Module: Concrete overlay – loads
The Reinforcement at interface calculation module is devoted to the subject of determining the anchorage depth of stapling reinforcement in composite structures.
Reinforced concrete composite elements are two or more layers of concrete laid at different times. If there are design requirements for these segments to cooperate with each other (according to the principles of composite constructions), then the resulting plane of merging should transfer the internal forces occurring in it. The theory of shear at the interface between concretes casts at different times is fully based on the Eurocode2 guidelines (6.2.5)
Loads | Design value of the shear stress
The basis for the calculation is the inputting of the shearing stress value νEdi in the plane of the merging, which according to Eurocode2 (6.23) should not exceed the design shear resistance (per unit merging area):
In the above formula:
c – coefficient reflecting the adhesion of both concretes
fctd – tensile strength of concrete in reinforced concrete structures
μ – coefficient of friction at shear
σ n – stress per unit area (positive when compressed and negative when tensioned). This stress is caused by the smallest external force constantly acting perpendicular to the interface.
ρ – participation of stapling reinforcement
fyd – calculated yield strength of reinforcing steel
α – the angle of inclination of the considered bars to the horizontal plane
In the EasyFix software, after entering the shearing stress value, we obtain the result of the minimum anchoring depth of the stapling bars for defined conditions previously entered in the appropriate tabs of the program. Unchecking Fatigue or dynamic Loads option will reduce the calculated shear load capacity. This is the effect of reducing the factor which depend on the adhesion of concretes.
It is recommended that the surface to be merged should be cleaned and abundantly moistened with water just before concreting. This process is intended to increase adhesion on the surface of the concretes mergence, and a properly selected participation of stapling reinforcement additionally affect the contact strength.