Analysis of holes in wooden rib panels

Abstract: The concern for the environment is one of the leading aspects in material choice within theconstruction industry. According to the Swedish National Board of Housing, Building andPlanning (2020) the construction industry is responsible for 19 percent of the total amount ofgreenhouse emissions in Sweden. Choosing wood over for example concrete or steel asbuilding material would result in beneficial impacts on the environment. The research in thefield of wood elements is ever growing and new materials are invented. A relatively newproduct on the market is the rib panel. The structure of the rib panel enables buildings withlarge spans and facilitates installations. Due to its properties and area of applications the ribpanel could be a strong competitor among other flooring systems.The objective of this thesis was to investigate the possibility of drilling holes aimed for airducts through the ribs. Investigations of location of the holes, maximum possible holediameter at minimum possible rib height and influence of the cross sectional properties of therib elements was performed.A numerical model was designed to calculate minimum required rib height for eight differentspans (6–13 m) according to EN 1995-1-1:2004 (2004). The model was constructed withspecific requirements for beam deflection (L/500 and L/300) and natural frequency (8 Hz).For each calculated rib height, the numerical model generated data of failure mode and usageratio for each design requirement. Based on the evaluated rib heights, computer simulationswere conducted in Abaqus FEA. From the computer simulation the maximum hole forspecific positions and different load cases could be found.The measured stresses in the vicinity of the hole was evaluated with Norris failure criterion.The result from the simulations showed that relatively large holes at the midspan of thebeams were possible with remaining bearing capacity according to SLS and ULS. Highrestrictions of SLS conditions caused a low usage ratio of stresses within the beam, whichwas a strong contributing factor for the possibility of large holes. Another contributing factor3for the possibility of large holes was the influence by the flange. By placing the holes at ahigher position, closer to the flange larger holes was possible.Using another failure criterion or different limitations according to SLS could have generateda different result. The investigation is limited to simulations and calculations from numericalmodels, hence load tests in reality have not been conducted. Performing tests in reality mightcover other aspects than in this thesis and possibly generate a more accurate result. The resultin this thesis can be seen as a guidance of possible hole diameter, but should not be directlyapplied to real structures. Further investigations need to be done if the result from this thesisshould be applied on real structures.