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CHAPTER 4: THE CONSTRUCTION PROCESS OF SEGMENTAL BRIDGES - page 33 / 47

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Chapter 4: The Construction Process of Segmental Bridges

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Construction stages are notable steps within the progression of work tasks from the initial site operations startup to the finished structure. These steps can be distinguished by the appearance of the structural system, loading conditions, or other factors.

Load steps can be defined as specific sets of loads on a structure in its current construction stages. These load steps or load cases are combinations of actions that are anticipated to occur at the same time with a certain probability, and are incorporated into analytical calculations with partial factors of safety.

4.3.1 Types of Construction Loads and Influences

Generally, construction loads are by nature of relatively short duration in comparison with the overall planned service life of a structure. Construction loads may influence a structure over a brief time only, e.g. from equipment or material for a new segment that is temporarily stored on an already completed part of the superstructure of a bridge. Construction loads can affect the structure in very unfavorable conditions, e.g. when a crane is located at the tip of a cantilever to place segments. Thus resulting stresses in the structure can even exceed stresses due to permanent and dynamic loads under service.

Real loads are generally distinguished into two classes, dead loads and live loads. During construction the structure has to carry its own weight, its dead load, and the superimposed dead loads of bridge parts that are not structurally important but necessary for service, as e.g. the bridge furniture, the so-called accessories.

Many different live loads influence the structure. In most of all cases, live loads are idealized either as uniformly loaded areas on the superstructure or as singular loads from larger pieces of equipment. Live loads can result from erection equipment, e.g. the launching nose in incremental launching and lifting devices placed on the structure such as cranes and launching girders. Forces are also imposed on the structure through restraints from fixed bearings during construction, e.g. on piers for cantilevering. Along with these structural details, the boundary conditions can still change; e.g. considerable settlements can occur when the soil is initially loaded. Temporary

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