International Concrete Abstracts Portal

New research funded by the ACI Foundation developed and tested retrofit techniques for diaphragms using externally bonded fiber-reinforced polymer (FRP). Key findings from the research are being translated into guidance on how to establish the effective FRP design strain and the nominal shear strength contribution of the FRP. The recommendations also address the use of intermediate and end FRP anchors and limitations on the clear spacing between sheets

Three bridge barriers were tested under pseudo-static loading to assess the effectiveness of a dowelling repair technique for restoring the capacity of damaged glass fiber-reinforced polymer (GFRP) reinforced systems. Barriers were 1500 mm (59.1 in.) wide and tested with an overhang of 1500 mm (59.1 in.). One barrier was entirely reinforced with steel reinforcement with the layout and geometry common in Alberta, Canada for highway applications. A second barrier replaced all steel reinforcement with GFRP bars. The third barrier simulates repair where the barrier is damaged and needs to be replaced by removing the barrier, drilling holes, and using epoxy to dowel GFRP bars into the deck. All barriers failed by concrete splitting at the barrier/deck interface which is attributed to the complex interaction of stresses from the barrier wall and overhang. The steel reinforced barrier was strongest but had slightly lower energy dissipation than the GFRP reinforced barriers. The repaired GFRP reinforced barrier had very similar response to the baseline GFRP reinforced barrier but reached a slightly larger capacity. Previously completed finite element models showed similar general responses and failure modes but larger stiffnesses and strengths than the tests which requires further investigation.

Fiber reinforced polymers (FRP) are commonly used to seismically retrofit concrete structural walls. Limited design guidance for the seismic application of FRP strengthening is currently available to designers in guidelines such as ACI PRC-440.2-17 or standards like ASCE/SEI 41-17. This paper presents the description and results of an experimental effort to investigate the effectiveness of FRP retrofitted concrete walls. The specimen wall thickness was either 6 in or 12 in, which represents a typical range of wall thickness seen in older buildings. To better reflect the most common applications seen in the industry, the walls were retrofitted with FRP, and anchored with fiber anchors only on one side of the wall. The study demonstrates that the effectiveness of FRP is reduced as the wall thickness increases and that the FRP must be anchored to the wall for any tangible benefit. The results are used to assess the current provisions in ACI PRC-440.2-17 and ASCE/SEI 41-17. It is apparent that additional testing is required to better understand the complexities involved in the FRP strengthening of shear walls and such testing is scheduled for the near future.

The application of fiber-reinforced polymer (FRP) jacketing for confinement may not always be feasible, particularly in cases where adjacent elements obstruct the structural member and prevent wrapping. To address this issue, the utilization of FRP laminate and spike anchors has been proven as an alternative solution. This study focuses on proposing a design methodology for this particular application. A stress-strain model was developed to assess the behavior of concrete prisms confined with FRP laminates and spike anchors under axial compression. The model adopts a bi-parabola stress-strain curve, with the coefficients derived from previously published experimental data on concrete prisms confined using this solution. The comparison between the analytical and tested stress-strain curves yielded a coefficient of determination (R2) averaging at 0.96, demonstrating the effectiveness of the bi-parabola model in describing the tested stress-strain responses.

The study delves into modeling the interface between Fiber-Reinforced Polymer (FRP) and concrete, with a specific emphasis on simulating the gradual deterioration of bond strength. A model rooted in continuum damage mechanics is integrated with an empirically derived relationship to address interfacial shear failure. Material models are defined for the concrete, the externally bonded FRP reinforcement, and the adhesive layer. These material models are implemented in finite element simulations, replicating experimental setups widely used to investigate the FRP-concrete interface. Key results are reported and discussed. More precisely, the numerically obtained load-slip relationships for the interface and visualizations of the damaged zones in concrete are provided. The numerical results are in close agreement with existing experimental data. The finite element analyses suggest that concrete degradation is not limited to the areas near the adhesive joint. This implies that the adhesive joint could influence the overall behavior of the structural elements, even when debonding failures are prevented by anchorage devices.