LONG TERM BEHAVIOUR OF POST TENSIONED CONCRETE GIRDER BRIDGES

Abstract

Long term behaviour of prestressed concrete girder refers to the time dependent deformation and prestress losses due to creep and shrinkage of concrete and relaxation of prestressing steel. Long term effects due to creep, shrinkage and relaxation causes significant increase in deflection of prestressed concrete bridges. This dissertation carries three major parts which includes the comparison of recently published IRC: 112-2011 and CEB-FIP 1990 for its material models on creep and shrinkage of concrete, effect of construction schedule on long term deformation of bridge structures and effect of time lag in between construction stage s on long term behaviour of bridge girders. The first part of the study carried out the comparison of two standard material models on creep and shrinkage of concrete and it is observed that IRC is giving more conservative output than CEB. The percentage difference between the two models were observed for creep coefficient and shrinkage strain under varying conditions of age after loading, age of concrete, relative humidity and temperature effects. Second part of the report describes about the effect of construction schedule on the long term behaviour of three different forms of structures namely simply supported, 3span continuous and integral girder bridges. Bridge models were made using SAP 2000 V14 and finite element meshing has done for the members. The effect is less in simply supported bridge and higher for integral and still higher for continuous type of structural forms. Study on the effect of lag on the long term behaviour of the above mentioned forms of structures is also done and the effect is negligible for simply supported and higher for continuous and integral form of structures.