International Concrete Abstracts Portal

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.

Most of the recent research on the bond characteristics of the concrete-FRP interface involves short-term behavior which may not be indicative of bond behavior following sustained forces on the adhesive joint, particularly in the case of ambient-curing adhesives which can take weeks to reach their full strength capability. The objective of the research effort is to investigate the effects of sustained loads and various temperatures on the bond behavior of FRP sheets bonded to concrete. The approach involves experiments and numerical analysis. The model was parameterized with experiments on the concrete, FRP, interface, and epoxy. Good correlation was seen between the numerical simulations and pull-off experiments. Parametric studies shed light on the influence of temperature, epoxy modulus, and epoxy thickness on the redistribution of interfacial shear stress during sustained loading. This investigation confirms the hypothesis that interfacial stress redistribution can occur due to sustained load and elevated temperature and its effect can be significant.

This paper presents a test methodology that can be used to evaluate the durability of bonded CFRP systems used to repair and strengthen concrete beams. The test specimen is a 100 x 100 x 350 mm (4 in. x 4 in. x 14 in.) beam, tested in three-point bending (flexure) on a 300 mm (12 in.) span length. Two conditioning protocols are proposed depending on the anticipated exposure. For unprotected service conditions specimens are submerged in 60C (140F) water for 60 days. For protected service conditions, the specimens are exposed to 100% relative humidity at 60C (140F) for 60 days. Although the test method will not give a direct service life prediction, the testing presented in this paper indicate that the procedures were capable of differentiating a wide range of responses of deterioration of CFRP systems subjected to the test procedures.

The behavior of seventeen RC beams strengthened with FRP laminates mechanically fastened to their tension soffits with concrete anchor bolts is presented. The beams were tested in four-point bending on a 7.5 foot (2286 mm) span. Bolt diameter and spacing and FRP strip length were varied. The beams exhibited increases in yield moment ranging from 12.5% to 46%, and increases in ultimate moment from 30% to 75%, while displacement ductility ratios were 75% of values from un-strengthened control beams. The number of fasteners in the shear span had a greater impact on ultimate strength than did FRP strip length. Terminating the FRP strips in regions of larger bending moment resulted in an unexpected change of failure mode from concrete compression to shear. Measured strains in the FRP were less than those calculated assuming fully bonded conditions.