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The practice of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) fabrics for structural strengthening increasingly shows evidence of effectiveness for the rehabilitation of existing structures. However, debonding of fiber- reinforced polymer (FRP), particularly in shear, is still a major premature failure mode when using FRP sheets to strengthen concrete structures. This paper presents the results of an experimental investigation of the performance of full-scale reinforced concrete (RC) beams strengthened in shear using EB-FRP U-wrapping (UW) and full wrapping (FW) with different fabric thicknesses. Full wrapping is used mostly on columns with all sides accessible and does not generally apply to beams. The main objectives of this study are to optimize FRP capacity and to evaluate the effect of confinement and the effectiveness of FRP using different strengthening configurations for RC beams, such as FW and UW. The results obtained in this study reveal that fully wrapped beams exhibit enhanced CFRP contribution to shear resistance compared to U-wrapped beams. In addition, the FW configuration eliminated the CFRP debonding failure mode and resulted in an increase in concrete strain. Key words: reinforced concrete (RC) beams, shear strengthening, CFRP fabrics, U-wrapping (UW), full wrapping (FW), codes and guidelines La pratique d'utilisation de materiel en polymere renforce de fibres de carbone (PRFC) pour le renforcement structurel montre de plus en plus l'efficacite de la remise en valeur des structures existantes. Cependant, le decollement de polymere renforce de fibres (PRF), en particulier en cisaillement, demeure un mode de defaillance premature majeur lorsqu'on utilise des feuilles de PRF pour renforcer les structures en beton. Cet article presente les resultats d'une etude experimentale sur la performance des poutres en beton arme (BA) renforcees en cisaillement a l'aide de PRF enveloppe en U (EU) et d'une enveloppe tout le tour (ETT) collees a l'exterieur (CE) avec differentes epaisseurs de materiel. L'ETT est utilisee principalement sur les colonnes avec tous les cotes accessibles et ne s'applique generalement pas aux poutres. Les principaux objectifs de cette etude sont d'optimiser la capacite des PRF et d'evaluer l'effet du confinement et l'efficacite des PRF en utilisant differentes configurations de renforcement pour les poutres de BA, comme l'ETT et l'EU. Les resultats obtenus dans le cadre de cette etude revelent que les poutres ETT presentent une contribution accrue du PRFC a la resistance au cisaillement comparativement aux poutres EU. De plus, la configuration ETT a elimine le mode de decollement du PRFC et a entraine une augmentation de la deformation du beton. [Traduit par la Redaction] Mots-cles : poutres en beton arme (BA), renforcement du cisaillement, materiel en polymere renforce de fibres de carbone (PRFC), enveloppe en U (EU), enveloppe tout le tour (ETT), codes et lignes directrices, Introduction U-wrapping fiber-reinforced polymer (FRP) configurations are a major shear-strengthening scheme in externally bonded (EB) FRP composites for restoring or upgrading the shear resistance of deteriorated reinforced concrete beams. However, [...]

In medium- to high-rise buildings, single shear walls (SSWs) are often used to resist lateral force due to wind and earthquakes. They are designed to dissipate seismic energy mainly through plastic hinge zones at the base. However, they often display large post-earthquake deformations that can give rise to many economic and safety concerns within buildings. Hence, the primary objective of this research study is to minimize residual deformations in existing SSWs located in the Western and Eastern seismic zones of Canada, thereby enhancing their resilience and self-centering capacity. To that end, four SSWs of 20 and 15 stories, located in Vancouver and Montreal, were meticulously designed and detailed per the latest Canadian standards and codes. The study assessed the impact of three innovative strengthening schemes on the seismic response of these SSWs through 2D nonlinear time history (NLTH) analysis. All three strengthening schemes involved the application of Externally Bonded Fiber Reinforced Polymer (EB-FRP) to the shear walls. Accordingly, a total of 208 NLTH analyses were conducted to assess the effectiveness of all strengthening configurations. The findings unveiled that the most efficient technique for reducing residual drift in SSWs involved applying three layers of vertical FRP sheets to the extreme edges of the wall, full FRP wrapping the walls, and full FRP wrapping of the plastic hinge zone. Nevertheless, it is noteworthy that implementing these strengthening schemes may lead to an increase in bending moment and base shear force demands within the walls. [ABSTRACT FROM AUTHOR]

Le present article traite du renforcement en cisaillement des poutres en beton arme (BA) a l'aide de materiaux composites a base de polymere renforce de fibres (PRF) colle en surface. La premiere partie de l'article fait le point sur l'evolution des codes et des normes nord-americains quant a la resistance a l'effort tranchant des poutres en BA renforcees a l'aide de composite en PRF colle en surface. La seconde partie presente une analyse exhaustive des parametres majeurs influencant la contribution du PRF a la resistance a l'effort tranchant. Elle presente egalement une comparaison des predictions des normes de conception en vigueur (ACI 440.2R 2017; CSA/S6 2019; CSA/S806 2012;fib-TG9.3 2001) avec les resultats des essais experimentaux rapportes dans la litterature. Il ressort de l'etude que des parametres majeurs influencant le comportement a l'effort tranchant n'ont fait l'objet, a ce jour, que de peu d'investigations. Parmi ces parametres, on peut citer en particulier : (i) la presence et le taux de l'acier transversal interne et (ii) le nombre de plis (couches) des PRF colles en surface. Cela peut expliquer les ecarts observes entre les resistances predites par les regles de calcul et celles obtenues a partir de tests. A la suite de ces observations, une base de donnees extraite a partir des etudes experimentales a ete elaboree dans le cadre de cette etude. Les resultats obtenus mettent en evidence et confirment l'existence d'une interaction entre le composite en PRF colle en surface et l'acier transversal interne quant a la reprise des efforts tranchants. Ils mettent egalement en evidence l'existence d'une rigidite optimale du PRF au-dela de laquelle le gain en resistance attribue au PRF colle en surface est plafonne. Mots-cles : beton arme (BA), cisaillement, materiaux composites, polymere renforce de fibres (PRF), renforcement, base de donnees, nombre de couches, acier transversal interne, normes de conception. This paper deals with the shear strengthening of reinforced concrete (RC) beams using externally bonded fiber- reinforced polymer (EB FRP) composite materials. The first part of the paper reviews the evolution of North American codes and standards for the shear resistance of RC beams strengthened with EB FRP composites, whereas the second part provides a comprehensive analysis of the major parameters influencing the contribution of FRP to shear resistance. It also presents a comparison of the predictions of current design standards (ACI 440.2R 2017; CSA/S6 2019; CSA/S806 2012;fib-TG9.3 2001) with the results 0f experimental tests reported in the literature. The study shows that major parameters influencing the shear behaviour have received little attention. These parameters include in particular: (i) the presence and ratio of internal transverse steel reinforcement and (ii) the number of EB FRP plies (layers). This may explain the observed discrepancies between the prediction models of existing equations for shear resistance and the results obtained from tests. Consequently, a database extracted from the experimental studies was developed as part of this study. The results obtained highlight and confirm the existence of an interaction between the EB FRP composites and the internal transverse steel reinforcement with regard to shear resistance of RC beams. They also show the existence of an optimal FRP stiffness beyond which there is no substantial gain in resistance attributed to the EB FRP. Key words: reinforced concrete (RC), shear, composite materials, fiber-reinforced polymer (FRP), strengthening, database, number of layers, internal transverse steel, design standards., 1. Introduction Les ouvrages en beton arme (BA) concus selon les regles en vigueur peuvent neanmoins presenter des deficiences durant leur duree de service. Ces deficiences peuvent etre dues a [...]

