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New Canadian and American standards for concrete and bridges now provide guidelines for the design, production, curing, material characterization, and installation of ultra-high performance fiber reinforced concretes (named UHPFRC or UHPC) on structures. However, some technical aspects require more research since fundamental knowledge about UHPC is not as complete as for normal strength concretes (NSC). Among these aspects, knowledge on the properties of UHPC produced under field conditions is scarce. The main goal of this work was to evaluate the fresh state properties (slump flow, air content, mass density, hydration heat) and hardened state properties (elastic modulus, Poisson ratio, compressive and flexural strengths) of a UHPC subjected to various mixing temperatures (10, 20, and 30 [degrees]C) and curing temperatures (10, 23, and 35 [degrees]C) encountered in field conditions. The impact of mixing and curing temperatures on each property is discussed and practical information is provided to help engineers planning UHPC curing duration and formwork stripping. Key words: UHPFRC, UHPC, mixing temperature, curing temperature, slump flow, air content, heat of hydration, compressive strength, flexural strength, fiber orientation, fiber density. De nouvelles normes canadiennes et americaines pour le beton et les ponts fournissent desormais des indications pour la conception, la production, la cure, la caracterisation des proprietes ainsi que l'installation de betons de fibres a ultra hautes performances (BFUP) sur des structures. Cependant, certains aspects techniques necessitent plus de recherche, la connaissance fondamentale des BFUP n'etant pas aussi complete que pour les betons ordinaires. Parmi ces aspects, la connaissance des proprietes des BFUP produits en conditions de chantier est limitee. L'objectif principal de ce projet de recherche etait d'evaluer les proprietes a l'etat frais (etalement, teneur en air, masse volumique, chaleur d'hydratation) et a l'etat durci (module d'elasticite, coefficient de Poisson, resistances en compression et en flexion) d'un BFUP soumis a differentes temperatures de malaxage (10, 20 et 30 [degrees]C) et temperatures de cure (10, 23 et 35 [degrees]C) que l'on retrouve en conditions de chantier. L'impact des temperatures de malaxage et de cure sur chacune des proprietes est discute et des informations pratiques sont fournies pour guider les ingenieurs dans la planification des durees de cure et des echeances de decoffrage. [Traduit par la Redaction] Mots-cles : beton de fibres a ultra hautes performances (BFUP - BUHP), temperature de malaxage, temperature de cure, etalement, teneur en air, chaleur d'hydratation, resistance en compression, resistance en flexion, orientation des fibres, densite de fibres., 1. Introduction Ultra-high performance fiber reinforced concretes (named UHPFRC or UHPC) are more and more present and used in civil engineering infrastructure, such as bridges, particularly because of their exceptional [...]

Bridges situated in northern climate regions, which face severe environmental conditions and daily fatigue loading, are prone to accelerated deterioration and corrosion of their components. The application of carbon fiber–reinforced polymer (CFRP) sheets bonding to the surface of bridge elements has emerged as an attractive solution for enhancing bridge strength. Past studies and field implementations have effectively showcased the viability of this approach in strengthening bridges. An exceptional opportunity arises with the deconstruction of a bridge in Canada, providing a unique chance to assess and study the condition of reinforced concrete elements strengthened with CFRP. These elements have endured real service conditions, including fatigue loads and exposure to aggressive environmental factors. This paper presents the experimental results of a research program that aimed to investigate the residual fatigue life and capacity of 60-year-old reinforced concrete bridge girders, which were strengthened using CFRP sheets. The study focuses on assessing the performance of these girders under different test conditions, providing valuable insights into their remaining fatigue life and load-carrying capabilities. The two 60-year-old girders have been strengthened with CFRP for the last 10 years of the service life of the bridge. The two full-scale girders were tested under 2 million fatigue load cycles and then tested monotonically until failure at the structural lab of the University of Sherbrooke. The test results revealed that the CFRP-strengthening technique can extend the service life of the bridge element and enhance its shear capacity. The CFRP–concrete interface and CFRP sheets showed excellent bonding behavior, as no damage-debonding failure or tensile rupture occurred until the formation of the diagonal shear crack. [ABSTRACT FROM AUTHOR]

