Master of Architecture Thesis Book - Spring 2014

RIGID FABRIC ANDREW RASTETTER | M.ARCH THESIS SPRING 2014

Design Project Study Models with Formwork

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CONTENTS 4

THESIS STATEMENT

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INTRODUCTION + AESTHETIC CONTEXT

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THESIS PROJECT ABSTRACT

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RESEARCH + BACKGROUND

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INITIAL MATERIAL INVESTIGATIONS

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INVENTORY OF FILLED-FORM TECHNIQUES

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MODEL STUDIES OF FABRIC-FORMED SHELLS

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DIGITAL SIMULATION OF FABRIC-FORMED SHELLS

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DESIGN PROJECT PROPOSAL

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DRAWINGS, RENDERINGS, AND MODELS

78 CONCLUSIONS 80 RESOURCES 82

IMAGE CREDITS

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THESIS STATEMENT Fabric formwork can be used to cast concrete into structural shapes that reflect the forces they resist. In doing so, fabric formwork increases material efficiency and produces forms that are beautiful, durable, and structurally honest. In a building, this can create an enlightening and pleasurable experience for its occupants.

INTRODUCTION + AESTHETIC CONTEXT: Symbiotic Relationship of Fabric and Concrete Throughout my time in graduate school, I have pursued dual interests in architecture and structural engineering. One of the greatest challenges of this process has been finding opportunities to explore these interests simultaneously while working on a single project.

Although the two disciplines are inherently linked, their associated pedagogies are disparate, and this has made it difficult for me to develop an integrated approach to design. This thesis is an attempt to combine these parallel interests and to develop an integrated approach. It is a marriage of architectural design and structural engineering through the symbiosis of two materials: concrete and fabric.

Concrete. Concrete is a familiar material that is all around us. Many people think of concrete buildings as boxy, rugged, dirty and cold. These negative impressions are the result of the typical appearance of the material, which is usually cast into plywood and lumber molds that are difficult to form into irregular shapes. The resulting drab and monolithic surfaces are durable and require little maintenance so they are rarely painted or cleaned. This predominant reality of inexpensive concrete construction along with the prohibitive costs of irregular formwork have prevented the construction industry from embracing the most amazing potential of concrete as a fluid material that can be cast into almost any shape. This potential has both aesthetic and structural implications.

For example, a typical concrete beam has a rectangular cross-section that does not vary along the length of the member. Usually it is larger and boxier than a beam constructed from steel, and its appearance rarely adds architectural interest. Given the nature of the material, there is no reason that it has to be this shape. The minimum cross-section of a beam is determined by its internal forces, which vary along the length of the span. An optimized beam that directly represents the forces it resists takes its shape in response to the changing distribution of forces. The resulting curved form can be beautiful and honest. Taking this concept one step further, the architectural design and shape of a concrete building’s structure can represent the structural forces at play, reducing waste and creating inherently beautiful forms.

Fabric. Fabric is the opposite of concrete in many ways. It is flexible; it provides warmth and protection; and it traditionally is used as skin rather than support. The flexibility of fabric allows it to be effortlessly shaped and produces a naturally organic surface quality. This flexibility, however, also can make it difficult to use fabric in a permanent way. In order to hold its shape a piece of fabric must be supported by a more rigid object: a shirt is supported by a 4

person’s torso; a fabric canopy is supported by frames or cables. Fabric also has a tendency to degrade rapidly over time. It is typically woven from small fibers that are vulnerable to degradation from environmental factors such as temperature, sunlight, rain, and wind.

Material Symbiosis. In some ways fabric and concrete are very similar. They both have infinite textural possibilities and they both can be draped or molded into almost any shape.

These similarities allow the two materials to be used together in a mutually beneficial way that mitigates many of their individual challenges. Fabric formwork releases concrete from the practical constraints of conventional wood and steel forms. This makes it easier to construct organic and curvilinear geometries that can in turn be used to optimize the shape of structural elements. As discussed in the “Research + Background” section, formwork made out of permeable fabric can increase the surface hardness and long-term durability of the concrete.

Concrete cast against fabric will assume the texture of the fabric that is used to construct the formwork. Because the textural possibilities of fabric are nearly infinite, this can soften or add interest to the surface appearance of the concrete.

THESIS PROJECT ABSTRACT Concrete formwork is traditionally constructed from rigid wood and steel molds that use large quantities of materials and are expensive to fabricate. Because it is difficult to construct curved formwork using these materials, most concrete structures have orthogonal shapes and simple geometry based on straight lines. Shapes of concrete elements also have been limited by traditional structural engineering methods, which typically have involved calculations that are difficult or impossible to adapt to irregular curved forms. Recent advancements in computer analysis, synthetic fabrics, and concrete technology now make it more feasible to use fabric formwork in everyday construction. Unlike traditional formwork, fabric is highly flexible and can be molded into almost any shape. This makes it possible to optimize structural geometry and create forms that are both beautiful and efficient. If fabric forms are permeable, they can also enhance the surface quality and durability of concrete by wicking excess moisture and increasing the surface concentration of cement.

This thesis project explores the architectural posibilities of fabric formed concrete. The designwork can be divided into two categories: technical investigations and design implementation.

The technical investigations are used to better understand both the potentials and limitations of fabric formwork techniques. They begin with an inventory of construction methods, which is developed in parallel with a set of physical studies. They culminate in a digital exploration that develops a working method for the subsequent design project.

In the design project, the existing structure of the 16th Street Station in West Oakland is used as scaffolding for a steel cable grid that is prestressed and covered with fabric formwork.

The formwork is sprayed with concrete to construct a thin-shell canopy that shelters a new semi-enclosed community center. The program includes a farmer’s market, a concert venue, an indoor event space, permanent food vendors, a beer garden, and parking for food trucks.

Over time, much of the existing structure is disassembled, leaving the self-supporting concrete canopy as an index of the original architecture.

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RESEARCH + BACKGROUND HISTORY OF FABRIC FORMED CONCRETE Although fabric formwork was not widely used until after the Industrial Revolution, early examples have been found in Roman ruins. In his Ten Books on Architecture, the Roman architect and engineer Vitruvius cites several methods of casting concrete using woven reeds as formwork.1 Roman structures showing evidence of this type of formwork have been uncovered in Algeria and in Rome. These examples are mainly underground structures where the technique probably was chosen because there were no requirements for surface finish, and because it would have been difficult to use conventional formwork materials. 2 British and American patents from the late 19th century document the first modern use of fabric formwork.3 In the most common application, inexpensive fabric was stretched over a temporary steel structure and then covered in concrete to form ribbed parabolic vaults with spans of up to 15m.4 The construction of these vaults was inexpensive and could be completed by just a few unskilled laborers. Because of its economy, this technique was widely used during World War II. By the early 20th century, hydraulic engineers also were using concrete-filled burlap mattresses for river and coastal revetments.5 In all of these applications the use of fabric formwork was purely utilitarian.

During the second half of the 20th century there was a shift towards applications that explored the architectural and aesthetic possibilities of fabric formwork. This shift is evident in the work of Miguel Fisac, who used fabric to produce patterns and shapes that would not be possible with conventional formwork [see figures 1-2]. Although Fisac’s projects are visually interesting, they ignore the more functional advantages of fabric formwork. The introduction of durable and inexpensive synthetic fabrics in the mid 1980s has significantly changed the evolution of the field. Research over the last 25 years has been focused on a more integrated approach that seeks to combine the formal, functional, ecological, and economic advantages of fabric-formed concrete. Examples of this more comprehensive approach are discussed in the “Applications and New Directions” section of this report.

Figure 1: Casa La Moraleja by Miguel Fisac 1 Veenendaal, D., M. West, P. Block. (2011). p. 164 2 Veenendaal, D., M. West, P. Block. (2011). p. 164 3 West, Mark. (2010).

