Civil Engineering Reference
In-Depth Information
FIGURE 13.29
Prestressed concrete piles have been installed, and the excava-
tions for the pile caps and grade beams are complete. The strands at the top of the
pile will be connected to the steel reinforcement in the pile cap and grade beam.
the seismic shaking. The strength of the foundation is due to its monolithic construction,
with the floor slab attached and supported by the grade beams, which are in turn anchored
by the pile caps and the prestressed piles. In addition, the steel columns of the superstruc-
ture can be constructed so that they bear directly on top of the pile caps and have fixed end
connections. This monolithic foundation and the solid connection between the steel col-
umns and piles will enable the structure to resist the seismic shaking.
Usually this foundation system is designed by the structural engineer. The geotechnical
engineer provides various design parameters, such as the estimated depth of the bearing
strata, the allowable end-bearing resistance, allowable skin friction in the bearing material,
allowable passive resistance of the bearing material, and any anticipated downdrag loads
that could be induced on the piles if the upper loose or compressible soil should settle under
its own weight or during the anticipated earthquake. The geotechnical engineer should also
perform pile load tests and inspect the foundation during construction in order to confirm
the design recommendations.
Design Considerations.
There are several important earthquake design considerations
for using piles, as follows:
