Title:
Evaluation of Flexural Strength and Ductility of Hybrid Prestressed Concrete Members
Author(s):
Wassim Nasreddine, Adi Obeidah, Mohamed Harajli, and Hani Nassif
Publication:
Structural Journal
Volume:
121
Issue:
6
Appears on pages(s):
91-103
Keywords:
carbon fiber-reinforced polymer (CFRP); ductility; flexure; hybrid beams; prestressed concrete (PC); strain compatibility; unbonded tendons
DOI:
10.14359/51740865
Date:
11/1/2024
Abstract:
Flexural strength and ductility of exclusively bonded or unbonded steel prestressed concrete (PC) members are well covered and documented in the literature and codes of practice. However, current design methods are limiting the use of hybrid (i.e., a combination of unbonded and bonded steel and Fiber Reinforced Polymer (FRP)) tendons, particularly when using brittle material such as FRP tendons. In this paper, a general procedure for evaluating the nominal moment capacity and ductility of hybrid PC members was developed using the strain compatibility approach. The procedure is applicable for members with any combination of bonded or unbonded steel and FRP tendons. Using a capacity design approach based on strain compatibility, the ductility performance of several hybrid systems with different parameters was compared. The parameters included, among others, the level of “net tensile strain” in the tension reinforcement at nominal strength adopted in ACI 318-19 as a measure of ductility; concrete compressive strength; and the newly defined hybrid prestressing ratio (HPR). HPR represents the ratio of the moment contribution of the unbonded tendons to the total moment capacity of the member with hybrid tendons. Non-linear analysis was carried out to generate the entire load-deflection and moment-curvature responses of the different systems. The accuracy of the nonlinear analysis was verified by comparing with available experimental data and the analysis results were used to compare traditional curvature ductility measures of the various systems against the ductility measure specified in the ACI Building code. A design example is provided in Appendix A to illustrate the use of the strain compatibility approach.
Related References:
1. Obeidah, A., and Nassif, H., “Serviceability of Beams Prestressed with Hybrid (Steel/Carbon Fiber-Reinforced Polymer) Tendons,” ACI Structural Journal, V. 119, No. 3, May 2022, pp. 179-190.
2. ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19) (Reapproved 2022),” American Concrete Institute, Farmington Hills, MI, 2019, 624 pp.
3. Mast, R. F., “Unified Design Provisions for Reinforced and Prestressed Concrete Flexural and Compression Members,” ACI Structural Journal, V. 89, No. 2, Mar.-Apr. 1992, pp. 185-199.
4. ACI Committee 440, “Prestressing Concrete Structures with FRP Tendons (ACI 440.4R-04) (Reapproved 2011),” American Concrete Institute, Farmington Hills, MI, 2004, 35 pp.
5. Park, R., and Paulay, T., Reinforced Concrete Structures, John Wiley & Sons, Inc., New York, 1975.
6. Naaman, A. E.; Harajli, M. H.; and Wight, J. K., “Analysis of Ductility in Partially Prestressed Concrete Flexural Members,” PCI Journal, V. 31, No. 3, 1986, pp. 64-87. doi: 10.15554/pcij.05011986.64.87
7. Harajli, M., “On the Stress in Unbonded Tendons at Ultimate: Critical Assessment and Proposed Changes,” ACI Structural Journal, V. 103, No. 6, Nov.-Dec. 2006, pp. 803-812.
8. Harajli, M. H., “Effect of Span-Depth Ratio on the Ultimate Steel Stress in Unbonded Prestressed Concrete Members,” ACI Structural Journal, V. 87, No. 3, May-June 1990, pp. 305-312.
9. Naaman, A. E., and Alkhairi, F. M., “Stress at Ultimate in Unbonded Post-Tensioned Tendons: Part 2—Proposed Methodology,” ACI Structural Journal, V. 88, No. 6, Nov.-Dec. 1991, pp. 683-692.
10. Lee, L.; Moon, J.; and Lim, J., “Proposed Methodology for Computing of Unbonded Tendon Stress at Flexural Failure,” ACI Structural Journal, V. 96, No. 6, Nov.-Dec. 1999, pp. 1040-1048.
