RESPONSE OF GRAVITY DAMS AGAINST STRONG EARTHQUAKE GROUND MOTIONS

Abstract

Dams are extremely important lifelines of a country. They aid in the growth of the economy. The large-scale devastation due to an earthquake can generate irreversible losses. 2% of the dam failures all around the world take place due to earthquakes. Earthquakes not only cause immediate damage but are also capable of weakening the structure by decreasing its resistance against further damages. In this work, we study the effect of strong ground motion earthquakes on concrete gravity dams. The strong ground motions lying within shallow depths are felt powerfully by the dams, since the high frequency waves are not filtered. This causes more damage to the dam as there is a high probability of resonance in higher modes, a result of the high frequency content in the ground motion. 5 strong ground motions in the Indian Subcontinent have been selected and applied on the Koyna dam which was constructed in the year 1963. 2D analysis of the dam has been performed in standard software. Qualitative analysis of dams shows that there are 3 regions which are most susceptible to damage within a dam cross-section i.e., neck, body and the heel of the dam. In this paper, the displacement of crest and the formation of tensile stresses at the 3 zones - neck, body, heel of the dam due to these 5 strong ground motions is analyzed. The point of highest tensile stress is most susceptible to damage and failure in the face of an earthquake. When the structure is exposed to the ground motions, under normalized peak ground accelerations (PGAs), the structure behaves differently based on the effect of the frequency content of the input signal. By Normalizing the PGA of the ground motion, we grasp an idea of the effect of frequency content on the dam structure. Keywords: Gravity dam; Stress analysis; Qualitative failure analysis; Frequency Content; Deterministic Analysis