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Point Load on Existing Stemwall and Footing? What Module to Use?

Hello,

I work on remodels and often need to know if the existing stemwall and footing are adequate for a new point load.  


Present issue:

I have a roof beam point load going down to an existing 8in x10ft tall stem wall on 16x8 footing.  


This is quite a different instance than a post on a footing.  My existing 10ft stem wall would spread that load out across the whole footing at 45 degrees from the point load 10ft above. 


Can you tell me the best module to use for this and how to?


Thank you, Barry




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Barry,

I have a way of doing this, but it takes some steps that are quick to get used to when you do it frequently as i have been. I have been doing the following with StruCalc to accomplish what you are asking:

  • Use continuous footing design
  • Use the Load Calculator for typical loading on the wall in which you are placing the point load (don't add the point load here.)
  • Input the existing footing and stem wall heights and calculate (this would be your existing conditions.)
  • In the Member Notes section, write down the LL/DL in plf for your reference of the typical wall conditions. Be sure to hit 'save' since you will lose this if you toggle away from the Notes tab.
  • Take your point load and convert it to plf based on the height of the stem wall. Here's an example: 1000# LL / 500# DL with a 4'-0" stemwall. The load travels in a 45 degree angle so the spread of the load is 4'-0" in each direction for a total of 8'-0". So the point load with a 4'-0" stem wall would be 125plf LL / 62.5plf DL. I write this below the other notes for the typical loading and state "point load in plf with 48" stem wall." Hit save again.
  • Now uncheck the 'load calc' button and add up the typical wall loading you made note of with the point load in PLF data and input that in the LL / DL area.
  • Click calculate.
  • If it passes, I will write a note stating that the existing footing is adequate for the new point load. I've had zero issues (so long as I have my notes filled out w/ existing and point load conversion) with the Northern VA building officials regarding this method.
  • If it fails, I delete all my notes and size an overall footing as if the column/post was an 8"x8" concrete column and insist the contractor supplement the existing footing. Depending on the age of the structure, the soil bearing pressure could be increased, but this is a case by case basis and only if the footing is very close to passing without it.
I do wish this could be automated in the program, but this works well for me.
I hope this helps.
Melissa



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