Abstract
Currently, the seismic designs of reinforced concrete (RC) bridges with tall piers are often accomplished following the ductility-based seismic design method. Though the collapses of the RC bridges with tall piers can be avoided, they are likely to experience major damage and loss of functionality when subjected to strong near-fault ground motions. The objectives of this study are to put forward an innovative design concept of a tall-pier system and its application in tall-pier bridges. The concept of the innovative tall-pier system is derived from the principle of earthquake-resilient structures, and is to improve the seismic performances of the tall-pier bridges under strong near-fault ground motions. The proposed tall-pier system has a box section and is composed of four concrete-filled steel tubular (CFST) columns and energy dissipating mild steel plates (EDMSPs). Trial design of a bridge with the new composite tall-pier system is performed based on a typical continuous rigid frame highway bridge with conventional RC box section tall piers. Both static analysis and nonlinear time history analysis of both the bridges with the new composite tall piers and conventional RC tall piers under the near-fault velocity pulse-type ground motions were conducted in Midas Civil2019 and ABAQUS. The results show that: under the design-based earthquake (DBE), the CFST columns and connecting steel beams remain elastic in the bridge with the new composite tall piers, while the damage is found in the replaceable EDMSPs which help dissipate the seismic input energy. The displacement responses of the new bridge are significantly smaller than those of the conventional bridge under DBE. It is concluded that the bridge with the new composite tall piers is seismic resilient under near-fault ground motions.
Highlights
When constructing an expressway or a railway in areas with high mountains and deep valleys, the total length of the route may be shortened by 200 m to 400 m as the height of pier increases 1 m [1].tall-pier bridges are the only design option most times
The results show that: under the design-based earthquake (DBE), the concrete-filled steel tubular (CFST) columns and connecting steel beams remain elastic in the bridge with the new composite tall piers, while the damage is found in the replaceable energy dissipating mild steel plates (EDMSPs) which help dissipate the seismic input energy
In the Specifications for Seismic Design of Highway Bridges (JTG/T 2231-01-2020) [12], it is required that specified research needs to be conducted if the maximum pier height exceeds 40 m or the effective mass of the first mode of the pier is less than 60%
Summary
When constructing an expressway or a railway in areas with high mountains and deep valleys, the total length of the route may be shortened by 200 m to 400 m as the height of pier increases 1 m [1]. Due to the lack of specialized seismic design concepts and design methods for RC tall-pier bridges, excessive displacement and deformation of the bridge may occur under near-fault ground motions, leading to severe structural damage, which requires costly and time-consuming repair, and even replacement [16,21]. The isolation system and self-centering system are widely investigated [22,23,24,25] and proved to be effective in decreasing the seismic vulnerability and improving the seismic performance of bridges These new tall-pier bridges have better seismic performance and some of them have been used in the engineering practice, the problem of complex construction, and time-cosuming repairment still exists, their seismic design concepts and design methods are not systematic and updated.
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