3D-printed construction of the Straitus Bridge completed,
has completed the construction of an arched pedestrian bridge at Giardini della Marinarica in Venice.
The project is a candidate for display at the 2021 Venice Architecture Biennale,
as the first pedestrian bridge of its kind measuring 12 by 16 metres.
The bridge structure is made of 3D-printed concrete blocks,
assembled without mortar or reinforcement.
The design proposes a new language for concrete,
through a structurally informed and environmentally responsible manufacturing technique.
Its construction methodology combines traditional techniques of master builders with advanced computational design,
engineering and automated manufacturing techniques.
Striatus Design enhances the properties of 3DCP concrete masonry structures,
contemporary design, and offers an alternative to traditional concrete masonry.
Its name reflects the structural logic and manufacturing process,
where the concrete is precisely printed in layers perpendicular to the main structural forces to create a compact structure,
requiring no mortar or reinforcement.
Since this construction does not require mortar,
the blocks can be disassembled and reassembled at a different location,
if construction is no longer needed, the materials can simply be separated and recycled.
3D printing can also be used to construct load-bearing concrete structures
that require significantly less materials and do not require steel reinforcement or mortar.
Building with reinforced concrete generates significant amounts of carbon dioxide emissions,
with steel used for reinforcement and cement for concrete being a particular problem in this regard.
The construction was called,
“Striatus” which was built using concrete blocks that form an arch much like traditional masonry bridges.
The pressure structure allows transfer to only the bases,
which are connected to each other on the ground, and the assembled building derives its stability solely from its engineering design.
3D-printed construction of the Straitus Bridge completed
Concrete is not applied horizontally in the usual way,
according to the type of 3D printed concrete, but is applied at specific angles so that it is perpendicular to the flow of compressive forces.
This keeps the layers printed in the blocks well pressed together,
without the need for reinforcement or tension later, and the concrete ink for the 3D printer was developed by Holcim specifically for this purpose.
This precise method of 3D printing allows concrete to combine the principles of traditional vaulted construction
with digital concrete manufacturing to use materials only when they are structurally necessary without producing waste.
Providing strength through engineering
The Striatus Bridge is an unreinforced concrete structure,
achieving strength through engineering, so that concrete can be considered an artificial stone that performs better in compression.
Materials can be placed precisely in arched and vaulted structures,
so that forces can be transmitted to the supports at pure pressure.
Strength is created through engineering rather than passive buildup of materials
as in traditional concrete beams and flat floor slabs.
This provides opportunities to significantly reduce the amount of material required to extend the space,
as well as the possibility to build with less robust and less polluting alternatives.
The sloping mountain shape of its structural arches was determined by techniques of finite analysis and equilibrium methods,
such as thrust network analysis, originally developed for the structural assessment of historic building vaults.
3D-printed construction of the Straitus Bridge completed’Striatus’ manifold surface geometry responds to its site conditions,
its crescent shape incorporating thrust lines that track compressive forces through the structure for all loading situations.
Steel tension ties absorb the horizontal thrust of the arches,
and neoprene pads placed between dry-assembled blocks avoid stress concentrations.
It also controls the friction properties of the facades,
echoing the use of lead sheets or fine mortar in the historic construction of the building.
In the plan, the borders of the structure form deep arches that transfer horizontal loads
(from visitors leaning on the balustrade) to the buttresses in pure pressure.
Advanced Discrete Element Modeling (DEM) has been used to fine-tune the modular block cutting,
and to verify the stability of the entire assembly under extreme loading conditions or differential strut adjustments.
53 3D falcons of the bridge were also produced using non-parallel printing layers perpendicular to the prevailing flow of forces,
avoiding this unraveling between the printing layers because they are held together in compression.
The additive manufacturing process ensures that structural depth of components can be achieved without producing blocks with a rigid section,
thus reducing the amount of material required compared to subtractive manufacturing or casting methods.
3D-printed construction of the Straitus Bridge completed
The design follows the principles of circular design, which places materials only where needed,
significantly reducing their environmental impact.
Striatus can be repeatedly installed, disassembled, reassembled and reused.
It redefines traditional interdisciplinary relationships,
integrating design, engineering, manufacturing and construction.
Precise block fabrication is enabled by well-defined data exchange between the different domain-specific
software tools chains involved in the process.
This co-development approach has also been facilitated by the use of COMPAS,
an open source computational framework for collaboration and research in the AEC industry.
Use alternative to standard floorboard
When comparing the structure to typical reinforced concrete flat floor slabs,
this new flooring system uses only 30% of the volume of concrete and only 10% of the amount of steel.
The very low pressures within the sloping mountain structure also enable the use of low carbon concrete,
which contains high proportions of recycled construction waste.