Method for assessing the load-bearing capacity of cross-laminated timber floor structures with variable section parameters

This paper presents a method for assessing the actual load-bearing capacity and stress-strain state (SSS) of cross-laminated timber (CLT) floor structures with variable section parameters. The method is based on a functional relationship between the natural frequency of oscillations and the maximum deflection of plates, expressed through a proportionality coefficient K. This coefficient remains constant for a given type of support conditions and has been numerically validated for multi-layer orthotropic CLT plates with various geometric configurations. Five different CLT panel types were tested in the study, each with varying layer geometries: three-layer solid sections, thickened longitudinal layers, thickened transverse layers, panels with gaps in transverse layers, and five-layer solid panels. All samples were simply supported along two sides. Natural frequencies, maximum deflections at the center of the structure, and normal stresses along the span under uniformly distributed loads were recorded experimentally. The multi-layer CLT structures were converted into an equivalent single-layer orthotropic plate using effective cylindrical stiffness values. Calculations of maximum deflection and bending moments were performed using classical plate theory and verified against experimental data. Deflection deviations did not exceed 10%, while normal stress deviations remained within 13% for most cases, confirming high accuracy of the proposed method. A key feature of the method is its ability to assess structural performance without requiring precise knowledge of actual stiffness, relying solely on one dynamic parameter — the fundamental frequency of natural oscillations. This makes the method fast, safe, and cost-effective for field testing. It is particularly suitable for evaluating structures under the second group of limit states and, under certain conditions (e.g., neglecting shear stresses and stress concentrations), can be applied to the first group as well. Further research is recommended to expand the applicability of the method to different support conditions and aspect ratios of CLT panels.