Blast & Impact Loading & Response of Structures
Blast analysis and design for U.S. Government and Department of Defence facilities are performed in accordance with a clearly defined set of codes and standards (e.g., UFC, GSA, etc.). Other public facilities, such as Veterans Administration hospitals and courthouses often invoke these same standards. In the case of privately-owned commercial buildings, in which the owner desires to incorporate blast protection as an additional layer of security, the design process can be performed in accordance with ASCE 59-11, Blast Protection of Buildings. This standard provides guidance on selecting performance criteria for structures and façade, materials detailing, and determination of blast loads. For exterior blast cases, empirical scaling relationships that relate key parameters, such as charge size and standoff, can be used to estimate corresponding peak pressures and impulses. These relationships can be used for the design of primary structure and façade elements. For confined or interior blast scenarios (e.g., lobbies, mailrooms, loading docks, parking garages), ASCE 59-11 provides guidance for estimating peak gas overpressures and applying them statically for design purposes. The standard also identifies that when blast effects are expected to cause plastic hinging or localized failure of individual structural elements, the damaged state of the structural system as a whole shall be evaluated to verify that global stability is maintained.
This paper will present an analysis approach developed for estimating internal blast pressures, and approximating the extent of damage in a complex internal building structure. An example application of design for progressive collapse in a below-grade reinforced concrete parking garage structure will be demonstrated. Parking garage blast is a common threat scenario and is based upon real world events, such as the terrorist attacks in Barcelona, Spain (1987) and at the WTC NYC (1993). The postulated scenario for this paper will involve an internal blast from a vehicle parked in a representative parking deck structure. A pragmatic analysis approach, which makes use of a range of tools (empirical, FEA, and CFD), will be developed to predict blast pressures, evaluate structural response, and assess levels of damage in an economical manner. Based on the resulting damage to the building structure, and redistribution of forces to the remaining structure, an assessment of the potential for progressive collapse will be performed to ensure building occupants can safely evacuate.