Abstract
The substructures of high-speed rail (HSR) structures are typically rigid, as they are designed to meet stringent longitudinal displacement limits specified in most HSR design standards. For site conditions such as deep valleys and soft soils, tall columns or low foundation stiffness can lead to a flexible substructure system. Flexible substructures are preferred for bridges in seismic areas because their lower horizontal frequencies yield smaller seismic forces. This cost-effective design strategy is recognised in the California HSR design criteria manual, which specifies larger relative longitudinal displacement limits. In this work, the influences of substructure flexibility on relative displacements were investigated through dynamic analyses of 36 different numerical models representing a 20-span viaduct supported by substructures with first horizontal frequencies of 0.566–3.706 Hz. Four key parameters were investigated: column height, span length, bearing plan layout and ratio of depth to span length. Train models from BS EN 1991-2:2003 were used as dynamic moving loads. The results of this study show that the chances of dynamic responses larger than design limits do exist as the stiffness of substructures departs from being rigid, where resonance effects on substructures are the main contributor to response amplification.
Highlights
High-speed rail (HSR) substructures are typically rigid, as they are designed to meet stringent longitudinal displacement limits specified in most high-speed rail (HSR) design standards
The results of this study revealed that, as the stiffness of the substructure departs from being rigid, the relative longitudinal displacements, relative rotations and relative vertical displacements typically used for design purposes can be influenced by the dynamic responses of substructures to a level exceeding design limits and resonance effects on substructures can be of significant concern
The results were compared with the design limits given in UIC 776-2 (UIC, 2009) and BS EN 1991-2:2003 (BSI, 2003), as these codes provide the most comprehensive suite of HSR load models for dynamic analysis purposes, have been extensively used and validated in many countries for decades and served as a basis for the development of recent HSR codes, including the California HSR
Summary
High-speed rail (HSR) substructures are typically rigid, as they are designed to meet stringent longitudinal displacement limits specified in most HSR design standards. (BSI, 2003) and UIC 776-2 (UIC, 2009) limit relative longitudinal displacements between two consecutive decks to 5 mm due to traction and braking actions and to 10 mm due to vertical traffic actions without consideration of the track–structure interaction. The Chinese high-speed railway design code (NRA, 2015) limits longitudinal displacements by specifying a minimum substructure stiffness. The minimum substructure stiffness of the Chinese code is equivalent to limiting relative longitudinal displacements to 4 mm due to braking actions (He et al, 2017). The design specifications for HSR in Taiwan, China (THSR, 2005) limit relative longitudinal displacements between two consecutive decks to 7 mm due to a combination of traction, braking and vertical traffic actions and to mm due to a combination of braking and vertical traffic actions of one train and an operational-level earthquake. Luo and Miyamoto (2008) developed a code-type provision using a method called spectral intensity for Japanese design standards, which requires that the stiffness of substructures be adequately provided to safeguard against train derailment during an earthquake
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