March_1970 — Page 31

Ribbed

concrete from rope-lined formwork

A NEW and unusual technique for pro- ducing vertically ribbed concrete has been successfully tried in England on the new Liverpool Dental Hospital and University School of Dental Surgery.

It involved the use of rope to create a deep-textured and attractive finish.

The hospital project consists of a two-storey podium block covering the whole site, above which rises a four- storey H-shaped block. There is also a separate twin lecture-theatre block. Two thirds of the building are given over to hospital use, mainly in the lower part, while the school is for the most part on the top two floors of the H block.

The need for large unobstructed floor areas for clinics and laboratories, and for simplifying the complicated services required, resulted in a long- span framed structure of composite steel and concrete construction. The columns are steel stanchions encased in reinforced concrete and are placed outside the external walls to give maxi- mum planning flexibility and a sculp- tural form to the building.

Example of vertical ribbed finish produced by rope lining

The external walls are of 127mm (5in.) thick in-situ concrete cast against permanent wood-wool form- work on the inside.

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A fairly definite textured finish. was required for the exterior walls one that would suit the physical pro- perties of concrete and complement the modelling of the facades. The tex- ture also had to be in scale with the projecting structural elements and the large unbroken areas of walling. For economy, the maximum re-use of formwork together with easy placing of concrete and striking of forms were obvious criteria.

After experiments in the architects' offices with thick cord and plaster, a method of using rope to provide a sur- face texture was finally evolved.

With this system, simple formwork can be used, the rope being pinned to the inside face of the forms before placing them in position. By using

ropes of varying diameter and at dif- ferent spacings, various patterns can be achieved.

After experiments on the site, it was finally decided to use only two types of rope - 12.7mm (in.) dia. rope at 28mm (1-1/8in.) centres for the smaller scale elements (i.e. the 18in. square free-standing columns and edge beams), and 20mm (13/16in. dia.) rope at 38mm (11⁄2in.) centres for the larger areas of walling. In all cases, the concrete was a 1:2:4: mix using 19mm (in.) down gravel aggregate.

The method of fixing the ropes was fairly simple. The formwork panels were prepared in the usual way. Ropes were then cut to length, one length being bent to form two channels. These were then rapidly fixed to the face of the forms with headless nails fired by hand from a compressed-air

gun.

A simple timber comb was used by

Far East BUILDER, March 1970

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