STRUCTURAL HEALTH MONITORING OF AN INNOVATIVE TIMBER BUILDING Claude Leyder 1,* , Eleni Chatzi 1 and Andrea Frangi 1 1 Institute of Structural Engineering (IBK), Department of Structural, Environmental and Geomatic Engineering (D-BAUG), ETH Zürich, Stefano Franscini Platz 5 - CH 8093 Zürich, Switzerland.*Email:leyder@ibk.baug.ethz.ch ABSTRACT A main focus in timber construction research is the development of innovative, sustainable and reliable structures. In order to determine the long-term structural behaviour of these novel structures, structural health monitoring is a valuable tool. In the past two years an innovative timber-hybrid pilot building has been conceived, designed and realized at ETH Zürich. The building contains four innovative structural systems, a post-tensioned timber frame, two timber-concrete hybrid floor systems using beech LVL, and a biaxial pure timber floor in beech wood. In order to fully understand the combined structural behaviour of these innovative systems an extensive monitoring system was set up. The dense sensor network was implemented along with the construction progress, in order to also quantify the effects of important construction stages on the structural behaviour (addition of significant loads, addition of stiffening elements, extreme changes in environmental climate, etc.). The installed setup includes 16 load cells, measuring the changes in the post-tension force in the frame, absolute deformation measurements, temperature and relative humidity sensors, as well as measurements of the moisture content of timber. The monitoring campaign is planned to be continued for several years beyond the completion of construction, in order to quantify the long-term behaviour during the use phase of the building. KEYWORDS Innovative hybrid-timber structure, Long-term structural performance, Structural monitoring under construction. INTRODUCTION Nowadays, the development of innovative structures, which are efficient and reliable throughout their life-cycle, is a main focus in the timber engineering field. Especially the implementation of hardwood elements opens up a whole range of new possibilities for timber structures. This is indeed favoured by the optimal strength and stiffness properties of hardwood. In addition hardwood is largely available in Swiss Forests and new implementations for the material are currently being investigated. Innovative structural systems are mostly developed and tested under laboratory conditions, i.e., small to mid-scale sample sizes in a controlled environment. From these tests valuable information about the short-term structural behaviour can be gained. However, the knowledge concerning the structural behaviour in an actual-scale building situation as well as in a long-term use, is limited. Therefore a pilot building demonstrating the implementation of hardwood as structural elements has been realized at ETH Zürich, under a project titled ``ETH House of Natural Resources (ETH HoNR)'' (Leyder et al. 2015). The building allows for the quantification of the structural behaviour of several innovative structures in a real building situation. Starting from summer 2015, the building will be used as an office building by the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) from ETH Zürich. The structure of the ETH HoNR is described in detail in Leyder et al. 2015. The following sections contains a short summary of the aspects that are most relevant for the monitoring setup. The ETH HoNR comprises four innovative structural systems using especially hardwood. The main lateral and vertical load-carrying structure is a post-tensioned timber frame, using columns made of ash wood, hybrid timber beams composed of ash and spruce and a steel tendon. The tendons span over the whole building length at mid-height of the beam, in a horizontal hole in the middle of the beam cross-section. The post-tensioned frame was developed and extensively tested in the ETH laboratory (Wanninger and Frangi 2014, Leyder et al. 2014). Two types of laboratory tests were conducted, first a single column-beam joint specimen was tested and second a two-dimensional 19.5m long, three-bay (3*6.5m span) frame was tested. The exact same frame is implemented in the ETH HoNR building in a three-dimensional setup, with spans of 6.5m in both directions, leading to a floor section of 19.5m*19.5m. In Figure 1 the position of the frame is highlighted in the floor plan of the first timber story and in the section of the building. The columns are entirely produced in ash wood and have a cross-section of 380mm*380mm. The beams are hybrid timber beams with four lower lamellas in ash wood and the remaining upper lamellas in spruce wood. The total cross-section of the beams is 280mm*720mm. The semi-rigid joint between the columns and the beams is created via the post-tension force, no additional steel 1383