Masonry blocks are usually made of Portland cement and cured by steam. This study explores the possibility of making masonry blocks using steel slag as binder and carbon dioxide as curing activator. By carbonation activation of steel slag blocks, carbon dioxide can be permanently sequestered in steel slag as calcium carbonates, leading to stronger and more durable construction blocks. In this paper, carbonated steel slag paste was first evaluated by thermogravimetry, derivative thermogravimetry, X-ray diffraction, carbon uptake, strength development, and leaching tests. Based on the preliminary results, the full-size masonry blocks were fabricated using steel slag as the binder and granite as the aggregates. The physical properties and durability of full-size steel slag masonry blocks were then examined through their density, water absorption, moisture content, compressive strength, and fire resistance. An economic analysis was performed and a carbon dioxide utilization capacity was estimated. This study demonstrates that production of steel slag masonry blocks by carbonation is an economically feasible way to utilize carbon dioxide. Key words: C[O.sub.2] utilization, steel slag masonry blocks, carbonation, pilot study, sustainability, construction. Habituellement, les blocs de maconnerie sont faits de ciment Portland et durcis a la vapeur. Cette etude explore la possibility de fabriquer des blocs de maconnerie utilisant le laitier d'acier comme liant et le dioxyde de carbone comme activateur de durcissement. Grace a l'activation de la carbonatation de blocs de laitier d'acier, on peut sequestrer de maniere permanente le dioxyde de carbone dans le laitier d'acier comme carbonates de calcium, donnant lieu a des blocs de construction plus forts et plus durables. Dans cette etude, la pate de laitier d'acier carbonatee a d'abord ete evaluee au moyen de la thermogravimetrie, de la thermogravimetrie en derivation, de la diffraction des rayons X, d'essais d'absorption carbonique, de developpement de resistance et de lixiviation. Selon les resultats preliminaries, des blocs de maconnerie pleine grandeur ont ete fabriques utilisant du laitier d'acier comme liant et du granit comme granulat. Les proprietes physiques et la durabilite des blocs de maconnerie de laitier d'acier pleine grandeur ont alors ete examinees en fonction de leur densite, de leur absorption d'eau, de leur teneur en eau, de leur resistance a la compression et de leur resistance au feu. Une analyse economique a ete effectuee et la capacite d'utilisation de dioxyde de carbone a ete estimee. Cette etude demontre que la production de blocs de maconnerie de laitier d'acier par la carbonatation est une facon economiquement realisable d'utiliser le dioxyde de carbone. [Traduit par la Redaction] Mots-cles: utilisation du C[O.sub.2], blocs de macnnerie de laitier d'acier, carbonatation, etude pilote, durabilite, construction., Introduction Concrete masonry blocks are commonly used in construction for load-bearing walls and partition walls. Traditionally, concrete masonry blocks are made with Portland cement as the binder. In the United [...]

Coupled shear walls (CSWs) are structural elements used in reinforced concrete (RC) buildings to provide lateral stability and resistance against seismic and wind forces. When subjected to high levels of seismic loading, CSWs exhibit nonlinear deformation through cracking and crushing in concrete and yielding in reinforcements, thereby dissipating a significant amount of energy, leading to their permanent deformation. Externally bonded fiber-reinforced polymer (EB-FRP) sheets have proven to be effective in strengthening RC structures against various loading and environmental conditions. In addition, their high strength-to-weight ratio makes them an attractive solution as they can be easily applied without significantly increasing the structure's weight. This study investigates the effectiveness of using EB-FRP sheets to reduce residual displacement in CSWs during severe earthquake loadings. Two series of 15-story and 20-story CSWs in Western and Eastern Canadian seismic zones, which serve as representative models for medium- and high-rise structures, were evaluated through nonlinear time history analysis. The numerical simulation of all CSWs and strengthened elements was carried out using the RUAUMOKO 2D software. The findings of this study provided evidence of the effectiveness of EB-FRP sheets in reducing residual deformation in CSWs. Additionally, significant reductions in the rotation of the coupling beams (CBs) and the inter-story drift ratio were observed. The results also revealed that bonding vertical FRP sheets to boundary elements and confining enhancement by wrapping CBs and wall piers is a very effective configuration in mitigating residual deformations. [ABSTRACT FROM AUTHOR]

Today's construction industry has been more inclined to apply innovative rehabilitation techniques, including externally bonded (EB) fiber-reinforced polymer (FRP) composites on existing RC structures, rather than traditional strengthening methods. Indeed, the higher fatigue resistance of carbon FRPs (CFRPs) has made them superior strengthening tools for structures subjected to fatigue loading, such as RC bridge girders against daily traffic loads. However, the performance of RC structures retrofitted with EB–CFRP composites can be highly influenced by the bonding mechanism at the CFRP-to-concrete interface. The occurrence of debonding failure at the CFRP-to-concrete interface can result in premature failure of the EB–CFRP retrofitting system, thereby leading to rupture of the deficient structure. Therefore, an in-depth understanding of the bond behavior, especially under fatigue loading, would contribute to improving the efficiency of EB–CFRP strengthening techniques. To this end, in this work, we investigated the bond fatigue behavior through an experimental study. The parameters of CFRP composite type (laminate vs. fabric sheet), bond length, and CFRP-to-concrete width ratio were considered herein in order to examine their effectiveness on fatigue bond performance at the CFRP-to-concrete interface. The research results revealed that the CFRP composite system composed of the fabric sheet CFRP and the corresponding epoxy adhesive performed better than the CFRP-bonded joint with laminate CFRP in terms of fatigue life and residual load-carrying capacity. Furthermore, a modified bond fatigue-life model (S–N model), validated with existing research data, was proposed that successfully takes into consideration the effects of fatigue loading, concrete compressive strength, and CFRP-to-concrete width ratio. [ABSTRACT FROM AUTHOR]

The application of externally bonded (EB) carbon fiber reinforced polymer (CFRP) systems for strengthening existing structures, such as RC beams, has been widely approved in the construction industry worldwide for its numerous benefits. The CFRP-to-concrete bond has a governing role in the reliability and effectiveness of EB-CFRP systems. Indeed, failure of the CFRP-to-concrete bond can lead to rupture of CFRP-strengthened structures. Hence, ongoing research into assessment of bond behavior at the CFRP-to-concrete interface helps to bring more insightful clarity to the use of EB-CFRP strengthening techniques. The aim of this study is to evaluate the bond behavior between CFRP and concrete by conducting a series of pullout tests. The parameters considered include CFRP type (sheet versus laminate), bonded length, and bonded CFRP width. The results show that using CFRP fabric sheets can contribute to higher bond load-carrying capacity and ductility than CFRP laminates. Furthermore, through the analyses of databases in the literature, a bilinear bond–slip model is proposed that takes into account the CFRP width factor. Through a comparison, it is shown that the proposed model performs well in terms of predicting the maximum local bond stress and CFRP slippage. This research was aimed at investigating the use of CFRP composites for strengthening RC structures. The complexities regarding the behavior of CFRP-strengthened RC beams and columns, especially at the CFRP-to-concrete bond, provoked the authors to conduct this experimental study. The testing program was intended to evaluate the effect of certain parameters on the bond behavior of a CFRP-to-concrete interface. In addition, an analytical study was carried out to develop a model, capable of characterizing the interfacial behavior in terms of bond shear stress and bond slip. The proposed model proved to perform well at predicting the bond–slip behavior in a validation study. Findings obtained from this research can better familiarize civil engineers with the application of EB-CFRP strengthening techniques in concrete surfaces and possibly enhance the design of such retrofitting systems in deficient real-life RC structures. [ABSTRACT FROM AUTHOR]

