Examination of strength reduction factor in CFRP-confined columns under axial compression

Abstract

In the strength design method, the safety level is tried to be reached by using strength reduc-tion factors ϕ applied to the nominal strengths. In the current ACI 318-19, the safety factors ϕ are suggested as 0.65 for tie-reinforced concrete columns and 0.60 for plain columns, respec-tively. The aim of the present study is to evaluate the strength reduction factors of the confined columns with Carbon Fiber Reinforced Polymer (CFRP) subjected to axial compression load according to ACI 318-19. For this purpose, a total of 298 column test specimens with circular and rectangular cross-sections confined with CFRP collected from 18 different experimen-tal studies in the literature were examined to determine the strength reduction factors. The first-order second-moment approach was used to determine these factors by reliability anal-ysis, and the correlation effects between random variables were not taken into account. The target reliability index and the corresponding probability of failure were taken as β=3.5 and pF = 2.33×10-4 for different coefficients of variation of random variables, respectively. Then, these factors were been separately compared to those of recommended in the ACI 318-19. At the end of the study, the upper limits of the coefficients of variation that should not be exceeded were determined to ensure the target reliability of the columns.

Keywords

• Strength Reduction Factor
• Carbon Fiber Reinforced Polymer
• First-order Second-moment Approach
• Axial load
• Column

References

1. REFERENCES
2. [1] American Concrete Institute Committee 318 (ACI 318-19). Building code requirements for structural concrete and commentary, Farmington Hills, MI: American Concrete Institute Committee; 2019.
3. [2] Ang AHS, Tang W. Probability concepts in engineering planning and design. 1st ed. New York: John Wiley & Sons Inc; 1984.
4. [3] American Concrete Institute Committee 440 (ACI 440.2R-17). Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures, Farmington Hills, MI: American Concrete Institute Committee; 2017.
5. [4] Tekin Özer A, Alacalı S. Analysis of strength reduction factor for axially-loaded circular columns with fiber reinforced polymer. Dokuz Eylul Univ Fac Eng J Sci Eng 2021;23:9951004. [Turkish]
6. [5] Gündüz, A. Probability, statistics, risk and reliability in engineering.İstanbul: Küre; 1996. [Turkish]
7. [6] Zou Y, Hong HP. Reliability assessment of FRP-confined columns designed for buildings. Struct and Infrastructure Eng 2011;7:243258. [CrossRef]
8. [7] Alqam M, Bennett RM, Zureick AH. Probabilistic based design of concentrically loaded fiber-reinforced polymeric compression members. J Struct Eng 2004;130:19141920. [CrossRef]

