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| Re: G Train: Present and Future (Opinion Piece) (1149690) | |||
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Re: G Train: Present and Future (Opinion Piece) |
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Posted by J trainloco on Sun Apr 8 21:27:27 2012, in response to Re: G Train: Present and Future (Opinion Piece), posted by Jackson Park B Train on Sun Apr 8 20:38:54 2012. It would not be a header, because as you described, a header is used in cold formed or wood framing in much the same way a lintel would be used in masonry construction. It represents an interruption in a continuous load bearing system (I know platform/balloon framing is not continuous, but it is spaced very closely). Tunnel structure, however, is a post and beam type construction. Beams span from column to column, and that distance between columns can vary as needed. In this instance, you would be removing columns and have the girder span a longer distance. Additionally, there isn't much clearance between the underside of the structure and the roof of the vehicles using the tunnel, so adding additional members as 'headers' underneath the existing girders is generally a non-starter. There are a number of ways one could attack this problem, but the simplest way IMO would be to either replace or thicken the bottom flange (by welding plates to it) of the tunnel roof beams which span perpendicular to the trackways so that instead of bearing on the column between the express and local tracks, it spans further to bear on the columns between the two express tracks. |
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