Study Material for Gates and Hoists

Introduction

� For optimum benefit controlled releases of water is of immense importance. Thus

hydraulic gates form the most vital component.

Though forms a very small component of the total project cost most crucial

parameter in determining the success of the project. With the increase in size,

head & discharge the complexities associated with gate structures have

increased manifold.Major causes of failure & malfunctioning attributed to faulty

hydraulic design / improper operation. Phenomenon of cavitation and vibration

threatens the very safety of the hydraulic structure.

� Thus the precise need for careful design.

NEED:

i. Gates are subjected to high static water loads & dynamic loading condition.

ii. Gates have to cater to complex flow conditions.

iii. Variation in flow conditions develops sub atmospheric pressures in the gate body

& its surroundings. Thus causing cavitations, vibration, down pull & uplift forces.

iv. Hence the need for proper inlet shapes of the conduit, its alignment, smoothness

of fluid path, profile of conduit down stream of gate slot ( fig below)

FACTORS GOVERNING THE HYDRAULIC DESIGN OF GATES:

i. Flow of water past various components – streamlined such that eddies or

vortices are avoided.

ii. Pressure – shall be positive to avoid leakage.

iii. Vibrations – kept minimum.

Classification of gates

i. High head - 30 m and above head

ii. Medium head - 15 m to 30 m

iii. Low head - less than 15 m

Types of Gates

1. Vertical Lift Gate

a. Fixed Wheel Gate

b. Slide Gate

2. Radial Gate

Design of Fixed Wheel Gate

Materials for the Components of Fixed Wheel Gates

Sl. No Component Part Recommended Materials Ref to, IS No

Cast steel 1030:1998

Cast iron 210 : 1993

Wrought steel 1

Wheel

Forged steel 2004 : 1991

2

Bearing / Bushing Anti-friction bearing / bronze,

phosphor bronze, aluminum

bronze, self lubricating bushing of

high strength brass castings

318 : 1981

305 : 1981

3

Wheel pins or axles Chrome nickel steel or corrosion

resistance steel, mild steel with

nickel or hard chromium plating

2004 : 1991

2062 : 1999

1068 : 1993

1337 : 1993

4

Structural parts of

gate leaf, track

base, etc

Carbon steel, structural steel 1875 : 1992

2062 : 1999

8500 : 1991

5 Seal Rubber 11855 : 1986

6 Wheel track a) Stainless steel 1570 (Part 5) : 1985

b) Corrosion resistance steel

7 Seal seat Stainless steel plate 1570 (Part 5) : 1985

8 Seal base, seal

seat base sill beam.

Structural steel of convenient

shape

2062 : 1999

8500 : 1991

9

Seal clamp Structural steel

Stainless steel

2062 : 1999

8500 : 1991

6603 : 2001

10

Guide Structural steel or corrosion

resistance steel or stainless steel

2062 : 1999

8500 : 1991

6603 : 2001

11 Springs Springs steel

Stainless steel

6527 : 1995

2062 : 1999

12 Anchor bolts Structural steel 6527 : 1995

13

Guide rollers and

guide shoes

Structural steel or corrosion

resistance steel, cast iron, cast

steel or forged steel

2062 : 1999

8500 : 1991

210 : 1993

1030 : 1998

2004 : 1991

PERMISSIBLE MONOAXIAL STRESSES FOR STRUCTURAL COMPONENTS

OF HYDRAULIC GATES

Wet Condition Dry Condition

Sl.No Material and Type Accessible Inaccessible

Accessible

Inaccessi

ble

a) Structural Steel

1 Direct compression 0.45 0.40 0.55 0.45

2 Compression /

Tension in bending 0.45 0.40 0.55 0.45

3 Direct tension 0.45 0.40 0.55 0.45

4 Shear stress 0.35 0.30 0.40 0.35

5 Combined stress 0.60 0.50 0.75 0.60

6 Bearing stress 0.65 0.45 0.75 0.65

b) Bronze or Brass

Bearing stress 0.035 UTS 0.030 UTS 0.040 UTS 0.035 UTS

Gate shall satisfy following requirements

a. Water light, leakage not more than 5 to 10 lit / m length of seal

b. Capable of being raised or lowered at specified speed

c. Partial open position regulation to pars required discharge.

Shall be designed for

a. Hydrostatic

b. Hydrodynamic

c. Wave effects

d. Seismic load

e. Ice formation.

