Developing a spreadsheet program in analysing continuous prestressed segmental box girders

Abstract

This study presents findings on developing a spreadsheet in analysing continuous prestressed Segmental Box Girders Bridge. Prestressing effects on a concrete structure can be categorized as Primary and Secondary effects. The analysis of an indeterminate prestressed structure is complicated due to the fact that it involves Secondary Moment which develops at intermediate supports when prestressing is applied. Primary Moment can be determined by P x e, where P is the axial force in the tendon and e is the eccentricity between the tendon location and neutral axis of the section. However, it is not an easy task to determine the Secondary Moment for a continuous structure. This study focuses on the influence line method where the prestress Secondary Moment can be determined by simple calculation using an excel spreadsheet. The 5 span prestressed Segmental Box Girder Bridge of Penang Second Crossing has been selected for the study. This bridge was constructed using span by span method. Based on the provided prestressing layout, it was found that the prestress Secondary Moment for this bridge is about 30% to 35% of the prestress Primary Moment. It was also found that the Secondary Moment reduces the design hogging moment at pier locations and increases the design sagging moment in mid span. Finally, it can be concluded that the prestress Secondary Moment for an indeterminate structure can be derived by using the influence line method and it is necessary to consider this Secondary Moment during the design stage