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.
External thermal insulation composite systems (ETICS) combined with cross laminated timber (CLT) reveal useful exterior wall constructions, which meet the requirements for sustainability, serviceability and durability of modern buildings efficiently. Associated thermal insulation and moisture protection requirements are essential design criteria to be considered in the planning process. In light of the European legal regulation concerning ETICS, our paper deals with the hygrothermal behavior of an existing exterior wall construction in solid timber construction with ETICS, experimentally determined by means of long-term monitoring situated in the residential project "_massive_living" (Graz, AT). Based on obtained data of temperature and rel. humidity for a period of two years, we not only evaluated building physics aspects concerning the suitability of the structure, but also derived the time depending course of the essential parameter "moisture content" for selected layers of the CLT element. In addition, corresponding data is compared with results gained from a hygrothermal simulation. Further investigation then was carried out determining the hygrical impact on the timber component by changing insulation material. Therefore, the hygrothermal behavior of commonly applied ETICS in combination with CLT as base material was simulated. Finally, resulting bandwidths of moisture content in dependence of the applied ETICS are shown and discussed.
Self-tapping screws (STS) have been proclaimed as the easiest solution for structural timber connections, in special for cross laminated timber (CLT) constructions. In order to understand deeply the composite model “CLT-STS”, an experimental campaign which comprised 270 withdrawal tests was carried out. Maximum withdrawal load capacity of self-tapping screws inserted in plane side of a three layered CLT panel was evaluated considering three main parameters: moisture levels of CLT (i), number of gaps (ii) and the width of gaps (iii). Regarding (i), connections were tested with CLT at 8%, 12% and 18% of moisture content. Concerning (ii) and (iii), different test configurations with 1, 2 and 3 gaps, with 0 or 4mm, were tested. The influences of moisture content and number of gaps were modeled. Further a correlation between test results and a prediction model developed by Uibel and Blaß (2007) has been proposed.
A large experimental campaign comprised of 470 withdrawal tests was carried out, aiming to quantify the withdrawal resistance of self-tapping screws (STS) inserted in the side face of cross laminated timber (CLT) elements. In order to deeply understand the “CLT-STS” composite model, the experimental tests considered two main parameters: (i) simple and cyclic changes on moisture content (MC) and (ii) number and width of gaps. Regarding (i), three individual groups of test specimens were stabilized with 8%, 12% and 18% of moisture content and one group was submitted to a six month RH cycle (between 30% and 90% RH). Concerning (ii), different test configurations with 0 (REF), 1, 2 and 3 gaps, and widths equal to 0mm (GAP0) or 4mm (GAP4), were tested. The influences of MC and number of gaps were modeled by means of least square method. Moreover, a revision of a prediction model developed by Uibel and Blaß (2007) was proposed.
The main findings of the experimental campaign were: the decrease of withdrawal resistance for
specimens tested with MC=18% in most configurations; the unexpected increase of withdrawal resistance as the number of gaps with 0mm increased; and, the surprising increase of withdrawal resistance for REF specimens submitted to the RH cycle.
Cross-laminated timber (CLT) is a very efficient and powerful building material and thus recently discovered for the erection of multi-storey timber towers. In our paper, we focus on building science and services related topics regarding these constructions. Thereby, we firstly identify moisture ingress as main problem worsening their durability and thus discuss possible detail solutions for both external and internal critical building zones such as flat roof, balcony system and wet rooms. The second main topic we are concentrating in this paper are simple measures to increase the efficiency of CLT constructions by simplifying and improving their structural systems (floors, walls and connections). Both topics are connected by the major importance of interdisciplinary thinking and acting when building with CLT.
Cross laminated timber (CLT) and self-tapping screws have strongly dominated the latest developments in timber engineering. Although knowledge of connection techniques in traditional light-frame structures can be applied to solid timber constructions with CLT, there are some product specifics requiring additional attention; for example in positioning of fasteners, differentiation in the side face and narrow face of the panels and the influence of potential gaps. The load–displacement behaviour of single, axially-loaded self-tapping screws positioned in the narrow face of CLT and failing in withdrawal was investigated. For the first time a multivariate probabilistic model was formulated together with models relating the parameters with the thread-fibre angle and the density. Different types and widths of gaps, initial slip and / or delayed stiffening as well as softening after exceeding of the maximum load can be considered. Beyond the scope of this contribution, the probabilistic model is seen as a worthwhile basis for investigations into the withdrawal behaviour of primary axially loaded, compact groups of screws positioned in timber products and subjected to withdrawal failure.
The overall aim of this report is to assess the earthquake resistance on the basis of calculating the seismic design of a residentual building errected in Solid Timber Construction. Thus, a detailed analysis of the sample building focusing on the instantaneous seismic design situation and using the currently valid ONORM B 1998-1:2006, will be conducted. In the context of assessing the earthqake resistance of a building, it is also hughly interesting to analyse the control of the regular criteria in plane and evaluation due to their significant importance to the calculation. The final determination of the primary seismic components, in this example the focus is on the bracing panels, is also made by using the Austria currently valid Eurocodes for Timber Design in combination with the guidelines taken from the previously mentioned European Standard for Earthquakes.
European Conference on Cross Laminated Timber (CLT)
May 21-22, 2013, Graz, Austria
Solid timber construction (STC) with Cross Laminated Timber (CLT), which was presented for
the first time to an international audience of specialists in the context of the concluding
conference of the COST Action E5 “Timber frame building systems” in September 2000 ,
can be definitely regarded as one of the most significant innovations in timber engineering within
recent decades. Worldwide sales figures of about 500,000 m3 and a wide area of application,
which includes not only modern one-family houses, multi-storey buildings, but also office- and
administration buildings, hall systems and bridge structures, prove this statement. However, the
motto “everything is possible”, which goes along with this rapid development, and the legitimate
concentration on the feasibility in static-constructive terms (ULS, SLS, fire, earthquake, etc.) lead
to the problem that interdisciplinary issues are considered insufficiently; this is in the context of
multi-storey buildings with questions concerning qualitative building services adapted to this type
Therefore, the aim of this report can be seen in dealing with these interdisciplinary problems. In
concrete terms this means facing them and offering possible solutions in the context of solid
timber construction out of Cross Laminated Timber. Due to the local processes on the subject of
using Cross Laminated Timber, this report is based on a number of selected and partly completed projects in the Graz (AT) conurbation.