Handling and Shipping of Long Span Bridge Beams

Abstract

n the early history of the prestressed concrete industry (up to 1960), bridge beams were very bulky (heavy) and their length seldom exceeded 100 ft (30.5 m). In fact, at that time, 80 ft (24.4 m) beams were considered quite long. With advancing prestressing technology, together with the improvement of materials (especially high strength concrete and high strength prestressing steels), beam sections became progressively more structurally efficient. As a result, beam sections became more slender and the spans much longer. Currently, on the West Coast, 148 ft (45.1 m) beams are common and 130 to 140 ft (39.7 to 42.7 m) bulb T beams and I beams are used frequently. Today, the length limit of bridge members is determined mainly by the mode of transportation (truck steering trailer) and allowable gross weight rather than any arbitrary span restriction. Over the years, as beam sections became more slender and their spans longer, producers soon discovered that these long beams had a tendency to crack or even collapse during handling or shipping unless the lifting points (shipping points) were moved away from the ends of the members, or special braces were attached to the beam. The lateral stability of these types of beams was discussed in the 1960s (see Refs. 1, 2 and 3). Further information on this topic may also he found in Refs. 4 and 5 (published in 1971). Currently, the PCI Design Handbook, in Section 5.2.9, Lateral Stability, briefly describes the problem and suggests solutions. Ref. 4 is the basis for this section. Lateral instability occurs during the handling and shipping of long prestressed bridge beams. This problem arises because of the imperfections