Experimental and Analytical Evaluations of Confinement Reinforcement in Pretensioned Concrete Beams

• Published in: Transportation research record 2011-01, Vol.2251 (1), p.59-67
• Main Authors: Ross, Brandon E., Hamilton, H. R. (Trey), Consolazio, Gary R.
• Format: Article
• Language: English
• Subjects: Beams (structural); Confinement; Failure; Mathematical models; Prestressing; Reinforcement; Reinforcing steels; Strands
• ISSN: 0361-1981; 2169-4052
• DOI: 10.3141/2251-06

The AASHTO LRFD Bridge Design Specifications require that confinement reinforcement be placed around prestressing strands in the bottom bulb of pretensioned concrete beams. Although the AASHTO specifications contain prescriptive requirements for the quantity and placement of confinement reinforcement, the effect of such reinforcement on end region behavior is not well understood. To evaluate the function and effect of confinement reinforcement, 12 tests were conducted on precast pretensioned beams loaded in three-point bending at a shear span-to-depth ratio of 1.0. Variables in the test program included strand size, strand quantity, prestressing force, and the presence or lack of confinement reinforcement. In the tests, the confinement reinforcement neither prevented nor delayed strand slip but improved shear capacity and displacement ductility and prevented splitting failure. Experimental results also indicated transverse strain in the concrete above the bearing pad, which eventually led to splitting failure in test beams without confinement reinforcement. An elastic finite element analysis of the test beam was conducted to model the strain distributions in the test beams before cracking. Results from the analyses matched well with the experimental results. In particular, the magnitude and distribution of the transverse concrete strain measured at the end of the beam agreed well with the experimental results.