On the Evaluation of Prestress Loss in PRC Beams by Means of Dynamic Techniques

Abstract

In the last few decades, prestressing techniques have been used to build very important structures and infrastructures. Since the serviceability and the safety of prestressed reinforced concrete (PRC) elements rely on the effective state of prestressing, development of tools and procedures capable of estimating the effective prestress loss would be very useful. Amongst other techniques, dynamic identification has proved to be an economical, quick and reliable method to evaluate structural integrity. However, the influence of prestressing in the dynamic behavior of PRC elements is not completely clear. In fact, while many references in the literature state that the prestressing force does not affect the frequencies of vibration, almost every experimental test carried out on PRC beams shows an increase in the eigenfrequencies for increasing value of the prestressing force. This paper aims to contribute to the debate, investigating the dynamic behaviour of PRC beams taking into account properties, such as nonlinearity, softening, confinement and micro-cracking of concrete subjected to compression and tension stress states, and the variation of the flexural stiffness of the PRC beam along its length according to bending stress distribution. Non-linear discrete modelling, in combination with system identification and optimization was used to define the dynamic properties of PRC beams, taking into account the effect of prestressing level. The proposed model was applied to four PRC beams with known mechanical and dynamic properties in literature. The influence of the prestressing force on the trend of frequencies of vibration was closely captured for each beam, with errors less than 3% of the estimated frequencies. The results of this investigation thus indicate that dynamic identification techniques can potentially be used to identify the prestressing force level, and consequently the prestress loss, provided the complete concrete mechanics is taken into account.

Aspects of Vibration-Based Methods for the Prestressing Estimate in Concrete Beams with Internal Bonded or Unbonded Tendons

“…Lastly, in 2018, Reference [34] solved an inverse problem and identified the stressstrain relationship of concrete, which yielded the experimental findings by [24,[30][31][32].…”

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

“…(4) Determining the side pressure to close the induced crack in a small cylindrical hole drilled adjacent to the tendon in the bottom flange of a PC girder [55,58]. (5) Vibration testing to determine the natural frequencies and/or dynamic responses of a PC girder [59][60][61][62][63][64][65]. (2) Destructive [23,56] Severing the prestressing tendon by cutting it into an exposed length after placing strain gauges It causes damages Table 3.…”

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

“…All cylinders were maintained under the same curing conditions, that is, close to each other and outdoor until the insertion of the PC beam-bridge in the test rig (Figure 2(a) and Evaluation of the time-dependent elastic modulus of the high strength concrete in ). Young's modulus of PC girders changes with time because of curing due to the consolidation or hardening of concrete and because of creep and shrinkage due to crack and microcrack formation (Breccolotti, 2018). After completing free vibrations and three-point bending at concrete ages of 421, 423, and 424 days (Free bending vibrations and Three-point bending), three cores were respectively drilled near the cross-sections at i = 2, 4, and 6 along the PC beambridge (Figure 1) to measure its time-dependent Young's modulus according to ASTM C 469/C 469M-14 (Annual Book of ASTM Standards, 2016) and Model B4-TW (Hu and Liao, 2020).…”