Second-order beam theory-based methods for the structural health monitoring of civil structures

Two static methods have been recently proposed in the field of structural health monitoring with the aim to determine the compressive axial loads in civil structures. In particular, the compressive load monitoring can be required for the columns of space frames to support a restoration project, or to ascertain how close the frame is to failure. A similar safety assessment is nowadays also required for concrete bridge beams. In fact, significant losses of prestress forces can indicate damage phenomena in the bridge decks. In the literature, the axial load identification in beam-column elements was mainly studied using vibration-based methods, but these approaches had to select a priori the best frequency. Moreover, some previous studies revealed that the natural frequency is not a reliable indicator for prestress loss detections in concrete beams, since the frequency remains constant when variations of the prestress force are induced. As a result, dynamic methods are particularly sensitive to experimental errors. Conversely, the proposed static approaches, based on the second-order beam theory, make use principally of displacements measured at given cross-sections along the beam under investigation and, moreover, they do not require any selection of the experimental data to be used in the processes. Laboratory tests and numerical simulations on a space frame prototype of aluminum alloy and on a prestressed concrete beam confirm the robustness of both procedures. Therefore, the methods could be successfully used for testing in laboratory or in real conditions. Results of these studies will be illustrated and discussed.