Research On The Stability Of Branching Structures

Branching structure, as a concept of structure morphology, was put forward by German architect Frei Otto, it is also a special form of architectural bionic structure. It branches with multileves, develops three-dimensionally, also with beautiful and natural shape. Besides, it has clear mechanics-flow, reasonable stress, high bearing capacity, as well as wider span it supports. And therefore, branching structure has been used in large span space structures more and more. While researches on branching structures have been focused on form-finding methods, joint form, etc, but research on the stability of braching structures has not been done very well. Accordingly, this research studied the structure stability as well as the effective length factor of components systematically, analysed the rules of parameter influence, discussed the methods of confirming effective length factors, and gave out the range suggestion of main parameters, as well as the formula of effective length factors. And this research can provide experience for the design of engineering constructions as well as furture researches.The major research contents are listed as follows:1. Research on the entire stability of branching structure.Two typicial types of branching structures have been classified, one with side sway and the other with no sway. Firstly, elastic buckling models were analysed, which revealed that bucking forms of branching structure are similar to the conventional column, the structure with side sway overturnes more easily, while the structure with no sway buckles around the joint of trunk and first-level branch. And the results indicated that entire buckling happened before components buckling. Then with the consideration of geometrical and material nonlinearity, completeprocess analysis has been conducted, and different buckling form together with process have been discovered. The structure with side sway buckles smoothly with larger displacement and smaller nonlinear influence, while the structure with no sway buckles suddenly, but which always has good stability. Besides, the influence rules of initial imperfection, structure span and total height have been analysed, too.2. Research on the methods of confirming effective length factor.Firstly, from the theory, derivation with displacement method about the calculation formulas of effective length factors has been done. And thereby found out the influence parameters as well as their influence principles. Then put forward the research method based on equivalent stiffness coefficients, and illustrated the analysis process using planar branching structures with side sway as an example. Afterwards, common methods to get the buckling load coefficient were summarized, then put forward that the mothed based on first buckling mode was suitable for branching structures.The analysis process of this mothed was illustrated, and the key problem was found out, which is to get the entire effective length factor of the structure. Finally, the dissertation compared the three methods above, and decided to do the furture research with the mothed of eigenvalue buckling analysis based on first buckling mode.3. Parameter analysis and value research on the effective length factor.Analysis about the influence parameters of main components has been done, and the range suggestion of main parameters has been given out. Then in the range of parameters suggestion, through a statistical parameters analysis with the mothed of eigenvalue buckling analysis, the calculation formulas of effective length factors have been put forward, and the range suggestion of effective length factors has been given out.