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Philip F. Yuan Philippe Block

A JOINT WORKSHOP OF MIT/ETH/TONGJI

TONGJI UNIVERSITY PRESS

CONTENTS

INTRODUCTION FORM FOLLOWS ROBOTIC FORCE PRINTING

Philip F. Yuan

PREFACE DIGITAL MASTER BUILDERS: EXPLORING STRENGTH THROUGH GEOMETRY

Philippe Block

PRECEDENTS FORM, FORCE AND FABRICATION

Gene Ting-Chun Kao Kam-Ming Mark Tam

BENDING-ACTIVE FORMWORK FOR SHELL STRUCTURES BASED ON 3D-PRINTING TECHNOLOGY

Xiang Wang

PROGRAMMING OF ROBOTIC FABRICATION Liming Zhang

METHODOLOGY

CONTENTS

INTRODUCTION FORM FOLLOWS ROBOTIC FORCE PRINTING

Philip F. Yuan

PREFACE DIGITAL MASTER BUILDERS: EXPLORING STRENGTH THROUGH GEOMETRY

Philippe Block

PRECEDENTS FORM, FORCE AND FABRICATION

Gene Ting-Chun Kao Kam-Ming Mark Tam

BENDING-ACTIVE FORMWORK FOR SHELL STRUCTURES BASED ON 3D-PRINTING TECHNOLOGY

Xiang Wang

PROGRAMMING OF ROBOTIC FABRICATION Liming Zhang

METHODOLOGY

PREFACE

PRELIMINARY GROUP WORKS SNAKE ROCK PAVILION

SHELL O

FRACTAL SHELL

FOLDED BRIDGE

EIGHT-LEGGED SHELL

106

WHITE HILL

114

THE RIBBON

122

FINAL FABRICATION WORKS BENDING SHELL PAVILION

130

FU BRIDGE

154

PREFACE

PRELIMINARY GROUP WORKS SNAKE ROCK PAVILION

SHELL O

FRACTAL SHELL

FOLDED BRIDGE

EIGHT-LEGGED SHELL

106

WHITE HILL

114

THE RIBBON

122

FINAL FABRICATION WORKS BENDING SHELL PAVILION

130

FU BRIDGE

154

ROBOTIC FORCE PRINTING

INTRODUCTION

ROBOTIC FORCE PRINTING

INTRODUCTION

ROBOTIC FORCE PRINTING the proper double curved geometry. Normally, large scaffoldings are used to control the form and take the load of the partial shell structure before it completes its shape (Figure 2). Therefore, it is this reason that makes the building of a shell structure not as efficient as it appears to be with its geometry and structural behavior. To solve this problem, architects and researchers have developed concepts with the smart usage of different geometry and materials. Felix Candela developed the way to only use a ruled surface and build with a linear mold system. Heinz Isler suggested the pneumatic formwork system and enabled a quick building process with removable, lightweight flexible material. Frei Otto applied the degree of freedom of a quadrilateral grid system to develop the gridshell structure concept. Nowadays, 3D-printing technology provides the building industry with a lot of possibilities. In this research, 3D-printed sheets with structural patterns are supposed to be used as the support of the shell structure, to enable a feasible and efficient building method. Bending-Active Structure and the Geometry of Bending Julian Lienhard proposed a potential structural typology which uses its curvature with the form to improve the stiffness of the structureâ€‰[8]. With suitable materials such as the FRP, which can offer enough strength at the same time with sufficient bending, it is possible to utilize the curved bending geometry to stabilize the structure with flexible materials (such structural behavior can be easily explained by the stiffening effect to use creases and bending for a sheet of paper as shown in Figure 3). o combine the basic requirement of the deliberately designed geometry based on a form-finding process with geometrical restrictions of the active-bending form, it is the first basic object of this pre-research to define the principles of the geometry. Experienced from a relevant research based on the curved-crease-folding and shell with thin sheets, a Y-shape prototype is used to define the total structure and also used in predominant form-finding. Based on a primary compression-only structural form designed with RhinoVAULT, spatial curves can be achieved from each leg of the Y-branch. By developing a quasi-developable surface by simply divide the adjacent curves into large amount

