دانلود رایگان مقاله انگلیسی طرح مطلوب میراگرهای ویسکوز غیر خطی برای حفاظت لرزه ای سیستم های ساختاری - اشپرینگر 2017

Abstract

Viscous dampers are widely employed for enhancing the seismic performance of structural systems, and their design is often carried out using simplified approaches to account for the uncertainty in the seismic input. This paper introduces a novel and rigorous approach that allows to explicitly consider the variability of the intensity and characteristics of the seismic input in designing the optimal viscous constant and velocity exponent of the dampers based on performance-based criteria. The optimal solution permits controlling the probability of structural failure, while minimizing the damper cost, related to the sum of the damper forces. The solution to the optimization problem is efficiently sought via the constrained optimization by linear approximation (COBYLA) method, while Subset simulation together with auxiliary response method are employed for the performance assessment at each iteration of the optimization process. A 3-storey steel moment-resisting building frame is considered to illustrate the application of the proposed design methodology and to evaluate and compare the performances that can be achieved with different damper nonlinearity levels. Comparisons are also made with the results obtained by applying simplifying approaches, often employed in design practice, as those aiming to minimize the sum of the viscous damping constant and/or considering a single hazard level for the performance assessment.

5 Conclusions

A novel and rigorous methodology has been proposed for the optimal reliability based design of viscous dampers in building frames subjected to a stochastic earthquake input with uncertain intensity, duration, and frequency characteristics. The sum of the damper forces for the target exceedance probability is considered for the objective function defi- nition. This parameter, accounting for the stochastic structural response, is more explicitly related to the dampers costs, differently from the other objective functions considered in the literature. An efficient reliability computational approach is used in the inner loop of the optimization process, and a robust gradient-free algorithm is employed for the optimization loop.

The proposed methodology has been applied to design the viscous dampers for protecting a steel moment-resisting frame, by considering both the cases of uniform and variable damper distribution along the building height. The following conclusions can be drawn from the design results:

• The combined use of Subset simulation and the auxiliary response method supports efficient evaluation of the quantities required by the inner loop. Thus, it can be conveniently employed for solving double-loop type RBDO problems.

• By reducing the damper velocity exponent a, the cost of the dampers, related to the sum of the damper forces for a target exceedance probability, decreases. In particular, a reduction of the sum of the damper forces of 30% is obtained for a = 0.3 compared to the case of a = 1, for a target failure probability of 10% in 50 years.

• Considering a variable distribution of the damper properties along the building height significantly reduces the cost of the dampers, while ensuring the same target performance of the system in terms of probability of exceeding the target value of the IDR.