×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Live Load Reduction for Foundations or Footings

Live Load Reduction for Foundations or Footings

Live Load Reduction for Foundations or Footings

(OP)
Here's an easy one for ya'll:
What KLL do you use for foundation design? I was looking for a code reference or commentary mentioning footings, but to no avail. Strictly by code -- I'd guess it falls to "All other members not identified" KLL = 1. Thanks in advance for your input.

RE: Live Load Reduction for Foundations or Footings

If it's a column footing, I would go by the KLL you use for that specific column. If the strip footing that supports a bearing wall, I do not consider any live load reduction.

Good Luck!

RE: Live Load Reduction for Foundations or Footings

Why don't you consider any live load reduction for a bearing wall based on influence area?

RE: Live Load Reduction for Foundations or Footings

(OP)
slickdeals - Do you matching the KLL of the member you are supporting for your footings typically?

RE: Live Load Reduction for Foundations or Footings

Slick:

Looking at the numbers, for live load only, for a one foot strip, say 25 foot bay, it would take up to the seventh floor to overcome the 400 square foot break point in ASCE7-10, section 4.7.2, no reduction could be taken until you reached the seventeenth floor... (400 / 25 = 16).

Hence, the tendency to ignore LLR for strip footings.

Mike McCann
MMC Engineering

RE: Live Load Reduction for Foundations or Footings

But wouldn't a bearing wall be able to distribute loads over the length of the footing. Let's for instance forget that we are designing it on a per foot basis and think of a 40 ft long bearing wall every 25 ft. Seems like we should be able to account for having probabilistic live load reduction.

RE: Live Load Reduction for Foundations or Footings

I tend to agree with slickdeals but the work we do is generally wood framed on concrete walls and so for the area calculation we use a footing length that is equal to the concrete wall height above, i.e. 10 foot tall foundation wall supporting 25 foot width per floor then we use 250sq ft per supported floor. We are fairly confident that the concrete wall will spread any loads over at least that length(in fact if you were to use the 45 degree "rule" you could in theory assume a 10 foot high wall will spread its load over 20ft).

RE: Live Load Reduction for Foundations or Footings

I can see that logic too if you treat the bearing wall as a deep "beam", but spreading out the load is really not part of the solution here. The code is not really clear on that though. Any reduction in live load allowed is due solely to the relative probability of not being fully loaded to the design live load, based on the total area supported - the more area, the more chance of not being fully loaded.

Mike McCann
MMC Engineering

RE: Live Load Reduction for Foundations or Footings

Mike,

I see what you are saying. I still feel that LLR should be able to be used for a strip footing as the wall will redistribute the loaded area to a neighbouring unloaded area and as such looking at only a 1 ft width of footing seems way too conservative.

RE: Live Load Reduction for Foundations or Footings

For walls, if I have some two-way action (such as in a CMU wall) I will use the area of the entire panel for things such as wind load reduction. A 12" strip is just to penal.

The footing just needs to carry the same load as the wall or column which sits on it.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources