×
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

Australian Standards Combination Loadcase Factor For Pad Footings

Australian Standards Combination Loadcase Factor For Pad Footings

Australian Standards Combination Loadcase Factor For Pad Footings

(OP)
Is there anywhere besides AS2870 that gives recommendations for load combinations to check against (soil) bearing failure.

I know the British Standards uses unfactored load case combinations but there doesn't seem to be any advise in the Aussie codes apart from the residential slabs and footing code.

RE: Australian Standards Combination Loadcase Factor For Pad Footings

Soil bearing capacity is usually given in allowable stress. When I have needed to give ultimate loads I have used the same load combinations as the column loading it (it is where the load comes from that counts not whether it is steel concrete, timber or soil).

By the way, there is an AS/NZS code forum under Engineering codes Standards and Certifications category.

RE: Australian Standards Combination Loadcase Factor For Pad Footings

Personally I don't like to combine ultimate limit state and geotechnical-structural design. The geotechnical engineer will give you an allowable bearing capacity and the structural engineer needs to ensure that the working loads do not exceed this bearing.

This can be any combination of Permanent Load (Dead Load), Imposed Load (Live Load) and Wind Load. For wind load, a working load must be used which is 1.5 times less than the ultimate wind load (refer AS1170.2:1989).

As for where the load combinations come from. I don't know because AS1170 (latest revision) is written in a limit state format.

AS4678 tried to incorporate a limit state approach to geotechnical parameters however there was some criticism because the material is not as well known as other building materials that structural engineers deal with so it is difficult to apply and material strength reduction factor (φ).

RE: Australian Standards Combination Loadcase Factor For Pad Footings

For mat-slab foundations it may be worth considering the reduction of live loads for cases with a number of stories, that can be substantial since the whole mat is an element receiving loads of many columns many stories high and unlikely to act at nominal live load value. Also, the failure would be less than critical in the sense that the mat ties together all columns. This reduction is permissible by spanish CTE code.

RE: Australian Standards Combination Loadcase Factor For Pad Footings

As ishvaaag has pointed out, area reduction factors for live loads can be found in AS1170.0 or .1. For footings supporting a large area the total live load run down can be decreased by 50%.

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