Three Radical Approaches to Structural Stairs

Thursday, January 30th, 2014
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Three new feature staircases at the world-famous New Mariinsky Theatre in St Petersburg cut to the essence of consulting engineering.

Engineers Malishev Wilson were the vital link between the architects (based in Canada), manufacturers (based in Austria) and installation team (based in St Petersburg).

Huge emphasis was placed on the internal design, underlined by the dynamic spaces. The creation of the dramatic staircases was integral to completing this vision, and Malishev Wilson has engineered three very different and unique solutions, each of which enhance the theatre’s sense of grandeur.

The Glass Stair

The most imposing of the trio in terms of pure size is the 34-metre long public staircase, which is the first such application of structural glass on this scale in Russia.

“Due to its unprecedented nature, our client relied heavily on our support from the concept design stage and testing to manufacturing and installation,” said Malishev Wilson director Gennady Malishev.

glass stairs

Laminated glass treads and landing panels span 1.9 metres between steel stringer plates, supporting an imposed load of four kilopascals or four kilonewtons at mid span. The stair is supported at each half landing level with brackets fixed to the RC columns and walls. The steel stringers’ span is approximately 7.4 metres. Laminated glass balustrade panels on each side of the stair are fixed into the steel stringer section.

The feature stairs have been designed to comply with Ultimate Limit State (ULS) design principles.

“Complying with the design criteria of the ULS is considered as the minimum requirement (among other additional demands) to provide proper structural safety,” he said. “Given the advances in structural glass design, the firm has been working on the new edition of the IStructE to formally introduce Ultimate Limit State (ULS) design principles into glass structures.”

The Oval Stair

The initial concept proposed by the architects was a stair with an elliptical geometry spanning five floors with a stair width of 2.3 metres and curved glass balustrade on both sides. To deliver this solution, the original engineers designed a curved steel truss on the inner perimeter and cantilevered steel beams supporting the floor and landings on top. This scheme was very heavy, however, and the dynamic performance of the stair was below allowable minimum.

“Instead we proposed the stair deck be comprised of a tapered fabricated steel box section,” said Malishev. “This was supported on the inner perimeter stringer edge by eight steel rods of 56 millimetres, which would work as a big spring in torsion. This enabled the original stair vision to be realised with the curved glass balustrades on both sides but with almost half the amount of steel required from other proposals. In addition, dynamic analysis showed that the natural frequency of our proposal was double of what was expected at the feasibility stage, resolving any initial worries about the stair’s dynamic performance of the stair.”


The Scissor Stair (main image)

As with the oval stair, the architect envisioned having the scissor stair with glass balustrades on both inner and outer stringers, while the original engineers proposed a steel truss one metre deep on the inner stringer side.

“By designing a solution based on a closed perimeter box girder, it gave us the opportunity to achieve maximum transparency with a minimum amount of steel,” explained Malishev. “Instead of the initial 150 millimetre diameter hanger, we have used two 56 millimetre Macalloy bars, which is a better solution for counter-balancing the structure under asymmetrical load conditions.”

The VIP Bridge

Tying all three feature stairs together is a VIP bridge, which spans approximately 21 metres. This redesign of the initial proposals was an interesting exercise in overcoming an unexpected problem.

“We were forced to design a 21 metre long span bridge simply because there was no space to put hangers anywhere on the ceiling due to services running everywhere,” admitted Malishev. “I quickly did some calculations over the weekend, created a quick 3D model and fabrication started very quickly after that.”

vip bridge

“The client thought I was joking at first, but to their delight we have resolved the issue with the services and also created another elegant structure to add to the family of stairs.”

There is an intermediate pinned support at the column location on one of the stringers. The steel deck structure is 500 millimetres deep at its centre and tapers to 250 millimetres deep at each edge. The section is fabricated from steel plates, with transverse stiffeners at regular centres to form a closed perimeter box girder, similar to other stairs.

“We insisted that all feature stairs should have a similar edge depth, hence 250mm “ribbon” wraps around the space connecting all the stairs visually into a coherent composition,” said Malishev.

The overall result is a dramatic, opening scene enhancing the anticipation of the audience prior to the main event.

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