A Smart Steel Strand for the Evaluation of Prestress Loss Distribution in Post-tensioned Concrete Structures

Abstract

Prestress loss adversely affects the behavior of in-service post-tensioned structures in terms of deflection/camber, cracking, and ultimate capacity. It is thus important to determine the level of prestressing force at various loading stages from the initial prestressing force transfer to the structure, through different in-service loads, to the ultimate load of the structure. Prestress loss is difficult to evaluate due to several intertwined factors such as creep, shrinkage, relaxation, geometric configuration, distributed friction, and slippage of post-tensioned strands. Till date, there is no cost-effective and reliable sensor and installation technique for the long-term monitoring and evaluation of prestress loss. In this study, a smart fiber-reinforced polymer (FRP) rebar with an embedded novel optical fiber (OF) is developed for the distributed strain of post-tensioned strands. The new OF is an integrated global and local monitoring technology developed by combining the Brillouin optical time domain analysis/refectory sensor and the optical fiber Bragg grating into one single fiber. The FRP rebar and six steel wires were bundled together to form a seven-wire steel strand for the post-tensioning and monitoring of concrete structures. The performances of the smart rebar and strand were validated with static tests of a prestressed steel frame structure and a post-tensioned concrete beam. The smart steel strand can accurately measure the prestress loss at each loading stage, which agrees well with that measured by a pressure loading cell and predicted by a design code.

Keywords

smart steel strand prestress loss Brillouin optical time domain analysis reflectometry optical fiber Bragg grating fiber-reinforced polymer long-term monitoring a single-fiber optical sensor.

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References

Deng, N.C. , Ou, J.P. and Zhou, Z. 2007. ‘‘Application of Fiber Bragg Grating Sensor to Monitor Tensile Stress in a Seven-wire Prestressing Steel Strand, ’’ Journal of Harbin Institute of Technology, 39(10):1550-1553.

GBJ 50010. 2002. Concrete Structure Design Code, No. 50010-2002, P.R. China.

Idriss, R.L. and Solano, A. 2002. ‘‘Effects of Steam Curing Temperature on Early Prestress Losses in High Performance Concrete Beams,’’ Transportation Research Record, 1813:218-228.

Kim, J.T. , Ryu, Y.S. and Yun, C.B. 2003. ‘‘Vibration Based Method to Detect Prestress Loss in Beam-type Bridges,’’ In: Proceedings of the SPIE - The International Society for Optical Engineering, Vol. 5057, pp. 559-568.

Kim, J.T. , Park, J.H. , Hong, D.S. , Cho, H.M. , Na, W.B. and Yi, J.H. 2009. ‘‘Vibration and Impedance Monitoring for Prestress Loss Prediction in PSC Girder Bridges,’’ Smart Structures and Systems, 5(1):81-94.

Kwun, H. , Bartels, K.A. and Hanley, J.J. 1998. ‘‘Effects of Tensile Loading on the Properties of Elastic-wave Propagation in a Strand,’’ Journal of the Acoustical Society of America, 103(6):3370-3375.

Lanza di Scalea, F. , Rizzo, P. and Seible, F. 2003. ‘‘Stress Measurement and Defect Detection in Steel Strands by Guided Stress Waves,’’ Journal of Materials in Civil Engineering, 15(3):219-227.

Lin, Y.B. , Chang, K.C. , Chern, J.C. and Wang, L.A. 2004. ‘‘The Health Monitoring of a Prestressed Concrete Beam by Using Fiber Bragg Grating Sensors,’’ Smart Materials and Structures, 13:712-718.

Nawy, E.G. 2006. Prestressed Concrete, 5th edn, pp. 73-75, Pearson Education, Inc., New Jersey.

10.

Sreeshylam, P. , Ravisankar, K. and Parivallal, S. 2008. ‘‘Condition Monitoring of Prestressed Concrete Structures Using Vibrating Wire Sensors,’’ International Journal of COMADEM, 11(3):41-54.

11.

Wang, M. , Lloyd, G.M. and Hovorka, O. 2001. ‘‘Development of a Remote Coil Magnetoelastic Stress Sensor for Steel Cables,’’ Proceedings of SPIE - The International Society for Optical Engineering, 4337:122-128.

12.

Washer, G.A. , Green, R.E. and Pond, R.B. 2002. ‘‘Velocity Constants for Ultrasonic Stress Measurement in Prestressing Tendons,’’ Research in Nondestructive Evaluation, 14(2):81-94.

13.

Xuan, F.Z. , Tang, H.W. and Tu, S.T. 2009. ‘‘In Situ Monitoring on Prestress Losses in the Reinforced Structure with Fiber-optic Sensors,’’ Measurement: Journal of the International Measurement Confederation, 42(1):107-111.

14.

Zhou, Z. , Zhang, Z.C. , Deng, N.C. and Ou, J.P. 2005. ‘‘Applications of FRP-OFBG Sensors on Bridge Cables,’’ SPIE, Vol. 5765:1166-1171.

15.

Zhou, Z. , He, J.P. , Yan, K. and Ou, J.P. 2008. ‘‘FRP-packaged Optical Fiber Sensors based on BOTDA (R) Technique,’’ Journal of Optical Engineering , 47(1):1-10.

16.

Zhou, Z. , Ou, J.P. and Wang, B. 2003. ‘‘Smart FRP-OFGB Bars and their Application in Reinforced Concrete Beams,’’ In: Proceedings of the First International Conference on Structural Health Monitoring and Intelligent Structure, Tokyo, Japan, pp. 861-866.