Anatomy of a Tension Structure

The Process of Designing and Buildinga Tension Structure

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Review case studies of

different PTFE and PVC tension

structures.

Assess the fabrication and

installation processes of

fabric structures.

Examine available materials,

components, and hardware used in tensile architecture.

Identify the forms and

uses of fabric structure design.

Learning Objectives:

Section 1: Overview1. General Forms2. Membrane Types

Section 2: Planning1. Concept Development and Analysis2. Preliminary Analysis & Material Takeoff3. Design Analysis and Final Pricing4. Design Considerations

Section 3: Construction1. Engineering2. Steel Fabrication3. Fabric Fabrication

Section 4: Installation1. On-site Installation2. Post-Construction Service

Course Outline:

Section 6: Case Studies1. Allianz Field2. DFW Terminal B TEXRail Station3. ATL Next Central Passenger

Terminal Complex

Section 5: ETFE Systems1. About ETFE2. Prestressed vs. Inflated3. Design-Build Process

Section 1Overview of Tension Structures: Identify the forms and uses of

fabric structure design.

Concept Considerations• Site plan: Do you know the boundaries of the area you want covered? Do you know the height of the

structure you are contemplating? Have a good understanding of the site on which the structure is being built, as well as any requirements or restrictions.

• Inspiration: What is driving your shape, form, or function of the structure? Having a good understanding of the overall design intent of the project can help steer initial concepts in the right direction.

• Budget: If you’re flexible with your design and material choices, the cost of a tension structure can vary wildly. Understanding your budget will help keep those concepts rooted in reality and examine the project’s feasibility.

• Pre-engineered structures: standard forms, quick turn around time, affordable• Tension awnings: minimal framing, lateral forces, variety of edge details, self-supporting or hybrid• Interior applications: special events, retail and restaurants, highly creative and flexible• Temporary structures: special events, short-term installation, lost cost alternative

Common Forms & Applications

Mast Supported Point Supported Arch Supported Ridge Valley Simple Saddle

General Applications:

Vinyl-Coated Polyester (PVC)

Membrane TypesTeflon-Coated Fiberglass (PTFE) Ethylene Tetrafluoroethylene (ETFE)

• Temporary and permanent structures

• Fire resistant (Class C NFPA 701)• Life span of 20-plus years• Variety of colors, weights,

topcoats, and textures• Self-cleaning• Recyclable• Most cost-effective option

• Large-scale permanent structures• Noncombustible (Class A)• Life span of more than 25-plus

years• Off-white during installation• Self-cleaning• Colors available in large quantity

• A clear polymer extruded into thin film (or foil) to form a single-layer membrane (supported by cable net), or two or more layers creating pneumatic cushions

• Both shatter and fire resistant (NFPA 701)

• Life span of more than 25-plus years• Weighs just 1 percent of the weight of

glass but transmits 95 percent of the same light

• Available in a variety of printing and tinting options

Components and Details

Bale Ring (Interior Support)

Base Plate

Membrane Plate

Edge Cable

Steel Column

Membrane (Fabric)

Tie Down

Section 2Planning: Identify the forms, uses, and

costs of fabric structure design.

Design Development and Analysis

1. Concept Development and AnalysisA 3-D model is developed using all the previous information collected and taken into appropriate program to communicate the concept to the client/decision maker. This allows for:

• Further visualization for the client• Overall aesthetic analysis of the size and shape

2. Preliminary Analysis – Material TakeoffThe approved model is then put into a non-linear analysis program specifically created to analyze membrane structures. An understanding of steel sizes and connection types is developed in a material takeoff. This allows for:

• Final optimization of the shape and form.• Determination of high stress points in the membrane.• Discovery of ponding issues in low-lying areas.• The estimating department to do a takeoff of the components for accurate budgeting.

Design Development and Analysis

3. Detail Analysis – Final PricingSome projects may require further detail or material development to help define different pricing aspects. Once completed, a final cost for the structure can be developed accurately.

Design Considerations:Once the project is approved and contracted, the design team, in conjunction with the engineering team, develops the final geometry with the most up-to-date information and then focuses on the most appropriate details for the structure.

Along with the steel connection plate designs, this is the time that the tensioning method is decided as well as the different connections, including clevis, shackle, turnbuckle, extrusion, etc.

