Although building systems made of cross-laminated timber (CLT) have become common in Sweden in the past 20 years and they have developed rapidly during the same period, steps remain to be taken to simplify the assembly of such systems, especially at construction sites. Current construction methods, however, remain labour-intensive and thus show room for improvement.

This paper describes a novel connection for the assembly of building elements made of CLT. Simple and inexpensive, the connection is fairly insensitive to manufacturing tolerances and enables rapid, more efficient construction than the connections for CLT structures currently used. Test results show the excellent strength and stiffness of the connection, which also allows the replacement of numerous fasteners, including nails and screws, with only a single steel rod. 

A modular wooden wind turbine tower has been developed by the Swedish company Modvion AB, where the prefabricated modular elements are connected by glued timber-timber edge joints and by hybrid timber joints with bonded-in perforated steel plates. The application of wood-based products in such a demanding application and highperformance structure is challenging and a variety of questions had to be solved to ensure a reliable performance. The fatigue performance of the adhesive bonded connections has been evaluated in a research project and is presented in this paper. Test specimens of the fatigue resistance of the adhesive and the bond line has been developed. Different stress ratios with alternating loads and high numbers of load cycles have been tested. The results of the tests are presented in this paper.

Today there is no standard for strength grading and CE-marking sawn timber of Birch grown in Sweden, which makes it impossible to use this material as structural timber. Internationally, there are standards for visual grading of hardwood in several European countries. However, these standards may not be used to classify Birch timber grown in Sweden without having been tested and verified to meet the standard's requirements. In a project (BizWOOD) run by RISE, 600 pieces of sawn birch wood from Sweden is visually graded and strength tested. The project aims to result in grading rules for birch, either by using international standards or where international standards will be used as references for the identification of defects that will be included in the grading model. This paper summarizes parts of the BizWOOD project and includes 1) description of sampling and timber origin, 2) visual grading according to international standards, 3) strength testing of the material, 4) evaluation of mechanical characteristics, 5) evaluation of grading techniques.

Laminated veneer products (LVPs) are veneers glued together into a predetermined shape. Experimental and numerical investigations were performed under lamination and simultaneously bending of veneer laminate to study the stress distribution in the laminate. Laminates of different thicknesses were made of peeled veneers of European beech. The veneers were coated with adhesive, inserted in a mould which had the shape of a semicircle, and finally pressed at 20°C to a laminate. Two Teflon-polymer films including sensors for measurement of the contact pressure were placed on both sides of the laminate to measure the local contact pressure (contact stress) between the laminate and the mould. At the beginning of the bending process, the contact stresses were locally distributed over the laminate in a similar pattern as in a three-point bending; after the laminate was further bent, the stress distribution rearranged to be as in four-point bending. In the end of the moulding, the local contact stresses increased over the entire laminate and reached a ‘peak-value’ over bent area in the middle part of the mould. A finite-element model was created to study the bending process. Regarding the overall development of the contact stress variations, the experimental and the numerical results agreed.

The presented project aims to develop prototypes for building connections inspired by the furniture and interior industry and explore them with representatives from the timber construction industry. The long-term vision is that actors from furniture and building industry together develop a smart system for assembly of building elements, which provide higher precision, faster and more efficient assembly than what is available today. The prototype connectiondeveloped in this project shows that the idea is ripe for full-scale investigation. Laboratory tests showed promising results due to the high failure loads obtained with very high stiffness.

Timber utilisation and wood construction are fundamental components of Europe's strategy on progressing towards a sustainable bio-based economy. Both components require optimised strength grading procedures in Europe's sawmills. To further improve the current procedures, quality assessment and segregation of the raw material need to start already at the roundwood stage. Furthermore, the quality information should be made accessible throughout the production process to leverage the full potential for optimisation. This paper discusses the current state of research on combined log and board strength grading with a focus on the situation in Europe. It highlights limitations due to technology and current standardisation and identifies knowledge gaps and research opportunities. The European research project READiStrength (resource-efficient and data-driven integrated log and board strength grading) has been initiated to address these issues.

This report is a state-of-the-art summary on industrial strength grading of wood. Some used methods for grading of wood, both logs and boards, are presented, as well as some new concepts. European standards for strength grading of wood are presented, as well as some national standards and regulations for Austria, Germany and Sweden.

This report presents the industrial view regarding strength grading, based on interviews with personnel of sawmills and manufacturers of grading systems. The sawmills are Swedish, German and Austrian enterprises, while the manufacturers are from Sweden, Finland, Germany and Italy. The interviews were performed during 2019 and 2020.

In the last two decades, knowledge has been accumulated with respect to raw material characterisation of wood, from the standing tree to the end product.

It is known that log pre-grading has the potential to significantly improve raw material utilisation, because at that stage of production one is still free to choose the cutting pattern(sawn product dimensions). 3D-log scanning immediately before sawing allows improving log rotation and positioning for cutting optimisation to maximise volume yield, which is already widely used in sawmills.

One of the major technological breakthroughs of the last years is the development of industrial computed tomography log scanning, which provides a much more detailed insight into each individual log than 3D outer shape log scanning and discrete X-rayscanning.

Three new approaches to strength grading is presented: pure log grading; integrated grading, where log information is used to improve the precision; sequential strengthgrading, where log pre-grading is followed by board grading.

The interviews show that the use of automatic strength grading is different between the countries. In Sweden all mills use some automatic grading system, while German mills rely to a large extend on visual grading.

The answers show that the interviewed industrial persons in general have knowledge about the capabilities of log sorting and grading with 3-D, discrete X-ray and computer tomography, CT. The knowledge about acoustic log scanning is not as good as for the other techniques.

The interviewed sawmillers had in general a strong sense that log tomography could improve the yield, both in volume and value, from the logs. But in contrast to that, the Swedish sawmillers were confident in that CT is a significant improvement over the other scanning techniques. The German sawmillers did not have the same confidence in the CT-scanning´s possibilities. Only few of the Swedish and the German sawmillers saw any large potential in adding acoustic scanning to the other log scanning techniques.

The large Austrian enterprises were mainly interested in the possibilities, the advantagesand disadvantages of the new technology of industrial computed tomographyfor round timber. For the other Austrian companies, the focus was on less cost intensive systems such as scanners for determining the dynamic modulus of elasticity, logouter shape or grain deviations.

The most important features for grading are knots, their position, status and size. Alsorot and top rupture are important to be able to make a good grading of the log. A more“fuzzy” grading is also wanted, meaning that the rules shall not be too strict.

The manufacturers in general said that normal development is ongoing. Larger, revolutionary, inventions will not be presented in this manner.

Tall timber buildings generally require fire resistance ratings of 90 minutes, 120 minutes or more. The vast majority of fire tested structural timber connections, however, did not reach a fire resistance that was relevant for these buildings. Commonly timber connections between glued laminated timber members comprise of exposed steel fasteners, such as bolts, screws, nails and dowels. However, it has previously been concluded that connections with exposed steel fasteners, generally do not achieve fire resistance ratings of 30 minutes and are, therefore, inadequate to be implemented in tall timber buildings without fire encapsulation. The research project presented in this report consists of four connection fire tests that are designed to achieve structural fire resistance ratings of 90 minutes, using different design strategies. This goal was achieved for all tested column-beam connections. A single test of a moment resisting connection did not lead to a fire resistance rating of 90 minutes, due to timber failure at the smallest cross-section after 86 minutes. The low temperature of the steel fasteners and the limited rotation of the connection, however, suggest that the connection would have been capable of achieving a 90 minutes fire resistance rating if larger beam cross-sections would be used.