Abstract
Seismic demand and performance of bridges are highly dependent upon the level of irregularity. Although previous studies have proposed methodologies so as to quantify the irregularity of the bridges in terms of global regularity index, it still remains unclear how to determine the distribution of irregularity along a bridge, as well as to discover the irregularity sources. This research project is intended to develop a quantitative vector regularity criterion for single- and multiframe bridges based on the modified correlation function for spatial locations of scaled mode shapes of deck-alone and whole bridge. The proposed criterion calculates two types of regularity indices, namely, local (LRI) and global regularity indices (GRI). The GRI is a scalar value representing the overall regularity of the entire bridge, whereas the LRI highlights vector irregularity distribution along the bridge. Since the deck discontinuity due to the in-span hinges is one of the leading causes for irregularity, the proposed index has been employed in case of multiframe bridges as well. Furthermore, the current study aims to investigate the correlation between the proposed irregularity indicators and the nonlinear to linear demand ratio. Therefore, the appropriate analysis method can be chosen based on irregularity extent of bridges. Obtained results of the proposed indices reveal that in-span hinge is one of the main parameters affecting the distribution of local irregularity along a bridge. Therefore, multiframe bridges need to be investigated in detail so as to validate the special design requirements recommended by design codes.
Highlights
In regard to past earthquakes, it is observed that, during severe earthquakes, seismic damage is highly dependent upon the level of bridge irregularity [1,2,3]
To validate the proposed criterion, the suggested regularity indices are calculated for all intended models and compared with the results of Calvi index. e RI proposed by Calvi [5] explained in (8) is a reliable criterion which has been used frequently by researchers [11]. e generality of Calvi and other previous methods is based on quantitative criteria for an entire bridge, whereas the sources of irregularity and their distribution along the bridge are not provided. e Calvi index is a measurement of differences between the transverse mode shapes of the deck without columns and the whole bridge based on the orthogonality property of the eigenvectors expressed in the following form:
Regarding the scalar definitions of the bridge regularity criteria, up till there has been no vector criterion representing the distribution of irregularity along the bridge length and determining the source of irregularity, especially in multiframe ones. erefore, this research project introduced the notion and formulation of local regularity index of bridges. e proposed criteria, referred to as global regularity indices (GRI) and LRI here, are based on the modified concept of correlation function for spatial locations of scaled mode shapes between deck-alone and entire bridge in the field of experimental vibration analysis
Summary
In regard to past earthquakes, it is observed that, during severe earthquakes, seismic damage is highly dependent upon the level of bridge irregularity [1,2,3]. Akbari and Maalek proposed a regularity index based on the differences between the seismic responses of the intended and reference bridges. Ayala and Escamilla investigated the modal irregularity index and the effect of this characteristic on the seismic performance of bridges using simplified methods of analysis [17]. It is shown that the GRI and LRI could be used for a variety of purposes, including detecting sources of irregularity, determining regularity of each node along bridge, choosing the appropriate analysis method, and positioning the in-span hinges, as well as estimating the nonlinear to linear demand ratio at different parts of a bridge. This study reveals that local and global regularity are in close correlation with the maximum nonlinear to linear displacement ratio in the cases of single- and multiframe bridges
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