TEXT:

The Iron Bridge crosses the River Severn at the Iron bridge Gorge , in Shropshire , England.
It was built in 1779. It was the first arch bridge in the world to be made out of cast iron , a material which was previously far too expensive to use for large structures. However , a new blast furnace nearby lowered the cost and so encouraged local engineers and architects to solve a long-standing problem of a crossing over the river.
Being the first of its sort, the construction had no precedent ; the method chosen to create the structure was therefore based on carpentry. Each member of the frame was cast separately, and fastenings followed those used in woodworking , such as the mortise and tenon and blind dovetail joints. Bolts were used to fasten the half-ribs together at the crown of the arch. Very large parts were needed to create a structure to span 100 feet , rising to 60 feet above the river. The largest parts were the half-ribs , each about 70 feet long and weighing 5.25 tons. The bridge comprises more than 800 castings of 12 basic types.

VOCABULARY:

Arch : arc
Blast furnace : haut fourneau
Blind : aveugle
Bolts : boulons
Carpentry : charpenterie
Cast iron : fonte
Dovetail : queues d'aronde
Fastenings : attaches
Half-ribs : demi- côtes
Joints : assemblage
Mortise : mortaise
Parts : pièces
Tenon : tenon
The crown : la couronne
The frame : le cadre
To fasten : attacher