M. K. Agrawal

Evaluation of Seismic Fragility of Structures - A Case Study

The present paper attempts to evaluate the seismic fragility for a typical elevated water-retaining structure. The structure is analysed for two cases: (i) empty tank; and (ii) tank filled with water. The various parameters that could affect the seismic structural response include material strength of concrete and reinforcing steel, effective prestress available in the tank, ductility ratio and structural damping available within the structure, normalised ground motion response spectral shape, foundation and surrounding soil parameters and the total height of water available in the tank. Based on this case study, the seismic fragility of the structure is developed. The results are presented as families of conditional probability curves plotted against peak ground acceleration (PGA) at two critical locations. The procedure adopted, incorporates the various randomness and uncertainty associated with the parameters under consideration.

Finite Element Simulation of Dynamic Behavior of Pressurized Piping System Under Large Seismic Load

The nuclear power plant piping systems are often subjected to the cyclic loading conditions due to transients, seismic or other unexpected events. During these events, the probable mode of failure for piping component is fatigue-ratcheting. Earlier the design of piping subjected to seismic excitation was based on the principle of static collapse. Later on, it was postulated that the cause of failure of piping components is fatigue ratcheting and not plastic collapse. The 1995 ASME Boiler & Pressure Vessel code, Section-III, has incorporated the reverse dynamic loading and ratcheting into the code. An Analytical study is carried out to investigate the behavior of the pressurized piping system under large seismic loading. The analysis is performed using equivalent inertial forces. Chaboche nonlinear kinematic hardening model is used for ratcheting simulation. The capability of the model to simulate the ratcheting response of the piping system is of particular interest. Comparison of analysis results against test results are presented in the paper.Copyright

Effect of Opening on the Response of Containment Model to Pressure Loading

The Containment Studies Facility (CSF) is being set up in BARC for studying various containment related thermal hydraulic and other phenomena which occur during simulated accident conditions in Nuclear power Plants. The facility consists of a concrete containment model having a volumetric scale ratio of 200:1 with respect to the actual containment of Indian Pressurized Heavy Water Reactor. The structure is designed for pressure of 1.73 Kg/cm2 for specified leak tightness. Adequacy to withstand design pressure is checked by test as well as numerical analysis before commissioning of the facility. Accordingly Containment building model has been analyzed by finite element method for internal design pressure and dead weight. Analysis has been carried out for the structure with and without the opening in the containment. Effect of opening on the response of containment has been studied. The paper includes the modeling methodology, maximum deflection and stress amplification around the opening for various models.© 2006 ASME