SuperSpan Structures

For years engineers and contractors have been designing and building economical underpass structures using MultiPlate products. The science of building with MultiPlate has advanced another step with SuperSpan. SuperSpan provides the world's largest corrugated steel, clear-span openings for underpasses, waterways and similar structures, while retaining the economy of the smaller MultiPlate construction.

Because SuperSpan achieves such large clear widths, it opens up many possible new uses. For example, a two lane vehicle underpass that previously required two side-by-side MultiPlate structures may now be built with a single wide SuperSpan underpass.

SuperSpan has long passed the theoretical stage. More than 300 different structures are in service in North America, Australia, New Zealand, the United Kingdom and South Africa.

An ecological bonus of SuperSpan structures is that they utilise a minimum amount of native materials, (rocks, earth) as backfill and do not infringe on the natural surroundings to the same degree as traditional structures.

Specification Factors

An important feature of SuperSpan design is the use of concrete 'thrust beams' cast 'in-situ' on the assembled structure, during backfilling. The thrust beams are positioned each side of the top arch, at the junction of the top arch and the side wall with reinforcing steel connected to the corrugated plates by clip angles. Because the top arc, or spreader arch, is of very large radius and low rise-to-span ratio, it would probably be quite unstable without thrust beams. It would be subject to either elastic or snap-through buckling by installation forces or final design loadings.

However, a flat steel arch is stiffer than a high steel arch, if the springline is restrained from significant outward movement.

In a conventional semi-circular top span, it is extremely difficult to obtain excellent compaction and positive lateral restraint at the critical point (approximately the 3/4 point, 40 degrees from the top).

The thrust beam reinforces the top at the point of critical buckling and provides good longitudinal distribution of concentrated live loads, particularly those of earth moving and compaction equipment. The thrust beam derives its name from its effective transfer of the thrust in the top arch into the well-compacted soil against its vertical face.

Therefore, the SuperSpan structure, by means of its shape and the thrust beams, which reduce the central angle of the effective top arch to less than 80 degrees, is stable against deflection and snap-through buckling and can be economically designed and installed within recognised critical buckling stresses, seam strengths and flexibility factors.

Standards and Approvals

A SuperSpan structure is inherently a major engineering combination of steel and soil. CSP Pacific regards each installation as a unique project. CSP Pacific engineers check every SuperSpan structure with the analysis based on NZS/AS 3703.2:1989

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