Marija Nefovska-Danilović

Cross-laminated timber (CLT) floors are increasingly used in long-span buildings as a greener alternative to reinforced concrete, steel and their composites. Despite high stiffness, relatively low mass of CLT makes such floors prone to pedestrian-induced vibrations. While these vibrations do not threaten structural integrity and safety, they often cause vibration serviceability issues. Therefore, vibration serviceability assessment (VSA) regularly governs their structural design. To address a high level of uncertainty pertinent to numerical VSA of CLT floors, in situ vibration measurements of as-built floors are essential. This study presents an experimental investigation of modal properties and pedestrian-induced vibrations of a full-scale CLT floor in an office building in Serbia. The study showed that its vibration behaviour is radically different from what is assumed in leading design guidelines for floor vibrations.

This paper discusses vibration serviceability assessment of cross-laminated timber (CLT) floors induced by human activities, with special emphasis on vibrations induced by walking. In the first part current design criteria for vibration serviceability check of timber and CLT floors were analyzed in line with the more general vibration performance-based approach applicable to any floor structure regardless of the material used. The second part focuses on the ongoing research achievements in the design of vibration resistant CLT floors carried out at the Faculty of Civil Engineering, University of Belgrade. In addition, challenges for future research were formulated as well.

Additional temperature stresses in continuously welded rails (CWRs) are caused by track/bridge interaction (TBI) due to thermal actions. Exceeding permissible stresses in CWRs on the bridge can lead to track buckling or rail cracking, compromising the safety of railway traffic. The main aim of the conducted study is to determine the effects of the key parameters such as rail cross-sectional area, track longitudinal resistance, bridge expansion length, and longitudinal stiffness of the fixed bridge support on the reduction of additional temperature stresses in CWRs on steel truss railway bridges. To quantify the effects of these parameters, two steel railway bridges with CWRs and the maximum expansion lengths according to UIC Code 774-3 were analyzed: (1) simply supported truss bridge with expansion length of 60 m and (2) continuous truss bridge with expansion lengths of 2 × 60 m. According to the obtained results, the track longitudinal resistance had the most significant impact on additional temperature stresses in CWRs, leading to their reduction of up to 72%. The bridge expansion length and the rail cross-sectional area led to reductions of up to 25% and up to 18%, respectively. Considering the deformation criteria of TBI, the longitudinal stiffness of the fixed bridge support had a minor effect on the reduction of additional temperature stresses in CWRs.

This paper considers the dynamic analysis of a spatially curved Bernoulli-Euler beam subjected to a moving load. The isogeometric approach is used for the spatial discretization of the weak form of the equation of motion. Both the reference geometry and the solution space are represented using the same NURBS basis functions that guarantee an accurate description of the beam centerline. The time integration is done by the explicit technique. The presented formulation is validated by the comparison with the existing results from the literature for the curved beam subjected to a constant load moving with a constant velocity. In addition, the influence of the moving load velocity on the dynamic response of a spatially curved beam has been investigated.

Variety of wood species and complexity of their structure make the reliable material properties of cross-laminated timber (CLT) difficult to obtain, which can lead to inaccurate prediction of CLT behavior. Due to high stiffness-to-weight ratio, CLT floors can suffer from vibration serviceability issues. This paper aims to quantify the uncertainties induced by material properties and investigate their effect on vibration performance of CLT floors. Analysis based on Monte Carlo simulations, considering material properties as random variables, is developed. Based on the conducted analysis, appropriate conclusions have been derived.

In this paper dynamic analysis of a curved Bernoulli – Euler beam subjected to a moving load ispresented. Moving load is modelled as a single force with constant magnitude and direction, whichmoves along its trajectory. Plane curved Bernoulli – Euler beam element is formulated usingisogeometric approach where both the displacement field and geometry of the beam are describedusing NURBS basis functions. Behavior of the beam element is defined and studied in the case oflinear formulation where displacements and displacement gradients are assumed to be small.Validation of the proposed approach is presented for the plane curved beam subjected to movingload with constant velocity, magnitude and direction.

A framework for free vibration analysis of plate‐like structures is presented in the paper. Based on the previously formulated dynamic stiffness elements, FREEVIB object‐oriented software in Python environment has been created. Software design and structure as well as a wide range of possible structural problems that could be analyzed using the FREEVIB are presented. Through several illustrative examples including free vibration analysis of stepped, stiffened and folded plate structures, implying isotropic or orthotropic material formulations, the efficiency and accuracy of the FREEVIB is demonstrated. The possibilities of further extensions and improvements of the software are discussed.