The structural system of a central core with perimeter structural mullions at 6 ft. 9 in. centres was established to give a clear span within the office space. The idea of using a diagrid post-tensioned floor was also developed at this stage.
The size of the external mullions was designed at the point of maximum stress at the bottom of the tower, which produced a size of approximate- ly 2 ft. x 1 ft. By setting back the win- dow facade 3 ft. from the face of the building the architects have created a 1 ft. space between the structural mul- lions and the glass facade; this provides effective sun shading, reduces street noise, facilitates window cleaning and gives the tower a pleasing elevational
treatment.
In the study of the elevation, several designs were produced. Fairly close- spaced mullions were finally selected in order to present an overall texture rather than emphasise a column and beam system. The mullions were spaced at 6 ft. 9 in. centres so that at the lower floors three spans would combine to form a 27 ft. span. This transition takes place between the ground and first floor through a deep transfer beam.
Mullion shape
The shape of the mullion itself was designed to be wider at the junction with the floor and ceiling and narrower at the middle. The extra width at the junction of beam and column could thus take the wind stresses. In fact this principle became redundant later when it was calculated that all the wind stresses could be taken by the core and only the vertical loading would be taken by external mullions. By this time the design had been accepted by the clients, so the shape of the mul- lions remained.
At the roof, the mullions are ex- tended to form a high colonnade, with the inner wall recessed. Behind the wall are hidden the lift motor rooms and the air-conditioning plant. The collon- nade gives a clean line to the roof, serves as a viewing platform during the day and provides for a band of feature lighting at night.
At ground floor level the columns are spaced at 27 ft. centres and are shaped like the mullions above: that is wider at the top so reducing the span of the beam.
A car display area was called for by the owners and this has been provided beneath three hyperbolic paraboloid structures placed in front of the build- ing facing Stubbs Road. Cars are dis- played on a platform under the
Main entrance from Stubbs Road
canopies, the single supports for which canopies, the single supports for which are shaped to be consistent with the rest of the building.
The ground floor lobby area is completely open and free from the intrusion of shops and banks.
Below the podium level there are three floors of car parks, a floor of service area and another floor in the basement for Hong Kong Garage. This area is designed in two sections at
split level to each other and connected by ramps, each going down half a landing.
Finishes
From the module of 6 ft. 9 in. for the external mullions and 27 ft. for the lower floors, a 2 ft. 3 in. module was established for the window mullion and the ceiling pattern. This module, applied to the size of the window,
Far East BUILDER, February 1969
19