4 Veenendaal, D., M. West, P. Block. (2011). p. 165 5 Veenendaal, D., M. West, P. Block. (2011). p. 168

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Figure 2: Centro de Rehabilitacion by Miguel Fisac

ADVANTAGES OF FABRIC FORMWORK Surface Texture, Quality and Strength. When concrete is cast in a permeable membrane, excess mix water and air bubbles are free to bleed out, and this results in a cement-rich paste at the surface of the form. The concentration of cement creates a high quality finish that is more aesthetically pleasing than concrete cast in conventional watertight formwork.6 It also eliminates the need for surface treatments such as sand blasting, acid etching, and veneers.

Additionally, the texture and shape of the fabric can be used to give the concrete a “softer” and more organic appearance.

The bleeding of excess water through porous formwork can also have a positive effect on the strength, hardness, and durability of concrete by improving its compaction and water cement (w/c) ratio.7 Tests on fabric-formed concrete have shown a reduction in carbonation depth, an increased resistance to chloride ingress, and “up to a 20% improvement in surface hardness compared to concrete cast against conventional formwork.”8 The process can be enhanced by forcing water through the formwork with either pumping pressure or the self-weight of the concrete.9 Material Cost and Labor Savings. The use of fabric formwork can result in significant material and labor savings, especially in countries where wood is scarce and formwork must be imported. Fabric formwork is 100 to 300 times lighter than conventional wooden forms and it is approximately 1/10th the cost of plywood formwork per unit area.10 Additionally, there is a significant amount of labor associated with the assembly and stripping of wooden formwork.

Fabric formwork can reduce these labor costs by as much as 27%.11 Because the formwork is lightweight and flexible, it can be prefabricated off site and then shipped at a relatively low cost.

Geometric Flexibility. Fabric formwork can be produced in almost any shape and thus provides an architectural and structural flexibility that cannot be achieved using conventional techniques. Fabric forming makes it easy to construct variable section members that follow the load path and distribution of their internal forces. This strategy allows for a significant reduction in the volume and deadweight of a structural member. Compared to an equivalent-strength prismatic member, the volume of a fabric-formed beam can be reduced by as much as 40%.12 Sustainability. Fabric formwork can significantly reduce the embodied energy and carbon generation that is associated with new structures. It can be used to form efficient structural members that require less cement than traditional shapes and generate less waste during construction. Fabric formwork is easy to remove and can be used many times. Additionally, the porosity of the formwork can bleed excess water and increase the durability of the concrete.

This reduces a structure’s maintenance and repair requirements and extends its lifespan.

6 Abdelgader, H., M. West, J. Gorski. (2008). p. 95 7 West, Mark. (2010).

8 Orr, J., A. Derby, T. Ibell, M. Evernden, M. Otlet. (2011). p. 98 9 Abdelgader, H., M. West, J. Gorski. (2008). p. 94 10 West, Mark. (2010).

11 Abdelgader, H., M. West, J. Gorski. (2008). p. 95 12 Orr, J., A. Derby, T. Ibell, M. Evernden, M. Otlet. (2011). p. 98

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CHALLENGES OF FABRIC FORMWORK Moisture Retention During Curing. Though permeable formwork offers advantages in terms of finish quality, durability, and strength, it does not retain moisture well during curing, which can in fact reduce the ultimate strength of the concrete. In order to counteract this affect, permeable fabric molds should be wrapped in a waterproof membrane during the curing phase of the concrete.13 An alternative option is to use impermeable fabric molds, but this does not offer the advantages of permeable formwork.

More Complex to Design and Engineer. From the standpoint of both the architect and the engineer, it is more difficult to design the complex curved shapes that are implicit in fabric-formed concrete. It is also difficult to design the formwork itself since the fabric can deform significantly during casting. Although normal structural engineering procedures can be adapted to some types of elements, including columns and walls,14 standard rules of thumb cannot be applied to more complex variable section members.

Lack of Construction Contractor Knowledge. Few contractors have experience working with fabric formwork. This lack of knowledge and experience discourages widespread use of the technology because contractors tend to favor techniques they are more familiar with.

Some applications, such as columns, footings, and walls are better suited to conventional construction skills. Other applications, such as beams and shells, require a familiarity with how fabric formwork deforms under loading and how the fabric sheets can be prestressed to create specific shapes and cross sections.15 Concrete cast in fabric formwork is also vulnerable to impact damage during its early stages of curing. Contractors must take additional measures to protect fabric forms from damage and this can affect the staging of a construction project.

Difficult to Reinforce. It is more difficult to reinforce concrete structures that have non-prismatic geometry. Conventional rebar reinforcement can be used but additional labor is required to bend it to conform to complex shapes. Recent research has investigated alternatives such as textile reinforcement, passive steel tendons, fiber reinforcement, and the use of fabric formwork itself as external reinforcement.16 MECHANICAL PROPERTIES OF FABRIC-FORMED CONCRETE 1. Compressive Strength Fabric formwork has an influence on the compressive strength of concrete because it is permeable and can allow water, air bubbles, cement, and fine aggregate to escape during casting and the early stages of curing. Several studies have investigated the relationship between the permeability of fabric formwork and compressive strength of the resulting concrete. One of the most comprehensive of these studies is outlined in the following sections. It was completed in 2001 by Mahdi Ghaib and Jaroslaw G贸rski at the Technical University of Gdansk in Poland.17 Testing Parameters. Ghaib and G贸rski chose four types of fabric to use in their tests. The pore size of these fabrics ranged from 0.15 x 10-3 m to 0.68 x 10-3 m. Each fabric was used to construct molds that were then filled with 12 different concrete mixes. The mixes varied in 13 West, Mark. (2010).

14 West, Mark. (2010).

15 West, Mark. (2010).

16 Veenendaal, D., M. West, P. Block. (2011). p. 172 17 All information in this section taken from: Ghaib, M., J. G贸rski. (2001). pp. 1459-1465

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their composition of cement, sand, gravel, and water and also in their w/c ratios. Two types of tests were conducted: permeability tests that measured the quantity of drained water and lost cement; and strength tests that measured the compressive strength of the hardened concrete samples. Permeability tests were conducted by filling an open-ended steel cylinder with concrete, covering one end with a fabric sample, and then applying pressure to the other end. At eight minute intervals the discharged liquid and solids were collected, separated, and measured. Compressive tests were conducted by cutting 10x10x10cm cubes out of larger specimens. The strength of these specimens was compared to control samples that were cast in similarly sized steel molds. All of the samples were mixed, compacted, and cured under the same conditions. A total of 232 samples were tested.

Results of Permeability Tests. The results of the permeability tests are summarized in figure 3. The tests showed that the majority of discharge occurred within the first five minutes of testing and that the rate of discharge decreased over time. The overall quantity of discharge increased with larger openings in the fabric and the quantity of lost cement was governed by the initial water cement ratio in every fabric except for the one with the smallest openings.

The tests resulted in noticeable changes to the w/c ratio in all mixes and fabric types. The w/c ratio decreased by 10 to 20% in the three densest fabrics and increased by 2% in the most porous fabric. The increase can be attributed to the large openings in the fabric, which make it easy for cement to escape along with water.