PRECEDENTS

Figure 2 Scaffolding system as formwork for the building of concrete shell structures

Figure 3 Top: Stiffening effect of folding with creases with a paper sheet[9], Bottom: the stiffening effect of bending (in single curve and a pseudo-doublecurve) to a paper sheet[10]

PRECEDENTS

Figure 2 Scaffolding system as formwork for the building of concrete shell structures

Figure 3 Top: Stiffening effect of folding with creases with a paper sheet[9], Bottom: the stiffening effect of bending (in single curve and a pseudo-doublecurve) to a paper sheet[10]

ROBOTIC FORCE PRINTING Figure 4

PRECEDENTS elements and connecting points to compose plenty of triangles, it is able to unroll the polysurface into a planar contour. By either laser-cutting the sheet material or 3D printing an arbitrary pattern inside the contour, it is able to bend the structure back to make a spatial shell surface that closely resembles the original design (Figure 4). It is obvious in the experience that the final form may have a deviation to the ideal one which is derived by the optimization for the developable surface, because the final forming process relies on the bending behavior of the material and the moving of the supports to the target position. For this problem, simulation and analysis of the active-bent form are made to work as an integral part of the workflow. The simulation of the bending-active geometry can generally be achieved either in a static way to analyze the postbuckling behavior or in a kinetic way to simulate the quasistatic problem. For a quick design feedback of the bent geometry, a simple kinetic analysis method is made with the Kangaroo plug-in in Grasshopper environment. Based on the Particle-Spring-Method, springs are generated with the original unrolled geometry as an input mesh. The target actuation of the system (the movement of the supports) is defined as the large forces added to specific lines. The whole system load is gradually added to slow down the actuation process to avoid a sudden large deformation in the structural system and hence generate a quasi-static result for the bent geometry (Figure 5). At the same time, similar simulations and analyzing workflows have been tested and achieved with the Finite-ElementAnalysis (FEA) software. In this research, software ABAQUS is used with its Python Interface to export the complicated boundary conditions directly from the Rhinoceros working environment. Different steps (Static-RIKS, Dynamic-Explicit) are tested based on different assumptions of the problem (imagine that as a static problem with a large deformation or a quasi-static problem based on the long-time-span kinetic problem). With the FE analysis, not only the final geometry but also the internal stresses caused by the bending can be analyzed and visualized in the result (Figure 6).

A relevant design experiment with the Y-shape prototype and bending form based on the curvedcrease-folding

Figure 5 Bending simulation of a planar strip based on different boundary conditions and actuation in different steps (simulated with GH plugin Kangaroo)

ROBOTIC FORCE PRINTING Figure 4

A relevant design experiment with the Y-shape prototype and bending form based on the curvedcrease-folding

Figure 5 Bending simulation of a planar strip based on different boundary conditions and actuation in different steps (simulated with GH plugin Kangaroo)

ROBOTIC FORCE PRINTING “Printing the Forces”—A Prototypical Pavilion With the aforementioned methodologies and design tools generated for the active-bending shell formwork, a prototypical pavilion is made to testify the feasibility and restrictions of this design method as well as the fabrication technique. The initial design started from a triangular planar design domain and the form-finding process is made with RhinoVAULT, to find a suitable compression-only form for the shell structure. To make the double-curved 3D printable, the optimization method is initially made with the division of the shell surface into numbers of strips and then bent and connected with glues to get the desired geometry (Figure 7). To enhance the structural behavior of the shell, principal stress lines are also generated and post-processed to be printed as the structural pattern of the shell. To achieve simple bending and reduce the welding procedure as well as the tolerance it will bring, a simple optimization quasi-loft method is used in the second test to directly get the unrolled shape of the bent shell. The bending process is then analyzed and tested with a 1:10 model to measure deviations. Construction details as well as the building sequence are tested to cast concrete on the formwork and the feasibility is testified with a small scale-model (Figure 8). As the first demonstrator of the structure concept as well as the building technique, a full-scale prototype is then 3D-printed and building according to the bending simulation (Figure 9). Three layers of Modified PLA are printed with a combination of a UV-grid and the principal stress line grid with an average width gap of about 5 cm. The forming process is actuated by the tensioning process of some strips to move the boundaries inwards to reach the target point. Finally, the structure shows its robust stiffness with its super thin cross-section and its light weight of roughly 20 kg. To show the feasibility of the building technique in a complicated design case of a shell structure, a more complex form is designed with the same methodology. The intercrossed geometry is then optimized into a combination of series of lofted-developable surfaces. To improve the building process, several side trusses are

