Title:  Prestress transfer in pretensioned high strength concrete beams

Author(s): R. Carmo, S. Lopes

Publication: KILW

Volume: 49

Issue: 4

Appears on pages(s): 491-509

Keywords: Prestress, bond, concrete beams, prestressed concrete structures

DOI:

Date: 10/1/2003

Abstract:
This paper presents an experimental study carried out on ten pretensioned concrete beams. Particular attention is paid to the transfer phase. During the transfer operation data was collected in order to study the behaviour of the beams relative to the development of bonding between strand and concrete. Two parameters are studies: method of release and concrete cover. Prestress transfer was gradual for eight of the beams and instantaneous for the remaining two beams. For the beams studied in this investigation, the cover takes the following values: 20, 30, 40 and 70 mm. The test results provide useful information on three important topics: influence of cover on pretensioned anchorage, evolution of the concrete strains in the transfer zone and the increase of the transfer length with time. Load tests were also performed using a point load at the mid span of the beams, which were simply supported at the extremities. Actual ultimate moments of resistance are compared with the theoretical ones, and it is interesting to notice that the beams with 20 mm cover withstood a load that was significantly less than was predicted theoretically. These and other observations are discussed and conclusions presented.