1 INTRODUCTION A Structural Health Monitoring (SHM) system for a civil infrastructure is the combination of equipment adequate to permanently characterize its actions and responses (or just the responses) with processing tools that transform the acquired data into relevant information, which should permit to assess the struc- tural performance of the instrumented elements. In this context, it is very important to develop systems based on the permanent acquisition of data and on its online automatic processing to provide valuable information to operators and owners of relevant in- frastructures. Nowadays, an increasing interest in permanent monitoring of the structural behaviour of crucial civil infrastructures, such as bridges, has been ob- served. This is due to the need of controlling a huge number of structures that are reaching their critical age and also to the necessity of validating the per- formance of new structures with high levels of com- plexity. Moreover, recent technological advances have contributed to make the installation and opera- tion of permanent monitoring systems more practical and economical and permit a very efficient transmis- sion and processing of the recorded data. All over the world there are already several ad- vanced applications of SHM systems on bridges. Trying to cover emblematic examples from different countries documented in available bibliography, the following applications can be mentioned: Tsing Ma Bridge in Hong Kong (Wong 2004), Akashi Kaikyo Bridge in Japan (Abe and Fujino 2009), Seohae Bridge in Korea (Koh et al. 2009), Confederation Bridge in Canada (Londono 2006), Commodore Barry Bridge in the United States (Aktan et al. 2003) and Oresund Bridge in Denmark (Peeters et al. 2003). A large number of other bridge monitoring systems are described in (Boller et al. 2009) and Ko and Ni (2005) present a brief synthesis of the moni- toring systems installed in twenty Chinese bridges. Despite the greater attention devoted to bridge ap- plications, SHM systems have also been imple- mented in other civil engineering structures. Brown- john (2007) describes relevant SHM applications in dams, offshore structures, buildings, towers, nuclear installations and tunnels. Descriptions of further ex- amples are also available in the databases of SAMCO (www.samco.org) and SHMII (www.ishmii.org) associations. The implementation of well designed structural health monitoring systems permits to: (1) check de- sign assumptions, specially when novel materials or structural systems are adopted; (2) verify service- ability limits and provide alerts when pre-defined thresholds are overcome (for instance the occurrence of strong winds may impose the closure of a bridge); (3) evaluate the structural condition and detect pos- sible damages at an early stage; (4) provide informa- tion for safety assessment immediately after extreme events such as earthquakes; (5) provide useful data for the planning of inspections and rehabilitation or maintenance operations; (6) evaluate the effective- ness of maintenance, retrofit or repair works; and (7) obtain large amounts of in-situ data useful to better Dynamo – software for vibration based Structural Health Monitoring F. Magalhães, S. Amador, Á. Cunha & E. Caetano University of Porto, Faculty of Engineering (FEUP), Porto, Portugal ABSTRACT: This paper presents an innovative software for continuous dynamic monitoring of civil infra- structures. The followed approach is based in the continuous on-line automatic identification of the structure modal parameters, using its response under operation and adopting state-of-the-art identification algorithms. Therefore, the monitoring software, called DynaMo, includes routines for data and results management, algo- rithms for operational modal analysis, statistical tools for elimination of environmental and operational fac- tors on the identified modal parameters and also statistical tools for automatic identification of abnormal fre- quency values that might be associated with the occurrence of damages. The utility and efficiency of DynaMo is illustrated with an application on a large span concrete arch bridge that is being monitored since 2007.