabs strengthened at two different load levels at the time of strengthening. The added shear reinforcement was distributed according to two different longitudinal spacings. The results show that,even in the presence of usual service loads, the shear strengthening of thick slabs with bondedbars offers a considerable increase in shear capacity compared to a thick slab without shear reinforcement.

Installation of drilled-in epoxy-bonded reinforcing bars is generally an effective strengthening method to increase the flexural and shear capacities of deficient concrete structures. However, most of the available studies characterizing the bond behavior of epoxy bonded bars in concrete have been carried out on sound concrete elements—that is, without any pathological material damage. This raises the question of bond capacities in existing damaged elements. This study investigates the influence of alkali-silica reaction (ASR) on the capacity of post-installed reinforcing bars. ASR is a deleterious mechanism that causes expansion and cracking in the affected concrete elements. Pullout tests on post-installed reinforcing bars having embedded lengths of 2db, 4db, and 5db with 15M reinforcing bars (db = 15.9 mm [0.626 in.]) have demonstrated a drop-in bond strength when concrete is affected by ASR. In addition, the study revealed that the progression of concrete expansion due to ASR may lead to some confinement of the post-installed reinforcing bar and possibly increases the bond strength.

Efficient shear strengthening techniques for thick concrete slabs were studied at Université Laval over the last decade. The strengthening techniques consist of adding drilled-in vertical reinforcing bars and to anchor the bars with bolted plates or expansion anchorage at the bar extremities (i.e. the bars are unbonded to the concrete), or to bond the bars to the concrete with high strength epoxy adhesive (no mechanical anchorage). For concrete members with unbonded bars, experimental loading tests and numerical analysis showed that large diagonal shear cracks are required to activate the shear reinforcement and therefore, the shear behaviour of the members is largely influenced by the stiffness of the strengthening. For specimens with epoxy bonded bars, results showed that the development length of the bars is determined by the locations of the shear cracks and thus, bars may debond before reaching their yielding strength. The efficiency of the shear strengthening techniques is therefore largely influenced by the bars spacing and the stiffness of unbonded shear reinforcement.

Many concrete bridges may be associated to a simple thick slabs structural system. With the increase in traffic loads and material degradation, some of these structures need to be strengthened in shear. The goal of this research is to study the behaviour of slabs strengthened with post-installed shear reinforcement and to provide an analytical method of design. The studied reinforcement methods consist in installing rebars into pre-drilled holes in the slab with different anchor systems. The first experimental results showed that shear-strengthened slabs can have failure loads 46% higher than an unstrengthened slab but 29% lower than the Canadian code prediction for conventional stirrups. The VecTor2 finite element analysis tool will be used to study the parameters influencing the slabs behaviour. The first experimental results and associated numerical models outcomes will be presented.

Le système structural de plusieurs ponts peut être associé à dalle épaisse en béton armé. Avec l’augmentation des charges routières ainsi que la dégradation des matériaux, certains de ces ouvrages doivent maintenant être renforcés en cisaillement. Le but de ce projet est d’étudier le comportement des dalles épaisses renforcées par divers types de renforcements et de déterminer une méthode de calcul de ce renforcement. La méthode de renforcement étudiée consiste à percer une ouverture verticale dans la dalle, y insérer une barre d’armature et la retenir par différentes méthodes d’ancrage. Les premiers résultats expérimentaux montrent que le renforcement d’une dalle peut accroître sa résistance en cisaillement de 49%. L’outil d’analyse par éléments finis Vector2 va permettre d’étudier les principaux paramètres influençant le comportement des dalles. Les premiers résultats expérimentaux ainsi que les modèles numériques y étant liés sont présentés.

One commonly used method to increase the shear capacity of existing concrete structures consists of adding vertical steel bars anchored to the structure by means of mechanical anchorages, such as expansion torque controlled anchorages or steel anchorage plates. If the drilled holes are not filled with adhesive then the bars are unbonded along their length. In order to study the behaviour of concrete members with unbonded transverse reinforcement, thick concrete beams (width of 610 mm and height of 750 mm) were loaded until shear failure. It has been observed that their shear capacity is closely related to the shear cracking behaviour. At shear cracking, the propagation of one large diagonal crack is required to activate the vertical unbonded bars, thereby reducing the aggregate interlock shear capacity along the cracks. Beams containing at least minimum amounts of conventional stirrups experience several diagonal cracks at shear failure, whereas a beam with unbonded bars tends to have one dominant crack and can therefore experience the size effect in shear. A finite element (FE) model was also used to study the parameters influencing the behaviour of concrete members with unbonded transverse bars. The finite element results show very good agreement with the experimental results.

