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| Re: G Train: Present and Future (Opinion Piece) (1149883) | |||
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Re: G Train: Present and Future (Opinion Piece) |
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Posted by J trainloco on Mon Apr 9 18:34:47 2012, in response to Re: G Train: Present and Future (Opinion Piece), posted by Jackson Park B Train on Sun Apr 8 22:56:51 2012. The concept is the same.Not really. A header intercepts truncated vertical structure when you have a solid structure. A girder is the primary horizontal structure carrying horizontal loads from slabs and beams and transfering them to vertical structure. Googling a header will get you results that describe a lintel, not a girde or a beam. I suppose you could chalk it up to semantics, but then the various different terms for horizontal structural members, such as girder, beam, lintel, header, spandrel, rafter, joist, purlin, have no use. Each term describes a specific condition. And yes, those conditions vary widely. The tight vertical clearance means the strengthened beams(headers) will expand horizontally rather than vertically so as to have more mass bearing the load which has increased by the removal of the columns to clear a crossover. Actually, no. Looking at it in section, Structurally, a beam supported on two sides under load is under compression at the top and tension at the bottom. Because of this, material towards the center of them beam (the neutral axis) is carrying almost no load. This is why trusses are such an attractive solution for spanning long distances: you reduce the material closest to the neutral axis, and push the top and bottom flanges farther away from that axis, causing them to resist the load more effectively. Therefore, simply trying to "expand the beams horizontally" won't work. You will need to expand them vertically. Additionally, since comercially produced wide-flange members in this country can only span at most 45', and the distance needed to add a switch is probably more than that, you would need to completely reconfigure the structure in the area as I mentioned before. Structural design is not always as simple as it looks. |
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