SPMT move (self-propelled modular transporters)

How bridges get built · Heavy lift, moving and accelerated construction · SPMT move (self-propelled modular transporters)

Also called: SPMT, bridge move, transporter erection, roll-in

How it is done

Select the staging area (ideally within a few hundred metres, on level, firm ground) and survey the route: grades, cross-falls, kerbs, utilities, overhead clearance and ground bearing; design mats or temporary pavement where needed.
Build the superstructure on temporary supports high enough for the SPMTs to drive beneath, with lift points designed into the deck.
Analyse the deck for the transport condition (supports at the SPMT points, dynamic and twist effects), add temporary bracing or strongbacks, and set limits on twist and differential deflection.
Configure the SPMT units with spreader beams or support towers; do a trial lift and a short trial move, weighing the structure at each support.
In the closure, remove the old bridge (often also by SPMT), then drive the new one along the route at walking pace, compensating grades with the axle hydraulics to keep the deck level.
Position over the bearings using the multi-directional steering, lower onto bearings or shims, and drive the SPMTs out.
Complete closure pours, joints and approach work, and reopen.

Key numbers

Axle line capacityabout 30–48 t per axle line
Typical movesabout 300–3,000 t, spans 20–100 m (Sam White Bridge, Utah, 2011: two spans totalling 108 m, about 1,730 t)
Route gradeup to about 5–8 % with levelling
Ground pressurecommonly about 100–200 kPa under the axles, spread with mats
Speedwalking pace when loaded
Move costUSD 200,000–800,000 (indicative)

Where it fits

Replacement bridges over motorways and railways with a staging area within a few hundred metres; spans 20-100 m; steel or concrete decks up to 3,000-4,000 t.

Where it does not

Routes with grades over 6-8 % or soft ground without mats, decks too flexible for transport without strongbacks, sites without a staging area.

Choosing it

Choose SPMT when a staging area is close by and the route is level and firm; the superstructure is built off line without temporary supports beside the bridge.
Prefer a lateral slide when there is room beside the bridge but no route for transporters, or the deck is too long for SPMT handling.
Prefer crane-set prefabricated elements (PBES) when the pieces are within crane capacity; SPMT pays off for complete spans with deck.
Avoid it when the deck cannot tolerate the transport support condition without heavy temporary strengthening.

Plant, pace and money

PlantSPMT modules (4-6 axle lines each, 30-40 t per axle line), power packs, jacking towers, mats.

ProductivityOvernight moves; assembly months.

CostUSD 200,000-800,000 for the move; the temporary staging is the larger cost.

Risks and controls

What goes wrong

Hydraulic failure, ground failure under the transporters, deck stress during transport, clearance conflicts on the route.

Quality assurance

Route survey and ground bearing checks, transport analysis of the deck, trial lift, contingency procedures.

Origins

SPMTs were developed for heavy industrial and shipyard transport; European practice, notably Dutch highway and rail bridge moves, was the model for the FHWA manual on using SPMTs to remove and replace bridges (2007), after which US moves multiplied.

Examples

Dozens of US and Canadian ABC replacements, Dutch railway crossings, Korean expressway overpasses.

Case studies

Sam White Bridge, I-15, American ForkUSA · 2011Two-span concrete bridge (2 × 54 m, about 1,730 t) moved about 150 m across I-15 in an overnight closure of about 8 hours; at the time the longest bridge moved into its final position in the US.

Florida International University pedestrian bridgeUSA · 2018A 53 m concrete truss span was moved into place by SPMT; it collapsed five days later. The NTSB attributed the collapse to design errors at a truss node, but cracks that grew after the move were not acted on: a reminder that cracking seen after a move must stop the work.

In the bridge game

What Bridge Master applies when you pick it

Deck types: Steel plate girder, Steel box girder, PSC I-girder, Steel truss, Orthotropic steel box, Steel arch, PSC U-girder, Spliced PSC girder, Precast segmental box, Voided slab, Network tied arch. Spans 30-90 m, up to 140 m.

+25: Overpass with a yard nearby: SPMT.
-45: SPMTs need ground.
+10: Feasible in a long possession if a haul path crosses the track at grade.
-25: A one-off operation for one span: on a multi-span viaduct it is the exception for the main span, not the method for the deck.
not allowed: SPMT over water.
not allowed: SPMTs need ground under the whole path of the span.

Try it in the game →