Utilizing structural Accoya® timber: Comparative analysis with non-acetylated timber
D.J. Droogleever (TU Delft - Civil Engineering & Geosciences)
J. W.G. van de Kuilen – Graduation committee member (TU Delft - Bio-based Structures & Materials)
Wolfgang Gard – Graduation committee member (TU Delft - Bio-based Structures & Materials)
Paul A. Korswagen – Graduation committee member (TU Delft - Applied Mechanics)
MAN Hendriks – Graduation committee member (TU Delft - Engineering Structures)
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Abstract
This
research focuses on comparing Accoya® with unmodified wood and investigates Accoya®’s
structural performance in environments with varying relative humidity levels.
The wood’s moisture content, and consequently its swelling and shrinking
behavior, fluctuates on an annual basis due to these varying relative humidity
levels, especially when exposed to outdoor conditions. FEM analyses were
conducted to investigate physical properties and the performance of
moment-resistant connections, with their implementation aimed at incorporating
rotational stiffness into a structural portal frame. Accoya® demonstrates
excellent moisture resistance and an increase in dimensional stability of
approximately 80%, based on Dutch climate conditions. The reduction in swelling
alleviates internal stresses within the connections, enhancing the strength and
stiffness of moment-resisting connections. Specifically, a clamped connection
and a circular dowel connection were analysed using a linear elastic static FEM
model, revealing internal stress reductions of 81% and 52%, respectively. This
reduction was observed during the simulated initial annual swelling cycle that
the wood may undergo. With the use of Accoya®, significantly less plastic
deformation is expected in connections due to swelling issues compared to
unmodified wood and reduced deflection in structures is expected. An increase
of 219% and 58% in rotational stiffness was observed for the respective cases.
To evaluate the impact on overall stiffness, these observed values were
implemented in a portal frame structure. A reduction in horizontal displacement
was observed ranging from 31% to 66%. This opens up new possibilities in
structural wood design, allowing for slimmer and lighter wood constructions. Due
to Accoya®’s lower property degradation and more stable structural performance in
high-humidity conditions, an adjustment of the kmod and kddef factors is suggested;
however, this is not sufficiently substantiated in the current study. Future research
could explore long-term performance factors with experiments such as creep and
fatigue to validate Accoya®’s structural reliability further.