State-of-the-Art Review on Determining Prestress Losses in Prestressed Concrete Girders

Abstract

Prestressing methods were used to realize long-span bridges in the last few decades. For their predictive maintenance, devices and dynamic nondestructive procedures for identifying prestress losses were mainly developed since serviceability and safety of Prestressed Concrete (PC) girders depend on the effective state of prestressing. In fact, substantial long term prestress losses can induce excessive deflections and cracking in large span PC bridge girders. However, old unsolved problematics as well as new challenges exist since a variation in prestress force does not significantly affect the vibration responses of such PC girders. As a result, this makes uncertain the use of natural frequencies as appropriate parameters for prestress loss determinations. Thus, amongst emerging techniques, static identification based on vertical deflections has preliminary proved to be a reliable method with the goal to become a dominant approach in the near future. In fact, measured vertical deflections take accurately and instantaneously into account the changes of structural geometry of PC girders due to prestressing losses on the equilibrium conditions, in turn caused by the combined effects of tendon relaxation, concrete creep and shrinkage, and parameters of real environment as, e.g., temperature and relative humidity. Given the current state of quantitative and principled methodologies, this paper represents a state-of-the-art review of some important research works on determining prestress losses conducted worldwide. The attention is principally focused on a static nondestructive method, and a comparison with dynamic ones is elaborated. Comments and recommendations are made at proper places, while concluding remarks including future studies and field developments are mentioned at the end of the paper.

Novel method for identifying residual prestress force in simply supported concrete girder-bridges

“…The measured vertical deflections v i , for i = 1,…,7 (Figure 1), along the simply supported PC beam-bridge are parameters of the proposed method according to the magnification factor formula of the compression-softening theory (equations (7a, 7b)). In fact, measured deflections indicate the changes that occur in the structural geometry due to prestress losses under equilibrium conditions, in turn caused by the combined effects of long-term aging of PC girder-bridges (Bonopera et al, 2020. Eleven test cases were defined (Table 1) resulting in a total of 33 test combinations of three-point bending (Three-point bending).…”

“…Vice versa, the identification based on static vertical deflections was preliminarily proved to be a reliable emerging technique (Bonopera et al, 2018b). By considering all the existing methodologies, Bonopera et al (2020) illustrated an extensive state-of-the-art review of researches conducted worldwide on identifying prestress losses.…”

“…Following the vertical load application in a three-point bending, the method estimates the prestress force by measuring the vertical deflection at a quarter or, alternatively, at the midspan of the PC girder-bridge. Indeed, measured deflections indicate the changes that occur in the structural geometry due to prestress losses under equilibrium conditions, in turn caused by the combined effects of tendon relaxation; concrete creep and shrinkage; temperature and relative humidity (Bonopera et al, 2020. In addition, the proposed method requires information regarding the flexural rigidity of the PC girder-bridge.…”

The Way Forward for Indirect Structural Health Monitoring (iSHM) Using Connected and Automated Vehicles in Europe

“…Nevertheless, over time and depending on the composition of the concrete and the environmental conditions, concrete loses its protective role against steel corrosion due to carbonation, which leads to a lowering of the alkalinity around the steel, resulting in reinforcement corrosion [39]. In addition, larger-than-predicted losses in precompression forces [40], which can be attributed, among other reasons, to poor models available in the past for the creep and shrinkage of concrete and a lack of proper cable grouting (due to poor quality control during construction in the past), are among the principal threats to prestressed concrete bridges.…”

Indirect Determination of Residual Prestressing Force in Post-Tensioned Concrete Beam

“…The classification of some methods is questionable because the line between destructive, semi-destructive, and non-destructive approaches is narrow. In general, methods with no or only minimal impact on the structural integrity are considered non-destructive [ 15 , 16 , 17 , 18 ]. Two main stress releasing methods are available.…”