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

The 16th International Symposium on Fiber-Reinforced Polymer (FRP) Reinforcement for Concrete Structures (FRPRCS-16) was organized by ACI Committee 440 (Fiber-Reinforced Polymer Reinforcement) and held on March 23 and 24, 2024, at the ACI Spring 2024 Convention in New Orleans, LA. FRPRCS-16 gathers researchers, practitioners, owners, and manufacturers from the United States and abroad, involved in the use of FRPs as reinforcement for concrete and masonry structures, both for new construction and for strengthening and rehabilitation of existing structures. FRPRCS is the longest running conference series on the application of FRP in civil construction, commencing in Vancouver, BC, in 1993. FRPRCS has been one of the two official conference series of the International Institute for FRP in Construction (IIFC) since 2018 (the other is the CICE series). These conference series rotate between Europe, Asia, and the Americas, with alternating years between CICE and FRPRCS. The ACI convention has previously cosponsored the FRPRCS symposium in Anaheim (2017), Tampa (2011), Kansas City (2005), and Baltimore (1999). This Special Publication contains a total of 52 peer-reviewed technical manuscripts from 20 different countries from around the world. Papers are organized in the following topics: (1) FRP Bond and Anchorage in Concrete Structures; (2) Strengthening of Concrete Structures using FRP Systems; (3) FRP Materials, Properties, Tests and Standards; (4) Emerging FRP Systems and Successful Project Applications; (5) FRP-Reinforced Concrete Structures; (6) Advances in FRP Applications in Masonry Structures; (7) Seismic Resistance of FRP-Reinforced/Strengthened Concrete Structures; (8) Behavior of Prestressed Concrete Structures; (9) FRP Use in column Applications; (10) Effect of Extreme Events on FRP-Reinforced/Strengthened Structures; (11) Durability of FRP Systems; and (12) Advanced Analysis of FRP Reinforced Concrete Structures. The breadth and depth of the knowledge presented in these papers is clear evidence of the maturity of the field of composite materials in civil infrastructure. The ACI Committee 440 is witness to this evolution, with its first published ACI CODE-440.11, “Building Code Requirements for Structural Concrete with Glass Fiber Reinforced Polymer (CFRP) Bars,” published in 2022. A second code document on fiber reinforced polymer for repair and rehabilitation of concrete is under development. The publication of the sixteenth volume in the symposium series could not have occurred without the support and dedication of many individuals. The editors would like to recognize the authors who diligently submitted their original papers; the reviewers, many of them members of ACI Committee 440, who provided critical review and direction to improve these papers; ACI editorial staff who guided the publication process; and the support of the American Concrete Institute (ACI) and the International Institute for FRP in Construction (IIFC) during the many months of preparation for the Symposium.

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.

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.

This study numerically investigates the long-term effectiveness of using externally bonded fiber-reinforced polymer (FRP) plates as a strengthening technique for reinforced concrete (RC) beams. A two-dimensional finite element model (FEM) that can accurately predict the flexural behavior of FRP strengthened RC beams, is developed. Weathering exposure time of 0.0, 15.5, 35, and 75 years were considered. In total, 28 different concrete beams were modelled using the developed FEM. The results show that prolonged exposure to natural weathering can cause premature FRP debonding, even before reaching the yielding load. The ultimate load capacity, midspan deflection, and ductility of strengthened RC beams can be reduced by up to 38%, 62%, and 100%, respectively. In addition, the findings raised concerns about the applicability of the ACI 440.2R-17 provisions for calculating the design flexural strength of FRP strengthened RC beams with prolonged exposure to natural weathering. To ensure a safe design for strengthened beams with FRP debonding or concrete crushing failure modes, this paper recommends an additional reduction factor ranging from 0.8 to 0.9. Furthermore, periodic inspection using non-destructive testing and FRP anchorage system are highly recommended for both existing and new applications of FRP in structures.