Smartphone application for structural health monitoring of stay cables: Edgar Cardoso Bridge

App4SHM is a mobile system for structural health monitoring (SHM) of bridges. It consists of a front-end smartphone application that is used to measure natural frequencies of vibration and to detect damage supported by a backstage server software, accessible through any internet browser. This paper focuses on the underdevelopment module for stay cables, where natural frequency observations are directly converted into cable tension forces based on the material and geometrical characteristics of the cable. The conversion considers an estimation of the forces given by the taut string theory. Regardless of the module, App4SHM works in two modes. The training mode is used to collect natural frequencies under normal operational and environmental conditions. The natural frequencies are used to train an unsupervised machine learning algorithm to learn the normal behavior of the structure. The damage detection mode collects unlabeled natural frequencies which are tested against the normal behavior to detect an abnormal performance that may be indicative of damage or excessive tensions. Preliminary results on the use of App4SHM for the measurement of cable tension forces are presented for the Edgar Cardoso Bridge - a large cable-stayed bridge in Portugal undergoing rehabilitation and stay cables replacement.