This report, Bridges for Service Life Beyond 100 Years: Service Limit State Design, describes research, outcomes, and products on the basis of the R19B project objectives. The objectives were to develop design and detailing guidance and calibrated service limit states (SLSs) to provide 100-year bridge life and to develop a framework for further development of calibrated SLSs. The products of this study are expected to be directly usable by the American Association of State Highway and Transportation Officials (AASHTO) and departments of transportation (DOTs) and include • Provisions needed to implement SLSs and the associated load and resistance factors necessary to produce calibrated bridge components and systems expected to have a predictable service life. • Detailed design and detailing provisions required to design and construct the calibrated component or system. • Databases used in the calibration, as well as instructions for a calibration spreadsheet, for use by DOTs to track and adjust service-based reliability with time. Consideration of SLSs requires different input data from the previously calibrated Strength Limit State I (also known as “ultimate or strength limit states,” or ULSs). In ULSs, the limit state function is defined by resistance, which is considered constant in time, and loads. For SLSs, a different approach is needed because • Exceeding a service limit state does not lead to a clear, immediate loss of functionality. • Acceptable performance can be subjective (full life-cycle analysis is required). • Resistance and load effects can be and often are correlated. • Load must be considered to be a function of time, described by magnitude and frequency of occurrence. • Resistance may be strongly affected by quality of workmanship, operation procedures, and maintenance. • Resistance is subject to changes in time, mostly but not only by deterioration. • Resistance can depend on geographical location (e.g., climate, exposure to industrial pollution, or de-icing agents). The topic of limit state design, also known as load resistance factor design (LRFD), within the United States has been under development and implementation for more than 25 years. The benefits of this design platform are now well understood by the bridge and structures community as well as by transportation decision makers. Generally, it has been assumed that maintenance activities will be sufficient to prevent significant loss of the strength and stiffness that would result in unsatisfactory service level performance. It has been recognized that advancements and further maturity of the LRFD platform need to focus on quantification and calibrations of the SLSs. Although previous work has been published in this area, the R19B study serves as a foundational reference to partially fill knowledge gaps and, perhaps more importantly, for direct application and reference for future study in this emerging technical area of design. (Author/publisher)
Samenvatting