| The abnormal joint in R.C. frame structure is widely present in large span, heavy industrial plants and high-rise building structures. The damage caused by earthquakes at home and abroad indicates that the force characteristics of abnormal joint are significantly different from normal joint. In order to understand visually force transfer mechanism,12specimens about abnormal joints of R.C. frame structure are designed for carrying out the low-cycle loading test. Failure mode, force transfer mechanism, characteristic load and energy dissipation capacity of abnormal joint are obtained, and the influencing factors of shear capacity of the joint are further analyzed.Finite element method simulation and analysis for R.C. abnormal frame joints are carried out by ABAQUS based on the test. The result shows that the following features. There is very obviously oblique compressive stress zone appears in joint core area diagonal line direction. The biggest of the stress exists in the small core area, and the maximum principal stresses is compressional stress. The crack appears firstly in the small core area, then arises and expand outside the small core of the big core areas after full-crack. Cracks of joint area of specimens which is a great difference of rigidity between the big-beam and the small-beam mainly appear in the area that there is height difference between big-beam and small-beam. And damage chiefly occurs along the direction from the upper end of small-beam to the lower end of big-beam. Distribution of inclined cracks is unidirectional. The distribution of cracks is dense and the main cracks are wide in diagonal line BE cracks of big core. Force transfer mechanism, the failure model, crack development trend, load-displacement curve of joints are consistent with the result of test through comparison and analysis.Components(J-11,J-12) with the special reinforced and structural measures are carried out the capacity analysis of the loading process by finite element software. The result of analysis shows that:the capacity of concrete in node core area can be strengthened and the beam plastic hinge is transferred efficiently after using the beam vertical axillary measures (component J-11), at the same time, the slip between the node in the core area of steel bars and concrete is reduced and the appearance of cracks in the node area can be delayed or reduced. Damages happen at first in the trabecular and haunched junction and avoid the premature destruction of the node area owing to stress concentration of trabecular bending reinforced. Measures that bending beam reinforcement (component J-12) is able to contribute to transferring efficiently the beam plastic hinge in early time of loading and improves relatively the constraint of the joint core area that brought out by beam. While the effect that transferring the beam plastic hinge through cross-bending reinforced is not obvious basic when the load increases, and the seismic performance of the component does not be improved.The abnormal joints of R.C. frame are analyzed based on the experimental studies by K. Kitayama in this paper. It can be found that the restraining effect in the joint zone by the straight across beam can not be estimated exorbitantly. According to the experimental value, FEA value and the value calculated by formula (5.7) of the shear force of joint in the penetrating crack load and on the basis of the Chinese code (GB50010-2010, GB50011-2010), the suggestion is that the shear capacity formulas of this abnormal joints should be deduced after amending the related parameters when concrete code (GB50010-2010) and seismic code (GB50011-2010) which meet the standard constraints and according to the based on he Chinese code (GB50010-2010, GB50011-2010), which can provide the basis to the reasonable design of this kind of joints. |
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