F00-P01 Phase 2:
Architectural Fabric Structures:
Exploration, Modeling, and Implementation
Alexander Messinger, Rob Fleming, Csilla Z. Wollner, Christopher Pastore
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Goal: To develop an understanding of the mechanical behavior of nonlinear anisotropic fabrics under tension and create a spatial vocabulary and grammar for architectural structures.
Abstract: In this year, work was developed to
characterize a new family of fabrics for potential application in architectural
structures and the development of a new type of fabric structure configuration
were realized.
The new fabrics have been tested for overall suitability and further environmental capabilities will be investigated in the coming year.
The new architectural module provides an interesting alternative to the traditional approach of rectangular parallelepipeds defining space.
Background: Currently in the industry, woven or warp
knitted coated fabrics are being used in membrane structures. The primary
requirements for these structures are tensile properties, shear modulus, tear
resistance, burst strength, and weatherability. The particular mechanical property requirements vary depending on
the actual application.
Most of the
fabrics in current use are either fiberglass or high tenacity polyester yarn
coated with PTFE (poly-tetraflouroethylene). The fabrics formed in this way have adequate performance, but are
limited in capability due to the relatively high areal density (from the PTFE
coating required for clean appearance over time) and the low shear modulus
(also from the PTFE coating).
ePTFE Fabrics: The fabrics under investigation in this section
of the report were designed to be lighter and have lower shear modulus to allow
more flexible design of architectural structures. We have chosen to explore knitted fabrics because they are
relatively unknown to the industry and thus require further investigation. Knit fabrics are also highly extensible
fabrics, with low shear modulus and markedly non-linear stress-strain
response.However, these fabrics are
very intriguing for architectural applications because they can be manipulated
to create shapes that cannot be reproduced by woven fabrics.
Industrial interactions during
this past year have allowed us to expand on our selection of available
materials. W.L. Gore has been quite
interested in our work and we have been collaborating with them on application
of a new fiber/yarn for the architectural industry called Tenara®
(ePTFE).
Tenara® is an ePTFE
fiber than can be formed into a yarn using slit film techniques.
Both regular and high tenacity versions are
available. Gore has experimented with
converting this to woven fabric and have had good response from the
community. Compared to other fabrics
used in the industry, it offers more textile aesthetics while maintaining the
characteristics and longevity of other coated fabrics.
They can be utilized in a wide variety of
uses including indoor and outdoor structures although up to this date Gore had
not knitted the fibers into fabric.
Upon receiving Tenara®
yarns, we weft-knitted fabric from them using a Master Sampler Electronic
Circular knitting machine. Two types of Tenara® yarn, a high
tenacity 400-denier (HT400d) yarn, and the regular 400-denier yarn were
converted to knitted fabrics at nominally 26 courses per inch and 40 wales per
inch, in a plain jersey configuration.
To provide a baseline
comparison, the 400 denier Tenara® yarn was also woven in a plain
weave configuration using an 8-harness loom, formed at nominally 43 ends per
inch and 43 picks per inch.
For mechanical characterization, the fabrics were subject
to ball burst experimentation. The results show that the knitted fabrics have a
significantly higher load to burst than the woven. This is not surprising, considering that in a knitted fabric the
higher degree of yarn mobility allows multiple yarns to respond to the load,
whereas in the woven fabric there is less reorganization to handle load
sharing. Also, there were some
inconsistent results in the woven fabrics due to slippage of the fabric in the
mount. The relatively low burst
strength of the high tenacity yarn formed into the knitted fabric requires
further investigation. It is possible
that the lower strain to failure of this yarn reduced the yarn mobility in the
fabric. Currently testing is addressing
tensile and shear properties and more will be learned about this behavior.
Preliminary testing to quantify
water and air permeability suggest that these fabrics have adequate properties
for small tent type structures.
Rapidly Deployable Structures: A dual use application that is investigated
in this work is rapidly deployable structures. The military interest in such structures is clear for rapid deployment
reduces time and cost and allows increase maneuverability to troops.