The primary seismic force-resisting system (SFRS) in middle- to high-rise reinforced concrete (RC) building structures often includes coupled shear walls (CSWs) and single shear walls (SSWs). These walls are designed to transfer lateral forces to the foundation and dissipate energy through the development of plastic hinges. The latter lead to residual displacement in these structural components. On the other hand, self-centering systems enable the structures to return to their initial position after severe loading or at least reduce residual displacement. The objectives of this study were, therefore, as follows: (i) to review the state of the art on shear wall self-centering techniques and retrofitting methods based on externally bonded fiber-reinforced polymer (EB-FRP); (ii) to evaluate research needs to improve the self-centering ability of shear walls using EB-FRP. [ABSTRACT FROM AUTHOR]

The embedded through-section (ETS) technique was recently developed to avoid the debonding failure that occurs with other fiber-reinforced polymer (FRP) strengthening techniques such as the externally bonded (EB) and near- surface-mounted (NSM) methods. The method offers greater confinement and leads therefore to a substantial improvement in bond performance. In addition, it requires less concrete preparation than the other strengthening techniques. In this study, experimental results from 13 direct-shear test specimens are reported. The influence of the following major parameters on the bond behaviour of FRP-strengthened reinforced concrete beams is examined: concrete strength, hole diameter, bar diameter, bar surface area, and bar bond length. The experimental results show that debonding can be avoided by providing a sufficient bar length and high concrete strength. Among the analytical models suggested in the literature for the bond behaviour of FRP reinforced concrete, the BPE modified model and the CMR model are compared with the experimental results obtained here. The CMR model with new fitting parameters is found to be an accurate way of simulating the experimental results. Key words: ETS method, FRP strengthening, direct shear, experimental test, parametric study, bond force-slip relations, analytical models. La technique de renforcement en cisaillement par insertion de barre en polymeres renforces de fibres (PRF) a travers la section (<< embedded through-section >> (ETS)) a ete recemment developpee pour palier aux ruptures prematurees dues a la delamination et au decollement du composite exhibees par les techniques classiques de renforcement externe en PRF (<< externally bonded >> (EB) et << near surface mounted >> (NSM)). La methode ETS offre un meilleur confinement et conduit a une amelioration substantielle du rendement de la matrice. De plus, la technique est facile a installer par rapport aux autres methodes de renforcement. Cette etude presente les resultats d'une etude experimentale impliquant des essais sur 13 specimens soumis a un cisaillement direct simulant la technique ETS. Elle compare egalement les resultats aux predictions des modeles existants. Les parametres suivants sont evalues : la resistance du beton, la section de la barre, le diametre du trou, le diametre de la barre et sa longueur de scellement sur le comportement de la matrice a l'interface PRF-beton. Les resultats experimentaux montrent que le decollement peut etre evite moyennant une longueur de scellement suffisante et une bonne resistance du beton. Parmi les modeles analytiques proposes dans la litterature pour le comportement des contraintes d'adherence PRF- beton, le modele (BPE) modifie et le modele (CMR) sont compares aux resultats experimentaux obtenus. Le modele CMR avec ses nouveaux parametres d'ajustement s'est avere un outil plus precis pour simuler le comportement des barres en PRF ancrees. Mots-cles : methode ETS, renforcement en PRF, cisaillement direct, essai experimental, etude parametrique, relation contrainte d'adherence-glissement, modeles analytiques d'adherence., Introduction Le renforcement des structures en beton au moyen de composites a base de polymeres renforces de fibres (PRF) colles en surface (EB) est considere comme une methode efficace pour [...]

The National Building Code of Canada (NBCC) takes into account the effect caused by the higher order vibration modes using the dynamic amplification factor [M.sub.v]. This factor depends on the types of systems used to resist seismic forces. However, for load-bearing partitions, the NBCC recommends using the [M.sub.v] that pertains to moment-resisting structures when the level of coupling, DC [greater than or equal to] 2/3 (coupled load-bearing partition system) or the [M.sub.v] pertaining to walls and structure-wall systems when DC < 2/3 (partially coupled load-bearing wall system). Consequently, the NBCC connotes a fundamentally different dynamic behaviour than these two load-bearing wall systems, even when the deviation of the respective DC on either side of the DC = 2/3 value is low. This deviation was the basis behind the present study to assess the effect caused by the higher order vibration modes in coupled and partially coupled load-bearing walls, and to propose an [M.sub.v] factor specific to these important structural systems. The numerical investigations of this study analyse a large array of load-bearing wall systems and take into account the following parameters: (i) three building heights (10, 20, and 30 storeys), (ii) two levels of coupling (DC = 0.6 and DC = 0.7), (iii) five soil classes (A to E), and (iv) two cities, Montreal and Vancouver, representative of the seismic risk zones for Eastern and Western Canada. [Journal translation] Key words: higher order vibration modes, dynamic amplification, level of coupling, elastic spectrum, coupled load-bearing partitions. Le Code national du batiment du Canada (CNBC) tient compte explicitement de l'effet du aux modes superieurs de vibration (EMSV) a l'aide du facteur d'amplification dynamique [M.sub.V]. Ce facteur depend, entre autres, du type de systemes de resistance aux forces sismiques (SRFS) adopte. Cependant, dans le cas des systemes de murs de refend (MR), le CNBC recommande de prendre le [M.sub.V] relatif aux ossatures resistant aux moments lorsque le degre de couplage (DC) est plus grand ou egal a 2/3 (systeme de MR couples) ou le [M.sub.V] relatif aux murs et aux systemes mur-ossature lorsque le DC < 2/3 (systeme de MR partiellement couples). Le CNBC sous-entend, par consequent, un comportement dynamique fondamentalement different de ces deux types de systemes de MR meme lorsque l'ecart de leurs DC respectifs, de part et d'autre de la valeur charniere DC = 2/3, est faible. C'est precisement cette incongruite qui a motive la presente etude qui a pour objectif d'evaluer l'EMSV dans les systemes de MR couples et partiellement couples, et de proposer un facteur [M.sub.V] specifique a ces systemes structuraux importants. Les investigations numeriques menees dans le cadre de cette etude portent sur une large gamme de systemes de MR couvrant les parametres suivants: (i) trois hauteurs de batiments (10, 20 et 30 etages); (ii) deux DC (DC = 0,6 et DC = 0,7); (iii) cinq classes de sol (A a E); et (iv) deux villes, Montreal et Vancouver, respectivement representatives du risque en zones sismiques de l'Est et de l'Ouest du Canada. Mots-cles: modes superieurs de vibration, amplification dynamique, degre de couplage, spectre elastique, murs de refend couples., Introduction Des etudes (D'Aronco 1993; Filiatrault et col. 1994) ont revele que durant les evenements sismiques majeurs, la demande en cisaillement dans les sections critiques des MR continue de croitre [...]

