Fracture Mechanics Based Unilateral and Bilateral Earthquake Simulations: Application to Cable-Stayed Bridge Response

Karthik Reddy, K. S. K. and Somala, S N (2020) Fracture Mechanics Based Unilateral and Bilateral Earthquake Simulations: Application to Cable-Stayed Bridge Response. In: 7th International Congress on Computational Mechanics and Simulation, 2019., 11 December 2019 - 13 December 2019, Mandi.

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Abstract

The phenomena of forward-directivity effects cause pulse-type earthquake ground motions that result in significant damage to structures. Forward directivity ground motions can be facilitated by typically simulating unilateral ruptures and occasionally by bilateral ruptures. Traditional analysis methods do not employ the dynamics of fault rupture hence are inadequate to capture the full effects of these pulse-type ground motions. Computational seismology overcomes this limitation and plays an important role to simulate dynamic earthquake ruptures. The objective of this paper is to use an open-source code SPECFEM3D to generate synthetic field vector data to improve the understanding of pulse-type ground motions generated using dynamic simulations. The software was used to generate synthetic earthquakes of moment magnitude, Mw = 7 with a strike-slip mechanism. Two cases were considered with nucleation at the end and in the center of the fault to generate unilateral and bilateral ruptures. The generated ground motions are then interpreted to comprehend the concept of directivity. Later, the seismic response of the bridge is evaluated for selected stations around the fault. The behavior of the bridge in terms of displacement field is evaluated which showed a similar response for stations located at a distance of 2 and 10 km in front of the fault. Further inference of bridge response is drawn by comparing the Fourier amplitude spectrum of velocities at these particular stations. The peak amplitude frequencies of the velocity fields at these stations lie in the regime of natural frequencies of the bridge which caused it to resonate in turn exhibiting high displacements at stations in front of the fault.

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