Title:
Immediate Deflection of Partially Prestressed Concrete Flexural Members
Author(s):
Peter H. Bischoff, Clay J. Naito, and Joseph P. Ingaglio
Publication:
Structural Journal
Volume:
115
Issue:
6
Appears on pages(s):
1683-1693
Keywords:
cracked section; deflection; live load; partial prestressing; prestressed concrete
DOI:
10.14359/51702381
Date:
11/1/2018
Abstract:
The ACI 318 Building Code permits calculation of immediate deflections for cracked prestressed concrete slabs and beams based on either a bilinear moment deflection relationship or an effective moment of inertia. The effective moment of inertia Ie is taken as a weighted average of the uncracked moment of inertia Ig and cracked moment of inertia Icr. Accuracy of deflection calculations based on Ie depends on the value of cracking moment and requires an upwards shift in the Icr response. A new approach is proposed for computing service load deflections of cracked prestressed members. The proposed approach is compared with the existing ACI 318 approaches using the measured load-deflection response of prestressed beams and is shown to provide a more accurate and consistent prediction of deflections than the existing approaches. An alternative trilinear model that is much simpler but not as accurate is shown to provide reasonable results as well. It is recommended to compute deflection of cracked prestressed members using the trilinear approach except in those instances where higher accuracy is needed.
Related References:
ACI Committee 318, 1971, “Building Code Requirements for Reinforced Concrete (ACI 318-71),” American Concrete Institute, Farmington Hills, MI, 78 pp.
ACI Committee 318, 2014, “Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14),” American Concrete Institute, Farmington Hills, MI, 520 pp.
ACI Committee 435, 2000, “Control of Deflection in Concrete Structures (ACI 435R-95) (Reapproved 2000),” American Concrete Institute, Farmington Hills, MI, 77 pp.
Aswad, A.; Burnley, G.; Cleland, N. M.; Orndorff, D.; and Wynings, C., 2004, “Load Testing of Prestressed Concrete Double Tees without Web Reinforcement,” PCI Journal, V. 49, No. 2, Mar.-Apr., pp. 66-77. doi: 10.15554/pcij.03012004.66.77
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, pp. 752-767. doi: 10.1061/(ASCE)0733-9445(2005)131:5(752)
Bischoff, P. H., 2007, “Rational Model for Calculating Deflection of Reinforced Concrete Beams and Slabs,” Canadian Journal of Civil Engineering, V. 34, No. 8, pp. 992-1002. doi: 10.1139/l07-020
Bischoff, P. H., and Scanlon, A., 2007, “Effective Moment of Inertia for Calculating Deflections of Concrete Members Containing Steel Reinforcement and FRP Reinforcement,” ACI Structural Journal, V. 104, No. 1, Jan.-Feb., pp. 68-75.
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, pp. 1-78.
Branson, D. E., and Trost, H., 1982, “Application of I-Effective Method in Calculating Deflections of Partially Prestressed Members,” PCI Journal, V. 27, No. 5, pp. 62-77. doi: 10.15554/pcij.09011982.62.77
Brewe, J., and Myers, J., 2010, “High-Strength Self-Consolidating Concrete Girders Subjected to Elevated Compressive Fiber Stresses, Part 1: Prestress Loss and Camber Behavior,” PCI Journal, V. 55, No. 4, pp. 59-77. doi: 10.15554/pcij.09012010.59.77
Brewe, J., and Myers, J., 2011, “High-Strength Self-Consolidating Concrete Girders Subjected to Elevated Compressive Fiber Stresses, Part 2: Structural Behavior,” PCI Journal, V. 56, No. 1, pp. 92-109. doi: 10.15554/pcij.01012011.92.109
Canadian Standards Association (CSA), 2014, “Design of Concrete Structures (CAN/CSA A23.3-14),” Canadian Standards Association, Mississauga, ON, Canada, 291 pp.
Collins, M. P., and Mitchell, D., 1997, Prestressed Concrete Structures, Response Publications, Canada, 766 pp.
CPCI, 2007, Design Manual: Precast and Prestressed Concrete, fourth edition, Canadian Precast/Prestressed Concrete Institute (CPCI), Ottawa, ON, Canada.
Mast, R. F., 1998, “Analysis of Cracked Prestressed Concrete Sections: A Practical Approach,” PCI Journal, V. 43, No. 4, pp. 80-91. doi: 10.15554/pcij.07011998.80.91
Naaman, A. E., 1985, “Partially Prestressed Concrete: Review and Recommendations,” PCI Journal, V. 30, No. 6, pp. 30-71.
Naito, C.; Cetisli, F.; and Tate, T., 2015, “A Method for Quality Assurance of 7-Wire Strand Bond in Portland Cement Concrete,” Journal of the Precast/Prestressed Concrete Institute, V. 60, No. 4, July-Aug., pp. 69-84.
Nilson, A. H., 1976, “Flexural Stresses After Cracking in Partially Prestressed Beams,” PCI Journal, V. 21, No. 4, pp. 72-81. doi: 10.15554/pcij.07011976.72.81
PCI, 2010, Design Handbook: Precast and Prestressed Concrete, seventh edition, Precast/Prestressed Concrete Institute (PCI), Chicago, IL.
Scanlon, A., and Bischoff, P. H., 2008, “Shrinkage Restraint and Loading History Effects on Deflection of Flexural Members,” ACI Structural Journal, V. 105, No. 4, July-Aug., pp. 498-506.
Suri, K. M., and Dilger, W. H., 1986, “Steel Stresses in Partially Prestressed Concrete Members,” PCI Journal, V. 31, No. 3, pp. 88-112. doi: 10.15554/pcij.05011986.88.112
Tadros, M. K., 1982, “Expedient Service Load Analysis of Cracked Prestressed Concrete Sections,” PCI Journal, V. 27, No. 6, pp. 86-111. doi: 10.15554/pcij.11011982.86.111
Young, M., 2016, “Comparative Study of Immediate Deflection Calculation of Partially Prestressed Concrete Flexural Members,” undergraduate research thesis, Department of Civil Engineering, University of New Brunswick, Fredericton, NB, Canada, 49 pp.