Figure 3: results from permeability tests for four different fabric types Results of Compressive Tests. The results of the compressive test are summarized in figure 4. The tests demonstrated a faster rate of strength development in samples that were cast using fabric formwork. This probably can be attributed to the drainage of excess water through the fabric. In general, the compressive strength was highest in samples that were cast in fabric with a moderate pore size. The strength decreased in fabric with very small or very large pores. When the pore size was too small, the fabric clogged easily, and it was difficult for free water to drain. When the pore size was too large, the mixture lost cement and sand as well as water, and there was no improvement to the w/c ratio. Almost all of the samples that were cast in fabric formwork showed a higher compressive strength at 28 days than samples of the same concrete that were cast in steel molds. The exception was concrete that was cast in molds that were made from the most porous fabric. Based on these results the study concludes that “it is not right to generalize the fact that concrete cast in fabric form is characterized by a higher compressive strength than the concrete cast in steel molds.�18 The authors used the results of the compressive tests to derive a formula that relates the compressive

18 Ghaib, M., J. GĂłrski. (2001). pp. 1462

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strength (ƒ’c) of concrete to its w/c ratio, the microscopic opening size (mos) of the fabric formwork in meters, and the cement quantity (q) in kg/m3: ƒ’c = 15.34 – 33.65(w/c)3 + 140.92q3 + 275.2(mos) – 625.4(mos)2 – 367.72(mos)3 Although there is some correlation between compressive strength and the use of fabric formwork, the results of this study demonstrate the complexity of this relationship. It is important to note that the concrete samples (even as they were cast) were relatively small and are not necessarily analogous with larger structural elements. Strength increases resulted from improvements to the w/c ratio that would not be as significant if the volume to surface area ratio were increased.

Figure 4: affect of fabric type on development of compressive strength 2. Durability The permeability of fabric formwork presents significant advantages in terms of durability. In traditional formwork, air and water gets trapped against the surface of impermeable molds and this causes pitting and other defects. These defects result in a more porous outer layer, which can adversely affect durability characteristics. In Japan it is common to wrap wood or steel forms with a layer of fabric that can wick away the excess moisture. Many studies have investigated the affect of fabric form liners but few have tested specimens that were cast with fabric formwork alone. The advantage of fabric formwork is that it wicks moistures without the need for an additional system. Recent work by John Orr at the University of Bath in England has investigated the effect of fabric forms on carbonation depth, resistance to chloride ingress, and surface sorptivity. The results, which are summarized in the following sections, confirm the durability benefits of fabric formwork.19 Carbonation Test. Carbonation test samples were prepared in a 10cm cube where one face was cast against fabric and the opposite face was cast against steel. After a sufficient curing period the sample was removed and placed in a chamber with 4% carbon dioxide to accelerate the affect of carbonation on the sample. Phenolphthalein was used to monitor the reaction between carbon dioxide in the air and the alkali in the cement. When no carbonation has occurred, the pH is lower and the phenolphthalein will show up as a light shade of pink.

In areas that are affected by carbonation, the acidity is high, and the phenolphthalein turns colorless. The test monitored the depth of carbonation at seven-day increments for 180 days 19 All information in this section taken from: Orr, J., A. Derby, T. Ibell, and M. Evernden. (2012).

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(the accelerated equivalent of approximately 25 years). The results showed a 51% decrease in the carbonation depth of concrete that was cast against fabric formwork.

Figure 5: results of carbonation test - purple areas have not been affected by carbonation Chloride Ingress Test. In the chloride ingress test, a 10x20cm cylinder was cast with fabric covering one end and steel covering the other. After curing the cylinder was cut in half and the exposed faces were submerged in a saltwater solution at 6-7 times the concentration of the Atlantic Ocean. The samples were tested at 53 and 90 days by incrementally removing material from the exposed faces and measuring the chloride concentration at various depths.

The data was then used to establish a coefficient that indicated the rate at which chloride diffused through the material. The results showed a 49.9% reduction in the sample that was cast against fabric formwork.

Surface Permeability. In order to better explain the relationship between formwork type and durability, a third test was undertaken to compare the sorptivity of samples cast in fabric and steel formwork. The two samples were suspended in water and then weighed at various time increments to measure the amount of water that had been absorbed into the pores of the concrete. In the first two hours of the test the steel-cast sample absorbed 40% more water water than the fabric-cast sample. Over a longer time period both samples absorbed water at roughly the same rate. The pattern suggests that the steel sample had larger surface pores while both samples had similar distributions at their centers. This was confirmed by a second test where the top inch of material was removed and there was no difference between the sorptivity of the two samples. The study also evaluated the surfaces of the two samples under a scanning electron microscope (SEM). The sample that was cast with fabric formwork had 14% more calcium at its surface and this indicated a higher surface concentration of cement.

APPLICATIONS AND NEW DIRECTIONS Because of its economy and versatility, fabric formwork has been widely used since the 1960s to form concre for applications such as erosion control, pond liners, pile jackets, shore protection, and bridge repair. Many of these applications use simple bag forms that can be cast above or below water, and which can be placed in difficult-to-reach locations. While these uses demonstrate some of the functional advantages of fabric-formed concrete, they do not explore its potential to create structurally efficient and architecturally interesting geometry.

Recent advances in synthetic fabrics, concrete pumping, and computer technology (for both analysis and fabrication) have prompted more sophisticated explorations of fabric formwork over the last fifteen years. Because the formwork is lightweight and easy to transport, the use of fabric-formed concrete is especially promising in developing parts of the world where it is difficult to find materials for conventional forms. The following sections outline some of the techniques that have been developed to form a variety of structural elements for buildings.

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Figure 6: examples of traditional fabric formwork applications - from left to right: pile jacketing, erosion control surface, bridge pier repair 1. Columns Columns are one of the simplest architectural applications for fabric formwork. A column form can be constructed from a single sheet of fabric that is wrapped into a tube and tied together along its longitudinal seam. It is often constructed as a double layer system so that excess bulging does not occur along the seam. The bottom of the fabric tube is attached to a footing or floor slab while the top is stretched vertically to a scaffolding structure above.

The formwork is pre-tensioned by hand in order to laterally stabilize it during casting.

Simple fabric-formed columns have regular cross sections that can be analyzed and reinforced with standard methods and details.

Figure 7: examples of columns cast with fabric formwork

Figure 8: examples of columns cast with “bulge wall� system 12

“Bulge Wall” Columns. Mark West, a professor at the University of Manitoba, has developed a more sophisticated column system that is constructed with a combination of standard plywood wall formwork and a fabric liner. 20 The technique can be used to create stand-alone columns or columns that are integrated with a wall system. Cut outs in the plywood formwork set the longitudinal profile of the column. The fabric liners are allowed to deflect through these openings, producing beautiful and structurally efficient variable cross-section forms.

2. WALLS AND PANELS Walls and panels are easy to construct using fabric formwork. They can be shaped into efficient and attractive geometries and the high quality of the surface finish allows the concrete to be left exposed without additional treatment. If walls are arranged vertically then traditional reinforcement can be used with little modification to design and construction procedures. Several methods for constructing fabric-formed walls have been developed by Kenzo Unno, a Japanese architect.21 Frame Method. In this method a double-layer stud wall is constructed from vertical pieces of dimensioned lumber or steel pipe and then the inside faces are wrapped with a geotextile fabric. The frames are held in place with external bracing or standard form ties. Concrete is poured between the two layers and allowed to set. Once removed, the frames can be reused for other wall sections. This technique produces an undulating wall pattern with vertical bands that correspond to the location of formwork supports. An example of a frame wall is shown in figure 9.

“Quilt-Point” Method. This method is less materially intensive and only requires a frame around the outside of the wall. Fabric is wrapped across the frame like canvas on a painting and then the two layers of fabric are held together with closely spaced form ties that control fabric deflection during casting. The form ties are provided with large washers to distribute the stresses imposed on the fabric. In some applications the wall’s vertical reinforcement can be used to support frames at the top and bottom, further reducing the amount of construction material. This technique produces a quilted surface with a soft appearance that is not usually associated with concrete structures. An example of a “quilt-point” wall is shown in figure 10.

