International Concrete Abstracts Portal

During past earthquakes, failures of beam-column joints have commonly been observed on the exteriors of buildings. However, only one side of these joints can be retrofitted because of the presence of beams on the other three sides. Therefore, this study aims to test four exterior beam-column joints with transverse beams, leaving the rear side as the only viable location for placing fiber-reinforced polymer (FRP) laminate. All four test specimens were designed with insufficient joint shear strength, as determined by ACI 318-19 equations, while satisfying the criteria for a strong-column/weak-beam mechanism and sufficient development length for bar anchorage. A total of two un-retrofitted specimens, with and without joint hoops, were constructed as controls. Subsequently, two similar specimens were retrofitted by applying FRP laminate on the rear side. The results show that sufficient FRP laminate can enhance the seismic performance of joints in terms of deformability, energy dissipation, and failure delay.

Several studies have revealed that slabs with cast-in-place over precast, prestressed panels (CIP-PCP) behave differently from traditional concrete slabs because of the panel joints between the PCP components. While high-strength reinforcing bars can improve load capacity or reduce reinforcing bar quantity in traditional slabs, limited research has focused on their application in CIP-PCP slabs. This study addressed this gap by conducting four-point bending tests on CIP-PCP slabs with normal- and high-strength reinforcing bars. Two configurations of high-strength steel were used: one with the same reinforcing bar layout as normal-strength reinforcing bars and another with increased reinforcing bar spacing to reduce the reinforcing bar quantity. Additionally, slab specimens were designed to replicate real-world bridge deck conditions, including longitudinal and transverse joints, for detailed analysis. The results indicated that reducing reinforcing bar quantity by adjusting reinforcing bar spacing based on the specified yield strength ratio between normal- and high-strength steels maintained a comparable load capacity, with crack widths magnitude similar to those in normal-strength steel layout in the service state.

Inner surface reinforcement is one of the most widely adopted techniques for upgrading or strengthening shield tunnels. An important failure mode in this method is the debonding of the thin plates from the segments, resulting in less reinforcement effect than expected. A shield tunnel lining is a discontinuous curved structure formed by connecting segments with bolts, and its structural form and internal force state are essentially different from reinforced concrete beams. However, there are few reports on the evolution process of debonding failure of similar structures. Therefore, to develop a thorough understanding of the debonding failure, a three-dimensional refined numerical model for a shield tunnel strengthened by a thin plate at the inner surface based on the mixed-mode cohesive method was proposed. The validity and rationality of the model were corroborated by a full-scale experiment. Then, the model was applied to other inner surface reinforcement schemes commonly used in practice to explore the debonding mechanism of the adhesive layer. Finally, anti-debonding measures were proposed, and their effectiveness was elucidated by numerical analysis. The results show that the proposed numerical model can accurately predict the failure process of the adhesive interface of the shield tunnel strengthened by a thin plate. There are obvious interfacial stress concentrations at the joints and the plate ends, which are the essential reasons for the debonding failure initiating from those places. Anchoring the thin plate only at the plate ends and joints can significantly and sufficiently increase the debonding load. Therefore, it is not necessary to add anchoring measures elsewhere.

In this study, the seismic performance of reinforced concrete beam-column joint subassemblies reinforced with steel fiber was evaluated through experiments. A total of seven specimens were used, and four steel fiber-reinforced specimens were planned based on the amount of steel fiber, the presence or absence of hoops of joints, and the spacing of hoops arranged in the beam. The steel fibers used were determined to have properties that could be used to replace the minimum shear reinforcement in beams proposed by ACI 318. To evaluate the seismic performance quantitatively, a loading protocol was applied based on the displacement control protocol of ACI 374. Experimental results showed that reinforcement of steel fiber improves the shear strength of the joint itself. The shear strength of the joint increased as the amount of steel fiber was increased. However, the increase rate of the shear strength of the joint decreased with increasing steel fiber content. A large seismic performance improvement was confirmed when the hoop spacing on the beam was widened and the steel fiber was used with the hoop of the joint. Simultaneous reinforcement of steel fiber and the hoop with increased hoop spacing on the beam caused more damage on the beam and reduced the joint shear strength. Seismic performance evaluations according to ACI 374 showed that performance similar to that of the hoop reinforced joint can be expected when steel fiber with 2% volume fraction is used instead of the hoop in the joint region.

Many of the existing reinforced concrete (RC) structures in Turkey built prior to 1999 have deficient design details due to their non-seismic design or construction flaws. In particular, the beam-column joints (BCJs) experience high shear forces during such events, mainly due to inadequate design detailing of transverse reinforcements as well as inadequate lap splicing. Severe damage or total collapse of structures often occurred. To enhance the performance of such deficient joint systems, several strengthening techniques such as reinforced concrete and steel jacketing, as well as fiber-reinforced polymer (FRP) wrapping, have been proposed. In this study, new shear strengthening techniques were developed using carbon fiber-reinforced polymer (CFRP) to retrofit these insufficient BCJs. The effectiveness of various CFRP wrapping methodologies was investigated experimentally. One control specimen was constructed according to provisions specified by the 1975 Turkish Building Design Code, whereas four other specimens were constructed with deficiencies observed in the practice. Moreover, three additional specimens were constructed to develop alternative shear strengthening techniques via CFRP wrapping. The quasi-static tests were carried out by applying constant axial load and reversed-cyclic lateral load at the top of the column. Comparative analysis of control and CFRP-strengthened specimens’ results showed that significant improvements in the lateral load and the energy dissipation capacities were achieved by using the proposed CFRP-strengthening techniques.