Prestress Losses and the Estimation of Long-Term Deflections and Camber for Prestressed Concrete Bridges

Prestressed concrete, an ideal combination of concrete and high strength steel, has emerged as an efficient material for modern construction. The construction of prestressed concrete bridges as a standard practice in the United States dates back to 1949 when the Philadelphia Walnut Ave Bridge was constructed. The technical and economical benefits of prestressed concrete permits longer spans and increased girder spacing. Complimenting this, higher performance concrete can feature lower water to cementious materials ratio (w/cm) and the inclusion of supplemental cementious materials that promote a dramatic improvement of concrete quality and durability. Efficient design of prestressed concrete bridges demands an accurate prediction of prestress losses. The prestress losses are defined as the loss of tensile stress in the prestress steel which acts on the concrete component of the prestressed concrete section. In pretensioned concrete, the four major sources of prestress losses are elastic shortening (ES), creep (CR), shrinkage (SH) and relaxation (RE). Additionally, prestress losses are further affected by variations in material properties of the concrete. Numerous research programs have been conducted and a variety of prestress loss prediction methods have been proposed. However, accurate determination of prestress losses has always challenged the prestressed concrete industry. Inaccurate predictions of losses result in excessive camber or deflection of prestressed concrete bridges. Excessive camber or deflection can, in turn, adversely affect the service conditions such as: cracking, ride and overall performance of the bridge. Excessive cracking can even reduce the bridge's durability since cracking can be a route for water borne contaminants to deteriorate the concrete and its reinforcements. The primary objective of this research is to review the relevant literature and databases available from prior research programs. This research will also develop design guidelines towards the accurate estimation of prestress losses, restricted to pre-tensioned concrete. The authors expect to develop equations for losses from the existing AASHTO LRFD time dependent equations for creep, shrinkage and relaxation. A spreadsheet was developed using the above proposed equations which can be used in design of prestressed concrete bridges. Additionally, some recommendations for design to ODOT will also be made.

• Record URL:
  http://www.okladot.state.ok.us/hqdiv/p-r-div/spr-rip/library/reports/fhwa-ok0708.pdf
• 
• Corporate Authors:

  Oklahoma State University

  School of Civil & Environmental Engineering
  207 Engineering South
  Stillwater, OK  United States  74078

  Oklahoma Department of Transportation

  200 NE 21st Street
  Oklahoma City, OK  United States  73105
• Authors:
  • Jayaseelan, Hema
  • Russell, Bruce W
• Publication Date: 2007-8

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Figures; References; Tables;
• Pagination: 108p

Subject/Index Terms

• TRT Terms: Creep; Curvature; Deflection; Mechanical relaxation; Prestressed concrete bridges; Prestressing; Pretensioning; Shrinkage
• Uncontrolled Terms: Prestress losses
• Subject Areas: Bridges and other structures; Design; Highways; Materials; I24: Design of Bridges and Retaining Walls; I32: Concrete;

Filing Info

• Accession Number: 01469407
• Record Type: Publication
• Files: TRIS, ATRI, STATEDOT
• Created Date: Jan 16 2013 10:17AM