10
8/10/2019 ArroDesign Research Paper Tabriz 82209 http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 1/10  Proceedings of the 1 st  International Conference on Concrete Technology, Tabriz, Iran, 6-7 November 2009 Paper Code. No. XXXXXX Page 1 Fabric Formwork for Architectural Concrete Structures Eleanor D’Aponte, Alexander Lawton, Russ Miller Johnson  Norwich University, ArroDesign, Engineering Ventures [email protected] , [email protected], [email protected] ABSTRACT This paper provides a general overview of fabric forming and illustrates the immense potential of the construction techniques. The concepts of tension forming and its application to the design and construction of rectilinear and curvilinear wall forming, columns, slabs, beams, variable section  precast beams, trusses panels and thin shell vaults will be discussed. The practical application of fabric forming allows for more complex shapes and structural configurations than previously  possible. Replacing rigid formwork panels and casting forms with a flexible polyolefin textile membrane allows for the economical production of simple and sophisticated concrete members with increased structural efficiency and exceptional physical beauty. The permeable fabric membrane allows air bubbles and excess bleed water to move through the membrane wall, resulting in increased strength and durability of the concrete (typically +10% to +15%). The concept of the fabric membrane as a “skin” over the form skeleton can produce complicated details derived using simple techniques. Practical techniques of forming, bracing and placement, and a history of constructed work and practical field results will also be discussed. Field results are impressive. The fabric lends itself to a reduction in form supports, bracing, and simplified form tie methods. Casting results rival large-scale gang forms, steel column forms, and exceed the possibilities of other panel form systems, and are simpler to construct. Additionally, examples of rudimentary and simplified techniques applicable to developing countries will be demonstrated. Finally, methods will be presented for integrating fabric forming with composite wall technology to produce unique, thermally efficiently, and durable structures. Fabric formwork techniques can be designed to conform to precise structural requirements resulting in a significant reduction in materials used, such as funicular compression shells and vault structures, as well as variable section beams. This paper will illustrate the immense potential of fabric forming and demonstrate the possibilities for constructing high efficiency, engineered structures as well as beautiful and diverse architectural designs. Key Words: (Fabric Formwork, Architectural Formwork, Architectural Concrete Components) CAST-University of Manitoba Curvilinear Form –AD Bulge wall - Chile Double Wall Construction - AD Point Wall - AD

ArroDesign Research Paper Tabriz 82209

  • Upload
    isdnman

  • View
    218

  • Download
    0

Embed Size (px)

Citation preview

Page 1: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 1/10

 

Proceedings of the 1st  International Conference on Concrete Technology, Tabriz, Iran, 6-7 November 2009

Paper Code. No. XXXXXX

Page 1

Fabric Formwork for Architectural Concrete Structures

Eleanor D’Aponte, Alexander Lawton, Russ Miller Johnson

 Norwich University, ArroDesign, Engineering Ventures

[email protected], [email protected], [email protected] 

ABSTRACT

This paper provides a general overview of fabric forming and illustrates the immense potential of

the construction techniques. The concepts of tension forming and its application to the design and

construction of rectilinear and curvilinear wall forming, columns, slabs, beams, variable section

 precast beams, trusses panels and thin shell vaults will be discussed. The practical application of

fabric forming allows for more complex shapes and structural configurations than previously

 possible. Replacing rigid formwork panels and casting forms with a flexible polyolefin textile

membrane allows for the economical production of simple and sophisticated concrete members with

increased structural efficiency and exceptional physical beauty. The permeable fabric membrane

allows air bubbles and excess bleed water to move through the membrane wall, resulting in

increased strength and durability of the concrete (typically +10% to +15%). The concept of the

fabric membrane as a “skin” over the form skeleton can produce complicated details derived using

simple techniques. Practical techniques of forming, bracing and placement, and a history of

constructed work and practical field results will also be discussed. Field results are impressive.

The fabric lends itself to a reduction in form supports, bracing, and simplified form tie methods.