PRECEDENTS Figure 6 Bending simulation of different types of activebending geometries in ABAQUS based on the DynamicExplicit Method to solve a quasistatic problem

Figure 7 Initial design test with the methodology with a simple triangular shell structure and printed in scale 1:20

Figure 8 Refinement of the developable surface and the casting test

PRECEDENTS Figure 6 Bending simulation of different types of activebending geometries in ABAQUS based on the DynamicExplicit Method to solve a quasistatic problem

Figure 7 Initial design test with the methodology with a simple triangular shell structure and printed in scale 1:20

Figure 8 Refinement of the developable surface and the casting test

ROBOTIC FORCE PRINTING added to support the structure and help the positioning of the shell surface. With such guides, the assembly of the 3D-printed formwork can be easily assembled to reach the geometry and make it as a purely geometric problem. In the final building process, 10 mm Glass-Fiber-ReinforcedConcrete (GRC) is casted on-site on the formwork with only supports on the curved edges to test the load-bearing capacity. Finally, the 80 kg 3d-printed formwork took the 400 kg dead load successfully (Figure 10). Conclusion With pre-research and full-scale pavilion, the efficiency and feasibility of the 3D-printed bending-active shell structure formwork are tested and demonstrated. The workflow is established and improved to enable designers and architects to combine structural considerations and geometrical requirements together in the first step of the design. More research and tests will be done in the workshop to find more potential improvements and possibilities of the structural concept and the fabrication technique. More analysis of the detailed structural behavior and the formfinding simulation should be further developed. The success of the two designs and pavilions in the workshop will further show the advantages and efficiency of this novel structure concept.

PRECEDENTS Figure 9 Bending process of the prototype printed in full-scale

Figure 10 Final assembly and concrete casting on the active-bent formwork

REFERENCES [6] Otto, F., et al. IL 10 Gitterschalen–Gridshells. Stuttgart: Institut für leichte Flächentragwerke, 1974.

[1] Méndez Echenagucia, T., D. Pigram, A. Liew, T. Van Mele, and P. Block. Full-Scale Prototype of A CableNet and Fabric Formed Concrete Thin-Shell Roof. Paper presented at the 2018 IASS Symposium, 2018.

[7] Chilton, John, and Heinz Isler. Heinz Isler. London: Thomas Telford, 2000.

[2] Flügge, W. Stresses in Shells. Berlin: Springer Verlag, 1973.

[8] Lienhard, Julian, and Jan Knippers. “Bending-Active Structures. Form-Finding Strategies Using Elastic Deformation in Static and Kenetic Systems and the Structural Potentials Therein.” ITKE, Stuttgart, 2014.

[3] Adriaenssens, S., P. Block, D. Veenendaal, and C. Williams, Shell Structures for Architecture: Form Finding and Optimization, London: Routledge, 2014. [4] Piker, D. “Kangaroo: Form Finding with Computational Physics.” Architectural Design 83, no. 2 (2013): 136-137.

[9] Siegel, C., Strukturformen der modernen Architektur: München: Callwey Verlag, 1960.

[5] Rippmann, M., L. Lachauer., and P. Block, “RhinoVAULT—Designing Funicular Form with Rhino”, computer software, 2012.

[10] Pini, V., J. Ruz, P. Kosaka, O. Malvar, M. Calleja, and J. Tamayo, “How Two-Dimensional Bending can Extraordinarily Stiffen Thin Sheets. ” Scientific Reports 6, Article number: 29627, 2016.