In response to the global drive towards sustainable construction, CLT has emerged as a competitive alternative to other construction materials. CLT buildings taller than 10-storeys and CLT buildings in regions of moderate to high seismicity would be subject to higher lateral loads due to wind and earthquakes than CLT buildings which have already been completed. The lack of structural design codes and limited literature regarding the performance of CLT buildings under lateral loading are barriers to the adoption of CLT for buildings which could experience high lateral loading. Previous research into the behaviour of CLT buildings under lateral loading has involved testing of building components. These studies have generally been limited to testing wall systems and connections which replicate configurations at ground floor storeys in buildings no taller than three storeys. Consequently, to develop the understanding of the performance of multi-storey CLT buildings under lateral loading, the performance of wall systems and connections which replicate conditions of those in above ground floor storeys in buildings taller than three storeys were experimentally investigated. The testing of typical CLT connections involved testing eighteen configurations under cyclic loading in shear and tension. The results of this experimental investigation highlighted the need for capacity-based design of CLT connections to prevent brittle failure. It was found that both hold down and angle bracket connections have strength and stiffness in shear and tension and by considering the strength of the connections in both directions, more economical design of CLT buildings could be achieved. The testing of CLT wall systems involved testing three CLT wall systems with identical configurations under monotonic lateral load and constant vertical load, with vertical loads replicating gravity loads at storeys within a 10-storey CLT building. The results show that vertical load has a significant influence on wall system behaviour; varying the vertical load was found to vary the contribution of deformation mechanisms to global behaviour within the elastic region, reinforcing the need to consider connection design at each individual storey. As there are still no structural design codes for CLT buildings, the accuracy of analytical methods presented within the literature for predicting the behaviour of CLT connections and wall systems under lateral loading was assessed. It was found that the analytical methods for both connections and wall systems are highly inaccurate and do not reflect experimentally observed behaviour.
To support the associated Sir Matthew Begbie Elementary School and Bayview Elementary School projects in pushing the boundaries forward for long-span floor and roof construction, this testing project aims to compare different connection approaches for composite connections between glulam and cross-laminated timber (CLT) – for vibration, stiffness, and strength. Working with the University of Northern British Columbia (UNBC), Fast + Epp aimed to complete a series of vibration and monotonic load tests on 30’ long full-scale double-T ribbed panels. The tests consisted of screws in withdrawal, screws in shear, and nominal screws clamping with glue. Both the strength and stiffness are of interest, including slip stiffness of each connection type. This physical testing was completed in January and February 2020, where the full composite strength of each system was reached. Initial data analysis has provided information for comparison with existing models for shear connection stiffness. Publications will follow in 2021.
Self-centring Cross-Laminated Timber (CLT) walls are a low damage seismic force resisting
system, which can be used to construct tall wood buildings. This study examines two
approaches to model self-centring CLT walls, one that uses lumped plasticity elements, and
another that uses fibre-based elements. Finite element models of self-centring CLT walls are
developed using the Python interpreter of Opensees, OpenSeesPy, and tested under monotonic
and reverse cyclic loading conditions. Outputs from the analysis are compared with data from
two existing experimental programs. Both models accurately predict the force displacement
relationship of the wall in monotonic loading. For reverse cyclic loading, the lumped plasticity
model could not capture cyclic deterioration due to crushing of CLT. Both models slightly
overpredict the post-tension force. Sensitivity analyses were run on the fibre model, which
show the wall studied is not sensitive to the shear stiffness of CLT.
OpenSeesPy models are also created of a two-story structure, which is tested dynamically
under a suite of ground motions. The structure is based on a building tested as part of the
NHERI TallWood initiative. During testing the foundation of the building was found to be
inadvertently flexible. To determine the appropriate model parameters for this foundation,
calibrations were performed by running a sequence of OpenSeesPy analyses with an
optimization algorithm. Outputs from the lumped plasticity and fibre models were compared
to experimental results, which showed that both could capture the global behaviour of the
system with reasonable accuracy. Both models overpredict peak post-tension forces. The suite
of analyses is then run again on the building to predict the performance with a rigid foundation.
Cyclic deterioration is more significant for the building with a rigid foundation, and as a result
the fibre mode is more accurate.
The objective of this research is to characterize of load-deformation responses of tested connections(stiffness, strength, ductility, energy dissipation, failure modes) by testing large STS connections with steel side plates under monotonic and cyclic loads.