Foundation design, Strength vs Working Stress

[StrEng007]

Do any of the more seasoned engineers here have experience with working stress design in regards to spread footing design?

All of my experience for foundation design has focused on ACI's strength design methods. I recently picked up a copy of an old foundation design book that utilizes strictly working stress methods. I'm interested in working through some examples as I see the value in being able to understand how structures used to be designed.

For those who still dabble in both worlds, what can you summarize in regard to your understanding of the different types of results you get? Are there any benefits or areas where knowing the working stress method provides a more direct answer that you can legally hang your hat on? I'm trying to determine if this is somewhat analogous to the engineers who still comfortably use the "ASD 9th Edition' for steel design.

 

[JLNJ]

Working stress for concrete was central to ACI318, then it got kicked to the Appendix as an alternate, then it was removed from 318 altogether. I don't think you can hang your proverbial hat on Working Stress for concrete any longer. Masonry, yes, but not concrete. I wouldn't want to explain to a judge or jury why I use working stress when it left the code 30 years ago.

Is it a pain in the neck to use ASD for soil and Ultimate Strength for the design of the concrete elements? Yes. But that's not insurmountable, especially since you just carry a few more load combinations in your analysis model.

 

[StrEng007]

Your response is appreciated. All my education, practice, and continuing education has focused on Strength Design so it's what I'm most comfortable with.

 

[Celt83]

For strip foundations, one-way slabs, retaining walls, etc. working stress analysis is useful to determine the stress in the reinforcement at service level to increase the permissible maximum bar spacing per ACI 318-19 24.3.2:

 

[lexpatrie]

I would suggest it's also useful for the "I don't know" period between the introduction of Strength design and the waning of working stress design. Particularly if you are evaluating an existing building without any modifications you've identified.