Analysis and Design of Prestressed Post-Tensioned I Type Girder Bridge

Abstract

Prestress can provide a solution to many structural problems. Prestress is a technique to create in advance accurately known permanent forces required. Prestressing in a member replaces structural steel in the member, which needs costly maintenance and corrodes under aggressive atmospheric conditions. Because of these short comings of structural steel, Pre-stressed concrete is ideal for the construction of medium and long span bridges. Pre-stressed concrete bridges offer a high degree of freedom from cracks, low maintenance and long life. The use of high strength concrete and high tensile steel results in slender sections, which are aesthetically superior, coupled with overall economy. In comparison with steel bridges, pre-stressed concrete bridges require very little maintenance and not easily damaged by fire. In a conventional approach to the design of prestressed concrete girders, a section of the girder and cable profile is required to be assumed. Thereafter, going through a series of typical and rigorous calculations, stress check is made and it is established whether the section and cable profile are suitable or not. If the design is not suitable, a revised section of girder and/or cable profile is tried. Since the process is repetitive, it can be better achieved by a computer software rather than repetitive hand calculation. In this program different cross-sectional dimensions of the girder and geometry and type of the of various types of strands, i.e. 7T13, 12T13, 19T13 etc. or any combination of these are to be entered for the purpose of preliminary design. From the available input data the program calculate sectional properties, Courban’s Factors, dead load analysis, live load analysis, prestressing forces, prestress losses and check for stresses at various sections of the prestress simply supported I- girder. The time dependent losses are considered as per IRC-18. At any specified section, checking of final stresses is possible. If the initial data fail to comply with iv the required condition as per IRC, the program does not move further for the check for ultimate shear, moment resistance of the section, design of diaphragm, end block and deck slab. Keywords: Prestress, I type girder, bridge, strand Lay out of Chapters Chapter 1 Covers the definition of prestress, methods of prestressing and application of prestressed concrete in the field of structural engineering. Various type of bridge superstructure are discussed at length. Chapter 2 The literature collected for analysis and design of Prestressed Post-tensioned I type girder bridge. Chapter 3 Theoretical background of the study is given in this chapter. The design procedure i.e. preliminary dimensioning, properties of section, distribution of loads, finding of bending moment and shear, losses in prestress, checking of stresses and check for ultimate strength are explained step by step. Chapter 4 In this chapter longitudinal analysis of I girder is explained. It contains detailed sectional property calculation, load calculation, cable layout and calculation for prestress losses and finally checks for flexural stresses and shear checks. v Chapter 5 In this chapter design of deck slab, diaphragm and anchor block is done. Chapter 6 This chapter describes with the help of flow chart structure of computer program made for simplified analysis and design of prestress I type girder bridge. Chapter 7 Conclusions of the study and future scope are explained.