Working stress conc. design

[cmbyrd77]

Can anyone please tell me approximately when the industry made the switch from designing reinforced concrete using the working stress method to using LRFD? Also, where I might find decent literature on the working stress method. The existing building I am looking at was built in 1965-66.

Thank you.

 

[ash060]

I am not sure about references for working stress design for concrete, but the ACI 318-63 is the first reference to have ultimate strength design in it (along with ultimate strength).

I would guess that it would have been designed by working stress given the age that you have, but if you are analyze it using the provisions of Chapter 20 of the current ACI 318 you should be all right.

 

[hokie66]

ash060 is correct. Mid-1960's is the period for transition from WSD to USD. LRFD came much later. One good reference is my college textbook by George Winter, who was one of the authors of ACI318-63. It has both WSD and USD. "Design of Concrete Structures", Seventh Edition, 1964, McGraw-Hill.

 

[ToadJones]

USD = LRFD, no?

 

[hokie66]

No, not the same thing. Limit states design is statistically based, at least that is what they tell us. And the different limit states, ultimate and serviceability, did not exist in ACI318-63. I don't think the word "serviceability" was even used in that code, although it had provisions for deflection and crack control.

The limit states concrete code development came along in the 70's and 80's.

 

[JAE]

cmbyrd77,
Take a look at the early Chapter 1 commentary in ACI 318. They have a discussion there about this topic. - I think they provide some history as well.

Note that the ASD method is no longer in the current versions of ACI 318 but the commentary in Chapter 1 allows the use of the ASD method based upon the 1999 ACI 318.

 

[msquared48]

My college RC textbook, "Reinforced Concrete Fundamentals, with an emphasis on Ultimate Strength" by Phil M. Ferguson 1965, also had some information on WSD in Chapter 5. I believe some Schaums outlines from the 60's and '70's had information on that too. I think I have a copy of that too, somewhere.

Mike McCann
MMC Engineering

 

[cmbyrd77]

Thank you all so much for your help. Very helpful.

 

[tumbleleaves]

I use WSD when I need a quick no nonsense conservative design. It's generally no longer used for bond or compression members. Typically for quick simple designs I would just assume j=7/8. My current employment requires little design work, but only a few years back I did design on a daily basis.

So far as theory, one could go to Google Books and download any number of public domain texts on the subject.

I would think a "structural" designer should be able to do WSD without needing a review, be competent to derive the theory, and have a few texts in addition to ACI and AASHO readily on hand.

Just a thought...

 

[msquared48]

By the way, WSD was developed in Washington State.

That's why it's called WSD.

Mike McCann
MMC Engineering

 

[TXStructural]

I am actually preparing a presentation on working with existing structures, and just picked up a 2nd edition of Ferguson's book tonight.

While you should use the old codes and design handbooks to figure out what was done, rework or reuse with modification have to meet current design practices. A resource like older editions of the CRSI Design Handbook (1952 to present) can be used to determine the expected load capacity for members.

There were many proprietary slab systems using very odd reinforcing patterns, including 3-way, 4-way, and 5-way straight bar systems, truss bar layouts, and concentric hoops in slabs. If you can't figure out the bar layout because nothing is where it is expected, look into those. These were primarily for flat slabs or flat plates. Also, beams may use truss bars and frequently had little or no shear reinforcement.