Study On The Behavior Of L-shaped Cft Stub Columns With Binding Bars Subjected To Eccentric Compression

Unlike circular CFT columns, of which the constraints on the core concrete are strong and approximately uniform,in special-shaped concrete-filled steel tube (referred to as CFT hereafter) columns, the constraints provided by the steel plates on core concrete are mainly in the corners and not very significant around the middle of each edge of the columns. Therefore, the deformations of core concrete around the middle of each edge depend mostly on the flexural rigidities of each corresponding plate. Thus the bearing capacity and ductility of special-shaped CFT columns are much lower than circular CFT columns.In order to overcome these drawbacks, various methods have been developed in the literature. One of the most effective approaches to improve the mechanical performance of special-shaped CFT columns is to set horizontal tensile bars on the edges of steel plates. Under compression loading, the core concrete within the column expands; while the horizontal bars along with the steel plates constrain the deformation of the core concrete. As a consequence of the expansion of core concrete, tensile stress is generated in these horizontal bars. Stemming from this mechanism, these horizontal bars are called constraint tensile bars in our research.Investigations conducted by the author's research unit have revealed that the mechanical performance of square, rectangular, as well as L-shape CFT short columns is greatly enhanced by setting constraint tensile bars. Premature failure caused by the local buckling of steel plates before their yield stresses are achieved can be delayed or even avoided by introducing constraint tensile bars in special-shaped CFT columns.This research project is a part of the investigations of CFT columns with constraint tensile bar series. Based on the previous research results, the mechanical performance of L-shape CFT short column with constraint tensile bars under eccentric compression is investigated. The research tasks are listed as follow:(1)The eccentric compression experiments of 9 L-shape CFT short columns are carried out. The experimental observations and experimental data are analyzed. The deformation mechanism under loading, ultimate bearing capacity, and ductility of this kind of specimens are studied. Finally, the influences of parameters, such as eccentricity ratio, eccentric angle, and the distance between constraint tensile bars on their mechanical performance are discussed.(2)Nonlinear finite element analysis of these 9 L-shape CFT short columns are performed by using the commercial finite element procedure ABAQUS. Comparisons between the numerical results and experimental results are made. The basic mechanical performance of this type of components is further revealed. By analysing the stress distribution in each material, the local mechanical behaviour of L-shape CFT short columns is better understood.(3)Numerical implementation procedure is coded in MATLAB for the numerical study of all the specimens. Comparisons between the experimental results and numerical results are made. Besides, the parametric study is also performed. Based on the results obtained from the parametric study, simplified formulas for the bearing capacity of equal length L-shape CFT columns with constraint tensile bars under eccentric compression are derived.