S. Ghosh, Graduate Research Assistant (sghoshz@engin.umich.edu),

K.R. Collins, Assistant Professor, (kevinrc@engin.umich.edu)

and

M. Kohno, Associate Professor

Reliability-based, performance-based seismic design is considered to be the future of seismic design of structures. However, the general public, and especially building owners, may not fully appreciate the significance of a statement such as "the probability of exceeding 1.5% drift for this structure is 10% in the next 50 years." Instead, they may prefer to think of the reliability and performance of a structure in economic terms such as its life cycle cost. The life cycle cost takes into account initial construction costs as well as repair costs of structural and nonstructural elements and the monetary consequences due to loss of building function.

Previous models for cost analysis have used empirical rules for relating damage to cost applying a combination of engineering judgement and cost data from past earthquakes. In this study, the cost model used in the HAZUS^®99 earthquake loss estimation methodology is adopted. The basic expression for damage cost, from the perspective of the building owner, is

(1)

where CD is the total damage cost, K_I is a city cost index, CS is the cost of structural damage, CNSD is the cost of nonstructural damage to drift-sensitive components, CNSA is the cost of nonstructural damage to acceleration-sensitive components, CCD is the cost of damaged contents, INV is the cost of damaged inventory, REL represents relocation costs, YLOS represents capital-related income losses, and RY represents rental income losses. The HAZUS^®99 technical manual provides suggestions for relating the values of each of these cost components to measures of structural response and damage (i.e., drift and acceleration). The HAZUS^®99 model represents a nationally accepted standard for performing cost analyses.

Presented here are the results of a simulation study to evaluate how the expected life cycle cost of a structure varies with the yield base shear strength of the structure, the design life of the structure, and other parameters. The cost analysis is performed for three-story and nine-story steel moment-resisting frame structures. A baseline (reference) design of the structure, based on current code requirements, is considered along with a set of modified designs. Monte Carlo simulation is used to calculate the expected life cycle costs of the various building designs for design lives of 20, 50, and 100 years. For each frame design, dynamic nonlinear time history analyses have been performed using a set of 1292 simulated earthquake records for a site near Los Angeles, California. The results include a set of graphs showing how the expected life cycle cost varies with the yield base shear force, the discount rate, and the assumed design life of the structure.