11. Tam, A., and Pannell, F. N., “The Ultimate Moment Resistance of Unbonded Partially Prestressed Reinforced Concrete Beams,” Magazine of Concrete Research, V. 28, No. 97, Dec. 1976, pp. 203-208.
12. Corley, W. G., “Rotational Capacity of Reinforced Concrete Beams,” Journal of the Structural Division, ASCE, V. 92, No. 5, Oct. 1966, pp. 121-146.
13. Mattock, A. H., “Discussion of ‘Rotational Capacity of Reinforced Concrete Beams’,” by W. Corley, Journal of the Structural Division, ASCE, V. 93, No. 2, Apr. 1967, pp. 519-522. 10.1061/JSDEAG.0001678
14. Harajli, M., and Hijazi, S., “Evaluation of the Ultimate Steel Stress in Partially Prestressed Concrete Members,” PCI Journal, V. 36, No. 2, 1991, pp. 62-82. doi: 10.15554/pcij.01011991.62.82
15. Moon, J. H., and Burns, N. H., “Flexural Behavior of Member with Unbonded Tendons II: Applications,” Journal of Structural Engineering, ASCE, V. 123, No. 8, 1997. doi: 10.1061/(ASCE)0733-9445(1997)123:8(1095)
16. Harajli, M.; Khairallah, N.; and Nassif, H., “Externally Prestressed Members: Evaluation of Second-Order Effects,” Journal of Structural Engineering, ASCE, V. 125, No. 10, 1999, pp. 1151-1161.
17. Popovics, S., “A Numerical Approach to the Complete Stress-Strain Curve of Concrete,” Cement and Concrete Research, V. 3, No. 5, 1973, pp. 583-599. doi: 10.1016/0008-8846(73)90096-3
18. Menegotto, M., and Pinto, P. E., “Method of Analysis for Cyclically Loaded R.C. Plane Flames,” IABSE Preliminary Report for Symposium on Resistance and Ultimate Deformability of Structures Acted on Well-Defined Repeated Loads, Lisbon, Portugal, 1973, pp. 15-22.
19. Naaman, A. E., “An Approximate Nonlinear Design Procedure for Partially Prestressed Concrete Beams,” Computers & Structures, V. 17, No. 2, 1983, pp. 287-299. doi: 10.1016/0045-7949(83)90017-2
20. Harajli, M. H., “Deformation and Cracking of Partially Prestressed Concrete Beams under Static and Cyclic Fatigue Loading,” PhD dissertation, University of Michigan, Ann Arbor, MI, 1985, 387 pp.
21. Abdelrahman, A. A., “Serviceability of Concrete Beams Prestressed by Fibre Reinforced Plastic Tendons,” PhD thesis, Department of Civil and Geological Engineering, University of Manitoba, Winnipeg, MB, Canada, 1995.
22. Ozkul, O.; Nassif, H.; Tanchan, P.; and Harajli, M., “Rational Approach for Predicting Stress in Beams with Unbonded Tendons,” ACI Structural Journal, V. 105, No. 3, May-June 2008, pp. 338-347.
23. Heo, S.; Shin, S.; and Lee, C., “Flexural Behavior of Concrete Beams Internally Prestressed with Unbonded Carbon Fiber-Reinforced Polymer Tendons,” Journal of Composites for Construction, ASCE, V. 17, No. 2, 2013, pp. 167-175. doi: 10.1061/(ASCE)CC.1943-5614.0000306
24. Jerrett, C. V., and Ahmad, S. H., “Behavior of Prestressed Concrete Strengthened by External FRP Post-Tensioned Tendons,” Advanced Composite Materials in Bridges and Structures, Canadian Society for Civil Engineering, Montreal, QC, Canada, 1996.
25. Ghallab, A., and Beeby, A. W., “Behaviour of PSC Beams Strengthened by Unbonded Parafil Ropes,” FRPRCS-5: Proceedings of the Fifth International Conference on Fibre-Reinforced Plastics for Reinforced Concrete Structures, C. J. Burgoyne, ed., Cambridge, UK, 2001, pp. 671-680.