1. Two-coat epoxy

finish

2. Three-coat epoxy finish with

a zinc primer

3. Powder coating

EPOXY FINISHES POWDER COATING

Other Considerations: Types of Finishes

Section 3Construction: Identify the forms, uses,

and costs of fabric structure design.

EngineeringRunning in conjunction with the design is the engineering analysis. The engineering team will analyze the structure software package and confirm that the structure performs well under all building code criteria as well as general tension structure design practices.

The engineering phase allows the engineer to check load cases, membrane stresses, and contour maps for ponding or softness in the membrane.

Steel FabricationFrom the completed and approved 3-D models created by the design and engineering teams, fabrication drawings are produced, and the steel is fabricated in a steel fabrication shop.

Fabric FabricationWith the same base model used for the steel shop drawings, the fabric geometry is finalized, and a patterning report along with cut patterns are created from a specialty software package. These cut patterns are used to cut pieces of fabric, and then the edge conditions and seams are welded together with high-frequency RF machines.

Upon completion of fabrication, critical planning and thought goes into the packaging of the membrane for transport to the site in order to prevent the membrane from being damaged while also ensuring that the panels are sequenced correctly.

Pattern Model Pattern Report Cut Pattern

Section 4Installation: Identify the forms, uses, and costs of fabric structure design.

InstallationA logistics team works on shipping all materials to the site, and an installation means and methods plan is developed to make sure the structure is properly installed in the least amount of time on-site as possible.

One advantage to fabric structures is their relatively quick installation time as compared to other construction.

Steps essential to a successful installation:• Ensure that the right equipment and tools are on-site.• Provide an adequate shake-out area and protect the membrane from

sharp surfaces.• Be mindful of the weather.• Complete a thorough inspection of all connections.• Close out and sign off with the client or general contractor.

Post-Construction Services

After installation is complete, post-construction services are available to maintain the structures cleanliness and appearance as well as ensure its structural integrity.

This includes: • Routine cleaning (“soap and water”)• NOT sandblasting • Annual inspections• “Fabric kits” and repairs• Warranty vs. lifespan• Material finish

Section 5Defining ETFE and

Understanding Its Properties

What is ETFE?

ETFE is copolymer of ethylene and tetrafluoroethylene, comprised of 25 percent ethylene and 75 percent tetrafluoroethylene. It belongs to the fluorine polymer family. Due to its chemical makeup, it is a very stable material offering:

• Good UV stability

• High transparency

• 1/100 the weight of glass

• No deterioration by most common materials

• Resistance to both high and low temperature variation

• Longevity (30-plus years)

• 100 percent recyclability

C

H

H F

C C C

H

H

F

F

F

nm

ETFE Chemical Compound:

Advantages of ETFE • Light, self-weight

• Long service life

• Light transmittance (controlled by

wavelength range)

• Chemical, heat, and UV resistance

• Electric and mechanical properties

• Non-flammability (DIN B-1)

• Self-cleaning

• 100 percent recyclable

• Weatherability

• Anti-stick property (antifouling)

• Anti-condensation can be added

Prestressed vs. Inflated

Inflated ETFE Cushions

PrestressedSingle-Layer ETFE

About Inflated “Cushions”

2-layer cushion

3-layer cushion

3-layer cushion with moveable middle layer

3-layer cushion, inner layer separately fixed

4-layer cushion, two separately fixed cushion

Types of Cushions:

How the Inflation System Works

Inflation Unit/BlowersDuct WorkTransparent TubeCushion tubes

Design-Build Process1. Concepts Development and Analysis2. Preliminary Analysis and Material Takeoff3. Detailed Analysis and Final Pricing4. Design Considerations5. Final Engineering6. Steel Fabrication7. Film Fabrication/Membrane Logistics Packaging8. Installation/Project Management9. Post-Construction Services

Cushion Patterning Process

1. A fine element mesh is used during analysis stage to represent the ETFE fabric. This FE mesh is inflated to obtain desired curved profile.

3. To check for errors, the 2-D patterns are essentially re-attached around the perimeter of the cushion and re-inflated.Then the re-inflated cushion is compared to the original cushion and any unusual stresses or areas of slack are corrected.

2.1

1.6

1.4

1.3

1.1

1.0

0.8

0.6

0.5

0.3

0.2

0.0

2. The 3-D profile is then flattened into an alternative cutting pattern. This causes unwanted stresses within the fabric that can even go into compression. If these stresses are ignored, the pattern will not be exact.

