It might be 0.3 to 0.4 (dimensionless) between concrete and steel, assuming no bonding. But in case, steel is embedded into concrete, you have to take appropriate bond stress value from the rcc-code of your country. You may please specify, when the steel is placed. At the time of concreting or on a set concrete.
One more question.
If I want to calculate the length of embedment need for an axial loaded column without considering end bearing (it does not sound right, but they have reasons for it which I don't agree) how do I come up with the shear force with the friction factor?
Is it (axial force) times (friction factor) like when we compute friction force or there are other equations for that case? FYI, bending is not an issue here.
We use 10 psf when computing resisting force between concrete tremie and steel sheet piling.
What do you think.
I dont see friction playing any role in the condition you are describing. What I can make out is as below:-
1. Bond stress- If the steel is placed at the time of concreting, a bond will develop as the concrete sets and shrinks. Code describes the value to be taken. Generally in the order of 0.8 N/mm2. You can use it to find out the surface area of embedment.
2. In another scenario, you can completely ignore the bonding and rely on shear strength of concrete (punching strength). In this case, steel length is of no consequence apart from affecting its own slenderness in compression.
Bond stress between concrete and a smooth steel rod seems to be an unreliable force transfer mechanism for structural applications. The current standard is to rely instead on mechanical interlock instead. Also, J-bolts are not as efficient as headed or nutted bolts. A good (U.S.) reference is "Strength Design of Anchorage to Concrete", by Ronald Cook, published by the Portland Cement Association.
