Theoretical And Experimental Research On A Novel Prefabricated Six-bar Tetrahedral Torsional Lattice Shell

People’s living quality has been improved a lot in our country with the great development of the construction industry.However,the extensive production mode of traditional construction process also brings greater contradiction with natural resources and environment.This situation gives rise to the higher demands for prefabricated structures,which are the representative of green structures and can be the key solution to the upgrading problem of the construction industry.Against this background,a new type of prefabricated torsional shell system is proposed,including several kinds of single shells and shells that are combined of multiple single ones.These torsional lattice shells are composed of a certain number of six-bar tetrahedral units whose planar projections are the same,which makes their configurations very simple.Theoretical and experimental studies are carried out in this paper and the research results show that such shells are reliable for application in real projects due to their simple configurations and rational loading behaviors.Chapter 1 summarizes the features and the main theories of torsional lattice shells,introduces the latest abroad and domestic studies for prefabricated grid structures,and clarifies the significance and the main content of this dissertation’s work.Chapter 2 gives the configurations of the new prefabricated torsional shells in details based on the geometric features of six-bar tetrahedral units and torsional shells.The new shell system includes 6 kinds of single torsional shells and 4 kinds of combined torsional shells.The characteristics of all these shells are summarized to provide advises for the application of real projects.Several kinds of joints’constructions are also introduced in this chapter.Chapter 3 carries out the static analysis for two kinds of single torsional shells,which are composed of orthogonal or diagonal tetrahedral units.The effects of different joint types on the structures’ performance are also investigated.The computational results can provide practical advises for real projects.Chapter 4 investigates the stability performance of the single torsional shells.The eigenvalue buckling analyses and the nonlinear analyses with initial geometric imperfections are all carried out in this chapter.The initial imperfections for single bars are also considered in this chapter,which solves the problem that pin-joint bars would not buckle in traditional nonlinear analysis.The effects of several parameters on the structures’stability performance are also studied.Chapter 5 focuses on the static and stability performance of the combined torsional lattice shells.A typical type of combined shell which is composed of four single torsional shells is selected as the numerical example.The results show the excellent economic and technical indicators for this kind of structures.Chapter 6 proposes a new shape optimization algorithm base on the gradient descent method,which tackles the problem of traditional shape optimizations methods and can be applied in all kinds of grid structures.The structure’s shape is gradually changed by remodifying nodal coordinates at each step to improve the structure’s stiffness.This algorithm is applied in a combined torsional shell and a free-form prefabricated lattice shell is generated.Chapter 7 conducts an experimental study on a 5.4m-long single torsional shell.The simulation of the design,production,deposit,transport and installation of the structure verified the practicability of such system.At last,the comparisons of experimental and computational results under full-span and half-span loads verify the accuracy of the theoretical method.Chapter 8 summarizes the work in this dissertation and points out some suggestions for further studies.