Brendan Coppinger - 40541331
Long-Span Timber Structures
Background & Aim
My first-choice honours project topic is long-span timber structures. I gravitated towards this
subject heading because I know that timber will play a huge role as a structural material in
the future of the construction industry. My father is a carpenter, I grew up working with wood
and have a natural interest and aptitude. There wasn’t any real emphasis on timber as a
construction material during my previous three years in Munster Technological University in
Ireland. Therefore, when I saw that topics were timber based, I put them as my first and
second choice.
Timber is going to play a huge role in the future of the construction industry (Hough, 2019).
Therefore, it is important to understand why, and to what extent? Like all plant life trees
absorb carbon dioxide, convert it into carbon and release oxygen into the atmosphere. This
carbon is retained in the timber and stored for years making it a sustainable material
(Zubizarreta, 2019). Sustainability is a word that will be found in every honours project in
2021. It must be considered in every aspect of engineering and it is especially topical here as
the world moves into the carbon-constrained future. With the development of more durable
Engineered Wood Products (EWP), such as Cross-Laminated Timber (CLT), the possibilities
for timber structures are getting greater. These woods insulate heat and sound, are light and
low maintenance. This allows a lot of off-site work to be done on a factory floor where the
upmost precision can be achieved (Zubizarreta, 2019). The energy efficient material of timber
combined with the low carbon footprint of constructing with it, makes this system a carbon
sink (anything that absorbs more carbon than it releases).
With my interest in timber construction and sustainability in mind, I began researching
related topics. Long-spanning timber really caught my eye because I had seen them being
used in the construction of a brewery in my hometown which I had been following
throughout the covid pandemic. The design includes eight curved glulam beams weighing 3.5
tonnes each to make up the main roof (Killarney Brewing Company, 2021). Glued together in
Austria and transported over these curved beams are designed to imitate the mountains in the
background as shown in Figure 1 (Killarney Brewing Company, 2021).
Figure 1 Curved Glulam Beams (Killarney Brewing Company, 2021)
For the actual brewery of this complex, the Killarney Brewing Company used a series of
bowstring trusses as seen in Figure 2 below. They were bent in the factory and blowtorched
for the nice finish (Killarney Brewing Company, 2021). These trusses were something I
could relate to from doing solid mechanics calculations.
Figure 2 Bowstring Truss (Killarney Brewing Company, 2021)
I researched long-spanning timber structures around the world and saw that the possibilities
for wooden structures are vast. This then got me thinking what are the limits for long-span
timber structures? Does everyone know the capabilities of them? This question may change
as I delve into the topic deeper or the question may become more specific, but I wish to find
out if timber structures have as many limitations as people perceive them to have.
The purpose of this dissertation is to discover the limits and capabilities of long-span timber
structures.
Research Agenda
This is the research plan that I aim to complete in order during my investigation into longspan timber capabilities:
1. History
Firstly, as I am relatively new to the topic, I will look to learn more of the history of longspanning timber, from old famous bridges to modern large-scale buildings. Timber
construction has an ancient history with humankind dating back to a well built in
Altscherbitz, Leipzig which is 7000 years old (Woodard, 2016). It is one of the oldest
materials used by humans and its importance now is greater than ever.
2. Types of Trusses/Beams
Here I will research the different trusses that make long-span structures possible. I do
acknowledge that many long-span structures are achieved using beams as seen in Figure 1.
Therefore, long-span beams will be researched also.
3. Efficiency/Sustainability/Cost Effectiveness
I will then move onto how well these trusses/beams work in timber structures, their strength
and load bearing capacity. Also, how sustainable and expensive the materials are to
manufacture and install.
4. Limits of Timber Trusses
After completing all the background research, I will begin exploring the limits of Trusses and
their maximum spans and loads. This will either be done by studying previous research or
carry out my own experiment. Granted this is an honours project and time/funds may prohibit
me from carrying out a full-scale experiment, it still may be worth undertaking on a smaller
scale.
5. Limits of Timber Structures
Finally, an investigation into the limitations of timber structures will be undertaken. Both
trusses and beams will feature heavily in this section and the whole process from felling trees
to the finished structures will be examined. Various methods of construction will be explored
and compared to one another. Structures from around the world will be looked at.
