Geopolymer Haunch Beam‒Column Connection Behavior

A haunch system improves the performance of a beam-to-column structure, in combination with a geopolymer haunch, the green-concrete concept is supported by reducing the Portland cement use. The energy dissipation, load‒deformation behavior, failure mode, residual deformation, and plastic hinge formation under a loading‒unloading scheme were studied based on experimental full-scale specimens. The responses of the loading‒unloading protocol were compared to the monotonic loading results. A geopolymer and conventional concrete haunch having similar compressive strengths were analyzed. It was shown that the geopolymer haunch performed excellently and that a concrete haunch remarkably improves the performance of a structure regardless of the haunch material. The geopolymer haunch enhanced the load level at first cracking for 10%, and the formation of plastic hinges 0.7% and 4.5% for the monotonic and loading–unloading, respectively, but slightly reduced the ultimate load by 1%. The loading‒unloading protocol had a negative impact of 3% to 7% on the overall performance, the reduction was lower for the geopolymer haunch underlining the superiority of this material. The loading–unloading scheme resulted in a monotonic strength degradation and deviation in failure mode. A finite element model was constructed to generate and analyze the relation of the haunch’s concrete strength to the load‒deformation response. It was found that the haunch’s compressive strength had no influence on the behavior of the beam-to-column joint, even for a haunch with a compressive strength as low as 25 MPa.