A reduction coefficient is applied in usual design of multiple dowels type connections. The numbers of stiffeners in row is one of important factor to decide this coefficient. CLT drift pinned joint showed small orthotropy against in plane tensile load. Tensile tests of multiple drift pins joints were performed to evaluate the effect of array. Numbers of drift pins n in each specimen were same (n=12), but the arrangements were different (2 x 6, 3 x 4, 4 x 3, 6 x 2). Also the grain directions were parameters (0, 90 degrees). The reduction of initial stiffness and proportional limit load showed good agreement between theoretical prediction and experimental results.
IASS WORKING GROUPS 12 + 18 International Colloquium 2015
April 10-13, 2015, Tokyo, Japan
This paper summarizes an experimental investigation on several innovative reinforcing techniques for the “Single Large Diameter Dowel Connection”, SLDDC in timber truss structures. Besides lateral reinforcing or prestressing, also steel plates glued on two sides of the glulam specimens were used as reinforcing measure. To study the efficiency of these techniques, 15 full-scale quasi-static tensile tests on glulam members with a SLDDC on either ends of each member were performed. It was found that the reinforcement significantly enhanced the bearing capacity of the SLDDCs. All of the reinforcing techniques showed a satisfactory efficiency, preventing splitting of wood. Moreover, most of the specimens remains showed a remarkable post failure strength.
Glued laminated timber (GLT) is a structural product composed of several layers of timber boards glued together. GLT components have many advantages, such as the larger range of available component dimensions to choose from, the environmental sustainability or the efficient ratio between weight and load-bearing capacity. Because of that, GLT beams have been established as one of the most important products in timber engineering in the last decades.
As a natural grown material, timber properties exhibit higher variability, compared with other building materials. The variability is pronounced not only between different structural elements but also within single elements, the latter being highly related to the occurrence of knot clusters. Due to the highly inhomogeneous structure of timber, the prediction of the material properties of GLT beams is affected by large uncertainties. In the presented thesis, the influence of varying material properties on the load-bearing capacity of GLT beams was investigated. Thus the thesis contributes to develop the quality of GLT beams, in terms of reliability and efficiency.
Detailed, non-destructive investigations of altogether 400 timber boards were performed. Thereby, different strength and stiffness related indicators, such as the position and characteristic of knots, or the eigenfrequency, were assessed. Furthermore, non-destructive tensile test were performed to estimate the stiffness properties of knot clusters. Out of the investigated timber boards, GLT beams having a precisely-known beam setup were fabricated. As a result, the exact position of each particular timber board (and each particular knot cluster) within the GLT beams was known. Afterwards, bending tests were performed to estimate the load-bearing capacity of these GLT beams. Thereby, the influence of knot clusters and finger joint connections on the deformation and failure behaviour was investigated.
In addition to the experimental investigations, a probabilistic approach for modelling GLT beams (referred to as GLT model) was developed. Thereby, at first, timber boards are simulated according to their natural growth characteristics. Afterwards, out of the simulated timber boards, virtual GLT beams are fabricated. Finally, the load-bearing behaviour of these GLT beams is estimated by using a numerical model. To assure the quality of the numerical model, it was validated with the test results. Using the GLT model, the influence of different parameters, such as the position and characteristics of knots, or the quality of finger joint connections, on the load-bearing capacity of GLT beams was investigated.
One further goal of this thesis was the investigation of machine-grading indicators, that are measured during the grading process. Therefore, all the investigations presented in this thesis are conducted for indicators measured in laboratory and machine-grading indicators. The same applies for the GLT model, which was also developed for both types of indicators.
The goal of this study is to determine the shear and tension resistance capacity of a tenon connector made out of beech plywood for the connection of cross laminated timber wall elements. To determine the tensile and shear capacity of the connector according to EN 26 891 , tensile and shear tests were performed on cross laminated timber elements with thicknesses of 100 mm, 150mm and 180 mm which were connected with the pin connector. The sample set consisted of 36 test specimens of which were 18 tensile specimens and 18 shear specimens. For each test series, three tensile and three shear tests with the top layer parallel and perpendicular to the load direction were performed. The test specimens were stored for four weeks in normal climate at 20 ° C and 65% relative humidity before they were tested. The shear and tension capacity shows a substantially linear behaviour by increasing the length of the connector. In the tensile tests a transverse tension failure happened in the transverse layer. In the shear tests a plastic failure of the beech plywood connector happened.
Finger joints are commonly used to produce engineered wood products like glued laminated timber beams. Although comprehensive research has been conducted on the structural behaviour of finger joints at ambient temperature, there is very little information about the structural behaviour at elevated temperature. A comprehensive research project on the fire resistance of bonded timber elements is currently ongoing at the ETH Zurich. The aim of the research project is the development of simplified design models for the fire resistance of bonded structural timber elements taking into account the behaviour of the adhesive used at elevated temperature. The paper presents the results of a first series of tensile and bending tests on specimens with finger joints pre-heated in an oven. The tests were carried out with different adhesives that fulfil current approval criteria for the use in loadbearing timber components. The results showed substantial differences in temperature dependant strength reduction and failure between the different adhesives tested. Thus, the structural behaviour of finger joints at elevated temperature is strongly influenced by the behaviour of the adhesive used for bonding and may govern the fire design of engineered wood products like glued laminated timber beams.
At the institute of structural engineering at the ETH Zurich multiple of investigations are conducted to analyse the material properties of Norway spruce timber boards. The investigations are part of the research project “Influence of varying material properties on the load bearing capacity of glued laminated timber (glulam)”. The majority of the investigations are non-destructively.
The investigations are taking place on 400 timber boards. On all specimens the moisture content, the density, the Eigenfrequency and the longitudinal ultrasonic runtime was investigated. Further all knots with a diameter larger then 10mm are measured. Thereby the position and the size of all the knots are documented. Subsequently on 200 selected boards non-destructive tensile test are performed to analyse the local young modulus. Herewith it was particularly focused on the investigation of the stiffness of areas having knots or knot clusters and areas without knots. The strains are measured with an optical coordinatemeasurement device. In the last part of the experimental investigation the deformation and failure behaviour of significant knot clusters is analysed. The strains are measured with digital image correlation.
Focus of the entire experimental analysis was the investigation of the young modulus and the quantifications of its variability within timber members and between timber members. Within this study a database was produced to evaluate existing test methods for the estimation of the young modulus. Further, the results can be used as a basis for further investigations on the variability of structural timber.
Double-shear steel-to-timber joints of beech laminated veneer lumber (LVL) with slotted-in steel plates using very high strength steel (VHSS) dowels have been investigated. Tensile tests on full-scale joints with one, two, three and six dowels have been carried out, using both VHSS and mild steel dowels. The goal of the research was to investigate the mechanical behaviour of joints of beech-LVL, with regard to load-carrying capacity (LCC), ductility, stiffness; and to find out whether the current design rules of Eurocode 5 are suitable for LVL and VHSS steels. Other examined aspects were the effect of multiple fasteners in a row and the influence of fastener steel grade. Tests showed higher values of joints with VHSS dowels, characterized generally by low scatter. The prediction ability of Eurocode 5 has been found to be inadequate and too conservative. A proposal for improvement is included.