Cyclic behavior of steel I-beams modified by a welded haunch and reinforced with GFRP

  • Egilmez, O. Ozgur (Dept. of Civil Engineering, Izmir Inst. of Technology) ;
  • Alkan, Deniz (Dept. of Civil Engineering, Izmir Inst. of Technology) ;
  • Ozdemir, Timur (Dept. of Civil Engineering, Izmir Inst. of Technology)
  • Received : 2009.07.25
  • Accepted : 2009.08.07
  • Published : 2009.09.25


Flange and web local buckling in beam plastic hinge regions of steel moment frames can prevent beam-column connections from achieving adequate plastic rotations under earthquake-induced forces. Reducing the flange-web slenderness ratios (FSR/WSR) of beams is the most effective way in mitigating local member buckling as stipulated in the latest seismic design specifications. However, existing steel moment frame buildings with beams that lack the adequate slenderness ratios set forth for new buildings are vulnerable to local member buckling and thereby system-wise instability prior to reaching the required plastic rotation capacities specified for new buildings. This paper presents results from a research study investigating the cyclic behavior of steel I-beams modified by a welded haunch at the bottom flange and reinforced with glass fiber reinforced polymers at the plastic hinge region. Cantilever I-sections with a triangular haunch at the bottom flange and flange slenderness ratios higher then those stipulated in current design specifications were analyzed under reversed cyclic loading. Beam sections with different depth/width and flange/web slenderness ratios (FSR/WSR) were considered. The effect of GFRP thickness, width, and length on stabilizing plastic local buckling was investigated. The FEA results revealed that the contribution of GFRP strips to mitigation of local buckling increases with increasing depth/width ratio and decreasing FSR and WSR. Provided that the interfacial shear strength of the steel/GFRP bond surface is at least 15 MPa, GFRP reinforcement can enable deep beams with FSR of 8-9 and WSR below 55 to maintain plastic rotations in the order of 0.02 radians without experiencing any local buckling.


existing steel buildings;plastic local buckling;glass fiber reinforced polymers;stability


  1. Accord, N.B. and Earls, C.J. (2006), "Use of fiber-reinforced polymer composite elements to enhance structural steel member ductility", J. Compos. Constr., ASCE, 10(4), 337-344.
  2. American Institute of Steel Construction (AISC) (2005a), Seismic provisions for structural steel buildings, ANSI/AISC 341-05, AISC, Chicago, IL.
  3. American Institute of Steel Construction (AISC) (2005b), Code of standard practice for steel buildings and bridges, AISC, Chicago, IL.
  4. American Institute of Steel Construction (AISC) (2005c), Prequalified connections for special and intermediate steel moment frames for seismic applications, ANSI/AISC 358-05, AISC, Chicago, IL.
  5. American Institute of Steel Construction (AISC) (1999), Modification of existing welded steel moment connections for seismic resistance, Steel Design Guide Series 12, AISC, Chicago, IL.
  6. ANSYS Inc. (2007), Finite element model users manual, Version 11.0, Canonsburg, Pa.
  7. Boone, M.J. (2002), "Mechanical Testing of Epoxy Adhesives for Naval Applications", Master of Science Thesis, The Graduate School of The University of Maine, December.
  8. Cadei, J.M.D., Stratford, T.J., Hollaway, L.C. and Duckett, W.G. (2004), Strengthening metallic structures using externally bonded fiber-reinforced polymers, CIRIA, Publication C595, London.
  9. Chen, M. and Das, S. (2009), "Experimental study on repair of corroded steel beam using CFRP", Steel Compos. Struct., 9(2), 103-118.
  10. Ekiz, E., El-Tawil, S., Parra-Montesinos, G. and Goel, S. (2004), "Enhancing plastic hinge behavior in steel flexural members using CFRP wraps", Proc. of the 13th World Conf. on Earthquake Engineering, Paper No.2496, Vancouver.
  11. El Damatty, A.A. and Abushagur, M. (2003), "Testing and modeling of shear and peel behavior for bonded steel/FRP connections", Thin-Wall. Struct., 41, 987-1003.
  12. Eurocode-8, Part 1, European Standard (2003), Design of structures for earthquake resistance- Part 1: General rules, seismic actions, and rules for buildings, prEN 1998-1: 2003 (E).
  13. Federal Emergency Management Agency (FEMA) (2000a), Recommended seismic design criteria for new steel moment-frame buildings, FEMA 350, Washington, D.C.
  14. Federal Emergency Management Agency (FEMA) (2000b), Recommended seismic evaluation and upgrade for existing welded steel moment-frame buildings, FEMA 351, Washington, D.C.
  15. Guven, C.A. (2009), "Experimental study on improving local buckling behavior of steel plates with glass fiber reinforced polymers", MS Thesis, Izmir Institute of Technology, March.
  16. Lili, S., Yan, Z., Yuexin, D. and Zuoguang, Z. (2008), "Interlaminar Shear Property of Modified Glass Fiber Reinforced Polymer with Different MWCNTs", Chinese Journal of Aeronautics, 21, 361-369.
  17. Nakashima, M., Suita, K., Morisako, K. and Maruoka, Y. (1998), "Tests of welded beam-column subassemblies I: Global behavior", J. Struct. Eng. ASCE, 124(11), 1236-1244.
  18. Nakashima, M., Kanao, I. and Liu, D. (2002), "Lateral instability and lateral bracing of steel beams subjected to cyclic loading", J. Struct. Eng. ASCE, 128(10), 1308-1316.
  19. Nakashima, M., Liu, D. and Kanao, I. (2003), "Lateral-torsional and local instability of steel beams subjected to large cyclic loading", J. Steel Struct., 3(3), 179-189.
  20. Okazaki, T., Liu, D., Nakashima, M. and Engelhardt, M.D. (2006), "Stability requirements for beams in seismic steel moment frames", J. Struct. Eng. ASCE, 132(9), 1334-1342.
  21. SAC (1996), "Technical report: Experimental investigations of beam-column subassemblies", Report No. SAC-96-01, SAC Joint Venture, Sacramento, California.
  22. Sayed-Ahmet, E.Y. (2004), "Strengthening of thin-walled steel I-section beams using CFRP strips", Proc. of the 4th Advanced Composites for Bridges and Structures Conf., Calgary, Canada.
  23. Schnerch, D., Dawood, M., Rizkalla, S. and Sumner, E. (2007), "Proposed design guidelines for strengthening of steel bridges with FRP materials", Constr. Build. Mater., 21(5), 1001-1010.
  24. Uang, C., Yu, Q.K., Noel, S. and Gross, J. (2000), "Cyclic testing of steel moment connections rehabilitated with RBS or welded haunch", J. Struct. Eng. ASCE, 126(1), 57-68.

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