Different Types of Bridges

Different Types of Bridges and Criteria of Site Selection

Definition

A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle.

Designs of bridges vary depending on

  •  The function of the bridge,
  • The nature of the terrain where the bridge is to be constructed,
  • The material used to make it and
  • The funds available to build it.

Different Types Of Bridges

  • Beam bridges
  • Cantilever bridges
  • Arch bridges
  • Tied arch bridges
  • Suspension bridges
  • Cable-stayed bridges
  • Movable bridges

Beam Bridges

Beam Bridge

Beam Bridge

Made up of simply supported horizontal Beams I-beams, trusses, or box girders.

End supports are known as abutments and intermediate supports are known as piers.

Weight on top of the beam pushes straight down on the abutments at either end of the bridge

Types of construction could include having many beams side by side with a deck across the top of them.

 

Cantilever bridges

Cantilever bridge

Cantilever bridge

horizontal beams supported on only one Support.

simple cantilever

formed by two cantilever arms extending from opposite sides of the obstacle to be crossed, meeting at the center.

balanced cantilever

cantilever spans is to counterbalance each cantilever arm with another cantilever arm projecting the opposite direction.

Arch bridges

Arch bridge

Arch bridge

bridge with abutments at each end shaped as a curved arch.

Arch bridges transfers the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side.

Tied arch bridges

an arch-shaped superstructure,

Instead of transferring the weight of the bridge and traffic loads into thrust forces into the abutments, the ends of the arches are restrained by tension in the bottom chord of the structure. They are also called bowstring arches.

Suspension bridges

Suspension bridge

Suspension bridge

Deck, the load-bearing portion, is hung below suspension cables on vertical suspenders.

This type of bridge has cables suspended between towers, and vertical suspender cables.

The suspension cables must be anchored at each end of the bridge, since any load applied to the bridge is transformed into a tension in these main cables.

Cable-stayed bridges

Cable-stayed bridges Fan Design

Cable-stayed bridges Fan Design

consists of one or more columns (referred to as towers or pylons), with cables supporting the bridge deck.

Two types of design–

harp design

The cables are made nearly parallel by attaching them to various points on the tower

fan design

the cables all connect to or pass over the top of the tower

Movable bridges

designed to move out of the way of boats or other kinds of traffic

powered by electric motors, whether operating winches, gearing, or hydraulic pistons

Survey for bridge site selection

  • Social feasibility survey
  • Level of local participation
  • Size of area of influence
  • Size of traffic flow
  • Socio-economic benefits produced by the proposed bridge

Technical survey

It includes Bridge site selection and Topographic Survey of the selected bridge site

Bridge site selection

The bridge site should fulfill a number of general conditions:

– The bridge site should be selected at or near to the traditional crossing point

– minimum free board

– maximum bridge span

– space for the bridge foundations

River condition

River condition

The selected bridge site must have favorable river conditions. Accordingly, a bridge should be located:

• on a straight reach of the river

• beyond the disturbing influence of larger tributaries

• on well defined banks

Slope and bank condition

If the slope and bank is soil, potential instability features and failure modes are:

• bank erosion

• toppling instability of the bank

• erosion of the slope

• land slide

If the slope and bank is rock, potential instability features and failure modes are:

• plain failures in a rock slide along the slope.

• wedge failure leading to the fall of rock mass.

• toppling leading to the fall of rock blocks.

• rotational slide is similar to the landslide in a soil slope. Such failure is likely when the material of therock is very weak (soft rock) and the rock mass is heavily jointed and broken into small pieces

General data collection

General data is required for needs assessment and construction planning of the proposed bridge.

Collect the following general data & information:

  • Location of bridge site
  • Transportation distance,
  • Nature of crossing and fordability
  • Availability of local materials
  • Availability of local bridge builders

Local participation

Traffic volume

Width of walkway

Temporary crossing

Evaluation of the bridge site

Good – All or most of the features are favorable and if the surveyor is confident about the

stability of the slopes. Proceed with further survey work.

Bad – Most of the features are unfavorable. Reject site.

Questionable – Most of the features are favorable and some are unfavorable. The site is questionable. In this case, further detailed investigation by an experienced geo-technical engineer is necessary.

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