Smooth Reinforcing - Concrete Design 3

[SteveRivard]

Does anybody have a good reference for the design of a reinforced concrete slab with smooth reinforcing? I'm trying to come up with a one way slab capacity for an existing slab. The testing agency has informed me that from visual observation in core holes, and the reinforcing samples that they've retrieved for testing, that the slab reinforcing is smooth. Obviously, not what I was expecting. I'm not familiar with smooth reinforcing, and was wondering if anybody out there has any experience, references or even thoughts on vintage for this type of construction.

Any help that you can offer is greatly appreciated.

Regards,
Steve Rivard, PE

 

[csd72]

Its also called plain reinforcing.

The strength depends on the date that it was built but could be as low as A36 steel.

Bond lengths e.t.c. are much greater for this type of reinforcement.

 

[frv]

If you look at ACI 3.5.1, it does not allow the use of smooth reinforcement.

I'm not an expert, but I would suspect this requirement has been in place for a long time. Is the testing agency just guessing, or have they recovered a sufficiently large piece of reinforcing to definitively state that it is not deformed?

 

[SteveRivard]

The testing agency, as I indicated above, has samples of the reinforcing and has visually observed the reinforcing in the core hole locations. It's definitely smooth.

I also realize that plain reinforcing is not allowed, nor has it been since the ACI 318-63 was in force.

This is an existing slab that I'm trying to determine a capacity for, and any references that anybody might have, is greatly appreciated.

Regards,
Steve Rivard, PE

 

[DRC1]

Masonary Structures by Spalding, Hyde & Robinson 2ed. 1926

Tests have shown steel embedded in concrete develops considerable bond strength and may be relied on to hold steel. If embeddment length is considerable, bond near load may slip, but deeper embedment will hold. Ultimate Bond strngth for ordinary concrete 200-700 psi of surface area.For structural work unit bond restiance 200-300 psi. Twisted or deformed may give higher values.

Also in the book they use concrete allowable stresses from 500 psi to 900 psi and steel allowable stresses from 14,000 to 20,000 psi.

Hope that helps somehow

 

[spats]

Any chance it's a welded wire mesh where cross wires aid in the development?

 

[SteveRivard]

spats,
The testing guys have indicated that it's 5/8" diameter individual bars at 4" o.c., so definitely not WWF.

Regards,
Steve Rivard, PE

 

[SlideRuleEra]

Steve - Today I scanned the Reinforced Concrete section of "Trautwine's Civil Engineer's Reference Book" and posted it on my website. It is a good reference on how reinforced concrete was designed at that time. The information is from the early 1900's (mostly before 1910). It supports the numbers that DRC1 has offered. The chapter does specifically talk about plain rebar; be sure to see the test result summary on pages 1331 and 1336. Here is a the link

http://www.slideruleera.net/miscellaneous.html

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[jike]

Back in the '63 code (my personal favorite), there was a provision that smooth bars had 1/2 of the bond strength of deformed bars.

Once a contractor demo'd a scale pit for me in a multi-story building (with smooth bars) and to my surprise all the trussed rebar was still hanging there and the concrete had just fallen off of the bars!

 

[msquared48]

In the first quarter of the 20th century, a lot of square, twisted bar was used that was smooth.

Is your section round or square?

Mike McCann
MMC Engineering

 

[SteveRivard]

msquared48,
Yeah, I've seen the square, twisted stuff before too. This stuff is round. It's just a bit different than I expected, based on prior experience.

Regards,
Steve Rivard, PE

 

[civeng80]

May also be mesh reinforcement which they still use commonly today.

 

[jheidt2543]

Ref: Handbook of Building Construction
by George A. Hool and Nathan C. Johnson
McGraw-Hill Book Co., Inc., 1929, vols. 1 & 2

Appendix D, p. 1485:
Yeild point for plain bars round)is 33,000 psi

Working Stresses, p. 1003:
"The generally accepted working stress for mild steel is 16,000 psi...

Bond and Anchorage, p.1579:

"...the bond stress shall be taken as not less than that computed by u=8V/7od."

"...shall have a length of anchorage...suffcient to develop the full maximum tension at an average bond stress not greater than 0.04f'c for plain bars or 0.05f'c for deformed bars."

page 1572 has a table of Allowable Unit Stresses in psi based on 2,000 psi, 2,500 psi or 3,000 psi concrete:

2,000 2,500 3,000
Flexure 800 1,000 1,200
Shear in slabs 60 75 90
Bond in slabs 80 100 120

Hope this is some help!