A6/GRK 2250: Strengthening of the impacted side
Table of contents
Project data
| Titel | Title TP A6: Verstärkung von flächigen Massivbauelementen gegen Impakt auf der impaktzugewandten Seite als Teilprojekt des GRK 2250 | TP A6: Strengthening of plane RC elements against impact on the impacted side as part of the GRK 2250 Förderer | Funding Deutsche Forschungsgemeinschaft (DFG) / GRK 2250 – Impaktsicherheit von Baukonstruktionen durch mineralisch gebundene Komposite | Mineral-bonded composites for enhanced structural impact safety Zeitraum | Period since 05/2017 Leiter | Project managers Prof. Dr.-Ing. Dr.-Ing. E.h. Manfred Curbach, Dr.-Ing. Silke Scheerer Bearbeiter | Contributors Dipl.-Ing. Lena Leicht, Saeid Zabihi Moghaddam M. Sc. Co-Betreuung | Co-mentoring Lehrstuhl für Betriebliche Umweltökonomie, TU Dresden Homepage des GRK 2250 | Website of GRK 2250 |
Report in the year book 2021
Well protected
Specimen in the SHB during a compression test
Protections against aggressors, weapons or collision in nature but also in technical applications are often layered. The outer layer distributes the impact load and prevents penetration to underlying materials. In nature, this layer is often lamellar and in the field of armors, carbon-fiber-reinforced epoxy matrices are widely used. The high stiffness and strength characterizes this layer. This layer is backed by a softer layer which is crushed and thus absorbs impact energy or it otherwise damps the impact for the being or structure it surrounds. Elastomers or foam-like structures are well-suited for this task.
However, the mineral-bonded composites studied in this research project are good candidates as well. Different types of lightweight concretes and a concrete with waste tire rubber aggregates were studied in a split Hopkinson bar.
A split Hopkinson bar consists of at least two slender bars which sandwich a specimen. A tensile or compressive wave is introduced in the first (incident) bar and protrudes towards the specimen. The specimen transfers one part of the wave into the second (transmission) bar and the other part of the wave is reflected back into the incident bar by the specimen. Strain measurements on the incident and transmission bar allow for the evaluation of the specimen’s response.
The goal of the small-scale specimens was to compare the material behavior under different loading rates. The energy absorption capacity, which describes the absorbed energy compared to the introduced energy, was of special interest. Above that, the failure mode of the specimens is an important criterion. After finishing the series of tests in the SHB, the most promising materials were chosen and tested on a larger scale. The protection layer was applied on a concrete cuboid specimen that was subjected to hard impact in the drop tower.
Report in the year book 2020
Soft, softer, damping
Cuboid without damping layer after an impact experiment in the drop tower
Impact damage is known in many engineering fields. Therefore, it is a normal task to prevent humans and goods from this type of threat. The protection can be granted by personal armour, but there are also protection systems in cars, stone fall protection systems, and systems to prevent damage of bridge piers due to ship collision. The research question in this project is similar to the aims of other engineers: how to protect humans and goods from the flying debris and other threats? As well as how to reduce the impact damage of reinforced concrete structures? A possibility to reach this goal is the damping of the impact load. For this sake, an energy-absorbing layer needs to be applied to the structure. The question is, how such a layer should be composed. Inspiration from nature and other engineering fields can be helpful to answer this question. In many cases, layered structures are used. They consist, for example in the case of armours, of a hard outer layer backed by other layers that can either behave softly and elastically or crush and thus absorb energy. Ceramics and fibre-reinforced polymers are typically used as outer layers and elastomers or foam structures with a high pore volume and generally applied underneath. Finding cementitious materials with comparable damping properties is the goal of the research project.
The dynamic material properties are examined with the help of a so-called split-Hopkinson bar. This is a facility consisting of two bars that sandwich a specimen. A compressive or tensile wave is generated in the first bar and transferred to the second bar via the specimen. The stress-strain-condition within the specimen can be derived from strain measurements on the bars. Suitable materials for the different layers need to be found in small-scale experiments but the efficiency and the damping properties of the layers and composites also need to be studied on a large scale and compared to one another. Damage criteria are necessary to compare the performance of the different materials by evaluating the damage of the structure beneath. The large-scale tests are carried out on cuboids and plates in the drop tower.
Report in the year book 2017
Bio-inspired impact-resistant structures
An elastic foamy material of the fruit’s peel protects the inside of the fruit
This project aims to increase the resistance of reinforced concrete (RC) elements against impact load using an energy-absorbing strengthening layer on the impacted side. In conventional approaches, the strain energy capacity of a structure, or its inertia, plays an important role to dissipate the energy of an impactor. Current methods of protecting structures against impact loading increase the energy absorbing potential of the elements, by using materials with high density or rigidity, which in turn increases not only a structure’s impact resistance but also its size and weight.
However, depending on the load intensity and strain rate some alternative materials or structures with specific properties can be utilized to protect the buildings against impact without a drastic increase in its weight. Therefore, it is necessary to investigate approaches that, in addition to energy dissipation, can fulfill the other requirements such as the lowest possible dead weight, adaptability to different geometries, cost and resource efficiency, and so on. For example, applications of foam-like materials or light honeycomb-like structures are known solutions. In different fields of science, in nature or industry, e.g., automotive or packaging industry, there are many different solutions established for damping elements or mechanisms. A systematic investigation and in-depth analysis of these approaches is the basis for developing impact-resistant layers which are suitable for use in reinforced concrete structures.
In a first step, the solutions found are evaluated regarding their efficiency for dynamic load scenarios and their applicability to energy-absorbing strengthening layers for RC structures to identify the most appropriate approaches. In a second step, the most promising solutions will be adapted for reinforced concrete elements and experimentally investigated, accompanied by numerical simulations.