Abstract
In this work, circular concrete-filled steel tubular (CCFT) columns, rather than the more popular H-shaped columns, were suggested as pre-founded columns for top-down construction. In addition, a novel shear connection system with headed stud shear connectors between the CCFT columns and the flat slabs was developed. It was noted that a CCFT column with a design compressive strength similar to that of an H-shaped column without consideration of length effects can be easily installed, even into a smaller borehole. Furthermore, compared to the H-shaped column, less steel is required for the CCFT column. It was shown that the amount of steel needed can be reduced by decreasing the wall thicknesses or diameters of the CCFT column depending on the exposed length of the column during excavation. The fillet-welded joint of the developed shear connector system was also tested before its in-situ application. The test results revealed that the joint possessed sufficient shear and deformation capacities. The CCFT column with the developed shear connection system was ultimately applied to an actual top-down construction process. The good constructability of the CCFT column system and reductions in construction costs and time were confirmed.
Highlights
In congested urban areas, underground construction using such methods as traditional bottom-up construction is becoming increasingly difficult due to the presence of surrounding buildings and roads, as well as possible complaints from residents regarding noise, dust, and vibrations during construction
Flat slabs can be constructed on the ground, such as in slab-on-ground foundations, and the construction method has the advantages of speed and safety because the formwork is very simple and shoring is not required under the forms
In the case of choosing the concrete-filled steel tubular (CCFT) column with a wall thickness of 14 mm, the amount of steel is expected to be reduced by 14% more per a unit length
Summary
Underground construction using such methods as traditional bottom-up construction is becoming increasingly difficult due to the presence of surrounding buildings and roads, as well as possible complaints from residents regarding noise, dust, and vibrations during construction. The bearing-shear band is a curved plate with a column section shape and is fillet-welded to the outer circumference of a circular steel tube. The purpose of this test was to survey the shear capacity of the fillet-welded joint between the bearing-shear band and a column subjected to an axial load. The fillet welds were considered to have sufficient shear and deformation capacities
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