Quantification of bond performance of 18-mm prestressing steel

[EN] The use of 18-mm prestressing strands has extensive advantages in building and bridge construction. Strand bond is a critical factor that constitutes the strand behavior in pretensioned concrete girders and directly affects the applicability of existing bonding equations. This study systematically examines the bond performance of 18-mm strands. The bond strength of untensioned strands was evaluated Using simple bond tests. Twelve pretensioned concrete beams were additionally cast using self-consolidating concrete to assess the bond-related parameters of transfer and development lengths. The experimental results indicate the bond performance of 18-mm strands complies with the current design codes of pre tensioned concrete members. (C) 2017 Elsevier Ltd. All rights reserved.This research is supported by the University of Arkansas at Fayetteville and Ton Duc Thang University. The authors would like to thank Insteel Industries Inc. for providing the strands and the RJ Peterman & Associates, Inc. for conducting the STSB tests for this research. The authors would like to thank Mr. Don Logan for providing the financial support to conduct the STSB tests. The authors are also thankful to a number of individuals at University of Arkansas for helping conduct the tests.Dang, C.; Hale, WM.; Martí Vargas, JR. (2018). Quantification of bond performance of 18-mm prestressing steel. Construction and Building Materials. 159:451-462. https://doi.org/10.1016/j.conbuildmat.2017.10.131S45146215

Spacing requirements of 0.7 in. (18 mm) diameter prestressing strands

[EN] The use of 0.7 in. (18 mm) diameter strands for pretensioned concrete girders is advantageous when increasing the flexural capacity and extending girder spans. The current codes have no design guidelines for predicting transfer length, development length, and minimum strand spacing for this greater-diameter strand. This study measures transfer and development lengths and evaluates the applicability of using a strand spacing of 2.0 in. (51 mm) for 16 pretensioned concrete beams with 0.7 in. diameter strands. These beams were fabricated with high-strength, conventional concrete or self-consolidating concrete. The Standard Test Method for Evaluating Bond of Seven-Wire Steel Prestressing Strand (ASTM A1081) was used to quantify the strand surface conditions. The experimental results indicate that the current ACI 318-14 and AASHTO LRFD specifications overestimate the measured transfer and development lengths for the beams. Transfer and development lengths of the beams containing two strands placed at 2.0 in. spacing were equal to or slightly greater than those of the beams containing one strand. Finally, the concrete region around the strands showed no sign of cracking.The authors thank Insteel Industries Inc. for providing the strands and RJ Peterman and Associates Inc. for conducting the ASTM A1081 test method for strand bond for this research. The authors thank Don Logan for providing the financial support to conduct the ASTM A1081 test method for strand bond. The authors are also thankful to Richard Deschenes Jr., Cameron Murray, Joseph Daniels III, William Phillips, Doddridge Davis, Alberto Ramirez, and Ryan Hagedorn for helping fabricate the beams at the Engineering Research Center at the University of Arkansas.Dang, C.; Floyd, R.; Hale, W.; Martí Vargas, JR. (2016). Spacing requirements of 0.7 in. (18 mm) diameter prestressing strands. PCI Journal. 61(1):70-87. http://hdl.handle.net/10251/81574S708761

Temperature Gradients in Bridge Concrete I-Girders under Heat Wave

[EN] This paper presents an experimental research work to determine temperature gradients in concrete bridge girders under natural environmental conditions. Three AASHTO Type I-girders having different configurations (with and without wide top flanges) were considered in the experimental program. Temperature was monitored in the bridge girders to determine the vertical and transverse temperature gradients in a predeck placement condition. It was found that uneven heating of optimized bridge girder sections results in large nonlinear temperature gradients. The current AASHTO design standard, which only uses a nonlinear vertical but no transversal temperature gradient, was found inaccurate to predict both shape and magnitude of temperature gradients for the analyzed girders.This research is supported by the University of Arkansas at Fayetteville, Ton Duc Thang University, and Southern Plains Transportation Center. The authors are thankful to a number of graduate students for their help during the experimental program.Hagedorn, R.; Martí Vargas, JR.; Dang, C.; Hale, W.; Floyd, R. (2019). Temperature Gradients in Bridge Concrete I-Girders under Heat Wave. Journal of Bridge Engineering. 24(8):1-14. https://doi.org/10.1061/(ASCE)BE.1943-5592.0001454S11424

