LONG-TERM DEFORMATION OF INDETERMINATE PSC BRIDGE STRUCTURES

Abstract

Bridge structures are of two types namely determinate and indeterminate. Simply-supported bridge girders come under the category of determinate bridge structures. The indeterminate bridge structures include continuous and rigid frame bridges. They can be constructed either by making precast, prestressed concrete girders continuous by cast-in-situ deck slab and diaphragm or by segmental construction. 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 cause significant increase in deflection of prestressed concrete bridges. In this dissertation long-term behaviour of indeterminate post-tensioned bridge structures has been investigated. To begin with, long-term deformation of simply-supported bridge girder has been presented. A program based on incremental time-step method has been written in MATLAB to estimate the long-term deformation and prestress losses for simply-supported bridge girder. Provisions of CEB-FIP90 and ACI 209R-92 model codes for creep and shrinkage of concrete and relaxation formulae for low relaxation and stress-relieved strands have been incorporated in the program. Numerical studies are carried out to develop quantitative information for the effect of change in material models and environmental parameters on long-term deformation and prestress loss. After that, time-dependent restraint moment for a two-span precast, prestressed bridge girders made continuous using cast-in-place diaphragm has been predicted using a computer program written in MATLAB. Numerical studies have been performed for this case also. Finally, a typical segmental bridge constructed by cantilever construction has been analyzed using LUSAS 14 software to predict the time-dependent deflection at each stage of construction and service life. The effect of construction schedule, age of precast girder at the time of erection and environmental parameters has been illustrated through numerical studies.