PAPERBOARD TUBES IN ARCHITECTURE AND STRUCTURAL ENGINEERING: A REVIEW

PAPERBOARD TUBES IN ARCHITECTURE AND STRUCTURAL
ENGINEERING: A REVIEW
Lawrence C. Bank1,a and Terry D. Gerhardt2,b
1
Professor, Department of Civil Engineering, The City College of New York, 160 Convent
Ave, New York, NY 10023, USA
2
Staff VP Intellectual Property and Mechanics Technology, Sonoco Products Company,
1 North 2nd Street, Hartsville, SC 29550, USA
a
[email protected], [email protected]
Keywords: C o n c r e t e F o r m w o r k , E x h i b i t i o n S t r u c t u r e , E m e r g e n c y
Shelters, Paperboard Tubes, Temporary Structures
Abstract. Paperboard tubes have been used throughout the world in the construction industry as
formwork for circular concrete columns since the 1950s and are well–known to structural engineers
and architects. Less well–known is that large, thick–walled paper tubes (also called cores),
produced for the printing industry, have been used in a number of architectural and housing
structures in the last 20 years. Paper tubes are 100% recyclable and are very inexpensive (relative
to other structural materials.) They also have mechanical properties (strength and stiffness) needed
to support structural loads mandated by building codes. The purpose of this paper is to provide an
overview of the ways in which paperboard tubes have been used in architectural structures over the
last 20 years and to explain how the tubes are produced, analyzed and designed for architectural and
structural engineering purposes.
Introduction
Paperboard tubes are ubiquitous and are found in every aspect of modern day life. In the
industry, the terms paperboard ‘tube’ and paperboard ‘core’ are used interchangeably. They are
produced for a myriad of industrial applications and consumer products and are sometimes
considered to be commodity products, but most are actually highly engineered. On a global basis,
the majority of paper tubes are used in industrial winding operations. In these applications,
immediately after being manufactured, either paper, film or textile yarn is wound directly onto
paper tubes. The paper tube helps the wound material develop a stable roll structure and enables
transportation of the manufactured material to a converting operation.
These tubes range from
small (10 – 25 mm diameter with 0.5 – 1.5 mm wall thickness) to wind paper, plastic, aluminum,
cloth and yarn consumer products, to large industrial cores (70 – 200 mm diameter having 10 – 25
mm wall thickness) to wind rolls of printing paper, plastic film, textiles, and specialty metals. Such
tubes are designed to be used in interior environments for winding, transportation and finishing
operations; not exterior environments where they are exposed to rain or high humidity. Most tubes
for industrial markets are structurally optimized and engineered products. This is achieved by
selecting proper paperboard strength and stiffness, tube thickness, ply positioning in the wall, and
adhesive type in the design process. For example, certain paper mill cores are designed both for
fatigue strength to support a heavy cyclic load from winding a large roll of paper and also sufficient
axial modulus to prevent core vibrations when unwinding the paper roll on high-speed rotogravure
presses. Such cores generally require thick walls (10 - 15 mm) and fabrication from high strength
paperboards. Many feature patented designs. Fig. 1a shows typical paper mill cores and Fig. 1b
shows typical concrete formwork tubes.
(a)
(b)
Fig. 1 – (a) High strength paper mill cores and (b) Concrete formwork tubes
More extensive details on key factors, such as, short and long–term mechanical properties of the
materials, environmental factors, structural system selection, analysis tools, design basis, member
design, connection details, construction detailing, construction techniques and aesthetics are
discussed in Bank and Gerhardt (2016).
Paper Tube Manufacturing and Primary Uses
Spiral paper tubes are manufactured using a continuous process as illustrated in Fig. 2 (Wang, et al.
1995). The belt is stretched and rotated to drive the entire manufacturing process. The belt pulls the
paper plies through an adhesive station onto a stationary winding mandrel to form a continuous
tube. The newly formed tube is cut to the desired length at the end of the mandrel.
