iv
assumption of a fixed base column. It seems that the test connection provided an
additional ductility to the system.
The general trend observed during testing is an increase in the rotational stiffness of the
anchor bolt- bearing pad connection with increasing axial load on the pads. As the lateral
deformation of the foundation element increases, the overall rotational stiffness tends to
decrease. The measured rotational stiffnesses were compared to rotational stiffness
values expected based on a static equilibrium model; this model tends to overpredict the
rotational stiffness compared to measured values. When the measured rotational stiffness
values are implemented in the nonlinear bent models, the overall behavior of the bent
depends on the relative ratio of the rotational stiffness of the connection to the stiffness of
the individual foundation elements. If the foundation element is much stiffer than the
connection, the bent behaves more like a free standing system without rotational restraint.
If the connection is stiffer than the foundation element, the system behaves more like a
bent with locations fixed against rotation.
The resistance factors for laterally and axially loaded drilled shaft are developed based on
test data from sites in North Carolina. Based on Davisson’s method of failure load
interpretation, the resistance factor for the axial loading condition is estimated as 0.38 at a
reliability index of 2.5. If the simulated loads are obtained from the Intermediate
GeoMaterial model as well as using methods in the AASHTO bridge specifications, then
the results, termed a “ combined” approach, show a resistance factor that is equal to 0.57
for the same reliability index. On the other hand, the resistance factors under lateral
loading based on 0.5 inches of lateral deflection at the top of the shaft ( at the ground
level) is estimated as 0.4 at a reliability index of 2.5.