In this study, two types of connecting method were suggested for modularized internally confined hollow reinforced concrete (ICH RC) beams. To evaluate their performances, bending tests were carried out with a single-body specimen and two modular specimens. The two modular specimens have different connections which are distinguished with the shapes of sheath tube and the existence of connecting steel plates. The four points loading tests were performed to investigate the behavior of the modular specimens and their failure patterns. The test results showed that modular specimens have lower strengths than the single-body specimen in the elastic region, but the modular specimens finally exerted almost equal strengths to the single-body specimen at the plastic region. The maximum loads of the modular specimens were measured as 90%~95% of the single body specimen. Those experimental results are supposed by the discontinuity of the concrete at the joint and the fracture of the reinforced coupler. If these defects are reinforced, a modular ICH RC structure may show similar behavior to a single-body ICH RC structure.

The new supporting structure, internally confined hollow reinforced concrete (ICH RC), was suggested by former researchers. It maintains the material saving effect, which is the advantage of the hollow concrete structure, and it solves the brittle fracture problem of the inner wall by the inner steel pipe to make it into the 3-axis confinement state. However, until now, its design and analysis model has been limited to a circular cross-section. In this study, to expand the applicability, research and development of an ICH RC structure with a polygonal cross-section were performed. The material model was developed by defining the constraint stress in the members of the concrete and deriving a reasonable stress-strain relationship. For the column model, it was developed to predict the behavior of the polygonal ICH RC columns by analyzing the axial force-moment correlation, moment-curvature, and lateral force-displacement relationship. Each model was verified not only by comparing with the results of previous experiments but also by analyzing the results according to parameters. The maximum load and ultimate displacement values through the developed model showed the difference with the experimental results within 6% of mean error. It was verified that the proposed analytical model reasonably reflects the behavior of actual columns.

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