Why is iron over aluminum in structural of bridges and buildings?
Aluminum is considerably more expensive than iron/steel and except in even more expensive alloys requires considerably more volume to get the same strength. Aluminum is used for bridges when light weight is important such as the extensible bridges mounted on tank launchers for crossing ravines or ramps carried on planes. In buildings, besides costing more, the additional volume would cut down on rentable space in the building. And the advantages of aluminum in standing up to weathering would be nulled by being covered.
