Serviceability analysis of continuous box-girder bridges constructed using different techniques

Abstract

There are different construction methods practiced in the bridge industry to erect bridge super structures. Among these, segmental Box-girder is the latest trend in the industry, which facilitates fast, versatile construction. In contrast to monolithic construction, these bridges consist of pre-cast pretensioned elements joined together by post-tensioning to form continuous bridge structures. Composite bridge cross-sections adopted in segmental construction use dissimilar materials such as precast concrete, prestressing and non prestressing steel components. Behaviour of these continuous bridges, are often influenced by time-dependent nature of the materials used. This study focuses on the analysis of time-dependent properties associated with the bridges constructed using different techniques. To analyse the short, medium and long term behaviour of the bridges, a rational analytical approach is chosen so that it can assess the time-dependant effects such as creep and shrinkage of concrete and relaxation of prestressing steel. So the structural analyses can model mathematically all associated changes in geometrical forms, statical conditions and material properties which are important with segmental construction. A computer program available, and which follows the above procedure has been enhanced by introducing a pre-processor to ease complications arising from the large number of analyses encountered with solution of continuous segmental bridge problems. In this research different construction techniques such as span-by-span construction, balanced and progressive. Cantilever methods and incremental launching have been examined. A four span continuous bridge example where each span is fabricated using eight equal segments have been studied under different construction techniques. These involve evaluating the effects of loads arising from force or displacement induced changes which occur during construction stages and perhaps be temporary or permanent depending on the circumstances. Also it has been possible to compare results and identify both advantages and disadvantages of the various methods. The study reveals the effect of serviceability indices such as stresses and deformations which are affected in different forms depending on the method of construction.