“C” and Learn more about Fabric Structures

FabricArchitect continues his series on the ABC’s of Fabric Structures.

When you “C” a structure like the one on the right that I worked on in New York City at South Street Seaport, you will know the difference between a tent and a fabric structure.

Todays words are:

  • Cables
  • Catenaries
  • Cutting Patterns
  • Cost

Cables

Most fabric structures have an “edge” which is made of a fabric pocket or “cuff” in which a cable is placed inside of it.

This cable is then connected to a membrane plate or directly to the structural steel component.

Cables are usually associated with permanent structures but can be used in temporary structures as well. The issue with cables is that they require an end fitting and can be quite bulky to store as opposed to kevlar rope and webbing belts which are more often used for tents and moveable canopies.

As for cables, they come in all shapes and sizes and strands. I like designing structures with edge spans less than 25′ feet in order to keep cables at a cost effective nice size (3/8″ to 5/8″) with small end fittings.

Otherwise, the price jumps fast when they get bigger and they are harder and heavier to move around. I also prefer stainless steel or coated galvanized over any other cable being offered.

I always say “pay now, pay later or have a plan”. Cables are the visual jewelry of a fabric structure. They will look bad if not taken care of or made of an inferior material.

As for end fitting, we can talk more when I get to “E”.

Want to get a sneak peak at  cables and end fittings?

Visit Ronstan, Jakob or Pfeifer.

Catenaries

I never used Catenaries in a sentence until I started designing fabric structures!

Good word to know.

Catenaries describes the scalloped edge shape of the boundary of a  fabric structures from one specific  end point or node. Fabric structures rarely have straight edges. They always have curved edges if they are only being held at two points.

An old friend of mine in the industry once told me that a typical catenary “scallop” is usually 10% of the distance between the two points. I use that as a rule of thumb before it goes into “form finding”. For example, if the distance between two points is 20 feet, the catenary “scallop” in plan will be about 2′. Try it at home.

Fabric Structure computer software allows one to get not only the forces but the cable lengths of those tricking catenaries.

Want to know more about fabric structure software?

Fabritec Structures has Marty Brown in their offices. He is the developer of NDN, the specialized Finite Element Method (FEM) modeling and analysis software that is used around the world by leading consultants and fabricators for the engineering, design and patterning of tensile membrane systems.

Cutting Patterns

I always like to use the analogy of a tailored suit to describe a fabric structure.

You have the body or the design to start with. You pick out the materials and the tailor measures, cuts the materials and fabricates a custom outfit.
fabric structures is done much the same way but all the work is done in 3D using fabric structure software.

However, one inputs material characteristics into the program because no two materials stretch alike.

The program and then unfolds the 3D image into 2D to determine what the structures will look “unstretched” and ultimately provide the fabricator with “cutting patterns”.

These patterns are made using a series of x, y coordinates that a CAD/CAM machine can read in order to cut the pattern from a sheet of fabric. Adjustments and modifcation to the cutting pattern report needs to be made before the membrane is cut to accomodate seams, overlaps, reinforcements and cuffs.

What do you need to know?

Ask to see the report.

You need to make sure they have input the correct material charateristics and thay you are aware and have apporved the seams orientation and the location of reinformcements and pockets.

See Tensys for more info on cutting patterns.

Cost

“How much does it cost any way?” That’s the number one question I get all the time.

Do a simple exercise.

Take the plan area of your space.

Multiply it by 1.5. This will give you an estimate of the surface area of your fabric structure and include a small amount of fabric that is wasted on the cutting room floor.

Take the surface area and multiply if by $100.

In 2011, that’s the range for designing, engineering, fabricating, and installing a fabric structure. The range does not include foundations and it does not take into consideration the material finished, the size of the overall project or the material chosen.

Surface Area X $100= Budget

It will tell you if you can afford a custom structure.

I got fabric structure ideas in all shapes and sizes and cost.

Contact me and lets “C” if I can help you.

Next in the series: Design, Details and Dirt.

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