An Introduction to bridges by Flourish Omotola

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BRIDGES

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BRIDGES
This is any structure used to transport people,
goods and services From one platform to another
over an obstacle e.g roads, valleys, rivers, e.t.c.
The earliest bridges were stone bridges in rivers
and rope bridges anchored by trees with wooden
panels as decks. Then came stone arch bridges, in
modern days we use concrete and steel to design a
range of bridges from 100 to 500m. They consist of
abutments, wingwalls, deck, piers, cables, parapets,
e.t.c.

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BRIDGES
TYPES OF BRIDGES BY SPAN
Short (<20m)
Medium (20-50m)
Long (> 50m)

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BRIDGES
TYPES OF BRIDGES BY DESIGN
1. Beam Bridges (15m< Span< 100m)
2. Arch Bridge (30m -500m+)
3. Cable Stay Bridge (200m - 1100m)
4. Suspension Bridge (850m+)
5. Truss Bridge (40m - 550m)
6. Rigid Frame (25m - 350m)

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BRIDGES
1. Beam/Girder Bridges (15m< Span< 100m)
A slab/deck rests on beams, girders or trusses
without the help of an arch/cable. Types include:
(a) Solid concrete slabs (3-10m)
(b) Voided concrete slab on RC beams (10-20m)
(c) Pretensioned concrete girders/ Steel girders
(medium span)
(d) Orthotropic box girders, prestressed/post
tensioned girders or truss support (Long Span)

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BRIDGES
2. Arch Bridge (30m -500m+):
Arches are good in compression. They
produce large thrust and need strong
abutments. Worst case bending moment
occur with UDL placed at half span. The
worst shear force and tangential
compressive force occurs with UDL at full
span. Types include: Masonry Arch, Spandrel,
Through and Half Through arch Bridges

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BRIDGES
3. Cable Stay Bridge (200m - 1100m)
There is tension in the cable stays and
in the mid span of deck. The piers and
the rest of the deck is in compression.
Types include: Mono, Harp, Fan, Star.

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BRIDGES
4. Suspension Bridge (850m+)
The Load is transferred from the deck
to the main cables (which are sagging)
through the suspender cables. The
main cable rests on towers/piers which
are in compression. The main and
suspender cables are in tension.

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BRIDGES
5. Truss Bridge (40m - 550m)
The bridge either rests on trusses or
within a truss system. Members are
designed for axial loads and local
flexure. Types include: Pratt truss,
Warren truss, Vierendeel Truss, Howe
Truss, K Truss, Waddel Truss, e.t.c

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BRIDGES
6. Rigid Frame (25m - 350m)
This is a combination between arch
and beam bridges. It is a slab
supported by two inclined struts on
both sides. The struts and mid deck are
in compression while the edges of the
deck are in tension.