For over 25 years, I have been actively involved in research to understand the behaviour of structural concrete members subjected to shear. The research aims to improve the safety of structures through the development of accurate and practical analysis models suitable for the design and evaluation of slabs and beams. The research methodology has used laboratory testing in combination with analytical and numerical modeling techniques.
Research has focussed on the primary parameters that are known to influence the shear capacity of so-called slender beams and slabs that are assumed to obey engineering beam theory. That is, members where plane sections before bending remain plane and perpendicular after bending.
Key paramters include:
Member effective depth – Prior work had demonstrated that the shear strength does not increase proportionally with member depth. This is the so-called “size effect” in shear. New laboratory testing of large-scale specimens in the early 2000’s was used to identify safety related concerns with the then current ACI 318 design provisions that ignored size effect, and to validate the Simplified and General Methods of shear incorporated in CSA A23.3 and other codes and standards.
Member width and member type – Shear capacity increases proportionally with member width; slabs behave like beams.
Concrete strength – Strength is not quite proportional to square root of fc’. High strenth concrete (above about 50 MPa) tends to fail in shear with cracks through the aggregate rather than around, thereby the decreasing the aggregate interlock on diagonal (shear) cracks, exacerbating size effect.
Reinforcement strains – first at UofT, then with high strength reinforcement at UofA. More inforcement is available –here–.
Key parameters and concepts:
Size effect – goes away
Longitudinal reinforcement strains – HSR research
Stirrup spacing along the length – how it affects Beta
Stirrup spacing across the width – link to other writeup
Anchorage of shear reinforcement – link to other writeup