Figure 9: example of wall cast with frame method

Figure 10: example of wall cast with “quilt-point” method

20 All information in this section taken from: West, M., C. Weibe, A. Hurdal, J. Zeng. “Bulge Wall Construction.” (2007).

21 All information in this section taken from: West, Mark. “Kenzo Unno Fabric-Formed Walls.” (accessed 11/2012).

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3. BEAMS AND TRUSSES Trusses and beams are some of the most promising applications for fabric formwork. Traditional concrete beams have rectangular cross sections and prismatic geometry, with constant moment and shear capacities at every point along their length. Because the actual forces vary greatly, much of a member’s capacity is underutilized. If the cross-sectional shape of a beam is adjusted to follow the force distribution in the member then the overall amount of material can be reduced by as much as 40%. An even greater savings can be achieved in trusses, which are not traditionally used in concrete construction because of their geometric complexity.

Variable section beams and concrete trusses can be constructed easily using fabric formwork.

The following sections outline techniques that have been developed at the University of Bath and the University of Manitoba.

Beams. The construction of variable cross-section beams is relatively simple. A plywood frame is constructed to hold the edges of the fabric formwork and to define the end cross sections of the beam.22 A “keel” mold is placed along the length of the beam and is shaped so that it follows the longitudinal variation of the beam’s depth. A piece of fabric is then secured to the rigid formwork and draped over the “keel” mold to create a trough for the concrete.

Flexural and shear reinforcement is added along the length of the beam and then concrete is poured into the open top of the mold. If the design calls for a T-beam then an additional layer of slab formwork can be added on top.

Figure 11: diagrams showing beam construction using fabric and keel mold Trusses. The construction of fabric molds for concrete trusses is more complex than for variable cross section beams and as a result this technique is most useful for precast construction. If a suitable fabric is used then the molds can be removed and reused after the concrete hardens. A truss mold is composed of three rigid portions that are built from plywood.23 The plywood components of the mold are milled from a computer model and then screwed together and draped with fabric formwork. Two symmetrical side pieces with “block-out clamps” (which define the voids in the truss) sandwich a center piece that is shaped so that its top edge follows the longitudinal shape of the truss’s bottom flange. When the truss is ready to be cast the three sections are clamped together, reinforcement is installed, and then the mold is filled with self-compacting concrete. If the shape of a truss is properly designed, then it can be built without the use of shear reinforcing stirrups. According to Mark West, “This is possible because the simplified force paths in bending moment-shaped beams eliminate or reduce shear stresses (diagonal tension) in the web.”24 West has performed strength tests on trusses that only have flexural reinforcement and these tests have shown no signs of shear failure.

22 All information in this section taken from: Orr, J., A. Derby, T. Ibell, M. Evernden, M. Otlet. (2011).

23 All information in this section taken from: West, Mark. (2006).

24 West, Mark. (2006). p. 52

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Figure 12: examples of trusses cast with fabric formwork 4. THIN SHELLS Curved concrete shells can be designed with thin and structurally efficient geometry that significantly reduces material use. These shapes, however, are difficult and expensive to construct using traditional formwork and reinforcement; therefore they have not been widely used in architecture. Additionally, steel reinforcement must be covered with a layer of concrete that is sufficiently thick to prevent damage from corrosion. The required minimum cover is often much thicker than the depth necessary for structural stability, and this reduces the potential for material savings. Fabric formwork presents an alternative construction method that can be easily molded to conform to complex geometry. Recent studies also have explored the possibility of using fabric reinforcement that is not vulnerable to corrosion and would not have the same cover requirements as steel. A recent study by Niki Cauberg, et al. investigates the intersection between fabric formwork and fabric reinforcement.25 Construction Technique. Two doubly curved shells were constructed, one with steel reinforcement, and one with fabric reinforcement. The formwork for each shell consisted of three fabric pieces that were attached to each other and then suspended between two vertical metal arches. The fabric forms were prestressed to compensate for deflections under the self-weight of the concrete. Concrete was spray applied and the thickness of each shell was determined through finite element analysis and code requirements for cover. The steel shell

Figure 13: fabric formwork for concrete shell

Figure 14: layer of fabric reinforcement

25 All information in this section taken from: Cauberg, N., T. Tysmans, S. Adriaenssens, J. Wastiels, M. Mollaert, and B. Belkassem. (2012).

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was reinforced with a grid of 6 mm rebar that was bent to conform to the curved geometry.

The total thickness of this shell was 50 mm, a value that was determined through European code requirements for cover. The fabric shell was reinforced with four textile layers (3% by volume) that were separated with 7mm of shotcrete. The total thickness of this shell was 36mm, a minimum structural thickness that was determined with finite element software.

Test Results. The two shells were tested under vertical loading and their displacements Figure 15: loading device setup for compression were measured throughout the tests. The tests steel shell failed at a load of 70 kN and the fabric shell failed at a load of 62 kN. The displacements at failure were almost identical, at 12 mm and 11 mm respectively. The most significant difference between the two tests was a strong improvement in the ductility of the fabric-reinforced shell. This shell continued to support load after it failed, whereas the steel-reinforced shell lost all of its load-bearing capacity. These tests demonstrate the potential for the combined use of fabric formwork and fabric reinforcement. Although the load bearing capacity of the two shells was similar, the fabric-reinforced shell was more ductile and used less concrete. The fabric formwork was easy to construct and offered shape flexibility.

Figure 16: compression test results for steel reinforced (SRC) and fabric reinforced (TRC) shells

CONCLUSIONS OF PRELIMINARY RESEARCH Fabric formwork provides many advantages that have been explored in academic research over the last few decades. It can be used to construct complex, variable cross section members that require less cement and generate less waste during construction. Permeable forms also have been shown to have a positive effect on the durability of concrete – this decreases long-term maintenance requirements and extends the lifespan of a structure. Together, these advantages can reduce the embodied energy of a project and mitigate some of the negative environmental effects that are associated with Portland cement and concrete construction.

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Though geometric flexibility is one of the most important advantages of fabric formwork, it also presents one of the greatest challenges. It is difficult to reinforce irregularly shaped concrete members, and this can offset some of the benefits of the technique. Recent studies have investigated the possibility of replacing conventional steel rebar with high strength textile reinforcement, a promising approach because the reinforcement has the same flexibility as the formwork. However, structural analysis is more challenging, and the reinforcement must be detailed so that it does not inhibit the concrete pour. An alternative option is to use the fabric formwork itself as reinforcement. This also presents challenges including protection from vandalism and fire damage, and making sure that an adequate bond is maintained between the concrete and reinforcement for the lifespan of a structure.

Fabric formwork will not be widely adopted by the construction industry until further advances have been made in the field. Design codes must be updated with provisions that encourage the use of irregular geometry. Additionally, designers must be equipped with software tools that can analyze complex concrete forms, that can anticipate fabric deflections during casting and curing, and that can generate templates for the manufacture of fabric formwork.

Research on these and other topics is being conducted at universities around the world so that fabric formwork technology should continue to improve in the coming years.

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INITIAL MATERIAL INVESTIGATIONS Fabric formwork can roughly be divided into two categories: (1) Filled forms and (2) Covered Forms. Filled forms include columns, walls, beams, and trusses. Covered forms are generally limited to shells. My initial investigations were organized around these two categories and are covered in the sections titled “Inventory of Filled Form Techniques,” “Shell Model Studies,” and “Digital Simulation of Fabric-Formed Shells.”

