טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentDvier Moria
SubjectAnalysis and Design of Segmental Cantilever Bridges
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Emeritus Yeoshua Frostig
Full Thesis textFull thesis text - English Version


Abstract

Segmental prestressed concrete bridges, constructed using the Balanced Cantilever method, are sensitive to time dependent deformations. In this method the construction of the superstructure is carried out from the piers, without scaffolding, by adding relatively short concrete segments, either cast in place or prefabricated, in a symmetrical manner and then prestressed. The continuity between adjacent cantilevers, after reaching their full length, is achieved by casting the closure segment and completing the prestress in the spans of the bridge. The changes in the deformations and accompanying stresses, with time are the result of the visco-elastic  (time dependent)  properties of concrete and the construction process. In order to realistically assess the expected stress and deformation in the structure, an analytical model based on the time behavior, must be employed. Excessive unexpected deformations are well known phenomena in cast in place segmental bridges and are of great importance for the serviceability, durability and reliability of the bridge. Another aspect of the time dependent deformations is their influence on the actual geometry of the bridge. During execution each free cantilever undergoes different deformation curves leading to geometric discontinuity at the connection points. Respectively, the calculated deformations must be compensated for by setting an appropriate casting geometry.

The complexity of the behavior and performance of segmental prestressed concrete bridges requires a deep understanding of the various aspects involved in the design and construction of such bridges. In such analysis it is important to consider the precise expected loads, time of loading and to consider second order effects.

Here time dependent effects such as creep, shrinkage and strength development of the concrete, and prestressing steel relaxation, are considered based on models available in the literature. Empirical models for evaluating the visco-elastic properties of the concrete and their time-dependent effect on the structure, as proposed in design Standards and Guidelines, are reviewed. Various methodologies for calculating the time-dependent static behavior of the superstructure, including approximate models and analytical models considering loading and material properties as per the construction stages (Step by Step Analysis) are presented. Three numerical examples are included in order to examine the time-dependent effects on the behavior of the structure.