Timber buildings go up in the world
Dr Andy Buchanan explains the science behind new building technologies.
There is growing international interest in tall timber buildings and there are many new buildings recently constructed around the world. Some of these buildings, especially in seismic areas, use the Pres-Lam technology developed at the University of Canterbury.
Pres-Lam is a system of prefabricated timber components tied together with high strength steel bars.
The Pres-Lam technology was created in Christchurch with collaboration between the university and PTL Structural Consultants, using concepts similar to those developed for prefabricated concrete structures in the US by New Zealand engineer Professor Nigel Priestley.
Tall timber buildings have only become possible with the development of engineered wood products and new fastening systems including post-tensioning. ‘‘Engineered wood’’ uses large prefabricated components of solid wood, glued together with high strength adhesives.
Traditional engineered wood is seen in plywood and glue laminated timber, now complemented by Laminated Veneer Lumber (LVL) and Cross Laminated Timber (CLT).
LVL consists of long and strong wood panels, made by gluing many thin wood veneers with the grain all going in the same direction. It is stronger than concrete.
CLT is made from solid sticks of timber glued together in alternating layers to make huge flat panels like oversized plywood. Both products are manufactured in New Zealand from locally grown radiata pine. The first PresLam building in the world was the arts building at the Nelson Marlborough Institute of Technology in Nelson.
Others in New Zealand include the College of Creative Arts at Massey University’s Wellington campus, and several in the Christchurch rebuild including Young Hunter House in Victoria Street and the Trimble building in Birmingham Drive.
Christchurch consulting engineers PTL Structural Consultants are experts in the design of Pres-Lam buildings. They have recently been timber engineers for the four-storey Peavey building at Oregon State University and a new prizewinning fire laboratory in Japan.
They contributed to the 12-storey Framework building under construction in Portland, Oregon (the tallest Pres-Lam building in the world) and the fourstorey Von Haast Building soon to be constructed at the University of Canterbury.
A big advantage of Pres-Lam buildings is that they will snap back into place after a major earthquake. Similar concepts are also available for steel and concrete buildings, but without the other benefits of timber. These include worker and user satisfaction, safe and quiet construction sites, rapid construction, and carbon neutrality.
Not every tall timber building needs to use the Pres-Lam technology. The 10-storey Forte building in Melbourne has enough internal walls to avoid post-tensioning, and the 18-storey Brock Commons building in Vancouver, Canada, resists lateral loads with an internal tower of reinforced concrete.
Many people are asking about fire safety of tall timber buildings after the disastrous fire in London recently.
The Grenfell building was made from non-combustible reinforced concrete, but it had many fire safety defects, especially the combustible plastic and aluminium cladding.
Well-designed timber buildings are just as safe as buildings of other materials, provided that they are fitted with proper detection, alarm and sprinkler systems, and do not have highly combustible facade materials.
Dr Andy Buchanan is a professor emeritus at the University of Canterbury.