The Study Of Local Pressure Of Unsealing Steel Tube Concrete Short Column

Local pressure is one of the most frequent bearing force forms in civil engineering. The past studies are more concentrated on local compression areas, that is the research in experimental aspect of uniform stress distribution. The application of Steel Tube Confined Concrete (STCC) has gradually been increased with the rapid development of high-rising buildings in China. Given the quality of pouring concrete into the bottom of steel tubes, the column base of STCC is not sealed or is not completely sealed. By doing so, the local compression under the non-uniform stress will be occurred in the column base because the differences of elastic modulus between steel tubes and concrete is quiet big. In addition, it is also worthy of consideration to develop the degree of bearing capacity of non-sealed STCC column. Therefore, the following main conclusions are initially got according to the comparative trial on local impression of 12 short columns of STCC.①The ultimate bearing capacity of Non-sealed Steel Tube Confined Concrete is quiet as the same as the value calculated with the present code. So it is initially concluded that the bearing capacity of non-sealed STCC short columns can still be calculated according to the present codes.②The phenomenon of non-uniform stress is occurred on the local compression surface which is under non-sealed STCC column; the stress concentration is occurred under steel tube wall or ring-shaped pad; and even the local pressuring subsidence phenomenon is obviously occurred on the bearing surface. The ring-shaped pads installed on the non-sealed STCC column base can release such non-uniform stress and reduce amount of the local pressuring subsidence. The local pressure under steel tube walls can be almost eradicated when the ring-shaped pads with proper radial width is installed (such as the 5 times thickness of wall steel tube walls in this paper).③Stress concentration is existed on the local bearing surface which is under non-sealed STCC column, but it will be rapidly declined as the distance from bearing surface is widen. Horizontal tension stress of the largest cross direction of the supports lies in the central line of lateral face, 1/6 ~ 1/5 height of cross section from the supporting surface.④Brittleness is presented in local bearing destroy of the supports without being configured by indirect bar reinforced meshes. The progress from cracking to destroy is very rapid and the ratio between cracking load and destroy load is approximately 0.9~1.0. Some ductility is presented in local being destroy of the supports with being configured by indirect reinforced meshes, so the ratio between cracking load and destroy load is approximately 0.7~0.9.⑤Stress concentration is occurred on the local bearing surface which is under non-sealed STCC columns, and even the local pressuring subsidence phenomenon is appeared on the bearing surface, however, the local bearing capacity of the supports can not be reduced and the calculating method about the local compression capacity listed on the present Concrete Structure Design Code (GB50010-2002) can still be followed.