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# Rotational resistance of steel to concrete

## Rotational resistance of steel to concrete

(OP)
Afternoon

I am working on a project where a steel column with a diameter of 140mm is planted 1 metre deep.

I have been asked to provide the frictional resistance of the steel column to the concrete grade C25/30. Basically, they are trying to establish if the columns require an additional anti-rotational device.

I am struggling to find the appropriate method of calculating the bond strength between the concrete and steel, any help is appreciated.

Thankyou

### RE: Rotational resistance of steel to concrete

There are a few papers on this subject. I have used "Bond Behavior of Concrete-Filled Steel Tube (CFT) Structures" https://www.researchgate.net/publication/288471569...
but few of them look at torsional loading. Tension and compression change the bond strength due to Poisson's ratio but I have not thought about the effects of torsion on bond strength.

### RE: Rotational resistance of steel to concrete

#### Quote (Dylanuk22)

I have been asked to provide the frictional resistance of the steel column to the concrete...

...trying to establish if the columns require an additional anti-rotational device.

The problem will be much simpler if the anti-rotational force needed is stated. (Surely this must be known.)

Then you need to determine only if frictional resistance will meet that requirement (i.e. establish a lower bound for anti-rotaional frictional resistance, not perform a research project to determine a precise value).

For example, bond between steel HP and concrete (in tension for uplift) is conservatively estimated to be 40 psi. As LittleWheels stated, bond for torsion could be expected to be higher (>40 psi) for torsion than for tension.

If 40 psi is enough... you are done.

### RE: Rotational resistance of steel to concrete

Let me correct if i understand wrong.. A CHS steel column with a diameter of 140mm is planted 1 metre deep to the concrete grade C25/30 and subject to torsion ..
In this case , the resistance against torsion is due to the bond btw concrete and steel surface..
In your case , the surface is plain and do not provide mechanical interlock and many codes prohibit the use of plain concrete ..

Some codes proposes design bond strength τ=1.4 mPa (for plain reinforcement , for tension)

In your case the torsional resistance will change if the CHS steel column has end plate or not..

Assuming it does not end cap and interior surface has also contact with conc. one may estimate the ultimate torsional resistance;

Tu= 140*3,14*2*1000*1.4= 1230880 N-mm =1.2 kN-m

I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

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