This article deals with the shear strengthening of reinforced concrete (RC) beams using externally bonded fibre-reinforced polymers (FRP). The requirements for shear strengthening of RC beams in CSA (Canadian Standards Association) S806-02 code are summarized and compared to other existing international codes. Moreover, a comprehensive analysis on major parameters influencing on shear contribution of FRP in relation with the current equations of the Canadian codes and other standards is represented in this article. Based on the mentioned analysis and recent achievements a new, rational and evolutionary predicting model to calculate the effective strain and the shear contribution of FRP is proposed. The new model takes into account the major parameters such as, the effect of transverse steel reinforcement. This model will ultimately be used in CSA S806-02. Key words: FRP composites, shear reinforcement, reinforced concrete, beams, parameters, standard, model. Cet article a trait au renforcement a l'effort tranchant des poutres en beton arme a l'aide de materiaux composites colles en surface. Il presente une synthese des prescriptions de la norme ACNOR (Association canadienne de normalisation) S806-02 relatives au renforcement a l'effort tranchant, en comparaison aux autres guides internationaux existants. Il presente egalement une analyse exhaustive des parametres majeurs influencant la contribution du composite a la resistance a l'effort tranchant en relation avec les equations actuelles de la norme canadienne et des autres guides. Sur la base de cette analyse et des recentes avancees en recherche, des perspectives pour l'elaboration d'un nouveau modele de calcul normatif et evolutif permettant de predire la deformation effective et donc la contribution du composite a base de polymere renforce de fibres (PRF) tenant compte des parametres majeurs, dont l'armature transversale en acier, sont enoncees. Ce modele sera ultimement integre a la norme ACNOR S806. Mots-cles : composites a base de polymere renforce de fibres (PRF), renforcement a l'effort tranchant, beton arme, poutres, parametres, norme, modele. [Journal translation], Introduction Les ouvrages en beton arme (BA) representent une partie importante du patrimoine bati au Canada et dans le monde. Beaucoup de ces ouvrages souffrent de degradation serieuse des materiaux. [...]

This paper presents results from an experimental investigation of the bond-slip performance of moderately confined concrete under monotonic and cyclic loading. The effects of six factors on the bond-slip response and on the bond mechanisms are investigated. These factors are grouped into two categories: the first category of four factors is related to the confining conditions, the second category to the loading conditions. A total of 43 pullout tests under monotonic and cyclic loadings were performed. Results show that the quantity of confining steel and the distance between the tested bar and the confining steel are the most important factors affecting the overall bond response. Bar spacing and height of concrete cast below the bar have less significant effects on the overall response, affecting mainly the initial response phase. The height of concrete cast below the tested bar is found to affect the maximum bond resistance to the same extent as in well-confined concrete. Cyclic bond behaviour of moderately confined concrete is found to be similar in shape and in cyclic degradation to that of well-confined concrete. It was also found that most of the bond response parameters, such as maximum bond resistance and the post-peak (softening) phase, can be predicted with excellent accuracy in terms of the factors investigated. Key words: experimental tests, reinforced concrete, bond performance, bond-slip response, moderate confinement, static loading, cyclic loading. Cet article presente les resultats d'une etude expeerimentale du comportement adherence-glissement du beton moderement confine sous chargement monotone et cyclique. Six facteurs influencant la response adherence-glissement et sur les meecanismes d'adherence sont etudiees. Ces facteurs sont regroupesen deux categories : la premiere categorie comporte quatre facteurs et est reliee aux conditions de confinement et la deuxieme categorie, aux conditions de chargement. Au total, 43 essais d'arrachement ont ete realises sous chargement monotone et cyclique. Les resultats montrent que le comportement de l'adherence est essentiellement affecte par la quantite de l'acier de confinement et la distance entre la barre mise a l'essai et l'acier de confinement. Les effets de l'espacement des barres d'armature et de la segregation du beton sur le comportement de l'adherence sont de moindre importance et affectent principalement la phase initiale dela reponse adheerence-glissement. L'effet de la segregation du beton affecte la resistance maximale de l'adherence au mieme titre que dans le beton bien confine;. Le comportement cyclique de l'adherence d'un beton moderement confine; est similaire en forme et en degradation cyclique a celui d'un beton bien confine;. Par ailleurs, la plupart des parametres de la reponse adherence-glissement, tels que la resistance maximale d'adherence et la phase post-pic (ecrouissage), peuvent eetre predits avec une excellente precision en termes des facteurs eetudiees. Mots-cles: essais expeerimentaux, beton arme, comportement de l'adherence, reponse adherence-glissement, confinement modere, chargement statique, chargement cyclique., Introduction Reinforcement slip is a fundamental and important aspect of the response of reinforced concrete (RC) structures. Under certain conditions, deformations arising from reinforcement slip within joints of structural members [...]

New technologies based on seismic isolation are gaining popularity among engineers given the savings on construction costs. The long-term advantage of these technologies preserve the serviceability of the structure after an earthquake and eliminate the cost of reconstruction. This advantage is critical for 'emergency' bridges, required to remain operational after an earthquake. The present article examines a method of isolating the foundation of existing bridges as part of a seismic retrofitting effort. This approach is supported by the increasing interest in this method, especially since its adoption by the Canadian standards and due to the fact that engineers are not too familiar with non-linear dynamic design methods. Another source of motivation is the opportunity to apply this technique to the refection of a few Quebec bridges. The steps of the antiseismic calculations as well as the results of non-linear analyses pertaining to the Madrid Bridge are presented and discussed. This paper may become a useful tool for engineers and their projects of retrofitting existing bridges. Key words: bridge, seismic retrofitting, standard, foundation isolation, Madrid Bridge, Quebec. Les nouvelles technologies basees sur l'isolation sismique connaissent un interet grandissant parmi les ingenieurs, compte tenu de l'economie sur le cout de la construction de l'ouvrage qu'elles offrent. Elles presentent egalement un avantage indeniable a long terme etant donne qu'elles preservent la fonctionnalite de l'ouvrage apres seisme et eliminent le cout de reconstruction. Cet avantage revet une importance capitale pour les ponts dits de secours qui doivent demeurer en service apres le seisme. Cet article presente une methodologie relative a l'isolation de la base des ponts existants dans un contexte de mise en conformite sismique. Cette demarche est motivee par l'interet grandissant de cette methode, notamment depuis son adoption par la norme canadienne d'une part et d'autre part par le fait que les ingenieurs praticiens sont moins familiers avec les methodes dynamiques non lineaires de conception. L'opportunite offerte aux auteurs de mettre en application cette technique pour la refection de quelques ponts au Quebec est une autre source de motivation. Les etapes de calcul parasismiques sont pourvues, et les resultats des analyses non lineaires relatives au pont Madrid sont presentes et discutes. L'article est destine aux ingenieurs praticiens qui y trouveront un outil utile pour leurs projets en rehabilitation de ponts existants. Mots-cles : pont, mise en conformite sismique, norme, isolation de la base, pont Madrid, Quebec., Introduction Les ponts sont des structures importantes dans la vie economique et sociale des nations. Dans les regions sismiques, de nombreux ponts, de part leur importance strategique, sont concus pour [...]

