94 research outputs found
Flexural performance of reinforced concrete beams strengthened with prestressed near-surface-mounted FRP reinforcements
YesA numerical method for estimating the curvature, deflection and moment capacity of reinforced concrete beams strengthened with prestressed near-surface-mounted (NSM) FRP bars/strips is presented. A sectional analysis is carried out to predict the moment–curvature relationship from which beam deflections and moment capacity are then calculated. Based on the amount of FRP bars, different failure modes were identified, namely tensile rupture of prestressed FRP bars and concrete crushing before or after yielding of steel reinforcement. Comparisons between experimental results available in the literature and predicted curvature, moment capacity and deflection of reinforced concrete beams with prestressed NSM FRP reinforcements show good agreement. A parametric study concluded that higher prestressing levels improved the cracking and yielding loads, but decreased the beam ductility compared with beams strengthened with nonprestressed NSM FRP bars/strips
Experimental behaviour of RC beams shear strengthened with NSM CFRP laminates
The near-surface mounted (NSM) is one of the most recent techniques applied for the increase of the shear resistance of
reinforced concrete (RC) beams. This technique involves the installation of carbon fibre reinforcement polymers (CFRP) laminates into thin
slits open on the concrete cover of the elements to strengthen. The effectiveness of this technique for the shear strengthening of T crosssection
RC beams was assessed by experimental research. For this purpose, three inclinations of laminates were tested (45º, 60º and 90º) and,
for each inclination, three percentages of CFRP were applied in RC beams with a percentage of steel stirrups of 0.10% (qsw). The highest
percentage of laminates was designed to provide a maximum load similar to the reference RC beam, which was reinforced with a reinforcement
ratio of steel stirrups of 0.28% (qsw = 0.28%). For each percentage of laminates, a homologous RC beam strengthened with
unidirectional U-shaped CFRP wet lay-up sheets (discrete strips) applied according to the externally bonded reinforcement technique was
also tested, with the purpose of comparing the effectiveness of these two CFRP-strengthening techniques. To evaluate the influence of the
percentage of steel stirrups in the effectiveness of the NSM technique, some of the abovementioned CFRP configurations were also applied in
beams with qsw = 0.17%The authors wish to acknowledge the support provided by the 'Empreiteiros Casais', Degussa, S&P (R) and Secil (Unibetao, Braga). The study reported in this paper forms a part of the research program supported by FCT, PTDC/ECM/73099/2006
Recommended from our members
Cracking behavior and crack width predictions of FRP strengthened RC members under tension
This paper presents and discusses the experimental results of uniaxial tensile tests of fiber reinforced polymer externally strengthened reinforced concrete (FRP strengthened RC) prisms in terms of crack width and crack spacing. As a non-contact and material independent system for in-time measurement of displacement and strain, the digital image correlation (DIC) technique has been used in this study for investigating the evolution of strains and formation of cracks during uniaxial tensile tests. As a result, the cracks were measured precisely at any load stage.
The experimental results of tests performed by authors and other researchers on FRP strengthened RC members in tension are compared to prediction models from code provisions and guidelines (Eurocode 2 and fib 14), and their suitability are analyzed and discussed. The results show the dependence of the behavior and crack characteristics of FRP strengthened RC members to parameters such as wrapping scheme and FRP reinforcement ratios which are not included in design provisions for crack analysis. A new formulation for predicting crack width and spacing in FRP strengthened RC members, calibrated using the experimental results, has been proposed which considers all the main affecting parameters
Shear strengthening of continuous reinforced concrete T-beams using wire rope units
A simple unbonded-type shear strengthening technique for reinforced concrete beams using wire rope units is presented. Ten two-span reinforced concrete T-beams externally strengthened with wire rope units and an unstrengthened control beam were tested to failure, to explore the significance and shortcomings of the developed unbonded-type shear strengthening technique. The main parameters investigated were the type, amount and prestressing force of wire rope units. All beams tested failed, owing to significant diagonal cracks within the interior shear span. However, beams strengthened with closed type wire rope units exhibited more ductile failure than the unstrengthened, control beam or those strengthened with U-type wire rope units. The diagonal cracking load and ultimate shear capacity of beams with closed-type were linearly increased with the increase of vertical confinement stresses in concrete owing to the prestressing force in wire rope units, while those of beams with U-type were minimally influenced. It was also observed that average stresses in closed-type wire ropes crossing diagonal cracks at ultimate strength of beams tested were much higher than those in U-type wire ropes, showing better utilization in the former case. The shear capacity of beams with closed-type wire rope units is conservatively predicted using the equations of ACI 318-05, modified to account for the external wire rope units. A mechanism analysis based on the upper bound approach of the plasticity theory is also developed to assess the load capacity of beams tested. The predictions by the mechanism analysis for beams with closed-type wire rope units are in good agreement with test results and showed a coefficient of variation slightly less than the modified ACI 318-05 equations. However, the modified ACI 318-05 equations are more conservative and simpler to use for design purposes
