Assessment of In-Plane Timber Floor Stiffness as Structural Diaphragms: A Numerical Approach to Lateral Load Response

The behaviour of horizontal floor diaphragms plays a crucial role in ensuring the overall response of a building during earthquakes, as the stiffness of these diaphragms determines whether the structure will act as an integrated system. If the diaphragms do not exhibit sufficient stiffness, differences in the redistribution of forces on wall elements arise, increasing the risk of significant deformations and even local damage, which is commonly observed in earthquake-affected areas. Additionally, flexible diaphragms heighten the risk of torsional effects. Due to these factors, more attention should be given to the response of buildings with flexible diaphragms. Eurocode standard specifies general requirements under which diaphragms should be considered rigid within their plane, depending on the maximum diaphragm moment. However, specific guidelines regarding the geometric and material properties of elements that significantly impact seismic behaviour are not included in the existing European standards. This served as a basis for conducting a numerical study analysing the in-plane behaviour of floor elements made from different materials. This study, limited to a simple box-shaped structure with masonry walls, symmetrical in both orthogonal directions, evaluated and thoroughly analysed the deformations for different types of diaphragms, including prefabricated wooden frame-panel floors, CLT panels, and reinforced concrete slabs. Special emphasis was placed on wooden structural elements due to the increased demand for timber construction, as the behaviour of these elements needs to be properly studied, especially in seismic regions. The study results were obtained through FEM analysis using the SCIA Engineer software, version 22. The modelling of elements was carried out considering the orthotropy of brick wall and wooden ceiling elements, as well as simulating the appropriate shear stiffness of the connecting means.