This paper presents a comprehensive review of the new provisions for the design of coupled shear walls in Canadian seismic zones. It follows major revisions that were incorporated in the National Building Code of Canada 2005 (NBCC 2005) and in the Canadian standard Design of concrete structures (CSA A23.3-04), which were due, in particular, to the adoption of a new Canadian map of seismic risk. The present study is intended to address recurring confusions in current practice and the difficulties expressed in the application and interpretation of the new NBCC 2005 and CSA A23.3-04 provisions. A design flowchart is thus proposed as a practical guide, describing, step by step, the required verifications at each stage of coupled shear walls calculation. Finally, to demonstrate the applicability of these new provisions, a numerical example is detailed, following the presented design flowchart. Key words: coupled shear walls, coupling degree, reinforced concrete, seismic design, NBCC 2005, CSA A23.3-04, ductility, dynamic amplification. Cet article presente une vue d'ensemble des dispositions nouvelles concemant la conception des murs de refend couples en zones sismiques canadiennes. Il fait suite aux revisions majeures incorporees dans le Code national du batiment--Canada 2005 (CNBC 2005) et la norme canadienne Calcul des ouvrages en beton (CAN/CSA-A23.3-F04), lesquelles etaient dues, en particulier, a l'adoption de la nouvelle carte canadienne du risque sismique. Cette etude a ete motivee par les confusions recurrentes observees dans la pratique courante et par les difficultes exprimees dans l'application et l'interpretation des nouvelles prescriptions du CNBC 2005 et de la norme CAN/CSA-A23.3-F04. A cet effet, un organigramme de conception est propose comme guide pratique, decrivant pas a pas les verifications requises a chaque etape du dimensionnement des murs de refend couples. Finalement, pour demontrer l'applicabilite des nouvelles prescriptions, un exemple numerique est traite dans le detail, conformement an dit organigramme de conception. Mots-cles : murs de refend couples, degre de couplage, beton arme, conception sismique, CNBC 2005, CAN/CSA-A23.3F04, ductilite, amplification dynamique., Introduction L'efficacite des systemes de murs de refend couples (MRC) comme systemes de resistance aux forces sismiques (SRFS) est desormais etablie. Elle resulte de la conjonction des proprietes mecaniques de [...]

Abstract: This paper presents results of an experimental investigation on the fatigue performance of the welded multiple support bar modular bridge expansion joint (MBEJ) used for the recent Jacques Cartier [...]

This paper describes the procedure and results of the field tests on high-density polyethylene (HDPE), PVC, and metal large diameter pipes subjected to a highway design truck loading. Numerical simulations using finite element method are performed to determine pipe-soil system response under live load application. Comparisons of field test data with the predicted responses are made for soil pressures around and above the pipes, deformed cross-sectional pipe profiles, and pipe deflections. The field test results indicated that the buried flexible pipes, embedded with highly compacted graded sand with silt, demonstrated good performance without exhibiting any visible joint opening or structural distress. Under shallow burial conditions, the AASHTO specified deflection limit of 5% is found to be adequate for installation of the flexible pipes during the construction phase, and a vertical deflection limit of 2% is suggested for HDPE pipes based on the truck load response and repeated loading effect. DOI: 10.1061/(ASCE)0887-3828(2006)20:1(21) CE Database subject headings: Soil-structure interaction; Soil pressure; Flexible pipes; Culverts; Storm sewers; Live loads; Load distribution; Highways; Trucks.

In the last three decades, glass fiber-reinforced polymer (GFRP) has gained wide acceptance as an alternative reinforcement to avoid the potential of corrosion and related deterioration of reinforced concrete infrastructure. Recent experimental results for concrete columns reinforced entirely with GFRP bars have demonstrated their effectiveness in resisting lateral loads induced by wind or earthquakes. However, in most of the research studies carried out so far, the columns were tested under reversed cyclic loading, while subjected to low to moderate levels of axial load that would be rather representative of columns located in the top stories of multi-story buildings. This has been the main impetus to investigate FRP-reinforced columns under high levels of axial load with different ratios of longitudinal reinforcement. To that end, a finite element model (FEM) that considers the material and geometric nonlinearity and the bond behavior of GFRP bars was developed and validated against the available experimental results. Twenty-one specimens encompassing wide levels of axial load and longitudinal reinforcement ratios were studied. Results are presented in terms of strength, stiffness, and deformation capacity as affected by axial load. The moment-axial load interaction diagrams for the simulated specimens are also discussed. The paper concludes by proposing the most appropriate performance design levels for GFRP-reinforced columns. Quantification of the seismic response parameters within this study is aimed at facilitating the adoption of GFRP bars in North American codes as internal reinforcement for earthquake-resisting systems. [ABSTRACT FROM AUTHOR]

The objective of this study is to conduct a finite-element (FE) numerical study to assess the effect of size on the shear resistance of reinforced concrete (RC) beams strengthened in shear with externally bonded carbon fibre-reinforced polymer (EB-CFRP). Although a few experimental studies have been done, there is still a lack of FE studies that consider the size effect. Experimental tests are time-consuming and costly and cannot capture all the complex and interacting parameters. In recent years, advanced numerical models and constitutive laws have been developed to predict the response of laboratory tests, particularly for issues related to shear resistance of RC beams, namely, the brittle response of concrete in shear and the failure modes of the interface layer between concrete and EB-CFRP (debonding and delamination). Numerical models have progressed in recent years and can now capture the interfacial shear stress along the bond and the strain profile along the fibres and the normalized main diagonal shear cracks. This paper presents the results of a nonlinear FE numerical study on nine RC beams strengthened in shear using EB-CFRP composites that were tested in the laboratory under three series, each containing three sizes of geometrically similar RC beams (small, medium, and large). The results reveal that numerical studies can predict experimental results with good accuracy. They also confirm that the shear strength of concrete and the contribution of CFRP to shear resistance decrease as the size of beams increases. [ABSTRACT FROM AUTHOR]

Coupled shear walls (CSW) are an efficient lateral load-resisting system. Their seismic performance depends primarily on their coupling beams (CBs) ability to provide adequate stiffness and strength. However, many existing buildings with CSW resisting system were designed and constructed according to old codes and standards with insufficient requirements for seismic design. These systems feature unsatisfactory behaviour and prematurely collapse in case of major earthquake events. Therefore, their seismic retrofit is urgently needed. The main objectives of this study are, i) evaluate and compare the seismic performance of CSWs designed to old and new codes; ii) highlight the deficiencies of CSWs designed to old codes; iii) investigate a retrofit method using externally bonded (EB) carbon fibre reinforced polymer (CFRP) composites to enhance the seismic response of deficient CSWs. To that end, a 20-story CSW is considered with different design details including one according to old National Building Code of Canada (NBCC) before the 1970s and the other one designed consistent with the new NBCC 2015 and the Canadian Standard Association, CSA A23.3–14, for Eastern seismic Canadian zone. The nonlinear analyses of CSWs under earthquake records are conducted in two steps. At first, the nonlinear time-history analyses of two types of CSWs are carried out using RUAUMOKO program and the deficiencies of old-designed CSW are identified through the comparison of obtained results. In the second step, the old design CSW is retrofitted using CFRP sheets and reanalysed to investigate the benefits of the retrofit technique in mitigating the shortcomings. The results indicate that CFRP retrofitting is an efficient method to enhance the seismic performance of deficient old CSWs in terms of story displacement, inter-story drift, CBs rotation, and ductility demand. [ABSTRACT FROM AUTHOR]

The use of externally bonded fiber-reinforced polymer (EB-FRP) composites for shear strengthening of reinforced concrete (RC) beams presents many challenges given the complex phenomena that come into play. Premature bond failure, the behavior of the interface layer between FRP composites and the concrete substrate, the complex and brittle nature of shear cracks, and the adverse interaction between internal steel stirrups and EB-FRP are some of these phenomena. Compared to experimental investigations, the finite element (FE) technique provides an accurate, cost-effective, and less time-consuming tool, enabling practicing engineers to perform efficient, accurate nonlinear and dynamic analysis as well as parametric studies on RC beams strengthened with EB-FRP. Since 1996, many numerical studies have been carried out on the response of RC beams strengthened using FRP. However, only a few have been related to RC beams strengthened in shear using EB-FRP composites. In addition, the analytical models that have been reported so far have failed to address and encompass all the factors affecting the contribution of EB-FRP to shear resistance because they have mostly been based on experimental studies with limited scopes. The aim of this paper is to build an extensive database of all the studies using finite element analysis (FEA) carried out on RC beams strengthened in shear with EB-FRP composites and to evaluate their strengths and weaknesses through various studied parameters. [ABSTRACT FROM AUTHOR]

This study presents the results of an experimental investigation on the seismic performance of two reinforced concrete coupling beams (CBs) for coupled shear walls, one with a conventional reinforcement layout designed according to the old National Building Code of Canada (NBCC) 1941 and the other one with a diagonal reinforcement configuration designed according to modern NBCC 2015 and Canadian Standard Association (CSA) A23.3 2014 requirements. Experimental tests were conducted to investigate the behavior of specimens under reversed cyclic loading. The experimental results reveal that the diagonal reinforcement configuration could increase the load-resisting capacity and energy dissipation capacity by 4.4 and 10.2 times, respectively. Moreover, the maximum rate of stiffness degradation decreased from 96% in conventionally reinforced CB to 57% in diagonally reinforced CBs. Furthermore, diagonal reinforcement layout led to more stable hysteretic behavior without considerable pinching. In contrast and as expected, the conventionally reinforced CB did not comply with the requirements of the new design code. Therefore, such CBs should be retrofitted to upgrade their seismic performance in conformity with updated standards requirements. [ABSTRACT FROM AUTHOR]

This paper presents the results of two parametric finite-element studies that were carried out using the PLAXIS-3D finite element (FE) computer code. The following objectives and corresponding parameters were considered: (i) to evaluate the soil pressure on the steel trench box shield; the parameters studied were related to soil type and material, and the study considered till, dry sand, wet sand, and sensitive clay soil; (ii) to assess the effect of trench box material and geometry on earth pressure; the parameters studied were related to trench box material (steel versus aluminum) as well as geometry (plate thickness and strut diameter). These studies included simulation of two steel (or aluminum) trench box shields stacked upon each other to cover the total 6 m (20 ft) deep trench. A Mohr-Coulomb (MC) constitutive material model was chosen for FE analysis (FEA). The FEA results were compared to empirical apparent earth pressure diagrams for a sensitive clay. Comparisons showed that the parameters related to the soil and the trench box have a significant influence on earth pressures. [ABSTRACT FROM AUTHOR]

A fatigue study was performed on two commercial high-strength concretes of 70 MPa and 95 MPa with water/cementitious material ratios of 0.28 and 0.23, respectively. Specimens were cast at the construction site and cured in the laboratory. Tests were performed under constant amplitude, and strains were measured continuously using strain gauges. The McCall model for fatigue life prediction was found to be satisfactory, and safer than the usual Wohler curves. Strain evolution and stiffness degradation with the number of cycles in high-strength concrete were found to be similar to those of normal concrete. Strain at failure under cyclic loading was found to be of the same order as the strain at peak load under static loading. Interesting correlations between strain rate and number of cycles to failure and between stiffness decrease rate and number of cycles to failure were found. Evolution of the hysteresis loop was studied. Energy dissipated was found to decrease after the first cycles, and increased steadily thereafter up to failure. Finally, the differences in deformation characteristics between the two high-strength concretes studied in this investigation were analyzed.

A finite-element (FE) numerical study using PLAXIS-3D software was carried out to reproduce and validate a full-scale experimental in situ test and to investigate the earth pressure on a flexible temporary trench box shield in soft and sensitive clay soil. The excavation trench model was 6 m (20 ft) deep and was considered as nonlinear and anisotropic clay. A 45 kPa (0.94 ksf) surface overload on top of the soil near the trench box was also simulated to produce a maximum load case on the flexible wall of the shield. Both Mohr-Coulomb (MC) and hardening soil (HS) constitutive soil models were considered for FE analysis. Different values of the modulus reduction factor (MRF) and the coefficient of earth pressure at rest ( K 0 ) were considered to validate the model. For a specific shear strength profile, FE analysis with a linear elastoplastic soil model showed relatively small differences in soil pressure with the field test results along the depth of the trench. Results were also compared with the predictions of well-established analytical formulae. [ABSTRACT FROM AUTHOR]

The need to demonstrate that a steel-reinforced concrete bridge pier wall resilient to strong earthquakes could be attained by the incorporation of glass fiber–reinforced polymer (GFRP) reinforcement has been brought to the fore by recent experimental results on GFRP-reinforced concrete bridge pier walls. The test results show that the GFRP bars assisted in crack recovery and the self-centering of walls between load reversals. Hence, GFRP bars could potentially be used to control the unrecoverable damage in steel-reinforced bridge pier walls after an earthquake. This study will use nonlinear finite element analysis (FEA) as a powerful tool to verify this expectation. A series of analyses will be implemented on concrete bridge pier walls reinforced with either steel or GFRP bars to demonstrate that the finite element (FE) procedure can provide quick and reliable simulation. The study is then extended to investigate the effect of using hybrid reinforcement through a comprehensive parametric study. Different configurations of GFRP bars are examined and compared with similar configurations of steel bars. The results show that hybrid reinforced bridge pier walls can undergo large displacements with minimal residual deformations. Nevertheless, a sensible selection of the GFRP bars location is necessary. The findings of this study could be considered as a fundamental step toward the development of code provisions for the use of hybrid GFRP/steel (GS) reinforcement in concrete bridge pier walls. [ABSTRACT FROM AUTHOR]

