Littlehampton Welding Ltd
The helical stair design follows the principle of creating a functional stair for escape purposes in an innovative aesthetic sculptural form.
The delicate structural steel elements of the spring-like form deceive the eye as to how the stair is supported. Steel bracing within the slender landings restrains the spring form to the building providing sufficient stiffness to avoid vibration and movement. The ribbon-like central steel stringer was formed from a steel CHS allowing for a seamless finish and consistent radius.
The steelwork contractor’s fabrication and finishing techniques demonstrate an elevated degree of craftsmanship. This is particularly evident in the hand cut and finished central stringer where all welds were inspected and ground flush to achieve a seamless finish.
Epitomising form follows function, each structural element was sized to be no larger than that required, thus emphasising the architectural concept. The tread goings and risings are set out to Building Regulations and governed the geometry. Provision of the internal hand rail set the structural central stringer height, incorporating the two functions. Trace heating, access call points and lighting cables from the building are routed within the steel hollow sections, concealing the cables from view.
The epoxy paint finish provides 20 years to first maintenance. The building façade is rated for 60 minutes fire resistance allowing the stair to perform its primary function without the need for expensive intumescent treatment.
Each steel member has been designed to be the minimum required size reducing the steel weight. With vertical support provided by the central stringer the traditional central column has been entirely removed.
Fully fabricated off-site in eight pieces including hand rails and finishes, each stair was erected in just two days, reducing demand on the site tower cranes. Site welding and flush finishing the central stringer welded joints gives the stair its continuous ribbon appearance.
Using the four-storey helical central stringer as the stair’s primary support is an innovative solution. The eye is deceived by how the spring-like form can withstand the vertical loading. Torsion in the stringer is braced back to the building by the thin landings and held at the base by the piled foundation. The restraint at these points enables the spring-like form to support the vertical load without deflection or resonant movement. The use of finite element modelling during the design allowed detailed stress analysis to make each structural element more efficient, using less material.
A template jig was constructed in the steelwork contractor’s fabrication facility which was then used to manufacture identical flights without locking in fabrication stresses and ensuring the identical segments matched up on site.
The dynamic sculptural form of the escape stairs provides a dramatic external feature to the building. The ribbon-like central stringer is formed from a hand-cut and finished CHS.
Designer and steelwork contractor have worked closely to achieve delicacy of the steel elements, and the outstanding results demonstrate craftsmanship of the highest order.