Trash Rack Calculation e6i

Design Calculations for Irrigation Project

Trash Rack Design: Slope provided = 15 Degrees (As per IS:11388 (1995) - Clause -5) C/C spacing of bars provided = Depth of bars provided = Thickness of bars

100

mm

60

mm

= 12 mm (As per IS:11388 (1995) - Clause -8.5.1)

So, opening size

=

Height of Trash Rack = = Total width provided

=

88

2 * 3.28 6.56 2940

Total opening width = =

mm

m m mm

88mm * 26 No. + 76mm * 2 No. 2440 mm

Design Discharge

=

6.9

So, Velocity

=

0.431

m/sec

0.862

m/sec

If 50% clogged, then velocity =

m3/sec

which is leass than 1.5 m/sec (As per IS:11388 (1995)) Check for lateral : Max. lateral unsuppored length of trash rack bar = Maximum allowed length = = =

730 mm 70 * thickness 70*12 840 mm

Therefore, track bars are safe.

Design of trash rack bars,

(Clause 8.3 of IS:11388)

Design differential head load=

6

m

So, applying an UDL of above load, with ends of trash racks as fixed, Max. beanding moment (at ends) = w.L.L/12 here, w = δ.g.h * width of bars = 0.7056 N/mm So, Max BM =

31334.5 Nmm

Maximim stress = M.y / I where y = distance of farthest fibre from centroid and I = moment of inertia y= I=

depth of bars/2 = b.d.d.d/12 =

Max. stress =

30 mm 216000 mm4

4.352

N/mm2

As per Clause - 8.5 of the code, Allowable failure stress of bars = Yield stress * (1.23 - 0.0153 L/t) Yield Stress =

250

So, Allowable failure stress =

N/mm2 74.813

N/mm2

This is more than the actual max. stress generated So, Safe.

Intake Design For bell mouth opening: curve provided should be: x2

+

a

2

According to Clause - 5.3.2 of IS-11570, a = 1.1 H

y2 b

2

=

1

b = 0.291 H where H = diameter of conduit = 3000mm

so, a = and b =

3300 875

So, bell mouth provided is having equation: x2 (3300)^2

+

y2 (875)^2

=

1

And for vertical sides, the corresponding equation is, x2

+

a2

y2

=

1

b2

(As per fig. - 8 of IS-11570 and fig.13 IS-9761) a = 0.55 b b = 0.214 b here b = width of conduit So, bell mouth provided is having equation: x2 (1650)^2

+

y2 (643)^2

=

1

om centroid