A large number of existing buildings have seismic-resistant systems designed according to old code provisions. These structural systems exhibit non-ductile behavior and can present a significant risk in the case of a moderate or significant seismic event. Reinforced concrete–coupled shear walls designed to old codes and standards are among those deficient structures that need to be seismically upgraded. This article aims to investigate a new retrofitting and upgrading method using externally bonded carbon fiber–reinforced polymer composites for existing or/and damaged reinforced concrete coupling beams that can improve the seismic performance of them during earthquakes. To this end, an experimental test was conducted to evaluate the seismic behavior of two identical reinforced concrete–coupled shear wall specimens under reverse cyclic loading. To simulate the old existing building, the specimens were designed and constructed according to the old 1941 National Building Code of Canada with a conventionally reinforced coupling beam. One of the specimens was tested as a control, and the other was strengthened using externally bonded carbon fiber–reinforced polymer composites to evaluate the improvement in its seismic performance. Results show that the retrofit using externally bonded carbon fiber–reinforced polymer resulted in significant enhancement in strength and energy dissipation capacity compared to the conventionally reinforced coupling beam from the control specimen. In addition, externally bonded carbon fiber–reinforced polymer sheets resulted in much improved hysteretic and ductile behavior and in lesser strength and stiffness degradation. [ABSTRACT FROM AUTHOR]

Shear-strengthening of reinforced concrete (RC) beams with externally bonded (EB) carbon fiber-reinforced polymer (CFRP) using L-shaped laminates is gaining popularity and is successfully used in practice. However, the technique may present some drawbacks related to FRP debonding at the FRP/concrete interface and lack of anchorage. This premature failure may inhibit the fiber-reinforced polymer (FRP) to reach its full strength, thereby limiting the cost-effectiveness of the strengthening material. This paper presents the results of an experimental investigation on RC T-beams shear-strengthened with new closed CFRP stirrup technology. The closed stirrup is made of prefabricated CFRP L-shaped laminates and a CFRP rope as a closure. The purpose of using such a technique is to inhibit premature debonding by reproducing the advantage of full-wrap strengthening configuration. This application method provides a durable and cost-effective solution because it requires less surface preparation and does not use mechanical anchors. This can also be practical in seismic regions where transverse reinforcement is required to be closed for confinement purposes. Laboratory tests were performed on full-size RC T-beams with three different ratios of internal transverse steel. The feasibility of the full-wrap shear strengthening using the closed CFRP stirrup technique and the influence of the internal steel stirrup ratio on the performance of EB CFRP composites were investigated. The results confirmed the effectiveness of using the closed CFRP stirrup technique in increasing the shear resistance of strengthened RC beams. The gain ranged between 20% and 140% for specimens with and without internal transverse steel reinforcement, respectively. The results also demonstrated the existence of an interaction between internal steel stirrups and EB CFRP. [ABSTRACT FROM AUTHOR]

This paper presents a summary of an experimental investigation and the derivation of a bond-slip model for reinforcing steel embedded in moderately confined concrete under monotonic and cyclic loadings. Moderately confined concrete encompasses the domain between unconfined and well-confined concrete, the limits of which are defined in the paper. The proposed constitutive law adapts and extends the well-known Eligehausen-Filippou model for well-confined concrete to moderately confined concrete. It is described by an envelope curve and degradation rules. The former is obtained through a confinement index, defined in this study as a function of the amount of confining steel and concrete, distance between confining steel and the rebar, and concrete segregation effect. It is proposed to adopt the same degradation rules used for well-confined concrete. These rules are validated through statistical tests for moderately confined concrete. They are found to predict correctly the main features of reduced envelope response under increasing cycling amplitudes but to underestimate response degradation under constant cycling limits for the subsequent cycles to the first cycle. To demonstrate the validity and limitations of the proposed model, its predictions under monotonic loading are compared with experimental results and analytical predictions from other studies. [ABSTRACT FROM AUTHOR]

This paper presents the results of an investigation of reinforced concrete (RC) T-beams retrofitted in shear with near-surface mounted (NSM) fiber-reinforced polymer (FRP) rods. Six full-scale 4,520-mm-long RC T-beams were tested to study the effects of important parameters such as the presence of NSM FRP rods, the presence of steel stirrups, and the steel stirrup ratio. This paper provides an insightful and comprehensive description of the behavior of strengthened T-beams under increasing load, from the formation of the first crack to ultimate failure. The results of this study and those gathered in the presented database show that existing steel stirrups and strengthening NSM FRP did not diminish each other's effect when failure modes unrelated to shear resistance of RC beams were prevented. The experimental results of this study and those in the database were used to verify a newly proposed model to predict the shear contribution of NSM FRP rods and laminates in RC beams strengthened in shear. The proposed model showed an improved accuracy compared with the existing models in the literature. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced polymer (CFRP) rope was recently developed to anchor fiber-reinforced polymers (FRP) shear-strengthened beams that conventionally uses U-wrap scheme. The rope is a bundle of flexible CFRP strands held together by a thin tissue net. In this technique, holes are drilled through the web at the web-flange intersection, and CFRP ropes are inserted through the holes and flared onto the two free ends of the U-wrap scheme. The technique offers substantial improvements in bond strength and ductility because it converts the U-wrap scheme similar to a full-wrap scheme. The objective of this paper was to investigate the bond behavior of CFRP L-strip plates anchored with CFRP ropes. The experimental program consisted of 16 tests on FRP-to-concrete joints, of which six were unanchored (control specimens) and 10 were anchored by CFRP ropes. The influence of concrete strength, rope length, and plate width on bond behavior was examined. Experimental results showed that the bond performance greatly improved with increasing FRP plate width and rope length, but concrete strength had a negligible effect, which is attributed to high thickness and narrow width of CFRP L-strips used. Theoretical formulations provided to account for the ultimate bond load were compared with the experimental results, and a modification factor to estimate the effect of the presence of CFRP rope was suggested. [ABSTRACT FROM AUTHOR]

The objectives of this study are to determine the short-term performance for shallowly buried [2,438 mm (up to 8-ft burial depth)] flexible pipes, evaluate joint performance requirements, and verify AASHTO design assumptions in the light of field test data from in situ measurements. The installation, instrumentation, and field test procedures are presented for high-density polyethylene (HDPE), PVC, and metal pipes under 2D, 1D, and 0.5D burial depths, where D is the pipe diameter. The field test is performed on 914 mm (36 in.) and 1,219 mm (48 in.) pipe diameters. A tandem dump truck is selected for the pipes under 2D burial depth, while the Florida Department of Transportation truck is adopted for the pipes under 0.5D and 1D burial depths. The field test results are presented in terms of the soil pressure distribution around the cross section, as well as the vertical and horizontal pipe diameter changes during construction and under the live load. Special emphasis is given to circumferential wall strains. The validity of the modified Iowa and Meyerhof formulae proposed to predict the horizontal deflection of buried pipes is also investigated. [ABSTRACT FROM AUTHOR]

This study presents the experimental results for seven different tests carried out on high-density polyethylene (HDPE), PVC, and metal pipes with medium-size diameters. The main objective of the experimental program is to evaluate and characterize, under laboratory conditions, the performance and mechanical properties of the various flexible pipes considered in the study. The diameters of the pipes studied are 36 in. (914 mm) and 48 in. (1,219 mm). The laboratory tests conducted are the simple-beam test, parallel-plate test, flattening test, curvedbeam test, joint-integrity test, and tensile test, as well as an environmental stress-cracking test. The results of the tests are presented in terms of load-deflection relations, load versus longitudinal and transverse strains, failure modes, and pipe stiffness. The test results indicate that HDPE and PVC pipes show good performance compared with metal pipes. In addition, the experimental results for flexible pipes meet AASHTO specifications. The HDPE and PVC pipes tested according to the ASTM and AASHTO Standards show pipe stiffness values higher than the minimum specified by the standards. The pipe stiffness values of the HDPE specimens based on the curved-beam test are two to three times greater than those based on the parallel-plate test. It was found that for a given vertical deflection, the HDPE pipe stiffness substantially increased with an increase of loading rate. [ABSTRACT FROM AUTHOR]

