Advanced Structural Materials

Development and investigation of advanced structural materials (e.g. shape memory alloys) for use in civil infrastructure is our primary mission. The importance of building modern structures and the renovation and conservation of existing infrastructure increases, therefore, advanced structural materials to improve the load-carrying capacity and serviceability of infrastructure and designing new structures are required. Our research aims to make urban living easier, more sustainable, more comfortable, more secure and more functional. Within our research area, new materials and systems are developed and studied in small and large-scale size to show their application feasibility for civil infrastructure. Current research projects include:

  • Feasibility study of a fiber reinforced polymer (FRP) composite train wheelset towards reduction in noise and weight
  • Mechanical modeling of concrete members strengthened and prestressed by a novel iron-based shape memory alloy reinforcement
  • Iron based Shape Memory Alloys as Shear Reinforcement for Civil Structures
  • Investigation on the short-term and long-term behavior of the developed iron-based shape memory alloy at Empa
  • Thermo-mechanical modeling of structures strengthened by iron-based shape memory alloy elements

To achieve our missions, we are strongly in collaboration with national and international research and industrial partners and experts in the field, including: material scientists, manufactures, acoustic scientists, electrochemistry scientists, engineering scientists and consulting and construction sectors. Our basic research and collaboration with industry result in “technology transfer” and “product development”.

 

Prestressed shape memory alloy reinforcement for 3D Concrete Printing
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With 3D concrete extrusion, custom concrete elements can be fabricated without formwork. An interdisciplinary research team embedded in the National Competence Centre of Research in Digital Fabrication (NCCR DFAB) is developing a concrete extrusion process. In order to apply concrete extrusion at building-scale, new reinforcement strategies are needed. Therefore, in a joint research study between Empa and ETH, we want to investigate the feasibility of prestressed shape memory alloy reinforcement for 3D printed concrete elements. The goal is to reduce weight and material of structural concrete elements, exploiting the full potential of both the concrete extrusion process and new prestressing strategies. Design and developing structurally optimized 3D printed concrete elements, their integrated reinforcement layout, strategies for its prestressing, analysis and optimization of the elements together with 1:1 prototyping and testing are planned.

Involved staff: Moslem Shahverdi, Pietro Lura

Project Partners:

  • ETH Zurich
Development and characterization of new generation of FeMnSi based shape memory alloys: Ultra-high Fe-SMAs
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In civil engineering, the formation of a recovery stress after heating and cooling of a strained FeMnSi based shape memory alloy (FeMnSi-SMA) is an essential characteristic to evaluate its potential as pre-stressing element such as in concrete. Recovery stress is dependent on the shape memory effect (SME) and the yield stress of the FeMnSi-SMA. Different heat treatment conditions, e.g. different aging temperatures and times, lead to the formation of different number densities and sizes of precipitates, which affect the SME and yield stress, and as a result, the recovery stress varies. In the first part of this PhD work, the impact of heat treatment of an existing FeMnSi-SMA with the composition of Fe-17Mn-5Si-10Cr-4Ni-1(V, C) (mass) % on the recovery stress will be studied. Besides, in the second and third parts of the PhD work, the effect of thermomechanical treatment (i.e. deformation of the FeMnSi-SMA at elevated temperature) on the recovery stress as well as the modification of the alloy composition to achieve better performance will be studied.


Involved staff: Yajiao Yang, Moslem Shahverdi, Christian Leinenbach and Ariyan Arabi-Hashemi.

Project Partners:

Self-centering and confining memory steel reinforcements
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Strengthening of existing RC bridges becomes more and more important due to the large number of existing bridges, which are aging or were designed according to old standards. Considering seismic loading, strengthening is even more demanded as most of the bridge columns do not satisfy the new regulations for seismic performance. Prestressing is known to provide recentering capabilities. However, the available techniques are either vulnerable to corrosion or are prohibitively expensive. In this project, an innovative application methodology for selfcentering and active confinement of concrete columns in bridges by using memory steel reinforcement will be developed. The proposed technology could have tremendous societal impact with respect to saving lives after extreme events and economic well-being of the affected area. By keeping bridges and the highway network open to traffic, ambulances, fire trucks, first responders, and damage assessors will continue to have the mobility that existed prior to the disaster. Such applications will be studied for the first time and the developed technique/product will be applied in a pilot project.

