Civil Engineering Reference
In-Depth Information
11.4.3 Prestressed concrete portals
Prestressing the slab allows it to be thinner when this is important, and has the other
advantages described in
11.3.6
. A span/depth ratio of 35-40 is quite practical for a
haunched slab as described above. The detailing of the node is again important, as it
is necessary to create effective continuity between the prestress in the slab, and the
reinforcement in the uprights. Normally this requires that the prestress anchorages are
placed outside the vertical steel, Figure 11.10 (a). It also requires that the reinforcement
of the uprights be anchored beyond its intersection with the tendons. If the uprights
are also prestressed, the anchors for the vertical tendons must be above the horizontal
tendons. This may limit the eccentricity of the horizontal tendons over the supports,
Figure 11.10 (b).
Figure 11.10
Nodes for prestressed portals
Figure 11.11
The effect of prestress parasitic moments on portals
