I have three questions for anyone who can help me out. We have read about engineers inspecting, testing and proving their structures and/or components. How is this done? Paxton had made his "prototype" for the Crystal Palace in the construction of the Lily House. Do engineers make physical models of their designs? Is this now all computer-generated?
Petroski also mentioned the testing/proving of beams. Is this still done the same way, by applying weight at different stress points. Do those of you how are not civil engineers have other ways of testing/proving your designs or materials?
My final question is, why did they have to test every cast iron beam, but only a sampling of the wrought iron beams? How are these different?
Engineers always prototype. When I worked in industry designing two way radios ("cop car radios"), we went through 4 prototype builds before fixing the design and putting it into the factory. All the way through everyone worked on their own pieces, but the overall radio had to work together, not just the individual parts on a workbench. Then there was months and months of testing and creating documentation and getting the factory up and running.
ReplyDeleteSome prototyping can be done on computers, but computers cannot model the variations that exist in the real world, so real physical prototypes are needed.
Cast iron is cast by pouring molten iron into a form. The molten iron varies quite a bit. However, wrought iron beams are formed essentially the way a blacksmith works. This process distributes impurities and weaves the iron into a more uniform structure.
One way to think about this is making bread. When you knead bread ("wroughting" it) you make the bread more uniform (no clumps of flour or yeast). However, if you just mixed up bread dough and poured it into the pan for baking, the bread would not have the uniform texture and properties that kneaded bread has. That's my 2 cent explanation. The wrought iron beams were made after the bread dough was fully kneaded, so each wrought iron beam had the same qualities as the others. That's why they did not all have to be tested.
Great analogy.
ReplyDeleteThank you so much! Your explanation is terrific - as a bread-making I truly get it (and the kneading also breaks down air pockets that can make the bread bake with "holes" in it!)
ReplyDeleteAs for the prototypes, I thank you for the clarification. I am happy to hear that there is modeling going on at each stage. That must be truly the only way to predict failure in a design that is new, or uses new materials.