Casting results rival large-scale gang forms, steel column forms, and exceed the possibilities of

other panel form systems, and are simpler to construct. Additionally, examples of rudimentary and

simplified techniques applicable to developing countries will be demonstrated. Finally, methodswill be presented for integrating fabric forming with composite wall technology to produce unique,

thermally efficiently, and durable structures.

Fabric formwork techniques can be designed to conform to precise structural requirements resulting

in a significant reduction in materials used, such as funicular compression shells and vault

structures, as well as variable section beams. This paper will illustrate the immense potential of

fabric forming and demonstrate the possibilities for constructing high efficiency, engineered

structures as well as beautiful and diverse architectural designs.

Key Words: (Fabric Formwork, Architectural Formwork, Architectural Concrete Components)

CAST-University of Manitoba Curvilinear Form –AD Bulge wall - Chile Double Wall Construction - AD Point Wall - AD

Page 2: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 2/10

Page 2

The principle ideas behind fabric forming are not radically new. The closest analogy for how it

works is (perhaps) harnessing the wind for sailing. Conceptually, a flexible plane is put into tension

and restricted to create an optimized shape. In the case of fabric forming concrete structures, most

of the restricting devices are in tension. However, the transition from traditional rigid formwork to

fabric formwork in most cases is as simple as replacing the wood planes with fabric planes. The

fabric acts as a skin over a skeletal structure. In this sense, the practical transition to the use of

geotextile fabrics over plywood, lumber, or steel forms is remarkably simple. Practical techniques

of fabric forming, bracing and placement are similar to current concrete practice.

Geotextile fabrics have widespread acceptance for site backfill applications because it is strong,

lightweight and inexpensive. The fabric works because they allow water to pass through the fabric

 plane while restricting the passage of fine and coarse particulates. It is also interesting to note that

this acceptance is also due to the ease of installation. Geotextile fabric is strong, lightweight and

inexpensive. The fabric conforms to the shape of the underlying surface structure. The fabrics are

immensely strong when put into tension. These attributes are positive features that directly apply to

casting concrete. The filtered passage of water acts as a pressure relief, reducing the hydraulic

 pressures that are the most significant factors in form and tie design. The surface of the fabric

formed concrete is also more durable due to the release of excessive bleed water and the filtering of

air bubbles. [3] The other significant advantage is the ease of producing out of plane and curved

features in fabric. Simple techniques are used to create curvilinear structures. More exciting,however is that fabric allows for precise tailoring of the form to more closely approximate structural

diagrams. Concrete and reinforcement can be minimized by determining the stresses using finite

element analysis, and shaping the fabric form to meet optimized structural requirements.

Thin-Shell Concrete From Fabric MoldsThe Centre for Architectural Structures and Technology (C.A.S.T) at the University of Manitoba,

directed by Mark West, has for several years been developing casting techniques for primary

structural members such as beams and columns. Recently, the work has shifted to developing

methods of forming prefabricated thin-shell concrete structures. The fabrics are “allowed to deflect

into naturally occurring funicular geometries, producing molds for lightweight compression vaults

and stiff double curvature wall panels” [1] The reduction in material, according to West, can be as

high as 200-300 percent. He states that “funicular compression shell and vault structures can be

formed through the simple act of inverting the tension curves obtained by a loaded fabric sheet. In

this instance the symmetrical inversion of tension and compression geometries is perfectly matched

 by the symmetrically opposite resistance capacities of the materials involved, i.e. the fabric in

tension and the concrete in compression.” [1} These simply constructed structural components

formed with flat textile sheets are compatible with flat sheet reinforcing such as carbon fiber grids

and AR glass fiber cloth.

Fig. 1. Fig. 2. Fig. 3.