• In addition to water load designed (if required)

Head to account sub-atmospheric pressures down stream of Gates in conducts / sluices

Operating Condition

i. Under its own weight with ballast

ii. Under its own weight without ballast

HYDRAULIC DESIGN FEATURES OF GATES LAYOUT

1 Gate slot

2 Gate lip

3 Aeration

4 Hydro-dynamic forces

5 Seal design

1. GATE SLOT:

i. Gate slot size kept to a minimum to avoid low pressure zone causing

cavitation.

ii. For fixed wheel gates slots are wider & deeper.

iii. Slots by virtue of discontinuity produce vortices

iv. Expansion of jet causes

a) vortices and eddies

b) Creates zone of negative pressure on the side walls of the conduit

v. Modern trend to have tamper 1/10 to 1/12 & rounded corners d/s up to 30 m

head and 1/24 or flatter beyond

vi. Optimum ratio w/d 1.4 to 1.8

vii. Type 3 & 4 for heads > 25 m or velocity > 25 m/s

viii. R = 0.1 D (R = 3 to 5 cm)

ix. Provision of liberal ventilation on the d/s

Gate Slot

i. It is extremely important to provide smooth continuous surface downstream of

gates (smoothness 250 microns or better). Abrupt into-the- flow offsets and

irregularities in flow surfaces should be avoided or must be grounded to a

smooth slope 1:40 to 1:60 for flow velocities up to 12m/sec and over 24m/sec

respectively.

ii. It is recommended to provide securely anchored and stiffened steel liners in

the conduits immediately upstream and downstream of the gate slots and

including the gate slots for all high head installations. In general, the liner should

extend at least 1 m upstream of emergency gate and 3m downstream of the

service gate slot (See Fig I). At heads above 50rn, it is recommended to protect

the fluid way surfaces with stainless steel linings. In boulder flows, hardened

material even with BHN as high as 400 have been employed as lining material.

iii. Provide minimum Centre to Centre spacing in between the two gate slots (i.e.

Service & Emergency gates) about 4 times the upstream slot width (W) from

hydraulic considerations, subject to a maximum of 1.5 times the conduit

diameter.

iv. Provision of "Slot flow deflector" with deflection angle upto 45° on the side

walls of the conduit to reduce the vortex action in the slots for gates with

upstream skin plate and sealing can be considered as a remedial measure. (

Refer under hydrodynamic forces also)

v. Tapering of downstream face of gate slot up to an angle of 45° or flatter to a

height of (Urn from the gate sill can be considered for upstream sealing gates to

prevent accumulation of debris within the gate slot.

vi. Provision of "slot fillers" can be made for spillway stop logs / bulkhead slots

upstream of spillway gates to bridge the slot and smoothen the pathway.

vii. Rectangular gate slots should not be provided except for very low head gates.

viii. Width (W) of gate slot should be kept as small as practicable. Depth (D) of slot

has little effect on cavitation hazard. The optimum WID ratio falls in the range

of 1.4 to 1.8. In practice, higher values can be adopted as per physical

requirements.

ix. For gates operating under a head of say 10m or more, the downstream edge of

the gate slot should be off-set to reduce the cavitation hazard. A downstream

offset (If 0.075 to 0.10 of the slot width (W) with gradient of 1/1 0 to 1/12 for

heads up to 30 m & 1/24 or flatter beyond 30m head, downstream of the gate

slot and a rounded point of intersection with Radius 'R' as 0.10 times the D (say

R=3 cm to 5 cm) is recommended. Upstream slot face should have a sharp and

not rounded corner.

2. GATE LIP:

i. Designed such that pressures are positive always.

ii. Flat lip for full gate thickness causes pockets of high negative pressures,

vibrations, and cavitation & down pull.

iii. Design of bottom lip has to meet the following requirements

a) Minimum cavitations hazard

b) Minimum vibration of the gate

c) Minimum up thrust forces

d) Minimum down pull forces

e) Minimum rate of change of down pull force during openings

f) Minimum air demand

g) Sound structure at the bottom portion of the gate

GATE LIP:

i. Gate leaf with flat bottom must be avoided.

ii. Gate bottom lip sloping at 45° to the downstrea m with sharp bottom and proper

negotiating curve should be adopted for gates with downstream sealing and

downstream (or upstream) skin plates. It may be noted that lip angles up to 60°

have also been used. It is advisable to provide drain holes in the curved lip plate

of the gate and also in webs of the horizontal beams covered by the curved plate.

iii. Avoid extended vertical lip type design at bottom for gates with downstream

sealing and downstream skin plate particularly for such gates which are meant

for operation at small gate openings.

iv. Locate the downstream flange of the bottom most girder at least at 0.6 times the

girder depth (i.e. 30° angle) to prevent the jet fr om hitting the gate bottom For

gates with upstream skin plate and upstream sealing, CWPRS recommends an

angle of 45° between the imaginary line joining the controlling edge of the gate

and downstream edge of the girder in such cases. However, location of bottom

most girders should be done judiciously as higher angles for ensuring clearance

of jet can sometimes cause development of uplift forces.

v. The minimum gate opening for regulating gates should not be less than one half

of the seating bottom lip of the gate or 75rnrn, whichever is more.

vi. Provide a stainless steel overlay along the gate leaf sloping bottom to resist

corrosion and cavitation damage.

