Fundamental Study on Requirements for Old RC Piers to Continue to be used without Seismic reinforcement

Abstract

Many older RC piers in Japan have stepped section (referred to as the cut-off section) where the amount of longitudinal reinforcement decreases in response to cross-sectional forces. In such piers, the cover concrete may delaminate at the cut-off section during a major earthquake.When damage progresses at the cut-off section of the axial rebar, RC piers are deformed so that they bend above the cut-off section. RC piers damaged at the cut-of section have inferior deformation performance compared to those damaged at base. Therefore, it is now a common design practice to avoid damage at the cut-off section of piers.In the current Japanese design method, the anchorage length of steel bars anchored in the middle of piers should be about 50φ, or axial steel bars should not be anchored in the middle of piers. In the case of existing piers where these design methods are not applied, the cut-off section are reinforced by wrapping steel plates or other materials. In this study, cyclic positive and negative loading tests were conducted on pier specimens with cut-off section, and dynamic response analysis was conducted for each soil type based on the test results.The analysis results showed that non-linear response spectrum were obtained for different yielding positions, and that response seismic yielding coefficient could be generally evaluated. This shows that for a given natural period and seismic yielding coefficient, it is possible for piers to withstand a large earthquake even if they yield at cut-off section.

Keywords: No Seismic Reinforcement Required, RC Piers, Cyclic Loading Test, Reduce Number of Axial Rebars to Match Moment Distribution

DOI: 10.54941/ahfe1005279