Delivered assembled, or as a kit

The two formats

An assembled span arrives on a flatbed, complete, and is lifted into place. The set is often about a day once the abutments are ready. Utility and Pedestrian bridges are built this way, and every span above 20 ft is made up of standard sections bolted together at a plate: a 72 ft Utility is two 20 ft sections and two 16 ft sections. That is why spans over 48 ft ship on two trucks and are bolted together on site before a crane sets them.

A bolt-together kit arrives flat and banded, and is assembled where it is going. It exists for one reason: some crossings cannot be reached by a crane, and a bridge that cannot be lifted into place has to be built in place.

What actually decides it

Span. Kits are 20 ft. If the crossing is longer than that, the question does not arise.

Rating. A kit carries 4 ton in the cataloged 20 ft configuration; a Utility span carries 16,000 lb across 20 to 72 ft. If a delivery truck, a loaded tractor, or a fire engine has to cross, that is a Utility bridge and the format follows from the rating.

Access. Whether a crane or an excavator sized for the span can get to the crossing, and whether the delivery truck can get close enough to be unloaded. Where it cannot, a kit is the answer, and its span and rating are the constraint you plan around rather than a starting point to negotiate up from.

What you have on site. An assembled span needs lifting equipment there on the day. A kit needs people, hand tools, and time.

What each one costs you

The trade is time against equipment.

An assembled span is faster and needs machinery. Most of the work happened in the shop, the crossing is closed for about a day, and the finish and decking arrive already fitted.

A kit is slower and needs almost no machinery. It takes longer to assemble than a span takes to set, because there is more to put together, and that is the whole point: the work moved from a crane to a crew.

Where people get it wrong

The common mistake is buying a kit for a crossing that will eventually take a vehicle heavier than 4 ton, because the site is awkward and a kit is the only thing that fits through the gate.

Access is a solvable problem and a rating is not. Where those two pull in opposite directions, it is worth pricing the harder delivery before accepting the lighter bridge.

The other one is assuming a bridge arrives ready to use. Unloading is the buyer’s or the contractor’s responsibility in both formats, and an assembled span needs equipment sized for it waiting when the truck arrives.