Section 6Case Studies: Identify the forms, uses,

and costs of fabric structure design.

Case Study: PTFE System

Allianz Field

Scope of work: 93,425-square-foot translucent PTFE facade

Location: St. Paul, Minnesota

Case Study 1: PTFE Cladding SystemAllianz Field, Minnesota United FC

Conceptual Design

Allianz Field is a soccer-specific stadium in Saint Paul, Minnesota, for the Minnesota United FC Major League Soccer team. On October 23, 2015, team owners announced that Minnesota United would build a stadium on the 35-acre Saint Paul bus barn site. The finished stadium seats approximately 19,400. The $200-million privately financed project was completed in spring 2019.

Case Study 1: PTFE Cladding SystemAllianz Field, Minnesota United FC

Engineering Analysis

Fabric FabricationCase Study 1: PTFE Cladding SystemAllianz Field, Minnesota United FC

Connection DetailsCase Study 1: PTFE Cladding SystemAllianz Field, Minnesota United FC

AssemblyCase Study 1: PTFE Cladding SystemAllianz Field, Minnesota United FC

InstallationCase Study 1: PTFE Cladding SystemAllianz Field, Minnesota United FC

The facade is Allianz Field’s defining characteristic not only for its shiny, see-through appearance but also for its contemporary, geometric shape.

Completed ProjectCase Study 1: PTFE Cladding SystemAllianz Field, Minnesota United FC

Allianz Field was the first project to use the unusual metallic, translucent PTFE material that accommodated all the envisioned features for the stadium in a way that other products, like metal, could not.

Completed ProjectCase Study 1: PTFE Cladding SystemAllianz Field, Minnesota United FC

Case Study: PTFE System

DFW Airport Terminal B TEXRail Station

5 saddle canopies 14,015 square feet 28 high/low canopies 7,380 square feet 3 pedestrian walkway canopies 4,760 square feet

Location: Dallas

Scope of work:

Case Study 2: PTFE SystemDFW Airport TEXRail Station, Terminal B

Conceptual Design

The TEXRail line connects Fort Worth to the DFW International Airport, where a series of fabric canopies and covered walkways greet travelers at the Terminal B station. The airport’s TEXRail station was designed to accommodate a second rail line for DART’s plan to extend TEXRailservice north and east.

Engineering AnalysisCase Study 2: PTFE SystemDFW Airport TEXRail Station, Terminal B

Fabric FabricationCase Study 2: PTFE SystemDFW Airport TEXRail Station, Terminal B

Connection DetailsCase Study 2: PTFE SystemDFW Airport TEXRail Station, Terminal B

AssemblyCase Study 2: PTFE SystemDFW Airport TEXRail Station, Terminal B

InstallationCase Study 2: PTFE SystemDFW Airport TEXRail Station, Terminal B

The look and feel of the station was designed to be very similar to the DART station at Terminal A, creating a modern atmosphere for travelers.

Completed ProjectCase Study 2: PTFE SystemDFW Airport TEXRail Station, Terminal B

The saddle canopies above the railway will protect travelers as they enter and exit the train, and the high and low walkway canopies will cover passengers as they wait for the next train. The night lighting adds to the aesthetic of their sleek, contemporary style.

Completed ProjectCase Study 2: PTFE SystemDFW Airport TEXRail Station, Terminal B

Case Study: ETFE System

ATL Next Central Passenger Terminal

Complex

Scope of work: 345,500-square-foot ETFE canopies

Location: Atlanta

Case Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

Conceptual Design

At the busiest airport in America, the Central Passenger Terminal Complex (CPTC) consists of two facilities for domestic and international passengers. On the north and south entrances of the domestic terminal is the largest ETFE membrane project in North America to date. Two 864-foot-long cushioned ETFE canopies shelter travelers as they come and go through Hartsfield-Jackson Atlanta International Airport.

Engineering AnalysisCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

Foil FabricationCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

Connection DetailsCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

InstallationCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

AssemblyCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

InstallationCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

InstallationCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

Completed ProjectCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

Completed ProjectCase Study 3: ETFE Cushion SystemATL Next Central Passenger Terminal

Thank you!Thank you for taking our Anatomy of a Tension Structure CEU course.

We are happy to answer any follow-up questions you may have or assist with any tension fabric structure designs you are considering. Contact FabriTec Structures by visiting us online at fabritecstructures.com or calling us at 877-887-4233.