ABSTRACT
The program comprised the test of 71 specimens and was organized in four phases as described in Table 1 below. The ends of the steel tubes were accurately cut and machined to the required length in a lathe at the steel factory, ensuring that the two ends were parallel to each other and normal to the sides. The inside of the tubes was wire brushed to remove any rust and loose scale, and it was carefully cleaned from deposits of grease and oil. The bottom end of each tube was welded to a square steel end plate of 15 mm thickness. Prior to casting the concrete, holes were drilled from the outside of the tubes, and then threads were made to install bolts via these holes. Bolts M16 grade 5.6 black bolts of 65 mm length were used as shear connectors in those specimens that contain the letter “B” in their designations see Table 1. Two, four, or six bolts were installed in the test specimens (2B, 4B, 6B). The inner surface of the tubes for specimens designated with “UD” was polished and oiled
thoroughly before casting the concrete to eliminate the bond between steel tube and concrete core. The tubes were filled with plain concrete in layers in the vertical position. The concrete core was compacted using a high-frequency vibrating poker introduced into the steel tube to eliminate air pockets in the concrete and to give a homogeneous mix. All test specimens were tested at the age of 28 days, except those designated with “C1-90S” or “C1-120S” that were tested at the age of 90 days or 120 days, respectively, after casting the concrete.
