Research On Morphopoiesis And Experiment Of Free-form Thin-shell Structure

The buildings develop gradually towards the direction of larger-span and higher-rise, and meanwhile people pursuit of buildings are not only a function space, but a humanized space with a good visual effect of free, flexible, a unity of diverse functions and mental feelings, enjoyment of beauty. Reasonable and good visual effect of architectural practice need the support of science and technology, it means the importance of mechanical properties of the structure in the conception of the construction scheme, the role of morphology become more and more important. Modern architecture requires a deep understanding of the relationship of building and structure, to recognize the connotation of the structure morphology. The structure is understood as a tool for constructing novel types of buildings rather than a pure skeleton of load bearing. Morphology method with reasonable and beauty architecture effect is not only a problem which should be concerned by each structural engineer, but also an important issue which must be solved by architect engineers in order to realize their building ideas and purposes. The minimization of the strain energy as the design objective of the structural morphopoiesis problem, using the properties of B-spline surface and the characteristic of the sensitivity of the strain energy of the structure, this paper proposes a high efficient and practical method for structural morphopoiesis of the free-form surface. To solve the nonlinear and more general morphopoiesis problem, this paper also proposes a morphopoiesis method with the difference algorithm of sensitivity. This paper conducted experimental study to the results given by the proposed method, developed the test method using the finite element method as a simulation tool, investigated the mechanical performance of the free-form surface structure during the evolution process, and summarized the mechanical properties of the free-form surface. The main research content is presented as follows:1. Initial model of the free-form surface thin-shell structure with arbitraryboundaryBoundaries of the building are complicated in practical projects. In order to adapt the practical engineering, the function of the B-spline curve was extended, and methods of generating various kinds of complicated boundaries are studied. The common used B-spline curve can only generate a free curve with fixed degree and cannot be used simply. This paper investigates the B-spline curve which can generate closed curves with multiple numbers and degrees. The interior and exterior boundaries are identified by arranging the external boundary nodes clockwise and the internal ones counterclockwise. The domains within the boundaries are considered as the design domain. And the plane design domain is triangulated using Delaunay triangle subdivision technology. Then the rectangular reference plane containing the design domain is introduced. According to the demand of the building shape and the nodes movement, the key point mesh is obtained and the surface is generated with B-spline surface. At last an initial structure with free-form surface satisfying arbitrary boundary conditions is obtained, by projecting all of the nodes in the design domain into the b-spline surface and recording the support information.2. Morphopoiesis of the free-form surface based thin-shell structure onB-spline functionMechanical performance of the free-form surface is closely related to the surface shape, and the strain energy is one of the comprehensive indicators of mechanics performance of structures. According to the relationship between the coordinate change of key points of B-spline surface and the strain energy of the free-form surface thin-shell structure, a highly efficient morphopoiesis method of free-form surface thin-shell is built. This method takes into account of the computation efficiency, the continuity of surface and the concave and convex characteristic of the free-form surface, chooses finite number of grid points in the process of forming the initial structure as key points as well as design variables, analyzes the relationship between the finite number of key points and all the nodes generated by the triangulation mesh, and derives the sensitivity of the strain energy with respect to these key points. By adjusting key points step by step iteratively, the rational and smooth free-form surface structure is generated finally. The feature of changes of the shape and mechanical performance during the evolution is investigated and the characteristic of the method is summarized. The method has high efficiency and can generate smooth and continuous surfaces. Various free-from surface structures satisfying architecture demand with rational mechanical performance can be created by this method, which can serve as a reference in the conceptual design stage.3. Morphopoiesis based on the difference algorithm of sensitivityBy the difference algorithm of sensitivity, combining the idea of morphology with the powerful calculation ability of the finite element software, this paper proposes the method of the structural morphopoiesis based on the difference algorithm of sensitivity. And the correctness of the proposed method is verified take the ANSYS for example. This method can solve complex nonlinear problems encountered in practical engineering projects, although it exhibits low efficiency as well as the complexity to determine the initial form of structures. This method can not only tackle the structural morphopoiesis problem of minimizing the strain energy, but also the structure formed satisfying the architecture demand and the objective function of other target goals, it provides a valuable reference especially in construction stage. The feasibility of the method is verified by numerical examples.4. Experimental on free-form surface thin-shell structure and the finiteelement simulation methodDue to the complexity of production and loading, the mechanical properties experiment on free-form surface has always been considered difficulties, and there is little such study in the world. Morphopoiesis method based on B-spline theory is based on the small deformation assumption and linear elastic theory, and it can provide reference for the study of the structure mechanical properties under the condition of nonlinear and further research on the special mechanical properties of the free-form surface. This paper carried on the experimental study to the model obtained by the proposed method and investigates the crack development characteristic, stress distribution feature and ultimate load-bearing capacity. Also the finite element simulation method which can replace the tedious experiment is studied. The reliability and the practicability of the method is validated by comparing with the test data. These research results and the finite element simulation method can serve as a reference to the further study of the mechanical performance of the free-form surface thin shell structure and the engineering application as well as the theory development of the free-form surface structure.5. Summarize the mechanics performance of free-form surface structureThere is not enough research on the subject of free-form surface structure as a new type of structure. In this article, by means of combining a large number of numerical examples and combining the theory and experiment, the feature of the deformation of the structure and the change of the mechanical performance during the evolution process are investigated, and the load bearing characteristic of the rational free-form surface is summarized. In the evolutionary process, the average and maximum displacement of the structure all have reduced to different degrees with the reduction of the strain energy. Decrease of bending moment is more obvious than axial force, the optimized structures are principally suffered with axial force and the stress distribution is more uniform. The optimized structures not only have higher ultimate bearing capacity, but also have lower sensitivity to imperfection. The distribution of the membrane stress, the characteristics of the first principal stress of top and bottom surfaces, the distribution characteristics of bending stress- membrane stress ratio and so on are studied.Morphopoiesis of free-form surface based on b-spline method is programed in FORTRAN language. Nonlinearity is analyzed and considered by using the finite element software ANSYS when investigating the load-displacement curves under different evolutionary step and the imperfection effect. The morphopoiesis method based on the difference algorithm of sensitivity uses the finite element software ANSYS as a FORTRAN subroutine. Two sets of morphology program of free-form surface are obtained.