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dhengr (Structural) |
24 Mar 12 1:34 |
Hokie: You know the expression 'a rose by any other same is still a rose.' Well I think a strut = a raker. But, I'm not sure I would consider them pinned at the ends, at the walers.
MJ23: I think the question of any moment in the strut/raker, other than self weight of the spanning beam/column/strut has to do with the connections at the walers. If you frame this sloped strut into the waler flange furthest in from the sheet piling then you induce a twisting moment (set of forces) into the waler, and this might be taken/reacted in partly by a strut fixed end moment, not an easy detail, but these forces still have to be taken back to the sheet piling. However, if you frame this strut into the underside of the web of the upper waler, and into the top side of the web of the lower waler, with some sort of gussets/web stiffeners, you prevent the waler from torsional loading (rolling), you put the load into the waler webs and into the flanges nearest the sheet piling, and you can pretty much rationalize most of the end moment or waler twisting away. This is still a pretty indeterminate structure and connection, so don't ignore the moment and summation of forces in the connection, resolve the statics right at the connection, but the moment shouldn't be too significant. You still do have horiz. and vert. force components on the waler flange right at the sheet piling though and this can start to pull/lift the piling out of the ground if your not careful. Of course, the waler still spans from one strut to the next raker, to react the sheet piling load (F). If you roll the waler too much, with your wedge scheme, you start to weaken it and have to deal with biaxial bending and torsion in the waler, not a good thing. There are several fairly good typical details of these type connections in the links which were posted, or the links within the links.
I agree with Hokie, the moment in the strut is certainly not (F)(y). Your design reviewer is ignoring the fact that there are horiz. and vert. forces at each wall keeping the whole system in equilibrium. Instead he is assuming that the only stability is offered by a fixed end moment at one wall or the other and that moment is (F)(y), and I don't agree with that. There may be some difference btwn. the horiz. force (F) at the two different walls, because of different wall heights, different surcharge loads, etc. But, I think even those can be resolved btwn. the horiz. and vert. forces in the two walls, through the compression in the struts. |
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