ANALYSIS OF THE EFFECTS OF VERTICAL PRE-RELEASE CRACKS ON PRESTRESSED CONCRETE BRIDGE GIRDERS

In modern high strength concrete construction, heavily reinforced sections with very long span lengths are being used for precast, prestressed concrete bridge girders. During production of these girders, it has been observed that vertical cracks may develop near the midspan of the girders if they are left on the casting bed for an extended period of time. The cracking, which is attributed to the restrained shrinkage of the concrete and thermal effects during the curing period, tends to be more critical for long-span girders with deep sections and large amounts of prestressing strands. This article reports on a finite element model study that investigated the effects of pre-release cracks on the behavior of bridge girders. In the study, full-scale Minnesota Department of Transportation (DOT) Type-28M prestressed concrete bridge girders incorporating artificially-made pre-release cracks were tested under four-point bending to verify the findings. The authors note that experimental results obtained from the static tests validated the results of the finite element study. The authors conclude that the existence of pre-release cracks affected the strain distributions through the beam depth. Even if the pre-release cracks close completely on the precasting bed under the effects of beam self-weight and the prestressing force, the stress distributions near the crack locations will be different than those of originally uncracked beams. The authors note that there are factors that will tend to neutralize these negative effects of the pre-release cracks: as-built concrete strengths tend to be higher than specified design values, and conservative distribution factors are used to calculate the loads on an individual girder.

Language

  • English

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 114-130
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00986578
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 28 2005 12:00AM