Development of Minimum Life-Cycle Cost Design Criteria
Y. K. Wen,* Y. J. Kang
National Science Foundation, CMS 95-10243; Campus Research Board

As a large number of the civil constructed facilities in this country were built in the first half of this century and many are too expensive to replace, the repair/retrofit problem will become more acute. The objective of this study is to develop design criteria for new and existing systems based on consideration of life-cycle costs. The emphasis is on proper modeling of the uncertainty in resistance of and loadings on the facilities, costs of failure consequences, and discounting of cost/loss over time. The problem is formulated as that of a constrained minimization problem. The results will have important implications in the development of future codes and will also have more immediate benefit in development of guidelines and criteria for repair and retrofit.

Fragility Analysis of Essential Facilities in Mid-America
Y. K. Wen,* S.-H. Song
National Science Foundation, CMS 97-01785 COOP

Essential facilities (EF) such as hospitals and fire stations are crucial in post-earthquake disaster relief. Based on inventories carried out in Memphis, Tenn., St. Louis, Mo., and Carbondale, Ill., representative EF structural types have been identified. Structural modeling and response analysis of these structures with or without retrofit can be then carried out under uniform hazard ground motions in the form of response spectra or ground motion time histories. The results are used to obtain the probabilistic performance curves of the facilities, which allow evaluation of the adequacy of the current facilities and the effectiveness of retrofit by comparing reduction in expected loss versus retrofit cost.

Live Load Design for Parking Garages
Y. K. Wen,* G. L. Yeo
Structural Engineering Institute, American Society of Civil Engineers

To recommend an appropriate value for design in ASCE-7, load surveys were conducted in nine commercial parking garages in four cities of various sizes. Statistical analyses were then carried out of the equivalent uniform distributed loads, which produce the maximum column axial load and bean midspan moments that the building is expected to experience during its lifetime. The dynamic amplification from vehicle motions on the decks and the ramps was also investigated. The results suggest a possible reduction of the current design load of 50 psf to 35 psf, with no allowance for reduction according to bay area.

Multivariate Regression Analysis of Tank Car Lading Loss
Y. K. Wen,* D. G. Simpson,* Y. J. Kang, L. Fu
Association of American Railway/Sims Engineers

A multivariate regression analysis is being carried out to establish relationship between probabilities of railway tank car lading loss and sources of loss as function of tank car attributes and track type. The results will provide basis for car manufacturers, railway regulators, and commercial shippers for better evaluation of future tank car performance and quantitative risk assessment. A database of accident records in the last 30 years of 6000 tank cars is used. Results obtained so far indicate the importance of insulation, shelf coupler, head shield, and shell thickness. Effectiveness of these features in reducing lading loss probability is also quantified.

Redundancy of Dual Systems under Random Dynamic Loads
Y. K. Wen,* S.-H. Song
National Science Foundation, CMS 95-10243, CMS 97-01785 COOP

The redundancy concept in structural engineering has been used often, but there is also misunderstanding of the concept and interpretation when there is uncertainty in both loading and structural resistance. The redundancy under static loads in terms of reliability has been investigated extensively by researchers in the past. Redundacy under random dynamic loads, such as seismic forces, has not been fully understood. This study concentrates on reliability and redundancy of dual systems under stochastic loadings. The first phase of a parametric investigation of simple series and parallel systems has been completed. Dual systems of moment frames and shear walls are being investigated to develop a more rational redundancy factor for design.

Redundancy of Structures Under Seismic Forces
Y. K. Wen,* C. S. Wang
National Science Foundation, CMS 95-10243, CMS 97-01785 COOP

The emphasis of this study is on randomness of ground excitation, inelastic structural response behavior, uncertainty in structural resistance, and torsional effect. The definition of redundancy in terms of probability of failure under random static loads is extended to dynamic loads. Time history analyses of typical steel structural frames are carried out under actual and simulated ground excitations. The probability of various response levels in the inelastic range are then calculated. Redundancy provided by different lateral force-resisting frames and redundancy of system in case of partial failure of structural components such as steel moment frame connections observed in 1994 Northridge earthquake, are examined.

Uniform Hazard Spectra and Motions
Y. K. Wen,* C. L. Wu
National Science Foundation, CMS 97-01785 COOP, CMS 95-31303

For evaluation of structural performance in future earthquakes in mid-America, accurate and efficient modeling of the ground excitation and structural response is essential. It is specially important when inelastic response and system deterioration are considered. The seismicity uncertainty and inelastic response behavior can be considered through the use of uniform hazard inelastic response spectra (UHRS). The dependence of the spectra on various hysteretic response behavior is examined. Also, for performance evaluation of buildings and structures, site-specific ground motions are also generated according to the seismicity of the region.