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  • Writer's pictureJhordy Rodriguez

Constructability in Bridge Design #4 - Transport Logistics

Updated: Mar 14

When it comes to bridge design, an often neglected aspect at the conceptual stage is transport logistics. It involves the movement of major factory-produced components such as girders and deck panels from the shop to the construction site. The transportation options largely depend on the nature and size of the components, and could involve road, rail, or river-based transport, or even a combination of these.


Understanding transport constraints is crucial at the conceptual design stage because it directly affects the feasibility of the project. For instance, the dimensions and weight of the girders must be compatible with the transport regulations in the area. If this isn't considered, the project could face significant delays and cost overruns due to difficulties in transporting the girders from the factory to the construction site. For example, in British Columbia, the Lower Mainland has weight limits of 90 tonnes and length limits of 60 meters for road transport. Ignoring these constraints during design could lead to a situation where the girders are too large or heavy to be transported, causing project delays and increased costs. If you're outside the Lower Mainland, the constraints become stricter: the lower of 44 tonnes in weight or 37 meters in length.


Another critical factor to consider is the local trailer capabilities and the regulatory requirements for permits, as these directly affect the cost and practicality of transportation. To provide some context, here are some basic trailer options and constraints in BC:


  • A standard 53-foot trailer can handle segments less than 19 meters long, with the weight constraint being 90 tonnes. It is also the most cost-effective option.

  • An extendable trailer, which has a medium cost implication, can handle segment lengths from 19 meters to 24 meters.

  • For segments longer than 24 meters, a steering dolly is required. However, the cost can be very high, ranging from $10k per load in the Lower Mainland to $30k per load in Northern BC.

Segment Length

Trailer

Cost/load

Note

< 19m

Standard 53-foot Trailer

Lowest

Need to check segment for 2.3m overhang at the back. Max. Weight: 90 tonnes

19m to 24m

Extendable Trailer

Medium


> 24m

Steering Trailer

Very High

$10k per load (Lower Mainland). $30k per load (Northern BC)

If the girders exceed the height restrictions of the transport routes, they must be transported on their side. Moreover, transported components like girders must undergo structural assessments for static and dynamic forces using a dynamic load allowance, as per jurisdictional guidelines. These components should be evaluated for service, ultimate, and fatigue limit states. The trailer and any steering dolly used must have sufficient restraint to secure the girders during transport. This ensures that support conditions align with the assumptions made in the structural assessment.


In conclusion, successful bridge construction requires an understanding of transport logistics, including the selection of the right transport method, consideration of route constraints, and understanding of local trailer capabilities and permit requirements.

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