The following is an excerpt.
If SFI CASA´s partners were asked to make a wish-list, some of them might put a validated material model for concrete on top.
Possibly, the Norwegian Defence Estates Agency (NDEA) would be among these. JSimply because an improved material model on concrete would be highly useful when dimensioning and designing facilities like centres for military operations, bunkers, aircraft- and air-raid shelters and other installations. For the time being two of NDEA´s senior engineers and researchers, Sumita Dey and Oda Toreskås engage deeply in SFI CASA´s activities on the topic.
They aim towards creating a virtual environment for safer and more cost-effective designs of protective structures.
Hope to replace physical tests
«Our main goal is to develop numerical models that can help NDEA to improve the design capacity of buildings and protective structures against any given threat. What we hope for is to replace physical tests with virtual simulations», Oda Toreskås explains. Dey and Toreskås work with research-and-development at the NDEA National Centre for Protection of Buildings. Toreskås heads a 3-year project funded by The Norwegian Ministry of Defence. The project is set up to develop complete and cost-effective protective solutions for buildings exposed to missile impact. In some parts, they join forces with Professor Tore Børvik and Post Doc Martin Kristoffersen at SFI CASA.
NDEA and SIMLab have a long story of collaboration. The starting point for the ongoing work is a previous joint project on a material model for concrete.
«The results back then were promising. Now we need more data to calibrate and validate the model», says Sumita Dey.
Ballistic capacity and blast loadings
Blast loads, either from an accident or a terrorist attack, are always accompanied by several damaging fragments hurled out at high speed. The blast wave arrives shortly after.
Sumita Dey is an expert on ballistic protection. She earned her PhD at SIMLab in 2004, and explains:
«Because of the last year´s development in the threat situation, NDEA addresses the need of facilities that could withstand large penetrating missiles such as warheads. Fragments from blasts become penetrating objects that vary in size and speed. The fragments could decrease the materials ability to withstand the subsequent blast wave». Just before Easter, the senior engineers from NDEA entered the SIMLab facilities.
Teamed up with MSc students
They teamed up with Tore Børvik, Martin Kristoffersen and MSc students Marte Vestermo Nesje and Guri Lillehaug. The title of the MSc student´s thesis is «Combined impact and blast loading on concrete plates. They are to make numerical models in LS-Dyna.
This visit was Oda Toreskås second this winter. Early in February, she and the students cast concrete plates of three different qualities.
READ MORE: Preparing to Attack Concrete
In SIMLabs Ballistic range, the plates were impacted by projectiles to reveal their ballistic capacity. Next step was to subject some of the impacted plates to blast loadings in the Shock Tube to investigate to what extent the impact had affected the blast resistance.
The tests imply filming with high-speed cameras. The recordings give detailed tracking of how the material behaves when the bullet hits or the explosion happens.
Relevant for other partners
The students work is also relevant for CASA-partner The Norwegian Public Roads Administration. They run the project ferry-free coastal highway E39 from Kristiansand to Trondheim.
The E39 project can realise the world´s first submerged tubular bridge. Irrespective of the choice of structure, the materials in use have to withstand powerful explosions and fragment impact – such as those from tanker truck accidents.
READ MORE: BBC Radio Popped up in the Shock Tube
Tests might be extended
NDEA often deals with structures too large and too complex to test physically. Thus, a better way of designing protective structures would be to combine experimental studies and numerical calculations.
During the second part of the concrete project, they look deeper into the material model. Then, in the final phase, there is time for some full-scale tests to validate the material model.
Project leader Toreskås says NDEA hope for further collaboration with SFI CASA. One option is to extend the tests on concrete – for instance to thicker plates and stronger qualities.
During this project, they also do tests at NDEA´s facilities.
«Collaboration is essential».
Oda Toreskås has an MSc from NTNU in nanotechnology. She has worked as a materials engineer in Aker Solutions and the Norwegian Defence Material Agency. Sumita Dey is one of several employees at NDEA that have earned their degrees in SIMLab.
The collaboration between SIMLab and NDEA has been going on for more than 20 years.
Professor Tore Børvik was once a full-time employee of NDEA. He still has a 20 per cent position there. Dey states that nationally, research environments that work with structures exposed to extreme loading are limited.
Likewise, there are just a few people at SIMLab and NDEA specialised on penetration.
«Thus, the collaboration between us is essential», she says.
Joint research on concrete as construction material started 10 years ago. Now the demand for more knowledge is increasing. Dey thinks the needs of NDEA and other partners can indicate the future direction of research in SIMLab.
NDEA project in three parts:
- The first part focus on the development of numerical calculation methods for protective structures of concrete.
- This work implies both experimental tests and numerical simulation. The aim is a validated material model for concrete exposed to penetrating objects.
- Further, the model forms the basis for experiments on penetration from large missiles and combined effects of penetration and blast in concrete.