Determining the Critical Intensity for Crack Initiation in Concrete Arch Dams by Endurance Time Method

This study aims at determining the critical seismic intensity at which cracks are expected to develop in a concrete arch dam. This intensity is referred to as crack initiation intensity. The crack initiation intensity measure implies that earthquakes with the intensity measure higher than this value are expected to induce cracks in the arch dam. This quantity is an indicator for seismic evaluation of arch dams. Determining this parameter using conventional time history analyses requires multiple trials and errors applying several up and down scaling of a suite of ground motions which can be very time consuming. As an alternative method, endurance time method is well suited for this kind of study. In the endurance time method, structures are subjected to predefined intensifying acceleration time histories and all intensity measures are continuously covered in a single time history analysis. The continuous coverage of intensity measures in the endurance time method provides a tool to conveniently determine the transition points such as crack initiation in a single time history analysis. In this regard, a framework is proposed and then applied to Morrow point dam, a doubly curved arch dam, as a case study. Results are obtained by using three different endurance time excitation series; ‘kn’, ‘kd’, and ‘lc’. The aim of using three endurance time series was to compare their differences in dynamic analysis of arch dams. Observations indicate the acceptable compatibility of different series of endurance time excitation. In order to investigate the accuracy of the results obtained by the endurance time method, the dynamic analysis of the arch dam subjected to ten ground motions scaled by the calculated crack initiation intensity measure is performed. It is shown that the proposed method can be conveniently applied for determining the crack initiation intensity.