In-span hinges can facilitate construction processes and diminish the adverse consequences of creep, shrinkage and thermal phenomena, but can also bring about detrimental effects such as impacts, unseating issues and large displacements. The seismic behaviour of concrete bridges has been addressed in previous studies, but it remains unclear how in-span hinges affect the seismic response of irregular bridges. The aim of this research was to determine the seismic performance of irregular multi-frame bridges. To consider a wide range of irregularity, four classes of single- and multi-frame bridges with low to high regularity indices were considered. An innovative parameter, the adjacent frame lateral stiffness ratio (AFSR), was introduced to determine the appropriate position of in-span hinges and investigate the performance of multi-frame bridges. The results showed that the beneficial or damaging effects of in-span hinges on the seismic behaviour of a bridge depend on its level of irregularity. The seismic demands of piers in multi-frame bridges are typically lower than those of single-frame bridges. The results also showed that the piers adjacent to an in-span hinge are more affected by the hinge. It is recommended that in-span hinges are located such that the AFSR approaches unity so as to avoid out-of-phase vibration of adjacent frames and unseating issues.
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.
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