CLASSIFICATION OF LIP SHAPES

i. Flat lip

ii. Vertical or extended lip

iii. Vertical or extended lip

iv. Sloping lip

v. 45dg to 60dg

vi. In some cases even 29dg to 35dg

vii. To minimize differential pressures a few drain holes are drilled in curved bottom

lip and web of lowest horizontal girder (figure below)

3. AERATION:

i. Air supply prevents dropping down of the pressure to vapor pressure reducing

chances of cavitation.

ii. Factors affecting air demand

a) Percentage of gate opening

b) Type of flow

c) Velocity

d) Conduit profile

e) Bottom shape of the gate

f) Head loss in the air vent

Aeration

i. The location and sizing of air vents is critical for minimizing cavitation and

vibration problems associated with regulating services of gated outlets. Such

installations should be provided with adequate air supply downstream of the

gate. The air vent should be located as near as possible to the gate.

ii. In the absence of model studies, volume of air required can be estimated from

the following expression for purposes of preliminary sizing of air vents for

regulating gates.

Qa / Qw = 0.03 (Fr - 1)1.06.

Where,

Qa = Volume of air required in m3/s;

Qw = Outlet discharge in m3/s;

Fr = Froude No. at vena contract i.e. just downstream of the gate;

iii. The air requirement for widely expanding sluices may be lesser than that derived

from above formula.

iv. For determining air vent size, the air velocity inside the pipe can be assumed up

to 50 m/s and the pressure drop inside the conduit pipe should be limited to 0.15

kgf/cm2. For non regulating type gates, higher air velocities and pressure drops

can be permitted.

v. The Froude Number is estimated based on the velocity and depth at the vena-

contract. Velocity is estimated based on the head corresponding' to maximum

reservoir level neglecting losses. The depth is estimated based on gate

contraction coefficient of 0.80 for 45o lip and 0.60 for a sharp-edged gate lip.

vi. The maximum air demand may be assumed to occur at a gate opening of 80%.

vii. Head loss considered in the design of air vents consists of those caused by

notches, bends, cross-sectional area changes, and friction and exit conditions.

Loss coefficients identical to those for water flow may be used for air flow in

vents.

viii. It is recommended that air vent pipe should have minimum bends and the angle

of bend (if at all provided) should be as obtuse as possible.

ix. The air vent pipe should be taken sufficiently above the maximum reservoir level

preferably on the downstream face of the structure so that there is no

interference with the airflow and no risk to the personnel by the strong inflow of

air during gate operation. If the air vent pipe opens into a gallery at a lower level,

an air valve should be provided at its end for air to pass through.

x. The air vent pipes of the adjoining sluices should not be joined into a common

header.

xi. The space between the downstream side of the gate and the sh8ft wall should

not substitute for an air vent for meeting air demand requirements except when

the sealing is effective for full travel of the gate.' However, it is desirable to

provide a separate air vent.

xii. It is recommended to make a nominal provision of air vent downstream of

emergency gate of conduits to supply/dispel air.

xiii. Provision of air ducts of depth of 300 mm to 500 mm can be considered fur air

circulation at such locations where negative pressures can occur to prevent

cavitation at flow separation points around the gate.

Design involves the following components

a. Skin plate

b. Vertical and horizontal stiffeners and main girders

c. Wheels and wheel tracks

d. Seals and accessories

e. Guide rollers / guide shoes

f. Wheel track and track base

g. Guides

h. Bearing Pad

i. Seal seat, seal base and sill beam and

j. Anchorages

� Skin plate

i.In bending across stiffeners, horizontal girders or as panels and

ii.In bending, co acting with stiffeners and or horizontal girders

� Horizontal and vertical stiffeners and main girders

i. Designed as simply supported or continuous beam

ii. Main horizontal girders carry almost equal loads

iii. End vertical girders as continuous beams resting on wheel centre points with

concentrated loads coming from horizontal girders at points of meeting end

vertical girders.

� HYDRO-DYNAMIC FORCES DETERMINED BY

i. Kings & Petricat curves

ii. Model studies.

iii. Magnitude of down pull is a function of

a) Location of the gate

b) Shape of the gate bottom

c) Flow passages around the gate top

d) Location of gate seals

e) Initial discharge

f) Air venting

g) Speed of gate travel

BASIC EQUATION:

P = W + A (d - u) w

WHERE:

P = HYDRAULIC AND GRAVITY FORCES.

W = DRY WEIGHT OF GATE

A = CROSS SECTIONAL AREA OF GATE

d = AVERAGE DOWN THRUST PER UNIT OF

AREA ON TOP OF GATE

u = AVERAGE UP THRUST PER UNIT OF AREA

ON SLOPING BOTTOM OF GATE

w = SPECIFIC WEIGHT OF WATER

� Hydrodynamic Forces

i. Broadly speaking, the magnitude of down pulI can be controlled in two ways;

through KB (coefficient of pressure' on bottom) by the design of geometry of the

gate bottom i.e. design of gate lip, and through KT (coefficient of pressure on top)

by the dimensioning of the flow passages around the upper portion of the gate.

