Shear at the interface between composite parts of a prestressed concrete section

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Composite concrete beams made of prefabricated prestressed or non-prestressed elements and cast-in-place reinforced concrete slab became very popular in present-day civil engineering practice.

Two concrete composite parts of the beam are cast at different times. Different moduli of elasticity, consecutive load application, and differential creep and shrinkage cause unequal strains and stresses in two adjacent fibers of the construction joint. The requirement is to ensure that both parts act fully compositely because the bending and shear designs of composite members are based on this assumption. Therefore the level of shear stresses at the interface between two parts must be limited. 

The objective of the paper is to review the methods for the calculation of shear stresses in the construction joint, and to evaluate the influence of different age of two concrete composite parts on the level of shear stresses. Calculation method alternative to Eurocode 2 method is proposed and tested. It is recommended to calculate the shear stress from the difference of normal forces acting on sectional components in two neighboring sections of the element. It was observed that differential shrinkage of concrete components can significantly affect the stress distribution. Numerical studies were performed based on real-life examples of composite beams.

The paper was published by the team of J. Navratil, L. Zvolanek and L. Michalcik at the Czech Concrete Days conference, 2014. 

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