doi:10.1016/j.engstruct.2006.03.031 
Copyright © 2006 Elsevier Ltd All rights reserved.
Fiber element modeling for seismic performance of bridge columns made of concrete-filled FRP tubes
Zhenyu Zhua, Iftekhar Ahmadb and Amir Mirmirana, 
, 
aDepartment of Civil and Environmental Engineering, Florida International University, Miami, FL 33174, USA
bONM&J Inc. 321 15th Street, Suite 200, West Palm Beach, FL 33401, USA
Received 18 January 2005;
revised 13 September 2005;
accepted 28 March 2006.
Available online 5 June 2006.
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Abstract
Concrete-filled fiber reinforced polymer (FRP) tubes (CFFT) are an alternative to reinforced concrete, providing for rapid construction with comparable strengths and higher ductility. Despite encouraging test data, it is not clear as to whether traditional analytical tools may be used for prediction of structural performance of CFFT, especially in seismic applications. This paper reports on modeling of CFFT either as cast-in-place reinforced or precast post-tensioned column in conjunction with a reinforced concrete (RC) footing. The model is verified against two earlier experimental programs at the member-level and subassembly-level. The model was then used to conduct a parametric study of different column configurations under a constant axial load and a reversed cyclic lateral load. Moreover, seismic performance of a typical CFFT column is compared with its RC counterpart under three different ground acceleration records. The study shows that seismic analysis of CFFT columns is possible using available analytical tools for conventional RC columns. Also, CFFT columns demonstrate superior performance over their RC counterparts in response to wide-ranging ground acceleration records. Fiber architecture of the FRP tube could be optimized for strength and ductility. Internal steel reinforcement and a minimum thickness of FRP tube are deemed necessary to provide adequate ductility and system integrity in seismic applications.
Keywords: Concrete; CFFT; FRP; OpenSees; Pseudo-static; Seismic
Fig. 1a. Concrete-filled FRP tube (CFFT) beam–column test setup.
Fig. 1b. Concrete-filled FRP tube (CFFT) column overview.
Fig. 1c. CFFT and RC column cross section configurations.
Fig. 2. Fiber element discretization of CFFT cross section.
Fig. 3. Schematics of cast-in-place and precast post-tensioned CFFT column models.
Fig. 4. Typical hysteretic stress–strain curve of concrete model.
Fig. 5. Typical hysteretic stress–strain curve of steel reinforcement model.
Fig. 6. Typical hysteretic stress–strain curve of FRP model.
Fig. 7. Comparison of tests and analysis for hysteretic response of CFFT beam–column.
Fig. 8. Comparison of tests and analysis for hysteretic response of cast-in-place CFFT column.
Fig. 9. Comparison of tests and analysis for hysteretic response of precast post-tensioned CFFT column.
Fig. 10. Comparison of tests and analysis for deflected shape of cast-in-place CFFT column.
Fig. 11. Effect of length-to-diameter ratio on hysteretic response of CFFT column.
Fig. 12. Effect of diameter-to-thickness ratio on hysteretic response of CFFT column.
Fig. 13. Effect of internal reinforcement ratio on hysteretic response of CFFT column.
Fig. 14. Effect of fiber orientation angle on hysteretic response of CFFT column.
Fig. 15. Effect of diameter-to-thickness ratio on cumulative energy envelope of CFFT column.
Fig. 16. Effect of internal reinforcement ratio on cumulative energy envelope of CFFT column.
Fig. 17. Earthquake ground acceleration records.
Fig. 18. Comparison of CFFT and RC column system responses under Tabas earthquake.
Fig. 19. Comparison of CFFT and RC column system responses under Sylmar earthquake.
Fig. 20. Comparison of CFFT and RC column system responses under Llollelo earthquake.
Fig. 21. Ground acceleration and CFFT column displacement response Fourier transformation.
Table 1.
Test data for concrete-filled FRP tubes of Y series [11]
a Manufacturer data.
b Burnout test result.
c A total of 17 layers test + 17 layers at +55
fiber orientation.
Table 2.
Case study parameter matrix
Note: The shaded areas indicate the base value for each parameter set.
Table 3.
FRP properties for different fiber orientations
Note: Symmetric performance of the FRP tube was assumed in the parametric study.
a 
.
Table 4.
Comparison of CFFT column performance measures for different parameters
a Pinching effect is the ratio of the minimum width of the hysteretic response to its width at the origin (see inset in
Fig. 11).
Table 5.
Comparison of CFFT and RC column responses to different earthquake records
a 
(32.2 ft/s
2).
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