Seismic Retrofit Technique Using Plywood and Common Nails for Connections of Low-Rise Timber Frame Construction

Since the Japanese Building Standards Act was revised in 2000, the installation of steel timber connectors (STCs) to reinforce timber frame (TF) connections has been mandated for new-build TF houses in Japan. However, for the TF houses built before then, more than 40% do not have sufficient STCs and are considered earthquake-prone. This study proposed a simple and easy seismic retrofit technique for such earthquake-prone existing houses. The proposed technique can reinforce TF connections using only plywood and common nails and achieve equivalent performance to the benchmark STCs used in Japanese TF houses, such as the "CP-T type" or the combination of "VP type" and "BP type" STCs. Experiments were performed to compare the proposed technique with the STCs using pullout and full-scale in-plane cyclic tests. The experimental results showed that the proposed technique had a higher seismic performance than the STCs, which was particularly excellent in displacement ductility to prevent a collapse of the TF house without damaging the timbers. The proposed technique will be accepted by many carpenters when retrofitting earthquake-prone existing houses because simple and easy.