Why Do We Need Corner Braces in Shoring Systems 3

[KootK]

Local shoring contractors in my area always seem to use corner braces in conjunction with their tie-back shoring systems. Why are corner braces used instead of continuing the tie-backs right into the corner? Is it because the machine used for tie-back installation cannot get physically close to the corner? Are there systems available that do not require corner braces?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Retrograde]

My guess is that the corner braces are less expensive than the ground anchors.

 

[PEinc]

Corner braces are usually less expensive than tieback anchors and the tieback drills can have a problem drilling so close to a corner. As long as the corner braces do not interfere with the new structure, they can be a good alternative to tiebacks.

http://www.PeirceEngineering.com

 

[jayrod12]

I've always just designed the waler to waler connection at the corner to act as a support and omitted the corner brace. In reality it's all welded together solid and will act that way regardless.

 

[KootK]

As long as the corner braces do not interfere with the new structure, they can be a good alternative to tiebacks.

So, if one were willing to pay extra, is it possible to not have corner braces then? My current issue is that some corner braces need to be removed prior to the casting of a foundation wall and now the shoring engineer is asking me to assess my parkade diaphragm's ability to resist considerably more than a single story worth of earth pressure. Frankly, in retrospect, I surprised that this hasn't cropped up before.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[PEinc]

A waler without a brace does not provide lateral support. With only the two, short, perpendicular walers but without the corner brace, one wall would need to be supported by the other, perpendicular wall that also is not braced. While it may sometimes work in the field, it doesn't work on paper. It should have the corner brace.

Another consideration is that the walers should be long enough and welded enough to the sheeting wall to properly transfer the walers' axial loads to the soil behind the walls or to the waler and wall on the opposite side of the excavation. I have seen soldier beams and SSP push laterally along the wall because the walers were not long enough. The hard question to answer is, "How long is enough?"

http://www.PeirceEngineering.com

 

[PEinc]

If corner braces are located below the top of the proposed foundation wall, then the forms for the concrete wall need to be boxed out around the braces. Then, after the walls are poured and have their final lateral support (floor slabs?), the braces can be removed and the wall box-outs can be patched.

If you need to have walers with your braces, then the sheeting needs to be offset from the proposed wall by about 3 to 4 feet to allow room for the waler, wall forms, waterproofing, and backfill. If the concrete wall needs to be poured directly against the sheeting wall, an alternative, SOMETIMES, is place the braced walers above the top of the proposed wall, if possible.

http://www.PeirceEngineering.com

 

[KootK]

Are we calling the non-hypotenuse members in my bracing sketch whalers? If so, mine currently exist in the same plane as the foundation walls.

If you need to have walers with your braces, then the sheeting needs to be offset from the proposed wall by about 3 to 4 feet to allow room for the waler, wall forms, waterproofing, and backfill.

This is essentially placing the whalers on the exterior side of the foundation wall, right? Wouldn't that mean that, in plan, the shoring would look like a castle with "turrets" offset out at the corners? I'm having a hard time imagining that a contractor could be persuaded to do that.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[PEinc]

Your non-hyp members are walers. Walers just collect the bracing load along the sheeting wall so that it can be applied to the braces and then be reapplied to a wale and wall on a different side of the excavation.

www.PeirceEngineering.com

 

[PEinc]

Corner braces also help reduce the required size of the walers by reducing the waler span length.

www.PeirceEngineering.com

 

[hokie66]

KootK,
Your initial sketch seems to indicate a secant pile wall with anchors. This type wall does not typically require walers.

 

[PEinc]

I don't understand your turret question. The attached PDF shows how wales and braces could be installed with off wall line sheet piling. Soldier beams or tangent pile walls would be similar. For this job, we located the braces and wales at elevations just above the wall construction joints. Therefore, you could shore the new walls in order to take out a brace level. Because this was a structure below the ground water table, the owner did not want the braces to penetrate through the concrete walls which would have needed to be patched after brace removal.

www.PeirceEngineering.com

 

[PEinc]

With the correct sized waler, you might be able to spread out your tiebacks and save some money. Eliminating several tieback anchors will pay for a lot of extra waler steel. Also, the sketch appears to show a waler for the tiebacks, in addition to the corner braced waler. If the tiebacks are on walers, you want to drill the ties through the unreinforced shafts, not through the shafts with the steel beams inside. Also, with the correct waler size, you can probably keep the tiebacks far enough away from the corners to eliminated the corner braces and still have enough room for the tieback drill.

http://www.PeirceEngineering.com

 

[Retrograde]

Your initial sketch seems to indicate a secant pile wall with anchors. This type wall does not typically require walers.

All the secant pile walls I have seen (and/or designed) have a waler unless lateral support is only provided at capping beam level.

 

[hokie66]

Walers can be a part of the support for the piles, but when you provide temporary ground anchors at alternate piles as indicated by KootK's sketch, walers would be superfluous. Walers do get in the way of further construction.

 

[Retrograde]

Walers can be a part of the support for the piles, but when you provide temporary ground anchors at alternate piles as indicated by KootK's sketch, walers would be superfluous. Walers do get in the way of further construction.

I agree. I had not noticed there was an anchor every hard pile. I am used to seeing an anchor every third soft pile with a waler.

 

[hokie66]

No doubt there are lots of variations of the system.

 

[KootK]

My system, and that most commonly used in my area, is secant piling that has no walers other than those that are part of the corner brace (if we're considering those to be walers).

I don't understand your turret question.

See the sketch below. It probably makes no sense. It was just my shot in the dark at trying to sort out this statement:

If you need to have walers with your braces, then the sheeting needs to be offset from the proposed wall by about 3 to 4 feet to allow room for the waler, wall forms, waterproofing, and backfill.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Panars]

So what is it that you are showing between the secant pile and the anchor head? That is what we were thinking was a waler beam.

 

[KootK]

Ah. What I'm showing between is a concerte basement wall. The anchors should have been positioned within the wall rather than in front of it.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.