Applicability of the Pushover Based Procedures for Bridges

摘要

Introducing new performance-based design procedures, pushover analysis has become increasingly popular. However, many of these procedures are simply extrapolated from buildings, not taking into account specific characteristics of the bridge structures. The specific and complex response of the bridge may preclude the use of the static, pushover based analysis. Thus, the objective of the reported research has been to identify the cases where the pushover analysis is acceptable and the cases where more rigorous inelastic time-history analysis is required for viaduct structures. Several cases of a three span single column bent viaducts were analyzed in the transverse direction. The stiffness of piers, the eccentricity of mass, the boundary conditions at the abutments, and the reinforcement of columns were varied. The N2 method, which combines inelastic static (push-over) analysis of the MDOF system and inelastic spectrum analysis of an equivalent SDOF system, was used. The results of the N2 procedure were compared by the inelastic time-history analysis. Although the N2 method frequently yielded similar results as the inelastic time-history analysis, there were several cases, where the two methods yielded significantly different results, not only quantitatively but also qualitatively. Qualitative differences were found in cases where the torsional structural stiffness was smaller than the flexural one. Other important parameters that influence the seismic response of viaducts in the transverse direction include the ratio of the stiffness of the deck and piers, eccentricity, boundary conditions at the abutments, and the relative strength of the columns. A "regularity index" has been proposed as a numerical measure to help the designer to decide about the suitability of the pushover analysis for bridges. The index is defined as a relative difference between the areas, bounded by the normalized displacement lines obtained within the first and second iteration of the N2 method. A general conclusion has been that the pushover based procedures for bridges should be used with care. In a case of rather complex bridges, time-history analysis may be more suitable solution.