User:Svss.Prudhvi Krishna/sandbox

PROJECT LIFT BRIDGE

Our project is on the analysis of vertical lift bridges.We designed the model of

the vertical lift bridge.Due to complex geometry and loading conditions, desing of vertical

lift bridge include many simplifying assumptions.Therefore it is difficult to design an exact

model of even newstructure.For existing structures,constructions,tolerances are factors that

further alter loading and structural conditions. In this job mechanical principles involved

are force,turning effect,tension,rolling friction.when any object like ships are to moved in

the water must be lifted up.If a force equal to the weight of the bridge is applied using

strings then the bridge will be in equilibrium. If the forced applied is more than the weight

of the bridge the bridge will be lifted up.

”IF THE TOTAL FORCE ACTING DOWN WARDS IS LESS THAN

EXTERNAL FORCE APPLIED THEN THE BRIDGE WILL BE LIFTED UP”.

INTRODUCTION:

Bridges: A transporter bridge (also ferry bridge or aerial transfer

bridge) is a type of movable bridge that carries a segment of roadway across a

river. The gondola is slung from a tall span by wires or a metal frame. The

design has been used to cross navigable rivers or other bodies of water, where

there is a requirement for ship traffic to be able to pass. This has been a rare

type of bridge, with fewer than two dozen built. There are just twelve that

continue to be used today, including one converted into a lift bridge and one

designed as, but not yet operating as, a transporter bridge.

Type of bridges:

1. Lift bridge

2.Draw bridge

3.Bascule bridge

4.Floding bridge

5.Rolling bridge

6.Rolling bascule bridge

7.Swing bridge

Definitions:

Lift bridge:

A vertical-lift bridge or lift bridge is a type of movable bridge

in which a span rises vertically while remaining parallel with the deck.

The vertical lift offers several benefits over other movable bridge such as the

bascule and swung snap. Generally speaking they cost less to build for longer

moveable spans.

Draw bridge:

Typically associated with the entrance of a castle surrounded

by a MOAT. The bridge would be raised or lowered using ropes or chains attached to a WINDLASS in a chamber in the gate house above the gate passage.

Only a very light bridge could be raised in this way without any form of

counterweight. Bascule bridge:

A bascule bridge is a movable bridge with a counter weight that

continuously balance the span, or leaf throughout the entire upward swing in

providing clearance for boat traffic. They open quickly and required reatively little relatively little energy

to operate.

Folding bridge:

An example of a floding bridge is the HORN BRUCKE in the city of

KIEL in the GERMAN state of schelswig Holstein. It is a three segment bascule

that flods in the shap of letter N.      Swing bridge:

vertical location pin and support ring, usually at or near to its center of

gravity,about A swing bridge is a movable bridge that has as its primary

structural support a which the turning span can then pivot horizontally as show

in the animated illustration to the right.

Rolling and Bascule bridge:

Pegasus bridge and the structure are examples of a distinct subtype of

bascule bridge,the Scherer rolling lift bascule bridge or rolling bridge.

Bridge of this type do not pivot about a hing point,but roll back on

curved tread plates attached to the girders of the main span.

Movable bridges have been an integral part of the U.S. transportation system,

their development being in concert with that of the development of the

railroads and the development of our highway system. While sometimes

referred to as draw bridges, movable bridges have proved to be an economical

solution to the problem of how to carry a rail line or highway across an active

waterway. It is not surprising to learn that movable bridges are found most

commonly in states that have low coastal zones such as California, Florida,

Louisiana, and New Jersey, or a large number of inland waterways such as

Michigan, Illinois, and Wisconsin Jurisdiction for movable bridges currently

lies with the U.S. Coast Guard. In most instances, marine craft have priority,

and the movable span must open to marine traffic upon demand. This

precedence is reflected in the terms closed and open, used to describe the

position of the movable span(s). A “closed” movable bridge has closed the

waterway to marine traffic, while an “open” bridge has opened the waterway to

marine traffic. Highway bridges are typically designed to remain in the closed

position and only to be opened when required by marine traffic. However,

movable railroad bridges can be designed to remain in either the open or closed

position, depending on how frequently they are used by train traffic. The

difference is important as different wind and seismic load design conditions are

used to design for a bridge that is usually open vs. one that is usually closed.

The first specification for the design of movable bridges was published by the

American Railway Engineering Association (AREA) in its 1922 Manual of

Railway Engineering. Until 1938 this specification was used to design both

movable highway and railroad bridges, when the American 2 Association of

State Highway Officials published its Standard Specifications for Movable

Highway Bridges.

Both specifications are very similar, but have remained

separate. Today, movable railroad bridges are designed in accordance with the

AREA Manual, and movable highway bridges are designed in accordance with

the American Association of State Highway and Transportation Officials

(AASHTO) Standard Specifications for Movable Highway Bridges. These

specifications primarily cover the mechanical and electrical aspects of a

movable bridge; the structural design of the bridge is covered in other parts of

the AREA Manual for railroad bridges or the AASHTO Standard Specifications

for Highway Bridges.

Research and Methodology:

	 It has one flat movable surface which can move freely up and down. 	Vertical lift bridge works under function of tension by using strings. 	 Strings are connected to four corners of bridge with engine roller  by  using pulleys. 	To decrease friction between bridge and the walls which support it rollers are used between them. 	 When a force equal to the weight of the bridge is applied using strings then the bridge will be in equilibrium. 	If the force is increased the bridge rises.

CONSTRUCTION:

Here A,B,C,D,H,G,E,F are the fixed joints at joint G,H,E,F are

connected to strings. This strings are passed through the rollers.This

strings are connected to the handle.When force is applied on strings at

point “J” then movable surface G,H,E,F rises up.

Conclusion:

By this proto type we can clearly know the principles of

mechanics involved in it ,advantages ,disadvantanges upto some extent.we can

also know the role play of movable bridges in transportation of ships.The

working of the movable bridges mainly depends on pulleys and strength of

cables. Rotational motion is converted into mechanical motion in this lift

bridges.

Advantages:

	A MOVEABLE BRIDGE is a bridge that moves to allow passage for boats or barges. 	An advantage of making movable bridges include lower price, due to the absence of high piers and long approaches. 	Vertical lift bridge need not bare much weight of the deck were as the bascule bridge. 	It is used for the passage of heavy vehicals.

Disadvantages:

It is difficult to halt the traffic when ever necessary It is most coastly bridge It is too risk to ship to pass down the bridge

BY                               PRUDHVI&NAGARJUNA