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re: Shear Friction Method in BS

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A good summary of codes and shear friction is found in "Comparison of Codes", page 81, Chapter 3, in the pdf document found at:
http://www.fire.nist.gov/bfrlpubs/build96/PDF/b96117.pdf

Title is "Shear Design of High-Strength Concrete Beams: A Review of the State-of-the-Art"
by: Dat Duthinh and Nicholas J Carino  1996

This publication focuses on High-Strength-Concrete (HSC) and the need for a better understanding and more testing of SHEAR FRICTION. See page 81, Chapter 3, 'Comparison of Codes".

It seems that shear friction is an important and emerging element of design. Now, more testing and understanding is needed.

Evidently, HSC shear cracking is smother than normal concrete, reducing the assumed shear frictions of empirical design criteria for normal strength concrete.

In in a horizontal beam, the HSC allows higher compression, that additional compression rotates shear cracking towards the horizontal and the vertical shear steel is less effective. Diagonal cracking shear strength is controlled by the vertical steel. The cracking will be more horizontal in an efficient HSC design. So, the shear-friction is more controlling.

High compressions may be more likely in a HSC design, making the shear cracking more vertical. Similar to the previous beam idea.

Other sources for rotating shear planes.

There is less horizontal flexural compression in a short deep beam. Consider a horizontal beam length half that of its depth, more shear steel needs to be horizontal rather than vertical (like a corbel).

In a very short and non-bearing shear wall, the cracking will be more horizontal than diagonal. The only time I have seen such was in an industrial concrete building where there was only a few vertical feet between two diaphragms.

It seems that because the reduced difference in strength of shear reinforcement and HSC leads to needing a better understanding of shear strength.

Fiber wraps is a reduced difference in strength of shear reinforcement and concrete. Fiber wraps as in what is used to reinforce existing walls and beams. Even though the concrete is normal, the repair is less effective than that of a full steel reinforced design. Is the understanding of shear friction enough to rely on fiber wraps?

Shear friction seems to require more consideration when *reviewing inadequate shear reinforcement *using less affective shear reinforcement (such as with HSC) *or a design decreases shear friction (such as with HSC).



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