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Entrance Locks

Entrance Locks of Harbors and Docks

Entrance Locks of Harbors and Docks


Entrance Locks are those which give access to docks

Components of Entrance Locks

1)Chamber: which is enclosed by quays wall on each side and bottom is paved by inverted arch flooring which resists upward water pressure when lock level is low
2)The gates closing entrance constructed of wood or iron of heavy design to withstand water pressure
3)The sill is raised above the gate floor by 2 foot
4)Sluice way provided in side walls for filling and emptying locks

Dimensions of Entrance and Locks

It main factor are width, size, and displacement of the longest vessels. Modern locks have width vary from 80 foot and above and depth 25 foot to 40 foot and length of 800 foot and over.

Construction of Entrance and Locks

Materials generally used are:
1)Wood
2)Iron

Wooden Gates
It consists of a horizontal beam that is spaced closer at the bottom to resist water pressure and joined together by heel post in such a way that two extreme ends meet at middle.

Iron Gates
It mainly consists of iron plates ribs which are fixed horizontally and vertically and further covered over with iron sheeting. 
The main point is to increase the thickness of the plate rib and spacing of rib is further reduce towards the bottom to withstand increasing water pressure. 

Forces on Entrance and Locks Gates

1)Transverse stress due to water pressure against the inner face with an increase in depth.
2)Compressive stress along with the gate due to pressure by another gate at the meeting
Component of heel reaction = WL/2 *S/2n
(It is a product of half water pressure and tangent of half-angle between gates)
  
Further, it can be seen that compressive force varies inversely proportional to rising and as the largest rise will ultimately decrease stress but by increasing the rise the length of gate is increased and further, it will increase transverse stresses due to water pressure on the gate. There is also increased in length of lock so it is suggested to provide rise from 1/4 to 1/5

Shapes of gates

The shape of gates has important value in the strength of gates. Therefore the shape is straight and curved. 
As the straight gate is subjected to force while the curved shape is strong against transverse water pressure because as arched shape transverse stress gets decreased as curvature increases and as such two gates form circular arch due to which transverse stress changes to a longitudinally compressive force.When a section of the gate at the bottom gets maximum compressive stress curved type of gate is the best choice.

Disadvantage of Curved Gate 

1)They are long and costlier
2)They require a large gate recess
3)The gate sills which is to be curved so such curving is a difficult task.

Working of Gates

The operation of This gate od opening and closing is handled by two sets of chain one for opening and other for closing which works simultaneously. 
The chain is fastened at 1/3rd height near the free end 

REFERENCES:

1. Railway bridge and Tunnel Engineering by Rangwala
2. Harbour dock and Tunnel Engineering by R.Srinivasan
3. Roads, Railways Bridges and Tunnel Engineering by Ahuja & Birdi




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