San
Pablo Outlet Tower is located about one mile upstream of the San
Pablo Dam in San Pablo Reservoir. It is a lightly reinforced concrete
cylindrical structure embedded 56 ft in rock formation,
only 53 ft of the tower stands above the ground surface.
The
tower was modeled as two-dimensional (2D) beam-column elements
supported by lateral and vertical foundation springs along the
embedment depth. The interaction with the surrounding and inside
water was represented by added hydrodynamic mass coefficients.
Nominal concrete properties were used but sensitivity of the seismic response to variation of concrete properties was also considered.
The assumed rock properties were used to compute the stiffness
of the foundation springs. Similar to concrete properties, foundation
spring values were also varied to assess their effects on the
seismic performance of the tower. Since the tower operates intermittently,
analyses were carried out with presence or absence of the inside
water to determine which case is more critical for the post-elastic
response analysis. The seismic input included two horizontal components
of acceleration response spectra, representing the maximum design earthquake (MDE) and the
MCE ground motions. The maximum section moments and forces were computed and compared
with the corresponding section capacities.
