{"id":1089,"date":"2012-12-04T23:46:00","date_gmt":"2012-12-04T23:46:00","guid":{"rendered":"http:\/\/compositesandarchitecture.com\/?p=1089"},"modified":"2012-12-05T18:55:58","modified_gmt":"2012-12-05T18:55:58","slug":"before-they-made-it-they-broke-the-mold","status":"publish","type":"post","link":"https:\/\/kreysler.zaab.org\/?p=1089","title":{"rendered":"Before they made it, they broke the mold."},"content":{"rendered":"

Pleated Shell Structures 1<\/span> \u2013 Part 1 of 2.
\nPart 2, an interview with designer Shajay Bhooshan, will post on Thursday, Dec 6.<\/p>\n

The Pleated Shell Structures recently exhibited at SCIArc (Southern California Institute of Architecture) are a pair of free-standing, canopy-like structures made primarily of FRP.\u00a0 They are the product of an experiment in fabric-forming of FRP instead of using hard molds, a method that uses the stretching properties of fabrics to define a minimal surface meeting certain boundary conditions.<\/p>\n

Forms were fabricated and cast at Kreysler & Associates in American Canyon, CA, north of San Francisco, and the project was assembled onsite at SCIArc in Los Angeles, all in just 8 days. It was a joint effort by Shajay Bhooshan of Zaha Hadid Architects (ZHA), Josh Zabel of Kreysler & Associates, and a group of SCIArc students.\u00a0\u00a0\u00a0 Students from UC Berkeley and the California College of the Arts also participated in the fabrication process at Kreysler.\u00a0 While ZHA is a design firm, and Kreysler is an FRP fabricator, both companies were involved in design, and both Bhooshan and Zabel were hands-on in molding and assembly.<\/p>\n

The importance of the project is its exploration of shapes defined by edge conditions, and their translation into an alternative method for forming FRP.\u00a0 Both ends of the process \u2013 the computational creation of shapes and physical fabrication \u2013 were experimental.<\/p>\n

The method under exploration is to make frames, composed of flat pieces of plywood, whose curvilinear edges have fabric stretched over them.\u00a0 The curved surface taken by the fabric becomes the basis of a hard FRP panel.<\/p>\n

To achieve this, it is necessary to make software that simulates the response of fabric to being stretched over a contoured frame.\u00a0 That is used to define surfaces \u2013 panels \u2013 that are parts of a free-standing structure.<\/p>\n

The frame shapes defined in software are cut out of flat pieces of plywood on a CNC router.\u00a0 The pieces are attached to a flat base to form a box: the top is open, and the edge is composed of the computer-cut shapes.<\/p>\n

When fabric is stretched over that curvy top edge, it takes on a uniquely curved shape.\u00a0 Stretching-tension is the principle force at work; the influence of gravity is ideally kept to a minimum.\u00a0 In this case, a Lycra-like fabric that could be stretched 200%-300% is used to form the surfaces.<\/p>\n

To \u201cfreeze\u201d the surface permanently, FRP is applied.\u00a0\u00a0 A mat of glass fiber is wetted down with resin, and then applied to the stretched fabric.\u00a0 Additional layers are added to build up strength.\u00a0 The stretched fabric becomes part of the final product.\u00a0 Foam implants in the corners of the legs create tubes of FRP around them in casting, forming a more structurally robust shape.<\/p>\n

Once the resin has cured and hardened, the plywood form is removed.\u00a0 The composite panel retains the stretched fabric\u2019s contour, and is self-supporting.<\/p>\n

That\u2019s the theory.<\/p>\n

For Josh Zabel, the most valuable aspect proved to be the move from theory to practice. \u201cFinding out whether you can actually form fiberglass this way, and do it predictably, that is, to predict in the computer what the form will be when stretched and cast.\u201d<\/p>\n

In practice, gravity remained a very small factor.\u00a0 \u201cWe tested with a flat frame, four feet square, to see how much the fabric would sag.\u00a0 Over 4 feet, it sagged maybe 1\/8 inch. It stretched to 200 or 300 %.\u00a0 One guy pulling \u2018kind-of-hard\u2019 was enough to put it in sufficient tension.\u201d<\/p>\n

Zabel muses on the unexpected aspects of taking theory into the physical world. \u201cI was leading myself to believe it was possible to do this computationally.\u00a0 Shajay spent a lot of time working on a way to create a realistic digital model of a minimal surface. It breaks a surface down into a bunch of tiny points, makes little simulated springs between the points, and tries to minimize energy in all of the springs simultaneously.\u00a0 That’s what fabric does naturally when stretched. It’s easy to simulate, but it turns out it’s not easy to simulate very accurately, especially when considering the variations in physical properties from one material to the next – or even one fabric to the next.\u201d<\/p>\n

In practice, when they cast panels, \u201cwe discovered there\u2019s actually a great deal of influence you have in the act of making it, specifically in putting the fabric onto the form.\u00a0 Machine stretching would be more repeatable.\u00a0 The material itself makes a big difference, the difference between the shape that\u2019s yielded by Lycra vs. canvas, for example. It seems obvious in retrospect, but that was the big discovery for me.\u00a0 Of course, the next step is to configure the computer model so it better mimics the structures of a specific material.\u201d<\/p>\n

Because of the very tight fabrication schedule, the design changed.\u00a0 The wooden structures now seen behind the FRP shells were originally going to be FRP themselves.\u00a0 When it became evident that there would not be time to mold them all, they were re-conceived as plywood skeletal structures.\u00a0 All elements are cut from flat pieces of plywood on the CNC router, similar to the molding forms.<\/p>\n

The plywood edging on the FRP shells was also cut this way.\u00a0 These thin wood strips were primarily an aid to aligning the panels in 3-D space during assembly.\u00a0 \u201cThey are probably not necessary structurally,\u201d says Zabel.<\/p>\n

He points out that this method is only for creating minimal surfaces, but within that application, it is very practical.\u00a0 \u201cIt\u2019s a very inexpensive way to make a fiberglass mold. This method can happen faster because you\u2019re not waiting for the CNC machine to mill the whole surface. EPS molds take a lot of manual preparation.\u00a0\u00a0 Between the two methods, the man-hours are probably about equal\u2026 although there is currently very little trade or institutional knowledge about forming FRP without a mold.\u00a0 A real comparison of the labor would take closer study.\u201d<\/p>\n

Photos courtesy of Kreysler Associates and Zaha Hadid Architects.<\/p>\n

Fabrication at Kreylser & Associates, assembly at SCIArc.<\/p>\n\n\t\t\t