Courtesy : hsr.ca.gov
Bullet train design
Aerial structures will carry the high-speed train alignments at grade separations over water and steep terrain, in congested urban areas, and will allow transverse access below the guideway. Due to the potentially large amount of aerial structures, development of design guidance is warranted to ensure that these structures will achieve the design and performance requirements, promote an efficient design, and allow for the preparation of capital cost estimates.
This technical memorandum outlines the important performance and functional needs of a basic aerial
structure carrying dedicated high-speed train operation. Design elements considered include:
• Structural Performance
• Functionality
• Safety
• Serviceability
• Construction Efficiency
• Trackside Environment
In this document, high-speed rail aerial structures currently in use are presented for illustrative and
comparative purposes. Design elements that are required for high-speed rail operation are identified
along with basic structural design parameters to be considered including material type selection,
construction options, approximate span length and span to depth ratio, and alternate span articulation.
Based on a qualitative assessment, a basic conceptual aerial structure cross section, span length, spanto-depth ration, and span articulation is proposed for advancing the preliminary design. Development of
substructure design concepts are specific to geologic and geographic considerations and are not included
in this design guidelines document.
Refined design is not included in the scope of this memorandum. Approximate dimensions are given to
initiate discussion and to establish the basic structural parameters for the basic design.
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INTRODUCTION
1.1 PURPOSE OF TECHNICAL MEMORANDUM
This technical memorandum identifies the basic elements of aerial, or elevated, structures and
assesses the benefits of using a standard design for aerial structures carrying high-speed train.
This document presents representative aerial structures for high-speed rail and introduces a
basic design for high-speed train structure for the purpose of advancing the preliminary design
and preparing capital cost estimates.
1.2 STATEMENT OF TECHNICAL ISSUE
This technical memorandum will serve as the basis for the CHST Design Manual, which will
present standards and criteria specific to design of the high-speed train system. Preliminary
structural design criteria for aerial structures are under development and contained within the
Technical Memorandum 2.3.2 – Structure Design Loads.
Since multiple designers will be involved in the design and construction of the high-speed train
system, alternate aerial structure designs are anticipated. A basic high-speed aerial structure
design will be used to ensure that the structures considered in preliminary design achieve the
CHSTP’s design and performance requirements. Presentation of an aerial structure design
concept is intended to provide designers with a basis for establishing structure footprints and
proportioning materials and to promote development of uniform description of construction
techniques and uniform cost estimates during preliminary design.
1.2.1 Definition of Terms
The following technical terms and acronyms used in this document have specific connotations
with regard to California High-Speed Train system.
Alignment: The horizontal and vertical route of the high-speed rail guideway.
Ballasted Track:Rail lines installed over a specific type of crushed rock that is graded in such a
manner that can support heavy loads of the rolling stock.
Ballast-less Track: Rail lines installed directly atop concrete slabs for support. Also referred to as
slab track or direct fixation track.
Contact Wire: A suspended (overhead) wire system that supplies power from a central power
source to an electric vehicle such as a train.
Footprint: Area of the ground surface covered by a facility, or affected by construction
activities.
Guideway: A track or riding surface that supports and physically guides transit vehicles
specially designed to travel exclusively on it.
High-Speed Train: A railroad system utilizing steel-wheel-on-steel-rail technology with a regular
operating speed greater than 125 mph (200 kph).
Program-Level: Refers to a CEQA or NEPA environmental review that covers the broad spectrum
of a large, complex, regionally extensive effort comprised of a number of smaller,
regionally focused projects or phases.
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Acronyms
CFR Code of Federal Regulations
CIDH Cast-in-Drilled-Hole
CISS Cast-in-Steel-Shell
CHST California High-Speed Train
CHSTP California High-Speed Train Project
EIR/S Environmental Impact Report / Statement
FAA Federal Aviation Administration
FRA Federal Railroad Administration
HST High-Speed Train
NFPA National Fire Protection Association
NIST National Institute of Standards and Technology
OCS Overhead Contact System
S/D Span to Depth Ratio
1.2.2 Units
The California High-Speed Train Project is based on U.S. Customary Units consistent with
guidelines prepared by the California Department of Transportation and defined by the National
Institute of Standards and Technology (NIST). U.S. Customary Units are officially used in the
United States, and are also known in the U.S. as “English” or “Imperial” units. In order to avoid
confusion, all formal references to units of measure should be made in terms of U.S. Customary
Units.
