Keywords: seismic behaviour, double deck bridge, modeling, soil-structure interaction, response spectrum analyses, curved bridge.

This paper presents a comprehensive analysis on the seismic response of a double-deck bridge in china. A three-dimensional model was developed for a curved double-deck bridge, using SAP2000 [1], and a linear dynamic analysis (response spectrum analysis) has been used to evaluate the seismic vulnerability of this bridge through the capacity/demand ratio analysis of the structural elements. Then a further parametric study was conducted to investigate the effect of different structural irregularities in terms of the non-uniform foundation conditions, the length of the lower columns of the bents, and also the irregular column lengths within the same bent. Three series of models including the regular, semi-regular, and irregular ones were employed for this study.

To simulate the actual links of the bridge, linear springs and rigid link elements have been used to model the bearings, while soil spring elements were used to model the soil-structure system. Cracked section properties have been considered, and ground motions at a sufficient number of angles around the bridge have been applied to capture the maximum deformation of all critical components as this case study is an S curved bridge.

Based on the results of this study, it has been found that the seismic response of the double-deck bridge influenced by the geometry of the bridge and the foundation conditions, and the soil-structure interaction should always be considered [2]. It was also found that the main factor to improve the seismic response in the transverse direction is the regularity of the bridge column lengths, while increasing the stiffness of the bridge plays the main role in improving its response in the longitudinal direction, on the other hand, the transverse and the longitudinal seismic response of the double deck bridge is sensitive to increasing the flexibility of the bridge, especially when the degree of irregularity of the column lengths decreases. Also it has been found that for equal displacements the short column attract the greatest force in the transverse direction [3], while the difference of the stiffness between the adjacent frames determines the critical pier bent for the longitudinal response.

1

CSI, SAP2000 V-14, "Integrated finite element analysis and design of structures basic analysis reference manual", Computers and Structures Inc, Berkeley CA, USA, 2009.

2

A. Aviram, K.R. Mackie, B. Stojadinovic, "Guidelines for Nonlinear Analysis of Bridge Structures in California", Pacific Earthquake Engineering Research Center, Richmond, California, USA, Report, PEER 2008/03, 2008.

3

A.K. Chopra, "Dynamic of Structures, Theory and Applications to Earthquake Engineering", 3rd edition, Prentice Hall, New Jersey, 2006.

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