Bond stress in plain reinforcing 1

[Polecat]

I am confronted with evaluating the strength of some base plate anchor bolts (undeformed, but with a standard hook) and embedded 5.5 ft into 3000 psi concrete. Current ACI codes do not permit using plain reinforcing bars and therefore do not specify any allowable bond stress or development lengths for them.

I found in ACI 318-63 (yes, that's 1963, Sect 1801) provisions for evaluating stress on plain bars, but it results in an allowable tension woefully inadequate.

Does anyone have any more recent or accurate data on this??? Any help would be appreciated.

http://www.spiraleng.com

 

[PEinc]

FHWA'a micropile design manual has a grout to smooth steel ultimate bond stress of about 435 psi. I'm not in my office now and can't check the actual stress. You can try looking online for the micropile manual on FHWA's geotechnical publications web site.

http://www.PeirceEngineering.com

 

[ishvaaag]

Development Length of Plain Bars fy=215 MPa in EHE-91, the last concrete code in Spain that adressed the issue. The compression bars need be developed straight. So if you want to apportion any reduction from full bar section capacity, do it against the averaged capacity on the full straight length capacity for the case.

 

[ishvaaag]

The adherence of plain and deformed bars per EH-73, the 1973 code.

In this and above statement, check against / consider factored loads.

 

[ishvaaag]

Calculation of the developable force in both plain and deformed rebar per EH-73 Commentary according to the averaged bond stresses per my previous post.

 

[ishvaaag]

The resulting development length for steel A 22 L

fy>=2200 kgf/cm2
3400 kgf/cm2 <= fu <= 5000 kgf/cm2

You can take the fy=215 MPa as per EH-91 above of the same characteristics

 

[ishvaaag]

Now development lengths for anchor rods straight and with a 90 deg hook, for A 4.6 and A 5.6 steels. I have pasted the properties of these steels. sigma r stands for fu, and sigma f for fy. Lengths are also based on EH-73 but corrected (as hinted in such code) to more conservative values for the anchor application



Straight,

 

[ishvaaag]

With a 90 deg hook,

 

[ishvaaag]

Hooked Anchor Rod by AISC Manual LRFD 1992 as portraited in a Mathcad worksheet

 

[ishvaaag]

Quoting Aghayere on Anchor Rods. Since this is a modern text it should portraint the US practice as of 2009. Referred ACI Code is 318-08.

Structural steel design: a practice-oriented approach
Abi Aghayere, Jason Vigil
Pearson Education, Inc., NJ

that by the way seems an excellent steel book.

I have found that the EC remits to National Annexes for the bond stress design for plain bars; as soon I find some relevant quote I may add to this body of references.

 

[ishvaaag]

Better read, it says National Annexes can modify what said in the Eurocode about bond to plain rebar. That is that the limit bond stress can be taken that accepted for deformed rebar but divided by 2.25

In french...

"Le présent NCCI suppose que la valeur de calcul pour une barre lisse est la valeur donnée au §8.4 de l'EN 1992-1-1 (c'est-à-dire la valeur de calcul pour une barre non lisse du même diamètre, de béton similaire et dans des conditions similaires) divisée par 2,25. Il se peut que l'Annexe Nationale pertinente donne des conseils sur la conception pour l'adhérence d'ancrage de barres lisses."

See Annex A of(attached) Access Steel document giving bond strength of plain rebar as per Eurocode 3.

 

[Polecat]

Thanks, Ishvaaag, for the numerous posts. I'm sure I'll find my answer among all those references.
Much obliged.

http://www.spiraleng.com

 

[ishvaaag]

Just another reference in french by Pierre Maître in his

Formulaire de construction metallique
Moniteur, Paris, 1997

It seems it uses a mix of french codes from CM66 to EC3

 

[TXStructural]

There is no "allowable" development since the code does not provide a value. If you are looking for an actual value, you might try looking for data from Darwin out of KU.

The hook on the end of smooth anchor rods is seldom, if ever, a standard hook. The anchor hook is quite a bit tighter and much shorter than a hooked reinforcing bar.

IIRC, The hook had been generally thought to provide the full development, but evidence says that hooked anchor rods do not provide adequate resistance to pull-out.

 

[ishvaaag]

This one is a modern experimental setup for plain rebar hook anchors.

"The bond stress for 16 mm rebars is about 1.75 MPa reached at a slip of about 0.18 mm; for 12 mm the values are 1.05 MPa and 0.03 mm respectively."

 

[ishvaaag]

What Engineering Data Report Number 11 by CRSI had to say about bond values of old plain rebar.