Tech Briefs Magazine - October 2021 - 22a

RESEARCH SPOTLIGHT
FIGURE 5   
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FIGURE 6   
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the urban green screen project. " We also
thought it could be a solution to more
than just the water problem. It serves as
a noise barrier and it could potentially
absorb particulate pollution from the
roads, " he says. Also, evaporative action
can lessen the " urban heat island " effect,
in which cities are often significantly
warmer than surrounding countryside.
» A FENCE, NOT A WALL: THE
NEED FOR A NEIGHBORLY
URBAN PARTITION
Along with addressing these functional
needs, the design team also had to
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consider the " holistic human perspective, "
as Prof. Jensen described it. A tall, solid
wall full of slowly evaporating water may
bring functional benefits, but it would not
be a welcome presence in people's front
yards. " We had meetings with residents
early in the project, " explains Prof. Jensen.
" Some of them feared [the screen] would
make their community feel like a prison. "
The residents' concerns were a
reminder that a neighborhood's
" furniture " must serve as architecture,
not just infrastructure. This is why the
urban green screen's steel frame and
mineral wool blocks are mostly invisible.
It looks like a wooden fence, not a metal
and masonry wall. The screen is also
equipped with benches for sitting and
with meadow vegetation. Two windows
give a look to the street, and a window at
each end of the screen gives security for
pedestrians so they can see what is going
on around the corner when passing.
Achieving this design, which meets water
management goals while being both
attractive and structurally sound, was a
challenge for the project team.
" I am a civil engineer, " says Ulbak.
" I know a lot about how to evaporate
water! But we had to address other
problems. We had meetings where some
people asked, 'Can you just put up a
glass wall?' They were concerned about
not being able to see the street. But the
project brief was to make a wall that
disperses water, and you cannot evaporate
much water from glass, " he explains.
" These are some of the obstacles we met.
Each step forward could take months of
back-and-forth toward a better solution. "
» A " WILLOW BUILDING " TO
CONCEAL A DRAINAGE SYSTEM
At this point, consulting structural engineer
and simulation specialist Tim Larsen, TLEngineering,
joined the project. His skills
and experience with infrastructure projects
helped the team address the green screen's
multiple challenges. " When I first joined
the project, there were a lot of ideas on
the table. They presented me with some
architectural drawings of a design that
would not stand if the wind was blowing, "
Larsen recalls. " I proposed a completely
steel structure, but I was told that the
community could not accept that. This is
when I suggested reaching out to Pilebyg. "
Pilebyg's name combines the Danish
words for " willow " and " building, "
and they have been building innovative
structures from willow trees for more than
30 years. Their process involves cultivating
willows so that their trunks grow into
relatively uniform curved shapes. The
harvested trunks can then be " woven "
around a support frame made from steel
or other types of wood (Figure 4). Special
treatment enables the willow sheathing
to last for decades, both protecting the
structure and helping it complement the
landscape. " You would not call a tree ugly
because it is old, " says Vibe Gro, Pilebyg's
co-owner and project manager for the
green screen project. " We offer a façade
that can age beautifully. "
» SIMULATION SUPPORTS
THE DESIGN/BUILD PROCESS
Pilebyg noise barriers have become a
familiar site along Danish highways,
but the company had never before
built a fence that concealed a drainage/
evaporation system. To help combine
multiple materials and functions into a
robust and harmonious structure, Tim
Larsen, who has a master's degree in
civil engineering, developed simulations
using the COMSOL Multiphysics®
software (Figure 5).
" It was funny, because Tim was not part
of the project when we started, but his
work was essential to our reaching a viable
solution, " explains Ulbak. He likens the
use of simulation to looking at instructions
for building a set of toys; the project
stakeholders were able to look at the
simulation results and tell how all of the
pieces of their project fit together.
Tim Larsen used simulation to ensure
that the structure was strong enough
for Copenhagen's climate (Figures 6-7).
Multiphysics analysis helped verify that
it could withstand wind pressure, the
varying loads resulting from water flowing
through its porous exterior, and water
saturating its mineral wool core.
" There are a lot of materials involved in
a structure like this, and small changes can
have a big impact, " says Larsen. " A little
overhang on the top does not look like
much, but when it fills with water, it can
create a heavy bending moment, especially
when the wind is blowing, " he explains.
As the project moved closer to
completion, images from the COMSOL
models were shared with other
stakeholders. The same schematics
provided to the crews building the
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Tech Briefs Magazine - October 2021

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