1,721,013 research outputs found
Pedestrian bridge as clarifying example of FRP-RC/PC design
No full textEmployment of corrosion-resistant reinforcement represents a widely-recognized effective strategy to ensure long-term durability of reinforced concrete (RC) and prestressed concrete (PC) structures. Fiber-reinforced polymer (FRP) composites have proved to be a reliable non-metallic solution, able to ensure both the required mechanical performance and corrosion resistance. FRP-RC infrastructural applications are currently spreading; conversely, FRP-PC bridges are still considered state of the art prototypes. Many are the conceptual and practical challenges accompanying this innovative technology: brittleness of FRP reinforcement, likelihood of tensioncontrolled failure, limitations on the initial pull force, limitations on the sustained load that the member can carry, and service requirements that may control the design. Reports published by ACI committee 440 do not yet address FRP-RC/PC provisions in a consistent way. Discrepancies exist on how ACI 440.1R and ACI 440.4R approach FRP-RC/PC design, having the latter not being updated since the first generation of FRP regulations. This paper deals with the philosophy behind the design of the precast Carbon FRP-PC/Basalt FRP-RC double-tee girders and the auxiliary Basalt FRP-RC/Glass FRP-RC members that constitute the structure of a recently built pedestrian bridge. This study is an attempt to address the challenges still preventing the wide acceptance of CFRP in prestress applications and to unify the design approach for FRP-RC/PC structures. This successful case-study validates the proposed rationale and supports a slight relaxation of the design limits in terms of initial pull force
Effects of recycled PET fibres on the mechanical properties and seawater curing of Portland cement-based concretes
No full textThis paper deals with an experimental study on the mechanical properties of recycled polyethylene terephthalate fibre-reinforced concrete (RPETFRC) and its durability in an aggressive seawater environment. A Portland limestone cement-based concrete with a 0.38 water/cement ratio is used to cast cubic and prismatic specimens, in association with two different PET fibres obtained through extrusion of recycled PET flakes (R-PET). Some of these specimens were conditioned in the Salerno harbour seawater for a period of 6/12 months. Compressive strength and four-point bending tests are performed in order to investigate the mechanical properties of such RPETFRCs. Comparison of the present results and those in the literature for air-cured RPETRCs highlights the influence of the analysed R-PET fibres on the mechanical properties of concretes showing different water/cement ratios and binders. The given results for seawater-cured specimens demonstrate that such a curing condition slightly modifies the first-crack strength and markedly reduces the toughness of the RPETFRCs examined in the present work. © 2014 Elsevier Ltd. All rights reserved
Experimental analysis on the time-dependent bonding of FRP laminates under sustained loads
No full textFiber reinforced composite materials are frequently used in the rehabilitation or upgrading of existing structures. From a design point of view, current international guidelines on FRP strengthening applications do not give rules based on rigorous approaches to evaluate the reliability and durability of strengthening interventions with respect to long-term behavior. In order to give a contribution on this topic, the authors have carried out a creep experimental program on retrofitting systems, either of carbon or glass fibers and subject to different stress values in regime of constant temperature. The tests have been carried out by means of a dedicated test device that provided a pure bending stress state in the strengthened beam, being the external loads held constant over time. In this paper the results of their investigation and critical analysis are presented. © 2012 Elsevier Ltd. All rights reserved
Buckling behavior of curved composite beams with different elastic response in tension and compression
No full textA geometrically nonlinear finite element model of a composite curved beam is presented, accounting for moderately large rotations of the cross-sections, moderately large shear strains, small axial strains, and different elastic response of the material in tension and compression (bimodular behavior). A path following procedure in displacement control is employed to compute the stability points and the post-buckling response of the given model. Several comparisons are established with different numerical approaches available in the literature, showing the accuracy of the proposed finite element scheme in the unimodular case. Some original results on the in-plane and out-of-plane buckling of bimodular arches highlight that the post-buckling response of such structures is strongly influenced by the ratios between tensile and compressive moduli. © 2013 Elsevier Ltd
Bend-strength of wound carbon fibre reinforced polymer shear reinforcement
