Teaching and research making a difference. By Michael Smith

Dr Pierre Quenneville is a Professor of Timber Design in the Department of Civil and Environmental Engineering at the University of Auckland – and an expert in bolted connector systems. Timber Trader News invited him to comment on the university’s teaching of timber solutions and its timber research facilities; the uptake of engineered timber in construction; and more.

Before taking up a professorship in timber design at the university in 2007, Professor Quenneville worked on timber connections in his native Canada. “At first, that involved looking at timber connectors [shear plates, split rings] that were used in large WWII timber hangars. The work on timber connectors opened my eyes to the issue of brittle failures and how to control them – obviously with the objective of preventing them.

“I then started to look at the issue of brittle failures in bolted connections. There had been a lot of work done in Canada on the variables that led to those connection failures – but the different studies were all done in isolation and the various “reduction” factors applied to bolted connection resistance equations would sometimes result in significant reductions in connection resistance.

“I approached this issue in a holistic way, looking at all the different variables at the same time and seeing what controlled what.  It resulted in a more comprehensive design approach for predicting the behaviour and resistance of bolted connections failing in a brittle manner … and design equations for these failure modes were developed.

“Thus, it gave the designers full control of the design of bolted connections – in the same way one would design a bolted connection in a steel structure.” By 2009, new design rules had been included in the Canadian timber design standard.

Professor Quenneville says the research has continued in Auckland, where he has been privileged to supervise some very capable PhD students who have expanded the research even further.

 

 

UNIVERSITY COURSES 

He adds that students at the university receive a solid grounding in timber engineering. “In addition to the basic material courses on timber and design of timber members [columns, beams, tension members], we have two courses. One is aimed at undergraduate/graduate students and covers CLT member design; the latest timber connections developments [ductile and brittle failure resistances]; and, finally, the issue of steel bracket design for timber connections.

“There is a lot of emphasis on connections design, going through case studies, and covering load paths. The last four weeks are on the topic of multi-storey design, looking at gravity systems and lateral load resisting systems.

“The second course involves advanced topics, covering timber portal frames, connections [further topics and case studies], and self-tapping screws. It concludes with five weeks on resilient timber structures subjected to earthquake events.

“The objective is to make sure that our graduates have all the tools and knowledge to undertake timber designs using the latest timber engineering developments, wherever they are located.”

Professor Quenneville says the university’s laboratories are well equipped to run a diverse range of timber experiments. “We have a conditioning chamber and the Materials Lab [part of the Structures Testing Laboratory in Newmarket, Auckland] is a conditioned environment.

“There is a diverse range of loading apparatus to test individual components or full-scale systems and structures – and test chambers to determine the durability of timber/glue components.”

 

 

PROMOTING TIMBER

There have been a number of initiatives to promote timber in New Zealand – including Wood First, the Structural Timber Innovation Company and, more recently, Timber Unlimited (now under the auspices of the Timber Design Society) and Mid-Rise Wood Construction.

“It is a never-ending story, and promotional efforts will always be needed. Timber is not the only material in that position: concrete and steel, albeit more mature in their promotional efforts, are doing the same thing.  They just have access to more resources.

“The Canadian experience is similar, but on a larger scale, and the Government has committed some funds to the development of the research environment to make sure there is a constant pipeline of able designers who know how to deal efficiently with timber as a material.”

TECTONUS

Professor Quenneville’s connections research has been applied in practical terms via Tectonus – a commercial operation he co-founded in the aftermath of the Christchurch earthquakes of 2010-11.

More than 70% of buildings in the central city were demolished because it wasn’t economically viable to repair them. “Anything with a residual drift over 0.5% was considered too far gone to fix.”

Tectonus’ founders began working on ways to protect buildings from damage – to reduce residual drift so damage would be minimal and occupants could return to work almost immediately, thus lessening the economic impact of an earthquake.

In mass timber buildings, “the Tectonus venture is all about providing a resilient solution to designers and clients. Timber connections using traditional timber fasteners are actually out of the ductility equation as they do not result in resilient solutions. The products we provide are meant to change the way ductility is provided in a timber structure.”

Tectonus seismic dampers add ductility, damping and self-centring all in one, and can be applied in braces, shear walls and columns. They effectively provide continuous protection through aftershocks, and limit residual drift to below 0.1%.

GRADUATE RESEARCH

A team led by Professor Quenneville and Dr Ashkan Hashemi has been looking to develop innovative wall-to-floor and beam-to-floor connections for mass timber structures that provide resiliency – and to align with the low-damage-design philosophy and promote the broader adoption of multi-storey mass timber wall systems with high seismic performance.

According to Soheil Assadi and Setu Agarwal (the two PhD students working on the programme), the goal “is to deliver a system that not only meets the structural demands of seismic resistance but also supports the sustainability mission inherent in mass timber construction.

“The research goes beyond performance during major earthquakes and also aims to ensure the protection of occupants and structural integrity during aftershocks. By minimising downtime and repair costs, these low-damage resilient systems increase the practicality and appeal of mass timber buildings, making them more likely to be adopted in future construction.”

Mr Assadi says the most effective approach, “both scientifically and from an engineering perspective,” was to conduct experimental tests on a full-scale, two-storey CLT structure.

“The structure underwent approximately 600 loading cycles, equivalent to simulating the effects of the 2011 Christchurch earthquake around 100 times. Even after all these tests, the structure continued to perform extremely well, confirming that mass timber structures can serve as reliable and robust systems capable of withstanding major earthquakes repeatedly without noticeable damage.”

He adds that the study has significant real-world implications, particularly for essential infrastructure. “If this were a school or hospital, it could be used immediately after an earthquake. This solution could not only save lives, but also ensure that buildings remain functional, reducing economic losses and recovery time.”

Professor Quenneville says the WIDE [Wood Industry Development and Education] Trust has been extremely generous in supporting the research.  “There are numerous publications already on the results and key findings, and there’s more to come.”