International Concrete Abstracts Portal

The paper deals with the results of an experimental program aimed at the investigation of the bonding behavior of different types of FRP materials for strengthening: externally bonded carbon (EBR) plates, and bars or strips externally applied according to the Near Surface Mounted (NSM) technique. The overall experimental program consists of 18 bond tests on concrete specimens strengthened with EBR carbon plates and of 24 bond tests on concrete specimens strengthened with NSM systems (carbon, basalt and glass bars and carbon strips). The performances of each reinforcement system are presented, discussed and compared in terms of debonding load, load - slip relationship, and strain distribution; the failure mode of each system is also analyzed. The results of the experimental program allow a comparison of the effectiveness of the various EBR and NSM strengthening systems tested and evidence of some differences in the bond behavior.

This paper presents a finite element (FE) modeling method for predicting the IC debonding failure when the FRP/concrete interface is subjected to coupled pull-out (shear) and push-off (dowel) actions. Damaged plasticity model was used to simulate the behavior of concrete close to FRP/concrete interface. A thin damage band exposed to mixed-mode loading condition was modeled separately along the FRP-concrete interface. Cohesive elements were used to model the FRP/concrete interface. A sensitivity analysis was performed to find the appropriate damaged band dimensions, bending stiffness of FRP, and tensile strength of concrete for the model. The numerical results were validated by the experimental data. It was found in this research that the thickness of damage band was not a key parameter when Mode I loading dominated the debonding failure, FRP flexural stiffness had significant effect on behaviors of the strengthened beams, and the concrete tensile strength itself cannot be used as the unique failure criterion for predicting debonding failure.

Based on an analysis of the experimental results of a proposed bond test method, significant differences are shown to exist between the local FRP bond stress-slip relationships in the uncracked anchorage regions and in the regions between cracks. The proposed method simulates the bond behavior between the flexural cracks and anchorage regions of a flexurally FRP-strengthened RC beam. The boundary conditions, including the presence of cracks and steel, are shown to have significant effects on the local bond stress-slip models. The results showed that, at the same force, the bond stresses in the regions between cracks were lower than in regions outside the cracks, so the debonding formed in the anchorage regions. The local bond stress-slip models in the anchorage regions can be obtained from the conventional bond test methods but these do not mimic the conditions between the cracks.

Adhesively bonded FRP plate on the tension face of RC beams and slabs increases their flexural strength. The behaviour of the strengthened structure depends on the robustness of the FRP-RC interface bond. Correct modelling of this interface bond behaviour is very important to understand and characterize the common intermediate crack-induced (IC) debonding failure. Existing literature based on simple pull-off test is inadequate to fully analyse this failure due to the differences in the mechanics of failure. This paper considers axial forces, transverse shear forces and bending moments in the adherends of the bonded joint and provides solutions for the different states of the interface experienced using a linearly softening bond-slip model. The inclusion of bending and shear deformations introduces difficulties in relating the applied loading and the interfacial deformation but they are overcome in this study through a section analysis with partial interaction and a closed-form solution is obtained.

This research investigated the development and characterization of different discrete fiber-reinforced polyurea systems for infrastructure applications. The behavior of various systems consisting of several polyureas with different fiber configurations was evaluated. Polyurea coating systems were previously evaluated for blast mitigation and impact resistance, and showed to be adequate in containing debris scatter from blast and impact. The purpose of further testing was an effort to develop a polyurea system for multi-hazard and/or repair-retrofit applications. The addition of fiber to a polymer coating provides improved stiffness and strength to the composite system while the polyurea base material provides ductility. Coupon tensile testing was conducted to determine the material mechanical properties in this study. The two parameters that were varied throughout testing were fiber volume fraction and fiber length. E-Glass fiber was used during specimen fabrication. Several optimal composite configurations of polyurea and fiber resulted from this coupon testing.