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Figure 17: Examples of Concrete Structures Cast with “Filled Form” Techniques

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Figure 18: Examples of Concrete Structures Cast with “Covered Form” Techniques

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INVENTORY OF FILLED FORM TECHNIQUES: Description of Method The first investigation was an inventory of filled form precedents that have already been developed and tested. Many of these techniques were discussed on pages 12-14 of this thesis book. The purpose of this investigation was to gain a better understanding of how fabric formwork can be applied, how different types of forms are constructed, and to compare each technique with conventional methods for building the same structural element. All of the fabric forming techniques and their conventional counterparts are compared in the matrix on page 27. They were each evaluated in terms of cost and, on a scale from 0 (best) to 3 (worst), in terms of material use, labor intensity, and reusability.

As part of this investigation, two scale models were constructed which are illustrated on pages 28-29. These models were constructed with 1/8� thick birch plywood and plaster to demonstrate the feasibility of the filled form techniques. They were also used to test different types of fabric and plaster and to help identify challenges with implementing the filled form techniques.

19

INVENTORY OF FILLED-FORM TECHNIQUES: Columns Free Standing Column

# Parts: Plywood: 2x4: 4x4: Fabric:

5 -34 ft -32 ft2

Cost:

$18

Labor Intensity: 0 Reusability: 3

Double-Layer Tube Column

# Parts: Plywood: 2x4: 4x4: Fabric:

13 -28 ft 42 ft 52 ft2

Cost:

$61

Labor Intensity: 2 Reusability: 1

20

“Bulge Wall” Column 1

# Parts: Plywood: 2x4: 4x4: Fabric:

28 62 ft2 95 ft 14 ft 84 ft2

Cost: $114 Labor Intensity: Reusability:

3 2

“Bulge Wall” Column 2

# Parts: Plywood: 2x4: 4x4: Fabric:

38 95 ft2 131 ft 26 ft 117 ft2

Cost: $172 Labor Intensity: Reusability:

3 2

21

INVENTORY OF FILLED-FORM TECHNIQUES: Walls Hanging Wall

Length: # Parts: Plywood: 2x4: 4x4: Fabric:

8.6 ft 30 32 ft2 82 ft 53 ft 138 ft2

Cost: $132 $15/ft Labor Intensity: 3 Reustability: 1

Frame Wall

Length: # Parts: Plywood: 2x4: 4x4: Fabric:

9.4 ft 28 -185 ft 19 ft 150 ft2

Cost: $116 $12/ft Labor Intensity: 2 Reusability: 3

22

“Quilt-Point” Wall

Length: 9.4 ft # Parts: 62 Plywood: -2x4: 58 ft 4x4: 38 ft Fabric: 150 ft2 Cost: $84 $9/ft Labor Intensity: Reusability:

3 2

Net Wall

Length: # Parts: Plywood: 2x4: 4x4: Fabric:

9.4 ft 28 -148 ft 38 ft 150 ft2

Cost: $120 $13/ft Labor Intensity: Reusability:

2 3

23

INVENTORY OF FILLED-FORM TECHNIQUES: Beams + Trusses Trough Beam with Wood Keel

Length: # Parts: Plywood: 2x4: 4x4: Fabric:

8 ft 26 41 ft2 76 ft -30 ft2

Cost: $68 $9/ft Labor Intensity: 1 Reusability: 3

Biaxial Trough Beam

Length: # Parts: Plywood: 2x4: 4x4: Fabric:

8 ft 38 25 ft2 76 ft -36 ft2

Cost: $58 $7/ft Labor Intensity: 3 Reusability: 3

24

Partial Trough T-Beam

Length: 8 ft # Parts: 16 Plywood: 39 ft2 2x4: 35 ft 4x4: -Fabric: 24 ft2 Cost: $49 $6/ft Labor Intensity: Reusability:

1 3

Truss Beam

(no fabric shown)

Length: 17.4 ft # Parts: 36 Plywood: 160 ft2 2x4: -4x4: -Fabric: -Cost: $128 $7/ft Labor Intensity: Reusability:

3 3

25

INVENTORY OF FILLED-FORM TECHNIQUES: Comparison with Conventional Wood Formwork Conventional Wood Column Form # Parts: Plywood: 2x4: 4x4: Fabric:

30 36 ft2 109 ft ---

Cost:

$72

Labor Intensity: 2 Reusability: 2

Cost of 8’ Column Labor Intensity Reusability

Conventional Wood Wall Form Length: # Parts: Plywood: 2x4: 4x4: Fabric:

9.5 ft 34 151 ft2 195 ft 38 ft --

Cost: $237 $25/ft Labor Intensity: 2 Reusability: 2

Cost per Linear Foot Labor Intensity Reusability

Convention Wood Beam Form Length: # Parts: Plywood: 2x4: 4x4: Fabric:

8 ft 28 30 ft2 58 ft ---

Cost: $47 $6/ft Labor Intensity: 2 Reusability: 2 26

Cost per Linear Foot Labor Intensity Reusability

Conventional Wood Form

Free Standing Column

Double-Layer Tube Column

Bulge Wall Column 1

Bulge Wall Column 2

$72

$18

$61

$114

$172

2

0

2

3

3

2

3

1

2

2

Conventional Wood Form

Hanging Wall

Frame Wall

“Quilt-Point” Wall

Net Wall

$25

$15

$12

$9

$13

2

3

2

3

2

2

1

3

2

3

Conventional Wood Form

Trough Beam w/ Wood Keel

Biaxial Trough Beam

Partial Trough T-Beam

Truss Beam

$6

$9

$7

$6

$7

2

1

3

1

3

2

3

3

3

3 27

INVENTORY OF FILLED-FORM TECHNIQUES:

Scale Models of “Bulge-Wall” Column and Wall Truss

28

29

MODEL STUDIES OF FABRIC-FORMED SHELLS: Description of Method and Materials

The second investigation was a series of physical models that investigate the “covered form” techniques for casting thin concrete shells with fabric formwork. The general sequence of this method is as follows: (1) A piece of fabric is draped from a supporting structure; (2) Plaster or concrete is sprayed onto the fabric; (3) The fabric deforms with the additional load and hardens in a permanent shape; (4) The hardened fabric is rotated or inverted into its final position; (5) Additional layers of concrete and reinforcement are applied to create a rigid structural shell.

During this process, fabric deformations occur at both the local and the global scale. At the global scale, pieces of fabric deform under loading (self weight and the weight of the plaster or concrete hardening agent) to create a catenary geometry. At the local scale, fabric buckles near supports as a result of stress concentrations within the material. Each of these deformations can be controlled by modifying the nature and location of fabric supports.

Technique. 8-inch squares of fabric were supported by a 12-inch square corkboard with its center removed. The fabric was secured to the corkboard with strategically placed T-pins. The location of supports was modified throughout the investigation to produce different deformation patterns in the fabric. In some cases the fabric was prestressed in order to further influence its deformations during loading. The fabric was covered with either plaster or a stiffening agent and then left in place until hardening had occurred. The investigation was divided into three categories: prestress only, prestress and gravity, and gravity only. The tests and results are illustrated on pages 31-33.

Types of Fabric Used. Two types of fabric were used in this investigation. The first was a “yoga cloth” that is woven from a blend of cotton and lycra. This fabric has very good elastic properties and deforms easily with minimal loading. When the load is removed the fabric returns to its original shape. The second fabric was a polypropylene geotextile material that is traditionally used for landscaping and gardening. This fabric also deforms easily but in a more plastic manner. Both of the fabrics are semi-permeable and have a tendency to wick moisture during curing.

Stiffeners Used. Two types of fabric stiffeners were used in this investigation: “Stiffen Stuff” and “Mod Podge.” Both are starch based stiffeners that are applied by saturating the fabric and waiting for it to dry. The stiffeners were initially investigated as a substitute for the plaster and concrete hardening agents that are described above. In the end, the stiffeners did not produce enough rigidity or permanence to be used in this way.

