Influence of changes in the prestress force on dynamic specifications of the prestressed concrete beam

Pre-stress techniques tend to increase cross-sectional capacity and optimize design. Such features have made these techniques rather popular. Over time, these structures tend to fail, and the reduction of pre-stress force over the lifetime of the structure is said to be one of the most significant destructive factors in these structures. This decrease in force occurs due to various reasons. In majority of cases, a cracking of pre-stressed concrete beams appears due to the reduction of pre-stress strength. Where there is permanent monitoring by the sensors buried within pre-stressed tendons, the force of the tendons can be investigated. But given the high cost of this procedure, such monitoring cannot be implemented in many structures. Nevertheless, it is possible to determine changes in pre-stress forces through investigating the dynamic behavior of structures. This paper examines the changes in the dynamic behavior of a pre-stressed beam experiencing a variety of pre-stress force levels. The idea is to monitor force changes in the pre-stressed tendons via examining certain dynamic characteristics of the beam (namely, modal damping and resonance frequency) and carry out repair prior to fail. The results show that with increasing the prestressing force, the system frequency increased and the system damping decreased.