Guidance for units of measure terminology, values, and conversions can be found in the Caltrans
Metric Program Transitional Plan, Appendix B U.S. Customary General Primer
(http://www.dot.ca.gov/hq/oppd/metric/TransitionPlan/Appendice-B-US-Customary-GeneralPrimer.pdf). Caltrans Metric Program Transitional Plan, Appendix B can also be found as an
attachment to the CHSTP Mapping and Survey Technical Memorandum.
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2.0 DEFINITION OF TECHNICAL TOPIC
2.1 GENERAL
This technical memorandum considers the following design parameters and identifies a basic
design for aerial structures suitable for dedicated high-speed train operations based upon the
following design parameters:
- Structural Performance: Achieve superstructure and substructure design requirements to
ensure compliance with stringent project specific design criteria, including seismic
resistance, fatigue resistance, strict train operation and passenger comfort issues. Ease
of reparability after seismic events and collision damage protection to allow quick
resumption of service. - Functionality: Provide rolling stock and trackbed support, meeting the electrification
requirements for traction power supply and distribution, communications, train control, as
well as providing space for walkways, duct banks, sound walls, and drainage. - Safety: At a minimum, no collapse structural criteria under extreme seismic events,
ccontinuation of safe revenue high-speed train operations, after a seismic event, and the
ability to perform required service, inspection and maintenance operations during routine
and emergency conditions. - Serviceability: Provide for ease of routine inspections, maintenance and repairs.
- Economy: Realize cost efficiencies based upon economy of scale, ease and speed of
construction, use of prefabricated segments or rolling forms in standard superstructure
cross sections. - Trackside Environment: Mitigate noise and vibrations, reducing visual and shadow
impacts, maintaining required property access, and promoting aesthetics appropriate with
surroundings.
This document has been developed concurrently with the structural loading and seismic design
guidelines for use in advancing the preliminary design.
2.2 LAWS AND CODES
49 CFR Part 213, Appendix C – Statement of Agency Policy on the Safety of Railroad Bridges, is
the current safety regulation of conventional railroad bridges in the United States. Federal
Railroad Administration (FRA) requirements for containment of high-speed trains on aerial
structures will be addressed in the design of the track structure.
Aerial structures located in proximity to airports or flight paths will be required to conform to
applicable Federal Aviation Administration (FAA) codes and regulations.
Applicability of National Fire Protection Association (NFPA) requirements with regard to highspeed train aerial structures will be assessed during preliminary design.
Compliance and/or demonstration of equivalency with safety and regulatory requirements will be
developed for the CHSTP Systems Requirements.
2.3 POLICY CONSIDERATIONS
Policy considerations may significantly influence the size, aesthetics and cost of the high-speed
train aerial structures. In order to advance the design of aerial structures, assumptions regarding
policy issues have been made which require confirmation. A summary of these issues and
assumptions follow:
• Dedicated High-Speed Train Operations. Design of aerial structures for dedicated HST
operation may restrict and potentially prohibit operation of conventional locomotives on
these structures due to the higher axial loadings and forces for conventional trains. The
potential operation of conventional rail vehicles on structures designed specifically to
high-speed train standards may require speed or route restrictions.
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• Intrusion Protection / Fencing. It is assumed that fencing around aerial structures will not
be typically required since the structures will be grade separated throughout providing
intrusion protection. A protective open rail or solid parapet approximately 4 feet high will
be required along external walkways. Access control/detection will be required at
maintenance access locations.
• Maintenance. It is assumed that, under normal conditions, regular maintenance activities
will occur outside of the hours of revenue service. Speed restrictions will be imposed if
emergency repair or maintenance is required on aerial structures during revenue service.
• Emergency Access. Walkways on aerial structures will be capable of safely exiting
passengers during emergency conditions in accordance with requirements of NFPA-130.
• Lighting on Aerial Structures. Permanent maintenance lighting is not required to be
installed on high-speed train aerial structures. Maintenance lighting will be provided as
part of maintenance operations. Aerial structures will be required to have lighting
facilities for emergency access and egress.
• Third Party Utilities. It is assumed that no leasing of cable space or duct banks is
provided on the structure for third party utilities and therefore access to the guideway is
not required by third parties.
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3.0 ASSESSMENT / ANALYSIS
3.1 STANDARD DESIGN FOR HST AERIAL STRUCTURES
Potential advantages associated with a system wide standard design for an aerial high-speed
train structure include:
• Economy. Design, construction and sourcing would take advantage of economies of
scale leading to reduced cost.
• Constructability. Due to the large number of aerial structures anticipated, there would be
opportunity for large-scale pre-fabricated assembly, potentially leading to simplified
construction techniques and quick erection schedule.
• Risk Reduction. A thoroughly vetted design and consistent method of construction,
inspection, and maintenance would reduce the risk of cost overruns and delays during
design, construction and operation.
• Aesthetics. A common system-wide aesthetic would introduce consistency and promote
a statewide identity to the high-speed train system.
• Quality Control. A standard design would simplify inspection and quality control.
• Ease of Maintenance. A standard design would allow for similar maintenance and
inspection procedures to be developed throughout the high-speed train system.
Additionally, with a standard design, an inventory of spare parts and segments can be
maintained to facilitate rapid repair.
• System Integration. A standard aerial structure cross section would promote integration
for structural and system interfaces.
Potential disadvantages associated with a standard design include:
• Reduced Flexibility. The high variability of conditions and environments that the highspeed train alignment would encounter may require non-standard structures.
• Discouraged Innovation. A standard design could potentially limit the structural
designer’s creativity and use of cost-effective alternative designs.
• Design Sequencing. A standard aerial structure design would need to be completed
early in the design process in order to distribute to the project’s design and construction
teams.
3.2 DESIGN CONSIDERATIONS
The design parameters considered when developing a basic design for high-speed train aerial
structures are summarized in the following sections:
3.2.1 Structural Performance
• Design Life. The design life of fixed facilities shall be 100 years. Elements that are
normally replaced for maintenance, such as expansion joints, may be designed to a
shorter term.
• Seismic Performance and Damage Resistance. The high-speed train alignment will pass
through active seismic regions. Modern performance based methods shall be used in the
aerial structure design. Resistance to damage due to multiple earthquake levels shall be
considered, as shall resistance to potential collision of automobiles and trains with
support columns and shared corridors.
• Reparability and Damage Protection. Design for pre-determined failure points and level
of associated damage shall provide for fast repair and return to service.
• Passenger Comfort. Passenger comfort criteria dictate that the aerial structures shall be
stiff and rigid structures.
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• Load-Bearing Capacity. The aerial structure shall be designed to carry the dynamic live
loads associated with the high-speed trains, maintenance trains, and potentially
conventional trains in the shared-rail corridors.
• Fatigue. Excess vibration can cause structural fatigue due to wide structural stress
variation, resulting in diminished structural capacity. The aerial structures shall be
designed to prevent excessive reduction in load bearing and seismic response capacities
due to fatigue.
3.2.2 Functionality
Aerial structure cross sections must accommodate all elements for high-speed operations,
maintenance and emergency response. These elements include: • Tracks • Walkways/Stairs
• Track Support • Maintenance Access
• Sound Walls • Overhead Contact System
• Drainage • Cable/Duct Banks
• Lighting • Signal Heads
• Walkway Railing/Parapet • Traction Power Supply System
• Communication System (Normal and Emergency Operations)
3.2.3 Safety
Emergency Egress and Access. Walkways provided on aerial structures shall allow safe egress
and access as required during emergency conditions.
3.2.4 Serviceability
Service Inspections and Maintenance. Aerial structures shall provide for service and inspection
of high-speed train track infrastructure.
3.2.5 Efficiencies and Economy of Scale
To take advantage of economy of scale and to facilitate rapid construction, aerial structures shall
be designed with an easily fabricated cross-section.
• Materials. Readily available materials such as reinforced concrete (either poured in place
or segmental precast pre-stressed) and steel sections shall be used.
• Poured-in-Place or Prefabrication. Poured-in-place concrete construction shall be the
typical method for the foundation, columns, and column caps. Pre-fabricated concrete
superstructures (i.e., box girders) would eliminate the need for erecting falsework and onsite curing time, and reduces temporary clearance requirements.
• Standard Cross Section. Use of a standard cross section would allow the use of
standard reinforcement details, pre-stressing details, bearings, and shear keys for a wide
range of conditions.
• Large Scale of Standard Elements. The expected total length of the aerial structures
would allow for large scale production of pre-fabricated elements or the development of
techniques for on-site implementation (i.e., poured-in-place with rolling forms).
• Manufacturing and Delivery. If a pre-fabricated cross sectional design is chosen, then
the segments shall be designed to be suitable for transportation, storage, and erection
on-site.
