Advantages of Steel
• High tensile and compressive strength
• High strength to weight ratio – low self weight & less
loading on substructure
• High quality material
• Speed of construction
• Versatility of construction
• Elasticity – follows Hooke’s Law very accurately
• Ductility – can withstand high deformations before
failure ➔ gives a warning before failure
• Modifications can be made easily – strengthening of
Disadvantages of Steel
• Maintenance cost is high – corrodes when
exposed to air, water and humidity
• Fire proofing cost – strength reduces at high
• Susceptible to buckling – slender structures
• Fatigue – strength reduces due to cyclic loading
Beam / Girder Bridges (Contd.)
• Rolled I sections are used as the main support
• Other members – cross girders, stringers, deck,
• Two beam/girder system or multiple beam/girder
system with cross beams (cross girders)
Truss Bridges (Contd.)
• Spans up to 200m possible
• Structurally efficient
• Reduced self weight
• Several types of truss arrangements possible –
Warren, Modified Warren, Pratt, Fink, Howe etc.
Movable Bridges (Contd.)
• Permits passage for navigation by moving /
swinging the bridge deck
• When it is either impractical or too expensive to
provide a bridge with sufficient vertical clearance
• Moving action – Lift/sink or swing
Advantages of Concrete
• Ingredients of concrete are easily available.
• Unlike natural stones Concrete is free from
defects and flaws (faults, joints, stratifications
• Concrete can be manufactured to desired strength
• The durability of concrete is very high.
• It can be cast to any desired shape.
• Casting of concrete can be done at work site
which makes it economical.
• Maintenance cost of concrete is almost negligible.
Disadvantages of Concrete
• Compared to other binding materials, the tensile
strength of concreter is relatively low.
• Concrete is less ductile.
• The weight is high compared to its strength.
• Suitable for small and medium spans
• Special requirements – restriction on provision of
formwork, construction period
• Most of highway bridges are RC
• Several types available
• Box girder
• Continuous girder
• Balanced cantilever
RC Slab serves as the main superstructure member,
requiring no other beams or girders to carry the
loads. Not suitable for larger spans since the slab
becomes thicker increasing the dead weight.
• Simple design
• Solid / hollow slabs
RC beams serve as the main superstructure member.
Widely used due to simplicity, economy, wide
availability of the standard sections, and speed of
erection. Precast beams are placed on the
supporting piers or abutments, usually on rubber
bearings which are maintenance free.
• I beams are used
• A deck is constructed on top of beams spanning
between the beams
Box Girder Bridges
For spans greater than around 45 metres, pre-
stressed concrete box girders are the most common
method of concrete bridge construction. The main
spans are hollow and the shape of the 'box' will
vary from bridge to bridge and along the span,
being deeper in cross-section at the abutments and
piers and shallower at mid span.
• Incrementally launched
• Span by span
• Balanced cantilever