Bending-active Gridshells:Numerical Simulation And Model Test

Bending-active gridshells are characterized by their unique forming process,through which their final curved shape is derived by bending a mat of initially planar grids consisting of bidirectional continuous members.The members are connected by cylindrical hinge joints,which are free to accommodate in-plane rotation.This feature allows a bending-active gridshell to be able to vary its shape in the forming process through the distortion of grid angles.Once the final shape is achieved,measures such as locking the cylindrical hinge joints(i.e.constraining in-plane rotation at the joints)are taken to introduce shear stiffness to the structureAlthough the applications of bending-active gridshells can be traced back to the 1960s,only about ten of them have been built across the world owing to the complexity and difficulty in their form-finding and construction.Since the beginning of the new century,however,with the advances in computation,construction and material technologies,this special type of structures has engaged a revival of interest from both the academic and engineering communities,giving rise to new major projects.To promote the wider applications of bending-active gridshells,professional software with integrated functions of form-finding,mechanical analysis and structural design is urgently needed.The central component of such software is its computation module that deals with the numerical simulation of bending-active gridshells’ forming behavior as a mechanism as well as their post-forming mechanical behavior as a structure.Such a computation module is developed in this thesis based on the theory of vector form intrinsic finite element(VFIFE)method.The VFIFE method discretizes a continuous system into a finite number of particles with lumped mass,whose motion is traced to seek the equilibrium of the system based on the Second Newtonian Law.This feature endows the VFIFE method with an innate advantage in handling problems of large deformation and discontinuity,such as those involved in the forming process of a bending-active gridshell and its transition from a mechanism to a structure.The main content of this thesis is summarized as follows:(1)the basic theory of the VFIFE method is first briefly presented,followed by the derivation of VFIFE formulation of spatial beam elements and spatial cylindrical hinge joints(including cases of being free,semi-rigid and locked);(2)on that basis,a program is developed to simulate the full-range behavior of bending-active gridshells,from the forming process,through the introduction of shear stiffness,to the post-forming structural performance;(3)the validity of the program is verified through numerical examples for spatial beam elements,spatial hinge joints,and bending-active gridshells,respectively;(4)forming and loading tests are conducted on a 4.62-m-span bending-active gridshell model made with carbon fiber reinforced polymer(CFRP)strips;and(5)the shape of the model after forming and loading is measured,respectively;the measured results are shown to be in close agreement with the simulation results,which further validates the simulation program.