Deformable concrete for earthquake-proof buildings

The SHDS (Seismic-resistant Highly Deformable Structures) project builds upon the results of another EU-funded project called ANAGENNISI, which is recycling tyre rubber particles into replacements for both fine and coarse concrete aggregates.

By using this ‘High deformability concrete’ (HDC) in flexible coupling beams and developing ductile shear walls, the team aims to develop a structure with controlled performance where structural damage is concentrated on specific, dedicated elements. This means easier and faster repairs, whilst contributing to a circular economy.

Dr David Escolano, Marie Curie individual fellow at the University of Sheffield and coordinator of SHDS, discusses the project’s ambitious achievements so far.

The project considers structure performance rather than its strength. How is it important?

Dr David Escolano: Under force-based methods, seismic action is defined using lateral ‘equivalent forces’ distributed over the structure’s height. The elastic magnitude of such forces depends on the hazard level at the site (ground accelerations), and, for sites with high seismic hazard, existing codes allow for reducing the lateral forces. This results in more cost-effective structures, provided of course that these structures can endure a certain amount of damage before collapse.

Whilst such design philosophy is straightforward, easy to use and effective at avoiding potential loss of life, engineers are moving towards a design philosophy that would allow them to design structures that can resist earthquakes of different severity within specified limiting levels of damage, that is, a Performance-based design (PBD). Such design would enable the development of optimal structures, maximise use of resources and minimise costs, all this while yielding acceptable levels of safety and empowering designers to experiment with new design solutions, innovative materials and structural components so as to achieve the desired performance levels.

What does SHDS bring to the table in this regard?

The SHDS project focuses on a very specific structural component: coupling beams in coupled wall systems. Two or more structural walls are linked through beams according to a regular pattern over the height of the structure, which improves the seismic performance of each individual wall and provides a very stable source of energy dissipation.

As the overall behaviour of the system depends heavily on the deformation capacity of the coupling beams, our goal is to develop innovative solutions for the construction of coupling beams with unparalleled deformation capacity thanks to the use of a newly developed HDC.

What is HDC and what’s its added value for this project?

HDC is a product of the ANAGENNISI project which aims at finding ways of using all components of post-consumer tyres in high-value concrete applications. One of its focuses consists in replacing the mineral aggregates in concrete with rubber particles so as to increase the deformation capacity of traditionally brittle concrete.

As high deformability requires high rubber content, which in turn can drastically reduce the material’s compressive strength by up to 90 %, HDC also uses advanced composite jackets to enhance the compressive strength to structural grade while keeping the desired large axial deformation capacity of rubberised concrete. A mere 1.6 mm thick Aramid jacket wrapped around rubberised concrete columns can lead to extraordinary strength and deformability enhancements.

Two of your main arguments in favour of this new concrete are its sustainability and ease of repair. Can you elaborate on these?

PBD allows engineers to design predetermined and well-engineered components that can attract damage during earthquakes. As a result, post-earthquake repairs in PBD-designed structures would focus on these components rather than on the whole structure. The coupling beams being developed in this project work as ‘fuses’ and are the first elements to sustain considerable damage during an earthquake, in turn protecting the majority of the remaining structural and non-structural components.

As for sustainability, the proposed coupling beams can be easily replaced after major seismic events, thus minimising costly repairs, and limiting the impact on the community by enabling a much faster occupancy. The proposed coupling beams also use materials recovered from waste tyres, thus assisting in achieving a greener economy with reduced waste production and pressure on raw materials.

What can you tell us about the results of the testing phase so far?

At the material level, we have tested more than 300 cylinders/cubes to analyse the fresh and hardened properties of rubberised concrete. Different mixes and rubber quantities were tested, which ultimately resulted in the development of an optimised mix with 60 % rubber replacement of the coarse and fine mineral aggregates. This optimised mix was adopted for the final development of HDC.

Different types of advanced composite jackets were then trialled to provide the optimal combination of deformation capacity and strength, including Aramid and Carbon FRP. The developed HDC can achieve compressive strengths suitable for structural purposes (40-120 MPa) with maximum axial deformations 20 times larger than possible with traditional concrete.
The results of SHDS so far are very encouraging and show that HDC coupling beams can resist similar loads to their traditional counterparts while exhibiting four times more deformation capacity.The results of SHDS so far are very encouraging and show that HDC coupling beams can resist similar loads to their traditional counterparts while exhibiting four times more deformation capacity.

Have you been in touch with potential investors so far?

We have not contacted any possible investors yet. For structural applications, we believe we are in a Technology Readiness Level of 5 and therefore we are not ready for commercialisation. We are still developing the technology and we need to further our understanding of the material and its structural performance before we are ready to move to the next level. We are also performing tests to assess the long-term durability of the new HDC.

Another important issue to keep in mind is that our new material and engineering solutions are not covered by any of the existing standards and more work needs to be done in this direction to allow adoption and use of such novel technologies. However, we are very excited about what we have seen so far and we hope that the construction industry will see the value of the several innovations we are proposing.

What are your plans after the end of the project?

The work on SHDS has led to some very positive outcomes, but has also raised a number of very interesting questions on both the physical and structural behaviour of HDC, and its many possible uses in structural applications. If given the opportunity, we would like to further develop our understanding of this material and examine its long-term performance (including creep and fatigue) and response to the likes of fire and impact.

SHDS
Funded under H2020-EU.1.3.2.
CORDIS Project page