Research On Mechanical Behavior Of Reinforced Concrete Joints In The Vertical Crossing Lattice Tube Structures

The vertical crossing lattice tube structure is used for outer tubes in super tall tube-in-tube buildings as an innovational system, it can blend architectural design and structure together to achieve a more perfect system. Under the effect of the vertical load and wind, earthquake and other horizontal loads, the internal force of components of vertical crossing lattice tube structures is mainly axial force. As the main structural components under the load of external load combination, the giant inclined columns are mainly responsible for the axial pressure, and the giant girts are mainly responsible for the axial tension. Therefore, reinforced concrete components which can give full play to material properties should better be adopted in vertical crossing lattice tube structures. As joints of the vertical crossing lattice tube structures play an important role in jointing the giant inclined columns, the giant girts and related sub-structure together, to obtain the mechanical properties of reinforced concrete joints of the vertical crossing lattice tube structures and present the design method of calculation is the main focus of reasonable and reliable design and construction of such structures.Considering that difference exists between the axial forces of the two coupled inclined columns at the facade space crossing joints as well as the space crossing joints of the vertical crossing lattice tube structures under the integrated application of vertical and horizontal loads, two types of loading modes, i.e. agreeing loading and differential loading, were taken as the first fundamental parameter. On the other hand, volumetric ratio of stirrup in the joint zone was chosen as another as expanding deformation of the concrete may develop in the joint zones of not only the facade crossing joints and inclined column conversional joints, both of which bear plane loads, but also the space crossing joints bearing spatial loads. In view of the before mentioned two basic parameters, 12 reinforced concrete specimens of the joints of the vertical crossing lattice tube structure was designed and fabricated. The inclined columns were strengthened with encased section steel or winded CFRP strips so that the full-process mechanic properties of the specimens'joint zones from loading to failure can be obtained and the objective of "strong inclined columns, weak joint zones" can be achieved.In conventional experiments, it is difficult to get data of joint tests just using reaction frame for loading under plane and space loading. In this article, steel rigid ring was used as the self-balance loading system, also with the application of diagonal loadinog pillar and wedge turning blcks, a loading system is funded. This system could test the performance of the two kinds of component bearing plane loads such as facade crossing joint and inclined column conversional joint. What's more, based on this system, the use of conventional solves the problems of test on space crossing joint.Analyzing on the modeling test data of joint zone in facade crossing joint, inclined column conversional joint and space crossing joint, the development of some parameters like inclined compressive deformation, horizontal expansion deformation, stress of longitudinal reinforcement, stress of core concrete, stress of stirrup, etc, were recognized. The principles are showed below: agreeing loading and differential loading has little influence on the load-bearing capacity of joints; horizontal expansion deformation happened in joint zone of each specimen; stress of longitudinal reinforcement traversing joint zone is large before specimen broken; stirrup of joint zone has good effect to keep joint from expansional deformation. Finite software ABAQUS was used to make nonlinear simulation analysis to the specimens. The characteristics of three kinds of concrete and stress development of longitudinal bars and stirrups were specially focused on, and the results of tests were proved. Effect coefficient of the ultimate bearing capacity, which was produced by stirrup of joint zone confining joint, was introduced. Based on axial compression calculation theory of reinforced concrete short columns of bearing capacity, the formulas were proposed based on the reseach above. Referring to corresponding standard, designing suggestion of reinforced concrete joints of the vertical crossing lattice tube structures were proposed in this article.