Structural Performance of a Large Column with an Outer Shell Formed by Short-Fiber-Reinforced Mortar-Extrusion (2024-07)¶

The authors have developed 3D printing technology in terms of both suitable cementitious materials and a refined printing system for layered extrusion since 2015. It was reported in Digital Concrete 2020 that a practical scale prestressed pedestrian bridge designed by topology optimization analysis was completed and the in-situ bending test provided good agreement with the prediction analysis. In other words, the bridge was demonstrated to be safe for operation and behaved as an elastic unit under crowded loading. In this study, the authors tried to manufacture a large column which can support the bridge girder mentioned above. The procedure consists of the following three steps; an outer shell to be formed by layered extrusion, placement of pre-crossed rebars as a unit into the shell and inner filling with self-compacting concrete. Considering its aesthetics, the cross-section shape of the column transforms gradually from a circle at the bottom to an oval at the top. The mortar used for the outer shell includes a large amount of short fibers, enough to bear the bending stress induced by inner filling without any outer supports. Its pumpability, dispersibility of fibers and structural anisotropy are investigated as a preliminary test. Finally, for a comparison of the 3D-printed column with the conventional column, reversed cyclic loading was carried out. As a result, it was revealed that the former shows the uniaxial distribution of short fibers along the extrusion process and achieves high ductility while unifying with inner concrete. It is suggested that the high structural performance results from the restraint of shear crack evolutions and the confining of cover concrete.