Research On Applicable Range Of Specially Shaped Columns By Fiber Beam-Column Element With Shear Effect

This paper is part of the National Natural Science Fund project″Researches on 3D nonlinear seismic response analysis methods and integrated seismic performance of reinforced concrete structure with specially shaped columns″(Project No. 50478067).Technical specification for concrete structures with specially shaped columns JGJ 149-2006 clearly define that specially shaped columns should be analyzed by three-dimensional model. Bend center, shear center and shape centre do not overlap, the internal forces of two-way bending couple, and axial and bend deformation couple, so specially shaped columns do often in complex stress of pressure, bend, shear and twist, which determine its internal forces analysis need set up a line element comprehensive consideration of effects of pressure, bend, shear, twist to get the right results. At present the general line element which apply to rectangular columns, can not consider biaxial loading and multi-axial loading coupling problems, it is unsuitable for analysis of specially shaped columns. Fiber beam-column element is now the most effective model in the analysis of axial force and two-way bending moment coupling, it is the ideal model for specially shaped columns at present.However,fiber beam-column element could not consider shear effect now , which result in the error of fiber element and the actual results of component still large. Research has shown that fiber element without shear effect is only applicable to large span ratio specially shaped columns. In practical engineering, span ratio of specially shaped columns is small, effect of its shear deformation will not be neglected, whether fiber beam-column element still apply to the analysis of specially shaped columns depending on whether or not the shear deformation in the proportion can be ignored comparative to the bend deformation of the component deformation. Therefore, adding shear effects to fiber element, and giving out applicable range of specially shaped columns by fiber element with shear effect will contribute to the further improve of fiber element and more accurate result, it has theoretical and practical significance. To reach the goal, this study is carried out through the following steps:①Through the comparative analysis with solid model of L-shaped columns ratio of height to thickness of column leg equal to 4:1, validate that general space line model are unsuitable for analysis of specially shaped columns; verify fiber beam-column element is currently the best model for the analysis of specially shaped columns. ②Analyze the influence of shear effect to the beam element. On the base of traditional fiber beam-column element as a basis consideration of bend and axial deformation which based on flexibility method of finite element, set up a fiber beam-column element which can comprehensive considerate effects of space pressure, bend, shear, twist. And verify the correctness of the theory of account for shear effect.③At the stage of elasticity, span ratio and ratio of height to thickness of column leg and equal or unequal leg are selected which mainly influence the shear effect, and according to the error analysis of displacement and angle of tip of column on member level; the applicability of L-shaped, T-shaped cross-shaped columns which technical specification for concrete structures with specially shaped columns defined by fiber beam-column element without and with shear effect have been studied. The applicable range of span ratio and ratio of height to thickness of column leg are given for specially shaped columns by fiber beam-column element with shear effect; it not only provide further information and recommendations for specially shaped columns, but also contribute to the non-linear analysis of specially shaped columns by fiber beam-column element with shear effect.