Review of Current Knowledge on the Project Topic
From the reading I have done I have raised more questions for myself than answers. I will
outline what I know and what I have learned up until now.
I know that sustainably, timber in construction is a viable option instead of concrete and steel
to decrease the carbon footprint (Zubizarreta, 2019). I know that wood retains carbon for
years even when it is built (Bateman, 2000). When a wooden structure is built it stores the
carbon which adds to the C02 emission reduction. The high durability of wood is seen in the
foundations of the bell tower in St. Mark’s Square which is traced back to 900 AD and have
lasted this long because of the lack of oxygen (Woodard, 2016). Although aiming for
anaerobic conditions in every day construction is not practical, this does highlight the
potential of wood in terms of resilience. I know that historically, impressive bridges with
large spans have been constructed of timber and some steel. One example is the Colossus
bridge in Philadelphia with a clear span of 104m, which far exceeded any other in the 19th
Century (Crocetti, 2016). With large spans being achieved as early as the 1800s, it begs the
question, what else can be done with modern methods. I know that large engineering firms
are using timber solutions for their structures more. ARUP published a report on the role
timber can play in construction and provides seven perspectives of timber design (Hough,
2019). it identifies timber construction as a viable way to reduce carbon emissions (Hough,
2019). It explores what role the traditional construction material of timber can play in
urbanisation (Hough, 2019).
I also got to see, firsthand, how the top chord of a Belfast truss performs. It is outside the
Merchiston Campus as seen in Figure 3 below. What’s interesting about this top chord is that
the screws seen in Figure 4, only hold the timber in place. They restrict it from moving
sideways and falling apart. Whereas the timber itself and the direction of the grain contributes
to resisting the downward force. The overall strength of the beam is due to the placement of
the timber sections.
Figure 3 Belfast Truss (Merchiston Campus)
Figure 4 Close up of Screws Holding the Truss Together
I know less about the technical side of long-span timber structure. I know that the majority
will be prefabricated and then installed. I know that long-spanning structures exist made of
huge glulam beams all tied together. I don’t know what’s too much for timber structures and
what are the limits. Examples: what span is too long? What load is too heavy? What timber is
too weak? What glue is used? What fire resistant is used? How efficient is the fire repellent?
Research Methods/Procedures to be used
It remains to be seen whether lab experiments will be undertaken. I will if I cannot gather the
information from using secondary data. It also depends on how much detail I go into
investigating the effectiveness of the trusses and glulam beams. It is an option I will explore.
It is too early to tell but a survey could be an option to find out people’s perception of timber
in commercial and residential buildings. Do people think that concrete and steel are better
materials for strength? Do people know of glulam and CLT? Do people know just how much
timber construction can help reduce carbon emissions? Do people know how much
construction contributes to carbon emissions and in turn climate change?
Once the data is gathered, it will be analysed to form conclusions on my research question.
Excel spreadsheets will be a quick and efficient way to display survey and lab experiment
results.
Resource Requirements
IT facilities will be required in Merchiston Campus. A new computer lab has opened in 32A
which I will utilise for my research. There is a possibility I will require the construction lab to
perform experiments, this is unknown to me at this stage of the project.
Timetable
This timetable is flexible and subject to change.
Bibliography
Bateman, I. J. L. A. A., 2000. Estimating and valuing the carbonsequestered in softwood and
hardwoodtrees, timber products and forest soils inWales. Environmental Management, pp.
301-302.
Crocetti, R., 2016. Large-Span Timber Structures. Prague, s.n.
Hough, R., 2019. Rethinking Timber Buildings, London: ARUP.
Killarney Brewing Company, 2021. Facebook. [Online]
Available at: https://www.facebook.com/killarneybrewing/videos/?ref=page_internal
[Accessed 19 October 2021].
Woodard, A. M. H., 2016. Sustainability of Construction Materials. Sustainability of timber
and wood in construction, II(7), pp. 129-157.
Zubizarreta, M., 2019. Modeling the environmental sustainability of timber structures: A case
study. Environmental Impact Assessment Review, Volume 78, p. 11.