Title:
Deflection Behavior of Beams Prestressed with Bonded FRP Tendons
Author(s):
Wassim Nasreddine, Peter H. Bischoff, and Hani Nassif
Publication:
Symposium Paper
Volume:
360
Issue:
Appears on pages(s):
491-510
Keywords:
cracking, deflection, effective moment of inertia, fiber-reinforced polymer (FRP) tendons, prestressed concrete
DOI:
10.14359/51740645
Date:
3/1/2024
Abstract:
The use of FRP tendons has become an attractive alternative to steel tendons in prestressed concrete structures to avoid strength and serviceability problems related to corrosion of steel. There is however a lack of knowledge in serviceability behavior related to deflection after cracking for beams prestressed with FRP tendons. Conventional approaches used to compute deflection of cracked members prestressed with steel is problematic at best, and the situation is exacerbated further with the use of FRP tendons having a lower modulus of elasticity than steel. Deflection of FRP reinforced (nonprestressed) concrete flexural members computed with Branson’s effective moment of inertia 𝐼 requires a correction factor (called a softening factor) that reduces the member stiffness sufficiently to provide reasonable estimates of post-cracking deflection. For FRP prestressed concrete however, this approach does not always work as expected and deflection can be either underestimated or overestimated significantly.
This study investigates the accuracy of different models proposed for estimating deflection of cracked FRP prestressed members using a database of 38 beams collected from the literature. All beams are fully prestressed. Results indicate that using Branson’s effective moment of inertia 𝐼 with a generic softening factor can produce reasonable estimates of deflection provided the 𝐼 response is shifted up to the decompression moment or adjusted with an effective prestress moment defined by an effective eccentricity of the prestress force. The former approach overpredicts deflection by 20% on average while the latter overpredicts deflection by not more than 5% based on the beams available for comparison. Assuming a bilinear moment deflection response overpredicts deflection by 12%, while an approach proposed by Bischoff (which also shifts the 𝐼 response upwards) overpredicts deflection by 23%. These last two approaches work reasonably well without the need for a correction factor.
Related References:
Abdelrahman, A. A., 1995, “Serviceability of Concrete Beams Prestressed by Fibre Reinforced Plastic Tendons,” PhD Thesis, Department of Civil and Geological Engineering, University of Manitoba, Winnipeg, Manitoba.
Abdelrahman, A. A., and Rizkalla, S. H., 1999, “Deflection Control of Concrete Beams Pretensioned by CFRP Reinforcements,” Journal of Composites for Construction, ASCE, V. 3, No. 2, May, pp. 55-62.
ACI Committee 318, 2019, “Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318-19R),” American Concrete Institute, Farmington Hills, MI, 624 pp.
ACI Committee 440, 2003, “Guide for the Design and Construction of Structural Concrete Reinforced with FRP Bars (ACI 440.1R-03),” American Concrete Institute, Farmington Hills, MI, 42 pp.
ACI Committee 440, 2004, “Prestressing Concrete Structures with FRP Tendons (ACI 440.4R-04),” American Concrete Institute, Farmington Hills, MI, 35 pp.
ACI Committee 440, 2006, “Guide for the Design and Construction of Structural Concrete Reinforced with FRP Bars (ACI 440.1R-06),” American Concrete Institute, Farmington Hills, MI, 44 pp.
ACI Committee 440, 2015, “Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer (FRP) Bars (ACI 440.1R-15),” American Concrete Institute, Farmington Hills, MI, 83 pp.
ACI Committee 440, 2022, “Building Code Requirements for Structural Concrete Reinforced with Glass Fiber-Reinforced Polymer (GFRP) Bars – Code and Commentary (ACI Code 440.11-22),” American Concrete Institute, Farmington Hills, MI, 255 pp.
Alameh, A. S., and Harajli, M. H., 1989, “Deflection of Progressively Cracking Partially Prestressed Concrete Flexural Members,” PCI Journal, V. 34, No. 3, May-June, pp. 94-128.
Arockiasamy, M.; Zhuang, M.; and Sandepudi, K., 1995, “Durability Studies on Prestressed Concrete Beams with CFRP Tendons,” Non-Metallic (FRP) Reinforcement for Concrete Structures, Proceedings of the Second International RILEM Symposium (FRPRCS-2), ed. L. Taewre, CRC Press, London, pp. 456-462.
Bischoff, P. H., 2005, “Reevaluation of Deflection Prediction for Concrete Beams Reinforced with Steel and Fiber Reinforced Polymer Bars,” Journal of Structural Engineering, ASCE, V. 131, No. 5, May, pp. 752-767.
Bischoff, P. H., 2007, “Deflection Calculation of FRP Reinforced Concrete Beams Based on Modifications to the Existing Branson Equation,” Journal of Composites for Construction, ASCE, V. 11, No. 1, Jan./Feb., pp. 4-14.
Bischoff, P. H., 2008, Discussion of “Tension Stiffening in Lightly Reinforced Concrete Slabs” by R. I. Gilbert, Journal of Structural Engineering, ASCE, V. 134, No. 7, July, pp. 1259-1260.
Bischoff, P. H., 2019, Discussion of “Deflection of FRP Prestressed Concrete Beams” by S. Pirayeh Gar, J. B. Mander, and S. Hurlebaus, Journal of Composites for Construction, ASCE, V. 23, No. 2, April, 07019001.
Bischoff, P. H., 2020, “Comparison of Existing Approaches for Computing Deflection of Reinforced Concrete,” ACI Structural Journal, V. 117, No. 1, January, pp. 231-240.
Bischoff, P. H., 2022, “Deformation Model for Reinforced and Cracked Prestressed Concrete,” ACI Structural Journal, V. 119, No. 1, January, pp. 243-254.