Bond model of 15.2 mm strand with consideration of concrete creep and shrinkage

[EN] The bond between prestressing strands and concrete in the transfer zone of pretensioned concrete members is a complicated mechanism. Concrete creep and shrinkage are dominant time-dependent factors that affect the strand bond. In this study, a semi-analytical bond stress-slip model was developed, based on test results of the standard test for strand bond for 15.2 mm strands. Effects of concrete creep and shrinkage are incorporated in the model. Measured transfer lengths collected from the literature are compared with predicted values, to validate the accuracy of the bond stress-slip model. Analytical results indicate that the strand bond decreases over time, and is almost constant after 360 d of age. An equation is proposed to predict the transfer length of the prestressing strand at 28 d, with an incorporation of concrete creep and shrinkage effects.This research is supported by the University of Arkansas at Fayetteville, the Ton Duc Thang University, and the Higher Committee for Education Development in Iraq (HCED). The authors are thankful to a number of graduate students at the University of Arkansas for their help in the experimental work.Kareem, R.; Al-Mohammedi, A.; Dang, C.; Martí Vargas, JR.; Hale, W. (2020). Bond model of 15.2 mm strand with consideration of concrete creep and shrinkage. Magazine of Concrete Research. 72(15):799-810. https://doi.org/10.1680/jmacr.18.00506S7998107215Balazs, G. L. (1992). Transfer Control of Prestressing Strands. PCI Journal, 37(6), 60-71. doi:10.15554/pcij.11011992.60.71Barnes RW (2000) Development Length of 0.6-inch Prestressing Strand in Standard I-Shaped Pretensioned Concrete Beams. PhD thesis, University of Texas at Austin, Austin, TX, USA. See http://catalog.lib.utexas.edu/record=b5227004 (accessed 22/01/2019).Briere, V., Harries, K. A., Kasan, J., & Hager, C. (2013). Dilation behavior of seven-wire prestressing strand – The Hoyer effect. Construction and Building Materials, 40, 650-658. doi:10.1016/j.conbuildmat.2012.11.064Canfield SR (2005) Full Scale Testing of Prestressed, High Performance Concrete, Composite Bridge Deck. MSc thesis, Georgia Institute of Technology, Atlanta, GA, USA. See http://hdl.handle.net/1853/7131 (accessed 22/01/2019).Caro, L. A., Martí-Vargas, J. R., & Serna, P. (2012). Time-dependent evolution of strand transfer length in pretensioned prestressed concrete members. Mechanics of Time-Dependent Materials, 17(4), 501-527. doi:10.1007/s11043-012-9200-2Claisse, P. A., Cabrera, J. G., & Hunt, D. N. (2001). Measurement of porosity as a predictor of the durability performance of concrete with and without condensed silica fume. Advances in Cement Research, 13(4), 165-174. doi:10.1680/adcr.2001.13.4.165Coello EDR (2007) Prestress Losses and Development Length in Pretensioned Ultra High Performance Concrete Beams. PhD thesis, University of Arkansas, Fayetteville, AR, USA. See https://search.proquest.com/docview/304897207 (accessed 01/03/2019).Dang, C. N., Murray, C. D., Floyd, R. W., Micah Hale, W., & Martí-Vargas, J. R. (2014). Analysis of bond stress distribution for prestressing strand by Standard Test for Strand Bond. Engineering Structures, 72, 152-159. doi:10.1016/j.engstruct.2014.04.040Dang, C. N., Hale, W. M., & Martí-Vargas, J. R. (2017). Assessment of transmission length of prestressing strands according to fib Model Code 2010. Engineering Structures, 147, 425-433. doi:10.1016/j.engstruct.2017.06.019Deng, Y., Morcous, G., & Ma, Z. J. (2015). Strand bond stress–slip relationship for prestressed concrete members at prestress release. Materials and Structures, 49(3), 889-903. doi:10.1617/s11527-015-0546-1Floyd RW (2012) Investigating the Bond of Prestressing Strands in Lightweight Self-Consolidating Concrete. PhD thesis, University of Arkansas, Fayetteville, AR, USA. See https://scholarworks.uark.edu/etd/457 (accessed 25/01/2019).Floyd, R. W., Pei, J.