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Email from Milosz 10/4


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In order to determine if a bridge will be a suspension or suspended, there are the two extremes in which your choice is clear: suspended for a deep gorge with steep sides, and suspension for a flat flood plain. Here in El Salvador, the terrain is almost never so extreme, and in order to know if your choice should be a suspended or suspension, you really need to survey the site and draw it up, and then try to fit a bridge into it.

Email from Milosz 9/28:

About the costs of cement, rebar, aggregate, etc., that's hard to figure unless you know what the site is. For example, some sites would require tall abutments in order to gain the freeboard you'd need; other sites are naturally high above the river, so no additional tiers are needs beyond the meter of foundation and meter for the cables to clear the ground. The ideal site to keep the costs low are rocky cliffs high above the river. This type of site is quite difficult to find.
I'm sending over a very rough sketch of terrain I did at one of the La Libertad sites that we're going to be doing, El Charcon (SEE ATTACHMENTS tab). You can see that the relative flatness of the terrain will require four tiers on one side, and three on the other. A suspension bridge is ideal here because of the terrain (but not because of other factors, such as a paved road where we would need to put the anchor if we were doing suspension, and powerlines overhead). If we had more slope, we would require less tiers. I'm also attaching a model of our ideal situation, in which the slope and height allows us to do very little masonry construction.