Sandip Kumar Saha

Earthquake Response of Base-Isolated Liquid Storage Tanks for Different Isolator Models

The effect of different isolator parameters on earthquake response of base-isolated liquid storage tanks is investigated herein. Mechanical analog, with three lumped masses, is used to model ground...

Reviewing dynamic analysis of base-isolated cylindrical liquid storage tanks under near-fault earthquakes

Base-isolated structures are susceptible to more damage under near-fault earthquakes, due to its long fundamental time period, than under far-fault earthquakes. A brief review of the literature, related to the response of base-isolated structures under near-fault earthquake and representation of near-fault earthquake motion using equivalent pulses, is presented herein. Dynamic analyses are carried out to investigate the response of cylindrical liquid storage tanks under near-fault earthquakes. The studies are carried out for ground supported, anchored without isolation and base-isolated anchored tanks, where the isolator considered is lead-rubber bearing. Two types of configurations of the cylindrical liquid storage tanks, i.e. broad and slender, are considered in the present study. Equivalent pulse type acceleration inputs are used to study their effectiveness to predict the seismic response of base-isolated liquid storage tanks. The response under equivalent pulse type acceleration inputs are compared with the response under recorded near-fault earthquake ground accelerations. The response under the residual motion is also investigated to study their influence on the different response time histories. The cylindrical liquid storage tanks are subjected to bi-directional earthquake excitation to examine the effect of the interaction between two mutually perpendicular displacement components of the isolator. Parametric studies were conducted to investigate the variation of the peak response with important isolator parameters such as isolation time period, characteristic strength and isolation damping. It is observed that equivalent pulses are suitable for predicting the unidirectional response for slender liquid storage tanks; however, under the bi-directional excitation, prediction of the response is less accurate. The effect of the interaction is observed more crucial for lower isolation time periods under bi-directional excitation. The base shear, base displacement and overturning moment of the tanks decrease with increasing isolation damping; however, the sloshing displacement is found to be less sensitive to the change in the isolation damping.

Fragility Analysis of Base-Isolated Liquid Storage Tanks under Random Sinusoidal Base Excitation Using Generalized Polynomial Chaos Expansion–Based Simulation

AbstractGeneralized polynomial chaos (gPC) expansion–based simulation technique is used to investigate the influence of input parameter uncertainty, on peak response quantities and fragility curves of base-isolated liquid storage tanks. Unidirectional horizontal sinusoidal base excitation is considered to develop the fragility curves for the base-isolated liquid storage tanks. Extensively used laminated rubber bearing (LRB), with linear force-deformation behavior, is considered as the isolation system. The liquid storage tank is modeled using a widely accepted lumped mass model. The failure of the liquid storage tank is defined corresponding to the elastic buckling of the tank wall. The uncertainties are considered in the isolator parameters and in the base excitation. Considerable difference in the peak response estimation is observed when the input parameters are represented using different probability distributions, especially when the uncertainties are higher. It is also observed that when the uncerta...

Fragility of Steel Frame Buildings under Blast Load

AbstractEffects of different structural configurations, member orientations and standoff distances on blast-induced failure of steel frame buildings are investigated through development of fragilit...

Reliability of Base-Isolated Liquid Storage Tanks under Horizontal Base Excitation

Reliability of base-isolated liquid storage tanks is evaluated under random base excitation in horizontal direction considering uncertainty in the isolator parameters. Generalized polynomial chaos (gPC) expansion technique is used to determine the response statistics, and reliability index is evaluated using first order second moment (FOSM) theory. The probability of failure (p f) computed from the reliability index, using the FOSM theory, is then compared with the probability of failure (p f) obtained using Monte Carlo (MC) simulation. It is concluded that the reliability of broad tank, in terms of failure probability, is more than the slender tank. It is observed that base shear predominantly governs the failure of liquid storage tanks; however, failure due to overturning moment is also observed in the slender tank. The effect of uncertainties in the isolator parameters and the base excitation on the failure probability of base-isolated liquid storage tanks is studied. It is observed that the uncertainties in the isolation parameters and the base excitation significantly affect the failure probability of base-isolated liquid storage tank.

Assessing Seismic Base Isolation Systems for Liquid Storage Tanks using Fragility Analysis

Liquid storage tanks are essential component of petroleum industries, thermal power plants, chemical factories and numerous other important industries along with civil society. Herein, seismic fragility of base-isolated liquid storage tank is evaluated to assess the performance of various base isolation systems in enhancing the seismic protection. The liquid storage tank is modeled using lumped mass mechanical analog. Failure of the liquid storage tank is defined in terms of buckling of the tank wall in elastic range. The maximum displacement at isolation level is also considered in the failure criteria. The equations of motion are solved using Newmark’s method to obtain the peak response quantities of the base-isolated liquid storage tank. Two different configurations, i.e. broad and slender, of the base-isolated liquid storage tanks are chosen for the comparison. Monte Carlo (MC) simulation is used to obtain the probability of failure (p f) at different seismic intensity level. The probability of failure for the slender tank is observed more as compared to the broad tank. The seismic fragility of the base-isolated liquid storage tanks is evaluated considering the randomness in the earthquake ground motion. Seismic performance of fixed-base tanks are compared with the base-isolated tanks in terms of the probability of failure. It is observed that the base isolation enhances the seismic performance of the liquid storage tanks irrespective of the type of isolation system. However, enhancement in the seismic performance of the liquid storage tanks varies significantly for different isolation systems considered in the present study.