“In terms of the building envelope, the main function was to provide a barrier from the extreme climate variations outside the main terminal building. The roof has a flat external surface to minimise the effect of snow loads, allowing a complex faceted internal soffit geometry. The roof soffit was folded in key places to maximise structural efficiency, removing weight in the clear spans, while defining expansive open spaces through variations in height.
The roof lights take inspiration from a common feature of the city’s skyline, focusing the low angled sun using gilded reflectors, and defining passenger flow. The striking 25m long concrete columns supporting the roof spring from ground level and are reminiscent of the angular soviet inspired forms found throughout the city.” Kevin Hares, Building Structures Design Engineer.
The faceted soffit for the main terminal roof created an interesting challenge to shape the form to maximise structural performance, and to utilize the space created inside the soffit as efficiently as possible. The linear arrangement of roof lights separated the roof into 45m x 18m bays, this grid could be most efficiently linked with steel trusses arranged as a star on plan, minimising any impact on the roof lights without compromising lateral rigidity. Planar trusses were chosen to aid the buildability, as they could be preassembled, simplifying the connections details and reduce piece count against space frame options.
The local climate was a huge challenge for the engineering of the main terminal building. The use of specialist scale model testing in a wind tunnel allowed us to apply accurate and realistic wind and snow loads in our structural models. The major benefit was seen here in rationalising our snow load patterns on the roof, eliminating overly conservative drift assumptions imposed by the approximations made in the local codes of practice.
The huge external temperature range in St. Petersburg posed many questions on how to deal with movement across the main terminal roof; we developed a solution which eliminated the need for any movement joints over the 160m x 240m roof. This balanced the allowable movements at the façade against locking in thermal stresses into the roof structure. The unique solution was to place the roof on bridge bearings to have full control over the movements and points of lateral restraint.