Current Issue : July - September Volume : 2014 Issue Number : 3 Articles : 5 Articles
This paper presents the results of an investigation aimed at developing reinforced concrete beams consisting of precast\npermanent U-shaped reinforced mortar forms filled with different types of core materials to be used as a viable alternative to the\nconventional reinforced concrete beam. To accomplish this objective, an experimental program was conducted and theoretical\nmodel was adopted. The experimental program comprised casting and testing of thirty beams of total dimensions\n300 X 150 X 2,000 mm consisting of permanent precast U-shaped reinforced mortar forms of thickness 25 mm filled with the\ncore material. Three additional typical reinforced concrete beams of the same total dimensions were also cast to serve as control\nspecimens. Two types of single-layer and double-layers steel meshes were used to reinforce the permanent U-shaped forms;\nnamely welded wire mesh and X8 expanded steel mesh. Three types of core materials were investigated: conventional concrete,\nautoclaved aerated lightweight concrete brick, and recycled concrete. Two types of shear connections between the precast\npermanent reinforced mortar form and the core material were investigated namely; adhesive bonding layer between the two\nsurfaces, and mechanical shear connectors. The test specimens were tested as simple beams under three-point loadings on a span of\n1,800 mm. The behavior of the beams incorporating the permanent forms was compared to that of the control beams. The\nexperimental results showed that better crack resistance, high serviceability and ultimate loads, and good energy absorption could\nbe achieved by using the proposed beams which verifies the validity of using the proposed system. The theoretical results\ncompared well with the experimental ones....
Many bridges are subject to lateral damage for their girders due to impact by over-height vehicles collision. In this\nstudy, the optimum configurations of carbon fiber reinforced polymers (CFRP) laminates were investigated to repair the laterally\ndamaged prestressed concrete (PS) bridge girders. Experimental and analytical investigations were conducted to study the\nflexural behavior of 13 half-scale AASHTO type II PS girders under both static and fatigue loading. Lateral impact damage due\nto vehicle collision was simulated by sawing through the concrete of the bottom flange and slicing through one of the\nprestressing strands. The damaged concrete was repaired and CFRP systems (longitudinal soffit laminates and evenly spaced\ntransverse U-wraps) were applied to restore the original flexural capacity and mitigate debonding of soffit CFRP longitudinal\nlaminates. In addition to the static load tests for ten girders, three more girders were tested under fatigue loading cycles to\ninvestigate the behavior under simulated traffic conditions. Measurements of the applied load, the deflection at five different\nlocations, strains along the cross-section height at mid-span, and multiple strains longitudinally along the bottom soffit were\nrecorded. The study investigated and recommended the proper CFRP repair design in terms of the CFRP longitudinal layers and\nU-wrapping spacing to obtain flexural capacity improvement and desired failure modes for the repaired girders. Test results\nshowed that with proper detailing, CFRP systems can be designed to restore the lost flexural capacity, sustain the fatigue load\ncycles, and maintain the desired failure mode....
The use of carbon fibers (CF) and glass fibers (GF) were combined to strengthen concrete flexural members. In this\nstudy, data of tensile tests of 94 hybrid carbon-glass FRP sheets and 47 carbon and GF rovings or sheets were thoroughly\ninvestigated in terms of tensile behavior. Based on comparisons between the rule of mixtures and test data, positive hybrid effects\nwere identified for various (GF/CF) ratios. Unlike the rule of mixtures, the hybrid sheets with relatively low (GF/CF) ratios also\nproduced pseudo-ductility. From the calibrated results obtained from experiments, a new analytical model for the stressââ?¬â??strain\nrelationship of hybrid FRP sheets was proposed. Finally, the hybrid effects were verified by structural tests of concrete members\nstrengthened with hybrid FRP sheets and either carbon or glass FRP sheets....
In the present paper, a behavioral model is proposed for study of the individual contributions to shear capacity in shearcritical\nreinforced concrete members. On the basis of the relationship between shear and bending moment (V = dM/dx) in beams\nsubjected to combined shear and moment loads, the shear resistant mechanism is explicitly decoupled into the base componentsââ?¬â?\nbeam action and arch action. Then the overall behavior of a beam is explained in terms of the combination of these two base\ncomponents. The gross compatibility condition between the deformations associated with the two actions is formulated utilizing\nthe truss idealization together with some approximations. From this compatibility condition, the ratio of the shear contribution by\nthe tied arch action is determined. The performance of the model is examined by a comparison with the experimental data in\nliteratures. The results show that the proposed model can explain beam shear behavior in consistent way with clear physical\nsignificance....
This paper presents an analytical model to calibrate the tension stiffening effect of tensile reinforced concrete\nmembers. The tension stiffening behaviour is a primordial task in reinforced concrete mechanic field. In this model,\nthe stressââ?¬â??strain relationship of the tension stiffening effect described in the cracking range is proposed. The\napplication of the analytical expression for tensile reinforced concrete member aims principally to quantify the\ntension stiffening phenomenon in the cracking range. In this concern, a parametrical study is established, which\nconcerns the influence of concrete strength, reinforcement ratio, bar diameter and instantaneous properties of\nconcrete on the tension stiffening behaviour. The obtained results relative to the influence of different parameters\nof the analysis are shown and commented....
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