Fig. 2 – Spiral winding of paperboard tubes
Paper tubes are typically used to wind materials such as paper, film, metal sheet or textile yarn into
a roll immediately after they are manufactured. Typically, the wound rolls are then transported to a
converting operation, such as a printing operation for paper or a coating operation for film. In some
applications, the wound roll is shipped for direct use after winding, such as a film roll used in
stretch wrapping operations. Paper tubes are also used in consumer markets to wind products like
paper towels and bathroom tissue. These tubes are typically small diameter and manufactured
using only a few plies of paper.
For these typical uses, paper tubes and the wound rolls are used inside manufacturing facilities or in
the household. Paper tubes are not designed for exterior use. Exterior applications are quite
challenging as paper tubes experience significant strength and stiffness loss when exposed to water
or even high humidity conditions. Since paper tubes are typically not treated to inhibit moisture
penetration, it is the paper’s strength loss when combined with water that enables paper tubes to be
easily recycled using standard pulping operations. Recycled paper tubes are an important raw
material source for manufacturers of recycled paperboard.
Paper consists mainly of cellulosic fibers held together by hydrogen bonds. A recent overview of
the papermaking process and the properties of paper is provided in Chamberlain and Kirwan
(2013). Paper is generally considered to be an orthotropic, non-linear viscoelastic material that also
exhibits an accelerated creep response when exposed to changing humidity conditions. Paper tubes
are typically manufactured from recycled paperboard, an even more complex material since
recycling paper impacts both fiber length and bonding capability. When spirally wound, a paper
tube becomes an anisotropic structure as the principal directions of the paper are not aligned with
the principal directions of the tube. This anisotropy is evident as even subjecting a tube to external
pressure causes it to twist. Therefore, sophisticated methods are required to design paper tubes for
either traditional or non-traditional uses.
To manufacture paper, a dilute mixture of fibers in water is distributed on a screen, pressed and then
dried to form a paper sheet. This process creates a preferential alignment of fibers in the direction
the paper is manufactured, the so-called paper Machine Direction (MD). For this reason, paper
strength and stiffness is highest in its MD. The perpendicular direction across the width of a paper
machine is called the Cross Machine Direction (CD). Typically, MD properties are 1.5 to 4 times
higher than CD properties. However, it is the thickness direction (ZD) properties that make paper
an extremely unique material. Paper’s ZD modulus is typically 100-250 times less than its MD
modulus. The orthotropic modulus values for milk carton stock have been reported as 7.44 GPa
(MD), 3.47 GPa (CD) and 0.039 GPa (ZD) (Mann et al., 1980). Such testing requires conditioning
paper at standard conditions of relative humidity (RH) and temperature: 50% RH and 22 C. Such
conditioning is required as all paper properties are sensitive to changes in moisture content and
temperature.
Fabricating paper into a spiral tube complicates the mechanics further as loading never coincides
with the paper MD or CD. Fig. 3 illustrates the geometric relationships in winding a paper ply to
form a layer in a tube, where  is the angle between the paper MD and the tube circumference, W is
the width of the ply and D is the diameter of the layer the ply forms in the tube. The winding angle
 can be determined from W and D.
Fig. 3 – Wind angle and tube geometry
Fig. 4 shows the dependency of tube flexural (bending) modulus on winding angle  for tubes
fabricated from four different types of paper (Haapaniemi and Jarvinen, 2005), where the
theoretical spiral angle range is plotted from 0 to 90 degrees.
Fig. 4 Flexural modulus as a function of wind angle
Manufacturers have designed and optimized paper tubes for their key market applications, i.e.,
industrial winding operations. The comprehensive test methods, property data, and optimization
strategies have been developed for these uses rather than structural applications. In fact, QC tests
do not exist to measure creep response of paper tubes, a key requirement for structural applications.
So it is not surprising that the projects reviewed next have often relied upon full-scale tests of tubes
to determine the properties needed for structural design.
Application of Paperboard Tubes in Architecture
Paper strength is significantly reduced when it is exposed to elevated humidity environments, so
the use of large paperboard tubes in load–bearing architectural structures is uncommon.