Types of Plaster Used. Two types of plaster were used in this investigation: a standard modeling grade plaster of paris (calcium sulfate hemihydrate, calcium carbonate, and crystalline silica) and Hydrocal Gypsum Cement (alpha-calcium sulfate hemihydrate). The plaster of paris was used for most of initial investigations but proved too brittle to produce thin shells. The Hydrocal is much more resilient and has a strength that is comparable to regular-strength concrete, which makes it an excellent candidate for this investigation.

30

MODEL STUDIES OF FABRIC-FORMED SHELLS: Prestress Only (Fabric + Stiffener)

In these studies fabric was prestressed (pulled) into buckling patterns, secured with T-pin supports, and then covered with a starch-based stiffening agent of either “Stiffen Stuff” or “Mod Podge.” The purpose of the investigation is to isolate the effect of prestress and boundary conditions. The location of supports and the magnitude of prestress forces were modified in order to produce specific local bucking patterns in the fabric.

1. Cotton / Lycra + “Stiffen Stuff”

2. Cotton / Lycra + “Mod Podge”

3. Cotton / Lycra + “Stiffen Stuff” + “Mod Podge” 31

MODEL STUDIES OF FABRIC-FORMED SHELLS: Prestress and Gravity (Fabric + Plaster)

In these studies fabric was prestressed (pulled) into buckling patterns, secured with T-pin supports, and then covered with plaster. The purpose of the investigation was to observe the combined effect of prestress, boundary conditions, and global deformations from loading.

The location of supports and the magnitude of prestress forces were modified in order to produce specific local bucking patterns in the fabric.

4. Cotton / Lycra + Plaster

5. Cotton / Lycra + Plaster

6. Cotton / Lycra + “Stiffen Stuff� + Plaster 32

MODEL STUDIES OF FABRIC-FORMED SHELLS: Gravity Only (Fabric + Plaster)

In these studies fabric with no initial prestress was secured by T-pin supports and then covered with plaster. The purpose of the investigation was to isolate the effect of boundary conditions on the global deformations that occur during loading. Support locations were modified in order to produce specific global geometries as well as local bucking patterns in the fabric.

7. Cotton / Lycra + Plaster

8. Geotextile + Plaster

9. Geotextile + Plaster 33

MODEL STUDIES OF FABRIC-FORMED SHELLS: AGGREGATIONS OF PHYSICAL MODELS

34

35

DIGITAL SIMULATION OF FABRIC-FORMED SHELLS: Description of Method + Results The third investigation was a translation of the physical “Shell Model Studies” to a digital format. This was done using Maya, a computer program that is typically used for animation.

Maya has an embedded fabric simulation tool that allows virtual pieces of fabric to be constrained and loaded in much same way that the physical studies were conducted. The purpose was to develop a working method for the subsequent design project that is faster, more flexible, and does not require the use of physical models.

Maya’s fabric simulation was used to model three of the same shells that had already been constructed as a physical model. This allowed a direct comparison between the digital and physical results. The digital fabric was assigned material properties and support constraints and then allowed to deform under a gravitational load. Next, the fabric was frozen, inverted, scaled, and extruded to give the shells a thickness that is analogous to a layer of concrete or plaster. The resulting shells exhibit deformations and bucking patters that are almost identical to their physical counterparts. This served as a proof of concept for this digital working method.

Once modeled, each shell was tested using finite element analysis software. This structural analysis was used to identify low-stress portions that could be removed for lighting, daylighting, or other services. The final analysis evaluates each shell with these low-stress portions removed. In order to better understand the experiential implication of the resulting shapes, two of the three shells were aggregated and then rendered. One of these renderings is illustrated on pages 40-41.

Top View

Perspective

Shell #8:

Step 1: digital fabric simulation of shell 8 36

Step 2: finite element analysis with self weight of shell

Step 3: finite element analysis with low-stress areas removed

Top View

Perspective

Shell #9:

Step 1: digital fabric simulation of shell 9

Step 2: finite element analysis with self weight of shell

Step 3: finite element analysis with low-stress areas removed

Step 2: finite element analysis with self weight of shell

Step 3: finite element analysis with low-stress areas removed

Top View

Perspective

Shell #5:

Step 1: digital fabric simulation of shell 5

37

DIGITAL SIMULATION OF FABRIC-FORMED SHELLS: Aggregation of Digital Shells

38

39

DIGITAL SIMULATION OF FABRIC-FORMED SHELLS: Visualization of Digital Aggregations

40

41

DESIGN PROJECT PROPOSAL: Description of Project + Site Through my initial research and inventories of fabric-forming techniques, I concluded that the most inefficient aspect of fabric formwork is the scaffolding structures that must be constructed to support the flexible formwork. Therefore I chose to investigate the possibility of using existing building structures as scaffolding for fabric formwork. The 16th Street Station in West Oakland was selected as the site for this investivation based on its location, ownership status, and redevelopment plans.

The 16th Street Station was designed by Jarvis Hunt, a well-known train station architect, and was constructed between 1910 and 1912. The 16th Street Station was the main Oakland stop for the transcontinental Southern Pacific Railroad and also served street car lines that were operated by East Bay Electric Lines and later the Interurban Electric Railway. Amtrak became the primary user of the station in the early 1970s and continued to operate there until the nearby Emeryville Amtrak Station was completed in 1994. The 16th Street Station was seriously damaged by the Loma Prieta Earthquake in 1989, which resulted in its abandonment.

Since 2002 the 16th Street Station has been owned by the BRIDGE Housing Corporation, a non-profit affordable housing developer that plans to retrofit and redevelop the station into a community center for West Oakland. The vacant lots around the station are also slated for redevelopment with plans to construct mixed-income housing that would mirror other housing developments that have been completed in the surrounding area over the last ten years. The footprints of these proposed developments are indicated on the “Proposed Site Plan� (pages 56-57).

The 16th Street Station consists of a tall beaux-arts building that is surrounded on three sides by peripheral platform and baggage handling structures. This design proposal preserves the main building while replacing peripheral structures with a semi-enclosed fabric-formed concrete canopy that provides shelter for a number of community-oriented functions. The program includes a farmers market, a concert venue, an indoor event space, permanent food vendors, a beer garden, and parking for food trucks.

42

Aerial Photograph of West Oakland

Aerial Photograph of 16th Street Station 43

DESIGN PROJECT PROPOSAL: Photographs of Existing 16th Street Station

44

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

45

DESIGN PROJECT PROPOSAL: Description of Construction System The existing structure of the 16th Street Station in West Oakland is used as scaffolding for a steel cable grid that is prestressed and embedded in a mesh of geotextile fabric formwork.

The first step in the construction process is to demolish existing concrete slabs, roof structures, and minor beams and girders. The structure included in this initial demolition is indicated by the red poche’ in the diagrams on pages 47, 50, and 51 and by the fine dashed line in the plans and sections on pages 48-49. After preliminary site grading, the next step is the construction of new, shallow-pier foundations, which are located between the columns of the existing platforms. These foundations are used as anchor points for prestressing the reinforced fabric formwork. The process by which these foundations are constructed is described in the axonometric diagram on page 51. Once these steps have been completed, the reinforced mesh, made up of geotextile fabric and 1/4� steel cables, is draped over the existing structure, prestressed, and pulled to the newly-constructed anchor points.

After it has been pulled into place, the steel and fabric formwork is sprayed with concrete on both sides. The minimum thickness of each layer of concrete is 1.5 inches (3 inches total thickness) which is required by the American Concrete Institute (ACI) to provide the steel with adequate protection from weathering and corrosion. The reinforced formwork mesh is left embedded in the hardened concrete to provide tensile resistance as is required by the ACI design codes.