Page 3: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 3/10

Page 3

Flat sheet fabric mold for 3cm thick, 5m long, carbon reinforced shell 4cm thick, thin-shell,

a double curvature shell cast from the fabric mold shown in fig.3 fiber-reinforced wall panel

Fig. 4. Fig. 5. Fig. 6

Test of hanging, fuzzy-backed The fig. 4 funicular mold inverted, 1m x 3m funicular test mold

Fabric, coated with 5mm

GFRCshowing the plastic-coated release surface

West is also working on techniques for allowing the fabric form to buckle by stressing the flat

sheets of fabric.to create molds that resist buckling in the structural panels. He states that “

 buckling perpendicular to the principle lines of tension stress in a loaded fabric sheet will naturally

 provide buckling-resistant corrugations in a thin-shell compression shell cast from such a ‘buckled’

mold surface.”. The issue at this point is that it is difficult to model and analyze the shapes. (figs.

7, 8, 9).

Fig. 7. Fig. 8. Fig. 9.

Corrugations in shell vault Flat fabric sheet buckled by selective 2m model funicular shell

mold

along principle stress lines Pre-stressing, prepared for a 6m shell mold buckled by selective prestressing

Site Built Fabric Forms

In order to employ the durable, functional, and aesthetic qualities of a concrete structural system in

locations where site logistics might be prohibitive or experienced labor less locally available,

alternative lightweight fabric forming systems may prove viable. The overall economy on

formwork material and construction operations is consistent with the sustainable practices of using

less material and energy in construction.

When compared with traditional rigid wood or steel panel formwork, less material by weight is

required on site for casting, with the possibility of less ensuing waste. The fabric formwork

systems can take advantage of designing formwork tie and support systems for lessened pressures at

greater heights. In practice, the height of the fluid concrete can be tactilely monitored on the form

surface, which can allow for fewer stages of concrete construction on site.

Case Studies

Two recent residential projects in rural Vermont are presented to illustrate the sustainable

advantages of geotextile fabric as part of formwork system.. In the case of the residential projects,

the fabric formwork was used for walls, columns, and elevated slab soffits, resulting in savings in

Page 4: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 4/10

Page 4

formwork material weight of at least 35% compared to a standard wood panel system. This also

translates to reduced energy use for material transport, less waste, fewer pour operations, and the

use of so-called local labor that is not dependent on larger scale concrete operations experience.

Once stripped, the fabric has the potential to be reused for future formwork or on-site as subgrade

stabilization.

• 

The use of fabrics for formwork pre-dates the currently available Geotextiles [2]. Here,

geotextiles concrete formwork is defined as woven polyester or polypropylene fabric used

 primarily for earth stabilization measures that allow for the filtered passage of water. Otherfabrics are used and are available.

In both projects presented here, the aesthetic of pillowed concrete surfaces were originated by the

design builder, Sandy Lawton of ArroDesign in Waitsfield, Vermont. Because of the inherent

interrelationship between materials and methods in the achieving the finished product, many

specific aspects of the construction are craft based and consequently described in general terms.

Engineering Ventures, Inc. performed structural engineering services, which included the concrete

specification consulting. Professor Eleanor D’Aponte designed the residence.

Porch Structure

The porch structure is a multi-level, seasonal building on a steep hillside that is adjacent to a

residence. Concrete had been decided on as the exposed structure material for long-term durability,

as opposed to wood. The aesthetic to blend in with the landscape, trying to reduce construction

waste, and logistics dictated by the site led the design builder to a pursuing fabric formwork option.

From a basic structural engineering point-of-view, the three-story porch tower, or “Treehouse,” has

cast-in-place reinforced concrete shallow foundations, columns, walls, beams, and slabs; all capped

 by a timber-framed roof. The reinforcing is conventionally designed, using merely the minimum

thicknesses and covers with conventional tolerances. The increased durability of fabric formed

concrete surfaces was not formally taken in any design measures, however, it is believed thatunreduced normal cover distances and crack control reinforcing design will augment long-term

 performance of the surfaces under the wide temperature swings for the unconditioned building.

The project is situated downhill from the road approximately 150 feet. The road is unpaved and

steep, a common situation for many homes in Vermont. The home lies between the Treehouse and

the road, further limiting access. The slope varies, but is generally about 1.5 Horizontal to 1

Vertical in pitch.

