Search

The present study focuses on the estimation of response of building structure supplemented with the superelastic shape memory alloy (SMA) damper under the stochastic seismic excitation. To this end, the stochastic response has been determined using the stochastic linearization method under random earthquakes and the control efficiency of the SMA damper is compared with the yield damper. As the response output, top floor root mean square (rms) acceleration and displacement are presented here in this study. Response analysis results show the presence of optimal values of damper strength which minimizes the responses. As observed, in this optimal condition of damper strength, compared to the yield damper, the SMA damper provided 17 % and 49 % improvements in the values of top floor rms acceleration and displacement. In the end, the parametric study has been performed under the varying strength and stiffness of the damper, time period of the structure, and earthquake excitation to establish the superior control efficiency of SMA damper over yield damper.

Blast-induced ground motions (BIGM) can cause significant damage to the structure, leading to loss of life and economy. Previous studies proposed the use of base isolation system to prevent such adverse effects of blast loading on the structures. This study explores the effect of parametric uncertainty on the performance of shape memory alloy-assisted lead rubber bearing (SMA-LRB) isolator for the vibration control of building, under the BIGM. Nonlinear time-history analyses are performed to estimation responses, and compared them with the LRB isolated building. The building is modeled as a linear system, and nonlinear force–displacement behavior of LRB and SMA has been modeled via Bouc–Wen model and thermo-mechanical material model. To identify the critical design parameters and study the effect of parameter uncertainty, sensitivity analysis and Monte Carlo (MC) simulation are performed. Study results reveal that, compared to LRB, SMA-LRB reduces the peak floor acceleration by 20% with an added benefit of 35% and 67% reduction in peak and residual isolator displacement. Parametric uncertainty causes noticeable increase in mean responses of LRB isolated system than deterministic case, which get diminishes for SMA-LRB isolation system. This increase in the mean value of peak floor acceleration, peak, and residual isolator displacement are 64%, 68%, and 60% less for SMA-LRB than LRB isolated building. Further, compare to the LRB, SMA-LRB reduces standard deviation by 77% for the peak floor acceleration and peak isolator displacement, and 85% for the isolator residual displacement. Thus, conjunction of SMA with the LRB isolator enhances the performance and provides robust control effect under parameter uncertainty. [ABSTRACT FROM AUTHOR]

The synthetic uncertainty (SU) method is introduced and applied to the optimal design of energy absorbing NiTi shape memory alloy (SMA) bars. A sensitivity analysis for a large number of stochastic parameters identifies geometrical grading, porosity, and imposed maximum nominal stress as critical design parameters for the energy dissipation capacity of the bars. Parametric uncertainty on the optimal design of the energy absorber is incorporated and estimated through the SU formalism. The SU method provides a unified approach to discover the critical design parameters, quantify uncertainty, and optimally design a system around its extreme response (maximum or minimum). Therefore, the SU method is placed next to the robust design optimization (RDO) process, yet with a discovery component. It is found that variations in porosity and shape factor can significantly alter the stress-strain response and energy dissipation capacity. For a given value of maximum nominal stress, it is found that there exists an optimal combination of shape factor and porosity which maximizes the energy dissipation capacity of a tapered and porous NiTi bar. [ABSTRACT FROM AUTHOR]

A study on shape memory alloy materials as vibration dampers is reported. An important component is the strain rate–dependent and temperature-dependent constitutive behavior of shape memory alloy, which can significantly change its energy dissipation capacity under cyclic loading. The constitutive model used accounts for the thermo-mechanical strain rate–dependent behavior and phase transformation. With increasing structural flexibility, the hysteretic loop size of shape memory alloy dampers increases due to increasing strain rates, thus further decreasing the response of the structure to cyclic excitation. The structure examined is a beam, and its behavior with shape memory alloy dampers is compared to the same beam with conventional dampers. Parametric studies reveal the superior performance of the shape memory alloy over the conventional dampers even at the resonance frequency of the beam-damper system. An important behavior of the shape memory alloy dampers is discovered, in that they absorb energy from the fundamental and higher vibration modes. In contrast, the conventional dampers transfer energy to higher modes. For the same beam control, the stiffness requirement for the shape memory alloy dampers is significantly less than that of the conventional dampers. Response quantities of interest show improved performance of the shape memory alloy over the conventional dampers under varying excitation intensity, frequency, temperature, and strain rate. [ABSTRACT FROM AUTHOR]

The past studies on optimisation of isolation bearings emphasise on the allowable limit on the isolator displacement without incorporating it in the optimisation process. Large bearing displacement of the isolator during strong motion is often linked to isolator damage and pounding to adjacent units. The present study addresses the limitation on the excessive isolator displacement in the optimisation process of the isolator. It is intended not only to assure optimal performance in terms of vibration mitigation, but also to reveal the importance of constraining excessive isolator displacements. The stochastic response required for the optimisation study is evaluated through nonlinear random vibration analysis. The consistency of the optimal response behaviour obtained through stochastic optimisation is validated for recorded earthquake ground motions. A Lead Rubber Bearing (LRB), isolating a multi-story shear building is used to elucidate the effect of this constraint on the optimum parameters and system performance. The results clearly indicate the existence of significant disparities among the conventional unconstrained and the proposed constrained optimisation approach. [ABSTRACT FROM AUTHOR]

Container cranes, an essential component in any seaport facility system, are highly susceptible to failure during natural disasters such as severe windstorms. Damage or collapse of these structures can lead to significant amount of economic loss in terms of both repair or replacement and downtime. To study how various parameters such as boom position, yaw angle, gradient height and gradient wind speed affect the failure vulnerability of a crane, in this work, a representative container crane has been modelled in a commercial software considering both material and geometric nonlinearities. Stochastic wind fields are simulated as a stationary process by means of the spectral representation method using power spectrum in conjunction with along- and across-wind coherence functions. Wind fields are also simulated as a non-stationary stochastic process utilising the modulation functions from the available literature to consider the situations of thunderstorm downbursts. Nonlinear time history analyses are then performed and a few responses are compared for stationary and non-stationary wind field cases. It is observed that for the given simulation parameters, the responses considering stationary wind fields are larger than those of the non-stationary wind fields. Failure vulnerability of the crane is then assessed in terms of fragility curves. The results of this study show that the failure vulnerability may not be maximum for the set of parameter values for which the aerodynamic forces are maximum. This study provides a better understanding of crane vulnerability that may be utilised to achieve a better crane design. [ABSTRACT FROM PUBLISHER]

ABSTRACT The shape-memory-alloy supplemented rubber bearing (SMARB) has been recently proposed as a superior alternative to traditional elastomeric bearing, such as lead-rubber bearing (LRB), because of the dubious performance of conventional bearings under near-fault earthquakes. The present study establishes the significant improvement of performances in SMARB over the LRB in isolating multi-storeyed building frame against earthquakes. The response of the isolated building is evaluated through nonlinear dynamic time-history analysis under a set of recorded, near-fault, fault-normal component of ground motions. The optimal characteristic strengths for both the bearings are obtained through parametric study. The robustness of the improved performances are studied under varying characteristics of the superstructure, isolation bearing, as well as scenarios of seismic loading. It is demonstrated that the improvement of isolation efficiency, accompanied by considerable reduction of peak and residual bearing displacements can be attained by the SMARB over the LRB. The SMARB is also found to be more effective in suppressing transference of high-frequency components of ground motions to the floor acceleration, which is expected to be beneficial for frequency-sensitive equipment, mounted on the floors. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]