Shape-Adaptive Reuse of Knitted Textile Formwork: Exploring Geometries, Design Parameters, and Combined Structures

Abstract

Concrete is the most used construction material worldwide and the cement industry is responsible for around 7% of the global CO2 emissions. Due to its cost efficiency, durability and ubiquity, it is being severely overused in current engineering practice, while material efficient construction can potentially save between 24-50% of the emissions associated with concrete and cement. Considering the overdesign of recently constructed buildings, structural design optimization represents an important tool in addressing material-inefficient construction, and can contribute significantly to the improvement of the ecological impact of our built environment.

This thesis explores the geometric design space and reuse potential of knitted textile formwork for the creation of concrete structures of various geometries. While traditional rigid formworks limit the creation of structurally efficient, doubly curved structures due to material intensiveness and high cost, flexible fabric formworks offer significant advantages in terms of sustainability, efficiency, and the ability to achieve complex shapes.

Through physical prototyping and computational analysis, the study identifies a wide range of achievable shapes and evaluates their design parameters, accuracy and structural performance. The physical prototyping phase involves the fabrication of multiple small-scale models and combining these to larger structures. Different tensioning methods, such as cables, rods, and weights, are applied to the fabric to achieve various geometries. Furthermore, the study investigates the effects of repeated use on the fabric's performance. The fabricated geometries are analyzed through 3D scanning to assess their accuracy and to determine the influence of tensioning and mortar weight on their resulting geometry. Through finite element analysis, the structural performance of combined shapes, created by connecting multiple shell elements, is evaluated.

The prototypes, built throughout this research, demonstrate the feasibility of creating complex, doubly curved shapes with the same fabric sample, applying various tensioning strategies, highlighting the adaptability and reusability of the formwork system. The study finds, that that the fabric can be reused multiple times for the fabrication of different elements without significant loss of quality or functionality. The geometrical analysis shows that the formwork system can produce accurate and repeatable geometries, despite the manual fabrication of the prototypes. The results of the structural analysis provide insight into the influence of the connection between individual elements, element orientation and their overall configuration on the structural performance of structures, composed of multiple elements. The results reveal, that that in the design of composed structures, special attention must be paid to the avoidance of alignment of flexible joints between elements and regions of single curvature and low stiffness to avoid the occurrence of mechanism-like effects.

The findings of this research contribute to the development of a design methodology for the creation of complex structures using flexible formwork systems. The findings shed light on the design space provided by the fabrication method and the mechanical behavior of the resulting structures, and thereby enables designers to make informed decisions to optimize material usage, reduce waste, and create innovative, sustainable structures. The study successfully demonstrates the potential of knitted textile formwork as a versatile and sustainable solution for the construction industry, offering new possibilities for resource efficient fabrication methods.