Sign Foundation 5

[rittz]

I have been asked to design a a concrete foundation and structute for a sign (piles and Pile Casp ?) Sign 8 to 10 ft wide 30 ft high. Not having done this before looking for source of information or other help . I would expect a geotech test would be a priority. The sign supports would be 2 30 ft WF's 10 ft apart with solid signage between.

 

[steellion]

A geotechnical investigation is ALWAYS a good idea for any foundation design. For design of the sign itself, see ASCE 7-05 Figure 6-20 which addresses solid signs specificially.

 

[Lion06]

You have 2 choices without a geotech report.


1.) Go to ASCE 7-05 and get the appropriate wind loading. Use that wind loading along with IBC 2006 1805.7 to determine the required embedment of the WF's.

2.) Go to ASCE 7-05 and get the wind loading. Use that wind loading along with IBC 2006 1805.7 to determine the required embedment of a sonotube pier.

 

[rittz]

Thanks for the info. We are in Canada and are not Familiar with ASCE 7-05 ...Sounds like American Society of Civil Engineers ...right ?
Ritz

 

[steellion]

Yes, ASCE 7-05 is the structural code in the US defining minimum load requirements on buildings and other structures. In Canada, the code requirements may be different.

 

[rittz]

Sign

I am thinking toward the columns base plate bolted to a the conc pile cap as opposed to straight embeddment of the cols

 

[RWF7437]

WinPost will help you analyze your embedded posts. The program will perform a stress analysis on the posts and determine how deep the posts must be embedded into the ground. The program has a simple section property calculator, soil database and Wind load calculator. You also have the option to enter a single lateral load on the posts as well as an axial bearing load.


Google Archon Engineering. Moderately priced.

good luck

 

[BAretired]

In Canada, climatic information is provided in the various provincial codes. You will need Commentary I "Wind Load and Effects" in the User's Guide to determine appropriate coefficients.

I would strongly suggest enlisting the help of a geotech to establish criteria for pile depth.

BA

 

[enginerding]

Direct embedment of the poles is the best way to go.

Piles, pile caps, and anchor bolt foundations will far too expensive to consider unless the soil conditions dictate this is the only way to go.

If you give them the design using piles and pile cap, my guess would be they would find another engineer that would provide direct embedment and use their design instead.

 

[BAretired]

enginerding,

I don't agree with your comment at all. The majority of signs I have seen are steel HSS or WF members with base plates.

The pile cap is handy for placing anchor bolts. It is usually formed with a sonotube of the same diameter as the pile.

BA

 

[youngstructural]

Agree with BAretired... Star.

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!

 

[MiketheEngineer]

Burying the posts is by far the easiest and cheapest today. But you will never be able to monitor corrosion or condition of the post. So if its for one year - sure. If is for 20 years - forget it.

 

[enginerding]

I am just telling you from my experience in the states.

Please let me know how you monitor corrosion or condition of the piles?

You have all the same problems (or more - e.g. anchor misplacement, bent bolts, jacked-up threads etc.), but you pay more than triple for the foundation at the start!

Drill the hole, drop the steel column to just above the bottom, pour concrete around it, done.

 

[youngstructural]

engineerding:

That's different from what I inferred from your first post... Obviously it's not what you expected to imply, but I (and I'll hazard to guess BAretired et al as well) though you meant naked driven column shafts as the foundation...

If you cast the column into the soil an pour concrete around it, I wouldn't call that direct embedment. I would agree, however, that it is an excellent solution and a good way to go. The solution is predicated on the ability to source and handle long enough columns to get the embedment required.

At 30ft out of the ground, and I'm guessing about 6ft into the ground, we're just about pushing for length. Also this commits the project to field work on site unless you can get the fabricator to deliver the fully assembled sign (not out of the question, but I've seen and heard of trouble in this regard).

A star for your excellent idea, now that I actually see what you meant! lol

Regards,

YS

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!

 

[asixth]

rittz,

Instead of posting for your thread under Concrete Pile Engineering I will post here because there seems to be much more discussion going on.

My design had an overturning moment of 340kN-m (250kip-ft), it was socketed 2m (7') into DW rock. So the passive pressure I needed to resist the overturning was 300kPa (6kips/ft^2). Can someone please correct me if my SI-US conversions are wrong.

I spoke with a geotech who recommended that the passive resistance is 9*Cu where Cu is an undrained shear strength of the soil. Once on site they drilled a borehole and certified that the DW rock had a Cu of 100kPa (2kips/ft^2) which gave the design a high enough safety factor.

This sign is slightly larger than yours and used W20 columns with a 1-1/2" baseplate. From memory there was 8-10 anchors (1-1/4" dia) embedded 2' into the pile.

Pile was reinforced with 0.5% longitudinal reinforcement.

I think YS is using a H/5 rule as a quick estimation of pile embedment for large sign structures which is a good rule of thumb.

 

[enginerding]

9*Cu is ultimate. You should use a factor of safety on that - usually 3.0.

 

[BAretired]

rittz,

I'm curious as to the ultimate passive pressure distribution in the little sketch to the right of your diagram, especially when the soil is softer than sandstone, say clay.

I have added a sketch showing my guess at the pressure distribution under rigid body rotation. For soft soils, you would need a considerable pile depth to develop the moment resistance you require.


BA

 

[jike]

In our area, I have seen a backhoe just simply dig a deep trench approximately the length of the sign to whatever depth is required by calcs, lower a cage of resteel in and fill with concrete. This can be done with steel columns or anchor bolts embedded into the foundation.

Quick and simple!

 

[youngstructural]

asixth: Exactly right. From there I use a set of modified Terzaghi equations to do the embedment.

As for actually calculating the depth of embedment there's some very good information for light poles (both timber and other materials) into all sorts of materials available.

Cheers,

YS

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!

 

[rittz]

asixth and/or BA
How do you get sketches into your message