Laterally loaded shallow pier - pressure on retaining wall 1

[RFreund]

I'm trying to figure out the "best" way to analyze the effects of a light pole or wood fence (any shallow pier foundation that is laterally loaded) foundation on a retaining wall. This may be a situation where there is more than one way to skin the cat.

I've attached 3 different analysis options that may be semi-reasonable and wanted some feed back as to whether one is more/less realistic than others or if they are way off and I should be using a different approach.

Thanks in advance.

EIT

 

[cap4000]

What is the average clear distance from the wall to the pier.

 

[RFreund]

Lets say 2 feet. However, why do you ask? I was trying to formulate something that I could use case to case.

EIT

 

[irawanfirmansyah]

RFreund,
The attachment shows the forces on rigid foundation of the pole, and the soil reaction induced by the forces.
The soil reaction will be distributed, and finally it works on the wall.

 

[RFreund]

irawanfirmansyah-

You post seems very helpful, however the attachment opens up to a blank word document. Not sure what the issue is.

Thanks

EIT

 

[ishvaaag]

Since I have "perfected" my initial model it has taken me half an hour to produce FEM model and results; if on a daily basis and with prefab pre-models it should take 10 or 12 mins. Just in this case an elastic model of soil and concrete, 100 kg horizontally atop a 16 m tall mast, 30 cm thick wall.

The model...

 

[ishvaaag]

... and results. (constraints, ranges... can be manipulated etc). Assumed weightless soil and concrete to only examine pole effect.

 

[irawanfirmansyah]

RFreund,
I resend the attachment. Hopefully it is useful

 

[RFreund]

Thanks guys for the responses, both are helpful.

Ishvaaag - I don't have access to an FEA program like that (I don't believe) However thats pretty cool how you did that. I'm not very well versed when it comes to FEA, I would like to be some day. What did you use to model this?

EIT

 

[ishvaaag]

The model was made in Spaceclaim. It is just a fraction more speedier than making it in "ordinary" Autocad. The finite element model was made in Autodesk Algor Simulation.

Note that not everything is perfect in the sense of that when attempting to put appropriate constraints at the interfacing surfaces etc difficulties arise for a proper representation of the interaction (friction-slippage, separation-compression only and so on) and the finite element program's capability varies at that; there are over there even papers on the proper representation of geotechnical matters for the constraints. Abaqus and ANSYS stand at the top but there are many others, even free ones, CAE Linux, for example, that I am yet to test and for a thing like this- should do I think as well as Algor; but it is Linux and I would have to set some machine for a CAE Linux environment, (it is just a Linux system regged to run the set of finite element programs, and when around a year ago I investigated such thing was not as satisfactory as following using our "ordinary" Windows, surely a matter of custom and having everything based on Windows).

I think there are also free FEM programs in the Windows environment but I have not yet tried the extent of their capabilities, there is so much software one doesn't reach what exists even if having whole dedication to it.

It is important to say that as soon as you are away of the point of application of the loads for elastic systems the St. Venant principle applies and even bad set constraints give reasonable estimates of the state; but your problem is one that (at least for the soil) closer stresses and strains are of interest and so you only will get proper estimates with refined models, in this case, through proper establishment of contact (footing or wall with soil) conditions. For the wall such issues would be of lesser interest since anyway the effect of the pole will be in a limited zone and some variation of the reaction on the wall should not mean much effect on the stresses induced there, relative to the whole extent and design of the wall.

Plus, it is unlikely that in one elastic model yo may get refined estimates of anything about actual behaviour of something having soil in the model; you soon will start to see staggering values for the stresses by what nor backhoes nor footings would stand in place, and soils would start flowing. They are stopped fortunately at secondary equilibrium and still limited damage to structures but your FEM analysis in an elastic setup is then of limited value.

 

[RFreund]

ishvaaag,

You are one smart dude.

EIT