ii. Down pulI reduces with an increase in angle of inclination of bottom

Consideration for structural adequacy should also be kept in view while deciding

the angle of inclination of bottom ‘

iii. Extremely flat lips cause the flow to separate completely from the gate lip and

hence cause a substantial increase in the downpulI and should not be provided.

iv. Both the field observations and model tests have shown that 450 sloping lip is

the best suited from hydrodynamic and structural considerations.

v. Supply of air to the downstream of gate reduces downpull force.

vi. Gates with upstream skin plate and upstream sealing produce nominal downpull

forces. It may be noted here that in spite of reduction in downpull in case of gates

with upstream sealing, these have only been used for relatively low heads for the

regulating service because of a number of problems resulting from extensive

vortex action in the gate slot.

vii. Incase of gates which are used for filling-up by crack-opening (such as Intake

gates for Power Houses used for filling Penstocks), care should be taken to

ensure that area of crack opening is smaller than area between the downstream

edge of the gate and the gate shaft, normally designated as 'Back of the gate

orifice' which otherwise could cause catapulting of gate. Such gates should

advisably be equipped with hydraulic hoist to absorb any uplift forces which may

develop because of the over-shooting of crack opened position.

viii. Downstream sealing quick shut-off ( or emergency gates) can be configured in

such a manner that the bottom seal is offset towards upstream side with respect

to top seal so as to generate dependable down pull to ensure self-closure of

gate.

ix. Incorporation of "Slot Flow Arrestors" in the gate slots can considerably reduce

the down pull force for gates with upstream skin plate and upstream seal, by

controlling the slot flow circulation vis-à-vis vertical upward flow, as a remedial

measure.

x. Incorporation of "Slot Flow Deflectors” upstream of gate slots to control slot

vortex flow can also considerably reduce the magnitude of downpull force for

gates with upstream skin plate and upstream seal, as a remedial measure. It

should be noted that such measures also cause reduction of flow passages.

� SEAL DESIGN:

i. Selection of sealing arrangement d/s or u/s

ii. Items affecting sealing method (fig below)

a) Hydraulic down pull & uplift forces on the gate

b) Gate operating equipment

c) Gate structural design

d) Seal performance

e) Aeration

f) Access for inspection.

� Seal Design

i. Upstream sealing gates have more chances of leakage as compared to

downstream sealing.

ii. A seal guard is usually provided for those installations, where presence of debris

is likely to damage the gate seals, particularly in case of bottom seals.

iii. Solid bulb music note seals are recommended at sides & top of gates operated

under medium head (i.e. at a head of water >15m but less than 30m). These

seals are also recommended for high head installations' (i.e. water head > 30m)

as side seals. However, double stem seals are recommended for application as

top seals because music note type seals at this location particularly for upstream

sealing gates suffer from rolling action, when the gate is moved

iv. Double stem seals should be clamped only on the extreme edges of seals.

v. Projection of gate bottom seal should be restricted to the minimum possible as

per design requirements as it can become one of the sources of gate vibration.

vi. Metal to metal seals are used for such high head installation, where access for

maintenance of sealing arrangements is difficult.

vii. Deflection of top and bottom cantilever portions of gates, particularly in case of

upstream sealing gates should be suitably restricted to ensure that sealing is

maintained.

viii. For gates with upstream skin plate and upstream sealing, the provision of contact

plate (i.e. seal seat) with height equal to gate height should be provided for

improving the flow conditions and elimination of curtain flow from top of gate.

Such provision also helps in reducing the magnitude of downpull force.

ix. The top seal radial gates are provided with two top seals, one fixed to the gate

and the other fixed to the embedded frame to minimize water spray in the gate

chamber during partial operation of gate.

x. It should be noted that substantial leakage past high head gates can lead to silt

cavitation (abrasive action of silt laden water) and vibrations of the structure.

xi. The high head Fixed-wheel gates with upstream sealing arrangement should

desirably be provided with two rows of top seals fixed on the skin plate to

mitigate occurrence of vibration.

xii. Fluoro-carbon (Teflon) Cladded seals should not be used for those gates which

are to be operated under silt laden conditions.

xiii. Upstream seal gates with upstream skin plate are preferable for silt sluices or

bottom outlets. Downstream sealing gates should not be used in such situation

unless provided with seals on upstream side also to prevent entry of silt into the

gate slots.

Design Aspects of Radial Gate

1 Design aspects of the Radial gate involves

i) Layout i.e. overall planning of the radial gate.

ii) Detailed design of component parts

2 Overall Planning Covers

i) Location of the Trunnion

ii) Radius of the gate

iii) Location of the sill

iv) Location of type of the hoist

3 Location of the trunnion (Clause 6.2 of 4633)

i) Standard practice 1500 mm clearance between the upper nappe and

trunnion pin

ii) Economical design of trunnion girder and anchorages 1/3H – Resultant

hydraulic thrust is close to horizontal.

iii) For smooth operation, proper maintenance 0.5 H to 0.75 H.

4 Radius of the Gate (Clause 6.3 )

i) Recommended radius H to 1.25 H

ii) Larger radius increases the pier dimensions.

5 Location of the sill (Clause 6.4)

i) Slightly down stream of crest to avoid cavitations of the down stream

glacis.

ii) General guidelines 0.30 to 0.80 m below the crest

6 Location of the hoist (Clause 6.5)

a) Down stream

i) Hoist force is at the largest possible lever arm.

ii) Hoisting angle does not change considerably during the hoisting

operation.

iii) Involves larger pier sizes

b) Up stream

i) Larger hoisting capacities.

7 Design of structural parts (Clause 6.1 (b)

i) Skin plate and stiffeners

ii) Horizontal girders

iii) Arms

iv) Trunnion hub

v) Trunnion pin

vi) Trunnion bush or bearing

vii) Trunnion brackets

viii) Trunnion girder or yoke girder

ix) Load carrying anchors

x) Anchorage girder

xi) Thrust block

xii) Trunnion tie

xiii) Seals

xiv) Seal seat, seal base and sill beam

xv) Guide roller

xvi) Anchor bolt

Materials for Parts of Radial Gates

Sl.

No Component part

Recommended

Materials

Ref to

IS No.

1. Skin plate, stiffeners, horizontal girders, arms,

bracings, tie members, anchorage girder, yoke girder,

Structural Steel 808

2062

embedded girder, rest girder, load carrying anchors. 8500

2.

Guide rollers

Cast Steel

Structural Steel

Forged Steel

Wrought steel

Cast iron

1030

2062

1875

2004

1570

210

3. Trunnion, hub and bracket Cast steel

Structural Steel

1030

2062

4.

Pin Structural Steel

Cast steel

Forged Steel

Corrosion resisting

Steel

2062

8500

1030

1875

2004

6603

Materials for Parts of Radial Gates

5.

Bushing Bronze / self

Lubricating

Bushing

305

306

318

6. Seal Seat Stainless steel plate 6911

7.

Seal base, seal-seat

base and sill beam

Structural steel 2062

8500

8. Pre stressed anchor rods

9.

Pre stressed anchor

cables, rods, HDPE

sheath and Corrosion

resistant grease

PERMISSIBLE MONOAXIAL STRESSES FOR STRUCTURAL COMPONENTS OF

HYDRAULIC GATES

Wet Condition Dry Condition

S.No Material and type

of Stress Accessible

(YP)

Inaccessible

(YP)

Accessible

(YP)

Inaccessible

(YP)

10. Structural Steel

1

Direct compression

and compression

bending

0.45 0.40 0.55 0.45

2 Direct tension and

tension bending 0.45 0.40 0.55 0.45

3 Shear Stress 0.35 0.30 0.40 0.35

4 Combined stress 0.60 0.50 0.75 0.60

5 Bearing Stress 0.65 0.45 0.75 0.65

11. Bronze

Direct bearing stress 0.035 0.030 0.040 0.035

8 Design of skin plate and stiffeners (Clause 6.6)

a) As per clause 6.6.2 the skin plate shall be designed for either of the

following conditions unless more precise methods are available.

i) In bending across the stiffeners or horizontal girders as applicable or

ii) As panels in accordance with the procedure and support conditions

given in Annexure ‘C’ of code 4623.

iii) Minimum thickness of stain plate excluding corrosion allowance may be

8 mm

iv) For large size crest gates it is economical to use two or more sizes of

the plates at different sections.

b) The skin plate while designing the stiffeners and horizontal girders can be

considered as [8 (i) (a)]

i) Co-acting width of skin plate is taken as the least of the following.

i. 40t + B where

t = Thickness of skin plate

B = Width of stiffener flange in contact with the skin plate

ii. 0.11 span and

iii. Centre-to-Centre of stiffeners and girders width of the skin plate

acting with beam or stiffeners in panel fabrication [ as per point 8

(b)] shall be worked out as per Annexure ‘D’ of 4623.

iv. The stresses shall be combined as per formula (6.6.6)

√ x 2 + y2 – x y +3 T2xy

Where

v = Combined stress

x = Sum of stresses along X – axis

y = Sum of stresses along y – axis

Txy = Sum of shear stresses in x – y plane.

duly considering appropriate signs x & y

i. Designed skin plate thickness to be increased by at least

1.5 mm for corrosion (6.6.8)

9 Design of Horizontal girders

a) Number of Horizontal girders and arms (6.7.1)

i) For height of gate upto 8.5 m – 2 No

ii) For height of gate upto 8.5 m and 12 m – 3 Nos.

iii) For height of gate upto above 12 m – 4 or more

b) In the case of the vertical stiffeners designed as continuous beam the

girders may be so spaced that bending moment in the vertical stiffeners

at the horizontal girders are about equal.

c) Girders shall be designed taking fixity at arms support. For inclined arms

the girders shall also be designed for the compressive stress induced

d) Girders shall be checked for shear at the point of support by the arms for

values not exceeding Annexure ‘B’ of 4623 (6.7.5)

10 Stiffeners and Bracings for Horizontal girders (6.7.6) Design of the

bearing and intermediate stiffeners shall be as indicated in IS800.