Shear strengthening of full-scale RC T-beams using textile-reinforced mortar and textile-based anchors
This paper presents a study on the effectiveness of TRM jacketing in shear strengthening of full-scale reinforced concrete (RC) T-beams focussing on the behaviour of a novel end-anchorage system comprising textile-based anchors. The parameters examined in this study include: (a) the use of textile-based anchors as end-anchorage system of TRM U-jackets; (b) the number of TRM layers; (c) the textile properties (material, geometry); and (d) the strengthening system, namely textile-reinforced mortar (TRM) jacketing and fibre-reinforced polymer (FRP) jacketing for the case without anchors. In total, 11 full-scale RC T-beams were constructed and tested as simply supported in three-point bending. The results showed that: (a) The use of textile-based anchors increases dramatically the effectiveness of TRM U-jackets; (b) increasing the number of layers in non-anchored jackets results in an almost proportional increase of the shear capacity, whereas the failure mode is altered; (c) the use of different textile geometries with the same reinforcement ratio in non-anchored jackets result in practically equal capacity increase; (d) TRM jackets can be as effective as FRP jackets in increasing the shear capacity of full-scale RC T-beams. Finally, a simple design model is proposed to calculate the contribution of anchored TRM jackets to the shear capacity of RC T-beams
CFRP flexural and shear strengthening technique for RC beams : experimental and numerical research
Near surface mounted (NSM) technique has proved to be a very effective
technique for the flexural strengthening of RC beams. Due to the relatively small
thickness of the concrete cover that several beams present, cutting the bottom arm of
steel stirrups for the installation of NSM laminates might be a possible strategy, whose
implications on the beam’s load carrying capacity need to be assessed. When steel
stirrups are cut, however, the shear resistance can be a concern. This also happens
when a strengthening intervention is carried out to increase the flexural resistance of a
beam, since in certain cases it is also necessary to increase the shear resistance in order
to avoid the occurrence of brittle shear failure. The present work assesses the
effectiveness of a technique that aims to increase both the flexural and shear resistance
of RC beams that have the bottom arm of the steel stirrups cut for the application of
NSM laminates. This assessment is performed by experimental and numerical
research. The main results of the experimental program are presented and analyzed,
and the innovative aspects of a constitutive model implemented in a computer program
are described, being their virtues and deficiencies discussed.The study reported in this paper forms a part of the research program "CUTINEMO - Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures" supported by FCT, PTDC/ECM/73099/2006. The authors wish to acknowledge the support also provided by the S&P, Casais and Artecanter Companies. The second Author acknowledges the grant under the aforementioned research project. The third author acknowledges the financial support of FCT, PhD Grant number SFRH/BD/23326/2005
Flexural strengthening of RC continuous slab strips using NSM CFRP laminates
To assess the effectiveness of the near surface mounted (NSM) technique, in terms of load carrying and moment
redistribution capacities, for the flexural strengthening of continuous reinforced concrete (RC) slabs, an
experimental program was carried out. The experimental program is composed of three series of three slab strips of
two equal span length, in order to verify the possibility of increasing the negative (at the intermediate support
region) resisting bending moment in 25% and 50% and maintaining moment redistribution levels of 15%, 30% and
45%. Though the flexural resistance of the NSM strengthened sections has exceeded the target values, the moment
redistribution was relatively low, and the increase of the load carrying capacity of the strengthened slabs did not
exceed 25%. This experimental program is analyzed to highlight the possibilities of NSM technique for statically
indeterminate RC slabs in terms of flexural strengthening effectiveness, moment redistribution and ductility
performance. Using a FEM-based computer program, which predictive performance was appraised using the
obtained experimental results, a high effective NSM flexural strengthening strategy is proposed, capable of
enhancing the slab’s load carrying capacity and maintaining high levels of ductility.The study reported in this paper forms a part of the research program "CUTINEMO - Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures" supported by FCT, PTDC/ECM/73099/2006. The authors wish to acknowledge the support also provided by the S&P, Casais and Artecanter Companies. The first Author acknowledges the financial support of National Council for Scientific and Technological Development (CNPq) - Brazil, Ph.D. Grant no. 200953/2007-9. The second Author wishes to acknowledge the support provided by FCT, by means of the SFRH/BSAB/818/2008 and SFRH/BSAB/913/2009 sabbatical grants
- …