An extremely complex design, possibly a first of its type in New Zealand, has resulted in a visually stunning staircase, which won the 2018 SCNZ Excellence in Steel Award for projects $0.5-$3m.
Fabricated by D&H Steel and engineered by BGT Structures, the B:Hive building’s distinctive helical stair was developed using 3D modelling BIM technology to deliver practical solutions to the complex spatial and engineering issues raised by the design.
No two flights are geometrically the same and each terminates at a different angle to its predecessor.
D&H Steel contract manager Colin Ross says early on it was identified that the original design would be too difficult to achieve within the timeframe and also too costly.
So at tender stage D&H Steel reviewed the staircase from both practicality and buildability aspects and requested that it be tendered as a facetted design on the grounds of buildability, cost and timescale.
“It made no sense to us that there was any advantage to be gained from a true rolled helical as opposed to a facetted one, due to the fact that the stair was going to be totally clad in MDF after the stair had been installed. All it would need was some skillful, innovative, attention to detail and commitment to the project, which D&H was more than willing to contribute,” he says.
So during the conception stage the D&H Steel detailer set out the 3D model of the facetted stair, and D&H Steel interacted with the original architects and structural BIM models to identify see how far their new proposal was from the original model.
“We also reviewed the design calculations and offered numerous alternative welding procedures to efficiently place cost effective welds, further minimize costs and labour,” he explains.
“After some seriously intense detailing and tweaking we honed in on the final design and details and all parties concluded that we had achieved the most viable practical solution.” All that was needed was for D&H Steel to produce the goods to make the stair a reality.
This involved manufacturing the stair using traditional boiler making skills due to the numerous uniquely shaped components, requiring skilful use of welding techniques to minimise distortions and control shrinkage.
Through clever innovative ideas during detailing and fabrication D&H Steel reduced shop and site welding costs, reduced stiffeners, folded plates as opposed to welding and simplified connections as well as buildability techniques, says Colin. Parts were fabricated in transportable and erectable sub-assemblies.
Every single piece of the staircase was unique and required considerable collaboration with all BIM models to maintain the extremely tight tolerances required during fabrication and installation.
Colin says that the inherent structural performance and adaptability made steel the only option for accuracy and speed of installation.
The project required very specific and complex methodology for installation due to limited access and to cater for differential load transfers for each sub assembly.
This meant extensive, elaborate and considerable fabrication, jigs and fixture design to achieve tight tolerances and buildability.
For example D&H Steel designed hybrid jigs to provide progressive continuity of the complex sub assemblies during fabrication and to maintain the extremely tight tolerances.
Stringer plates were laser cut with temp fixing holes to allow D&H Steel to pre-assemble the stair flights and minimise assembly lead times.
A jig system was devised for site installation for the individual stair flights to cater for differential floor loadings when the final stair loads were transferred sequentially.
Colin says that it was the ability of D&H Steel to provide practical solutions to complex details, which added considerable value to the project. Health and safety w as another important aspect.
Methodology of fabrication and installation was designed to minimize and eliminate risks and also help maintain a sound quality assurance process along the way.
As a result of D&H Steel’s commitment to quality assurance and health and safety for all its in-house and site installation tasks, there was zero loss of production time on the project and no personal injuries.
Colin says that D&H Steel’s extensive skills in all fields of engineering, including 3D modelling, detailing, fabrication and installation, was one of the main factors in the project’s success.
“The stair provides an inspiring example of the seamless melding of design disciplines working together. The final result is an elegant solution that has become the focal point of the building.
“Overall the combined efforts of our team produced a very satisfying result. Judging by the interest this staircase is now receiving the client is more than happy with the end result.”
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The distinctive helical staircase has become the focal point of the new B:Hive building.
