Ultra-high-performance concrete (UHPC) features tensile strain-hardening behavior and a high compressive strength. Existing studies on the shear behavior of UHPC structural members have been focused on prestressed UHPC girders. More experimental data of the shear behavior of non-prestressed UHPC beams are necessary to quantify the safety margin of shear designs for structures. Moreover, while the UHPC members in most studies did not contain coarse aggregate to strengthen their microstructure, the inclusion of coarse aggregate has been shown to substantially reduce the autogenous shrinkage and enhance the elastic modulus for UHPC materials, which is beneficial for structural applications of UHPC. This study experimentally investigated the shear failure behavior of eighteen non-prestressed rectangular UHPC beams. The experimental variables included the volume fraction of fibers, shear span-to-depth ratio of the beams, and coarse aggregate. The detailed shear failure responses of the UHPC beams were discussed in terms of the damage pattern, shear modulus, shear strength, shear strain, and strain energy. The test results showed that the inclusion of coarse aggregate increased the beam shear strength, and its enhancement became more significant with a higher volume fraction of fibers and a lower shear span-to-depth ratio of the beam. In addition to the experimental investigation, a shear strength model for non-prestressed rectangular UHPC beams that accounts for the interactive effect of the key design parameters was developed. An experimental database of the shear strength of the UHPC beams in existing studies was established to assess the performance of the proposed model. It was shown that the proposed model reasonably predicted the shear strength of the UHPC beams in the database with a higher accuracy and lower scatter compared to the results of existing models.

This paper presents the current code provisions on strut-and-tie analysis and design of disturbed regions of deep concrete beams reinforced with fiber-reinforced polymer reinforcing (FRP) bars. A literature review of the large-scale experiments published to date is included with a comparison of their results to strut-and-tie predictions. Several published works have recommended modifications to strut-and-tie provisions for FRP reinforced deep beams, and those modifications are summarized within this paper.

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.

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.

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.