This report represents the results of the activities performed in working group 1, Basis of Design. The most important task of working group 1 was the defragmentation and harmonization of techniques and methods that are necessary to prove the reliable, safe and economic application of timber materials or products in the construction industry.
This report is structured into five parts. At first general principles regarding the design formats are addressed (Part I). Afterwords timber specific aspects regarding code calibration (Part II) and serviceability (Part III) are summarized. In Part IV other demanding issues for the implementation into Eurocode 5 are addressed. Here also summaries of joint activities with other working groups on cross laminated timber and timber connections are presented. The report concludes with a guideline for data analysis (Part V).
Timber connections with steel dowel-type fasteners may fail in ductile or brittle ways. The design of this joints was traditionally focused on ductile failure, assuming that brittle failure could be avoided by means of geometrical limitations. However, recent studies demonstrated that these assumptions do not always guarantee ductile failure. A new design model for timber connections with small diameter dowel-type fasteners is provided in this paper. Its improved accuracy is demonstrated by analysing an extensive database of experimental tests and comparing its prediction accuracy to that of existing models.
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.
This state-of-the-art report has been prepared within COST Action FP1402 Basis of structural timber design from research to standards, Working Group 3 Connections. The Action was established to create an expert network that is able to develop and establish the specific information needed for standardization committee decisions. Its main objective is to overcome the gap between broadly available scientific results and the specific information needed by standardization committees. This necessitates an expert network that links practice with research, i.e. technological developments with scientific background. COST presents the ideal basis to foster this type of joint effort. Chapter 8 Connections presents an integral part of Eurocode 5 and is in need of revision. This state-of-the-art report shall provide code writers with background information necessary for the development of the so-called Second Generation of the Eurocodes, now aimed to be produced in 2022.
The aim of this document is to report the state of the art in terms of research and practice of Timber-Concrete Composite (TCC) systems, in order to summarize the existing knowledge in the single countries and to develop a common understanding of the design of TCC.
This report was made within the framework of WG4-Hybrid Structures within COST Action FP1402. It intends to reflect the information and studies available around the world, but especially in Europe through the active contribution and participation of experts from various countries involved in this Action.
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.