Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads (2017) / Chapter Skim
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6C h a p t e r 2 To understand the current state of research and practice in light rail structures, a literature review was conducted. When technical information related to light rail transit was not available, the behavior of conventional rail bridges carrying heavy-haul and high-speed trains was reviewed, which can assist a general understanding of light rail bridges although their loading characteristics are different.
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State of the art review 7 • Open deck: This type was used in the late 1800s with a simple system comprising timber crossties installed to a bridge superstructure. Although open deck systems are light, they generate substantial noise and vibration.
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8 proposed aaShtO LrFD Bridge Design Specifications for Light rail transit Loads measured axle weight was calibrated with a typical error range of ± 4%. A comparison showed that the in situ axle weight was greater than the nominal axle weight.
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State of the art review 9 Chebli et al.
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10 proposed aaShtO LrFD Bridge Design Specifications for Light rail transit Loads Colorado 75.6ft (train length) California Massachusetts (Orange line rapid)
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State of the art review 11 no standard live load for light rail bridges, contrary to the case of highway and railway bridges. For design purposes, one light rail train is loaded per track to determine structural load and associated forces, which is analogous to traffic lanes in design of highway bridges.
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12 proposed aaShtO LrFD Bridge Design Specifications for Light rail transit Loads 2.5 Train-Structure Interaction Train-structure interaction generates several force components to be considered in designing railway bridges, such as impact, rail break, and centrifugal forces. Endeavors have been made to examine these forces associated with train configurations and bridge properties.
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State of the art review 13 The following is a summary of selected papers concerning the impact behavior of railway structures. Dukkipati and Dong (1999)
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14 proposed aaShtO LrFD Bridge Design Specifications for Light rail transit Loads Summary: Impact increased static load owing to dynamic amplification; however, it tended to converge with train speed. This implies that a threshold train speed exists in design of rail structures.
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State of the art review 15 distress to supporting members. A sudden reduction in train speed can impact rail components and bridge substructure (Azimi et al.
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16 proposed aaShtO LrFD Bridge Design Specifications for Light rail transit Loads effects. Since each model had its own advantages, careful selection of appropriate models was suggested.
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State of the art review 17 was developed. Okelo and Olabimtan (2011)
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18 proposed aaShtO LrFD Bridge Design Specifications for Light rail transit Loads gap allowed was 3 in.)
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State of the art review 19 Phoenix, AZ; UTA Light Rail, Salt Lake City, UT; and SoundTransit, Seattle, WA. It is, therefore, worthwhile to calibrate load factors associated with light rail transit loadings.
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20 proposed aaShtO LrFD Bridge Design Specifications for Light rail transit Loads corresponding effects on the behavior of bridge structures, as well as forces related to train -- rail– structure interaction. To better utilize light rail transit systems and to advance the state of the art of light rail bridges, the following challenges should be addressed: • There is a practical need for the design of light rail bridges carrying both light rail train and highway traffic loads, which is not actively considered in practice.
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