Mortise-and-Tenon Connections for Rebar-Free ECC Beams: Experimental and Numerical Investigation

Engineered cementitious composites (ECCs) combine high tensile ductility, multiple cracking, and sustained post-cracking load transfer, making rebar-free structural members feasible. However, eliminating longitudinal reinforcement also removes the conventional load-transfer path across prefabricated components, making reliable connections a key obstacle to their wider application. Mortise-and-tenon joints offer a potential solution through geometric interlocking and local strengthening. This study experimentally investigated one monolithic cast beam and 19 mortise-and-tenon-connected ECC beams considering ECC strength, joint geometry, CFRP strengthening, loading direction, and connection location. A finite-element model was further developed to capture mortise-and-tenon contact, interface degradation, and CFRP strengthening. The results show that mid-span connections strengthened with one and two CFRP layers increased the average peak load by approximately 20% and 47%, respectively, compared to unstrengthened specimens. However, excessive local strengthening may shift damage toward the CFRP termination. Straight joints exhibited smaller loading-direction differences in peak load (1.5–7.4%) than dovetail joints (15.4–21.7%). Moving straight connections from mid-span to the shear span allowed specimens to retain approximately 89–94% of the monolithic reference peak load and 74–90% of its peak deflection. These findings provide a basis for efficient connection design in prefabricated rebar-free ECC structures.