In steel-concrete composite beams, the friction force in the contact between the I-beam flange and concrete slab significantly influences the shear resistance of the composite section?
I would like to know the opinion of some experts.
For example, Eurocode - 4 for tests on shear connectors (push out test) in Annex B (Informative) state: The bond at the interface between flanges of the steel beam and the concrete should be prevented by greasing the flange or by other suitable means.
On the other hand, several authors of the consulted literature do not place grease in the contact and apply a normal force in the push-out test specimen.
Thank you very much in advance.
Best regards,
This a very interesting question
First, we have to remember that the friction between the I beam and the concrete slab is already small, since steel is usually a smooth material. That is why we usually use shear connectors to enable both materials to work together. However, and even if such force existed, I don't think it has a significant influence on the shear resistance giving the fact that shear stresses are usually concentrated near the natural axis, which is expected to be lower than the flange location in most cases. That said, of course such force will maintain a single section between the concrete and steel, which ensures a higher shear resistance than that produced by each section alone
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Regards…
In Poland, friction is ignored in calculations. The horizontal separating force should be transferred (transmitted) by rigid or susceptible connectors
Dear Colleagues, Thank you very much for your answers. Some comments:
The push out test specimen is an approximate physical model. It does not simulate completely the real behaviour of the shear connection on a full-scale composite beam.
Test on full scale steel-concrete composite beams have shown that, for low load values, there is an uplift of the slab respect to the flange. This implies a loss of contact and a decrease in friction contribution. The above can be observed in the paper:
J. C. Chapman and S. Balakrishnan (1964): Experiments on composite beams, The Structural Engineer, Vol. 42, No. 11, p 369-383.
I believe, in my opinion, that more test on full scale steel-concrete composite beams should be performed in order to be able to draw more accurate conclusions. I also think that now it cannot be assured that friction has a significant contribution.
Best regard,
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