Cross-laminated timber (CLT) structures are increasingly being used for housing due to their economic and environmental benefits. However, the structural calculations for these structures must undergo rigorous static testing. Furthermore, high-energy-efficiency construction, such as the Passivhaus standard, requires special attention to minimize deformations that could compromise the building's airtightness, whether this airtightness is based on the building components themselves or on membranes with limited tear resistance.
Today, modeling wooden buildings with finite element software can be complicated: in particular, correctly assessing the lateral stiffness of the walls is difficult to determine, as it depends on different contributions (shear deformations of the walls, deformations of the connections, rotation of the rigid body due to deformations of the fittings) that are difficult to define in the model.
On the other hand, with the TimberTech Buildings software, the definition and modeling of timber walls (CLT or light-frame) is easily achieved because the "assembly" of all wall components corresponds to the implemented numerical models derived from research conducted at the University of Trento. The model implemented in the software is capable of considering all the stiffness components in a timber wall and its connections. A detailed description of the model can be found in the document "Daniele Casagrande, Simone Rossi, Tiziano Sartori, Roberto Tomasi: 'Proposal of an analytical procedure and a simplified numerical model for the elastic response of single-story timber walls to shear,' in the journal Construction and Building Materials (2015).".
Introduction
This section presents a comparison between a framed wall modeled using finite element software and one modeled using TimberTech Buildings software. The objective of this comparison is to calculate and compare the various stiffness contributions provided by the elements that make up the wall. A framed wall with studs and sleepers is modeled, completed with structural sheathing used to transfer horizontal loads to the base of the structure.
The elastic horizontal displacement of a lightweight timber frame wall subjected to a horizontal force can be obtained by adding the following deformation contributions.
Modeling with finite element software
Modeling a framed wall using finite element software is very expensive and complicated. As shown in the following figure, created with SAP2000, to correctly evaluate the horizontal stiffness of the wall, the following elements must be used: – “Frame” elements to model the framing; – “Shell” elements to model the sheathing; – “Link” elements to model the connections between the sheathing and the frame. Each connection is modeled with a link representing the actual stiffness of the fixing; – “Link” elements to simulate the hardware.
Modeled using Timbertech software
Modeling with TimberTech Building is very simple and fast. The user must define the geometric and mechanical properties for each wall type.
Comparative practical example
This example shows a comparison between TimberTech Buildings software and finite element software for a timber-framed wall with a length of 2 m and a height of 3 m. The wall has the following characteristics: – The framing is 160 mm thick, the studs are 100 mm wide and spaced 1000 mm apart; – The structural sheathing is OSB/2 with a thickness of 12.5 mm. The nail stiffness is 918 N/mm.
– The spacing of the external fittings is 100 mm and the spacing of the internal fittings is 200 mm; – The wall is attached to the foundations with a bracket with a stiffness of 19977 kN/m and with two angle supports with a stiffness of 52186 kN/m.
In the image above, we can see how the results of the analytical model implemented in Timbertech Buildings are very similar to those obtained with finite element software. We achieved a wall stiffness very close to that obtained with finite element software despite a more simplified wall model. The image above shows that the contribution of deformation due to rigid body translation is negligible. On the other hand, the deformations of the hardware and rigid body overturning (attachment connection) are very significant.
Conclusions
TimberTech Buildings is structural design software for analyzing load-bearing timber structures with CLT (Cross Laminated Timber) and light-frame construction. Developed at the University of Trento and created by TimberTech, it is highly reliable, quick to learn, and easy to use. Constantly and automatically updated, TimberTech Buildings is designed to meet all the needs of timber structure designers, from DXF import to high-speed modeling and exporting design reports in Word format.
As we have seen in this example, it presents a robust numerical calculation method supported by the Eurocodes and which allows for very fast modeling of complex structures.
For more information about the software:
https://www.ingemade.com/timbertech
Credits: Jesús Menéndez, Timbertech Srl
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