Bischoff, P. H., and Scanlon, A., 2007, “Effective Moment of Inertia for Calculating Deflections of Concrete Members Containing Steel Reinforcement and Fiber-Reinforced Polymer Reinforcement,” ACI Structural Journal, V. 104, No. 1, Jan.-Feb., pp. 68-75.
Bischoff, P. H.; Gross, S.; and Ospina, C. E., 2009, “The Story Behind Proposed Changes to ACI 440 Deflection Requirements for FRP-Reinforced Concrete (SP-264-4),” Serviceability of Concrete Members Reinforced with Internal/External FRP Reinforcement, SP-264, eds. C. Ospina, P. Bischoff and T. Alkhrdaji, American Concrete Institute, Farmington Hills, MI, pp. 53-76.
Bischoff, P. H.; Naito, C. J.; and Ingaglio, J. P., 2018, “Immediate Deflection of Partially Prestressed Concrete Flexural Members,” ACI Structural Journal, V. 115, No. 6, November, pp. 1683-1693. doi: 10.14359/51702381
Branson, D. E., 1965, “Instantaneous and Time-Dependent Deflections of Simple and Continuous Reinforced Concrete Beams,” HPR Report No. 7, Part 1, Alabama Highway Department, Bureau of Public Roads, Montgomery, AL., 78 pp.
Burke, C. R., 1998, “Flexural Design of Prestressed Concrete Beams with FRP Tendons,” MScE Thesis, Department of Civil and Architectural Engineering, University of Wyoming, Laramie, Wyoming.
Gao, D.; Benmokrane, B.; and Masmoudi, R., 1998, “A Calculating Method of Flexural Properties of FRP-Reinforced Concrete Beam: Part 1: Crack Width and Deflection,” Technical Report, Department of Civil Engineering, University of Sherbrook, Sherbrooke, Quebec, Canada, 24 pp.
Jeong, S.-M., 1994, “Evaluation of Ductility in Prestressed Concrete Beams using Fiber Reinforced Plastic Tendons,” PhD Thesis, University of Michigan, Ann Arbor, Michigan.
Kato, T., and Hayashida, N., 1993, “Flexural Characteristics of Prestressed Concrete Beams with CFRP Tendons (SP 138-26),” Fiber-Reinforced-Plastic Reinforcement for Concrete Structures – International Symposium, SP-138, eds. A. Nanni and C. W. Dolan, American Concrete Institute, Farmington Hills, MI, pp. 419-440.
Kim, Y. J., 2009, “Effective Moment of Inertia of Concrete Beams Prestressed with Aramid Fiber-Reinforced Polymer (AFRP) Tendons (SP-264-9),” Serviceability of Concrete Members Reinforced with Internal/External FRP Reinforcement, SP-264, eds. C. Ospina, P. Bischoff and T. Alkhrdaji, American Concrete Institute, Farmington Hills, MI, pp. 147-162.
Martinez, S.; Nilson, A. H.; and Slate, F. O., 1984, “Spirally Reinforced High-Strength Concrete Columns,” ACI Journal, Proceedings, V. 81, No. 5, May, pp. 431-442.
Mertol, H. C.; Rizkalla, S.; Scott, P.; Lees, J. M.; and El-Hacha, R., 2007, “Durability of Concrete Beams Prestressed with CFRP Bars (SP-245-1)”, Case Histories and Use of FRP for Prestressing Applications, SP-245, eds. R. El-Hacha and S.H. Rizkalla, American Concrete Institute, Farmington Hills, MI, pp. 1-20.
Nasreddine, W.; Obeidah, A.; Bischoff, P. H.; and Nassif, H., 2023, “Assessment of Deflection Prediction Models for Cracked Prestressed Concrete Beams,” ACI Structural Journal, V. 120, No. 6, Nov. – Dec.
Nilson, A. H., 1976, “Flexural Stresses after Cracking in Partially Prestressed Beams,” PCI Journal, V. 21, No. 4, July-Aug., pp.72-81.
Pirayeh Gar, S.; Mander, J. B.; and Hurlebaus, S., 2018, “Deflection of FRP Prestressed Concrete Beams,” Journal of Composites for Construction, ASCE, V. 22, No. 2, April, 04017049.
Precast/Prestressed Concrete Institute (PCI), 2017, PCI Design Handbook: Precast and Prestressed Concrete (MNL-120-17), eighth edition, PCI, Chicago, IL.
Scanlon, A., and Bischoff, P. H., 2008, “Shrinkage Restraint and Loading History Effects on Deflections of Flexural Members,” ACI Structural Journal, V. 105, No. 4, July-Aug., pp. 498-506.
Selvachandran, P.; Anandakumar, S.; and Muthuramu, K. L., 2017, “Influence of Deformability Behavior in Prestressed Concrete Beams using Carbon-Fiber-Reinforced Polymer Tendon,” PCI Journal, V. 62, No. 1, Jan.-Feb., pp. 66-77.
Slamah, K., 2013, “Bond and Flexural Behavior of Self-Consolidating Concrete Beams Reinforced and Prestressed with FRP Bars,” PhD Thesis, University of Waterloo, Waterloo, Ontario, Canada.
Tadros, M. K.; Ghali, A.; and Meyer, A. W., 1985, “Prestressed Loss and Deflection of Precast Concrete Members,” PCI Journal, V. 30, No. 1, Jan.-Feb., pp. 114-141.
Zhao, L., 1994, “Behavior of Carbon Fiber Composite Tendon Prestressed Concrete Planks under Static and Fatigue Loading,” MScE Thesis, University of Wyoming, Laramie, Wyoming.