11 Arms : (6.8)

i) As many pairs of arms as the number of horizontal girders shall be used

unless vertical end girders are provided.

ii) Inclined arms used to economize on the horizontal girders.

iii) Designed as columns for the axial load and bending moment

transmitted by horizontal girders and shall be as per IS 800.

iv) The inclined arms fixed to horizontal girders at about one-fifth of the

width of the gate span from each end of girder.

v) The joints between the arms and the horizontal girders shall be

designed against the side thrust due to the inclination of the arms.

vi) Bracings connecting the arms spaced to satisfy equal l/r ratio of the

arms in both longitudinal and transverse directions is nearly equal.

12 Trunnion Hubs (6.9)

i) Minimum thickness of steel hub

t = 0.3 d upto 450 mm dia. shaft

= 0.25 d subject to a minimum of 135 mm for shafts above 450 mm

dia.

where,

t = Hub thickness and

d = diameter of the pin.

For large size gates hub may be designed as thick cylinder

13 Trunnion pins (6.10)

i) May be solid or hollow and designed against bending for the total load

transferred through the trunnion hub

ii) Check for shear and bearing also due to the same load.

iii) The bending, bearing and shear stress shall not exceed 0.33 YP, 0.35

UTS and 0.25 YP respectively.

iv) The pin shall be a medium fit in the bearing lugs and locked.

v) The trunnion pin shall be subjected to ultrasonic / radiographic tests to

ensure soundness against manufacturing defects.

vi) For materials other than corrosion resistant steel pin shall be coated

with hard chromium plating to a minimum thickness of 50 microns.

14 Trunnion Bush / Bearing (6.11)

a) Material

i) Slide type bronze bushing or self lubricating bush bearings.

ii) Antifriction roller bearings.

iii) Spherical plain bearings.

b) Minimum thickness of bushing in mm

= 0.08d + 3 not less than 12mm

Where‘d’ is the pin diameter in mm

15 Trunnion Bracket (6.12)

i) Bracket shall be rigidly fixed to yoke girder by bolts or welding.

ii) Arms of the Bracket shall be designed to bearing act bending.

16 Anchorage system (6.13)

a) The anchorage system shall be designed to with stand the total water

load either.

i) In bond as a bond stress between the anchors and concrete (fig) or

ii) In bearing as a bearing stress between the concrete and the embedded

girder at the upstream end of the anchors duly insulated (fig 2) or.

iii) Through a pre-stressed anchorage system using either steel rounds or

steel cables.

b) The maximum horizontal and vertical force on the trunnion pin shall be

calculated for

i) Gate resting on sill and head varying from Zero to maximum.

ii) Gate position varying from fully closed to fully open at maximum

constant water level.

iii) Worst of the two is chosen.

iv) For combined anchorage the loading shall be determined with one gate

closed and the adjacent gate fully open.

v) For inclined anchors at angle ‘m’ to the horizontal, the horizontal force

determined shall be multiplied by sec m.

vi) The length of embedment of anchors for bonded type shall be such that

the bond stress shall not exceed the permissible values of concrete used

subject to a minimum of two-thirds of radius of gate leaf. Anchors may be

hooked at end or provided with anchor plates. The bonded anchors shall

be insulated for a minimum of 500 mm length from the concrete face to

avoid cracking of face concrete.

vii) Normally bonded anchorages are selected upto 12m X 12m size gates

17 Radial gates with common anchorages

i) The hydraulic thrust on the gate is transmitted to the trunnion girder

through brackets.

ii) Load is transmitted through the anchor bars as bonded anchorages.

iii) The rods are used as load carrying anchorages.

iv) Anchors are not welded to trunnior girder but are fixed with nuts and

pre-tensioning can be carried out

v) Additional flats can also be welded after pre-tensioning.

Limitations:

i) Advantageous for construction of piers since no accurate pier shape is

required.

ii) Economical upto gate size 12 m width X 10 m height.

iii) Due to common trunnion girder for adjacent gates failure of anchorage

of one gate may trigger failure of all gates.

18 Radial gates with independent anchorage system.

i) Hydraulic thrust transmitted from trunnion bracket to yoke girder and to

anchor girder through un-bonded tie flats.

ii) Anchor girder embedded in concrete transmits to pier.

Advantages:

i) Gates can be made to suit the vent width even when there is variation in

civil construction.

ii) No successive failure of gates when anchorage of one fails.

iii) Suitable for large size of gates.

Disadvantages:

i) Need for shaping of pier for movement of arms.

ii) Thorough checking of weld between anchor girder and tie flats.

iii) Large width of piers compared to common anchorages

19 Anchorages with post-Tensioned anchor rods

i) The hydraulic thrust is transmitted from trunnion girder to anchor plate

through high-tensile anchor bars.

ii) Anchor rods are horsed in galvanized steel tubes

iii) After installation there rods are to be post-tensioned on down stream of

trunnion girder to share the equal load.

iv) Used for the larger gates.

