Vibrations induced by people walking is one of the most important issue in timber floor design. Low natural frequency and low mass require a careful analysis in order to prevent significant annoyance and to guarantee an acceptable human comfort. This paper is concerned with the assessment of vibration performance of a timber-concrete composite timber floor and a cross laminated timber floor used in two timber buildings under construction in Trento (Italy). Different approaches suggested by Standards and literature were employed: analytical methods, numerical analyses and laboratory tests. About analytical methods the uniformed distributed load deflection criterion (ULD), the Eurocode 5 criterion and some criterions from literature were compared, whereas the Vibration Dose Value (VDV) method, as suggested by ISO 10137, was used for the numerical models and the laboratory tests. The numerical analyses were carried out by means of a finite element modelling. The load due to footfall was simulated by static and dynamic vertical forces. The laboratory tests were characterized by thirty walking tests for each floor. Impact testing with modal hammer was also undertaken in order to investigate the dynamic properties of the specimens. All results are compared and discussed.
Cross Laminated Timber (CLT) at in-plane beam loading conditions present a very complex stress state and many failure modes need to be considered in design. The work presented here aims at finding improvements of a specific analytical model for stress analysis and strength verification that has been suggested in literature and which is also suggested as a basis for design equations for the next version of Eurocode 5. Although the model has appealing properties it suffers from some drawbacks related to the assumed distributions of internal forces which, based on comparison to finite element analysis, appear to be inaccurate. The main focus in this paper is on model predictions regarding the distribution and magnitude of internal forces acting in the crossing areas between longitudinal and transversal laminations. The proposed modified model assumptions regarding the distribution of lamination shear forces, which in turn influence the forces acting in the crossing areas, are suggested to be taken into account in design of CLT beams.
International Conference on Contemporary Theory and Practice in Construction
Invention of cross-laminated timber (CLT) was a big milestone for building with wood. Due to novelty of CLT and timber’s complex mechanical behavior, the existing design codes cover only rectangular CLT panels, simply supported along 2 parallel or all 4 edges, making numerical methods necessary in other cases. This paper presents a practical engineering tool for stress and deflection prediction of CLT panels with non-classical boundary conditions, based on the software for the computational analysis of laminar composites, previously developed by the authors. Diagrams applicable in engineering practice are developed for some common cases. The presented methodology could be a basis for more detailed design handbooks and guidelines for various layouts of CLT panels and different types of loadings.
An economic-design optimization of cross-laminated timber (CLT) plate with stiffening ribs is presented. For the structural analysis, an enhanced assumed strain (EAS) solid finite element is used. It behaves well for thin plates (with no shear locking) and delivers reasonable approximations for the transverse shear stresses in layered composites. Eurocodes 5 (EC5) are followed in defining the optimization constraints, which include deflections, stresses and fundamental eigenfrequency. The gradient optimization is performed. Analytical expressions for sensitivities are obtained by an automatic differentiation tool. The result is an economic timber plate configuration that complies with the EC5 requirements. Numerical examples are presented in order to illustrate the approach.
The present paper deals with the effect of moisture induced stresses (MIS) on the mechanical performance of a glulam beam of Vihantasalmi Bridge in Finland. MIS caused by high moisture gradients in a cross section of the glulam beam are calculated by a hygro-thermal multi-Fickian model for evaluation of moisture content, relative humidity and temperature in wood that is sequentially coupled with an orthotropic-viscoelasticmechanosorptive model for calculation of wood stresses. Both models, already developed in Abaqus FEM code by some of the authors in their previous works, had to be modified for the Nordic climate. The obtained levels of MIS are then compared to the Eurocode 5 design resistances. The study aims at providing suggestions to future developments of Eurocode 5 for the correct evaluation of the influence of moisture content on service life in timber bridge elements.