Design concept of spliced holed web post tensioned concrete girders

Post-tensioned concrete girders have been popular for the superstructures of bridges because of simple design and low maintenance cost. Nevertheless, the traditional I-type PSC girders are limited in their girder length due to allowable stress limitations at each loading step. Prestressing force which is large enough to compensate the total external service loads can't be implemented in the girder at the initial prestressing stage since stresses in concrete which are larger than the allowable stresses should not be developed at subse- quent loading steps. In order to design longer PSC I-type girders, several aspects should be considered and overcome. Three important and different design concepts were implemented in this work to achieve bridge spans up to about 70 meters; 1) Girders are divided into several pieces. Girders can be precast at plants and transported to the construction site without being deterred by transportation problem in Korea. In this way, concrete quality can be ensured, and construction period at the site will be reduced dramatically as well. 2) A numerous number of holes was made in the web of the girder. Some of the anchorage devices were moved from the girder ends into the holes, and the magnitude of negative moment and compressive stresses devel- oped at the girder ends were reduced. 3) Prestressing force was introduced through multiple stages. This con- cept of incremental prestressing overcomes the prestressing force limit restrained by the allowable stresses at each loading stage, and maximizes the magnitude of applicable prestressing force. A full scale girder was fab- ricated. Five pieces of concrete girder members were cast and assembled by post-tensioning to build a 50 me- ter long full scale girder. Test results showed that the spliced holed web post-tensioned concrete girder design concept worked well and would replace steel box girders in competitive span length 1 SCOPE 2003).