Stress evaluation of prestressed concrete beam based on cracking and incompatible deformation

To effectively evaluate the actual stress level of prestressed concrete (PC) beams in service, the stress assessment method of prestressed tendons in PC structures after cracking is proposed based on incompatible deformation of the cracked structure and the stiffness reduction model. The stiffness reduction model of the cracked beam is determined by experiment data and plastic hinge theory. The measured mid-span deflection was used to solve the stress of the PC beam, and the stress calculation formula was derived. The experimental study was carried out on three specimens of prestressed concrete T-shaped model beam with 6 m length and one 30 m box beam in an actual engineering project. This method is used to estimate the actual stress level of model (PC) beams and 30 m box girders before the yielding of longitudinal reinforcement. Experimental results are compared with the measured data; the results show that the stress of the prestressing tendons estimated by this method is in good agreement and has a specific safety margin, which can evaluate the actual state of the prestressing tendons of PC structures in service. It is concluded that incompatible deformation significantly influences the stress level of the prestressing tendons of PC structures after cracking. Thus, it avoids the unsafe consequences caused by the evaluation according to the design specifications. Moreover, it provides a simplified method for assessing the actual state of the PC structure in service.