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Moment in Inclined Raker

Moment in Inclined Raker

Moment in Inclined Raker

I did come across the following related threads:


The question I have, which did not appear to be explained (or at least to the point that I was not sure), was if the inclined raker should be designed for bending moment or not.

At the moment I have two sheet pile walls with a strut in between them.  The strut between the two walls must be inclined instead of being level (a design requirement due to field conditions).
I was planning to detail the ends with wedge plates so that the waler will be rotated (instead of waler web being horizontal it is rotated).

I did note from other threads that at least one respondent indicated that they typically did not design rakers for moment (just axial force).  However our design reviewer has suggested that the moment (due to the inclination of the anchor generating a moment M = F * y, where F = horizontal component at the brace level and y = vertical distance between elevations of the strut at each sheet pile wall).

Any insight appreciated.



RE: Moment in Inclined Raker

Sounds like a strut to me, but I couldn't open the attachments.  Just because the strut is inclined, it does not have to be subject to bending (except for self weight bending).  If the end connections are considered pinned, then no moment.  If there is bending, it is not F * y.  Perhaps your reviewer can give you a better explanation of his thinking.

RE: Moment in Inclined Raker

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.

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.

RE: Moment in Inclined Raker

Hi MJ23bridge

As others have said I can only see an axial force running parallel with the strut, if the ends are considered as pin joints then it cannot carry a moment and further more it becomes a two force member which means the resultant load run through it from one end to the other.

RE: Moment in Inclined Raker

Can read it now.  The strut is subject to axial load, but you need to prevent rotation of the walers.  Some of the details in the previous threads are applicable.

RE: Moment in Inclined Raker

As the excavation proceeds, the top of the sheet piles will deflect inward.  That deflection will cause rotation at the point where the waler meets the sheet pile.  The outer flange of the waler will rotate so that it is flush with the sheet pile.  The connections are not hinged and there will be negative moment (tension in top fibers) at each end of the strut.  

The weakest part will be the web of the walers and some web stiffeners may be required.

The negative bending moment is not caused by the slope of the strut. It would occur for a perfectly horizontal strut.


RE: Moment in Inclined Raker

You have a single bolt fastening the clip angle to the wedge plate.  If that bolt could be aligned on the centerline of the strut so that the clip angle could rotate freely to match the slope of the sheet pile, then you would have a pin connection, hence no moment.

Also the clip angle should project slightly beyond the wedge plate so that rotation is possible without the waler flange bearing against the wedge plate.


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