Webinar: Tension Stiffening Related to Cracking and Deflection of Reinforced Concrete

Hardy Cross once wrote that “strength is essential and otherwise unimportant” to emphasize it makes little difference what other attributes a structure has if it is not sufficiently strong. Looking at this from a different perspective one could say that “strength is essential and otherwise unimportant … when serviceability governs” to ensure the structure performs adequately under the day-to-day service conditions once we know the structure has adequate strength. In fact, certain types of structures such as elevated slabs and fiber reinforced polymer (FRP) reinforced concrete members are often stronger than needed once serviceability requirements are satisfied, and in these types of cases the structure is designed for serviceability first and then checked for strength. Hence, safety and serviceability related to cracking and deflection play an important role in the design of concrete structures.

This presentation is focused on deflection of reinforced concrete. The role of cracking, tension stiffening and shrinkage in understanding deflection behavior of reinforced concrete is explored. In particular, emphasis is placed on the pitfalls of ignoring the concrete shrinkage. Rationale and justification are provided for the recent adoption by most codes in North America of a new approach for the effective member stiffness used to calculate deflection. Work is presently underway with colleagues from Rutgers to extend this approach to prestressed concrete.

Presented by Peter H. Bischoff, Department of Civil Engineering, University of New Brunswick, Fredericton, NB, Canada

Peter H. Bischoff is an Honorary Research Professor in the Department of Civil Engineering at the University of New Brunswick in Fredericton, New Brunswick, Canada, where he has contributed to teaching and research in reinforced and prestressed concrete. He is a fellow of the American Concrete Institute (ACI) and Canadian Society for Civil Engineering (CSCE) and has served on numerous ACI Committees during his career. Dr. Bischoff is a recognized expert in serviceability of concrete structures related to deflection and has received several awards for work in this area. He has also been involved in development of a design code for fiber reinforced concrete (FRC) and UHPC that has been implemented into the Canadian Highway Bridge Design Code S6.