Foreword by Ian Thompson, Editor
When optimising our design and build projects using mass timber, it’s crucial to carefully consider the connection types. This largely dictates the composition of our mass timber post and beam elements. A minor misstep could lead to over-designing our building elements, resulting in unnecessary costs, and in some cases a switch to a more traditional construction method.
This brief interview with German Professor of timber engineering Hans Blass also highlights the need for updates in our building codes. Modern building systems, such as mass timber, necessitate these changes, particularly for countries like Australia and New Zealand.
Pioneering the Future of Timber Connections: Unveiling the Evolution and Sustainable Impact of Timber Engineering
Video Transcript
Hans Blass is a professor of timber engineering at Karlsruhe Institute of Technology, the world-renowned authority on his work in innovative and reliable structural timber connections. He is the author of the book “Timber Engineering: Principles for Design” and the previous winner of the Marcus Wallenberg Prize for a significant contribution to forestry and forest industries.
So he came to Australia for the Pacific Timber Engineering Conference (PTECH), where I was lucky enough to catch him and talk to him about connections, sustainability, and get a taste for how timber is developing in Germany. As we were speaking at the conference, you’re going to hear a bit of background ambient noise, so bear with me. But I’m sure you’re going to enjoy it all. So without any further ado, we’ll get into the interview with Hans.
“Well, I’m a structural engineer. I finished in Rusty and Council in southwest of Germany in 1980, then went to work in the concrete industry. And for, yeah, ecological reasons really, I decided to switch to timber. And then I wanted to join a timber company, but then there was a possibility to join University of Karlsruhe as a PhD student, so I did my PhD in Karlsruhe.
Then left for one year to Forintek in Canada as a postdoc. After that, came back to Karlsruhe and left for the Netherlands with my family. We were there for four years. I was professor for timber structures at Delft University of Technology. And from then, I came again back to Karlsruhe, and since 1995, I’m professor for timber structures at Karlsruhe Institute of Technology.”
“Well, timber engineering certainly has changed a lot during her last, let’s say, two or three decades. What we see today is really a move upwards, which has been made possible by three main reasons. One reason is the possibility of machining timber with computer-controlled machinery. The second reason is to have the mass timber products available: LVL, CLT, glulam. And the third reason is connection technology, which has evolved also to a high extent.”
“And at first principles, what are the connections trying to achieve, because this is the area where I think you focus much of your career on research in this area?”
“Yes, that’s right. What a connection wants to achieve is, let’s say, balance member capacities. So if there, if the member capacity can be matched by the connection, then you can design economic timber structures. If connection capacities are below member capacities, then the members are overdesigned. So good connections and strong connections are important to get member sizes down in timber structures.
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And we worked on that, and have reached nearly a hundred percent efficiency, we call that, efficiency in timber connections. For example, using self-tapping screws in softwood timber members. Now we have the challenge of using more hardwoods, and we have to repeat the exercise basically. If the connection can only carry 50 percent of the member capacity, then you only need 50% of the member size rate, just to accommodate the connection. You wouldn’t need that if, yeah, if the connection would be stronger.”
“And what I see, you see obviously from Germany, what what can Australians take away from all the research in Europe? How much of that can be translated, since Australia, have a big problem with earthquakes?”
“I think you can transfer almost everything which has been developed, not only in Germany, but in Central Europe, in Switzerland, Austria. They also have contributed a lot. And I don’t know about your building authority system, but technically you could use all our solutions. And partly you are using them, for example, the connectors which are prefabricated in the workshop and then on the building side just being fixed or hang hang in. You could all use these long screws, fully threaded screws, both for connections as well as for reinforcements. All these solutions are readily available also for application in Australia.”
“And a view you familiar with the Australian standards, AS 1720? Do you think it’s, do you have any comments on on how we use that? And do you think the your Hansen theory is something we should be applying in Australia?”
“Obviously you use tables with fixed values or capacities for connections, which is non flexible solution I would say. It’s easy for the engineer for maybe an everyday task, but if it gets more complicated or if you get out of standard cross section, standard situations, it’s very difficult then to get appropriate connection design. And to my view, you should keep these tables for, let’s say, simple jobs, but you should in parallel allow, for example, the Johansen model or the extended Johansen model, the European yield model in general, to be applied also in Australia. This would create more freedom to those designers who are familiar with timber structures.”
“Well, the market for timber connections is so much larger than for steel or concrete structures. Even if you look at steel structures, they are bolted connections basically, of course welded connections as well. But if you look at mechanical connections, its bolted connections, whereas in timber we have six different types of dowel type fasteners already. And then there are so many proprietary connection systems, it’s very difficult to keep the overview and to, let’s say, look for the right connection for the right task.”
“Most connections may also be used in a fire. We can maybe distinguish between two approaches. You could use contact connections, they may be prepared also by CNC machines, and they are, there are no steel parts, no metal parts. You can just design them like a member, so you could get a charring layer, you calculate the charring layer, and then you check whether the connection is still sufficiently strong. The other way is to use the traditional connections, including maybe steel plates, dowels, nails, screws, whatever. And then you just hide the steel parts in in the timber, so you protect the steel with a layer of timber thick enough to provide a charring time required.”
