Technical note | Modelling Australian Red Brick and Bluestone Walls in VAPO
To confidently predict structural and building damage due to explosive blast loads, Threat Mitigation Group, Weapons Systems Division, is comparing, improving and validating existing modelling tools. For conventional structures, the Vulnerability Assessment and Protection Options (VAPO) software, a product of the Defense Threat Reduction Agency (DTRA), is DSTO's primary effects prediction software tool due to the rapidity with which an analysis can be conducted and the ability of the software to predict potential human casualties due to blast or building debris. VAPO is well-suited to model and analyse complex urban scenarios but lacks the ability to model certain Australian building materials. This report provides details on how to input material engineering data for structures with walls composed of Australian Standard size single and double red brick as well as bluestone building blocks. The response of these materials to blast loads was determined through a single degree of freedom analysis which represented a dynamically equivalent system.
The objective of this work was to provide the Threat Mitigation Group, and thus the Defence Science and Technology Organisation (DSTO), with a means of predicting the response of a building to an explosive blast load where the building is composed of Australian standard size red bricks or bluestone blocks. The Threat Mitigation Group uses the Vulnerability Assessment and Protection Options (VAPO) software, licensed from the Defense Threat Reduction Agency (DTRA) of the United States, Department of Defense, to model conventional buildings. VAPO allows the user to create complex building structures, which can be analysed for structural damage and personnel casualties when subjected to a blast load from high explosives. As provided, the VAPO software contains material data for Concrete Masonry Units (CMU), a form of masonry commonly employed in the United States of America. The CMU is not similar to Australian size red brick and therefore the damage to the building, and injury to building occupants from building debris, could not be predicted accurately by VAPO if the standard CMU was used when modelling a building containing Australian masonry.
The resistance of Australian red brick and bluestone to deformation when subjected to blast loading was determined using a single degree of freedom analysis which allows the masonry to be replaced by an idealised, dynamically equivalent system. The Component Explosive Damage Assessment Workbook (CEDAW), and the Single-degree-of-freedom Blast Effects Design Spreadsheet (SBEDS), both products of the U.S. Army Corps of Engineers (USACE), allow the user to predict a resistance-deflection function based on material properties and geometries, which is then used to predict the pressure and impulse loads at which a component will deform or fail.
VAPO uses Pressure-Impulse (P-I) diagrams when determining building damage. To 'create' the Australian masonry materials in VAPO required the adjusting of Concrete Masonry Unit properties until it behaved in a similar manner to Australian red brick and bluestone. This was effected through matching of P-I diagrams and, in this manner, it became possible to model buildings containing Australian red brick and bluestone materials in VAPO.
This work is highly relevant to Defence outcomes as it falls within the DSTO National Security mandate and provides the ability to advise on the probable damage to Australian buildings, and potential loss of life, from terrorist threats on home soil.