In view of the large damage suffered in recent earthquakes and hurricanes, building design criteria are developed to protect life and reduce damage and loss to an acceptable level. The problem is minimizing the expected total life-cycle cost with respect to the design load and resistance. Load uncertainty includes occurrence time, intensity, and duration. The costs of construction, maintenance, and failure consequences, including deaths and injuries, as well as discounting cost over time, are considered. Optimal values are obtained of design variables and target reliability under single and multiple time-varying loads. Also investigated is sensitivity of the optimal design to important loading and structural parameters. The optimal design is found to depend primarily on the limit state consequences (costs), and to a lesser degree on the structural life. For multiple hazards, the optimal design is controlled by the hazard with large uncertainty and severe failure consequences. In a companion paper applicat...

Minimum Building Life-Cycle Cost Design Criteria. I: Methodology

In recent years, significant advances have been accomplished in the fields of modeling, analysis, and design of deteriorating civil engineering systems, and novel approaches to life-cycle assessment, maintenance planning, and optimal design of structural systems have been proposed. Despite these advances, life-cycle concepts are far from being explicitly addressed in design and assessment codes and effectively implemented into practice. There is, therefore, a need to promote further research in the field of life-cycle performance of structural systems under uncertainty and to fill the gap between theory and practice by incorporating life-cycle concepts in structural design and assessment codes. An effort is currently ongoing within the Structural Engineering Institute (SEI)/ASCE to meet this need. This paper is part of this effort and is aimed at presenting a review of the main principles, concepts, methods, and strategies for life-cycle assessment and design of deteriorating structural systems un...

Life-cycle performance of deteriorating structural systems under uncertainty: Review

Decision-making under uncertainty is a difficult task when the information available is scarce and consequences are large. Such is the case in assessing vulnerabilities of buildings and transportation facilities to earthquakes in Mid-America where large events have occurred in the past and yet very few events have been recorded at intensity levels of interest to engineers. A rational approach to this problem requires careful consideration of both aleatory and epistemic uncertainties in the demand and capacity of the systems under consideration, the performance of those systems, the consequences of unsatisfactory performance in terms of direct damages and costs incurred over time, and costs required for retrofitting existing systems or building new systems. A balance must be achieved between risk and benefit for an optimal design decision. Some recent developments in this approach as it applies to design and retrofit for earthquake effects are briefly reviewed. A risk–benefit-based procedure is proposed and illustrated for buildings that must withstand earthquake effects in Mid-America. Copyright © 2005 John Wiley & Sons, Ltd.

Risk‐benefit‐based design decisions for low‐probability/high consequence earthquake events in Mid‐America

A new methodology for the performance-based optimum design of steel structures subjected to seismic loading considering inelastic behavior is proposed. The importance of considering life-cycle cost as an additional objective to the initial structural cost objective function in the context of multiobjective optimization is also investigated. Life-cycle cost is considered to take into account during the design phase the impact of future earthquakes. For the solution of the multiobjective optimization problem, Evolutionary Algorithms and in particular an algorithm based on Evolution Strategies, specifically tailored to meet the characteristics of the problem at hand, are implemented. The constraints of the optimization problem are based on the provisions of European design codes, while additional constraints are imposed by means of pushover analysis to control the load and deformation capacity of the structure.

Performance-based multiobjective optimum design of steel structures considering life-cycle cost

A multi-objective optimization procedure is presented for designing steel moment resisting frame buildings within a performance-based seismic design framework. Life cycle costs are considered by treating the initial material costs and lifetime seismic damage costs as two separate objectives. Practical design/construction complexity, important but difficult to be included in initial cost analysis, is taken into due account by a proposed diversity index as another objective. Structural members are selected from a database of commercially available wide flange steel sections. Current seismic design criteria (AISC-LRFD seismic provisions and 1997 NEHRP provisions) are used to check the validity of any design alternative. Seismic performance, in terms of the maximum inter-storey drift ratio, of a code-verified design is evaluated using an equivalent single-degree-of-freedom system obtained through a static pushover analysis of the original multi-degree-of-freedom frame building. A simple genetic algorithm code is used to find a Pareto optimal design set. A numerical example of designing a five-storey perimeter steel frame building is provided using the proposed procedure. It is found that a wide range of valid design alternatives exists, from which a decision maker selects the one that balances different objectives in the most preferred way. Copyright © 2003 John Wiley & Sons, Ltd.

Optimal seismic design of steel frame buildings based on life cycle cost considerations

The design criteria for a nine-story office building, subject to earthquakes and winds, are developed based on the method in the companion paper The seismic and wind hazards, structural response analyses, and cost estimates are based on recent literature Structural limit states in the nonlinear range and consequences are considered The optimal design is obtained by minimizing the total expected life-cycle cost using a numerical procedure A sensitivity analysis is conducted comparing the optimal design to the important but controversial parameters, such as design life, death and injury cost, structural capacity uncertainty, and discount rate The method is applied to design under earthquakes, winds, and both hazards at Los Angeles, Seattle, and Charleston, South Carolina, and compared with current design As expected, the seismic load controls the optimal design in Los Angeles The optimal design is “dominated” by seismic load in Seattle and wind load in Charleston These hazards, however, do not “cont

Y. K. Wen

Papers

Minimum Building Life-Cycle Cost Design Criteria. II: Applications