Advantages:

i) Less steel is required for the bars which results in a more compact beam.

ii) Anchorage movements due to extension of the anchor bars are virtually

eliminated.

iii) Piers may be narrower

Disadvantages:

i) Compilers joining the rods are susceptible for failure

20 Post-Tensioned pre-stressed concrete anchorages

i) Water thrust is transmitted to the common trunnion girder.

ii) Trunnion girder shall be anchored to the spillway pier by a post-

tensioned anchor system.

iii) Tested in un-bonded condition

Advantages:

i) Narrow spillway piers

ii) Frictional forces due to movement of trunnion brackets are eliminated.

iii) The pre-stressed anchorages puts pier concrete in compression.

iv) The anchorage are less bulky

Disadvantages:

i) Loss of pre-stress due to creep in concrete.

ii) Loss of pre-stress due to shrinkage of concrete.

iii) Loss of pre-stress due to relaxation of steel.

iv) Loss of pre-stress due to elastic shortening of concrete.

v) Loss of pre-stress due to slip in anchorages

vi) Loss of pre-stress due to friction along the cable and the anchorages

21 Trunnion Girder or yoke Girder

i) Designed to be safe in bending, shear and torsion

ii) May or may not be embedded in concrete. If embedded wrapped with

cork mastic or thermo Cole.

iii) The concrete immediately is contact with the trunnion girder which takes

the thrust in bearing from it should be non-shrinkage quality for a

minimum thickness of 300 mm

iv) To-allow for the elongation of the insulated load carrying anchors and

trunnion tie, the trunnion bracket shall be fixed to slide on the rest chair

using bronze or steel pads.

22 Thrust block and Trunnion Tie (6.15)

i) Required when inclined arms are used.

23 Seals, seal interference (6.16)

i) For reducing seal friction, clad seals are used.

ii) Cladding may be of brass, bronze, stainless steel, fluorocarbon or

Teflon

iii) Seal interference shall vary from 2 to 5mm.

24 Seal – Seat, Seal – Seat base and sill beam (6.17)

i) Minimum thickness of stainless steel seal seat plate – 6mm for low head

gates and 8 mm for others after machining.

ii) The minimum thickness of stainless steel flat provided on sill beam shall

be 6 mm after machining.

25 Guide Roller (6.18)

i) Limits the lateral motion to not more than 6 mm in either direction.

ii) Designed to 5 % of gate weight.

26 Sizing of components

i) As derived from design

ii) Minimum 10 mm for structural components of the gate.

iii) For webs of bracing members 8 mm is permissible.

iv) Fillet welds – minimum 6 mm leg size, continuous and water tight.

Satisfy IS 9595 regarding thickness of members being welded.

27 General Features of Design

i) Considerations for choice of radial gate.

i. Most economical, most suitable for spillways and out lets.

v) Simplicity of operation and smooth flow pattern past the gate in

spillways.

vi) For out lets, high co-efficient of discharges favours of choice.

vii) For heads over 8 m over the spillway proves economical than other

types.

28 Requirements to be satisfied

i) Water tight

ii) Capable of being operated by the hoist at required speed.

iii) Amenable to manual operation

iv) Should be capable of regulation at required discharge without

cavitations and undue vibration.

29 Loads acting on the gate

i) Hydrostatic

ii) Hydrodynamic

iii) Wave action

iv) Dead weight

v) Silt load

30 Advantages of Radial Gates

i) Grooves are not necessary hence no cavitation

ii) Gates curved bottom acts as a bell mouth, thus the flow is smooth

iii) Outfall slope can be steeper, thus saving in concrete and no cavitation.

iv) Vibrations are less for partial opening due to bell mouth shape.

v) Simple in construction, hence less cost. Hoist capacity is low due to

additional leverage

vi) Less hoist capacity as no rollers are used

vii) Wearing of parts is less in radial gates

viii) Maintenance is easy in closed position also

ix) Erection is easy once the Trunnion is fixed.

x) Weight of the gate is less

HYDRAULIC HOIST

1. Need.

1) This type of hoist is used in the gates which are not self closing. This type of hoist is

capable to produce thrust both in opening and closing of gate.

ii) This type of hoist has given more precise and easy control in operation of gate.

iii) It requires less space.

iv) This are mainly used to operate bonnet gate and radial gate.

2. General

A hydraulic hoist consists of a cylinder with upper and lower cylinder head, piston

and stem passing through a packing in the lower cylinder head. The hoist is operated by

a motor and oil pump arrangement with the directional control by valves which are

actuated by electric contact from any desired position.

3. Factor governing the choice of hydraulic hoist:

1. High capacity and low travel.

2. Larger range of hoisting / lowering speed,

3. Limited space availability,

4. Dampening of vibrations of gates,

5. Requirement of positive thrust.

4. Parameters in the design of hydraulic hoist

1. Capacity of hoist

2. speed of lifting and lowering

3. Position of Oil Tank.

In case of gate that are lowered by gravity, the oil tank should preferably be kept

at the level higher than the cylinder top.

