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In one of our buildings, the University Centre at Cambridge, a great area of commonroom space was required on several floors and the site was on a corner. The problem, as we saw it, was to evolve a structural system that articulated the space into a series of units of domestic scale which would go round the street corner in a seemly manner and whose spans would reduce the floor slabs to an economic minimum. All precast bits had to be capable of travelling on a low–loader and getting under railway bridges, ie, should not be wider than about 9ft.
On this page and opposite are sketches interchanged between HKPA and the structural engineers – you can tell which are Frank Newby’s because his are less inhibited than mine. Starting from a rough, workable pile–up of the accommodation, various anatomical arrangements were tried, the decision having already been taken to try first those with columns inset. We early on articulated each bay from its neighbour so that, both from inside and out, the commonrooms would read as a set of spaces rather than a single continuous one. In fact, a certain degree of subdivision by means of moveable screens was asked for. A rough bay–size emerged from an exploration of the arithmetic of floor area in relation to depth and frontage available. Various carve–ups were explored and a rough number of square bays emerged as a likely solution.
Later it became clear that only a set of off–square (ie, rectangular) bays would get the accommodation on to the site. Thinking ahead to cladding and windows, we considered bays whose sides were made of a number of equal–sized bits. Eventually we settled on a three–to–four relationship – three windows down one side to four down the other. What we eventually arrived at was a 9ft wide central rectangular ring beam, held up on four inset columns, with hammerheads whose back ends supported an outer ring made up of separate bits. The whole was post–tensioned by means of high tensile bolts, and locked together with an in situ slab.
The main dining hall in this building has a two–way roof supported on hip trusses with timber compression members and steel ties, paired so as to admit a diagonal cruciform of top light. In this part of the building, inset columns would have inhibited use considerably, so they were set in the line of the wall – ie, 1ft columns with 10in thick infilling. There is not much modelling, but the column is articulated by its shape and colour from the adjacent blockwork, which saves it from getting lost in the wall.
We returned to the question of the relationship between wall and column in the new combination room at Downing College, Cambridge, designed with David Powell. Our desire not to lose the columns, either within the room or from the outside, led us to devise a structure of paired columns cantilevering up from the ground and supporting brackets which reach inward to hold up a central precast lantern.
We swung back to columns set in the line of the wall at St Antony’s College, Oxford, designed with Harris & Sutherland. The structure is again two-way, consisting of a diagrid made up of precast elements, supporting small timber pyramids with a rooflight in each. Between the columns are large precast panels. The problem of having to interrelate structural and cladding tolerances was obviated by leaving a relatively large gap on either side of each column, and filling it with that easy–to–cut, durable, waterproof material, glass.