-S., & Wright, J. P. (2018). Simple model for time-dependent bond transfer in pretensioned concrete using draw-in data. Engineering Structures, 160, 546-553. doi:10.1016/j.engstruct.2018.01.031Grace, N. F. (2000). Transfer Length of CFRP/CFCC Strands for Double-T Girders. PCI Journal, 45(5), 110-126. doi:10.15554/pcij.09012000.110.126Gustavson, R. (2004). Experimental studies of the bond response of three-wire strands and some influencing parameters. Materials and Structures, 37(2), 96-106. doi:10.1007/bf02486605Kose MM (1999) Statistical Evaluation of Transfer and Development Length of Low-Relaxation Prestressing Strands in Standard I-Shaped Pretensioned Concrete Beams. PhD thesis, Texas Tech University, Lubbock, TX, USA. See http://hdl.handle.net/2346/17441 (accessed 01/03/2019).Lane SN (1998) A New Development Length Equation for Pretensioned Strands in Bridge Beams and Piles. Federal High Way Administration, McLean, VA, USA, Report No. FHWA-RD-98-116. See https://ntlrepository.blob.core.windows.net/lib/21000/21800/21887/PB99146664.pdf (accessed 22/01/2019).Mitchell, D., Cook, W. D., & Tham, T. (1993). Influence of High Strength Concrete on Transfer and Development Length of Pretensioning Strand. PCI Journal, 38(3), 52-66. doi:10.15554/pcij.05011993.52.66Morcous, G., Hatami, A., Maguire, M., Hanna, K., & Tadros, M. K. (2012). Mechanical and Bond Properties of 18-mm- (0.7-in.-) Diameter Prestressing Strands. Journal of Materials in Civil Engineering, 24(6), 735-744. doi:10.1061/(asce)mt.1943-5533.0000424Park, H., & Cho, J.-Y. (2014). Bond-slip-strain relationship in transfer zone of pretensioned concrete elements. ACI Structural Journal, 111(3). doi:10.14359/51686567Peterman, R. J. (2009). A simple quality assurance test for strand bond. PCI Journal, 54(2), 143-161. doi:10.15554/pcij.03012009.143.161Pozolo, A., & Andrawes, B. (2011). Analytical prediction of transfer length in prestressed self-consolidating concrete girders using pull-out test results. Construction and Building Materials, 25(2), 1026-1036. doi:10.1016/j.conbuildmat.2010.06.076Ramirez JA and Russell BW (2008) Transfer, Development, and Splice Length for Strand/Reinforcement in High Strength Concrete. NCHRP, Washington, DC, USA, Report 603, 12-60. See https://library.uark.edu/record=b2651369~S1 (accessed 25/01/2019).Seo J, Torres E and Schaffer W (2017) Self-Consolidating Concrete for Prestressed Bridge Girders. Department of Civil and Environmental Engineering, South Dakota State University, Brookings, SD, USA, Report No. 0092-15-03. See https://rosap.ntl.bts.gov/view/dot/34197 (accessed 22/01/2019).Staton, B. W., Do, N. H., Ruiz, E. D., & Hale, W. M. (2009). Transfer lengths of prestressed beams cast with self-consolidating concrete. PCI Journal, 54(2), 64-83. doi:10.15554/pcij.03012009.64.83Tadros MK, Hanna K and Morcous G (2011) Impact of 0.7 inch Diameter Strands on NU I-Girders. Nebraska Department of Roads, Lincoln, NE, USA, SPR-1(08) P311. See https://digitalcommons.unl.edu/ndor/88 (accessed 22/01/2019).Unay IO, Russell B, Burns N and Kreger M (1991) Measurement of Transfer Length on Prestressing Strands in Prestressed Concrete Specimens. University of Texas at Austin, Austin, TX, USA, Research Report 1210-1. See https://trid.trb.org/view/367710 (accessed 22/01/2019).Vázquez-Herrero, C., Martínez-Lage, I., & Martínez-Abella, F. (2013). Transfer length in pretensioned prestressed concrete structures composed of high performance lightweight and normal-weight concrete. Engineering Structures, 56, 983-992. doi:10.1016/j.engstruct.2013.06.020Vidales MD (2011) Effect of Partial Debonding of Prestressing Strands on Beam end Cracking. MSc thesis, Michigan State University, East Lansing, MI, USA. https://doi.org/10.25335/M5Z095.Mostafa, T., & Zia, P. (1977). Development Length of Prestressing Strands. PCI Journal, 22(5), 54-65. doi:10.15554/pcij.09011977.54.6

A New Smoothing Technique for Transfer-Length Determination

[EN] Transfer length is a significant parameter in the design of pretensioned concrete members. This study reports the measured transfer length of 15.2 mm (0.6 in.) prestressing strands. Twenty-four pretensioned concrete beams were cast using conventional concrete. The compressive strength at release ranged from 27 to 65 MPa (4000 to 9500 psi). Transfer lengths were determined by measuring concrete surface strains and using the average maximum strain (AMS) method. A new technique was developed to smooth the measured concrete surface strains. The measured transfer lengths were compared to the predicted transfer lengths using ACI 318-14 and AASHTO-LRFD equations. The results indicate that the proposed smoothing technique provides better results than the current threepoint moving average technique. The current code equations are conservative to predict transfer length for pretensioned concrete members having concrete compressive strength at release greater than 27 MPa (4000 psi).The authors acknowledge the financial support from the Mack-Blackwell Rural Transportation Center (MBTC) and Ton Duc Thang University.Ramirez-Garcia, AT.; Dang, C.; Deschenes, R.; Hale, WM.; Martí Vargas, JR. (2018). A New Smoothing Technique for Transfer-Length Determination. ACI Structural Journal. 115(6):1551-1561. https://doi.org/10.14359/51702380S15511561115