Chapter 4: The Construction Process of Segmental Bridges
develop new concepts of design, to adopt new methods of calculation such as the computer and to encourage the production and use of improved materials, as high tensile steels and pre-stressed concrete. (…) It is however necessary to emphasize that when leading designers are working as pioneers, only just within the bounds of the engineer’s knowledge, some slight misjudgment, or failure to appreciate every aspect of a new problem may prove disastrous and bring fatal and tragic results. Under these conditions, it is more than ever necessary to employ really adequate margins of safety and to ensure that they are not eroded by various unexpected and accidental factors, including of course, imponderables and human fallibility.”
4.3.2 Influence of Erection Method and Construction Sequence
Typically, every erection method with its succession of construction stages brings about a characteristic stress development in the structure. Examples from different erection methods that are presented in more detail in Section 4.2 illustrated this point.
Wide use of segmental bridge construction, which is described in Section 3.6.1 makes it possible to clearly distinguish steps whenever a new segment is placed. Computer software is used to model these steps and analyze them to ensure that limit stress values are not exceeded at any time.
Goñi (1995) describes how calculations for the Chesapeake and Delaware Canal Bridge were carried out. This cable-stayed bridge was modeled with plane frame analysis software that accounted for the stepwise construction and time-dependent material properties as needed by the structural engineers. Input data that were used for processing are given in the following (Goñi 1995, p31):
“Material properties of each segment including their creep and shrinkage
Data of casting and erection of each box girder segment.
Material properties of each tendon including area, modules of elasticity, relaxation characteristics, and the friction and wobble parameters that affect the force along the length of the tendon.