cedures which were decided at this stage included:-
(a)
a
The quantity surveyors drew up a schedule of prices in agreement with the contractor, including the cost of operating the necessary plant in order to determine the actual cost of the work when completed and to establish basis for progress payments. (b) On the basis of a schedule of prices and accepting a number of unknown factors which could af- fect the final figure, the quantity surveyors estimated the probable total cost of the project. It was given as HK$1.83m., of which the sum of $1.21m. was reckon- ed as being the ceiling price. (c) Tenders for piling and other sub- contracts had to be invited, and the contractor was given the op- portunity to tender for any or all of these, just as he wished. The design work having dragged on for a very long time, it seemed clear that the presence of the ceiling price could only result in a substantial loss to the contractor, and it was consider- ed reasonable to allow him to claim for extra labour costs over and above those pertaining in June/July 1964, when the work was originally expect- ed to proceed. As proper records existed, no difficulty was foreseen in completing the necessary cost involv- ed, and it was decided to adopt the P.W.D. Architectural Office system of payment for any such extras over and above the first 20 per cent, which was to be carried by the contractor.
Permission was next obtained from the District Office, Tsuen Wan, for the use of the area adjoining the site as a casting yard and workshop, and preparatory work for the Tilt-up operations started in February 1966 with the arrival of three Japanese site engineers.
June 1966.
Construction
starts with The Tilt-up process concrete precasting work, either at the workshop or, as in this case, in the vicinity of the site of the proposed building, to prepare reinforced con- crete wall and floor panels of specific dimensions matching with dimensions of one wall section (approximately, for Fuk Loi 12 ft. x 8 ft.) and floor (14 ft. x 8 ft.) for one compartment in the building.
The concrete is mixed in a central batching plant fed from silos of sand, cement and aggregate, carried by a gantry-hoisted hopper to steam curing beds: laid in steel moulds, the surface trowelled lightly and the covers of the beds slid into position.
Steam is fed into the chamber, at a temperature of 70°C. and the com- ponents removed by gantry crane after an average of four hours de- pending on ambient temperature and, particularly, humidity. They are then stacked in tubular steel racks to await assembly.
Component panels thus prefabricat- ed are later lifted by a tower crane and placed in pre-determined posi- tions, respectively, supported by telescopic struts at a 40° angle with the floor and temporarily fixed to lugs cast into each panel.
This process. therefore, can be termed the "assembly of large-size precast concrete panels". and the important factor to ensure its strength is the method of joining the individual panels together.
The jointing procedure is divided broadly under two heads, wet and dry. The wet joint calls for joining the panels by concrete after they have been set in position; and the dry joint is, instead of concreting, the joining of reinforcing steel members in pockets in each panel. by means of welding or bolting.
In
Casting of panels between steel forms laid in the curing beds. the foreground surface finishing is in progress and behind concrete is being levelled after being deposited by the hopper
In the actual work, the two al- ternatives are combined in varying proportions depending on the type of constructional rigidity called for by the design. It was this factor which, with Hong Kong's high wind require- ments, gave most trouble in design and which, it was believed, would call for most care and supervision during construction.
Construction of the steam curing chamber, including the "Fuji" type M.G. 10 steam boiler, the assembly of the British-made rail-mounted tower crane and the Japanese and locally made travelling gantries took approximately six weeks.
The tower crane was a Babcock & Wilcox G.H. 75 HVZ, with a 33- metre boom capable of lifting two tons to eight tons with a height of 112 ft. under the hook, and two of the travelling gantries were Ishikawa- jima-Harima, each 40 ft. wide and hoisting seven tons.
While these preparatory details were going on, work on the sub- structure was progressing side by side with excavation and the construction of pile caps.
Both the preparatory work and the sub-structure works were completed in the beginning of April 1966. Two weeks of trial with the plant was carried out, and, during this period, different concrete mixes were tried, to
produce concrete of the required strength and workability, and various ways of surface finishing for the panels were tested out.
A concrete batching plant of West German origin Stetter BMD 375
including mixers and a cement silo, was also erected, to produce 350 cu. ft. of concrete per hour. By April, the in-situ substructure for one of the two blocks was completed and work on the steam curing chamber and boiler was also finished.
Casting Commenced
By mid-April, four out of the eighteen curing chambers were ready for use and casting commenced. These chambers finally totalled 66 ft. 8 in. in length, were 13 ft. 10 in. wide and 3 ft. high, and as soon as they were ready, trial cubes of vary ing mixes and different curing periods were made and tested, as were also trial panels, these being subjected to a variety of hoisting arrangements to see if cracking occurred.
Assembling and fixing of the components started on May 1, 1966 when some 50 panels had already been cast and stored in the storage racks. The speed of both casting and assembling was slow in the beginning, as might be expected, as during this period the contractor's workmen were being trained in the use of the plant by the Taisei operators. After two weeks, it began to improve and at the end of four weeks, the average rate of both casting and assembling_was approximately 20 panels a day. Thus, the first storey of the two blocks was
32
Far East Architect & Builder February, 1968