International Concrete Abstracts Portal

This paper presents a closed-form procedure to evaluate the shear strength contribution provided to a Reinforced Concrete (RC) beam by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips. This procedure is based on the evaluation of: a) the constitutive law of the average-available-bond-length NSM FRP strip effectively crossing the shear crack and b) the maximum effective capacity it can attain during the loading process of the strengthened beam. Once the constitutive law of the average-available-bond-length NSM strip is reliably known, its maximum effective capacity can be determined by imposing a coherent kinematic mechanism. The self-contained and ready-to-implement set of analytical equations and logical operations is presented along with the main underlying physical-mechanical principles and assumptions. The formulation proposed is appraised against some of the most recent experimental results and its predictions are also compared with those obtained by a recently developed more sophisticated model.

Retrofitting of existing concrete structures and civil infrastructure has become necessary due to environmental degradation, changes in usage and heavier loading conditions. The use of advanced carbon fiber composite materials (CFRP) as externally bonded reinforcement has found wide application in recent years and has proven to be an effective method of improving the structural performance of existing structures. A good example of this is the West Gate Bridge in Melbourne, Australia for which the following case study is presented. Key innovations in CFRP technology developed specifically for this project have been described in the areas of design and testing of CFRP anchorage technology, involving the utilization of unidirectional and bidirectional fabrics together with mechanical substrate strengthening. These have all resulted in increases in material utilizations and enabled successful transfer of combined shear and torsional forces. Key aspects of the detailing, application, quality control and monitoring program adopted in the project are also presented along with the key aspects which resulted in the successful execution of this world class project.

Debonding of fibre-reinforced polymer (FRP) composites externally bonded to reinforced concrete (RC) structural members can severely limit the effectiveness of the FRP strengthening. Anchorage of the FRP with anchors made from fibre sheets (i.e FRP anchors) is an effective means to increase its usable strain (and strength). This paper in turn reports the results of tests on one-way spanning RC slabs strengthened in flexure with FRP composites and anchored with FRP anchors. The tests reveal the strategic use of different types and positions of FRP anchors to increase the strength and deflection capacity of the strengthened slabs by up to 30 % and 110 %, respectively, above that of the unanchored but strengthened control slab. FRP anchors of greater strength placed closer to the peak bending moment region were found to be most beneficial in addition to closer spaced anchors of lesser fibre content in the low bending moment region.

Carbon Fiber Reinforced Polymer (CFRP) composite fabrics have been used to provide compression strengthening of Reinforced Concrete (RC) columns and bridge piers as well as tension strengthening of RC beams and slabs. Based on the literature review, however, it has been found that the combined tension and compression strengthening of RC structural members have not yet been fully explored. To further understand the structural behavior of various RC structural members strengthened by CFRP composite fabrics using both tension and compression strengthening, this paper will analytically and experimentally investigate the load – deformation behavior of RC beams and biaxially loaded RC slender columns using both tension and compression strengthening technique by CFRP composite fabrics. The computer methods used in this study are then compared with the experimental test results to verify the behavior of tested beams and columns. In this study, different wrapping methods using the CFRP composite fabrics are applied. Test results show that the RC members strengthened with both longitudinal and transverse fabrics (tension and compression strengthening) have achieved the best flexural performance and ductility of the repaired structural members.

Two types of arrangements of NSM CFRP laminates for the flexural strengthening of continuous RC slabs were investigated, one with CFRP laminates exclusively applied in the intermediate support, H series (hogging region), and the other with laminates applied in both the hogging and sagging regions (HS series). In the H series the increase of load carrying capacity was limited to 10% (for a target value of 25%) and 17% (for a target value of 50%), and the moment redistribution capacity () did not attain the target value (30%) and has decreased with the increase of the CFRP strengthening ratio. In the HS series the increase of load carrying capacity has exceeded the target value (25%) and the moment redistribution capacity was not significantly affected. For the HS series the flexural strengthening effectiveness was limited by the detachment of the concrete cover that includes the laminates, at the hogging region.