15-Reference 02- FR2X Memo Design Live Load for New DMU 20241119.pdf

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Memo

To Jeremy Harbaugh

From David McCune

Date November 19, 2024

Re FrontRunner Design Live Load Summary for New Vehicle Procurement

Executive Summary

Utah Department of Transportation (UDOT) will procure new commuter rail vehicle for Utah Transit

Authority (UTA) in conjunction with the FrontRunner 2X (FR2X) project. It is currently anticipated that the new vehicles will be Diesel Multiple Units (DMU). While commuter rail design live loads used for existing

FrontRunner infrastructure includes a DMU consist, it is likely the newly procured DMUs will have different axle weights and spacing. To avoid the need to re-analyze existing infrastructure for the new DMU consist, the demands of the current FrontRunner Design Live Loads were compared to several hypothetical DMU load patterns with varying axle spacing to determine the limits of the spacing that should be placed in the new DMU Request for Proposal (RFP).

The results of this investigation led to the following stipulations to be placed in the RFP:

• Maximum Axle Load = 59.2 kip

• Minimum Length of Four Axle Grouping at Coupler or Power Pack = 30’-0”

• Minimum Bogie (Truck) Spacing within a Car = 51’-0”

Frontrunner Design Live Loads

The UTA design live loads for existing FrontRunner structures that are design for commuter rail loading include:

• Commuter Rail Train – Four 75 kip axles for the locomotive and up to ten sets of four 41 kip axles for the bilevel coaches

• Maintenance Train – Up to four 100 Ton Ballast cars with four 66 kip axles each without live load impact

• Diesel Multiple Unit – Up to 10 cars with four 59.2 kip axles each

The load patterns (axle spacing) of these three vehicles are shown below:

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Analysis

The intent of the original DMU loading was to design the FrontRunner infrastructure so it could accommodate a future DMU vehicle. Expected DMU car designs with the current FR2X project may differ substantially from the axle weights and spacing of the DMU load pattern in the current FrontRunner Design Live Load. Boundaries need to be set in the Vehicle RFP for maximum axles weights and minimum axles spacing so that the new DMU trains do not produce a load effect greater than the maximum demand of the existing design live load. The pairs of new DMU axles may be slightly closer together than the current design live load DMU diagram, but retaining walls should be designed for the 75 kip axles spaced at 9’ from the commuter rail locomotive.

All bridges on the existing FrontRunner system are simple spans except for the flyover structure near the Ogden Yard. That bridge has a 3-span continuous unit (151.5’/172’/151.5’). To determine the limits on axle spacing for the new DMU vehicle, the following analysis was performed:

• Simple span models in LARSA built for spans ranging from 60 feet to 200 feet at 5 foot increments.

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• Continuous span model (151.5’/172’/151.5’) built for the one continuous span structure on the system

• All three design live loads (Commuter Rail Train, Maintenance Train, and DMU) were run across every span in the model in a moving load analysis to determine the maximum existing demand for each span configuration. In this comparison, live load impact was applied to the Commuter Train and DMU but not the Maintenance Train.

• A representative “modified” DMU load pattern was created with the following characteristics:

• 59.2 kip axles

• Slightly reduced distance of the four axle groups at each coupler of 30’-0” (compared to 34’-0” in the FrontRunner DMU design live load).

• Reduced the bogie spacing within a vehicle by 5’ increments to create multiple new modified DMU cases

• The demand of each modified DMU case was compared to the controlling demand of the three current design live loads

• The minimum bogie spacing was set to that the corresponding modified DMU load pattern did not have a higher demand than the controlling demand of the current design live loads.

Results and Recommendations

For the simple span load cases, the bogie spacing in the modified DMU train could be reduced up to 30 feet and still not control over current design live loads. For the one continuous span case, the bogie spacing could be reduced by between 10 feet and 15 feet before the modified DMU train controlled the demand. As such, a maximum reduction of 12’-6” was chosen for the limit which reduced the modified DMU bogie spacing to 51’-0”.

Based on the analysis, the following limits should be set in the DMU RFP to ensure the new DMU vehicles do not control structural demand on any existing FrontRunner infrastructure:

• Maximum Axle Load = 59.2 kip

• Minimum Length of Four Axle Grouping at Coupler or Power Pack = 30’-0”

• Minimum Bogie (Truck) Spacing within a Car = 51’-0”

If the proposed axle loads are less than 59.2 kip, the bogie spacing could be further reduced. That request could be investigated if the carbuilders have a need to proposed bogie spacing less than 51’-0”.