Large diameter steel tubular piles installed vertically or on a slight rake, offer
many advantages as the foundations of major overwater bridge in regions of high
seismicity. By proper selection of diameter and wall thickness, an optimum
balance between stiffness and strength can be achieved. Under strong seismic
motion, the piles will deflect and bend so as to reduce the acceleration forces
transmitted to the superstructure, while still limiting drift. A major advantage of
this concept is that the mass of the footing block is significantly reduced from that
of the conventional pier. The design of the footing block requires great care in
order to transfer the high shears and moments. Where the soils consist of
significant depths of sediments, the kinematic interaction of soils, piles and
structures must be considered. Moments will be a maximum just under the
footing block. Filling the top portion of the pile with concrete will prevent local
buckling and assure ductile behavior even under overload. Typically the piles will
be long, with most or all of their support furnished by friction and will require the
use of very large pile hammers to achieve the required capacities. Where the
piles are founded on rock or in hardpan, sockets will be drilled and filled with
reinforced concrete. For these piles, high moments can occur both at the head
and just below the rock surface, so the concrete infill should extend the full
length. This paper describes the use of tubular piles driven through the deep silty
sands of the Jamuna River, Bangladesh, and also where socketed into the nearsurface
rock for the mail pylon pier of the new San Francisco-Oakland East Bay
Bridge in California.
Author: Ben C. Gerwick, Jr. & Robert B. Bittner, Ben C. Gerwick Inc.
Publisher: DFI