Rapid deployment has civic use as emergency
relief shelters. There are also a wide
range of traditional commercial applications for temporary housing, fairs,
meetings, etc. For the rapidly
deployable structure considered here, airbeams are used to provide the
structural skeleton over which the knitted ePTFE fabric will be deployed.
The weft knitted ePTFE fabric is
an excellent choice for self-deployable temporary structures. These structures not only require a medium
to lightweight architectural fabric but the fabric must satisfy certain
requirements: non-combustible, not affected by acid rain, unlimited flex life,
inert to UV radiation, undamaged by extreme temperature, and unlimited chemical
resistance. These are satisfied by the ePTFE fiber/yarn.
The first step to create a scale
model self-deployable structure was to construct a small-scale skeletal model
representing the desired shape and configuration. The base or skeleton was constructed of inflatable rubber
bladders with T-joints as the supports for the junctions.
After assembling the bladders together for
the desired shape, inflation was successful although after several time the
tubes expanded severely due to plastic deformation. To avoid this and put a limit on the expansion of the tube, the
bladders were braided over with Spectra and re-sealed. The over braiding allows a significantly
higher internal air pressure, while controlling the overall distortion of the
beam. For this airbeam, a highly
oriented polyethylene fiber (Spectra® 1000) was used.
After the skeleton for the scale
model was finished, the knitted fabric is attached to the structure. Due to relays in machinery and materials,
the fabric has not been attached yet.
Since the knitting machines diameter is 10 inches it will be necessary
to make a pattern and sew the fabric to appropriate specifications. Tenara® sewing thread will be used to ensure
a homogeneous and long-lasting construction.
Novel Architectural Structures: A three-dimensional
fabric module was developed based on the assumption that the module could be
used in combination to assemble larger scale complex structures. As an analogy
one can look at a brick building where the modular brick unit was used to
generate a complex architectural environment. One of the basic requirements for
the 3-d module was to create a 3-d complex curvilinear surface that
approximates a minimal surface structure (monkey saddle). A computer simulation
was produced to model various combinations of the module and also to explore
the visual effect of different fabrics. This is called phase one of the
project. Phase two (to be completed soon) is to create walk-throughs, quick
time VR’s and interactive models to further explore issues of perceptual
qualities of space as defined by fabric structures.
Process: The
module itself is derived from connecting the opposite boundaries of a cube (see
figure 1a). A surface was created by extending lines from the midpoints on the
cube in order to generate a hyperbolic paraboloid structure. This allowed the
ability to construct a complex curvilinear surface using straight lines that
define the boundaries of the curved surface while using the midpoint lines as
the major defining elements (figures 1b, 1c). The module is proposed to be 8’ x
8’ x 8’ to be able to use standard lumber for future construction.
Figure 1a: wire frame of
module Figure 1b, 1c: Rendered views of surface of module
Four prototypical 3-D environments were designed that
explored the potential of the basic 3-d module (see figure 2). For this phase,
we focused on exploring the potential of a smaller unit composed 4 modules
because this was the one most likely to be built in future phases of the
project (see figure 3). The minimum enclosed environment of this prototype will
be approximately 16’ x 16’ x 16’.
Figure 2: Four prototypical
3-d environments
Figure 3: Selected prototype
We then assigned different properties to each segment of
the module in order to be able to evaluate various types of fabrics (see figure
4). This computer model will help us, and others to understand the impact of
various fabrics on the environment by manipulating the use of light, color,
texture, and transparency values (see figure 5,6,7, 8)
Figure 4: selected prototype with assigned fabrics with different
properties
Figure 5: Top view of proposed environment w/ artificial lighting
Figure 6: Side view of proposed environment w/ artificial lighting
Figure 7: Front view of proposed environment w/ artificial lighting
Figure 8: Interior view of proposed environment w/ artificial lighting
The above computer model will help us to construct a full
scale prototype that will evaluate various fabrics in the real environment
dealing with elements such as wind, snow, rain, solar radiation, human
interaction/perception. The impact of texture, color, shading qualities will
also be evaluated and documented. In the future fabric manufacturers will be
invited to experience the environment, leading towards test of specific fabrics
that possess potential for exterior application.
Selected prototype with one fabric
Web
Site:
http://fibers.philau.edu/ntc/f00p01/