Strut and tie model for a hybrid nodes in beam of concrete and steel beam under gravitatory loads

Abstract

Experimental tests carried out in the laboratory of structures of the National Polytechnic School (Ecuador) in beams with hybrid nodes, increasingly used in the construction of buildings with steel deck slabs, demonstrated that the hybrid nodes does not decrease the strength of concrete beams, reaching approximate values to the theoretical ones for the beam without nodes. With the results of the experimentation and models in finite elements, the trajectory of efforts to perform a Strut and Tie Model (STM) was sought, obtaining areas of steel 15% superior to the design with the flexion formulas of the ACI 318-14. General formulas of the STM are presented for beams of any light with a single hybrid nodes, but it is possible to extend them to several nodes. The experimental evidence and STM shows that the point load is transferred better with the steel beam penetrating the concrete beam, which does not decrease the strength.