do estimate settlement in your foundation calculation?

[delagina]

I'm looking at Bowles book, settlement chapter. It said settlements must be estimated for buildings, bridges, towers, etc.. However, ALL excel and foundation software I have used doesn't have settlement check. I also haven't seen a foundation calculation in my industry where there was settlement check.

 

[jayrod12]

Generally the bearing pressure we receive is determined based on allowable settlement. The report will generally indicate what settlement is expected at the bearing pressure indicated.

For deep foundations there's generally something about expected settlement in the reports as well.

 

[delagina]

I think this is in soil report. I read one of the soil reports and it said, if recommendation is followed, settlement should be within tolerable limits.

 

[BigH]

That would be a typical statement in a soils report @delagina. Usually this is taken as 25 or 40 mm (India seems to use 40 mm as their "benchmark" - USA, Canada use 25 mm (i.e., 1").

As a structural engineer, however, you should be very specific to your geotechnical consultant if you have maximum settlement criterion/criteria. In other words, some equipment may only accept a maximum of 10 mm of settlement. The geotechnical consultant needs to know this. As settlement computations are only "estimates" (I wrote a post in another forum on this - post is called FOS for settlement or something like that), with stringent requirements you may very well get a very conservative value - but for such structures look on this as additional 'insurance'. (Remember, your COV on concrete and steel properties is typical 5% or so; on soil properties it is in the order of 25 to 50%).

 

[oldestguy]

To elaborate a little, if you have a situation where you may be able to accept more settlement than some local rule, etc. or can't stand much differential settlement, you may ask your geotechnical engineer (usually a separate company) to provide you with a chart relating load on one axis and footing size on another, but with then lines of equal settlement shown. That way, the design would vary the pressures on the footings so that the predicted settlements would be equal. On that basis you may be able to use larger footing pressures (and smaller footings) for your project. I've done this for a few differential settlement touchy jobs, but rarely.

I should add that I use a spreadsheet program I made up for individual settlement computation estimates. To prepare that chart I'd probably run at least 10 such computations and then prepare the chart from that group of points. One probably could go to work with that system and have it do the whole batch of computations and result in the chart. More that I want to attempt. You need the soil settlement parameters for the whole depth of influence from the structure as part of the input.