September 23, 2011
Highlights of the 14th ISIEMS
by & Andy Coughlin Brian Katz
This week myself and fellow co-worker, Andy Coughlin, attended the 14th International Symposium on Interaction of the Effects of Munitions with Structures (ISIEMS) conference in Seattle, Washington. This conference represents a collaborative effort of North American, Asian, and European blast engineers to come together and share advancements and conceptual innovations with the hope of equipping engineers with the best tools to mitigate man-made threats and implement physical security design solutions. Andy and myself were among an impressive roster of speakers presenting on a wide variety of topics.
Andy Coughlin: Designing for Close-In Blast Using Spall-Resistant Cementitious Composites
It is well known that close-in blasts can cause damage that is quite different from failure mechanisms due to far-field blasts. Spalling, scabing, and breach of concrete elements due to close-in blasts can be predicted with empirical curves by Marchand and Plenge and those implemented into the U.S. military document UFC 3-340-01. Mitigation of spalling is usually achieved by increasing standoff, when possible, or increasing concrete thickness. However, the concrete thickness required to prevent spall due to close-in blasts from even small charge weights is often prohibitive because of cost and spatial constraints.
Alternative materials for breach and spall mitigation include steel plates, fiber-reinforced concrete (FRC), and micro-reinforced concrete: a cementitious matrix reinforced with multiple layers of steel wire mesh. All three materials have been shown to reduce spall in close-in blast tests; however, little information currently exists for the design of these materials for close-in effects. The goal of this research was to develop curves similar to those in UFC 3-340-01 that would provide design guidance for these alternative materials.
Blast test data from literature and unpublished sources was aggregated and plotted based on normalized parameters capturing the effects of charge weight, standoff, specimen thickness, and compressive strength. Finite element models were developed to accurately predict damage for known test cases using triaxial concrete damage models: Arbitrary-Lagragian-Eulerian (ALE) elements for surrounding air, and the Jones-Wilkins-Lee (JWL) equation of state for high explosives. Parameters such as standoff and specimen thickness were varied in the models and the results were used to fill in data points where no test data was available. Design procedures are presented which will aid blast designers in the preliminary design of spall-resistant elements and give facility owners a greater range of tools to mitigate close-in blast effects.
Brian Katz: An Integrated Approach to Facade Design and Multi-Hazard Risk Mitigation
Current analytical and design practice considers non-structural facade systems primarly for their contribution to a structure's mass and encourages a limited interaction between cladding elements and the building superstructure. However, this study explores the potential for facade systems, engineered to meet specified performance goals in response to extreme loading, to additionally enhance global building response to a variety of hazard events - seismic, severe storms, blast, fire, etc. Specific focus is given to the capacity for a blast-resistant curtain wall system to impact the stiffness and expected dynamic response of a structural system based on the character of the connection between the two building systems. The observed positive correlation indicates the potential for a robust building envelope system with equally robust connections to the superstructure to be incorporated into multi-hazard design solutions, seeking to optimize building performance while minimizing design efforts and construction costs.
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