International Concrete Abstracts Portal

The release of ACI 440.11-22 building design code for concrete structures reinforced with GFRP bars comes with several challenges at various fronts. One such challenge is tackled in this paper which is the development of limit interaction diagrams for elliptical bridge columns reinforced with GFRP bars under biaxial bending plus axial compression/tension. This type of columns requires special considerations at all levels. This paper depicts the various formulations encountered herein in a detailed treatment highlighting the critical steps to build an efficient analysis algorithm. The formulation is implemented into a user-friendly software developed using object-oriented programming, namely the C# programming language. The robustness of the formulation is tested by comparing interaction diagrams of elliptical sections to those of corresponding rectangular sections. The significance of an ACI code comment requiring bar orientation being considered for circular sections with less than 8 bars is also examined in this paper. This paper also tests the ACI recommendation to neglect GFRP action in compression. Results indicate reasonable similarity among interaction diagrams of elliptical and rectangular sections leading to the conclusion that the formulation presented herein provides an accurate tool to analyze elliptical sections.

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.

This paper presents a new methodology for characterizing the failure mode of structural walls reinforced with glass fiber reinforced polymer (GFRP) bars. An analytical model is used to derive a non-dimensional failure determinant function, which is validated against existing test results. The function involves geometric attributes (wall length, wall height, and boundary element size), reinforcement ratios (horizontal and vertical), and material properties (compressive strength of concrete and tensile strength of GFRP bars). According to the determinant function, structural walls fail in flexure when a high aspect ratio is associated with a relatively low reinforcement ratio in the boundary element. The proposed methodology and design recommendations provide valuable guidance for practitioners dealing with GFRP-reinforced concrete walls.

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 seismic performance of reinforced concrete (RC) structures relies on their ability to dissipate earthquake-induced energy through hysteric behavior. Ductility, energy dissipation, and viscous damping are commonly used as performance indicators for steel-RC seismic force-resisting systems (SFRSs). However, while several previous studies have proposed energy-based indices to assess energy dissipation and damping of steel-RC SFRSs, there is a lack of research on fiber-reinforced polymer (FRP)-RC structures. This study examines the applicability of the existing energy dissipation and damping models developed for steel-RC columns to glass FRP (GFRP)-RC ones, where the relationships between energy indices and equivalent viscous damping versus displacement ductility were analyzed for GFRP-RC circular columns from the literature. In addition, prediction models were derived to estimate energy dissipation, viscous damping, and stiffness degradation of such types of columns. It was concluded that similar lower limit values for energy-based ductility parameters of steel-RC columns can be applied to GFRP-RC circular columns, whereas the minimum value and analytical models for the equivalent viscous damping ratio developed for steel-RC columns are not applicable. The derived models for energy indices, viscous damping, and stiffness degradation had an R2 factor of up to 0.99, 0.7, and 0.83, respectively. These findings contribute to the development of seismic design provisions for GFRP-RC structures, addressing the limitations in current codes and standards.