ACI STRUCTURAL JOURNAL (American Concrete Institute)
Impact Resistance Design of Porosity-Free Concrete Beams Strengthened with Aramid Fiber-Reinforced Polymer Sheet
Kurihashi, Y; Kono, K; Yasuda, E; Komuro, M
ACI STRUCTURAL JOURNAL, Vol.118, pp.101-111, 2021, JAN.
(https://doi.org/10.14359/51728090)
Abstract
In this study, an impact resistance design method for steel fiber-reinforeed porosity-free concrete (PFC) beams strengthened with aramid fiber-reinforced polymer (AFRP) sheets was established using static and impact loading tests. The influence of the loading method on the deformation behavior of the beams was investigated, and it was determined that the maximum deflection under impact loading can be estimated using the load-deflection curve calculated under static loading. Then, a performance-based impact resistance design concept was demonstrated using the magnitude of the tensile strain in the AFRP sheet as a performance index. By establishing an impact resistance design method for the FRP sheet-reinforced PFC members based on this study, it is possible to improve the impact resistance of concrete structures subject to impacts from falling rocks, debris flows, flying objects, and so forth.
Ultimate Flexural Strength and Plastic Deformation Performance of Reinforced Concrete Section in Hybrid Beams
Singh, R; Sasaki, H; Sato, Y
ACI STRUCTURAL JOURNAL, Vol.118, pp.301-310, 2021, JAN.
(https://doi.org/10.14359/51728187)
Abstract
In Japan, steel is mostly used to construct large-span buildings such as logistic terminals, office buildings, shopping malls, and medical facilities. However, in recent years with the fabrication cost of steel soaring, there is a concerted e f fort to reduce construction costs and at the same time increase productivity. Therefore, research investigations are being carried out and one of the methods involves using an innovative hybrid system where the columns are reinforced concrete and the beams are hybrid beams. In this study, concrete design strength, shear reinforcement ratio and length of RC section were altered to examine the structural performance of hybrid beams under flexural failure in a beam-column subassemblage. The results showed that ultimate flexural strength of a reinforced concrete section can be evaluated using an Architectural Institute of Japan abbreviated equation, and a coefficient of shear reinforcement of more than 2.5% will assure a plastic deformation capacity of more than 2%.
Mitigating Bond Deterioration under Cyclic Loading and Water Exposure
Saito, T; Chijiwa, N; Shinozaki, H; Iwanami, M
ACI STRUCTURAL JOURNAL, Vol.117, pp.17-30, 2020, NOV-DEC.
(https://doi.org/10.14359/51725885)
Abstract
Several cases of premature damage of wind turbine tower foundations constructed using the anchor-ring method have been reported to cause towers' uplift. Sludge buildup (in the form of crushed concrete) was evident along the periphery of the damaged base towers and was found to originate mainly from the concrete-steel interface around the steel anchor foundation that is embedded in concrete, due to the cyclic movement of the anchor steel and the induced water pressure at the interface. This study experimentally investigated possible repair and reinforcing methods to mitigate this problem. Cyclic load tests were carried out on three steel anchor mockup specimens. In the first two specimens, the anchor steel was retrofitted with a nonshrink mortar and epoxy resin, respectively, whereas in the other specimen, the anchor steel was further restrained against uplift by additional anchorage bars. The results indicate that the non-shrink mortar was not effective in preventing water ingress into the interface and could only delay the extent of concrete damage and the progress of bond deterioration during cyclic loading. Epoxy resin was found to perform much better in this regard. In addition, the epoxy layer could also help to dissipate the induced bearing stresses under cyclic loading, thereby making it the best candidate for repair and reinforcing materials in such applications. The use of additional anchorage bars was also found to be effective, although it still requires additional measure to prevent moisture ingress.