4. Number of hoist and their method of operation.

Whether from separate hydraulic system or from a centralized system. In latter

case whether the gate are to be lowered selective or simultaneously.

5. Stroke of hoist.

This will determine the capacity of oil tank.

6. Frequency of operation.

7. Space limitations if any

5. Hoisting capacity:

• Weight of the Gate along with all its component including the weight of wire rope

and its attachments

• All Frictional Forces

• Wheel Friction

• Guide Friction

• Seal Friction

• Trunnion friction in case of radial gate

• Friction of moving parts of hoist.

• Any Hydrodynamic Load, like down pull force / uplift.

• Silt and ice load, wherever encountered

The worst combination of these forces either lowering or rising cycle should consider

and these should increase to 20% as reserve.

6. Design Involve following component

1. Cylinder

2. Cylinder head

3. Piston stem.

4. Couplings

5. Piston

6. Piston rings and packing

7. Seals and packing.

8. Hanger stud

9. Gate position indicator

7. Design of hoist component :-

i) Cylinder

Operating pressure: - Maximum operating oil pressure should be 20N/mm2 for

design of hydraulic cylinder.

ii) Cylinder head

The cylinder head should be designed as a thick flat plate, held down at outer

perimeter in accordance to IS 2825:1969.

When bonnet cover is providing to work as one of the cylinder head than it

should be design accordance with IS 9349: 1979.

iii) Stems

Piston stem should be solid or hollow construction and if made of forged steel

should be hard chromium plated to at least 0.05 mm thickness with stress limited

to 0.4 of yield point at pressure setting of pump relief valve.

iv) Couplings

Couplings for connecting the stems between the gate and hoist are:-

a) Clevis coupling: - The male and female parts of clevis should be

connected by steel pin. The pin should be designed against shear,

bending, and bearing.

b) Split collar coupling: - This type of coupling is more convient to

assemble and disassemble can be used generally for vertical stem gate.

c) Hook and eye type coupling: - this type of coupling is suitable for

gate on slope of about 15 deg. with vertical. This is similar to clevis type

of coupling except the addition of skid pads on the loop of hook to provide

an easy method of holding the stem for alignment on the slope.

v) Piston

Piston should be designed for operating pressure. The steel piston should be

provided with suitable protection so that the finish piston may not affect the

smooth cylinder wall.

vi) Piston rings and packings:-

The piston should be fitted with hydraulic type piston rings and also with a

stuffing box having V- packing rings. These packing rings should eliminate

leakage past the piston and permit holding of piston in any position for long

period of time when outflow of oil from below the piston is blocked.

vii) Gate position indicator

An indicator to show the position of gate in its full travel should provided.

viii) Test pressure:-

The hoist cylinder, cylinder heads, piston appurtenant, piping, valve other parts

and control subjected to oil pressure should be tested at 150% of the operating

pressure for period not less than 30 min.

8. Fabrication:-

The hoist cylinder should be composed of flanges of weldable forged steel forges steel;

shell of pierced, rolled steel forging or flat steel formed to cylindrical shape; joined to

each other with not more than two longitudinal welds. If the cylinder is forged, the flange

should be forged as integral part of cylinder, otherwise the flange of the cylinder should

be butt welded to cylinder shell. In either case cylinder should be annealed and stressed

/ relived before machining. All butt weld in the cylinder and cylinder head should be

tested for full strength by 100% radiographic examination.

The cylinder bore should be honed to finish of 1.6 micron.

9. Hydraulic operating system

The hydraulic- electric operating system consists of:-

1. oil tank

2. Filter and strainers

3. Pumps with motors and starting equipment

4. control valve

5. Pressure relief

6. Piping

7. Pressure gauge

8. pressure switches

9. push buttons, relay, and other electrical equipment for actuating and controlling

the system

10. Stand – by pump and driving device as necessary.

10. Hoist support frame

It should be designed to withstand the maximum load occurring at the time of operation

of the gates.

11. Oil

The oil should be suited to the viscosity and temperature range of operation.

12. Advantage of hydraulic hoist:

1. Hoist capacity: - Hydraulic hoist of higher capacities are economical and

operationally better suited.

2. Space: - Layout of work and space being smaller in case of hydraulic hoist.

3. Speed: - They are lowered at almost any desired speed. Moreover the speed can

be easily adjusted within the limits of system.

4. Economy of installation: - The oil tank and the cylinder are paced at any desired

location and it is only necessary to interconnect these unit, the various units are

installed at most economical location.

5. Minimum maintenance: - parts are self lubricated and also they are totally

enclosed and protected against outside contaminants, these required minimum

maintenance.

13. Disadvantage of hydraulic hoist:

The hydraulic hoist required a good honed cylinder of sufficient length depending on

the lift of gates. Sometimes the availability of these cylinders is a problem.