Steel bridges may be classified into various types according to:
- the kind of traffic carried,
- the kind of main structural system,
- the position of the carriage way subjective to the main structural system
Classification based on kind of traffic carried
Based on traffic carried, bridges can be categorized into following types:
- Road bridges or Highway bridges
- Railway or rail bridges
- Road cum rail bridges (facilitating both rail and road way)
Classification on basis of main structural system
Different kinds of structural systems are utilized in bridges based on the span, carriageway width and assortments of traffic. Categorization, in accordance to make up of major load carrying system, is as follows:
Girder Bridges: Flexure or bending among the vertical supports is the basic Structural action in this kind. Girder bridges can be either solid web girders or they can be truss girders or box girders. Plate girder bridges are utilized for the reason of simply supported spans not exceeding 50 m and box girders for incessant spans upto 250 m. Truss bridges are appropriate for the span range of 30 m to 375 m. Cantilever bridges have been constructed successfully with main spans of 300 m to 550 m. In another chapter girder as bridges are explained in point. They might be additionally, classified into simple spans, continuous spans and suspended-and-cantilevered spans.
Arch Bridges: Loads are shifted to the bases by arches performing as the basic structural element. Axial compression in arch rib is known as fundamental force, blended with some extent of bending. Arch bridges are spirited in span range of 200 m to 500 m.
Cable stayed bridges: Cables in the vertical or hold up the major longitudinal girders. These cables are suspended from one or additional high towers, and are typically anchored at the base to the girders. Cable stayed bridges are inexpensive when the span is about 150 m to 700 m.
Rigid Frame bridges:
Classification on basis of position of carriageway
- Deck Type Bridge: The carriageway lays on the highest point of the fundamental load conveying members. In the deck sort plate girder bridge, the roadway or railroad is put on the top flanges. In the deck sort truss girder connect, the roadway or railroad is set at the top chordlevel.
- Through type bridge
- Semi-through type bridge
Loads on Bridges
- Seismic load
- Racking force
- Forces due to curvature.
- Forces on parapets
- Frictional resistance of expansion bearings
- Erection forces
- Dead load
- Live load
- Impact load
- Longitudinal force
- Thermal force
- Wind load
Dead Load: The dead load refers to the mass of the structure and any stable load fixed thereon. The dead load is at first understood and checked after design is undertaken.
Live Load: Bridge design standards state the design loads, which are supposed to replicate the worst loading that could be occurred on the bridge by traffic, allowed and anticipated to pass over it.
IRC AA loading: IRC class AA stacking consists of either a tracked automobile of 70 tons or a wheeled vehicle of 40 tons with measurements as appeared in Fig. . The units in the figure are mm for length and tons for load. Regularly, connects on national thruways and state interstates are intended for these loadings. Configuations intended for class AA ought to be checked for IRC class A stacking likewise, since under specific conditions, bigger loads might be gotten under class A stacking. Some of the time class 70 R stacking given in the Appendix – I of IRC: 6 – 1966 – Section II can be utilized for IRC class AA stacking. Class 70R stacking is not examined advance here.Class A stacking comprises of a wheel stack prepare made out of a driving vehicle and two trailers of indicated pivot spacings. This stacking is regularly received on all streets on which perpetual scaffolds are built. Class B stacking is embraced for transitory structures and for extensions in indicated areas.For class An and class B loadings, peruser is alluded to IRC: 6 – 1966 – Section II.
Foot bridges and Footpath on Bridges: The live load because of pedestrian traffic have to be treated as consistently dispersed over the pathway. For the blueprint of footbridges on the railway bridges, the live load counting dynamic effects have to be in use as 5.0 kN/m2 of the footpath area. For the configuration of footpath on a road bridges the live load counting dynamic effects have to be taken as 4.25 kN/m2 apart from that, where crowd loading is probable, this might be augmented to 5.0 kN/m2.The live load on footpath for the reason of scheming the main girders has to be in use as follows in accordance with the rules of bridges.
For effective spans of 7.5 m or less – 4.25 kN/m2
The intensity of load is reduced linearly from 4.25 kN/m2 for a span of 7.5 m to 3.0 kN/m2 for a span of 30m