 |
In
early 1998 construction began on Guam’s first privately
funded and operated power-generating facility. Piti Power
Plant Units 8 and 9 were constructed of structural steel
with precast concrete perimeter wall panels. The
slow-rotation diesel generator was exhausted via a 150 foot
(46 m) tall structural steel stack, consisting of two inner
oval-shaped stacks, surrounded by a larger circular-shaped
stack.
Shortly after the construction of the concrete foundation
pedestal for the stack, the contractor undertook a series of
pullout tests of the large diameter anchor bolts. All tested
anchor bolts failed at pullout loads of less than 10% of
that load required to be resisted. It was revealed that the
220 smooth (unthreaded) anchor bolts, without an end-bearing
plate, were installed with the shafts of all anchor bolts
being painted. It was also discovered that the embedment
length of the anchor bolts was insufficient to resist the
accumulated pullout loads from a group of anchor bolts for
the outer stack. The mode of failure in this instance was a
cone-failure mechanism due to group load effects.
To reestablish the anchor bolt pullout capacity, each bolt
was removed, sandblasted, and the hole from which it was
removed was acid etched. The anchor bolts were replaced and
epoxy-resin was pressure-injected into the small annular
space. To increase the global pullout capacity of the
pedestal due to the inadequate anchor bolt embedment length,
additional #10 vertical reinforcing steel was epoxy-doweled
into 6 foot (2 m) deep concrete core holes. The size and
depth of the reinforcing steel enabled the potential
concrete cone-failure surface to be strengthened. To verify
that all anchor bolts were able to withstand the intended
loads, all 220 anchor bolts were proof loaded to their
intended force for a period of one minute. The work was
carried out in 21 days.
|
LOGIN