Plusieurs phénomènes de dégradations des ouvrages en béton armé sont la cause de déficiences structurales. Les ponts de types dalle épaisse sans armatures de cisaillement sont particulièrement sensibles à la dégradation du béton car ce matériau est le seul pouvant résister aux efforts de cisaillement. Cette recherche porte donc sur l’effet de l’endommagement du béton sur la résistance au cisaillement des dalles épaisses existantes et sur les moyens de les renforcer en cisaillement. Pour y arriver, trois axes de recherche sont étudiés : les effets de l’endommagement et de la réaction alcali-silice sur la résistance au cisaillement du béton, l’effet de l’endommagement du béton sur leur ancrage et les méthodes de postrenforcement. Le type de postrenforcement étudié consiste à installer des barres verticales à l’intérieur d’ouvertures percées dans la dalle et d’y ancrer des renforcements selon différentes méthodes : ancrage époxydique, ancrage mécanique interne ou externe.

In order to study means of improving the behaviour of thick slabs without shear reinforcement a series of large-scale beams representing thick slabs was constructed and tested. Companion specimens were strengthened using drilled-in reinforcing bars to study the effectiveness of this repair technique. The behaviour of these beams, before and after strengthening, is compared. An additional experimental program using pull-out specimens enabled a study of the bond characteristics of drilled-in reinforcement having different embedment lengths. An analytical model to predict the bond-stress versus slip relationship enabled the development of a method for predicting the influence of the added shear reinforcement in improving the shear strength. These predictions are compared with the experimental results and provide a practical means of assessing the influence of post-installed shear reinforcement.

In order to evaluate the performance of drilled-in bonded shear reinforcement, two series of largescale slabs were tested before and after shear strengthening. Experimental results indicate that the 2006 Canadian Standard and the 2010 fib Model Code provisions overestimate the shear strength of such strengthened slabs by about 29% if the drilled-in shear reinforcement is assumed to be totally effective. The main goal of this research is to develop a method for predicting the shear strength of slabs with bonded shear reinforcement. A non-linear finite element model using the program VecTor2 was used to study parameters influencing the slab behaviour up to failure. Results showed that both the behaviour and ultimate strength of slabs are predicted well by the model while taking account of a stress-slip relationship for the bonded reinforcing bars. Moreover, the experimental observations during the loading corroborate the cracking pattern predictions.

This paper presents different strengthening techniques to improve the shear capacity of existing thick concrete slab structures that were constructed without shear reinforcement. Reinforcing bars are installed into vertical drilled holes and anchored with epoxy adhesive to increase the shear capacity. Experiments on retrofitted beams, representing slab strips, showed that all of the strengthening techniques investigated resulted in increased shear capacities. The shear failure mechanisms of the strengthened beams showed that, as expected, current evaluation methods for elements with conventional, well-anchored stirrups can lead to an overestimation of the shear capacities. The efficiency of the strengthening techniques is strongly influenced by the performance of the end anchorage of the drilled-in bars. The effectiveness of the epoxy-bonded bars is a function of their embedded length and they can, in some cases, debond before they reach their yield strength. By using the maximum bar spacing required by the Canadian design code for bridges or the AASHTO-LRFD design specifications, bonded shear-reinforcing bars may debond and offer poor performance. A maximum transverse reinforcement spacing criterion is therefore suggested for the added bonded bars.

