Bond Strength and Transfer Length of Pre-tensioned Bridge Girders Cast with Self-Consolidating Concrete

Self-consolidating concrete (SCC) is becoming increasingly popular in the precast/prestressed concrete industry in the United States. However, there have been concerns regarding the bond strength, transfer length, and development length of prestressing strands and mild steel reinforcement with SCC. Further, there are no design guidelines for using SCC. In this study, a literature survey on the bond strength of SCC was conducted. Moustafa pullout tests were performed to determine the bond strength of 0.6 in. (15.2 mm) pretensioning strands with sec. The transfer lengths of three pretensioned concrete bridge girders were measured using Demec points. Pullout tests were also performed on 41 specimens using No. 4, No. 6, and No. 8 mild steel reinforcing bars and 0.6 in. prestressing strands. All the tests were performed using specimens cast with both SCC and conventional concrete. Test data have shown that the bond strength of sec with deformed reinforcing bars is adequate. However, the use of viscosity-modifying admixtures in sec may adversely affect its early compressive strength and its bond strength with pretensioning strands

Optimization of spliced precast concrete I -girder superstructures

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 ft–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 dissertation 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 towards 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 dissertation 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 dissertation summarizes an extensive theoretical and experimental research into the feasibility of splicing a haunch block onto a standard I-girder to form an efficient negative moment zone