International Concrete Abstracts Portal

The linear characteristics of fiber reinforced polymers (FRP) up to failure and their relatively low elastic modulus and strain at ultimate has raised concerns with structural engineers regarding their use as reinforcement for flexural members. Based on a nonlinear finite element analysis and testing of a full-scale model at the University of Manitoba, Canada, design guidelines on the use of glass and carbon fiber reinforced polymers (GFRP and CFRP) as reinforcement for bridge deck slabs are proposed. The accuracy of the nonlinear finite element model is demonstrated by comparing the predicted behavior to test results of two models. The influence of the degree of edge restraint, percentage of reinforcement of CFRP and GFRP, type of reinforcement and presence of top reinforcement on the structural behavior and mode of failure of continuous concrete bridge decks is discussed. Based on serviceability and ultimate capacity requirements, reinforcement ratios of CFRP and GFRP for typical bridge deck slabs are recommended.

FRP composite materials have mechanical properties which are beneficial and advantageous for design of bridges. The application of these FRP composite materials are currently being used for demonstration projects for repair/retrofit/ rehabilitation of existing bridges and a few for new installations. The future applications of these materials will depend upon the development of the appropriate material/product standards and performance criteria for special proprietary products. The need for coordinated research projects is outlined for the development of the necessary standards and design requirements. Only with proper documentation will the FRP composites become another material available to the construction marketplace for bridges. An outline for the required research projects is presented for the FRP composites for bridge construction.

Twenty cantilever type specimens and four beam specimens were tested to evaluate the bond behavior in reinforced concrete members confined with carbon or aramid FRP sheets. The main test variables were the vertical cover depth, the diameter and the number of longitudinal bars, and the type and the amount of FRP sheets. The test results showed that the confined specimens had higher bond strength, larger peak load slip displacement and lesser bond degradation after the peak than their unconfined prototype counterparts. Based on the test results, an equation was developed to predict the increase in bond strength due to the FRP sheet confinement. That increase was expressed similarly to that due to transverse steel reinforcement except that the elastic modulus of the FRP sheet was important but the number of longitudinal bars was not. The proposed equation was validated using results of column specimens tested in other research institutes and by cantilever and beam specimens tested by authors. It was proved that as long as the bond strength of an unconfined prototype specimen is evaluated properly, the total bond strength of confined specimens can be predicted accurately using the proposed equation although the limitations of the proposed equation still need to be clarified.

In this paper results of an experimental investigation on bond between a glass fiber reinforced plastic (GFRP) rebar and concrete are presented and discussed. Rebars used in tests are the FRP C-BarTM produced by Marshall Industries Composites, Inc. Bond tests were carried out by using a test machine obtained from a modification of the standard scheme of the beam-test and were conducted on prismatic concrete specimens within which a #4 Grade B E-Glass C-Bar was embedded: the embedment length was ranging from 5 to 30 times the bar diameter, thus obtaining different test arrangements. Bond-slip relationships were obtained and bond mechanisms discussed. Furthermore, values of elastic modulus and tensile strength of rebar were evaluated. Finally, a bond-slip constitutive law obtained by means of a system identification procedure is presented. Numerical simulations of bond tests have been performed by using such bond-slip relationship and the obtained bond-slip curves have been compared with the experimental ones.

One of the major disadvantages of the plate bonding technology is the premature and brittle debonding failure of the bonded plate. It has been assumed, quite logically, that the stress concentration at the plate end is the primary cause of such premature plate debonding failure. However, there is no direct evidence of the validity of these stresses as to whether the predicted stresses agree with the experimental data or not. Also there is concern if they can form the basis and criteria for the design and prevention of debonding failures. This paper presents a critical analysis of the calculated peak shear and normal stress values at the plate end using Roberts’ approximate model, and derived from a wide range of published data involving steel, glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) plates. It is shown that these calculated stresses are far too high, and cover unacceptably wide range of values, without any consistent pattern of variation with the plate stiffness. It is clear that the peak stresses are influenced by other parameters which are not taken into account in the approximate model used in the calculations. The wide range of the peak stresses obtained from a large number of tests seems to indicate that these stresses cannot form a reliable basis to explain or design the prevention of premature plate debonding failures.