Design Review - Minipe Radial Gate Height Extension
by 400mm
Location - Mannanna Oya (04 No. of Gates)
Assumptions
1. Due to the unavailability of specific details, gate
members sizes are estimated according to the physical
observations when drawing of the gate structure.
2. Design head = 3.871 m / Gate Span = 6m
3.The
safety
factor
of
the
piers
and
other
civil
structuresare as the same as the mechanical structure under
new loadin conditions
according
to
design
norms.In
similar civil structures
safety
factor
will
be
maintained
at
40% higher
than
the
safety
factor
of
the
mechanical structure.According
to
DIN19704 the
safety
factor
of
the
gate under
permanent
load
shall
be
1.3
and
considering fatigue,creep,occational turbulences
and
also
other
impacts,
the
safety factor of the gate
structure shuld be maintained at 1.8.
To minimize the presently observed over flowing (above the top of
gate), the possibility of extending the gates vertical height by
400mm is explored. This analysis is done for checking the holding
capacity of the newly added water volume by extending the
existing vertical stiffness of the gate structure.
The figure given below illustrates the dimensions of the gate
used for the calculations of the report
Figure-1 Basic dimensions for the calculation
Load Calculations
Horizontal component of the water load on the newly added 400mm
gate portion is given by the equation 1,
Wh = BH(H-h/2)
(e1)
Wh = 14.126 kN
Vertical component of the water load on the newly added 4 00mm
gate portion is given by the equation 2,
(e2)
Wv = -4.78 kN
Then the resultant force acting on the newly added gate portion
is given by the equation 3,
(e3)
W = 14.9 kN.
During the above calculations, it was assumed that the total load
acting on the gate portion is equivalent to 30 kN and that the
gate portion is restrained by the welding along the mating faces
of the skin plate and the mating faces of vertical stiffeners.
The following figures illustrates the graphical representations
of the analysis
Figure -2 Solidworks static analysis (Stress)
Assumptions - Total load 30 kN
Material - plain carbon steel
Figure -3 Solidworks Static Analysis (Factor of Safety)
Initially it was decided to add 600mm extension for the gate height
under 4.171m design head. For the above condition load applied on the
gate,
Wh
Wv
new
new
= 504.64 kN
= 133.41 kN
The new resultant force acting on the gate is 521.98kN along the 14.57
degrees to the horizontal axis.
Under the above load conditions, gate arms undergo a safety factor of
approximately 1.1, which is inadvisable for this type of a structure.
Thus gate height extension was limited to 400mm and analyzed under new
load conditions.
Design Head = 3.871m
Hence; Wh
Wv
new (400mm)
new (400mm)
= 436.289 kN
= 127.970 kN
Resultant = 454.67 kN acting along the axis of 16.34 degrees to the
horizontal axis.
Figure 4 - Total load acting on the gate with 400mm extended part
According to the newly acted loads on the gate, the stability and the
strength of the gate arms was checked. Upper and Lower arms results
were as follows.
Each upper and lower arms loads are,
Rup = 137.87 kN
Rlow = 94.49 kN
Figure -5 Stresses analysis of Gate Arms
Figure -6 Factor of Safety analysis of Gate Arms
According to above results that is not advisable for gate
height extension without introduction of any reinforcement
arrangement for the gate arms. Then the analysis was
carried out with arm strengthening process with 8mm MS
plates for both sides of the arm.
Figure -7 Factor of Safety analysis of Gate Arms with reinforcements
Conclusion
1. Addition of 400mm vertical height to the existing gate structure
is recommended with necessary reinforcements to the gated
structure since the new load conditions would result the system
undergoing a minimum factor of safety of 1.51. Then with the
reinforcements it can be improved upto 3 as per above mentioned
analysis results.
2. It is also recommended to introduce a side stiffener plate to the
gate arm at the connection point before the trunnion assembly
according to the drawing provided.
3. Trunnion assembly should be needed to strengthen as per the given
sketch, since the embedded J- bolts' present condition is not
discoverable. This can be mentioned as an essential remedy.
Figure -8 proposed trunnion-strengthening method