Recent years have seen valuable research work and widespread applications of fiber-reinforced polymer (FRP) bars as flexural and shear reinforcement for concrete structures. Nonetheless, the axial compression behavior of FRP reinforced concrete (RC) columns has not yet been defined. This study introduces equations and a confinement model to predict the stress-strain envelope responses of RC columns reinforced with carbon-FRP bars (CFRP) and confined by CFRP spirals or hoops. The model takes into account the effect of many parameters such as transverse reinforcement configuration, longitudinal reinforcement ratio, volumetric ratio, and the size and spacing of spirals or hoops. Results of analysis using the proposed confinement model were verified by means of a series of experiments with full-scale circular CFRP-RC columns. The proposed equations have been shown to predict accurately confined concrete core stress, corresponding concrete strain, and prepeak and postpeak stress-strain relationships for the tested CFRP-RC column specimens. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of a new anchorage technique for fiber-reinforced polymer (FRP) shear-strengthened reinforced concrete T-beams using carbon fiber-reinforced polymer (CFRP) ropes. The rope is a bundle of flexible CFRP strands held together using a thin tissue net. In this technique, holes are drilled through the web at the web-flange intersection, where the CFRP ropes are inserted and flared onto the two free ends of the U-wrap scheme. This converts the U-wrap scheme to a full-wrap scheme. The experimental program includes three series based on the number of steel stirrups. No steel stirrups are provided in the first series, whereas the spacing between steel stirrups is 260 and 175 mm in the second and the third series, respectively. Each series includes a control specimen, with no external CFRP for shear strengthening, a specimen strengthened with CFRP sheets, a specimen strengthened with CFRP L-strips, and a specimen strengthened with CFRP L-strips and anchored with CFRP ropes. Two strengthening procedures are used in this study to investigate the effect of the FRP-width to concrete-width ratio. In the anchored specimens, the CFRP rope covers half the depth of the L-strips. The results of this study reveal that the beams anchored with CFRP ropes achieve an enhanced contribution to the shear resistance compared to the beams with CFRP sheets and CFRP L-strips with no rope. In addition, the method eliminates CFRP debonding and achieves rupture of steel stirrups. [ABSTRACT FROM AUTHOR]

Much existing reinforced concrete (RC) civil infrastructure worldwide is in need of shear strengthening and rehabilitation. The use of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) sheets and laminates to strengthen deficient RC beams in shear is now an acceptable and cost-effective practice, particularly under static loads. However, due to its complexity, the cyclic (fatigue) behavior and performance of shear-strengthened beams is not fully documented. Recently, use of CFRP continuous sheets wrapped over the shear length for fatigue upgrade has been studied. This technique may present drawbacks related to surface preparation and FRP debonding. Therefore, when possible, prefabricated CFRP L-shaped laminates can be a cost-effective alternative because they require less surface preparation and do not peel off easily. The objective of this paper was to present the results of an experimental investigation that compared cyclic (fatigue) and static (post-fatigue) behavior of two EB CFRP techniques (sheets vs. laminates) for shear retrofit of RC T-beams. In total, six laboratory tests on full-size 4520-mm-long beams were conducted. The specimens were subjected to fatigue loading of up to 6 million load cycles at a rate of 3 Hz. Specimens that sustained 6 million cycles were then tested monotonically up to failure. The variables examined in the paper were: (1) the EB CFRP strengthening scheme, and (2) the presence and ratio (spacing) of internal shear reinforcement. The test results confirmed the effectiveness of using EB CFRP shear-strengthening methods under cyclic loading. They also revealed that the fatigue performance of RC T-beams strengthened with L-shaped laminates is significantly superior in extending fatigue life compared to corresponding T-beams strengthened with U-wrapped sheets. This was quantified in terms of deflection response (47% increase due to fatigue loading for specimens with L-shaped laminates compared to 90% for specimens with U-wrapped sheets), and the level of increase in steel-stirrups strain range (9–42% vs. 62–114%) and in EB CFRP (36–97% vs. 58–163%). [ABSTRACT FROM PUBLISHER]

The objectives of this study are to evaluate the parameters that affect the behavior of flexible pipes for culverts and storm sewers and to examine the strength-limit states of such pipes proposed by the AASHTO bridge-design specifications. The flexible pipes investigated in the study are high-density polyethylene (HDPE), PVC, and metal pipes. The pipe diameters considered are 914 mm (36 in.) and 1,219 mm (48 in.). A three-dimensional finite-element (FE) model has been developed to simulate the behavior of buried pipes under truck load. Results from field tests conducted by the authors for large-diameter pipes under 2D, 1D, and 0.5D burial depths, where D is the pipe diameter, were used to evaluate the accuracy of the numerical model. Extensive parametric studies were then carried out to examine the effect of burial depth, backfill soil quality, and compaction level on the buried pipes, and their results are reported in this paper. The effect of these parameters has been evaluated in terms of thrust values at the pipe shoulder and springline, vertical diameter changes, and longitudinal strains. Regression analysis was carried out based on the FE model predictions for the first load pass and on results from a research study available in literature to predict the behavior of buried pipes with multiple load passes. The parametric study has shown that the performance of buried pipes varies with the soil type, and the increase of compaction level and soil cover reduces the stresses on buried pipes. The numerical predictions indicate that the provisions of AASHTO bridge-design specifications for HDPE pipes need to be reassessed for very shallow burial depths. [ABSTRACT FROM AUTHOR]

Single-support bar modular joints are widely used in large-span bridges because of their competitiveness and their ability to accommodate larger movements than conventional multiple-support bar joints can accommodate. Despite their general acceptance and use, detailed fatigue testing and design guidelines well suited for these joints are still not well documented. This has been the main impetus for carrying out this experimental and analytical investigation on the fatigue performance of a single-support bar modular bridge expansion joint with welded stirrups. Three identical subassemblies were tested in fatigue to establish the experimental fatigue S-N curve for the main critical details. In addition, a few variants of stirrup specimens were separately tested under static and fatigue loadings to investigate failure modes and the effects of important geometric parameters such as bottom-plate thickness on the stress range and fatigue resistance of the stirrups. The tested joint subassemblies and stirrup specimens developed characteristic fatigue cracks in and around the stirrups and their welded connections. These cracks are classified into three distinct categories, and expressions for computing their associated stress ranges and fatigue resistance are presented. This study reveals that secondary bending moments within the stirrup make a major contribution to the stress range at critical sections of the stirrup. This contribution should be included for adequate prediction of the fatigue life of single-support bar modular joints and can be reasonably determined with basic models using one-dimensional (1D) beam elements for the center beam and for the stirrup. The importance of secondary bending moments within the stirrup is strongly related to the relative stirrup bottom plate-to-vertical leg bending stiffness and to the relative stirrup vertical leg-to-center beam bending stiffness. [ABSTRACT FROM AUTHOR]