Roman Truss Bridges Rule!

[caesar novus]

Quote

Other advancements Romans made in construction involved timber and metal. The  truss was a Roman invention. Roman armies used bridges with trusses that allowed them to cross the Danube. The truss was also carried out using metal, with the first appearance of it in bronze (... from moduloc.ca)

Roman truss bridges get such little appreciation, built of biodegradable triangles of timber, so let me try to remedy with half remembered fun facts. Have you ever seen a railroad bridge that WASN'T a truss? Trains almost always need the rigid strength of triangles rather than fooling with those pretentious cable monstrosities for vehicles. Do you know that famous suspension bridges like in Tacoma and San Francisco had to be retrofitted with underside trusses to avoid whipping in the wind? https://www.youtube.com/watch?v=XggxeuFDaDU

I didn't fully understand this until the video below. A simple beam construction, whether for bridge or temple or aqueduct is fragile because it bends in proportion with the CUBE of it's length. Double the length makes it one eighth as strong. You can address this with a very expensive stone arch bridge. Or make a truss bridge which oddly has NO bending stress at all if built correctly. BTW a bridge building class I took claimed that many modern designs would be cheaper as intricate truss bridges if labor for public projects stayed at fair market levels.

 

[caldrail]

Railroads also use girder frames. Truss bridges are not universal.