Applying the deflection measurement technology to identify the prestress force of beams

In order to manage the full lifecycle of bridges effectively, it is necessary to grasp reasons that may possible damage bridge members. Pre-stressed beams are broadly applied in the urban, railway and highway bridges. During the design process, prestress forces are decided through existing norms or theoretical formula. Within their serviceability life, after the construction, many factors such as relaxation of tendons, shrinkage and creep of concrete, friction between tendons and tendon ducts, anchorage slip and ambient temperature can lead to the change of the applied pre-stress forces. So, in order to control the status of pre-stressed bridges, the identification of prestress force is inevitable. This study conducted the prestress force identification by using displacements measured after applying a vertical load in the mid-span of the beam. The identification of prestress force can be made on pre-stressed steel box beam and pre-stressed concrete beam, respectively. Post-tensioning method is considered during the experimental tests. Axial force, which is prestress force, can be estimated by using displacements measured in certain sections and the formula of axial buckling load. Comparing estimated axial force with existing axial force, which is measured by a load cell at one end of the beam, it is possible to verify the feasibility of axial force identification proposed in this study and then, enlarge the size of specimen and plan for further study in the near future.