Engineering Wonders of the World
Volume I

330 ENGINEERING WONDERS OF THE WORLD. liable to expand and contract as were the members of the cantilevers and suspended girders. For this reason it Provisions was impossible to anchor all f°r . the tower columns immovably of the°n thoir piers. Had such a Metal. thing been done, great cold would have tended to draw the piers together and the intense heat of summer pier heads. To the bottom of each upper plate was attached a key-plate, circular at the “ fixed ” points, and oblong at the others, engaging with recesses of corresponding shape in the lower bed-plates. The appended dia- gram on page 331 will explain better than words the shapes and functions of the key- plates. The letters ccc indicate the fixed points, a a a a the key-plates able to move TOWERS COMPLETE, BOTTOM BOOMS AND FIRST STRUTS PARTLY BUILT. to thrust them further apart, to the utter destruction of the masonry or steelwork. It was therefore decided that each tower should be fixed at one corner only, and that a certain amount of movement should be possible at the other three. Kev— , / For the sake of exactness we plates. should add that even at the “ fixed ” corner a slight circular movement was allowed. The system adopted included upper bed-plates anchored to, but able to slide upon, the lower bed-plates affixed to the (By permission of Messrs. Baker and Hurtzig.) in all directions, and llll the keys allowed a longitudinal movement and also slight play in a circular direction. The independent but closely fitting packing-plates b b b b prevent llll from moving laterally. Further provision for expansion was made at the end piers of the approaches, and at the Inchgarvie ends of th© suspended girders, and for circular movement at all cantilever ends. This subject will be touched again on a subsequent page. While the masonry progressed the work-