Title: Structural design and analysis of elastically bent gridshells – The development of a numerical simulation tool
Type: Master’s thesis in Structural Engineering and Building Technology
Author: Emil Poulsen
Supervisor: Mats Ander (Chalmers), Niklas Johansson (Ramböll Byggteknik)
Publisher: Chalmers University of Technology – Department of Applied Mechanics
An elastically bent gridshell is a type of freeform shell structure composed by a network of continuous elements across its span. It is assembled by straight members into a two dimensional mat which subsequently is bent into a three dimensional doubly curved shell. In contrary to gridshells made of discrete members, the continuous elements can easily be connected using identical clamps or bolts. The material of the structure must exhibit a low Young’s modulus – bending capacity ratio in order to facilitate the elastic formation process without breakage. Actively bent gridshells can cross large spans with a small amount of material due to its shell action. They can be considered a sustainable design option to achieve large and architecturally qualitative roof structures, especially with local timber as the material of choice. Even though the benefits of elastically bent gridshells seem apparent, only a handful large scale structures of this kind have been built so far. A reason for this is thought to be the involved design process and lack of intuitive tools. The objective in this thesis is to formulate a design and analysis process of elastically bent gridshells. Included in this is to develop a codebase which can simulate the highly non-linear bending process with automatic supervision of the material capacity. The mechanics used is based on a nodal six degree of freedom formulation of the Dynamic Relaxation method. All equations and logics are compiled into a C# .NET class library which functions as an application programming interface (API). It is given the name EMU.dll and has been implemented as a plugin to the parametric 3D modelling software Grasshopper3d® for Rhinoceros®. In order to achieve good code design which easily can be maintained and extended, the concepts of object oriented design patterns are used.
The structural output of the developed numerical framework is compared against analytical and physical models. Through four test cases the code is benchmarked and proven to be performing accurately. As a real-time structural analysis plug-in in a parametric environment, the user can easily interact with the model during run time. Suggestions of how the developed tool fits into a bigger system of the gridshell design and analysis process are presented. The implementation of software design patterns makes EMU.dll straightforward to extend and modify to suit project specific needs.