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RISS 인기검색어
- 검색키워드
- 저자 : Mohamed Nour El-Din Abdalla (검색결과 1 건)
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Mohamed Nour El-Din Abdalla Sungkyunkwan University 2014 국내박사
After large economic losses followed Northridge earthquake, the need for simple and realistic quantitative seismic risk-analysis tool becomes obvious. The present study contributes to satisfy this need by developing a simple methodology for seismic life-cycle cost (LCC) estimation. This methodology accounts for accuracy of LCC modeling as well as simplicity of application. Accuracy is achieved through incorporating the effect of aleatory and epistemic uncertainty in the LCC estimation framework. Simplicity is achieved, firstly, by considering equivalent single-degree-of-freedom (ESDOF) system instead of the full multi-degree-of-freedom (MDOF) structure. Further simplification is achieved by reducing the computational cost significantly through eliminating the full construction of fragility curves and incremental dynamic analysis curves. Instead of the latter curves, an approximate fragility curve (AFC) and localized incremental dynamic analysis (LIDA) curve are used. Moreover, a probabilistic simple closed-form solution for loss estimation is used. This solution considers the randomness and the uncertainty in seismic demand and structural capacity. A steel jacket offshore platform is used as a case study. The soil-pile-structure interaction (SPSI) is considered in developing the numerical model of the offshore platform with actual soil-in-situ characteristics. In order to investigate the importance of the seismic design method on LCC estimation, different design philosophies are used for the seismic design of the offshore platform, such as force-based and performance-based designs. In order to examine the effect of high ductile structure system on LCC, numerical models are developed using buckling-restrained braces (BRB) system and compared with the conventional bracing in the as-built platform structure. As an application on the proposed LCC methodology, a comparative assessment study based on deterministic sensitivity analysis is conducted to investigate the relative importance of different uncertain variables on the LCC estimation. This sensitivity analysis is conducted using different methods such as tornado diagram analysis (TDA), first-order second-moment (FOSM) and Latin hypercube sampling (LHS). The considered uncertain parameters are categorized with regard to different sources such as, structural capacity, seismic hazard, soil-pile-structure interaction, loss estimation, and LCC formulation. This study introduced a new relative stiffness index, which relates the stiffness of the sub-structure and super-structure. Based on this index, the results have shown the significant effect of SPSI on the seismic performance and consequently on the seismic LCC estimation of the platform models. However, it is found that for system designed with large ductility, i.e. large response modification factor, R, simplified SPSI modeling can be used to reduce the computational cost especially for the preliminary design stage. In order to have an insight into the expected LCC estimation through structural seismic behavior, a seismic performance evaluation is conducted on the platform models. From the seismic LCC standpoint, using systems designed with large R factor, such as BRB models, provide more economical alternative, even though the initial cost is higher, compared to models designed with small R factor, such as conventional bracing. The displacement-based design (DBD) method shows that increasing the structure elements cross sections, to fulfill the required drift limit, may increase the initial cost of the structure; however, it decreases the total LCC when compared to the performance plastic-design method. On the other hand, the force-based design shows higher LCC estimations compared to the performance-based design. The sensitivity analysis results show that loss estimation and seismic hazard uncertain variables have a more dominant influence on the LCC variability compared to the other variables. The LCC is found to be particularly sensitive to the drift-intensity regression coefficient “b” and seismic hazard slope “k”. Among the structural uncertain parameters, the variability in plastic hinge strength and modal damping ratio have the most significant impact on the LCC. Soil-pile friction variable proves to be the most important uncertain variables among the soil-pile modeling parameters. The initial cost has the most influential effect among the different cost items of LCC estimation. The variability in parameters such as yield strength, Young’s modulus, pile driving factors, maintenance cost,…etc, turned out to have insignificant impact on the LCC variation.
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