No full textThe filament winding of Fibre Reinforced Polymer (FRP) tows around longitudinal reinforcing bars provides a novel method for the fabrication of shear reinforcement cages. A key limitation on the contribution of FRP to the shear capacity of a concrete member is found at corners, where the presence of stress concentrations in different directions can lead to premature failure. Current methods to test FRP reinforcement at corners have limited use for filament wound reinforcement. A new test methodology was developed to allow for rapid testing of curved FRP reinforcement that allows for sample re-alignment during load application, reducing the effects of eccentricities. An experimental programme, comprising of 8 test samples, was undertaken to assess the bend capacity of wound Carbon FRP (CFRP) shear links, considering three variations in bend radius and two variations of cross sectional area. It was found that an increase in bend radius resulted in increase in failure load. It was also observed that an increase in cross sectional area led to a decrease in the ratio between the bend capacity and the ultimate tensile capacity. From comparison between the experimental results and values from theoretical bend strength estimations, it was established that further developments of bend strength predictions for wound shear reinforcement are required in order to accurately reflect their behaviour
Design analysis and experimental behavior of precast concrete double-tee girders prestressed with carbon-fiber-reinforced polymer strands
No full textNew frontiers for the use of FRP reinforcement in geometrically complex concrete structures
No full textThe development of flexible formwork has made it possible to cast optimised geometrically complex and thin walled reinforced concrete structures. At the same time, advanced composite materials offer the opportunity to solve the problem of steel corrosion, which can affect aging of concrete structures. With the goal of achieving sustainable design, being able to combine optimised geometries with durable construction materials is a major challenge for civil engineering. New research at the University of Bath and the University of Miami aims to completely replace internal steel reinforcement in geometrically complex concrete structures with durable and ready-to-use cages made of fibre reinforced polymer (FRP) reinforcement. By fabricating the reinforcement in the desired geometry, it will be possible to provide the required strength exactly where needed, thereby reducing the amount of concrete required to resist internal forces and capitalizing on the extraordinary possibilities offered by both concrete and FRP construction materials. The design of such optimized elements and the automated process of manufacturing the Wound FRP (W-FRP) reinforcement are presented in this paper
Bend-strength of novel filament wound shear reinforcement
No full textThe winding of Fibre Reinforced Polymer (FRP) tows around longitudinal reinforcing bars provides a novel method for the fabrication of reinforcement cages. Complex geometries of internal reinforcement can be fabricated using this technique, a particular advantage for the construction of optimised concrete beams. A key limitation on the contribution of FRP to the shear capacity of a concrete member is found at corners, where the presence of stress concentrations in different directions can lead to premature failure. A new test methodology was developed to allow for rapid testing of the samples as well as sample re-alignment during load application, reducing the effects of eccentricities and imperfections created during their fabrication. An experimental program, comprising 30 test samples, was undertaken to assess the bend capacity of filament wound FRP (W-FRP) shear links manufactured using a carbon tow impregnated with epoxy resin. A fixed bend radius of 5 mm and six non-circular fibre cross sectional areas having different width-thickness ratios were considered. Additionally, 18 samples were tested to measure the tensile properties of the straight reinforcement. The test results indicate that W-FRP shear links exhibit improved bend strength as compared to conventional stirrups with circular sections (up to +53%), as a larger width-thickness ratio of the reinforcement provided more strength for a given cross sectional area. A good correlation between the test results and predictions of the W-FRP bend strength was observed when the specimens were modelled as a collection of transformed individual circular sections
Effectiveness of FRP stirrups in concrete beams subject to shear
No full textIt can be shown theoretically that two key parameters that govern the shear strength of FRP reinforced concrete structures are the angle of inclination of the diagonal struts, θ, and the strength of the FRP stirrups, fv. Existing standards for FRP reinforced concrete differ in their provisions for the determination of these quantities and to date there is paucity of experimental evidence to conclusively support the superiority of a particular standard. To address this problem, an extensive experimental program is undertaken at the University of Salerno with focus on determining the above quantities in GFRP reinforced concrete beams. Beams with different amounts of transverse reinforcement and span to depth ratio are tested to investigate the variation of θ and the magnitude of fv, with the purpose of determining their effect on the beams shear strength
I beni culturali non architettonici: emergenza, recupero e valorizzazione. Un bilancio a vent' anni dal terremoto
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