Upload
isdnman
View
218
Download
0
Embed Size (px)
Citation preview
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
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.
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
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
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
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
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.
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
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
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