“If you obviously an avid research out, what is some of the research you’ve been working on recently?”
“Well, the most exciting new product is certainly BG LVL, ‘beach LVL’ is a hardwood LVL. It’s just a normal aerial, if you like. The challenges are the high density of more than eight hundred kilogram per cubic meter. The exciting thing are the high strength values, tensile strength about three times as high as for glulam for softwood glue.
And also embedding strength and withdrawal capacities are much higher. But there are many challenges regarding connections. For example, you can’t just put a nail or screw without pre-drilling into this material. Even if you look at traditional connections with bolts, fridge plates, you might see other failure modes, new types of failure mode. And we all need to cover that and and understand that before you can freely use this new material.”
“What we can do with this new material is, for example, large timber trusses. We haven’t seen large timber trusses in the last decades, even though trusses are a very economic type of structure. You don’t use a lot of timber, however, due to the large number of connections they are expensive because work is as expensive. And if we are able to again optimize the connections, kept some standardized solutions for connections, then we are able to do economic trusses.”
“And replay is a huge glulam beams, for example, with depth of two or two-and-a-half meters. And in this respect, we should look more at LVL with cross layer, so cross banded LVL. You could argue that tensile member made of cross banded LVL is less strong than a similar member made of parallel reveal. This is true, however, again look at the balance between connection capacity and a member capacity. You lose some member capacity, but you win a lot of connection capacity because we all cross pendant LVL will not split, and therefore fasteners will carry much more load than in a product where you only have parallel fibers.”
“At the moment we are doing a research project about a new type of timber product made from sawn timber, where the timber is not so in the traditional way where you produce rectangular cross sections, but where you produce trapezoidal cross sections. So you cut the cross section like a cake, and by doing that and arranging the pieces intelligently, you can use 85% of the volume of a log instead of 60% when we do just by changing sewing technology. But there’s much more behind that because you can’t use trapezoidal pieces, so you have to reglue them. This is difficult, you can’t plain them and so on.
There’s a whole technology behind it, but you we are nearly there of applying this product. And with a much much higher yield from-from logs untie one of these conference hands. When I first met you, you mentioned here in Germany they’re actually bringing in legislation about timber relative to concrete and steel. Can you tell us a little bit about what’s happening in Germany.
Yes there’s a bylaw at least in two provinces now in Germany or in two states that government buildings which are newly erected or rehabilitated need to be done in timber, unless it can be proven that the timber solution is not possible. The reason for that is climate change and the necessity of reducing our CO2 emissions and it’s part of an agenda we have in Germany Carta timber it’s called, where we also want to use the building sector which produces a lot of greenhouse gases to the group.
The building sector has to contribute to a reduction of greenhouse gases and using more timber structures is certainly one solution to that. I’m not a friend of doing everything in timber each material for each purpose and we will do the foundations and the basement certainly in concrete but we can do much much more in timber and we should do that. And what do you think about the future of timber in general? Yes, well depends who what who or what excites you I think it will
“It will be exciting. We will see much more markets in, for example, four to ten storey buildings, for example, for offices, for accommodation and things like that. That will be a huge market in the in the near, in the next ten years. And this will take a lot of research and development.
But it, we will build much more intimate. In the last 20 years, the share of timber structures in the one and two family houses in Germany increased from about 15 to 30 percent, so it doubled. It’s it’s not by far not as much as in Australia, but still there’s a move upwards. And if we see a similar move in in four to ten storey buildings, then this will be a huge opportunity for timber and timber structures.”
“Something I hear a lot about, professors and industry experts heading toward the end of their career, is that they always stress the importance of the older generation to transfer their knowledge and wisdom on to the next generation coming through. So do you have any advice for any younger engineers listening right now?”
“Well, this is difficult to answer really. The market for structural engineers, and I only know it from Germany at the moment, it’s crazy. The young people leaving the university, they send out five applications, they do five interviews, and take at five job offers.
And so it’s very difficult at the moment to find engineers really. And this is now, this goes on for five to ten years now, and it doesn’t look like it will end soon. So in terms of career planning, it just doesn’t matter which material you you follow, but also timber, of us really very very interesting jobs and things to do. And my experience is timber is attractive to people.
This starts at the laboratory in the university, when our steel or concrete colleagues come into our laboratory in the timber laboratory, they also probably say ‘Hmm smells good here, it doesn’t stink like it in a steel lab when they are welding’ or something like that. And and it’s similar if you go to a building site, it’s much nicer to check a timber structure compared to a concrete or steel structure.”
“If you got a question about wood, I recommend you check out the WoodSolutions website. It’s the world’s best website on wood. And on it you’ll find the technical design guide, so right now there’s 48 of them with that number of growing all the time, where we get Australia’s leading experts really going deep and detailed in a range of different topics. So if you’ve got a question, or if you want to just upskill yourself in timber design, then go and check it out.”
