Civil Engineering Reference
In-Depth Information
Figure 3.16
Opening in beam web
3.10.3 Openings in beams
It may be necessary to locate an opening in the web of a beam near the support. If it
is possible to choose the shape and position of this opening, the strut-and-tie analogy
described shows where it will have the minimum effect, Figure 3.16 (a). However, if
the opening has to go in an inconvenient place, the loads may have to be carried round
the hole in Vierendaal action.
A further example of this was a project for a bridge deck carrying an elevated urban
railway shown in Figure 3.16 (b). The deck was in the form of a large prestressed
concrete box girder, with the railway inside and traffi c on the top fl ange. At stations
it was necessary to create regular openings for passengers to exit from the train. The
detailed shape of these openings, as well as their exact spacing, could be tuned so
that they left a viable Warren truss system intact, with prestressed concrete tension
members and compressed concrete struts. If this had not been possible, it would have
been necessary to adopt a far more heavily reinforced Vierendaal girder system.
