International Concrete Abstracts Portal

A shear retrofitting method for reinforced concrete (RC) beams has beendeveloped that uses external CFRP straps to provide additional shear capacity.Research has been undertaken to develop an installation technique that allows theCFRP strap to encompass the full depth of the beam, without requiring access to the topsurface of the beam. The current testing scheme investigates the durability of the CFRPstrap system using the new installation technique. A long-term load test was conductedon a RC T-beam which indicated that the straps continued to provide shear capacityafter 7 months under a load equivalent to 80% of the ultimate capacity of the retrofittedbeam. A cyclic test conducted on another similar T-beam specimen demonstrated thatafter 1,000,000 cycles, under a load that varied between 0.5 and 0.8 times the ultimateretrofitted beam capacity, the straps continued to provide effective shearenhancement.

In the fall of 2002, a two story parking garage in Bloomington, Indiana, builtwith precast prestrestressed concrete (PC) double-T beams, was decommissioned dueto a need for increased parking-space. This led to the opportunity of investigating theflexural performance of the PC double-T beams, upgraded in the positive momentregion with steel reinforced polymer (SRP) composite materials, representing the firstcase study where this material has been applied in the field. SRP makes use of high-strength steel cords embedded in an epoxy resin. This paper reports on the test resultsto failure of three beams: a control specimen, a beam strengthened with one ply of SRPand a third beam strengthened with two plies of SRP anchored at both ends with SRP U-wraps. Results showed that SRP can significantly improve both flexural capacity andenhance pseudo-ductility.

This paper deals with a new material for external reinforcement: Steel WireReinforced Polymer (SWRP). It consists of thin high-strength steel fibres embedded in apolymer laminate. This innovative material combines the advantages of steel platesand CFRP, which are already used today. The material cost of SWRP is relatively low,and the laminate is quite flexible. In the feasibility part, the practical use of SWRP isstudied. Further, the available design model for externally bonded reinforcement forconcrete elements is confronted with the results of an experimental program, carriedout at the Reyntjens Laboratory of KULeuven. The model is adapted accordingly.

This study presents the results of experiments performed on RC (ReinforcedConcrete) beams strengthened with NSM(Near Surface Mounted) reinforcement. A totalof 8 specimens have been tested. The specimens can be classified into EBR(ExternallyBonded Reinforcement) specimens and NSM(Near Surface Mounted) reinforcementsspecimens. Two of NSM specimens were strengthened with 12 mechanical interlockinggrooves with a width of 20 mm and spacing of 200 mm in order to prevent debondingfailure of the CFRP(Carbon Fiber Reinforced Polymer) reinforcement. Experimentalresults revealed that NSM specimens used CFRP reinforcements more efficiently thanthe EBR specimens, but debonding failure between adhesive and concrete occurred.This showed that, similarly to EBR specimens, NSM specimens also requiredcountermeasures against debonding failure. Failure mode of NSM specimens addedwith mechanical interlocking grooves failed by rupture of CFRP rod and strip. Themeasured ultimate load showed an increase of 15% compared with the common NSMspecimens. The application of mechanical interlocking grooves made it possible toavoid debonding failure and to enhance strengthening performance.

To assess the strengthening efficiency of near-surface mounted (NSM)carbon fiber reinforced polymer (CFRP) laminates according to their groove depth anddisposition, 4-point bending tests were performed on 4 specimens strengthened withNSM CFRP. A structural model for the finite element method (FEM) able to simulateaccurately the experimental results was determined to analyze the strengtheningefficiency of the NSM technique analytically. Applying the model, parametric analysiswas performed considering the groove depth and spacing of CFRP laminates. Analyticalstudy on the groove depth revealed the existence of a critical depth beyond which theincrease of the ultimate load becomes imperceptible. In other words, this means thatthere exists a limit of strengthening efficiency where it remains in a definite level evenif the groove depth is increased. Analytical results regard to the spacing of the CFRPlaminates showed that comparatively smooth fluctuations of the ultimate load wereproduced by the variation of the spacing and the presence of an optimal spacing rangefor which relatively better strengthening efficiency can be obtained. Particularly, aspacing preventing the interference between adjacent CFRP laminates and theinfluence of the concrete cover at the edges as well as allowing the CFRP laminates tobehave independently was derived. Using the analytical results, various strengtheningschemes could be established with different numbers of CFRP laminates, groove depthsand dispositions of the reinforcements for a determinate quantity of reinforcements.