De-tensioning
Main beam for high block being taken off bed
those permissible during transfer, handling and construction and under working loads. The units were design- ed for an ultimate flexual strength of 11⁄2 times the dead load plus 21⁄2 times the imposed load, or twice the dead. plus imposed load, whichever was the less.
The inverted T beams were also de- signed for simple support to take the dead load and for composite continu- ous beams to take the imposed load. Negative moments over the supports were designed as ordinary reinforced concrete beams. The original design adopted deflected tendons but the contractor found this difficult to work to and a revised design using a de- bonding method was finally used.
Precast column casing
The column casings were designed in high strength concrete 6000#/sq.in. with high tensile steel as reinforcing bars. The bracket was designed to take full dead loads plus a quarter of live load.
Far East BUILDER, January 1971
Loading test to main beam for high block
Actual loads on this bracket are the dead load of the beam plus half the dead load of floor planks and topping, any additional loads beyond this are taken by the in-situ brackets as the in- situ column heads were cast before the floor planks were erected. The results of full scale loading tests supported assumptions made in the design.
Joints
Fig. 4 shows an isometric view of the joint. The method of jointing was devised, taking the following points into consideration:
1) To avoid a dry joint. 2) To avoid any bolting.
3) To avoid welding to the main steels and minimize welding to the temporary works.
4) To find a satisfactory way of transmitting the floor loads to the in- situ part of columns to conform with the design assumption.
5) To minimize the shrinkage effect.
6) Rigidity of the joint.
High block construction
Pile foundations were used in the project. As the structural cores were built first, using the slip-form method, it was necessary to check the founda- tion for wind load on the completed cores without taking the full dead load into account.
An Australian system of continu- ously moving shutters was used to build the two cores. A rate of advance varying between 6in. and 15in. per hour was achieved, the stipulated tolerance being in. A specially designed static panel method was in- corporated to form the brackets.
A casting yard with long line pre- tension beds was required to manufac- ture the composite components. This was a relatively new technique in Hong Kong and the contractor experienced some initial difficulties in setting up the casting yard. For instance, the ori- ginal de-tensioning device was a screw- control collapsible type device. A fai- lure occured during the first de-tension operation which caused damage to the
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