Once the concrete canopy has sufficiently hardened (roughly 28 days), the remaining scaffolding structure of the platforms and baggage handing area will also be removed. The self-supporting fabric-formed canopy remains as a record of the original structure. The last step in the construction process is to demolish and replace the original ground-level concrete slabs and platform foundations. This allows the ground plan to be re-graded between the newly constructed anchor points. The ground is sloped to drain at center points along the new structure and to create a staggered viewing area in front of the stage. A series of vegetated hills are constructed along the northwestern edge of the project to provide an outdoor gathering space and a buffer from the adjacent freeway.

46

3. Steel and fabric formwork is sprayed with concrete on both sides. Once concrete has hardened, the remaining platform structure is demolished.

2. The reinforced mesh (geotextile fabric with 1/4� steel cables) is attached to existing platform structure.

The mesh is pretensioned to connect to prescribed anchor points.

1. Ground is graded to support canopy and to provide acoustic barrier from freeway. Parts of existing platform structure are demolished (indicated in red) to make room for fabric formwork.

Exploded Axonometric View of Construction Components 47

DESIGN PROJECT PROPOSAL: Anchor Point Layout There are four levels of anchor points that are used to support the fabric formwork. These levels are indicated by the key on the following page and are dictated by the existing structures of the platform and main station building. In plan, the anchor point locations for the fabric formwork are determined by the arrangement of program and by the location of existing structural members. There is a greater density of anchor points in the farmer’s market area where they are arranged to delineate space for individual vendors and to define vaulted circulation paths. In other areas, including the concert venue and the beer garden, a lower density of anchor points allows larger spaces that can be used in a more flexible manner.

Anchor point locations are optimized in order to minimize the number of collisions between the reinforced fabric formwork and the scaffolding of the existing structure. These collision points complicate the construction process because the fabric formwork must be fabricated with additional reinforcement at these locations and because their exact locations are often difficult to anticipate.

The fabric formed canopy enters the main station building in several locations along the building’s northwest facade. This interface occurs through existing window openings and is intended to create a visual relationship between the concrete canopy and the interior of the historic building. Inside the building, the reinforced fabric formwork is anchored to the steel truss structure of the station’s existing hip roof, and the vertical height of anchor points is staggered so the concrete canopy can also serve as an interior light fixture.

As-Built Ground Floor Plan 48

Framing + Demolition Plan with Formwork stage 1 demolition (pre formwork)

+ 0 ft

+ 28 ft

stage 2 demolition (post formwork)

+ 16-24 ft

+ 42 ft

As-Built Transverse Section with Formwork

As-Built Longitudinal Section with Formwork 49

DESIGN PROJECT PROPOSAL: Typical Construction Details at Anchor Points

1. Existing concrete slabs and minor horizontal structure are demolished to make room for fabric formwork.

2. Segments of steel and fabric mesh are joined along lines of supporting structure. Reinforcing rings are added around anchor points.

3. Steel and fabric formwork is pulled to anchor points on existing structure and new footings. Concrete is sprayed on both sides of fabric formwork.

Typical Construction Process at High Points 50

1. Portion of existing slab is demolished.

Shallow friction piers are drilled and filled with concrete to support new column footing.

2. New water collection pipe is installed under existing slab. New slab is poured over friction piers. Brackets are installed to hold fabric formwork.

3. Fabric formwork is installed and pulled to connection points on new slab footing. The threaded drain pipe is used to pretension the fabric formwork. Concrete is sprayed onto both sides of fabric formwork.

Typical Construction Process at Low Points 51

DESIGN PROJECT PROPOSAL: Reinforced Mesh Formwork with Scaffolding

Northeast View

Northwest View

Southwest View 52

Reinforced Mesh Formwork without Scaffolding

Northeast View

Northwest View

Southwest View 53

DESIGN PROJECT PROPOSAL: Working Methods + Structural Analysis Simulation of Form. The form of the canopy was designed using the Kangaroo Physics simulation tool for Grasshopper which is a plugin for Rhinoceros Version 5 modeling software.

This tool includes a Live Physics engine that allows the model to be updated in real time as anchor points and other parameters are adjusted on the model. The base model consists of a planar mesh with divisions that correspond to the cable grid that is used to reinforce the fabric formwork. These divisions are extracted from the mesh and assigned the physical properties (elastic modulus, rest length, etc.) of 1/4” diameter steel cables. Next, anchor points are added along the lines of reinforcement, and gravity loads are defined that correspond to the self weight of three inches of concrete. During each simulation, the planar mesh is deformed by the vertical translation of anchor points (prestress), by the physical properties of the reinforcing cables, and by the gravity load from the wet concrete.

Structural Analysis. A series of finite element analyses (FEA) were conducted with the Millipede structural analysis component for Grasshopper and Rhinoceros Version 5. The canopy was modeled with a constant thickness of three inches and loaded with a vertical dead load and a lateral seismic load. The dead load was determined by the self-weight of the concrete canopy and the seismic load was determined by the simplified procedure that is described in ASCE 7. Both load cases were applied simultaneously. The results of these analyses are shown on the following page. Areas of the surface that are rendered in yellow experienced a maximum von mises stress of greater than 2000 psi. Areas of the surface that are rendered in red experienced a maximum von mises stress of greater than 6000 psi (roughly the yield strength of high-strength concrete). The results show that only several percent of analysis points on the canopy yield under the combined loading condition. The regions where the yield strength is exceeded are generally near support points and would be thickened during construction to reduce stress. It is also important to note that the analysis was conducted for a pure concrete shell and does not account for the composite effect of the reinforced fabric mesh.

Layout of Skylights. The location of skylights was determined by two factors: the process of constructing the fabric formwork, and the results of the finite element analysis. The base condition (shown in “Iteration 1” of the FEA) was the canopy without any holes. In the second iteration skylights were added at all of the peaks of the fabric formed canopy. This allows the reinforced formwork to fit around the existing platform structure during construction (see page 50), and creates an adjacent diffusing surface for distributing the incident daylight. In the final (third) iteration additional skylights were added in low-stress areas that are not adjacent to high points in the canopy structure. The FEA results on the following page show that the addition of skylights has only a minimal affect on the stress distribution in the concrete canopy. The affect of the skylights on daylighting can be seen in the renderings on pages 6269.

54

Iteration 1 (no holes): Max Von Mises Stress

red ≼ 6000 psi

yellow ≼ 2000 psi

Iteration 2 (skylights at peaks): Max Von Mises Stress

Iteration 3 (additional skylights in low stress regions): Max Von Mises Stress 55

Proposed Site Plan

56

57

Proposed Ground Floor Plan

58

59

Proposed East Elevation

Proposed Longitudinal Section

60

61

Interior of Beer Garden

62

63

Farmers Market Looking Toward Old Station

64

65

Farmers Market with Vendor Stands

66

67

Concert Venue

68

69

Concrete Canopy Invading Old Station Building

70

71

Physical Model of Station and Canopy

72

73

Physical Model of Station and Canopy

74

75

Large-Scale Proof of Concept Model

76

77

CONCLUSIONS: Lessons Learned + Future Directions This thesis project was a two-year-long journey, bridging my parallel interests in architecture, building science, and structural engineering. I was introduced to fabric-formed concrete in a civil engineering course. I was impressed by the architectural and structural possibilities of this technique, which could dematerialize concrete into soft and unexpected forms. My initial research (summarized on pages 6-17 of this book) demonstrated additional benefits of fabric formwork including improved surface finish quality and durability, increased structural efficiency, and reductions in labor and material use. Despite these many benefits, the research also revealed some significant challenges associated with fabric-formed concrete, particularly in anticipating its loaded behavior during the design process.

