Ultimate Tendon Stress in CFRP Strengthened Unbounded HSC Post-Tensioned Continuous I-Beams

Authors

Department of civil engineering, Shahid Bahonar University of Kerman, Kerman, Iran

Abstract

The use of unbounded tendons is common in prestressed concrete structures and evaluation of the stress increase 
in unbonded tendons at ultimate flexural strength of such structure has posed a great challenge over the years. Based on the bending experiment for two-span continuous post-tension beams with unbounded tendons and externally applied CFRP sheets, the monitoring of the stress increment of unbounded tendons is made in the loading process. For these aims, in this paper there are presented results of two continuous un-bonded post-tensioned I-beams were cast with high strength concrete (HSC) and monitored by electrical strain gauges. The beams are made of which are compared with the theory proposed by different codes. The results indicate that the ACI 318-2011 provides better estimates than AASHTO-2010 model whereas this model provides better estimates than BS 8110-97. Comparison of experimental ultimate tendon stress increase of strengthened and non-strengthened beams casted with HSC indicates that increase in tendon stress at an ultimate state in strengthened unbounded post-tensioned beam is lower than non-strengthened unbounded post-tension beam casted with HSC.

Keywords


[1] Warwaruk, J., Sozen, M.A., Siess, C.P. (1962), “Strength and Behavior in Flexure of Prestressed Concrete Beams”, Engineering Experimental Station, University of Illinois,  Urbana, Bullten No. 464.

[2] Cooke, N.I., Park, R., Yong, P. (1981), ‘‘Flexural Strength of  Prestressed Concrete Member with Unbounded Tendons", PCI Journal, Vol. 26, 52-80.

[3] Elzanaty, A., Nilson, A.H. (1982), ‘‘Flexural Behavior of Unbonded Post-Tensioned Partially Prestressed Concrete  Beams”, M.Sc. Thesis, Department of Structural Engineering, School of Civil and Environmental Engineering, Cornell University, Ithaca USA.

[4] Du, G., Tao, X. (1985), ‘‘Ultimate Stress in Unbounded Tendons of Partially Prestressed Concrete Beams”, PCI Journal, Vol. 30, 72-91.

[5] Chouinard, K.L. (1989), ‘‘Tendon Stress at Ultimate in Partially Prestress Concrete Beams”, Master’s thesis, Department of Civil Engineering, Queen’s University, Kingston, Ontario.

[6] Harajli, M. H., Kanj, M. (1991), ‘‘Ultimate Flexural Strength of Concrete Members Prestressed with Unbounded Tendons”, ACI Structural Journal, Proceedings Vol. 88, 663-671.

[7] Ozkul, O., Nassif, H., Tanchan, P. and Harajli, M. (2008), “Rational approach for predicting stress in beams with unbonded tendons”, ACI Structural Journal, Vol. 105, 338–347.

[8] Naaman, A. E. , Alkhairi, F. M. (1991), “Stress at Ultimate in Unbounded Post-Tensioned Tendons: Part 2—Proposed Methodology”, ACI Structural Journal, Vol. 88, 683-692.

[9] Ament, J. M., Chakrabarti, P. R. and Putcha, C. S. (1991), “Comparative Statistical Study for the Ultimate Stress in Unbonded Post-tensioning”, ACI  Structural Journal, Vol. 94, 171–180.

[10] Harajli, M. H. (2006), “On the Stress in Unbonded Tendons at Ultimate: Critical Assessment and Proposed Changes”, ACI Structural Journal, Vol. 103, 803–812.

[11] Manisekar, R.  and Senthil, R. (2006), “Stress at Ultimate in Unbonded Post Tensioning Tendons for Simply Supported Beams: A State-of-the-Art Review”, Adv. Struct. Eng., Vol. 9, 321–335.

[12] Dall’Asta, A., Ragni, L. and Zona, A. (2007), “Simplified Method for Failure Analysis of Concrete Beams Prestressed with External Tendons”, J. Struct. Eng., Vol. 133, 121–131.

[13] He,  Z., Liu, Z. (2010), “Stresses in External and Internal Unbonded Tendons: Unified Methodology and Design Equations”, ASCE Journal of the Structural Division, Vol. 136, 1055–1065.

[14] ACI 318-11 (2011), ‘‘Building code requirements for structural concrete and commentary”, Michigan (USA), American Concrete Institute.

[15] BS 8110 (1997), ‘‘Structural Use of Concrete”, Part 1, British Standards Institution, London, UK.

[16] AASHTO (2010), “LRFD Bridge Design Specifications”, American Association of State Highway and Transportation Officials, 16. Washington, D.C.

[17] Mattock, A.H., Yamazaki. J., Kattula, B.T. (1971), ‘‘Comparative Study of Prestressed Concrete Beams, with and without Bond", ACI Journal, Proceedings Vol. 68, 116-125.

[18] Mojtahedi, S., Gamble, W.L. (1978), ‘‘Ultimate Steel Stresses in Unbonded Prestressed Concrete”, Journal of Structural Division, ASCE, Vol. 104, 1159-1165.

[19] MacGregor, R.J.G. (1989), “Strength and ductility of externally post-tensioned segmental box girders”, PhD dissertation, The University of Texas at Austin.

[20] MacGregor, R.J.G., Kreger, M.E., Breen J.E. (1989), “Strength and ductility of a three-span externally post-tensioned segmental box girder bridge model”, Research report no. 365-3F, Center for Transportation Research, The University of Texas at Austin, Austin.

[21] Pannell, F.N. (1969), “Ultimate Moment Resistance of Unbounded Prestressed Concrete Beams”, Magazine of Concrete Research, Vol. 21, 43-54.

[22] Tam, A., Pannell, F. (1976), “The Ultimate Moment of Resistance of Unbounded Partially Prestressed Reinforced Concrete Beams”, Magazine of Concrete Research, V. 28, 203-208.