تجزیه و تحلیل هزینه فایده چرخه عمر ساختمان ایزوله

Seismic isolation is effective in reducing seismic demand to buildings and mitigating seismic damage costs. To corroborate this fact quantitatively by taking all possible seismic events that occur during the service period of a building into account, this study investigates probabilistic characteristics of the peak ductility demand of inelastic superstructures with linear/bilinear base isolators subject to hundreds of strong ground motion records, and then assesses the cost-effectiveness of seismic isolation technology from the lifecycle cost–benefit perspective. Based on results from nonlinear dynamic analyses of two-degree-of-freedom systems with the Bouc–Wen hysteretic model, a prediction model for the peak ductility demand of isolated structures is developed and used in lifecycle cost analysis to assess the cost-effectiveness of seismic isolation systems. The analysis results show that seismic isolation reduces vibration in superstructures significantly and can be cost-effective in mitigating seismic risk.

Strong earthquakes cause tangible and intangible losses and disrupt normal operation of structures and infrastructure. Such destructive seismic effects can be reduced by installing energy dissipation devices and seismic isolation systems. It is noteworthy that lifecycle cost–benefit assessments of seismic risk mitigation activities provide important information to decision makers [1], [2], [3], [4] and [5]. The results are also valuable in performance-based and consequence-based earthquake engineering [6]. Seismic isolation has been successfully applied in practice to mitigate seismic risk [7]. The success of this technology is based on that an isolated structure, which includes a superstructure and isolator, has a much longer vibration period as compared with a fixed structure (i.e., structure without base isolation), and that strong ground motions (mostly, shallow crustal earthquakes in California) contain less energy in the long vibration period range. Consequently, seismic isolation systems are very effective. One exception could be when isolated structures are excited by near-fault motions containing strong velocity pulses. The performance of isolated systems subjected to near-fault motions has been investigated [8] and [9]. Assessments are usually carried out by considering that superstructures are rigid or elastic [7]; this consideration facilitates the design of isolated structures to limit seismic damage. However, to carry out cost–benefit analysis of isolated structures, it is necessary to characterize linear and nonlinear responses of a superstructure and base isolator by considering record-to-record variability of strong ground motions, which has a significant impact on the assessment results. A study of probabilistic characterization of these responses and cost-effectiveness of seismic isolation systems has not been reported in the literature, although Kikuchi et al. [10] carried out a parametric study on dynamic responses of yielding isolated structures by considering wide ranges of model parameters subjected to harmonic excitations and transient excitations (only three ground motion records). This study investigates probabilistic characteristics of the peak ductility demand of inelastic superstructures with seismic isolation and assesses the cost-effectiveness of seismic isolation technology. The aims of this study are to develop a simple and generic lifecycle cost model of an isolated structure by taking all possible seismic events during its service period and nonlinear responses of superstructures into account, and to corroborate the empirically proven cost-effectiveness of seismic isolation from the lifecycle cost–benefit perspective. The hysteretic behavior of superstructures is represented by the Bouc–Wen model [11], [12] and [13], which incorporates stiffness/strength degradation and pinching behavior due to cyclic loading. For the assessment, an isolated structure is modeled as a two-degree-of-freedom (2DOF) system, the bottom layer representing a seismic isolation system and the top layer representing a superstructure, and is subjected to a set of 381 California strong ground motion records (762 components) that were selected from the Next Generation Attenuation database [14] to account for record-to-record variability of strong ground motions. The considered isolation systems are low-damping rubber bearing systems (i.e., linear base isolators) and lead rubber bearing systems (i.e., bilinear base isolators). By carrying out nonlinear dynamic analysis, a prediction model for the peak ductility demand of isolated structures is developed, and is used in cost–benefit analysis to assess the cost-effectiveness of seismic isolation systems. In the following, governing equations of motion for an inelastic 2DOF system are given, and nonlinear dynamic analysis is carried out to assess the effectiveness of seismic isolation in reducing seismic demand and to investigate probabilistic characteristics of the peak ductility demand. Subsequently, an empirical model for predicting the peak ductility demand of isolated structures is developed. The developed empirical model is used in illustrative lifecycle cost analysis to investigate the cost-effectiveness of seismic isolation for mitigating seismic risk.

The present study investigates the statistics of peak elastic and inelastic responses of structures with base isolators under seismic excitations, and assesses the cost-effectiveness of seismic isolation in mitigating seismic risk, aiming to corroborate the empirically proven successful performance of seismic isolation technology from the lifecycle cost–benefit perspective. For assessment, an isolated structure (i.e., base isolator and superstructure) is idealized as an inelastic two-degree-of-freedom system with the Bouc–Wen hysteretic model, and an empirical model of inelastic peak responses of isolated structures is developed by performing nonlinear dynamic analyses using a set of 381 California records. The developed model is employed to assess the cost-effectiveness of seismic isolation technology. The conclusions that can be drawn from the results include: 1. Seismic isolation significantly reduces peak structural responses of superstructures by as much as 70–80%, and is particularly beneficial for stiff superstructures. This effectiveness decreases as the seismic excitation level increases because of the progressive degradation/deterioration of superstructures, resulting in the elongated vibration period. 2. Bilinear isolators are slightly less effective against ordinary ground motions compared with linear isolators. However, if near-fault motions are of interest, bilinear isolators can reduce seismic demand in isolators significantly as well as in superstructures. Thus, use of bilinear isolators rather than linear isolators may be preferred to enhance reliability of isolated structures against near-fault motions. 3. For a model structure considered in numerical applications, seismic isolation can reduce the expected lifecycle cost by about up to 20%, in comparison with a fixed structure, depending on the design level of a superstructure. This seismic risk reduction could be more than sufficient in compensating the required design/construction/installation costs of base isolators. In such a case, seismic isolation technology is cost-effective and should be adopted. Finally, the developed ductility demand model as well as the lifecycle cost model of an isolated structure is based on a number of simplifications and assumptions. The analysis could be enhanced and expanded by considering sophisticated structural modeling and using strong ground motion records for different earthquake types.