June_1966 — Page 66

Pin joints at slab ends.

tage, spoilage of work through warp ing and reduced handling, stripping and erection time. so that overall the plywood became comparable in cost. When the greater number of usages and the lesser amount of making good of the struck concrete surface were also taken into consideration, it was realised that the plywood was more economical than loose boarding.

Taking into account ambient tem- perature, rate of filling of the moulds, the early initial setting time of the cement, and the size of sheathing panels, it was decided to support the plywood on vertical 4 in. x 2 in. studs at 16 in. centres. The walings were supported by twin 4 in. x 2 in walings at 4 ft. centres. The walings were tied through the mould by 1⁄2 in. diameter bolts in loose sleeves to per- mit withdrawal. After concreting this system was found to be satisfactory.

In addition to forming facets on the ends of the piers, it was decided to break up the rather large expanse of the flat sides by inserting hard- wood fillets in the mould so as to achieve a pannelled effect in the finished concrete surface. The section of the fillets was so chosen that the vertical grooves were deeper and wider than the horizontal in order to accentuate the slenderness of the

Sliding joints

piers. The position of horizontal fillets was closed to cover the joints in the plywood and to mark the con- struction joint at the end of a normal day's concreting.

Although the piers seem compara- tively simple, great care had to be taken in deducting their dimensions. Corrections had to be applied to al- low for the effect of skew in relation to the crossfall and longitudinal sec- tion through the finished flyover.

After steelfixing, concreting to the piers followed in 4 ft. lifts. Each lift was broken by a construction joint prepared by washing to expose the aggregate in the partially set concrete or by hacking. This surface was sub- sequently treated with a layer of grout and mortar immediately prior to placing the subsequent lift of 1:6 mix concrete.

The tops of the piers and abut- ments alternately have either pinned joints formed by 1 in, dowels or slid- ing joints formed by 1⁄2 in. M.S. plates set in the concrete and rubbing over each other.

Deck Spans

The falsework for the soffit shut- tering consisted of China fir poles at about 3 ft. centres braced in both dir-

Completed pier. Pattern formed by hardwood fillets inserted in the formwork

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ections with bamboo. The tops of the poles were trimmed to about 9 in. below the required soffit level and linked with other fir poles to form a series of continuous beams running the length of the span. Fortunately the line of the flyover was immediate- ly over the old southern carriageway of Harcourt Road which was still in- tact apart from openings for the foundations and this provided an ex- cellent support for the foot of the poles.

When the framework of poles was completed the 4 in. x 2 in. bearers for the soffit sheathing were fixed at 16 in. centres across the flyover and carefully lined and packed to 1 in. be- low the longitudinal profile of the sof fit of the flyover.

A camber was also applied in ad- dition to the requirements of the sof- fit profile so as to allow for the dead load deflection of the structure. The 4 in. x 2 in. bearers were extended beyond the width of the soffit so as to provide support for the separate framing for the sides and cantilevers of the deck.

Plywood sheathing was used for the whole of the deck spans with the exception of the internal shuttering for the hollow cells. Loose timber boards were used for this work so as to facilitate striking and manoeu- vering in and out of the restricted space.

After completion of the soffit form- work, the formwork for the sides and cantilever portion of the deck was erected and steelwork for the lower flange was fixed in position so that the deck could be concreted up to 3 in. above the level of the bottom of the webs.

After removal of the starters for the webs, framework steel fixing and concreting then followed up to the top of the webs. After setting, the formwork to the webs was removed and new formwork was erected to form the soffit of the upper flange.

It was considered desirable to strike the web formwork "in the open" so as to leave the minimum amount of material to be removed through the ends of the hollow boxes' when these

Far East Architect & Builder June, 1966