Involved staff: Moslem Shahverdi, and Julien Michels

Project Partners:

  • Swiss Innovation Agency - Innosuisse, financing
  • re-fer (technical support and material supply)
Mechanical modeling of concrete members strengthened and prestressed by a novel iron-based shape memory alloy reinforcement
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In the this project, the idea is to embed bars made of the novel iron-based shape memory alloy (Fe-SMA) with standard rib geometries in grooves in the cover of concrete structures by using a cement-based grout in order to strengthen and prestress existing RC structures. The bond behavior of the SMA bars is different and more complicated as compared to that of conventional internal steel reinforcement bars because of the different elastic modulus of iron-based shape memory bars, the heating process, and phase transformation in Fe-SMA bars, the existence of prestress force in the Fe-SMA bars, and the NSM technique. Based on the experimental results, existing closed-form analytical expressions and models from the literature will be adapted, extended, and validated for the application of Fe-SMA bars as prestressing elements to strengthen and prestress RC structures. Furthermore, advanced FE modeling of material behavior, bond behavior, and the NSM Fe-SMA strengthened RC beams will be conducted by using the 3D FE-software Abaqus.



Involved staff: Bernhard Schranz, Moslem Shahverdi, and Christoph Czaderski

Project Partners:

  • SNSF (financing the project), Bern
  • re-fer (material supply and technical support), Seewen
  • ETHZ, Zurich

 

Investigation on the short-term and long-term behavior of the developed iron-based shape memory alloy at Empa
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A cost-effective iron-based SMA (Fe-SMA) has been developed for application in civil engineering structures. The composition of the developed alloy is Fe–17Mn–5Si–10Cr–4Ni–1(V,C) (mass%). This Fe-SMA exhibits high tensile strength, excellent shape recovery stress (prestress force), and high elastic stiffness. Moreover, its material cost is low and it is easier to manufacture than nickel-titanium (NiTi) alloys. Recently, Fe-SMA strip and bars production has been started at an industrial scale. In this project, the experimentally determined properties of such industrially produced Fe-SMA strips and bars are investigated, and their recovery stress and recovery strain have been measured. The effects of prestraining and maximum heating temperature on the obtained recovery stress have been studied.

Involved staff: Moslem Shahverdi, Julien Michels, Christoph Czaderski, Matteo Breveglieri, and Yajiao Yang

Project Partners:

  • re-fer (financing, technical support, and material supply), Seewen

 

Thermo-mechanical modeling of the concrete elements structures by iron-based shape memory alloy elements
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The development of new SMAs in the recent years, with the focus in research shifting to new Fe-Mn-Si SMAs, a significant cost reduction can be achieved and will help to broaden the application fields of SMAs.
An important step to extend the application range of the advanced material as iron-based shape memory alloys is having reliable simulation tools. A lot of work has already been done in this respect, but reliable tools to simulate the composite system (SMA bars/strips and the sub-structure) during activation of the SMA are still missing. The activation of iron-based shape memory alloy bars/strips is a process that incorporates four different physical processes: electrical current flow, heat propagation, continuum mechanics and martensitic phase transformation. In this project a macroscopic analysis of the interaction between the individual constituents of iron-base shape memory alloy bars/strips during the activation procedure is intended. While the sub-structures are modeled using elastic-plastic constitutive models, two different phenomenological material models are being employed for the SMAs. The proposed approaches succeed in reproducing experimental observations attributed to the SMA-concrete interaction.


Involved staff: Moslem Shahverdi and Paul-Remo Wagner (now PhD student at ETHZ)

Feasibility study of a fiber reinforced polymer (FRP) composite train wheelset towards reduction in noise and weight
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Railway noise is often an important source of annoyance for people near the railways. The constantly increasing market demand in transport leads to a less calm transport system affecting many citizens both during the day and over the night. Within the scope of this project, feasibility of application of FRP composites materials to manufacture a train wheelset which, potentially, will generate less noise is studied. In addition to noise reduction, such FRP wheelsets will lead to weight savings which brings associated benefits of high-speed, reduced power consumption, lower inertia, less track wear and the ability to carry greater pay-loads. 3D finite element models are being developed to analyses the stresses and deflection of the FRP wheelset.

Involved staff: Moslem Shahverdi, Christoph Czaderski, Masoud Motavalli

Project Partners:

  • BAFU, Ittigen
  • PROSE AG, Winterthur
  • Carbo-Link, Fehraltorf
  • Empa Laboratory Acoustics / Noise Control, Dübendorf
Iron based Shape Memory Alloys as Shear Reinforcement for Civil Structures
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Empa developed a new iron based shape memory alloy (Fe-SMA). This material can be used as prestressing system for concrete. In this project, ribbed Fe-SMA bars will be used for shear strengthening of reinforced concrete structures so that shear cracks width can be reduced and new shear cracks occur under higher loads. So far, small scale experiments for investigating the overall principle have been carried out. The tests showed the feasibility of Fe-SMA shear reinforcement. The bending of the SME did not hinder the system to work. Based on the understanding and results from small scale experiments of the project, T-beams with a span of 5 m have been designed to study the application of Fe-SMA bars for pre-stressed shear strengthening of concrete beams.

Involved staff: Moslem Shahverdi, Christoph Czaderski, and Julien Michels

Project Partners:

  • Swiss Innovation Agency - Innosuisse, financing
  • re-fer (material supply), Seewen