In Japan, design ground motion has increased due to the frequent occurrence of large earthquakes. To improve seismic performance, dams and spillway gate piers (hereafter, piers) are being reinforced. The methods used to strengthen them include concrete overlay, jacketing, etc. On their boundaries, there are concrete joints. These joints are designed as integrated bodies. However, although no accidents have been reported, the joints may be a weak point. The purpose of this study is to understand the effects of concrete joint condition, assuming strengthening for dams and piers such as concrete overlay and jacketing. Dynamic splitting tensile tests of concrete specimens joining old and new bodies were conducted. In dynamic splitting tensile tests, the experimental parameters are the condition of joint surfaces in terms of strengthening and strain rate for earthquake ground motion. The conditions of joint surfaces are raw concrete surfaces, chipped surfaces, and surfaces with rebar insertion. Three cases of strain rate are considered, including a static case and two dynamic cases (about 1,000 μ/s and 10,000 μ/s). Test results showed all joint conditions caused a decrease in tensile strength. There was the effect of increasing tensile strength due to strain rate, regardless of joint condition. It was shown that concrete joints without adhesives might be weak points in reinforced structures.
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