failure guidelines of the American Society of
Mechanical Engineers. 1 A deformed model
with superfcial corrosion was used.
Te geometry of the spillway gate was gener-
ated based on engineering drawings provided
by Mercury and photographic documentation
taken during the site visits. Te models were
generated using the fnite element modeling
software Abaqus CAE 6. 12-1. Two diferent
models were generated:
• As-designed model with no corrosion
• Deformed model based on reported vertical
defection with superfcial corrosion.
To reduce the computational cost of the
fnite element analysis, some non-load-bearing
features of the spillway gate were not included
as part of the modelled geometry. Tese
included the diagonal reinforcement plate
between beams A1 and A2 (see Figure 1 on
page 34); latching racks; and rope retainers,
guides and anchor brackets.
Based on engineering drawings provided by
Mercury, the skinplate material was specifed as BS 4360:1968: Grade 43A, with a
minimum tensile strength of 430 MPa, yield
strength of 230 MPa, and elongation of 20%.
Based on these properties, an elastic-plastic
stress-strain curve was generated based on the
Ramberg-Osgood methodology found in the
ASME FFS- 1 standard. 1
Loads and boundary conditions
Te applied hydrostatic load to the two
models was based on a maximum operating
level of 52.9 m, per the Hydraulic Structures
Hydrological Data Book. 2
Boundary conditions were applied to the
side joists to represent their interaction with
the spillway gate slots. Only rotation with
respect to their own axes was allowed.
Stress results were obtained for the two
diferent scenarios considered. Te highest
level of stresses occurred at the bottom of
the gate and was due to hydrostatic loading.
Te locations that exhibit the highest levels
of tensile stresses are at the top plates of the
two bottom I-beams. Te deformed model
with superfcial corrosion undergoes a higher
level of stresses, especially at the center of the
top plate of beam A3.
Mercury requested an additional assessment
to evaluate the possible efect of the gate
deformation and corrosion on its operation.
Terefore, reaction forces at the side joists
were also extracted, using both models, from
the results for comparison purposes.
The direction and magnitude of the
extracted reaction forces was determined
for both models, and no diference was
found between the as-designed model with
no corrosion and the deformed model with
Deformation load estimation
Te stress results were subsequently used
to estimate the required load to cause the
current spillway gate deformation. Te process
of estimating this deformation load was done
in two steps by: