Prevention of Splitting Failure at Ends of Prestressed Beams during Fabrication

The purpose of this research project was to determine the cause of vertical cracks that sometimes occur near the ends of the bottom flange of prestressed AASHTO, Florida Bulb-T, and Florida U beams. These vertical cracks were primarily observed on long-span beams and occurred during the transfer of the prestressing force to the concrete. The project initiated with mail surveys submitted to three FDOT prestressed beam manufacturers in Florida to determine the extent and types of end cracking each manufacturer was experiencing during the production process of their AASHTO, Florida Bulb-T, and Florida U beams. Site visits followed the surveys to observe the beam production process and to discuss when each type of crack forms with field personnel. The primary recommendation resulting from this research was that the coefficient of friction be reduced at the ends of the beams in order to reduce the tension stresses caused by friction as the beam displaces and cambers. A possible method for accomplishing this is to provide embedded steel base plates at the ends of the beams. Requirements for manufacturers to install embedded steel plates were implemented by the FDOT. Two years following this implementation, follow-up studies with the manufacturers indicated that the addition of the embedded plate has been effective in eliminating vertical end cracking. In addition to the work originally planned for this project, an analytical vertical crack sensitivity model was developed to evaluate the sensitivity of the beams to friction and other effects that could potentially contribute to vertical cracking. This prototype crack sensitivity model is based on a linear elastic spring model that incorporates the effects of static and dynamic friction at the ends of the beams during the detensioning process.

• Record URL:
  • http://www.dot.state.fl.us/research%2Dcenter/Completed_Proj/Summary_STR/FDOT_BD545_30_rpt.pdf
• 
• Corporate Authors:

  University of Florida, Gainesville

  Department of Civil Engineering, P.O. Box 116580
  Gainesville, FL  United States  32611-6580

  Florida Department of Transportation

  Structures Research Center, 605 Suwannee Street
  Tallahassee, FL  United States  32399
• Authors:
  • Cook, Ronald A
  • Reponen, Michael J
• Publication Date: 2008-1

Language

• English

Media Info

• Media Type: Print
• Edition: Final Report
• Features: Appendices; Figures; References; Tables;
• Pagination: 237p

Subject/Index Terms

• TRT Terms: Beams; Coefficient of friction; Cracking; Fabrication; Failure; Prestressed concrete; Prestressing; Stresses; Tension
• Uncontrolled Terms: Beam ends
• Geographic Terms: Florida
• Subject Areas: Bridges and other structures; Design; Highways; Materials; I24: Design of Bridges and Retaining Walls; I32: Concrete;

Filing Info

• Accession Number: 01091757
• Record Type: Publication
• Report/Paper Numbers: 00051118
• Contract Numbers: BD545 RPWO #30
• Files: TRIS, STATEDOT
• Created Date: Apr 23 2008 9:27AM