By Aman Kumar ▪ Introduction ▪ Types of Bridges ▪ Bridge Components Definition :- Bridge is a structure having a total length of above 6 metres between the inner faces of the dirt walls for carrying traffic or other moving loads over a depression or obstruction such as channel, road or railway. Bridge is a structure corresponding to the heaviest responsibility in carrying a free flow of transport and is the most significant component of a transportation system in case of communication over spacings/gaps for whatever reason such as aquatic obstacles, valleys and gorges etc. Minor Bridge Major Bridge Structure having a total length of below 6 metres between the inner faces of the dirt walls is know as Culvert. Minor Bridge:- Total Length of the bridge is 60m Major Bridge:- Total Length of the bridge is above 60m High level bridge Submersible bridge/vented causeway High level bridge:- A high level bridge is a bridge which carries the roadway above the highest flood level of the channel. Submersible bridge:- A submersible bridge/vented causeway is a bridge designed to be overtopped during floods. • Beam Bridge • Arch Bridge • Suspension Bridge • The type of bridge used depends on various features of the obstacle. The main feature that controls the bridge type is the size of the obstacle. How far is it from one side to the other? This is a major factor in determining what type of bridge to use. Beam Bridge:- A beam bridge is basically a rigid horizontal structure that rest on two supports, one located at each end of the bridge as shown in Figure (a). A simple beam bridge is flat across and supported by two ends. When the load pushes down on the beam the top edge is pushed together or compressed, while the bottom of the beam is stretched or is under tension. What factor(s) should you consider when you build a beam bridge? The beam must be strong enough so that it doesn't bend under its own weight and the added weight of the traffic crossing it. Arch Bridge:- An arch bridge is composed of a curved structure with abutments on each end. The weight of the load is carried outward along the curve of the arch to the abutments at each end of the arch. The abutments also keep the end of the bridge from spreading outward. What factor(s) should you consider when you build an arch bridge? The arch bridge is always under compression because the weight of the deck is pushed outward along the curve of the arch towards the abutments. The rise in the form of the curved arch causes the vertical load to have a horizontal thrust. Suspension Bridge :- The suspension bridge literally suspends the roadbed from huge cables, which extends from one end of the bridge to the other. The cables are attached to two tall towers and are secured at each end by anchorages. What happens to the bridge when a load is put on the bridge? The cable carries the weight on a suspended bridge to the anchorages that are imbedded in solid rock or massive concrete blocks. The cables are spread over a large area in order to evenly distribute the load inside the anchorages to prevent the cables from breaking free. What factor(s) should you consider when you build a suspension bridge? The anchorages help to stabilise the bridge. Therefore, the tower must be embedded to earth firmly. In such a way, the cables transfer the forces to the towers which carry the forces directly into the earth where they are firmly imbedded. Horizontal slabs or girders supported by abutments and piers. ▪ Common types: ➢Slab type ➢I-beam type ➢Box girder Slab type ➢ The width B is comparable to the span length L ➢ Applied in case of small spans ➢ The deck is usually made with voids ▪ I- beam type ➢ Precast (usually) or cast-in-situ beams (rarely) ➢ Beams are usually prestressed ➢ Various methods for placing the precast beams at their position (crane, “caro ponte”) ➢ Can be used in difficult site conditions Box girder bridges ➢ Deck comprises of hollow box of single or multiple cells ➢ Applied in case of long spans ➢ The height H might vary along span Balanced Cantilever Arch Bridge Suspension Bridge Cable Stayed Bridge Normal Bridge Skew Bridge Curved Bridge ❑ Simply supported spans Advantages ➢ Can take differential settlements and tectonic displacements ➢ Allow prefabrication (precast beams) Disadvantages ➢ Large moments at the middle of the spans ➢ Danger of deck fall during earthquakes (require wide sitting areas) ➢ Not clear seismic response: o Asynchronous movement of decks o Danger of impact between adjacent decks ❑ Continuous deck ▪ Advantages ➢ Good distribution of moments between supports and spans → small deck thickness ➢ Good seismic behavior: ➢ The deck acts as a diaphragm → all piers move similarly Practically, no danger of deck fall ▪ Disadvantages ➢ Sensitive to differential settlements of piers ➢ Cannot accommodate tectonic movements ❑ Decks with Gerber beams ▪ Advantages ➢ Best balancing of moments between spans and supports ▪ Disadvantages ➢ Serious danger of deck fall during earthquakes due to narrow supports ➢ Special connecting systems required to reduce possibility of fall Simply support beam Continuous beam Monolithic ▪ Advantages ➢ Small displacements (stiff structures) ▪ Disadvantages ➢ Development of seismic moments at the deck ➢ Thermal variations, shrinkage and creep produce deformation of the piers Through bearings ▪ Advantages ➢ Flexible systems type of seismic isolation ▪ Disadvantages ➢ Large seismic displacements (danger of deck fall) ➢ Piers behave as cantilever large moments at the base .