Switched from ASD to LRFD for anchor design

[gbuell]

I work for a company that makes lots of standardized steel structures, and our design method is currently ASD. We have loads of calculation templates that use ASD for design. We have historically used post-installed epoxy anchors to attach our columns to concrete, but we are now running into a few jobs that would benefit from using cast-in-place anchors instead of post-installed anchors, because of scheduling etc., and I have no standard calc templates for designing cast-in-place anchors. Up to now, I've been using Hilti's PROFIS anchor software for designing post-installed anchors, and that has the option to use ASD for design. If you're curious, here is what the PROFIS program says about using ASD:

"3b. Allowable Stress Design; United States
Allowable Stress Design is based upon applying a safety factor to a mean ultimate load for a given anchor diameter and embedment.
Load data is derived from testing per the provisions of ASTM E-488, ICC-ES Acceptance Criteria AC01 for mechanical anchors and AC58 for adhesive anchors.
Safety factors are determined using statistical analysis.
Allowable Stress Design can be used pending approval by the Official Having Jurisdiction and the Engineer of Record. Allowable Stress Design is only used with post-installed anchors."

I understand that designing cast-in-place anchors by ACI 318 requires the use of LRFD. My question is this: is there anything wrong with taking service reactions from my standardized ASD structural calcs, applying the LRFD load factors to them and designing my cast-in-place anchors that way? Or is there any reason that mixing the design methods is a bad idea? (Before you suggest it, I should say that I'm in no position to convert all my standardized structural calculations to LRFD at this point.)

 

[fancypants]

Factor for strength design and forge ahead.

 

[DST148]

Agree with fancypants. Per AISC Manual 14th Ed., Section J9 - Anchor rods and embedments: Design of column bases and anchor rods for the transfer of forces to the concrete foundation including bearing against the concrete elements shall satisfy the requirements of ACI 318 or ACI 349. You may refer to commentary for additional info.
We still design multistory steel framed buildings using Allowable Stress Design of AISC 9th Ed., but use ACI 318 for foundation design including anchoring to concrete.

 

[southard2]

I do almost everything is ASD in my practice. When I get to those concrete foundations I simply take the service load reactions and multiply by the appropriate factor. I'll admit though to routinely over doint it a bit. If I have a 20 psf roof load and a 20 psf live load I'll simply multiply my total load by 1.55 which is conservative. So if your in doubt you can always factor all of your reactions by 1.6 and that would be a conservative way of factoring your service loads.

John Southard, M.S., P.E.

http://www.pdhlibrary.com/

 

[hokie66]

Strange, isn't it? For years, a lot of us designed concrete buildings with Ultimate Strength Design, but reverted to Working Stress Design for the footings. Now folks want to go the other way.