International Concrete Abstracts Portal

This paper presents experimental and theoretical investigations on the residual tensile and bond response of polypara-phenylene-benzo-bisthiazole (PBO) fabric reinforced cementitious matrix (FRCM) composites after the exposure to elevated temperatures ranging between 20 °C [68 ºF] and 300 °C [572 ºF]. Experimental results obtained from direct tensile (DT) and single-lap direct shear (DS) tests carried out respectively on PBO FRCM specimens and PBO FRCM-concrete elements were reported and discussed. Overall, specimens exposed to temperatures up to 200 °C [392 ºF] did not present significant reductions of both bond and tensile properties. This result can be attributed to the thermal shrinkage underwent by the inorganic matrix, which may enhance the bond between the fibers and the matrix. On the other hand, when the specimens were heated at 300 °C [572 ºF], marked reductions were observed, primarily stemming from the degradation of both mechanical properties of the FRCM constituent materials and the fiber-to-matrix bond. Subsequently, the experimental results were used for the following purposes: (i) to assess whether the Aveston–Cooper–Kelly (ACK) theory is able to describe the tensile behavior of FRCM materials at elevated temperatures; (ii) to define temperature-dependent local bond stress vs. slip law and (iii) to evaluate the ability of degradation models to simulate the variation with temperature of the FRCM tensile and bond properties. The results obtained from the theoretical analyses showed that, for all the tested temperature, the relative differences between predicted and experimental results are very low, confirming the accuracy of the proposed approaches.

Concrete beam-column joints are critical elements in the seismic performance of reinforced concrete (RC) structures. The use of carbon fiber-reinforced polymer (CFRP) reinforcement in these joints has gained attention due to its superior mechanical properties and corrosion resistance. This paper presents a comprehensive study of the seismic performance of CFRP-reinforced concrete beam-column joints, focusing on the development of a suitable formula for estimating the seismic shear capacity. Utilizing a finite element analysis (FEA) that was both developed and validated using pre-existing test data, a comprehensive parametric study was undertaken to explore the impact of several factors. These factors encompassed axial load, longitudinal reinforcement ratio, and transverse reinforcement ratio, and their effects on the seismic performance of CFRP-RC joints were thoroughly investigated. Eventually, a suitable formula was proposed for estimating the seismic shear capacity of CFRP-RC joints. Research results will lead in a better understanding of the seismic behavior of CFRP-reinforced concrete beam-column joints, which will consequently guide the design and analysis of CFRP-reinforced concrete structures for enhanced seismic performance.

While reinforced concrete is one of the most used construction materials, traditional reinforcement steel may cause undesirable side effects, as corrosion and the associated volume changes can lead to damages in the concrete matrix and can cause spalling, which may significantly reduce the load-bearing capacity and service life of structures. Alternative reinforcement methods, such as glass or basalt fiber reinforced polymer rebars, can serve as a viable alter-native to reduce or eliminate some of the disadvantages associated with steel reinforcement. In addition to an increased tensile strength and a reduction in weight, fiber reinforced polymer rebars also offer a high corrosion resistance among other beneficial properties. Because these materials are not fully regulated yet and the durability properties have not been conclusively determined, further research is needed to evaluate the material durability properties of FRP rebars. To determine the durability properties of GFRP and BFRP rebars in cold climates, the freeze-thaw resistance of these materials was evaluated throughout this study. Specifically, two types of materials (basalt and glass reinforced polymers) and two common rebar sizes (8 mm (#2) and 16 mm (#5) diameters) were tested. To quantify the freeze-thaw-durability, tensile tests according to ASTM D7205, transverse shear strength tests in line with ASTM D7617, and horizontal shear strength tests as specified in ASTM D4475 were conducted on numerous virgin fiber rebars and on fiber rebars that were subjected to 80 and 160 freeze-thaw cycles. While the results from the virgin materials served as benchmark values, the measurements and analysis from the aged (by freeze-thaw cycles) materials were used to quantify and determine the strength retention capacity of these bars. The results showed that a higher number of freeze-thaw cycles lead to lower strength retention for some rebar types. In addition, it was seen that rebar products respond differently to the aging process; while some material properties notably deteriorated, other material properties were insignificantly affected.

Carbon Fibre Reinforced Polymers (CFRPs) are a material of choice in the aerospace and automotive industry, but despite decades of research into their application in structural engineering applications, and in particular in new-build construction of buildings and bridges, CFRP elements remain regarded as somewhat exotic in structural engineering and their widespread take-up is mostly limited to the non-prestressed strengthening of conventional structural members. The study presented in this paper assessed the performance of CFRP bridge tendons, prestressed for 18 years at 45% of their design ultimate tensile capacity in a non-conditioned outdoor environment, over water, in Lucerne, Switzerland. The performance of the tendons is considered alongside pristine samples of the same tendons never used and stored, unstressed, indoors since 1997. Thermal characterization (matrix digestion, thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC)) was used to determine the fibre volume fraction and glass transition temperature, and tensile tests were performed and compared against available original baseline results from 1997. This comparisons show that the in-service tendons do not appear to have been adversely affected by 18 years service under sustained loading, and have retained the vast majority of their original, unstressed material properties. The in-service tendons only lost about 10.5% of their ultimate tensile capacity over time, while the pristine (unstressed) tendons also lost 7.9% of their capacity; this suggests that sustained loading and an external, unconditioned service environment do not significantly adversely affect the mechanical properties of the tendons after 18 years in service.

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.