Precise levelling method - precast

Modelling of “precise levelling” method in precast segmental cantilever construction method is quite simple. Let’s assume that segments are always cast 60 days before the attachment to the cantilever. Further let’s assume that a five-day assembly cycle is used. It means that one segment will be installed in each five days. Individual steps are shown in colour in Fig. 8 where just one cantilever is displayed, i.e. a half of the fixed beam. The time schedule of segmental construction (introduction of the segment into the structure stiffness matrix) for individual segments can be seen in Table 1. The origin of the closing joint in Fig. 8e is related to its introduction into the structure stiffness matrix and not to the casting itself.

 

Dead load of segments and also the equivalent load due to prestressing of segments is defined precisely in the time of installation (attachment) of segments. Loads imposed by possible crane motion or prestressing device can be input as variable loads in the given construction stage or as loads on a completed part of the structure. Dead load of the closing joint is, according to Table 1, applied after 20 days and not in the time of casting, which is 15 days, when this load acts in reality. The reason is that in fact the joint in the model does not exist between days 15 and 20 and therefore, it is not capable of transferring any load. The same applies to other construction approaches described below.

The deflections of a half of the symmetrical structure calculated after the installation of segment 4 made in 1000 days after the two cantilevers have been made monolithic are given in Fig. 9. The deflection curve shows apparent breaks that are not real in fact, but they result from the fact that the deflection of the free-end of the newly attached segment of the model is zero in the time of attachment.