My thesis project attempted to address many of the challenges identified in my background research. Through this work I developed a method for designing fabric-formed shell structures with currently available computational modeling tools and finite element solver software. In doing so, I realized that there are many software tools already available for other purposes that can be adapted to design fabric formwork. These digital tools open up new possibilities in the design of fabric formwork by allowing formwork to be planned in a quick and fluid process without complete reliance on the time-consuming construction of physical models. They also allow direct feedback loops between modeling and structural analysis tools so that formwork can be designed and optimized in an iterative process.

Through this work I also have explored the idea of recycling an existing structure as cost-saving formwork for a new type of organic structure that grows out of the old. The 16th Street Station redevelopment proposal is a case study for this idea and was used as a trial run for the digital design methods that I developed. I also considered the potential for designing the new canopy as part of a seismic retrofit for the 16th Street Station.

78

OPPORTUNITIES FOR FUTURE RESEARCH This thesis is the first chapter of a much longer exploration necessary to realize the redevelopment project using the proposed fabric-formed concrete techniques. The following list identifies some future avenues for research. The list is divided into two categories: items that are related to the general construction technique, and items that are related to the specific redevelopment proposal.

General Technique (fabric-formed shell structures): •

Calibrate computational design tools to the behavior of large-scale physical models to ensure their accuracy.

•

Develop details for the reinforcing cable mesh and the connections between the steel cables and the fabric formwork. If the steel cables will be used as the primary reinforcement for the concrete then they must also be detailed to maximize the bond between steel and concrete.

•

Improve digital simulation techniques to more accurately represent the deformations and buckling patterns that will develop in the fabric formwork during the construction process.

•

Develop computational methods for the fluid translation of digital formwork models into fabrication-ready cutsheets.

•

Test the proposed construction sequence with large-scale physical models in order to document actual deflections during concrete casting and to test the strength and behavior of the proposed reinforcing strategy.

Project Specific (16th Street Station Redevelopment): •

Perform structural analyses on the existing platform structures of the 16th Street Station to determine the feasibility of proposed loading patterns during construction.

•

Integrate daylight analysis with the final design and placement of openings in the canopy.

Adjust the placement of openings to provide the desired distribution of natural light.

•

Investigate the feasibility of using the fabric-formed concrete canopy to brace the main station building as part of a seismic retrofitting strategy to preserve the historic structure.

79

RESOURCES Abdelgader, H.S., and A.S. El-Baden. “Compressive Strength of Concrete Cast In Fabric Forms.”

SBEIDCO 1st International Conference on Sustainable Built Environment Infrastruc

tures in Developing Countries. ENSET Oran, Algeria. (2009).

Abdelgader, H., M. West, and J. Górski. “State-of-the-Art Report on Fabric Formwork.” ICCBT. (2008).

Cauberg, Niki, Tine Tysmans, Sigrid Adriaenssens, Jan Wastiels, Marijke Mollaeri, and Bachir

Belkassem. “Shell Elements of Textile Reinforced Concrete Using Fabric Formwork: A

Case Study.” Advances in Structural Engineering. (2012).

D’Aponte, Eleanor, Alexander Lawton, Russ Miller Johnson. “Fabric Formwork for Architectural

Concrete Structures.” Proceedings of the 1st International Conference on Concrete

Technology. Tabriz, Iran. (2009).

Ghaib, Mahdi Al Awwadi, and Jaroslaw Górski. “Mechanical Properties of Concrete Cast in Fab

ric Formworks.” Cement and Concrete Research. (2001).

Koerner, Robert M., and Joseph P. Welsh. “Fabric Forms Conform to Any Shape.” The Aberdeen

Group. (1980).

Long, A.E., A.A. Sha’at, and P.A.M. Basheer. “The Influence of Controlled Permeability Formwork

on the Durability and Transport Properties of Near Surface Concrete.” American Insti

tute of Concrete Special Publication. (1995).

Orr, John J., Antony P. Derby, Tim J. Ibell, and Mark Evernden. “Optimisation and Durability in

Fabric Cast ‘Double T’ Beams.” ICFF Conference. University of Bath, Bath, England.

(2012).

Orr, John J., Anthony P. Derby, Tim J. Ibell, Mark C. Evernden, and Mike Otlet. “Concrete Struc

tures Using Fabric Formwork.” The structural Engineer. (2011).

Schmitz, Robert P. “Fabric Formed Concrete Panel Design.” 17th Analysis and Computation

Specialty Conference in conjunction with the 2006 ASCE Structures Congress. Saint

Louis, MO. (2006).

Veenendaal, Diederik, Mark West, and Philippe Block. “History and Overview of Fabric Form

work: Using Fabrics for Concrete Casting.” Structural Concrete. (2011).

West, Mark. “Fabric-Formed Concrete Columns for Casa Dent in Culebra Puerto Rico.” Center

for Architectural Structures and Technology. Web resource: http://www.umanitoba.ca/cast_building/assets/downloads/PDFS/Fabric_Formwork/

Casa_Dent.pdf. (accessed 11/2012).

West, Mark. “Flexible Fabric Molds for Precast Trusses.” Concrete Plant +Precast Technology.

(2006).

West, Mark. “Kenzo Unno Fabric-Formed Walls.” Center for Architectural Structures and

Technology. Web resource: http://www.umanitoba.ca/cast_building/assets/down

loads/PDFS/Fabric_Formwork/Kenzo_Unno_Article.pdf. (accessed 11/2012).

West, Mark. “Fabric Formwork for Reinforced Concrete Structures and Architecture.” (2010).

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West, Mark, Chris Weibe, Aynslee Hurdal, Jiameng Zeng. “Bulge Wall Construction.” Center

for Architectural Structures and Technology. (2007).

BRIDGE Housing. “16th Street Station | History.” Web resource: http://www.16thstreetstation.

com/history/. (accessed 05/2014).

BRIDGE Housing. “16th Street Station | The Future.” Web resource: http://www.16thstreetsta

tion.com/the-future/. (accessed 05/2014).

Wikipedia. “16th Street Station.” Web resource: http://en.wikipedia.org/wiki/16th_Street_Sta

tion. (accessed 05/2014).

Torres, Blanca. “Bridge Housing looks to revive 16th Street Station in West Oakland.” San

Francisco Business Times. (2012).

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IMAGE CREDITS Figure 1: http://blog.alexwebb.com/wp-content/uploads/2012/02/casa-la-moraleja.jpg. (accessed 11/2012).

Figure 2: Veenendaal, Diederik, Mark West, and Philippe Block. (2011).

Figures 3-4: Ghaib, Mahdi Al Awwadi, and Jaroslaw G贸rski. (2001).

Figure 5: Orr, John J., Antony P. Derby, Tim J. Ibell, and Mark Evernden. (2012).

Figure 6: Ghaib, Mahdi Al Awwadi, and Jaroslaw G贸rski. (2001).

Figures 7-10: http://www.umanitoba.ca/cast_building/. (accessed 11/2012).

Figure 11: Orr, John, Anthony Derby, Tim Ibell, Mark Evernden, and Mike Otlet. (2011).

Figure 12: http://www.umanitoba.ca/cast_building/. (accessed 11/2012).

Figures 13-16: Cauberg, N., T. Tysmans, S. Adriaenssens, J. Wastiels, M. Mollaeri, and B. Belkassem. (2012).

Figure 17: Image 1: Anne-Mette Manelius, Royal Danish Academy of Fine Arts; Images 2-4: Mark West, University of Manitoba.

Figure 18: Images 1-2: Mark West, University of Manitoba.

Pages 44-45: Images 1-5: Matt Beardsley: http://vimeo.com/47492274 (accessed 01/2014); Images 6-8, 12: https://www.flickr.com/photos/wiredforsound23 (accessed 01/2014); 9-10, 14-15: http://www.jeremyriad.com (accessed 01/2014); 11, 13: Lila Kahn; 16-21: Wayne van der Kuil.

Pages 70-71: Background Source: Wayne van der Kuil

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