Nevertheless, such applications are quite well-known due to the unique and pioneering work of the
2014 Pritzker prize-winning Japanese Architect Shigeru Ban (Anon, 2014a) who has designed and
constructed many temporary or semi-permanent paperboard tube structures for exhibition spaces
(Fig. 5a), for entertainments spaces (Fig. 5b)), humanitarian emergency shelters (Fig. 5c), single
family houses, and a bridges since 1989 (Fig. 5d) (McQuaid, 2003; Miyake, 2009; Jodidio, 2010).
(a)
(b)
(c)
(d)
Fig. 5 – Structures designed by Shigeru Ban (a) Nomadic Museum (New York, 2005) (b) Madrid Paper
Pavilion (Madrid, 2013), (c) Paper Log House (Kobe, 1995), (d) Paper Bridge (Remoulin, France, 2007)
Ban’s paperboard tube structures have been designed using a rigorous structural engineering
approach that has included special treatments of the tubes to inhibit moisture penetration, material
and structural testing of the structural components and joints, and structural analysis and design to
ensure appropriate structural stability, safety and serviceability, and compliance with appropriate
local permits (McQuaid, 2003; Correa, 2004). In these projects Ban has collaborated with structural
engineers (e.g., Minoru Tezuka, Geno Matsui), major international structural engineering firms
(e.g., Buro Happold, ARUP, Terrell (Miyake, 2009)) and major universities in Europe and Japan
(Tezuka et al., 1998).
A number of other designers and engineers have experimented with paperboard tube structures
and installations in recent years including a small school building by Buro Happold (Cripps, 2004)
(Fig. 6a), “Public Farm 1” by WORK Architecture Company (Anon, 2014b) with LERA (structural
engineers) (Fig. 6b), “Portals to an Architecture” by Steve Preston (Preston, 2006; Preston and
Bank 2012) (Fig. 6c), and “Brunkebergstorg 2014” by Guringo (Anon, 2014c) (Fig. 6d). Much of
the appeal of using paperboard for structures comes from their aesthetics, inherent recyclability and
potential for use as a sustainable building material.
(b)
(a)
(c)
(d)
Fig. 6 – Other paperboard structures, (a) Wall detail in school building (Buro Haphold, 1999), (b) Public
Farm 1 (WORK Architecture, 2008), (c) Portals to an Architecture (Preston, 2004), (d Brunkebergstorg
(Guringo, 2014)
Paper and paperboard are one of the most highly recycled materials in the world (60 - 70%
according AFPA (2014)). The use of paperboard tubes for construction of temporary exhibition
booths is common and Life-Cycle Assessment (LCA) analyses have been conducted to evaluate the
environmental impact of cardboard exhibition materials (Toniolo et al., 2013)
Structural Analysis and Design
When paperboard tubes are intended for building structures and may provide shelter or enclosure
or be of sufficient size that their collapse could endanger those in and around them, they must be
designed to ensure the safety of their occupants and bystanders (even if they are temporary
structures or not fully enclosed). In most cases a building permit will be required to build a
structure of this sort and a structural engineer should be engaged in the analysis and design.
The analysis (determination of the forces and displacements in the individual members and the
entire structure under all possible load conditions) and the design (selection of the structural system
(scheme), the materials, the member sizes and the connection types to ensure local and overall
structural stability and serviceability) of a structure is typically the responsibility of the structural
engineer. Structural engineers are well versed in performing these tasks when the materials (such as
steel, reinforced concrete and timber) are standardized and explicitly included in applicable
structural design and building codes. When the structural materials are not explicitly included in
applicable building codes, such as in the case of paperboard tubes, the structural engineer must
establish an appropriate design basis for the structural elements and then perform an analysis and
design according to this pre–developed “design basis.”
