Testing and finite element modeling of wooden stairs and bridge decks

Sammanfattning: Development of new products in the joinery industry has traditionally been based on testing of prototypes. Computer-aided design tools and finite element analysis can supplement traditional prototype testing and improve the product development process. The objective of this research was to study the structural behavior of wooden products and wood joints and investigate how to calculate them with a finite element program. Joints in wooden products can be designed in various ways. For structural analysis, timber joints are today usually considered either rigid or pinned, although their behavior in reality is semi-rigid. The products studied were wooden staircases and bridge decks. The wood products were made by manufacturers and tested in the laboratory. Displacement was measured for different loads and load configurations. The products were modeled in a computer with 3D solid models and the results from simulations were compared to test results. Variations in the wood material properties and tolerances in joints may explain some of the differences between finite element modeling and results from testing of actual wood structures. A wooden spiral stair modeled as one solid unit was more rigid than the tested stair. The rigidness at the connection of tread to the center pole showed some dependence on the prestress of the pole. In straight stairs, the joints between treads and strings are often made with different types of tenons. Tests and simulations showed that the joints were not very rigid, and that the level of rigidity depended somewhat on the wood species and the design of the tenons. A stress-laminated bridge deck with box beam cross-section was tested and modeled to investigate what material properties that should be used in calculations of this type of deck.