International Concrete Abstracts Portal

This paper presents an analytical investigation conducted to study theflexural behavior of reinforced concrete beams strengthened with various Near-SurfaceMounted (NSM) Fiber-Reinforced Polymers (FRP) reinforcements. The materials used inthis investigation included carbon-fiber-reinforced-polymer (CFRP) rebars and strips,and glass fiber-reinforced-polymer (GFRP) rebars and strips. The analysis included theeffects of strengthening on the serviceability and ultimate limit states as well the effectof tension stiffening. The effectiveness of NSM FRP rebars and strips was examined andcompared to externally bonded (EB) FRP strips and sheets using the same material typeand axial stiffness. Results from the analytical models were compared with thoseobtained from experimental studies. The analytical results agree very well with thoseobtained from the experimental results. It was found that the analytical model couldeffectively simulate the behaviour of the reinforced concrete beams strengthened withvarious NSM FRP and EB FRP reinforcements. Using the same axial stiffness of FRP tostrengthen reinforced concrete beams, the beams strengthened with NSM FRPreinforcement achieved higher ultimate load than beams strengthened with EB FRPreinforcement. This result is due to the high utilization of the tensile strength of the FRPreinforcement.

This paper presents the application of a new generation of externallybonded composite material in flexural strengthening of reinforced concrete beams. Thesteel reinforced polymer (SRP) composite consists of high-carbon steel unidirectionalHardwire® fabrics embedded in epoxy resin, and offers high strength and stiffnesscharacteristics at a reasonable cost. In this paper, the mechanical properties of SRP areevaluated and its application in flexural strengthening of RC beams is investigated. Sixbeams have been tested in three-point bending to study the effect of SRP retrofitting onflexural behavior, failure modes, and crack patterns. Test parameters include variationof the width of SRP sheets and the use of SRP U-wraps to prevent premature failurecaused by delamination of the longitudinal sheet. Significant increase in flexuralcapacity, up to 53%, and pseudo-ductile failure modes were observed in SRP-strengthened beams. Failure was governed primarily by concrete cover delamination atthe ends of SRP sheets or concrete crushing. The U-wraps improved flexural stiffness bymeans of controlling diagonal cracking and providing anchorages to the longitudinalSRP sheets, which reduced their slip. Shear stress concentrations near cut-off points ofSRP sheets have also been investigated. An analytical model was used to predict thenominal flexural strength of SRP-strengthened beams.

The FRP system is a good alternative of the traditional shear strengtheningtechnique. This study evaluates the shear strengthening effects on the reinforcedconcrete beams strengthened with varying types of FRP materials, CFRP, CFS and GFRP.The entire strengthened specimens were failed in the mode of brittle shear failure withdebonding of the FRP materials. The shear capacities were improved mostly by morethan 54%. The different types of the strengthening materials did not yield a noticeabledifference in the shear strengthening effect. The orientation of the fibers, however,was found to be an important factor. With a 45° fiber orientation, greater strengtheningeffect and better control on the shear crack propagation were observed. A numericalmodel predicting the shear capacity of the shear-strengthened beams was suggestedalong with the strength efficiency factor from the test results. The predictions were ingood agreement with the test results.

Externally bonded FRP has been established as the technology of choice tostrengthen RC beams. Researchers and practicing engineers have recently developeddesign guidelines for FRP strengthening. However, the current state of the art flexuraldesign procedure suggests an iterative process. No earlier efforts have been devotedto develop direct strength design equations on the failure mode of FRP rupture that canfacilitate structural calculations. This study develops exact and approximate sets ofclosed form equations to design singly and doubly reinforced strengthened rectangularsections that fail by FRP rupture. Comparisons with reported experimental strength dataindicate excellent agreement. A comprehensive parametric study has yielded a simplelinear regression equation that has an almost perfect statistical correlation and isequally applicable in cases of analysis and design. Comparison between the exactsolution and the regression equation confirms the accuracy of the latter. The latter isused in a design example.

Five square columns were constructed to model shear-deficient columnsand tested under constant axial compression and reversed cyclic lateral load,simultaneously. The retrofitting scheme consisted of wrapping the column along its endparts, i.e. around the plastic hinge area, by use of FRP in the form of three-centimeterwide belts. Both carbon and aramid/epoxy belts were used in this study. Moreover, fortwo of the specimens, the FRP belts were prestressed before applying the lateral loadto the columns, and thereby, the effects of active confinement in addition to passiveconfinement were investigated. The proposed prestressing technique is an innovativemethod and can be applied manually. According to test results, while the originalcolumn exhibited brittle shear failure, all retrofitted columns developed ductile flexuralresponse. Despite the different initial confining pressures, yet the same lateralstiffness of the confining device, the deformation ductility of all retrofitted columns wassimilar.