A design basis for a structure includes the choice of (1) the design philosophy (Allowable Stress
Design (ASD) or Limit States Design (LSD) (applied in US design codes for strength only as Load
and Resistance Factor Design (LRFD) or Ultimate Strength Design (USD))), (2) the loads and load
combinations to be applied, (3) the resistance factors or safety factors to be used, (4) the ultimate
member capacities or allowable stresses in the elements or materials, (5) the member effective
lengths based on end-conditions, (6) the allowable member and global displacements (and natural
frequencies), (7) the methods of structural analysis (linear, non-linear (material and/or geometrical),
and (8) the identification of material standards and test methods (such as those published by ISO
and CCTI). Eurocode 1990 provides details of the basis for structural design according to the
Eurocodes (EN, 1990). A similar situation currently exists for the design of fiber-reinforcedpolymer pultruded structures and this issue is discussed in greater detail in Bank (2006).
Typically not all the steps listed above need to be developed from first-principles. For example,
often the load cases and combinations will be taken from an existing code of loads on structures
(e.g. ASCE 7 (ASCE, 2013), Eurocode 1 (EN, 1991). In that case the design basis simply needs to
specify the exiting code document and its relevant sections. Such approaches are generally taken in
the design of paperboard structures. A set of structural engineering contract documents for a
building project must include drawings and specifications that contain the details of the elements
and systems, and must list the appropriate codes and standards followed.
Paperboard Tubes in Construction Engineering
The use of paperboard tubes in construction engineering is much more well-known than in
structural engineering primarily due to the popularity of paperboard tubular forms for concrete
columns for building frame construction. Often called “SONOTUBES,” they were originally
trademarked by Sonoco Products Company in 1945 (SONOTUBE®) and a US patent was granted in
1954 patent for a design with an improved inside tube surface (polyethylene) (Copenhaver et al,
1954). Such tubes are now produced worldwide by many manufacturers. Forms are commercially
available in standard diameters ranging from 50 to 1500 mm and in lengths up to 18 m. Paper tubes
can also be used in the construction of voided-slabs. Fig. 7a shows large diameter concrete form
tubes being stripped after casting concrete columns and Fig. 7b shows SONOVOID tubes in a
concrete horizontal element during casting.
(a)
(b)
Fig. 7 – (a) Stripping column forms (b) Pouring a voided slab
In a recent study, segments of large diameter (1500 mm) SONOTUBES were investigated for
use as recyclable and inexpensive bridge deck formwork for concrete bridges having wide-flange
prestressed girders with narrow gaps between the girders (Spottiswoode, 2007; Spottiswoode et al.,
2012). Fig. 8a shows a large diameter tubes, Fig. 8b shows a cartoon of how the tube segments can
be used as horizontal formwork, and Fig 8c shows an experimental 200 mm deep slab section cast
casting on a paperboard segment.
(a)
(b)
(c)
Fig. 8 – (a) 1.5 m diameter paper tube, (b) schematic of tube segment on wide–flange bridge girders (c)
mock–up of concrete slab cast on paper tube segment from 1.5 m diameter tube
Summary
This review paper has provided a brief overview of paperboard tube manufacturing, properties of
paper and tubes, examples of different architectural, structural and construction applications, and
design procedures for paperboard structures. While paperboard tubes are readily available from
many suppliers for potential use in structures, the authors stress the fact that currently available
tubes are manufactured for the converting industries and are not intended for, nor optimized for,
structural applications and designers should proceed with caution. Close coordination with the tube
manufacturer is needed to ensure that tubes produced for structural applications meet required
structural and environmental demands for the intended duration of service.
Much of the interest in designing structures from paper tubes lies in the inherent recyclability of
the paperboard materials and in the novelty of using materials that are generally perceived as being
weak and not particularly durable. This paper has demonstrated that highly engineered paperboard
tubes can be used in large structures, many of which have endured over 20 years in- service in the
outdoor environment. Those that have been built for temporary exhibitions are typically recycled
after their use. Paper tubes have also been used very effectively in humanitarian disaster relief
efforts by Shigeru Ban to build shelters and other enclosures. In these cases the light weight,
machinability with light hand-tools, ease of self-assembly and local availability, as well as, their
low price and low environmental impact give paper tubes a significant advantage over conventional
construction materials.
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