UCSD announced on Dec. 13 the beginning of construction on the worldas first bomb blast simulator. The simulator will be built at the Field Station at Camp Elliot, and will be used by structural engineers at the Jacobs School of Engineering to test the effects of bomb blasts on structures.
The blast simulator is constructed through a contract from the Technical Support Working Group, which is a federal interagency entity organized to fight terrorism. The results from the simulator will be used to devise methods to protect high-risk buildings in the event of terrorist bombings.
“”No two blast loads are the same. In order to do detailed development, we need to do fully repeatable tests which can only be done in a lab,”” UCSD Jacobs School of Engineering dean Frieder Seible said. “”The whole goal for us is to move from field testing on buildings to field testing on components to quasi start testing in the laboratory to real-time blast testing under laboratory conditions. And this is what we’re doing at Camp Elliot.””
The project will cost $4.2 million and is expected to be complete and active by early 2005.
Previous field tests have been conducted at various air force bases, including at the White Sands and Kirkland bases in New Mexico. Until now, these test blasts done on real structures have been the only option for engineers. According to Seible, completely accurate results are impossible to obtain during these tests, as each blast differs from the next.
There have been field tests conducted on full-scale four-story structures, along with more focused tests that measure how a certain element of a structure will hold up under the impacts of a blast. These more focused experiments usually test the strength of columns, as the ability of a column to hold up under a blast is directly related to how the structure will react. While the blast load typically impacts only a column, if the column is destroyed, the structure will not be able to stand.
“”For example, here in America, like in the Oklahoma City bombing, the blast loads typically affect our structures in a way that there is a regressive structural collapse following the initial blast loading,”” Seible said. “”This collapse accounts for most of the casualties.””
The previous tests on columns have showed that wrapping a column in carbon composite can help the column to withstand the original blast.
Another technique is to wrap the columns in steel. This technique has also proved successful in stopping much of the damage so far. These techniques strengthen the column and make it able to withstand the bending and swaying that occurs during and after a bombing. Both wrapping materials can be retrofitted to structures, making current buildings safe against blasts without changing most of the structure of the building.
The simulator will allow for further tests on columns and buildings to take place, both using previously developed technologies in old and new ways and developing new technologies. The engineers will be able to refine the wrapping technologies by continuous tests on the same structure. They will also be able to use these technologies on parts of the building not previously tested, such as walls.
The blast simulator is constructed as a floating slab on rubber bearings, which ensures that the excitations from the blasts will not be felt anywhere else. The blast is simulated by creating an impact through loading units which can be adjusted according to the strength the engineer would like to test. The loading units are elastic pads and can be shaped and arranged differently to create different layouts for an experiment and allow for more tests. The blast simulator does not simulate the thermal energy which occurs during a blast, but only the pressure created. According to Seible, this is because in most cases, thermal load is not important in terms of the structural response.
“”The goal of the program is to identify the response of structures during the blast loads,”” Seible said.
The tests will be focused on common blast scenarios. These scenarios will be repeated multiple times in order to determine the ability of a structure to resist energy imposed by the blast. High-speed cameras will be used to capture the result. The ability to view each moment of impact is important for the development of structural technology, and was not available for use in field tests as the cameras would have been destroyed in the blast. The tools used in these tests are particular to the laboratory conditions and are some of the main reasons behind the change from field tests to simulations.
“”It is very important to us to develop analytical tools which allow us to simulate these blast loads and their impact on structures. So what we’re doing here is developing a facility which will allow us to validate our analytical model and tools,”” Seible said.
The blast simulator will be created in a site adjacent to the world’s first outdoor shake table, which will be completed by September 2004 and will be used to test structures during simulated earthquakes.
