Research On Mechanical Performance And Optimization Strategies Of Free-form Surface Supported By Branching Strecture

Since entering the 21 st century,with the development of science and technology,people have higher and higher requirements for architectural functions and aesthetics.Intersecting the traditional plane structure,the "shape resistant" space structure,which is closely related to the architectural form,is easier to meet the requirements of designers.As a representative of "shape-resistant" structure,free-form surface structure is favored by many architects at home and abroad for its smooth lines,graceful shape and ability to express architectural implication to a large extent.As a multi-branching column supporting structure,the branching structure gathers the forces of the superstructure together through branches at all levels,which has superior force transmission performance and can effectively reduce the span of the structure without affecting the use space of the lower part of the structure.The free-form surface structure supported by branching structure is composed of two parts: the lower tree-supported free-form surface structure and the upper free-form surface structure.It belongs to the shell-rod "hybrid" structure system,the structure is relatively complex,and the mechanical properties of the initial structure created by the designer are not always good,so it needs to be further improvedIn this paper,the B-spline theory and fractal theory are used to generate two kinds of structures respectively,and a set of geometrical construction ideas suitable for free-form surface structures with tree-shaped supports are formed mainly by introducing parameter space to solve the intersection point of shell and rod,and the structure is analyzed and summarized from the aspects of geometry and performance characteristics.Secondly,taking the coordinates of key points of the structure as the design variables,a form optimization method based on the total strain energy of the structure is established by using the sensitivity analysis method.By adjusting different design variables,the following four optimization strategies are adopted to optimize the structure.The first strategy is to control the movement of control points on the free-form surface.The second strategy is to control the free node movement of the branching structure.The third strategy is to control the movement of the intersecting point of the shell and rod.The fourth strategy is to control the simultaneous movement of the free node of the branching structure and the intersection point of the shell and rod.In addition,based on the bearing more free-form surface structure as the research object,by changing the structure of supporting form,quantity and the shape of free surface,analyzes the structure shape change situation when using different optimization strategy,and the overall structure,free-form surface structure and branching structure three layers structure and mechanical properties are analyzed with the change trend and law of optimization steps,put forward the optimization advice,It is expected to provide a reference for the optimization of free-form surface structure supported by branching structure.At the same time,finite element software is used to calculate the load-displacement curves of the free-form structure with tree-shaped support before and after optimization when different optimization strategies are adopted.The initial defects of the structure are simulated by "characteristic defect mode method",and the influence of the initial defects on the load-displacement curves of the structure is discussed.The results show that with the optimization,the ultimate bearing capacity of the structure increases gradually,and the sensitivity to the initial defects increases,but the stability of the structure is still greater than that of the initial structure under the same initial defects.