Experiments for design and optimization of thin shell structures

Shell structures have been a focus of interest for many years by architects and engineers because of aesthetic concerns and their ability to cover large spans. Finding the ideal form for shell structures can be traced back to Robert Hooke, who has examined the ideal arch form by gravity-impacting chains. Inspired by Hooke's work and Catalan vaults, Gaudi has carried out experiments on finding ideal forms with chains in three dimensions. With the development of the reinforced concrete, the Spanish architect Felix Candela was able to reveal new and revolutionary shell experiments. Candela, who usually used hyperbolic paraboloid in shells, has reached to a thickness of 4 cm. Heinz Isler, who also saw and was impressed by Candela's work, further advanced form finding experiments. In order to reach the ideal form, the fabric which is covered with plastic is hanged from the support points so that they can be shaped by the force of gravity. Later on, these forms are reversed and large openings passed through the forms, which only work with compression and carry their own weight. Another pioneer in the area is the Frei Otto. Otto has also done gravitational form finding experiments using cable networks. In some experiments he used soap bubbles to reach minimal surfaces. He has worked on suspension systems and wood grid shells in the following years. Developments in the aviation and car manufacturing sector have facilitated mathematical identification of the forms and their transfer to the computer environment. Computer-assisted form finding methods have progressed, parallel to this situation. These methods are also described in the scope of the study. These methods are described as Force Density Method (FDM), Thrust Network Analysis (TNA), Dynamic Relaxation (DR) and Particle-Spring Method (PS). FDM is a form-finding method that Frei Otto and his team use more widely. It is more suitable for membrane structures. TNA is a form finding method more suitable for masonry and concrete shells developed by Block Research Group. This method is also independent of the material and it allows to see and intervene the process because it is a geometric method. DR, on the other hand, is a form finding method used mostly in the design of wooden gridshell structures. In this method, connection points are very important and physical modeling as well as complex calculations must be done in order to be successful. PS is a computerized version of the chain method developed by Hooke and Gaudi. It aims to find an equilibrium between the elements by dividing them into nodes and springs. It is a convenient way to produce quick form alternatives. Gaussian curvature is an important criterion that determines the production and durability of surfaces. It is determined by the state of the main curves over the surfaces. If the curvatures of these curves are in the same direction they are positive, if in different direction they are negative. If one of the curves is flat, the Gaussian curvature is 0 and these surfaces are single curved surfaces. If this curvature is different from zero, it is a double curved surface. If surfaces can be formed with straight lines, they become ruled surfaces. All single curved surfaces are such surfaces. Surfaces such as hyperbolic paraboloid are also such surfaces from double curvature surfaces, and architects have always been interested in them, because the ease of production of these types of ruled surfaces. There are also free-form surfaces defined by NURBS curves that require special production, and special optimization is required for their production. Within the scope of the study, three shell structures were designed by different base surfaces, and after they were analyzed, openings were extracted on them and weights were reduced and form alternatives were formed. The resulting forms were analyzed again and the structures were stayed in the structural safe zone. Thus, a process for the formation of shell structures has been proposed.