Some background of monitoring and NDT also useful for timber structures

Extension of the life of existing and historic timber structures has increased steadily in the last decade. Sustainability and low carbon emission have influenced activities in the construction industry. In the frame of the European COST Action FP 1101, several activities related to timber structures have been clustered. The COST Action FP 1101 consists of three working groups, namely Assessment (Working Group 1), Reinforcement (Working Group 2) and Monitoring (Working Group 3) of Timber Structures. This special issue of the Journal of Civil Structural Health Monitoring gives an overview of timber structure monitoring activities mainly from a European perspective. This paper is an introduction to this special issue and gives an overview of monitoring concepts and applications related to non-destructive testing (NDT). The prime intention is to give contextual crosslinks to other fields in which NDT methods and monitoring principles have already been developed so that synergies can be realized for timber structures. Outside urgent structural safety issues, monitoring of timber structures has the potential to become a state of the art technology for which material models and NDT-based sensors allow a design criterion for an optimized and highly efficient use of said structures. The sensor concepts may further be enhanced, however, with possible lower cost alternatives in terms of sensors and electronics