Chapter 4: The Construction Process of Segmental Bridges
the stability of precast members and prestressing should be taken into account. “Environmental loads… should be considered during construction using an appropriate return period or reduced severity. Lower load factors may be used to account for the acceptability of higher temporary stress levels” (ACI 1995, p51). The aforementioned load factors are provided in tables in the same code.
How the actual process has to be accomplished in detail remains the structural engineer’s task. Close cooperation of designer and contractor in development of the construction sequence contributes to quality.
For better understanding of the relationship between structures under construction and actions influencing them it is useful to get a clear definition of the technical terms related to this topic. The nature of actions has been explained in Section 3.5.3 as any loads or restrained deformations that can cause stresses within the structural system. The term construction loads should in this context be understood as the broader sense of any actions that occur during construction of the structure prior to normal service conditions.
Then again, the concept of construction loads needs to be extended by consideration of the uncompleted structure during construction, which may not have reached full resistance to imposed actions.
The term erection method denotes the physical means of putting the foundations, bridge substructure, and especially its superstructure into place. Every type of erection method requires certain equipment and site installations to carry out the work tasks. The erection methods goes along with specific limitations imposed on the flow of work tasks to be scheduled, e.g. that bridge piers have to be finished prior to begin of incremental launching of a bridge superstructure.
The construction sequence is the specific succession of work tasks for one particular project developed under consideration of the erection method chosen for its conditions and restraints for economic construction.