CHAPTER 4: THE CONSTRUCTION PROCESS OF SEGMENTAL BRIDGES
The following Chapter 4 presents the important techniques for erection of concrete segmental bridges. Their characteristics are outlined so that understanding of the specific nature of each of these methods can be achieved. Apart from that this chapter deals with the most important issue of construction loads by distinguishing the various types of construction loads and showing their relation to the erection method used for a specific project.
DEVELOPMENT OF PRESTRESSED SEGMENTAL BRIDGES
Application of prestressed concrete for bridge construction was developed by French engineer Eugène Freyssinet, as described in Section 2.1.6, and has spread widely thereafter. Only prestressing made the slender, long-span concrete bridges of today possible. The basic principle of prestressing is to induce an initial compressive force in the concrete that will balance tensile stresses that occur in the member under service conditions before any tensile stresses occur in the concrete and cause cracking. Menn (1990, p126) names the two methods of inducing these stresses in the structure:
By imposed forces from reinforcing steel that is prestressed to a certain degree;
By imposed “artificial displacements of the supports”, e.g. bearings.
The second method according to Menn (1990) is much less used because of high losses of the prestressing force due to concrete creep and shrinkage. Prestressing tendons that are used for the first method consist of high-strength steel and are fabricated as wires, strands, or bars (Nilson and