International Concrete Abstracts Portal

Due to a dynamic development of infrastructure, engineers around the world are looking for new materials and structural solutions, which could be more durable, cheaper in the life cycle management, and built quickly. One of prospective solutions for building small-span bridges can be precast lightweight concrete reinforced with glass fiber-reinforced polymer (GFRP) rebars. Thanks to prefabrication, it is possible to shorten the construction time. Using lightweight concrete affects structure weight as well as transportation costs. GFRP rebars can make the structure more durable and also cheaper in terms of life cycle management costs. The paper focuses on the fatigue performance of a real-scale arch (10.0 m (33 ft) long, 1.0 m (3.3 ft) wide, and 2.4 m (7.9 ft) high) made of lightweight concrete and GFRP rebars (LWC/GFRP) in comparison with an arch made of normal weight concrete and typical steel reinforcement (NWC/steel). The fatigue loads ranging from 12 to 120 kN (2.7 to 27 kip) were applied in a sinusoidal variable manner with a frequency of 1.5 Hz. This research revealed that the NWC/steel arch exhibited significantly better fatigue resistance when compared to the LWC/GFRP arch. Differences in the behavior of the NWC/steel and LWC/GFRP models under fatigue load were visible from the beginning of the research. The LWC/GFRP model was exposed to fatigue loads, resulting in gradual deterioration at an early stage. This degradation was evident through stiffness being progressively reduced, leading to increased displacements and strains as the number of load cycles increased. The model did not withstand the fatigue load and was destroyed after approximately 390 thousand load cycles, in contrast to the NWC/steel model, which withstood all 2 million load cycles without significant damages or the stiffness being decreased. However, the prefabricated lightweight concrete arches with composite reinforcement seem to be an interesting alternative of load-bearing elements in infrastructure construction.

Mehdi Khorasani, Giovanni Muciaccia, and Davood Mostofinejad Synopsis: The externally bonded reinforcement on grooves (EBROG) technique has been recently shown to outperform its rival techniques of surface preparation (such as externally bonded reinforcement, EBR) employed to delay the undesirably premature debonding of fiber reinforced polymer (FRP) from the concrete substrate in retrofitted structure. However, the behavior of EBROG method under fatigue loading has not been assessed yet, and the present study is the first attempt to achieve the above aim. For this purpose, an experimental program is conducted in which 16 CFRP-to-concrete bonded joints on the concrete slab prepared through the EBROG and EBR techniques are subjected to the single lap-shear test and fatigue cyclic loading. Furthermore, the bond behavior of CFRP strips-to-concrete substrate is investigated in this research in terms of the load capacity, slip, debonding mechanism, and fatigue life. The results showed that the grooving method improved the bond properties of CFRP-to-concrete joints under fatigue loading. By using this alternative technique, the number of cycles until failure (fatigue life) increases incredibly under the same fatigue cycle loading and the service life of strengthened members could be improved under fatigue loading. Furthermore, the effects of different loading levels on the behavior of CFRP-concrete joints installed by EBROG method are evaluated. The results showed that fatigue life of strengthened specimens decreases by increasing fatigue upper load limit. Finally, a new predictive equation was developed based on plotting the maximum applied fatigue load versus fatigue life curves for CFRP-to-concrete bonded joints for the EBROG method.

This paper presents an indeterminate strut-and-tie (IST) method to analyze concrete deep members reinforced with fibre-reinforced polymer (FRP) bars. Because FRP bars are linear-elastic and brittle at failure, the classical ST method based on steel yielding cannot be used to analyze FRP-reinforced concrete deep beams, and current code provisions lack guidance on such designs. Thus, the IST method is proposed for the analysis. This work addresses the details of using the proposed IST method to analyze FRP-reinforced concrete deep beams, including how to size the struts and nodes without assuming steel yielding, how to model the compressive behaviour of concrete struts reasonably, and how to construct and analyze statically indeterminate ST models. Six FRP-reinforced concrete deep beams with stirrups and six beams without stirrups are analyzed in this work, and it is found that the proposed method works well to predict the shear strength of FRP-reinforced concrete deep beams by comparing the analytical results with the test results.

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.

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.