| Summary: | Engineered cementitious composites (ECC), also known as flexible concrete, is a ductile and tensile strain-hardening material. These characteristics make it a suitable material to be used in beam-column joints under seismic loading. In a recent study conducted by Lee (2017), ECC demonstrated the potential to eliminate the need for transverse joint reinforcements in beam column joint when the joint core region is cast with ECC. By substituting normal concrete in beam-column joint with ECC, it helps to reduce the number of joint stirrups and avoid steel reinforcement congestion at joint core, thus enhancing the workability of casting at site.
In this paper, the seismic behaviour of beam-column joints with ECC will be studied. Three exterior beam-column joint (EJ) specimens and three interior beam-column joint (IJ) specimens were designed, constructed and tested. The specimens were loaded under lateral cyclic loading to simulate the behaviour of beam-column joints with different number of joint stirrups, i.e. No stirrups, two stirrups and four stirrups, under seismic movements. In addition, a 3D non-linear finite element model was also proposed in this study. Comparison between the model and the experimental data was made to evaluate the accuracy of the model.
The results show that all of the specimens failed by ductile failure with plastic hinges developed in the beams, which is a desirable mode of failure in seismic structures. With more detailed analysis, it was found that specimens with four joint stirrups performed better in terms of delaying the first crack and preventing the longitudinal beam bar from yielding at locations such as the joint core in EJ specimens and near cold joint interface in IJ specimens. Therefore, higher reinforcements at joint core still have an advantage over poorly reinforced joint core in beam-column joint with ECC.
The three-dimensional nonlinear finite element model proposed in the study also confirmed the hysteresis responses of the specimens, with a slight difference in its prediction of the pinching effect of the hysteresis loops.
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