SPLICED I-GIRDER CONCRETE BRIDGE SYSTEM

A number of prestressed concrete I-girder bridges built in the past several decades have demonstrated the ability of precast, prestressed spliced girder bridges to compete with structural steel plate girder bridges in the 120-300 ft span range. Some states limit the maximum transportable length of a member to 120 ft and the weight to 70 tons. Others, including Nebraska, have permitted lengths up to 175 ft and weights up to 100 tons. When span lengths exceed the maximum shippable length or weight, however, girder segments must be spliced at intermediate locations in the girder away from the piers. There are several other ways to extend the span capacity limits of standard products. These include using high-strength concrete, establishing moment continuity for superimposed deck and live loading, and utilizing pier geometry to allow longer spans. Each of these methods is discussed and examples are provided. This report discusses the design and construction of spliced-girder bridges. Design theory, post-tensioning analysis and details, segment-to-segment joint details and examples of recently constructed spliced-girder bridges are given. In recent years the trend toward increased span capacity of girder bridges has continued due to the need for improved safety and fast bridge replacement. Precast concrete members must now span further while minimizing the superstructure depth in order to compete favorably with a new breed of high-performance structural steel I-beams. This report presents four systems for creating continuous spliced concrete I-girders. For continuous large-span precast/prestressed concrete spliced I-girder bridges, the optimum solution is often a haunched girder system. Because of the need to use standard sizes as repetitively as possible and to clear overhead obstructions during shipping, a separate precast haunch block attached to the girder bottom flange is used to form a deeper section for the negative moment zone. This report summarizes an extensive theoretical and experimental research project on the feasibility of splicing a haunch block onto a standard I-girder to form an efficient negative moment zone. Approximate formulas are developed to estimate losses in post-tension spliced girder construction based on NCHRP 18-07. An overview of NCHRP 18-07 is given followed by an explanation of the work done to extend the results of NCHRP 18-07 to post-tensioned construction. A parametric study undertaken to develop the approximate formulas is then discussed. Finally, the formulas are presented and evaluated. The importance of protecting the corrosion sensitive post-tensioning steel is a focus in this research as well. After the collapse of two post-tensioned structures in England and the recent discovery of corroded tendons in several Florida bridges, many owners began to investigate their grouted post-tensioned structures more closely. Numerous investigations found that typical grout mixes, equipment, and procedures used in the past, as well as field inspection procedures, were not adequate to protect the steel.