The Effect of Fatigue on Understrength Shear-Critical Reinforced Concrete Beams Reinforced with External CFRP Stirrups

This is a technical report detailing the testing of six understrength reinforced concrete beams subjected to fatigue loading. Three beams were tested as-built, and three were reinforced with external carbon fiber stirrups. Tests to failure of as-built/retrofitted beam pairs were conducted statically, and after 100,000 and 1,000,000 cycles respectively. The beams subjected to fatigue loading were first loaded quasi-statistically to first cracking. The load amplitude for fatigue was set to give a peak load at 75% of that for first cracking. The as-built beams failed through rupture of the internal steel shear reinforcement. The carbon fiber-reinforced polymer (CFRP) beams failed through rupture of the concrete under the CFRP-concrete interface. The load distribution mechanism in the fatigue loaded CFRP-reinforced beams was different from the statically loaded example in that the strains in the CFRP were substantially higher through the post-fatigue loading regime. This suggests that the crack surfaces were 'worked', or polished by fatigue loading, degrading the concrete shear-resisting mechanism. The CFRP-reinforced beams also displayed different crack patterns from the unreinforced examples, in that a small number of wide shear cracks formed, inclined at 45°. Cracking in the as-built specimens was more widely spread, and the cracks were narrower. The force-displacement response of CFRP-reinforced beams was found to be bilinear in all cases, as was the response of the as-built beam subjected to 1,000,000 cycles. The as-built beams subjected to no cyclic loading, and 100,000 cycles, had a linear force-displacement response. An equation is presented which predicts ultimate shear strength of the CFRP-reinforced beams within an LRFD framework.

• Supplemental Notes:
  • This research was funded by the U.S. Department of Transportation, University Transportation Centers Program.
• Corporate Authors:

  University of Missouri, Rolla

  Center for Infrastructure Engineering Studies
  1870 Miner Circle Drive
  Rolla, MO  United States  65409

  Research and Special Programs Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Budek, Andrew
  • Taylor, Jedediah
  • Nash, Philip
• Publication Date: 2007-1

Language

• English

Media Info

• Media Type: Print
• Edition: Final Report
• Features: Figures; Photos; Tables;
• Pagination: 20p

Subject/Index Terms

• TRT Terms: Beams; Carbon fibers; Cracking; Fatigue (Mechanics); Fiber reinforced plastics; Load transfer; Reinforced concrete; Shear reinforcement; Shear strength; Stirrups; Testing
• Uncontrolled Terms: Understrength
• Subject Areas: Highways; Materials; I32: Concrete;

Filing Info

• Accession Number: 01044276
• Record Type: Publication
• Report/Paper Numbers: UTC R144, 00001406/0008404
• Contract Numbers: DTRS98-G-0021 (Grant)
• Files: UTC, TRIS, USDOT
• Created Date: Feb 28 2007 7:18PM