Steel Wing, St Marylebone CE School

Steel Wing, St Marylebone CE School

Architect

GUMUCHDJIAN ARCHITECTS

Structural Engineer

CONISBEE

Steelwork Contractor

KL DESIGNS LTD

Main Contractor

MANSELL CONSTRUCTION SERVICES LTD

Client

LONDON DIOCESAN BOARD FOR SCHOOLS

The brief was to extend the existing school to provide a sports hall and associated arts and drama facilities on a very constrained 30m sq site. The solution was to build down instead of up with an 8m deep basement being constructed across the available site footprint. The majority of the brief was satisfied using well detailed in-situ concrete with very little in the way of finishes, which saved money but meant that every structural element was on show and required careful detailing.

The existing arts building was a 5-storey insitu concrete sway frame with 2-storeys below ground and 3-storeys above. The new east wing and the open courtyard use steel elements to maximise spans and create a lighter, more refined structure. The steel frame extends from basement level where fabricated steel box section and flat plate columns rise 11m to support in-situ concrete intermediate basement floors and ground floor structure. At ground floor the column sections turn through 90 degrees to form the cantilevered steel and ETFE canopy over the courtyard stair.

During the design of the steel wing, it was decided that a concrete prop spanning the courtyard and providing lateral support to the capping beam would be more buildable and practical in steel. By introducing a 457mm diameter tubular section this enabled ease of connectivity of the canopy support and cantilevered steel staircase to the buffer prop. Not only was this prop providing lateral support to the open courtyard capping beam, it was now supporting the entrance landing, stairs and canopy.

The canopy is supported on articulated pinned connections at two points vertically and two points laterally with stability provided by a combination of lateral supports and slender tubular bracing in plan. The main sections are supported on two vertical and two raking columns and have a 4m cantilever sailing out over the 8m deep open courtyard. The main sections consist of RHS with welded flat plate to enhance stiffness and also to form a gutter for draining the ETFE fabric which is tensioned between the main members.

The feature staircase is a double height 5m cantilevered scissor stair with one flight connecting ground to basement -1 level and then another slightly smaller flight between basement -1 to basement -2. Upper flights are detailed to dovetail with the landing structure before double continuous steel flat stringers supported by the tubular buffer prop cantilever out 8m high over the courtyard light-well. The fully welded continuous structure then returns to three 30mm diameter steel hangers which support the basement -1 landing and enable the second flight to continue down to basement level.

The stairs are deliberately designed to be independent of the main concrete frame and flow elegantly through the double height space.

Judges’ Comment

s:

This is an inner-city school with great pressure on space. The project provides a sports hall beneath the playground, and links the buildings above. Steelwork provides the unifying element in the core, balcony and link structures. Being painted orange makes it fun for the children.

The outstanding characteristic is careful foresight and detailing, and the results show they are worth the effort – and the children love it!