9. [8] Zhou YW, Feng X, Sui LL. Reliability Assessments of Concrete Filled FRP Tube Columns. Appl Mech and Mater 2013;405408:731734. [CrossRef]
10. [9] Mirza SA. Reliability-based design of reinforced concrete columns. Struct Saf 1996;18:179194. [CrossRef]
11. [10] Hao H, Li ZX, Shi Y. Reliability analysis of RC columns and frame with FRP strengthening subjected to explosive loads. J Perform Constr Facil 2015;30:115. [CrossRef]
12. [11] Ali O. Structural reliability of biaxial loaded short/slender-square FRP-confined RC columns. Constr Build Mater 2017;151:370382. [CrossRef]
13. [12] Jafari F. Reliability of FRP reinforced concrete columns. 1st Persian Gulf International Conference on Sustainable Concrete; 2014 Dec 1718; Bandar Abbas, Persia, 2014.
14. [13] Val D, Bljuger F, Yankelevsky D. Reliability evaluation in nonlinear analysis of reinforced concrete structures. Struct Saf 1997;19:203217. [CrossRef]
15. [14] Atadero RA, Karbhari VM. Calibration of resistance factors for reliability based design of externally-bonded FRP composites. Compos B Eng 2008;39:665679. [CrossRef]
16. [15] Hong HP, Zhou W. Reliability evaluation of RC columns. J Struct Eng 1999;125:784790. [CrossRef]
17. [16] Monti G, Santini S. Reliability based calibration of partial safety coefficients for fiber-reinforced plastic. J Compos Constr 2002;6:162167. [CrossRef]
18. [17] Taki, A. Firouzi A, Mohammadzadeh S. Life cycle reliability assessment of reinforced concrete beams shear-strengthened with carbon fiber reinforced polymer strips in accordance with FIB bulletin 14. Struct Concr 2018;19:20172028. [CrossRef]
19. [18] Wieghaus KT, Atadero RA. Effect of existing structure and FRP uncertainties on the reliability of FRP-based repair. J Compos Constr 2011;15:635643. [CrossRef] [19] Okeil AM, El-Tawil S, Shahawy M. Flexural reliability of reinforced concrete bridge girders strengthened with carbon fiber-reinforced polymer laminates. J Bridge Eng 2002;7:290299. [CrossRef]
20. [20] Ghobarah A, Aly NM, El-Attar M. Seismic reliability assessment of existing reinforced concrete buildings. J Earthq Eng 1998;2:569592. [CrossRef]
21. [21] Kim JH, Lee SH, Paik I, Lee HS. Reliability assessment of reinforced concrete columns based on the P-M interaction diagram using AFOSM. Struct Saf 2015;55:7079. [CrossRef]
22. [22] Ellingwood B. Toward load and resistance factor design for fiber-reinforced polymer composite structures. J Struct Eng 2003;129:449458. [CrossRef]
23. [23] Huang Q, Gardoni P, Hurlebaus S. Probabilistic capacity models and fragility estimates for reinforced concrete columns incorporating NDT data. J Eng Mech 2009;135:13841392. [CrossRef]
24. [24] Stewart MG, Attard MM. Reliability and model accuracy for high- strength concrete column design. J Struct Eng 1999;125:290300. [CrossRef]
25. [25] Mestrovic D, Cizmar D, Miculinic L. Reliability of concrete columns under vehicle impact. Struct Under Shock Impact X 2008;98:157165. [CrossRef]
26. [26] Chastre C, Silva M. Monotonic axial behavior and modeling of RC circular columns confined with CFRP. Eng Struct 2010;32:22682277. [CrossRef]
27. [27] Benzaid R, Mesbah HA. The confinement of concrete in compression using CFRP composites-effective design equations. J Civ Eng Manag 2014;20:632648. [CrossRef]
28. [28] Faustino P, Chastre C, Paula R. Design model for square RC columns under compression confined with CFRP. Compos B Eng 2014;57:187198. [CrossRef]
29. [29] Peker Ö. Low strength reinforced concrete members strengthened with CFRP sheets. Master's thesis. İstanbul: Istanbul Technical University; 2005.
30. [30] Li YF, Lin CT. An effective peak stress formula for concrete confined with carbon fiber reinforced plastics. Can J Civ Eng 2003;30:882889. [CrossRef]
31. [31] Karabinis AI, Rousakis TC. Concrete confined by FRP material: a plasticity approach. Eng Struct 2002;24:923932. [CrossRef]
32. [32] Vincent T, Ozbakkaloglu T. Influence of concrete strength and confinement method on axial compressive behavior of FRP confined high-and ultra-high-strength concrete. Compos B Eng 2013;50:410428. [CrossRef]
33. [33] Ozbakkaloglu T, Vincent T. Axial compressive behavior of circular high-strength concrete-filled FRP tubes. J Compos Constr 2014;18:04013037. [CrossRef]
34. [34] Berthet JF, Ferrier E, Hamelin P. Compressive behavior of concrete externally confined by composite jackets. Part A: experimental study. Constr Build Mater 2005;19:223232. [CrossRef]
35. [35] Wu Y, Jiang J. Effective strain of FRP for confined circular concrete columns. Compos Struct 2013;95:479491. [CrossRef]
36. [36] Theodoros R, Tepfers R. Experimental investigation of concrete cylinders confined by carbon FRP sheets, under monotonic and cyclic axial compressive load. Publication 01:02.Chalmers University of Technology, 2001.
37. [37] Zeng JJ, Lin G, Teng JG, Li L. Behavior of large-scale FRP-confined rectangular RC columns under axial compression, Eng Struct 2018;174:629645. [CrossRef]
38. [38] Wang Z, Wang D, Smith ST, Lu D. CFRP-Confined square RC columns. I: Experimental investigation, J Compos Constr 2012;16:150160. [CrossRef]
39. [39] Belouar A, Laraba A, Benzaid R, Chikh N. Structural performance of square columns wrapped with CFRP sheets. Procedia Eng 2013;54:232240. [CrossRef]
40. [40] Al-Salloum YA. Influence of edge sharpness on the strength of square concrete columns confined with FRP composite laminates. Compos B Eng 2007;38:640650. [CrossRef]
41. [41] Ozbakkaloglu T, Oehlers DJ. Concrete-filled square and rectangular FRP tubes under axial compression. J Compos Constr 2008;12:469477. [CrossRef]
42. [42] Rochette P, Labossiére P. Axial testing of rectangular column models confined with composites. J Compos Constr 2000;4:129136. [CrossRef]
43. [43] Wang LM, Wu YF. Effect of corner on the performance of CFRP-confined square concrete columns: Test. Eng Struct 2008;30:493505. [CrossRef]
44. [44] Tekin Özer A, Analysis of strength reduction factor for axially-loaded columns with fiber reinforced polymer (master thesis). Istanbul: Yildiz Technical University; 2021. [Turkish]