WACA Light Towers
The unique structures for the Western Australian Cricket Association (WACA) light towers were conceived to meet several different requirements. These were:
- it was necessary for the towers to be built in a short time frame to meet the client’s planned schedule of night games of cricket and Australian Rules football;
- safe and convenient means of access to the light frames and the top platforms had to be provided;
- the towers were to be as economical as possible while still providing high quality lighting to the headquarters of Western Australian cricket;
- the appearance of the towers had to enhance the WACA ground and to provide a signature showpiece for that ground; and
- if possible, the towers were to be fabricated in WA.
Site conditions that had to be contended with were:
- the WACA ground is on old river flats that are not stable and have poor bearing qualities. It was therefore necessary to found the towers on piles; and
- there was a fragile building close to one of the selected sites.
Several options were looked at. The option that was adopted had the most all round appeal. This was to build the structures of the towers in precast, reinforced and prestressed concrete modules around a lightweight steel core that provided access during both erection and when the towers were in their final form. The steel core was also required to provide a sufficient framework to which the precast concrete panels could be fixed as they were set in place and before they were grouted and prestressed into their final form.
The panels were all cast in only two steel forms that were simply modified to provide the tapering that is a feature of the towers. Tapering is obviously for structural reasons – moments due to wind loads and seismic movements are at a maximum at ground level – and material is saved at higher levels. The tapering had another advantage. Because the panels weighed less per unit length at higher levels they could be made longer and still be within the lifting capacity of the cranes that were being used to erect them. This allowed one set of panel lifts and one set of grouted joints to be saved for each of the towers and, at the same time, their appearance was enhanced.
A prestressing tendon in a duct was installed in each corner of the towers. These tendons had four duties: the first was to provide sufficient compression in the concrete panels to prevent tensions developing in the towers due to horizontal loads; the second was to enable stage stressing during the building process to ensure stability at all times, the third was to anchor the steel frames that house the lights to the tops of the towers and the fourth was to anchor the towers to the piles. The ducts housing the prestressing tendons were grouted in as the towers were built.
All towers are founded on piles taken down to a depth at which the ground was stable. Five of the towers are supported on driven precast concrete piles and one, situated close to a fragile building, is on bored piles.
A feature of the entire design and construction process of the WACA light towers was the high level of cooperation between the designers and the various contractors and sub contractors involved. All realised they were embarking on a previously untried area of design and construction and all contributed to making the towers the success that they have been.
Shortly after they were completed, the towers received several industry excellence awards.
Author:
Peter Bruechle, 17 August 2020.
