Research outcomes that matter
Lucas Hogan is a Quake Centre research engineer based at the University of Auckland. His main area of focus is on Lightly Reinforced Concrete Walls, just one of five projects prompted by the Canterbury Earthquake Royal Commission (CERC) recommendations, being carried out by the Quake Centre with funding from the Ministry of Business Innovation and Employment (MBIE).
Originally hailing from Ohio, Lucas gained his degree in Structural Engineering from the Cal Poly, San Luis Obispo, before making his way to New Zealand. His original background lies in the field of bridges, and more specifically in testing how they perform and behave in the event of seismic activity. As he explains, it can be tricky testing the integrity of a bridge, given the size of the structure, and their method is somewhat unorthodox.
“If you’ve ever thrown a pair of trainers in the washing machine, and it hits that spin cycle and starts going back and forth. Basically we have a $200,000 washing machine!”
By putting sensors on to a bridge, Lucas and his team are able to determine how it moves dynamically.
With this research background, Lucas’ focus has now moved into reinforced pre-cast concrete panels. While this is a name that might not be common knowledge, as Lucas explains, they are fairly ubiquitous throughout the country, particularly in low-rise commercial buildings.
“If you go to the supermarket for example and take a look around, you’ll often see a steel frame and there are concrete panels about two metres wide. You’ll see a vertical strip where they’ve been joined together with weather-proofing, and those envelope the building.”
This research came about as a result of the CERC enquiry, which found that many of the buildings of this nature in Canterbury did not necessarily perform as predicted during the devastating earthquakes which struck the region.
“Some of the buildings did not behave as expected, particularly down at the foundation connections. The work that we’re doing is to test the existing connections, and find out - why did they behave the way they behaved?
Through a series of experimental programs the researchers are now well on their way to determining why the structures performed the way they did during the earthquakes. In the first program they looked at bending the panels out of plane by pushing them back and forth to see how the connection at the base foundation behaves.
“If these joints are damaged, out-of-plane they really only need to hold themselves, but if we have loading coming from the other direction in-plane, they’re holding up the whole building. So the concern raised by those first tests was that if you initiate some damage by moving them out-of-plane, what happens to their in-plane capacity?”
The expected outcome of this research is a logical one - to create a pathway of understanding for how these structures are likely to perform in the event of an earthquake.
“If we have that understanding, we can improve that detail so that we can provide safe structures. In structural engineering, it’s often a case of safety equals predictability. If you can predict it, you can understand how it behaves and then you can ensure that the structure does what you expect it to do.”
“While we develop these new details we do a lot of work with the pre-cast industry, both manufacturers and design engineers. This ensures that we’re not proposing ideas that are unfeasible. It’s all well and good to do the research but at the end of the day that research - particularly in Civil Engineering - has to get picked up and be useable.”
The ultimate goal, as Lucas explains, is to update the existing guidelines for the design of precast panels.
“Because it is a potentially far-reaching document we want to be sure that what we put forward works for the industry, the public, the design community - all the various stakeholders.”
For Lucas, having the stakeholders involved in the process has been very beneficial, helping put a lot of context around it.
“As a structural engineer and a researcher, you tend to see the problem in the form of free body diagrams and force vectors and so on and you think - ‘this will be a great theoretical solution, we’ve checked all the boxes and we test it and it looks great’ - but then you might have the pre-caster come back and explain that they can’t build to that tolerance. So understanding the problem holistically has helped us to focus on solutions that will have uptake.”
The benefits of collaboration
As part of the experimental testing that Lucas is focusing on, he will be performing some bi-directional testing at Swinburne University of Technology in Melbourne, who are partnering with the University of Auckland on this project.
“This will be the start of a collaboration between Swinburne University and New Zealand wide institutions including the University of Canterbury and the University of Auckland, as well as industry bodies such as BRANZ. So it’s sort of paving the way for that.”
Swinburne University have a very specialised piece of equipment at their disposal in the form of a ‘MAST’, or Multi Axial Sub-Assemblage Testing facility, which as Lucas puts it is essentially a large cruciform that can be clamped down on a structure, to simulate the movement created by a seismic event.
“Think of it like a marionette’s gimbal. It can simulate any moment, force, or left and right movement in all degrees of freedom, much like the marionette can move. That’s a way to test a portion of a structure with more realistic loading, and therefore get a better understanding of how it’s going to perform when a real earthquake comes along.”