A bridge is a structure built to span a valley, road, railroad track, river, body of water, or any other physical obstacle, for the purpose of providing passage over the obstacle. Designs of bridges will vary depending on the function of the bridge and the nature of the terrain where the bridge is to be constructed. There are six main types of bridges: beam bridges, cantilever bridges, arch bridges, suspension bridges, cable-stayed bridges and truss bridges.

Solid pillar on both ends

Truss

Uses strength and rigidity of triangles

Cantilever

Anchor one end, and rest the other on beam with a bit hanging out

Cantilever with suspended span

Suspension

Need real solid anchor for the cable

May flap in the wind

Portable bridges – pontoon bridges

What materials are used in bridge construction?

Wood

Quick

Deteriorates quickly

Burns

Stone

More durable

But span is limited

Iron

Strong

Expensive

Upkeep is difficult (rust)

Concrete

Usually with steel rods inside it – rebar

Road surface

Asphalt

What does an engineer have to consider in building a bridge

Length of the crossing

Weight the bridge must carry – vehicle weight plus its own

Ice loads

Ship collision loads

Water eroding the support piers – erosion

Seismic effects – earthquake – applies even here

Height of the bridge – do ships have to go underneath? CONFEDERATION BRIDGE VG

Strength of the land it will sit on – PEACE RIVER BRIDGE VG

Weather conditions – HARTLAND BRIDGE VG

Wind affect – TACOMA NARROWS BRIDGE VG

Environmental effects – what will the bridge do to the environment?

How long must it last?

Funding

What if we have to put a support in the middle of the river?

Supports must be on bedrock

Use a cofferdam and pump out the water – good for shallow water

Large metal cylinder (caisson) and gradually dig it into the river bed – pressure becomes a problem, because the pressure inside the cylinder must be high enough to keep the water out – nitrogen narcosis – the bends – Brooklyn Bridge

Dredge the silt and place pre-assembled pieces in place from a floating barge – Confederation Bridge

Expansion Joint

Allows the bridge to expand with differences in temperature

One end fixed – the other slides

Cable stretches – bridge moves up and down

Simple Beam Bridge

Truss – Uses strength and rigidity of triangles
 Cantilever SpanAnchor one end, and rest the other on beam with a bit hanging ou
Cantilever with suspended span in the middle Suspension Bridge