Skjuvkapacitet i råspontsluckor - Undersökning av råspontsluckors skjuvkapacitet samt momentmodell för stabilisering av byggnader

Sammanfattning: In Sweden there is a long-standing tradition of building houses out of wood. In the year 2022 it is expected that 15 000 houses will be built, where the majority are built out of wood. There is an aim to build more out of wood since it has less impact on the climate than other materials. To build roofs prefabricated trusses are often used, and the trusses are covered by tongue and groove (t&g) paneling or plywood sheeting. There is often no dedicated system for stabilization, and it is assumed that the paneling or sheeting transfers the horizontal loads. There are no established methods for calculating the capacity of t&g paneling or sheeting and there are no explicit requirements to do so for single family homes. This might change with the upcoming revisions of Eurocode 5. There is an interest from the industry to find ways to calculate the horizontal capacity for t&g paneling and sheeting. Previous studies have shown that the metal connectors used to combine multiple t&g boards into t&g paneling contribute to increase the shear capacity, and therefore the ability to stabilize roof trusses. The focus of the report is to investigate how the shear capacity is affected by the number of connectors used between the t&g boards. This is done with a test where three t&g boards are used in a symmetric shear test, connected with metal connectors. Load and deformation are measured and the shear capacity can be determined depending on the amount of connectors used. To understand how multiple t&g panels interact with each other, tests are performed where 2,4x2,5 m walls are built and are covered with t&g paneling. A horizontal load is applied to the wall while the load and deformation are measured. The tests are performed with three connectors per shear plane, which is standard for 2,4 m panels, and with the double number of connectors, six per shear plane. Other tests are performed where the t&g panels are connected with metal connectors to create one large panel. To have a reference, the same test is performed with plywood sheathing, both 600 mm and 1200mm sheathing is tested. A model to calculate the horizontal capacity of t&g paneling and sheathing is presented, the model is based on a model by Prion and Lam. The model is based on that each of the nails between paneling and truss creates a moment that counteracts the moment created from wind and other loads. To get an idea of which size of building can be stabilized using only this model the capacity needed for different sized buildings is calculated. The result shows that each metal connector contributes to a shear capacity of 0,94 kN and it increases linearly with the number of connectors used. There are quite large variations in stiffness, but the stiffness increases when more connectors are used. When connectors are used to connect the panels there is an increase in capacity, especially when six connectors are used. The plywood sheathing has higher capacity then the t&g paneling. The 1200 mm sheathing has higher capacity than the 600 mm sheathing. The model presented for calculating the capacity worked very well for plywood sheathing. For t&g paneling the model worked well for calculating the load where the behavior stopped being linear, there was however more capacity as the deformation increased. The results showed that t&g paneling (3 or 6 connectors) is not sufficient to stabilize any of the buildings when the model is used. When the measured capacities are used it is sufficient to stabilize the smaller buildings with 3 connectors. If 6 connectors are used the measured capacity is sufficient to stabilize almost all the buildings. For 1200 mm plywood sheathing the capacity is sufficient to stabilize all the buildings even when partial coefficients are used. The 600 mm sheathing is sufficient to stabilize the smaller buildings.