The fabric formwork system is lighter in than conventional wood or steel forms for both the curved

and straight elements of the project. For the intended pillowed effect, battens of wood were

Fig. 10

Finished concrete surfaces on porch structure

Page 5: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 5/10

Page 5

required to hold the fabric and define the insets. This limited use of wood allowed for the use of

less material by approximately 35% from even just a solid batten formed walls. The battens were

easily reused at many locations because they were not the formed surface. The timber was a

“lower” grade and less manufactured than comparative wood panel formwork for an architectural

grade surface. As a side note, the use of form oil, whether petroleum or vegetable based, was

obviated.

Fig. 11. Fig. 12. Fig. 13.29’ single pour columns Column grouping and bridge Hybrid fabric formwork

A concrete mix with plasticizers and without flyash was used. The plasticizers minimized

desegregation during placement with the larger “drops”. However, the larger drops resulted from

fewer pours, which saved on overall transportation. Because flyash could possibly “block” the

openings in the fabric, it was not used.

The columns were formed with a proprietary polyethylene system, “Fast-Tube” by Fab-Form

Industries Ltd. It allowed for a single 29 foot form without joints, clear of the floors from the

foundation to the roof without any visible jointing, to be placed from scaffolding without a crane.

The single pours also allowed for fewer staging and pouring operations. The framing is attached to

the columns at “ledged” blockouts and post-applied dowels.Exposed elevated slabs soffits used fabric formwork. Although the shoring capacities are obviously

the same as for a rigid panel system, again less waste and material transport effort was achieved.

Fig. 14.

Elevated Slab Soffit

Page 6: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 6/10

Page 6

The savings in material use and transportation (delivery and removal conventional formwork) was

significant on this project. The lighter system also eliminated the requirement for a formwork

crane. Furthermore, independent lightweight scaffolding was used in lieu of heavier systems for the

wall pours at the upper levels.

Residence

The residence is a two-story structure with footprint of approximately 900 square feet. While thesecond floor and roof are timber and steel framed, cast-in-place reinforced fabric formed concrete

was used for walls, as well as elevated beams and slabs that support deck and porch roof features.

The home is on a steep unpaved narrow road off the highway, which enforces certain economies in

materials. Additionally, the cost of obtaining commonly experienced concrete labor on site for

 pouring was not favorable due to travel. Concrete was desired here for both its thermal and durable

qualities. It is anticipated that the fabric will be redeployed as the geotextile fabric on the driveway.

The 14 foot high walls were part of a “sandwich” system that enveloped a 3 inch panel of

 polyisocyanurate insulation. The faces of the interior and exterior wythes are “pillowed” and

exposed. The inner wythe is 5 inches minimum thickness at the battens, performs as the gravity and

lateral superstructure, and contains electrical conduit. The outer concrete is 4 inches due to

concrete placement and crack control concerns. A tie system that held the formwork and theinterstitial insulation was used.(fig 16) The system does not constitute a structurally composite

element between the wythes. Consulting on tilt-up and precast systems was provided before using

cast-in-place construction. A limiting factor was accessibility for transporting and erecting the

walls on site.

In consulting on the tie system capacity, a reduction in the wet concrete’s lateral pressure from the

loss of free water through the fabric was considered, but due to a wide variation in bleed rates at

various locations, was not used. However, because the set of the mix in the form can be monitored

directly by hand, the height of the wet concrete, the placement rate, could be controlled. Fewer ties

were used than for a rigid form surface of similar height. There was sufficient capacity to withstand

accidental form tie breakage at a couple of individual locations. The battens “spanned” to the

adjacent ties without obvious distortion and the formwork’s integrity was maintained.

Fig. 15. Fig. 16.

Wall Formwork before pour Insulated wall system

The walls were poured in one operation. Concrete sets and “wet” heights in the forms were tactilely

monitored on the fabric. Pour rates were adjusted to not exceed the maximum pressures. The

vibration was done by hand rubbing of the fabric. The process is found more capably applied by

Page 7: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 7/10

Page 7

laborers less familiar with concrete construction than mechanical vibration for achieving a quality

finish. This suggests that the method is adaptable to locales and labor that are not able to or

required to mobilize large-scale and frequent concrete constructions.

Fig. 17. Fig. 18.

Southwest Elevation Northwest Elevation

Fig. 17. Fig. 18.

Southwest Elevation Northwest Elevation

Fig. 19.

Screen wall cast with only top

And bottom plates pinned

After the residence was constructed, ArroDesign constructed

this screen wall with the intention to eliminate as many form

members as possible. It is an 8’x5’ curvilinear wall. The fabric was

 pinned to a footing and fastened to a ¾” plywood top plate supported

on either end by a 2x4 upright. The form was then cabled with 4

straps before it was poured. 3/8” nylon rods were threaded on site

and placed at 12” centers to tie the fabric together. Essentially, the

wall was constructed as an elongated column form from on sheet of

fabric. As noticed in the photo, the top plate deflected as concrete

filled the bottom of the form and stretched the fabric down,demonstrating the need to have a rigid top plate. This seems to be the

 principal requirement for a successful pour. Otherwise, the fabric can

act on its own if restricted with ties.

Page 8: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 8/10

Page 8

Rudimentary and Simplified techniques for Developing Countries

Two projects in the Dominican Republic demonstrate the simplicity of fabric forming techniques

that make the technology a viable construction option for developing countries. The first was

constructed in 2007, in Pomier, Dominican Republic as part of a design build workshop. The

 project was to create an entry to a proposed UNESCO World Heritage site. The techniques were

 principally developed to allow for the reinforcing to be used as form support, and then recycled intoother projects. In this case, reinforcement was driven into the ground (which is bed rock) with

 picket forms installed to hold the fabric in place. The fabric was obtained locally, and was not a

geotextile, but simply a plastic fabric made for a shade structure..

Fig. 20 Fig. 21

Driving reinforcement Tying reinforcement cageFig 22

Installin fabric

Fig 23

Complete Project - Entrance

Fig 24

Complete Project - Garden

Page 9: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 9/10

Page 9

The second project is a public plaza in the small village of El Rincon, Dominican Republic located

along the Samana Peninsula. The solid were clay, so the formwork frame was constructed of

wooden stakes driven into the ground. The stakes were generally lashed together and covered with

a geotextile fabric. Elevation changes and various forms could be easily obtained by stitching and

 pulling the fabric into place.

Fig 24

T in stakes for formwork

Fig 25

Installed fabric

Fig 26

Stripped formwork

Fig 27

Completed Plaza

Fig 28

Tying fabric for formwork Fig 29

Circular benches

Page 10: ArroDesign Research Paper Tabriz 82209

8/10/2019 ArroDesign Research Paper Tabriz 82209

http://slidepdf.com/reader/full/arrodesign-research-paper-tabriz-82209 10/10

Page 10

CONCLUSION

The properties of geotextile fabrics as a tensile membrane, when properly restricted lends itself to

the fluid nature of concrete. It is strong, lightweight and reusable. As shown, fabrics can be used in

 precasting operations as well as the simplest cast in place projects. However, the most exciting

aspect of the fabric is that is can be shaped so that the concrete can be cast in a way to work in pure

compression. In this way, there is less concrete and reinforcement used. The results can be durable

and efficient. Perhaps more importantly, the simplified techniques can be used to once again create beautiful masonry structures, at all scales, which express natural forces that are so important in the

creation of our built environment. The simplification of formwork due to the use of fabric returns

the making of a structure to the craftsmen. It also allows engineers and architects a freedom to

explore the shaping of concrete that has been elusive due to the complexities of the formwork.

REFERENCES

[1] West, Mark, "Fabric Formwork for Concrete Structures and Architecture,” unpublished abstract , pp. 2-3

[2] Malone, Philip, G., "Use of Permeable Formwork in Placing and Curing Concrete," High-Performance Materials and Systems

 Research Program, Technical Report SL-99-12, October 1999

[3] West, Mark, "Fabric Formed Concrete Members,” Concrete International, October 2003, pp. 55-60

[4] http://www.fab-form.com/projects/Fast-Tube/arro_design.html