Composite Columns Steel Pipes With Square and Rectangular Sections and High-Strength Concrete Core

High-strength concrete columns, usually reinforced, require high rates of confined transverse reinforcement to obtain ductile fracture. In this paper the composite columns of steel pipes with square and rectangular sections, and cores consisting of high-strength concrete, are analyzed with the objective of changing the usual confining reinforcement. The metal pipes were fabricated with steel plates with 5,0 mm and 6,9 mm thickness, on cold cutting and folded in "U" form, and then subsequently compounding pipes with transverse sections of 60 mm x 60 mm and 60 mm x 100mm, and 460 mm height. The wall cross-section of steel pipes was determined by section of transverse and longitudinal reinforcement used in the square and rectangular columns reinforced conventionally. In the design the differences between yield strain of steel plates and yield strain of the reinforcement concrete columns were computed. To define the yield strain of steel plates, specimens were tested and analyzed under axial tension. With the mechanical properties of the metal pipes and the mixture of the high-strength concrete core, eight models were tested - four with square transverse sections and four with rectangular transverse sections. The specimens were tested under concentric compression loading, on a rigid hydraulic press with load controlled capabilities, having a maximum compression load of 10.000 kN. It is concluded from the investigation that composite columns with square sections were efficient in the confinement of high-strength concrete core and presented global instability. However, the composite columns with rectangular sections presented localized instability near the extremities, probably due to compression of the concrete core.