Installation of drilled-in epoxy bonded reinforcing barsis generally an effective strengthening method for deficient concretestructures. However, this method of rehabilitation has largely been studied and tested on sound concrete elements, i.e. without any pathological damage, which raisesthe question of bond capabilities inexisting damaged elements. This investigation studies the influence of alkali-silica reaction (ASR) onthe capacity of epoxy bonded anchors. ASR, which is very common in eastern Canada, results from the chemical reaction between the alkali hydroxides in the concrete’s pore solution and some siliceous mineral phases inthe aggregates. Pull-out tests on epoxy bonded anchors havingembedded lengths offourtimes the bar diameter(Ø= 16 mm)have demonstrated a drop in bond strength when concrete is affected by ASR. In addition, the study revealed that the progression of concrete expansion due to ASR, leads to a confinement of the epoxy bonded anchor and increases the bond strength. These conclusions are therefore considered for the development of a model for the design of epoxy bonded anchors in existing concrete infrastructure affected by ASR.

This paper presents different strengthening techniques to improve the shear capacity of existing thick concrete slab structures that were constructed without shear reinforcement. Reinforcing bars are installed into vertical drilled holes and anchored with epoxy adhesive to increase the shear capacity. Experiments on retrofitted beams, representing slab strips, showed that all of the strengthening techniques investigated resulted in increased shear capacities. The shear failure mechanisms of the strengthened beams showed that, as expected, current evaluation methods for elements with conventional, well-anchored stirrups can lead to an overestimation of the shear capacities. The efficiency of the strengthening techniques is strongly influenced by the performance of the end anchorage of the drilled-in bars. The effectiveness of the epoxy-bonded bars is a function of their embedded length and they can, in some cases, debond before they reach their yield strength. By using the maximum bar spacing required by the Canadian design code for bridges or the AASHTO-LRFD design specifications, bonded shear-reinforcing bars may debond and offer poor performance. A maximum transverse reinforcement spacing criterion is therefore suggested for the added bonded bars.

One commonly used method to increase the shear capacity of existing concrete structures consists of adding vertical steel bars anchored to the structure by means of mechanical anchorages, such as expansion torque controlled anchorages or steel anchorage plates. If the drilled holes are not filled with adhesive then the bars are unbonded along their length. In order to study the behaviour of concrete members with unbonded transverse reinforcement, thick concrete beams (width of 610 mm and height of 750 mm) were loaded until shear failure. It has been observed that their shear capacity is closely related to the shear cracking behaviour. At shear cracking, the propagation of one large diagonal crack is required to activate the vertical unbonded bars, thereby reducing the aggregate interlock shear capacity along the cracks. Beams containing at least minimum amounts of conventional stirrups experience several diagonal cracks at shear failure, whereas a beam with unbonded bars tends to have one dominant crack and can therefore experience the size effect in shear. A finite element (FE) model was also used to study the parameters influencing the behaviour of concrete members with unbonded transverse bars. The finite element results show very good agreement with the experimental results.

A large proportion of concrete bridges in North America are reaching the end of their service life. An important factor that accelerates deterioration is the amount of salts used during winter months. The chloride ions from the salt enter the concrete and destroy the passiveoxide layer that protects the reinforcing steel from corrosion. The TransChlor® software is used to simulate the time history of chloride ion ingress into a typical concrete bridge. A climate model is used to simulate the exposure of the structure to winter conditions. A probabilistic method is used to propagate the uncertainty on material properties in the model and to obtain the distribution of chloride ion concentrations. A procedure for updating the distribution is proposed using data from core samples at two depths (25/50 mm) and for the two types of exposure (splash/direct). The procedure is shown to be very efficient in reducing bias and variance from model predictions.

L’installation d’ancrages époxydiques à l’aide d’armatures conventionnelles constitue une méthode généralement efficace de renforcement d’infrastructures en béton armé. Toutefois, cette méthode de réhabilitation a été étudiée, puis testée sur des éléments de béton sain, c’est-à-dire sans endommagement pathologique. Le projet de recherche étudie donc l’effet de l’endommagement dû au développement de la réaction alcalis-silice (RAS) sur la capacité des ancrages époxydiques. La RAS, très présente à l’est du Canada, résulte de la réaction chimique entre les hydroxydes alcalins à l’intérieur de la solution interstitielle du béton et certaines phases minérales siliceuses qui composent les granulats. Des essais d’arrachement réalisés sur des ancrages époxydiques de longueur 5ø(~80 mm) ont montré une diminution de leur résistance en adhérence avec l’augmentation de l’endommagement causé par la RAS. Cette perte de capacité doit donc être considérée lors du calcul d’un renforcement de structures atteintes de RAS à l’aide de ce type d’ancrage adhésif.

In order to study means of improving the behaviour of thick slabs without shear reinforcement a series of large-scale beams representing thick slabs was constructed and tested. Companion specimens were strengthened using drilled-in reinforcing bars to study the effectiveness of this repair technique. The behaviour of these beams, before and after strengthening, is compared. An additional experimental program using pull-out specimens enabled a study of the bond characteristics of drilled-in reinforcement having different embedment lengths. An analytical model to predict the bond-stress versus slip relationship enabled the development of a method for predicting the influence of the added shear reinforcement in improving the shear strength. These predictions are compared with the experimental results and provide a practical means of assessing the influence of post-installed shear reinforcement.

In order to evaluate the performance of drilled-in bonded shear reinforcement, two series of largescale slabs were tested before and after shear strengthening. Experimental results indicate that the 2006 Canadian Standard and the 2010 fib Model Code provisions overestimate the shear strength of such strengthened slabs by about 29% if the drilled-in shear reinforcement is assumed to be totally effective. The main goal of this research is to develop a method for predicting the shear strength of slabs with bonded shear reinforcement. A non-linear finite element model using the program VecTor2 was used to study parameters influencing the slab behaviour up to failure. Results showed that both the behaviour and ultimate strength of slabs are predicted well by the model while taking account of a stress-slip relationship for the bonded reinforcing bars. Moreover, the experimental observations during the loading corroborate the cracking pattern predictions.

Plusieurs phénomènes de dégradations des ouvrages en béton armé sont la cause de déficiences structurales. Les ponts de types dalle épaisse sans armatures de cisaillement sont particulièrement sensibles à la dégradation du béton car ce matériau est le seul pouvant résister aux efforts de cisaillement. Cette recherche porte donc sur l’effet de l’endommagement du béton sur la résistance au cisaillement des dalles épaisses existantes et sur les moyens de les renforcer en cisaillement. Pour y arriver, trois axes de recherche sont étudiés : les effets de l’endommagement et de la réaction alcali-silice sur la résistance au cisaillement du béton, l’effet de l’endommagement du béton sur leur ancrage et les méthodes de postrenforcement. Le type de postrenforcement étudié consiste à installer des barres verticales à l’intérieur d’ouvertures percées dans la dalle et d’y ancrer des renforcements selon différentes méthodes : ancrage époxydique, ancrage mécanique interne ou externe.

Many concrete bridges may be associated to a simple thick slabs structural system. With the increase in traffic loads and material degradation, some of these structures need to be strengthened in shear. The goal of this research is to study the behaviour of slabs strengthened with post-installed shear reinforcement and to provide an analytical method of design. The studied reinforcement methods consist in installing rebars into pre-drilled holes in the slab with different anchor systems. The first experimental results showed that shear-strengthened slabs can have failure loads 46% higher than an unstrengthened slab but 29% lower than the Canadian code prediction for conventional stirrups. The VecTor2 finite element analysis tool will be used to study the parameters influencing the slabs behaviour. The first experimental results and associated numerical models outcomes will be presented.

Le système structural de plusieurs ponts peut être associé à dalle épaisse en béton armé. Avec l’augmentation des charges routières ainsi que la dégradation des matériaux, certains de ces ouvrages doivent maintenant être renforcés en cisaillement. Le but de ce projet est d’étudier le comportement des dalles épaisses renforcées par divers types de renforcements et de déterminer une méthode de calcul de ce renforcement. La méthode de renforcement étudiée consiste à percer une ouverture verticale dans la dalle, y insérer une barre d’armature et la retenir par différentes méthodes d’ancrage. Les premiers résultats expérimentaux montrent que le renforcement d’une dalle peut accroître sa résistance en cisaillement de 49%. L’outil d’analyse par éléments finis Vector2 va permettre d’étudier les principaux paramètres influençant le comportement des dalles. Les premiers résultats expérimentaux ainsi que les modèles numériques y étant liés sont présentés.