Steel plate / concrete bonding

[mobe]

I am currently looking at bonding steel plates to the sides of a concrete beam to transfer shear across an opening to be cut through the mid-section of the beam. Although adhesives available give around 10 N/mm2 shear, the ultimate value of shear at the interface appears generally to be taken as about 0.8 N/mm2, due to failure of the concrete substrate. This figure originates, I think, from BS5400. This figure seems low & I have been told that a figure of 1.5 N/mm2 is more realistic. Has anyone any ideas of where I can find any more info on thus?

 

[ishvaaag]

The use of one or another value will afect the reliability of your design. For example, the tensile strength of concrete is given in Spain's standing EHE code as

fct=k·(fck)^(2/3)

where fck is the characteristic compressive strength of the concrete, and fct (here) the tensile strength

all in N/mm2, k adimensional

if we use k=0.21 we get the (normative) characteristic tensile strength, that is, 95% of the tests are expected to surpass this strength. For any structural purposes, this is the value one should count on.

if we use k=0.30 it is expected the formula to give the average of the tensile strength in the tests. The average value might be of some interest where the actual behaviour is paramount.

if we use k=0.39, only 5% of the times the concrete is expected to attain this tensile strength. Of course this rarely will be used in any design.