Cracks in timber members influence the stiffness and load-carrying behaviour but only rudimentary rules are given to evaluate cracked members. Therefore, an investigation to gather information about the most frequent characteristics of cracked timber structures has been carried out. This investigation provides the main characteristics of both the timber elements and the crack distributions encountered. These main characteristics have then been used to define a numerical model in order to investigate the impact of cracks on the stiffness and load-carrying capacity of timber beams. Based on these results, the existing rules considering cracks in timber beams can be evaluated and new rules can be developed.
This paper illustrates arrangements of self-tapping screws to reinforce the mechanical behaviour of transverse compression. Several experimental approaches are studied such as the reinforcement below the support, beside the support or the combination of these two reinforcements. The last experimental approach is explored to solicit the shear over the entire height of the screw. These different approaches of reinforcement allow seeing a panel of constructive solutions to transverse compression reinforcement by screws. This panel allows adapting the type of reinforcement with the studied building.
In timber engineering, self-tapping screws, optimized primarily for axial loading, represent the state-of-the-art in fastener and reinforcement technology. Their economic advantages and comparatively easy handling make them one of the first choices for application in both domains. This paper focuses on self-tapping screws and threaded rods applied as reinforcement, illustrating the state-of-the-art in application and design approaches in Europe, in conjunction with numerous references for background information. With regard to medium to large span timber structures which are predominately erected by using linear timber members, from e.g. glued laminated timber, the focus of this paper is on their reinforcement against stresses perpendicular to grain as well as shear. However, latest findings with respect to cross laminated timber are included as well.
The United States military is constantly evolving into an organization equipped by the latest technology and seeking the greatest protection per cost ratio for its members in harm’s way. While new protection methods are steadily produced by the Engineering Research and Development Command, most protective structure options fall into either very expensive or very labor-intensive structures with widely varying degrees of reusability and transportability. Furthermore, there is currently no widely accepted quantitative approach to help the decision-making process when choosing which system to use in a specific condition. This study will seek to create a framework which can be used to aid the decision-making process based on quantitative calculation of cost benefit of various protective systems. The framework will encompass resource metrics of man-hours, machine hours, and monetary cost. The calculations and assessments will also be affected by quantitative evaluations of military situations which can increase or decrease each value of resource metric. This study will also investigate the potential of using a mass timber product, namely Cross Laminated Timber (CLT) panels, as a protective structure that may be useful in certain military situations. While not designed to replace other systems, it is another option for military commanders and staffs to consider when choosing the most efficient and economical protection method for their soldiers.
The current research investigated the delamination process of adhesively bonded hardwood (European beech) elements subject to changing climatic conditions. For the study of the long-term fracture mechanical behavior of gluedlaminated components under varying moisture content, the role of moisture development, time- and moisture-dependent responses are absolutely crucial. For this purpose, a 3D orthotropic hygro-elastic, plastic, visco-elastic, mechano-sorptive wood constitutive model with moisture-dependent material constants was presented in this work. Such a comprehensive material model is capable to capture the true historydependent stress states and deformations which are essential to achieve reliable design of timber structures. Besides the solid wood substrates, the adhesive material also influences the interface performance considerably. Hence, to gain further insight into the stresses and deformations generated in the bond-line, a general hygro-elastic, plastic, visco-elastic creep material model for adhesive was introduced as well. The associated numerical algorithms developed on the basis of additive decomposition of the total strain were formulated and implemented within the Abaqus Finite Element (FE) package. Functionality and performance of the proposed approach were evaluated by performing multiple verification simulations of wood components, under different combinations of mechanical loading and moisture variation. Moreover, the generality and efficiency of the presented approach was further demonstrated by conducting an application example of a hybrid wood element.
A set of novel structural fire tests on axially loaded cross-laminated timber (CLT) compression elements (walls), locally exposed to thermal radiation sufficient to cause sustained flaming combustion, are presented and discussed. Test specimens were subjected to a sustained compressive load, equivalent to 10 % or 20 % of their nominal ambient axial compressive capacity. The walls were then locally exposed to a nominal constant incident heat flux of 50 kW/m2 over their mid height area until failure occurred. The axial and lateral deformations of the walls were measured and compared against predictions calculated using a finite Bernoulli beam element analysis, to shed light on the fundamental mechanics and needs for rational structural design of CLT compression elements in fire. For the walls tested herein, failure at both ambient and elevated temperature was due to global buckling. At high temperature failure results from excessive lateral deflections and second order flexural effects due to reductions the walls’ effective crosssection and flexural rigidity, as well as a shift of the effective neutral axis in bending during fire. Measured average one-dimensional charring rates ranged between 0.82 and 1.0 mm/min in these tests. As expected, the lamellae configuration greatly influenced the walls’ deformation responses and times to failure; with 3- ply walls failing earlier than those with 5-plies. The walls’ deformation response during heating suggests that, if a conventional reduced cross section method (RCSM), zero strength layer analysis were undertaken, the required zero strength layer depths would range between 15.2 mm and 21.8 mm. Deflection paths further suggest that the concept of a zero strength layer is inadequate for properly capturing the mechanical response of fire-exposed CLT compression elements.
Mechanical Performance of Glue Joints in Structural Hardwood Elements as those for solid beech wood, wherein also the crack propagation takes place. It can be concluded that such joints have the necessary strength to be used in timber constructions. Joints of phenol resorcinol formaldehyde (PRF) showed constantly good results, the determined characteristics generally lay in the same range as for beech wood.
In timber construction, curved timber components have been used repeatedly. Yet the use of curved CLT elements is a relatively recent phenomenon. To obtain a European Technical Approval (ETA) for so-called radius timber (single curved CLT elements), Holzbau Unterrainer GmbH commissioned the accredited testing institution TVFA – Innsbruck to carry out the tests required for this purpose. To this end, overall 158 tests were performed in building component dimensions from December 2013 to May 2014, and several laboratory tests were carried out to monitor adhesive joint quality. Due to the single curved shape of radius timber elements, it is key to particularly focus on possible implications on load bearing capacity due to pre-stress of the slats and to the tensile stress perpendicular to grain resulting from deflection forces. To comply with the criteria laid down in the semi-probabilistic safety concept used in Eurocode 5, the impact caused by these pre-curvatures on strength, rigidity and gross density must be known.