Estimation of Friction Coefficient Using Smart Strand

Shin

Int J Concr Struct Mater

2016

The compression or tension-controlled failure mode of concrete beams prestressed with unbonded FRP tendons is governed by the relative amount of prestressing tendon to the balanced one. Explicit assessment to determine the balanced reinforcement ratio of a beam with unbonded tendons (q U pfb) is difficult because it requires a priori knowledge of the deformed beam geometry in order to evaluate the unbonded tendon strain. In this study, a theoretical evaluation of q U pfb is presented based on a concept of three equivalent rectangular curvature blocks for simply supported concrete beams internally prestressed with unbonded carbon-fiber-reinforced polymer (CFRP) tendons. The equivalent curvature blocks were iteratively refined to closely simulate beam rotations at the supports, mid-span beam deflection, and member-dependent strain of the unbonded tendon at the ultimate state. The model was verified by comparing its predictions with the test results. Parametric studies were performed to examine the effects of various parameters on q U pfb .

Section: Modified Algorithm To Include Frictional Lossesmentioning

confidence: 99%

Balanced Ratio of Concrete Beams Internally Prestressed with Unbonded CFRP Tendons

Shin

Int J Concr Struct Mater

2016

“…Kim et al [6] previously noticed fiber Bragg grating (FBG) coupling at the center of the central wire of a 7-wire steel strand, extended the range of FBG with polyamide recoating and casing, and then applied it to monitor the internal prestress loss of concrete I-beams with a span of 20 meters [7][8][9]. Jeon et al [10,11] investigated the temperature compensation of a smart steel strand and evaluated its friction resistance. Ou et al [12][13][14] earlier proposed to introduce optical fiber sensing technology in structural composite reinforcement, and for the first time embedded FBG and Brillouin fiber in carbon fiber tendons to replace the central wire of steel strand.…”

Section: Introductionmentioning

confidence: 99%

Application research on internal prestress monitoring of box girder based on FBG self-sensing steel strand

Zeng,

Zhu,

Liu

et al. 2024

Preprint

Internal prestressing is an effective prestressing approach in the concrete box girder that ultimately plays a vital role in their construction. In practical engineering, accurate measurement and long-term monitoring are still challenging. FBG-based self-sensing steel strand (FSS) possesses the advantages of quasi-distributed monitoring of internal cable prestress and long-term stable monitoring. To examine its application in monitoring the internal prestressing of the actual box girder project, as well as to reveal the law of prestressing distribution and prestressing loss in the box girder, the self-sensing steel strand is appropriately experimented by using the cyclic tensile test. Precast and cast-in-place beams are then selected to examine the prestressing process and long-term prestressing monitoring of box girders with single-ended and double-ended tensioning processes. The results reveal that the linearity of FSS is 0.84%, the hysteresis is 0.75%, and the repeatability is 1.87%, which exhibits a good prestress monitoring performance. In the comparative application with the Elasto-Magnetic sensor and the reverse tension method, the instantaneous prestress monitoring results are basically consistent with the Elasto-Magnetic sensor. Due to the influence of the friction resistance of the anchorage, it is slightly lower than the measured value of the reverse tension method. Therefore, the FSS exhibits the accuracy of prestress monitoring and consistency of the actual box girder engineering application. In the monitoring of instantaneous prestress loss, such a loss at the tension end of the box girder mostly caused by the internal shrinkage of prestressed tendon, accounting for 81.3 % on average. The mid-span and the fixed end of the box girder, which experience tension under the single-ended tension conditions, are affected by friction and concrete compression loss. Therefore, reducing the amount of shrinkage of steel strands and adopting the double-ended tension method is still the key to reducing the instantaneous prestress loss. In the long-term prestress loss, the measured value exhibits a certain discontinuity. Compared to the theoretical value, the amount of prestress loss of the box girder tensioned at both ends is linearly positively correlated with the magnitude of applied effective prestress, and the amount of loss is negatively correlated with channel curvature.

Advances in Civil Engineering

“…When the friction loss data of prestress is obtained by tests, the corresponding friction coefficient can be got according to the prediction equation of prestress. In addition, the post-tensioning method cannot guarantee the accuracy of stress measurements of steel strands [9,10]. e total prestress loss at the beam end and the stress distribution are measured by the pressure sensor at the anchorage point [11] and the electromagnetic (EM) sensor [12][13][14], respectively.…”

Section: Introductionmentioning

confidence: 99%

Friction Characteristics of Post‐Tensioned Tendons of Full‐Scale Structures Based on Site Tests

Yuan

Zhou

et al. 2020

In the design of prestressing concrete structures, the friction characteristics between strands and channels have an important influence on the distribution of prestressing force, which can be considered comprehensively by curvature and swing friction coefficients. However, the proposed friction coefficient varies widely and may lead to an inaccurate prestress estimation. In this study, four full-scale field specimens were established to measure the friction loss of prestressing tendons with electromagnetic sensors and anchor cable dynamometers to evaluate the friction coefficient. The least square method and Bayesian quantile regression method were adopted to calculate the friction coefficient, and the results were compared with that in the specifications. Field test results showed that Bayesian quantile regression method was more effective and significant in the estimation of the friction coefficient.