This paper focuses on the design as well as on the experimental and numerical validations of the mechanical behavior of a precast ultra-high performance fibre reinforced concrete (UHPFRC) retaining walls. The design, made in accordance with the Canadian Highway Bridge Design Code (CSA S6, 2019), led to the fabrication of a full-scale UHPFRC retaining wall with 3% fibre content which had dimensions of 3 m in height, 2 m in length, 2 m in width, with two vertical and horizontal stiffeners, and very thin vertical and horizontal panels of 40 and 65 mm, respectively. The experimental tests showed that the UHPFRC retaining wall exceeded by 42% the ultimate limit state (ULS) design factored bending moment and showed a very ductile behavior under flexural loading. At service limit state (SLS), the retaining wall had maximum crack opening between 0.15 and 0.28 mm, and a maximum lateral displacement of 4 mm. The finite-element model developed for the application captured accurately the flexural behavior of the UHPFRC retaining wall and was used later in parametric studies to optimize the design. The retaining wall optimal design includes UHPFRC with 3% fibre content and stiffeners with variable cross-section which allows volume reductions of 73% for concrete and 86% for rebars in comparison to the conventional reinforced concrete design. [ABSTRACT FROM AUTHOR]

Concrete T-beams are commonly used in building slab systems and bridge decks. They may require strengthening in shear when they are deteriorated or when loading requirements increased. This research project studied the shear behaviour of concrete T-beams using cast-in-place Ultra High-Performance Concrete (UHPC) layers as a lateral strengthening method avoiding beam depth modification. Three UHPC strengthened beams together with one reference reinforced concrete beam were tested in monotonic three-point bending. Parameters investigated include the thickness of UHPC layers and the presence of steel anchors at the UHPC-concrete interface. A digital image correlation (DIC) technique was used to investigate the strain distribution of T-beams during the testing. Strain distribution, failure modes and strengthening effects provided by the UHPC lateral strengthening were analyzed. Results show that UHPC strengthening can substantially improve the stiffness and shear capacity of concrete T-beams, 25 and 50 mm lateral layers increased by 102% and 113% the T-beam shear capacity, respectively. Typical bending-shear behaviour were observed on each strengthened beam with UHPC layers. A final shear failure was observed in the T-beam with 25 mm UHPC layers and 50 mm UHPC layers without anchors, while a combination of shear and bending failure was noted in the T-beam with 50 mm UHPC layers and steel anchors. The steel anchors at the UHPC-concrete interface can further increase the ultimate shear capacity and beam stiffness, but at a limited extent. Therefore, experimental results confirmed that cast-in-place UHPC lateral layers are an effective way to strengthen existing concrete T-beams with inadequate shear capacity

Downside risk measures play a very interesting role in risk management problems. In particular, the value at risk (VaR) and the conditional value at risk (CVaR) have become very important instruments to address problems such as risk optimization, capital requirements, portfolio selection, pricing and hedging issues, risk transference, risk sharing, etc. In contrast, expectile risk measures are not as widely used, even though they are both coherent and elicitable. This paper addresses the bidual representation of expectiles in order to prove further important properties of these risk measures. Indeed, the bidual representation of expectiles enables us to estimate and optimize them by linear programming methods, deal with optimization problems involving expectile-linked constraints, relate expectiles with VaR and CVaR by means of both equalities and inequalities, give VaR and CVaR hyperbolic upper bounds beyond the level of confidence, and analyze whether co-monotonic additivity holds for expectiles. Illustrative applications are presented. [ABSTRACT FROM AUTHOR]

Ultrahigh-performance concrete (UHPC) strengthening is an efficient technique to improve the capacity of shear-deficient members. However, the applicability of UHPC strengthening on a T-beam has been scarcely investigated, particularly with regard to repair configurations not reaching beam supports involving a higher delamination potential. In this study, the shear behavior of concrete T-beams with cast-in-place UHPC strengthening is investigated with 10 concrete T-beams, including different strengthening configurations, layer thicknesses, and anchors at the repair interface. Beams with a UHPC bottom layer ending before the support are investigated for the first time. Load–deflection, lateral, and cross-sectional cracking patterns in each beam are analyzed. Besides, strain distributions of the beams are recorded and analyzed through a digital image correlation system to distinguish different failure modes. The efficiency of UHPC strengthening for improving the shear behavior of concrete beams is clarified, and recommendations are provided for a UHPC-strengthened beam design to avoid delamination. The testing results show that UHPC strengthening using lateral layers is the most efficient configuration for improving shear capacity and does not increase the sectional height, while a U-shaped jacket configuration is recommended when a substantial increase of beam stiffness is required. A combination of shear and separation failure is found in beams with a UHPC bottom layer ending before the support, and it is, therefore, suggested not to use a UHPC bottom layer alone due to the development of separation cracks. More ductile failure modes obtained with 50-mm lateral layers and a 25-mm U-jacket are suggested. Installation of anchors at the repair interface is recommended to achieve more ductile failure modes. [ABSTRACT FROM AUTHOR]