Knee brace to timber pile connection 3

[delagina]

I have a steel platform with cantilever that I need to have a knee brace. It is supported by 14" dia timnber pile. what is the best connection (easiest in construction, cheaper) for the knee brace to timber pile?

 

[mike20793]

Why don't you propose a detail so we can comment on it?

 

[delagina]

I couldn't think of a good detail. If I try to bolt the knee brace on the side of the pile, it would not be on center with the beam.

 

[tempeng]

Can the pile be notched to accommodate a bolted connection?

 

[MotorCity]

Maybe design the beam as a cantilever and eliminate the knee brace? The pile must be some distance above the water or ground line. With the knee brace, it appears that you will be imposing a lateral load on a portion of the pile that is not embedded in the soil. I would try to avoid this condition because I think it will greatly increase the chances of splitting in the pile

 

[delagina]

yes, it can be notched but I still cant figure out the appropriate detail with a notched pile.

it was the skin friction of soil that was critical which is not affected by the notch.

 

[msquared48]

If you could bolt two halves of an exterior steel sleeve together around the pile, thru-bolt the assembly to the pile, and then bolt the tee to a steel plate field welded to the sleeve, that could work.

Mike McCann, PE, SE (WA)

 

[jayrod12]

I'm with motor city. A 5' cantilever isn't that excessive. Why not just design the beam to eliminate the brace

 

[Lomarandil]

Can you get away with a through-bolt perpendicular to the beam, and symmetric knee braces from each side of the pile?

Otherwise, a pile friction collar like Mike suggests is a common option (more expensive than some, but cheaper than an engineer getting clever).

 

[CELinOttawa]

Spike Grids.

 

[BAretired]

Why bother with a knee brace at all? Do as others have suggested and eliminate the knee brace.

BA

 

[thaidavid40]

Similar to msquared48, if you must have a brace, but use half (or a third) of a pipe section, through-bolted top and bottom, with a tab plate projecting to bolt (or weld) to your WT brace section.
Dave

Thaidavid

 

[KootK]

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.

 

[SlideRuleEra]

Sometimes I like to do a "sanity check" on the questions... and this one is a good case.

The OP has provided no info on the loading this brace is intended to resist.
A W12x53 is a pretty capable pile cap compared to typical allowable bearing capacity of a 14" timber pile.
Since there is little info offered, I made assumptions just to see what kind of loading on a W12x53 would need a brace.

Say the W12 is a fixed cantilever beam, 60" long. Not true, but without information, I'll make that assumption.
What point loading at the tip of the beam is needed to produce an assumed modest bending stress of 18 KSI in the (unbraced) cantilevered beam? I get a point load of 21.2 kips. Deflection at the tip would be 0.37".

Ok, what does my little numbers game suggest? Quite a bit, actually.

1. A load of 21.2 kips (or whatever may be) is large enough to ask if the timber pile is capable of supporting this load (both structurally and geotechnically).

2. Any knee brace resisting a 21.2 kip force is going to put a significant bending moment into the timber pile. Again, is the pile capable of this loading? With a load of this magnitude even if it is, bending of the timber pile will probably make an brace essentially worthless (As the W12 deflects, the timber pile bends. Result - less than expected compression in the brace). Because of this horizontal load, I would be reluctant to notch the timber pile.

Maybe, if the OP provides the needed information, a realistic assessment can be made.

Note: My point in the above exercise is to try to demonstrate to the OP that "details" depend on the conditions. Don't just "pull out" some "detail" that may or may not be suitable.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[delagina]

@sliderulera, thanks for the "sanity check"

the load is less than that and yes, the cantilever would work.

i'm just used to using knee brace regardless of the load if the cantilever is more than 4'.
it's just a habit i got from my previous company, we usually design industrial structures not commercial.