Working Stress 7

[structdtl]

Looking at existing dwgs from the early 60s which list fc = 1,350 psi for reinforced concrete - what is the equivalent of working stress 1,350 psi to today's?

Also, what is the equivalent of today's 5000 psi concrete strength to working stress?

Is there a chart somewhere I can use and keep for reference?

 

[dik]

I would think about 2000 psi... low strength may only be an issue for shear and compression.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[structdtl]

Thanks, Dik - That is very low strength. Is there a chart somewhere? I am also looking for the equivalent of today's 5000 psi converted to WSD

 

[mtu1972]

Looked at my first concrete textbook and for Working Stress the maximum concrete compressive stress for bending was 0.45f’c. For 3000 psi concrete that would equal your 1350 psi value.

When I started working, in 1973, 3000 psi concrete was the standard, unless you were willing to pay more for higher strengths.

gjc

 

[dik]

as mtu notes, 5ksi was not common... back in the early 70s we often spec'd 4.5 for parkades, which was not common at the time. Most conc was 3ksi... and 3ksi could beis likely the magic number.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAretired]

If you are doing a lot of work with old concrete buildings, you should download a copy of ACI 318-63, which is the last code to permit WSD (Working Stress Design). It also includes USD (Ultimate Strength Design). The document is in the public domain and can be found at the following address:

https://www.academia.edu/31580117/B...rete_ACI_318-63_reported_by_ACI_Committee_318

In particular, you will be interested in the following pages, but you may find other portions of ACI 318-63 helpful.

BA

 

[structdtl]

thank you all for the links and responses!

 

[JLNJ]

Working stress was allowed by ACI long after 1963 as part of the Appendix. If memory serves it was still in the code in 1989.

 

[BAretired]

That is possible, JLNJ. My memory is certainly fallible, but I believe ACI-63 was the last American code I had which permitted WSD. As I recall, there was considerable resistance among Canadian engineers but, for me, once I was introduced to USD, there was no going back.

BA

 

[SlideRuleEra]

BA & JLNJ - You are both right:

Most of my design work was with structural steel or wood, but on occasions requiring reinforced concrete, I used WSD to the bitter end (2002).

http://www.SlideRuleEra.net

 

[BAretired]

Thanks, SlideRuleEra. Nice biography of ACI 318.

BA

 

[dik]

Other than for historic reasons, we did not look at WSD... and that was '65. I don't recall any resistance... LSD just made more sense. My only concern was that with the changes to get load factors for steel and concrete to match, they introduced a number of fictitional material factors to get things to blend. Before that I had a pretty good idea of how strong concrete was... afterwards, I was never sure.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik