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Suggested Citation:"Overview." National Academies of Sciences, Engineering, and Medicine. 2005. Direct-Fixation Track Design Specifications, Research, and Related Material. Washington, DC: The National Academies Press. doi: 10.17226/13542.
Page 1
Suggested Citation:"Overview." National Academies of Sciences, Engineering, and Medicine. 2005. Direct-Fixation Track Design Specifications, Research, and Related Material. Washington, DC: The National Academies Press. doi: 10.17226/13542.
Page 2
Suggested Citation:"Overview." National Academies of Sciences, Engineering, and Medicine. 2005. Direct-Fixation Track Design Specifications, Research, and Related Material. Washington, DC: The National Academies Press. doi: 10.17226/13542.
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This report documents direct-fixation track design principles and specification prac- tices in Part A and direct-fixation fastener research in Part B. Direct-fixation track is the earliest form of track without ballast, originating with a fastener in the 1960s on the New York subway system. The New York fastener was a plate on a pad, both of which were anchored directly to supporting concrete. This track form received broader attention in the early 1970s when the Long Island Railroad and the Bay Area Rapid Transit System (BART) implemented a modern version to reduce dead load on their aerial structures. These systems implemented a fastener, the first bonded metal-rubber “sandwich,” which is also bolted to a concrete deck or plinth. That original design criterion from BART has evolved but remains central in most of the “conventional” direct-fixation specifications to 2004. Direct-fixation track has won acceptance as a cost-effective measure in reducing tun- nel and aerial structure construction costs. It has been promoted further for reducing track maintenance, stray current, and ground-borne vibrations. The aggregation of attributes has spawned an array of direct-fixation fastener products1 and parallel con- cepts, now generally termed “ballastless track.” Ballastless track now includes embedded block track and embedded rail track as par- allel categories to direct-fixation track. Subcategories of embedded block track are “resilient tie,”2 embedded concrete tie, and embedded wood tie3; all are cast into sup- port concrete. Embedded rail track is generally street track where the surrounding sur- face is at the top of rail with only the top of rail and flangeway visible. Embedded rail OVERVIEW TRACK-RELATED RESEARCH VOLUME 6: DIRECT-FIXATION TRACK DESIGN SPECIFICATIONS, RESEARCH, AND RELATED MATERIAL 1 Direct-fixation fasteners are all “plate-type” fasteners, meaning the fastener units are uniformly supported in the same sense as the common tie plate. Direct-fixation fastener designers attempt to distinguish their products by creating distinct direct-fixation category names. Among the plate-type direct-fixation fasteners are “constrained elastomer” or “framed fasteners” (elastomer is constrained within a frame); sandwich fasteners (top plate, with or without a bottom plate, with elastomer under the top plate); bonded fasteners (either sandwich or framed fastener designs with the elastomer vulcanized to the steel plates or frames); and non- bonded (sandwiched or framed fasteners without elastomer vulcanization). 2 The resilient tie system is a concrete block set on an engineered pad, with the block’s lower portion and pad encased in an elas- tomer “boot” that is embedded in support concrete up to the top of the boot. The resilient tie system uses one block on each rail located directly across from each other. The resilient tie concept was developed in Europe in the 1960s, originally on the Swiss Federal Railway system, then on other properties. It was introduced into North America in the 1970s. 3 Embedded concrete or embedded wood tie track types may be single blocks under each rail (sometimes termed “dual block” ties) or may be a single monoblock tie supporting both rails.

track may be designed with direct-fixation fasteners, with conventional crossties and fasteners, or without any ties or fasteners. The scope of this work is focused on direct-fixation track and fasteners, the subcat- egory of ballastless track that implies “plate-type” fasteners. Embedded block track is sufficiently close in many aspects that the report’s information is generally relevant. The practices and results offered in this report may not be applicable to embedded rail track depending on whether it uses direct-fixation fasteners and whether embedment material is in contact with the rail. The reason for this report is to address several industry concerns. When faced with various claims for performance characteristics among competing ballastless track products and a history of expensive implementations based upon the recommendations of specialist consultants, transit agencies expressed their desire for objective information on direct-fixation characteristics to allow independent judgment of supplier and consultant claims and recommendations. Suppliers question the expense and complexity of qualification testing. Transit agen- cies are questioning both the qualification and construction specifications based on experiences with subtle conflicts that have created awkward results and experiences in which key stipulations were missing, such as minimum fastener bearing contact on the support. Additionally, successful completion of the qualification tests has not proven to be a guarantee of expected in-track performance. Direct-fixation procurement and construction specifications have largely been mod- eled on past projects since the first implementation; therefore, the industry has stated a need for an independent review of common direct-fixation qualification specifications and construction specifications. Central to these concerns is the industry’s uncertainty as to whether specifications relate design intent with direct-fixation performance expectations. Addressing these concerns is the underlying theme of this report. The relationships among direct-fixation fastener parameters, the specifications, and expectations for long-term performance are central to all other issues. The subsection “Discussion on Basics” in Part A, Section 1, Direct Fixation Track Design, presents a general view of track mechanics that ballastless track systems can affect, along with mechanics beyond the capability of these devices. “Discussion on Basics” provides perspectives on the influences of fastener properties, track design, and specifications on track mechanics and how practical variations in fas- tener parameters and variations in manufacturing and construction may create deviant performance. “Discussion on Basics” also includes broad insight on key specification requirements and inherent limitations in some requirements, particularly laboratory tests. “Discussion on Basics” is the prelude to the detailed design issues, methods, and data in the balance of Part A, Section 1, Direct Fixation Track Design. Section 1, Direct Fixation Track Design, is the framework for subsequent sections of Part A, which provide examples of direct-fixation specifications along with com- mentary on each specification. There are three specification sections in Part A: • Direct-fixation procurement specifications (Section 2), • Direct-fixation test specifications (also referred to as “qualification tests”) (Sec- tion 3), and • Direct-fixation track construction specifications (Section 4). A fifth section in Part A is an example concrete specification, considered to be a highly useful reference complementing discussions of construction issues important for direct-fixation track design and construction. 2

3The technical perspectives in Part A are formed in large part by a body of research work performed by Battelle Laboratories. The industry, including an international agency, commissioned Battelle in three sep- arate programs between 1995 and 1999 to quantify ballastless track product character- istics including stiffness and dynamic response among other important parameters. The characterizations were performed on every major type of ballastless track product except embedded rail track and embedded wood tie track. Part B, Final Research Report, summarizes the results of those studies. With the array of ballastless track types, confusion has arisen on terminology for fasteners, track configurations, and some esoteric terms that describe materials. Appen- dix A to Part B provides a complete, cross-referenced glossary of ballastless track terminology. The goal of this report is to bridge research and practice in order to address industry concerns and provide an informed basis for the continued evolution of advanced track forms.

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TRB’s Transit Cooperative Research Program (TCRP) Report 71, Track-Related Research, Volume 6: Direct-Fixation Track Design Specifications, Research, and Related Material is a two-part CD-ROM formatted report that suggests guidance on the design and construction of direct-fixation track systems. Part A of the report describes track-design principles and material-evaluation methods for direct-fixation fasteners and track, as well as example specifications. Part B of the report provides data, evaluations, field reviews, and analyses of direct-fixation fasteners from a variety of sources, to allow a fuller understanding of their characteristics and proper application.

Links to instructions on burning an .ISO CD-ROM for and the download site for the CD-ROM for TCRP Report 71, Volume 6 (CRP-CD-61) are below.

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