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Parametric study of highway bridges with irregular substructure and superstructure

This paper is available in a repository.
This paper is available in a repository.

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Abstract

Irregular structures have a more complex behavior, and therefore their analysis, design, inspection and maintenance require more attention. For bridges, ir-regular conditions are presented in superstructure and substructure systems. A bridge have and irregu-lar superstructure if it is curved or skewed, or if its spans have different lengths. By the other side, sub-structure irregular condition is presented when the piers have variations in length or resistance. In addi-tion, bridges are also considered as irregular in structures with important variations in the stiffness between superstructure and substructure elements. Some analyses for irregular substructure bridges show notorious variation in the deformation de-mands of piers, concentration of shear forces in short piers, variation of ductility demands and more participation of superior modes (Moehle & Eber-hard, 2000, Kappos et al., 2005, Isakovic & Fischinger, 2008). Experimental studies demonstrate that the absorbed energy of an irregular bridge was concentrated in the shorter pier, almost 70% of the total energy dissipation (Tehrani & Mitchell, 2010). Bridge design codes, as AASTHO (2007), Cal-trans and Eurocode 8, consider bridge irregularity in a similar practice. AASTHO classifies as a regular bridge those structures with curvature angle minor than 90°, or with maximum stiffness thresholds be-tween adjacent spans or piers in the same bent. In the AASTHO Guide Specifications (2009), some minimum stiffness relations are indicated for ele-ments and subsystems. Curved and skew bridges or structures with various levels, not balanced mass or with important variation in piers stiffness are classi-fied as irregular by Caltrans. The Eurocode Code 8 classifies the bridge irregularity in function only of a ductility factor. In these codes the irregularity of bridges is considered in a simple form, causing in some circumstances systems with insufficient secu-rity levels, as it was demonstrated by Calvi et al. (Tehrani & Mitchell, 2010). In recent years, some irregularity indices were proposed to classified bridges. These indices are used to predict if a bridge will behave as was pro-jected (Isakovik & Fischinger, 2000). These indices are classified as elastic and inelastic indices, consid-ering that irregularity conditions are exhibited by elastic or inelastic parameters. Escamilla et al. (2011) compare different irregular indices for bridg-es with variation on piers length. Through this com-parison it is observed that irregular indices are not an absolute valuation of bridge irregular condition, as a result of different values obtained for the same structure. Irregular indices could be an adequate tool to characterize bridges irregularity; however more researches would be needed to define the practical meaning of some values and of some indices. Inspection preliminary programs of bridges are necessary to clarify the current condition of a group of structures. There are some inspection programs proposed for bridges, in most of them is common to consider as an influent parameter of their seismic behavior the superstructure and substructure irregu-Parametric study of highway bridges with irregular substructures and superstructures