The Effect of the Near-Fault Velocity Pulse Type Ground Motions on the Response of Concrete Arch Dams (Case Study)

Because of the importance of the dam safety and to overcome the damages caused by the failure of the concrete dams under the earthquake, the seismic performance assessment of concrete dams needs more attention. This study deals with the investigation of the effect of the near-fault velocity pulse type ground motions and their effective parameters on the structural response. For this purpose, the Morrow Point arch dam has been considered as the case study. The dam is modeled in the SOLIDWORKS software and analyzed in the finite element ABAQUS software, considering the dynamic interaction of dam-reservoir-foundation and nonlinear behavior of concrete. In a nonlinear seismic analysis of dam-reservoir-foundation system, the crack propagation and the dam failure due to the low tension strength of concrete is necessary to be considered. Therefore, this study uses the concrete damage plasticity (CDP) model to consider the nonlinear behavior of concrete in tension and compression. Generally, near-fault ground motionshave short effective duration and contain long period pulses with big pulse amplitude. Three types of pulses have been introduced in the literature to show the velocity pulse type ground motions. Pulse A is a one-sided type (one half cycle pulse) thatresults in fling step in its displacement time history. Pulse type B represents for the forward directivity effects and contains a two-sided pulse (a pulse with two half cycles), which has a long period and amplitude in its velocity time history and its displacement time history includes just a one-sided pulse. Nevertheless, all the near-fault ground motions do not follow the forward directivity or fling step patterns; hence, another pulse type named C has been introduced. These pulses have at least three halfcycles in their velocity time histories, more than those of pulse types A and B. These pulses result in at least two half cycles in the displacement time history. In order to consider the effects of near-fault ground motions on the dam response, a collection of ground motions with B and C pulses in their velocity time histories have been selected and used in this study. For comparison purpose of the near-fault pulse like records, one should keep some of the effective parameters constant in the analysis process in order to study the effects of the other parameters. Unlike previous studies that only consider the peak ground acceleration (PGA) as the constant and common parameter of the records, the similar energy of the records is also taken into account in this study. The records are divided into two categories according to their specific energy density; so that, after scaling their PGA to 0.3 g, the specific energy densities of each category of the records are relatively similar. In the first group in which the maximum velocity, the Arias intensity and maximum displacement are relatively similar, the results indicate that the records which contain pulse type C, show more destructive responses. The difference is due to the shape nature (more half cycles) of this pulse type. In the second group, generally, the surveys also show more destructive responses of the records with pulse type C. Further investigations also present relatively much more effects of the "Arias Intensity" and "Pulse Duration” on the responseforthe records with relatively the same specific energy density. Besides, inthe case ofthe relatively the same values for the above-mentioned parameters, other parameters such as the maximum displacement are effective. The results of this study could be useful for the structures designed and constructed for the near-fault regions.