Performance Evaluation of Structural Systems For High Speed Rail In Seismic Regions

Link to Latest Report: June 2019 Progress Report

Background:
High Speed Rail (HSR) imposes demands on the supporting structure that differ significantly from those imposed on highway bridges. Furthermore, the CAHSR project travels through several very different physical environments, each of which creates its own demands.  For example, the section passing through the Central Valley (flat and hot, easy construction access) faces construction challenges that differ from the sections that traverse the mountainous regions closer to the coast (widely varying column lengths, more difficult construction access, etc.)  Thus, any work aimed at developing an optimal system must start by understanding the design criteria and knowledge gaps perceived by the CAHSR design team.  Only then can research be targeted and effective.

The structural systems to be used for the bridges along the route presently focus on large, stiff structures that are intended to minimize displacements and that do not rely on the development of ductile response to the same extent that highway bridges typically do.  However, such stiff structures induce large forces in the substructures, which are consequently expensive.  CAHSR has identified cost containment as a critical issue, so the “strong” approach faces budgetary constraints.

At the other end of the stiffness spectrum, seismic isolation offers reduced forces (and potentially lower cost), but the displacements at the track level are likely to be much larger (Li and Conte 2017), and may exceed levels for safe vehicle operation. Thus, careful concept design will be necessary to resolve the conflicts between these two requirements (low forces and low displacements).  Selection of a suitable concept must precede any detailed design considerations.

Objective:
The overall goals of the proposed research are to:

  • Evaluate the structural systems presently under consideration by CAHSR.
  • Develop alternative concepts, and to obtain feedback from CAHSR to guide their further development.
  • To develop preliminary calculations and drawings for selected Conceptual Designs, so that CASHR can evaluate their expected structural performance, their speed of construction and cost.

Scope:
This project focuses on the development of seismically suitable and economically efficient structural designs for the California High Speed Rail system.  The following tasks will be undertaken:

  • Task 1 – Literature Review and Agency Discussions:  The first task is to find out what agencies in other parts of the world have done in developing High Speed Rail. This will be achieved by a review of the literature and by contacting rail authorities, such as those in Japan, China, Taiwan, Germany, France and Spain.
  • Task 2 – Meet with Personnel from CAHSR to Determine Design Criteria:  The team will meet with technical personnel from the CAHSR Authority to determine the design criteria for the rail infrastructure in the different regions in which it will be built.  They may differ in the different regions of the planned route, such as the Central Valley and more mountainous regions.  We will also seek information about the present approaches to project delivery (Design-build, Design-bid-build, etc.) and the structural concepts on which the present design approaches are based.
  • Task 3 – Performance Evaluation of System Presently Under Consideration:  We will conduct structural evaluations of the present design approaches, using relatively simple computational models, to determine their ability to satisfy the design criteria obtained in Task 1.   The use of highly detailed models is not warranted at this stage, because it is the overall behavioral trends that are sought, rather than the behavior of a local detail.  It is likely that the various loadings will impose competing constraints on the design, and these will have to be evaluated.  For example, the displacement limitations imposed by the needs of High Speed Rail may require a stiff, strong structure, whereas environmental loadings, such as thermal and shrinkage, may require a flexible one.
  • Task 4 – Identification and Performance Evaluation of Alternative Systems:  Alternative system concepts will be developed, guided by CAHSR’s design criteria and the concepts in use elsewhere in the world.   Their ability to meet the design criteria will be established through the use of simple mechanistic models, so that their first-level evaluation can be conducted in a reasonable amount of time.  Then we will meet with CAHSR personnel to discuss the alternative approaches, and to obtain feedback with which to refine the underlying structural concepts.  The feedback will be used to select the most promising concepts and to conduct more detailed evaluations on them.
  • Task 5 – Design Calculations and Drawings for Selected Conceptual Designs:  For each of the selected conceptual designs, we will provide preliminary calculations, approximate member sizes and connection details, and drawings.  The purpose is to provide a basis for evaluating the expected structural performance, the methods of construction, the time needed and the cost.  The research team will provide a written evaluation of the expected structural performance.  For the construction-related characteristics (methods, time, cost), the team will provide quantitative information on the underlying systems, but the CAHSR staff will themselves need to develop reliable estimates.
  • Task 6 – Final Report:  A Final Report will be written that summarizes the methods used and the findings reached during the project.  The Design calculations and drawings for the alternative systems will be included in appendices

Research Team:
Principal Investigator:  Prof. John Stanton
Co-Principal Investigator:  Prof. Marc Eberhard
Research Assistant:

Previous Progress Reports: