At the Commerce Building on UCT’s Hiddingh Campus. A double header with Henry Fagan telling us about the design of the Bosjes Chapel (between Worcester and Ceres) and Andrew Rowe about the part PERI-Formwork played in making it happen.
Henry told of receiving an email from Steyn Coetzee Architects in London, which set it going. The form is not a true shell as it is not all in compression – those wings that cause that. Foundation buttresses “pick up” the shell at four points…. He then digressed a little to tell of other structures elsewhere in the world, Oscar Niemeyer’s Cathedral de Brazilia, Nervi’s Sports Palace in Rome, Candela’s Los Manantiales Restaurant in Mexico (thin walls!), Eladio Dieste’s bus terminal in Uruguay, Santiago Calatrava’s Opera House in Valencia (high costs and many problems, which seem endemic to his designs), Mapungubwe’s shutterless brick shells (perhaps not quite the right shape to start with, since they have bulged a little), Gawie and Gwen Fagan’s house in Langebaan and Henry Fagan & Partners own Dube Canopy at Durban Airport. The latter started with very heavy structural sections but the introduction of folds (corrugations, he said) made the end result 10 times lighter.
Back to Bosjes Chapel and choices between plywood formers, steel frames, fins…but the lot fell on concrete. Then choices of precast concrete (what the Architect thought, but..); normal reinforced (steep slopes, costly); ferro-cement (scale and shapes ruled against this); Gunite (strength, shrinkage, creep); shotcrete. Eventually it was normal reinforced in the lower reaches and shotcrete higher up where they had to contend with the steeper slopes. Strand 7 finite element analysis, thickening of the shell at the supports and where moments from the wings had to be accommodated, stirrups to keep the reinforcement right (adjustable stainless steel triangles to act as guides where no top shutters were used), some glazing slots to be fitted in and a pool in the middle to receive attention.
Andrew Rowe, Snr Project Engineer from PERI Formwork then told of his experiences in construction overseas and of his battle to convince their sales people that they had dealt with complicated forms before and should tender for the staging / formwork (theirs was the only tender). They set up terraced platforms on free-standing shoring towers (no columns to yoke them to) with 2 x 9mm ply shuttering. The props have built-in tape-measures and the whole structure was built to level from those.
Some very minor surface cracks were found in an area where tension might be expected, but they did not go deep. The whole was eventually plastered with some sealant but this was not necessary from a need to waterproof the concrete.
And by the way, Mr Fagan has been exporting Boomslang walkways to other countries, including to a property in the UK owned by Koos Bekker! The steelwork was put together in South Africa and shipped to the UK – better that way, says he.