Holy Rebar!

[DaveVikingPE]

What do you folks think about this:

Got a retaining wall that's GOT to be a certain maximum thickness, no more. Idea! Drill holes in the waler beam and insert vertical rebar through the holes.

Me? I don't like the idea too much, but...

 

[dlew]

DaveViking,

Is the wall cantilever or anchored? If anchored (I assume it is anchored since it has a waler), the moment in the wall due to soil pressure will increase with the stiffer wall section.

Is there a steel sheetpiling wall on the back? If so, you should give some consideration on how are the loads going to be distributed to the sheetpiling and to the concrete.

Regards

AEF

 

[DaveVikingPE]

Cantilevered.

It's a soldier pile wall and instead of lagging between soldier piles, there's going to poured-in-place concrete "curtain" panels. The waler tranfers the loads to the soldier piles, etc.

What I'm concerned with is the technique of cutting (drilling, burining, etc.) holes through the waler and setting vertical reinforcing steel through the holes. Is this a common technique?

 

[dlew]

DaveKing,

A very common waler for bulkheads is made of two channels back-to-back, but separated enough for the anchor rods to pass through. These channel are connected togethers at their webs with bolts and spacers, normally at 18" on centers. Thus, those walers have a lot of holes in their webs.

Small holes (less than 1/3 the depth of the shape) can be drilled in the web of beams without reducing their flexural or shear capacity.

Is there enough space between the waler and the forms to pour and compact the concrete? It may be a little tricky to get the concrete to fill all the space under the waler.

Regards

AEF

 

[DaveVikingPE]

Aye, there's the rub...

The configuration of the wall is such that there are no anchor rods. And... using double-channels isn't an option...

Here's what I've got: two 24-inch concrete-filled caissions act as soldier piles, they're spaced at some distance. Between them - and covering them - is a concrete wall. If you didn't know about the soldier piles, you'd think the wall was simply a reinforced concrete T-wall. Well, let me be more clear: the concrete wall is fronted by sheet piling.

Because of customer constraints (totally out of my control as I'm being directed by a much more senior engineer than I) the wall cannot exceed a certain thickness. The much more senior engineer than I directed me to put a waler (for lack of a better term) between the caissions in case the reinforced concrete cannot take the loads (these being wave loads). OK, even though I designed the wall for these loads, there's no harm in beefing up the design since the money is there, etc., etc.

So I came up with a "waler" (OK, this is more like a vierendeel truss-frame system than a soldier pile wall, no?) that was adequate for the loads in question and layed it out in what I figured was appropriate:

A lightest-weight W shape (like a W18xless-than-100lbs/foot) would be connected to the caissions such that the centerline of the caissons and the waler (strong-axis facing horizontal) lining up. This allowed enough inches for placing rebar in front of the waler and in back of the waler as my wall design required. The wall would be poured in lifts, the first up to the waler, then the waler is connceted, then complete the wall in a second lift, keying appropriately into the first pour, etc.

The senior engineer became concerned that torsional effects would cause cracking in the concrete and to avoid this I should bolt the waler to the sheet pile. OK, if I do that I lose the symmetry (centerlines of caisson - centerline of the waler, etc.) of the connection and the waler requires that the vertical rebar be discontinous as the waler is now in the way.

"Cut holes in the waler and call-out the rebar to be continuous through the waler."

These are #8 bars. So.... 8/18 = .44444 > .33333.

I don't like the idea, frankly of cutting holes in the waler as, well, it just doesn't seem correct and would add a lot of cost to construction (a lot of holes...).

 

[PEinc]

Contact a specialty design-build contractor, such as Schnabel Foundation Company (

http://www.schnabel.com)

to see hoe permanent, soldier beam/lagging/tiedback walls are designed and constructed. Usually, soldier beam walls with permanent concrete facings do not have wales.

 

[DaveVikingPE]

Thanks, PEinc, but that's really not what I'm after at all. I know how to design soldier pile walls (the CALTRANS manual, "Solider Pile systems" is my "soldier pile bible" perhaps I should've qualified my description with "...the caissons, for lack of a better term, may be considered soldier piles..." Though I did put the word "waler" in quotes so I did qualify my description to some degree.

I am in a situation where the structure has to be designed as I've described. The design has gone out for review by several engineers, so we'll see what the reviewers have to say about putting holes thorough the "waler."

But if anyone has any tips on the "holy rebar" issue, please add to the discussion!

 

[ChipB]

I don't know anything about this type of wall system but, if I'm reading this right:

Senior Engineer is suggesting to bolt directly to the sheet pile? How are you planning on keeping the water (permanently) away from your W18? Steel embedded in concrete with water (potentially) intrusion through the bolt holes. Ugh! I don't think it would last for the life expectancy of the wall. The process of the steel embed corroding will cause serious spalling in the concrete. Better to do it with adequate concrete coverage of your steel, as you initially intended.

You stated there would have to be two lifts. You'll need to provide holes in the web anyway (strong axis horiz. right?)for the air to escape during the pour. Otherwise you'll have a serious void on the underside and will not transfer the shear forces to the beam as you intended.

Can you decrease the size of the W-beam by using shear studs for composite action? That would give you even more room to get the reinforcing by, and thereby more concrete cover.

To your original question, if I did this, I would detail it such that I used dowels through the holes in the beam and provided the required lap above and below the beam with these dowels. I'd be really worried about the steel corrosion issue though.

Hope this helps

 

[DaveVikingPE]

Excellent questions to bring up, ChipB!

Yep, water coming through the bolt holes worries me, but... hey, I'm just doing what I'm told to... I made not of it; the upside is that this is a preliminary design, i.e., feasibility-level and a lot of other engineers will be/are reviewing the work - and I anticipate that they'll bring up corrosion issues related to the bolt holes - though we could add a water barrier of some sort...

As far as shear studs go, yep, I have 'em in my original design, welded to the sheet piles, too! But no, gotta bolt the W to the sheet piles, too.

Since there have to be some holes in the beam for air to escape, I don't - at this point - feel so apprehensive about cutting through it, at least for that purpose.