114
modulus value does not include the initial part of the stress- strain curve because this
deformation was due to a seating error. Table 25 presents the input values for the
predicted rotational stiffness.
Table 25. Input parameters for rotational stiffness model
Parameters Values Units Values Units
t 3.563 inch 9.05 cm
d 28 inch 71.12 cm
Es 29000000 psi 19957840 kN/ cm2
Ep 16714 psi 11503 kN/ cm2
As 6.28 inch2 40.5 cm2
Ap 325 inch2 2097 cm2
Using the parameters in Table 25, a rotational stiffness was calculated and directly
compared to the results from full scale testing in Figure 104. The comparative results
show that the theoretical equation overestimates the measured response from the full
scale tests. The predicted rotational stiffness from Equation 13 yielded a rotation
stiffness of approximately 1700 k- ft/ degree ( 131,000 kN- m/ rad) which is roughly five
times greater than the average rotational stiffness from the measured results.
Possible reasons the predicted rotational stiffness was greater than the measured results
could be attributed to several factors. Below is a list of possible sources of error:
i. The elastic modulus assumed for the bearing pad has a significant effect on
the connectionâ€™s rotational stiffness. The elastic modulus was taken from
independent, compressive tests, with stress applied uniformly on the bearing
pads. In the full scale testing, the bearing pad experienced non- uniform
compressive stresses.