Phil Gardiner
Irwinconsult, Melbourne

The cutting edge structural solutions used for a composite-steel tower in Melbourne, circa 1969 and a new, nearby tower currently in construction address similar issues and requirements of contemporary solutions.

In 1969, 140 William Street was a world leader in the use of a steel outrigger and belt truss system for lateral stability. The tower was an early adopter of permanent metal deck formwork, high strength bolted connections, Core-Ten Steel, fire-rated coatings (passive fire coatings were removed in 1990s) and a sophisticated computer analysis utilized by Irwinconsult Engineering with input from Fazlur Khan. Initiating significant research into new materials and systems, the adopted solutions and structure would not be out of place today, albeit availability of materials and contemporary digital processing have improved.

Fifty years on, the 300 Lonsdale Street tower (currently in construction), addresses similar issues. It requires contemporary solutions and innovations, including increased sustainability for tall buildings. The 25,000-square-meter timber office tower comprises 13 levels of office framed with engineered timber columns and beams and cross-laminated timber floors. A timber braced façade provides lateral stability. The tower includes three new retail floors utilizing composite steel and concrete construction supported over a six-level department store, originally constructed in 1990 using conventional in-situ concrete with normal and post-tensioned reinforcement. Like 140 William Street, the 300 Lonsdale Street tower has required considerable research into available materials (namely timber), systems, products and connections with significant work undertaken to prevent fire spread in the exposed timber structure. Substantial design input also minimizes the impact of enhanced stability systems through the existing structure.