Striatus, an innovative 3D printed masonry bridge recently opened to the public
as part of the Venice Architecture Biennale. The 16x12 meter or 52x40 foot bridge was built by
The Block Research Group (BRG) at ETH Zurich The Computation and Design Group at Zaha
Hadid Architects incremental 3D
Holcim A basic 2d form was decided on
and the bridge was extruded and analysed in 3D modelling software. Thrust network analyses
created force diagrams for every design iteration. At the ideal curvature and extrusion of 2 meters,
balustrades or railings were designed 3 meters high. A Sterotomy mesh divided up the bridge
into 53 voussoirs or wedge-shaped blocks. A load causes stress, deformation and displacement
in a structure. Advanced discrete element analysis calculated the structural load at different points
on the bridge and the effect they would have. Excess load may cause structural failure,
so this was considered and controlled by the design of the bridge.
The bifurcating decks and balustrades transfer loads to the 5 steel footings
or base supports. Since these footings want to move outward and flatten the bridge,
underground steel tension ties were added to pull the footings together,
absorb the horizontal thrust of the arches and keep the bridge intact.
Once the design was optimized and finalized each of the 53 blocks
were sliced in non-parallel layers that are orthogonal to the dominant flow of forces.
This avoids delamination between the print layers as they are held together in compression.
As a whole, the bridge behaves as a series of leaning voussoir arches,
similar to a Roman arch. During construction, arches are supported by a temporary wooden frame.
Wedges are stacked around the frame until the central keystone is placed at the top of the arch.
The keystone bears almost no weight, but is the center of redirecting the weight of the structure
down and outwards. This is called compressive stress, because the pressure of the weight is
compressed by the shape of the arch. Once the rest of the pieces are in place, the formwork
can be removed and the arch remains standing. In addition to behaving like a Roman arch,
the Striatus bridge also behaves like a Nubian vault, an ancient architectural technique
that uses earth or adobe and mortar to create vaulted structures.
Unlike typical extrusion 3D printing in simple horizontal layers,
Striatus uses a two-component concrete ink with corresponding printing head and pumping
arrangement. Each of the blocks was printed in non-uniform and non-parallel layers via a 6 axis,
multi-DOF or degrees of freedom, robotic arm. This new generation of 3D concrete printing
allows the resulting forms to be used structurally without any reinforcement
or post-tensioning. Every single printed layer is aligned with the direction of compression
forces throughout the entire bridge and also locally through each block. The name Striatus
reflects this logic and manufacturing process. Compared to conventional concrete construction
where beams and floor slabs are solid, heavy blocks,
the bridge uses just 30% of the total volume of concrete and 10% of steel. Strength is achieved
through geometry rather than mass. Every section of the bridge is hollow, thus minimizing material
and reducing transportation and labor costs. The forms were printed in Germany in an indoor,
controlled environment. Once cured, they were strapped to pallets and transported to Venice,
Italy. A laser cut osb formwork was on site, ready to receive the 3d printed concrete forms.
Once the steel footings and tension ties were in place, a cane carefully lifted the voussoirs.
The pieces do not interlock and are not attached in any way to each other.
A neoprene pad is all that separates them. Once all the pieces were in place,
the formwork was disassembled. Wooden stairs and a walkway were the last components to be built.
The bridge is inspiring for so many reasons. Aesthetically, it’s unique,
sleek, intriguing and works with the surrounding trees and landscape.
While it doesn’t have a functional purpose in a park, it’s experiential art. It also
follows the 3 Rs that I mentioned in an earlier video, reduce, reuse and recycle.
It uses minimal material for maximum strength with no waste. All components are designed to
be disassembled and reused at another location. It can also be easily recycled because it doesn’t use
any reinforcements, glue or binders. I’m always disappointed when companies
use 3D printers to build boxes. When you have this incredible technology at hand,
you should push its limits and build structures that can’t be built with manual labor
and traditional methods. This bridge has combined human intellect, machine computing,
and the latest technology. The designers looked at historically proven structures like the Roman
arch and Nubian vault for inspiration and adapted the design to work with today’s technology.
The companies involved in this project were located in 5 different countries
and were working with a very tight schedule and budget. Since travelling was restricted last year,
they had to pull this off with just remote communication. It’s very impressive.
However, there are a few drawbacks. The bridge isn’t wheelchair accessible. The designers were
probably constrained by the dimensions of the site, and since ramps need a lot more space, they
couldn’t make it work. Also, since the 53 modules or wedges were so lightweight and fragile, 3 of
them broke during the shipping and installation process. They had to be re-printed in Switzerland,
allowed to cure and shipped separately to Italy. This caused massive delays because
the bridge is built sequentially. You can’t just skip a piece and move on to the next part.
The last issue is the clash between the precision of machines and 3d printers and human inaccuracy.
Even though every concrete section was printed accurately and the formwork was lazer cut,
the footing foundations were made by humans and the osb formwork was assembled by humans.
There was a 2 cm difference between some of the foundations, so the workers on site had to use
a good old-fashioned chainsaw to level it. All in all, it’s a beautiful, inspirational piece
of art. I hope it’s used a case study for future 3d printed projects. Let me know what you think
about this bridge in the comments below. I’ll also link my Patreon page, if you can support me,
I’d really appreciate it. A big thank you to everyone already supporting me. Don’t
forget to hit the like button and subscribe to my channel. Thanks for watching. See ya.