5.1 Goals of the Design Approach

It is impractical to design a civilian structure to remain undamaged from a large explosion. The protective objectives are therefore related to the type of building and its function. For an office, retail, residential, or light industrial building, where the primary asset is the occupants, the objective is to minimize loss of life. Because of the severity of large scale explosion incidents, the goals are by necessity modest. Moreover, it is recognized that the building will be unusable after the event. This approach is considered a damage-limiting or damage-mitigating approach to design.

To save lives, the primary goals of the design professional are to reduce building damage and to prevent progressive collapse of the building, at least until it can be fully evacuated. A secondary goal is to maintain emergency functions until evacuation is complete.

The design professional is able to reduce building damage by incorporating access controls that allow building security to keep large threats away from the building and to limit charge weights that can be brought into the building.

Preventing the building from collapsing is the most important objective. Historically, the majority of fatalities that occur in terrorist attacks directed against buildings are due to building collapse. Collapse prevention begins with awareness by architects and engineers that structural integrity against collapse is important enough to be routinely considered in design. Features to improve general structural resistance to collapse can be incorporated into common buildings at affordable cost. At a higher level, designing the building to prevent progressive collapse can be accomplished by the alternate-path method (i.e., design for the building to remain standing following the removal of specific elements) or by direct design of components for air-blast loading.

Furthermore, building design may be optimized by facilitating evacuation, rescue, and recovery efforts through effective placement, structural design, and redundancy of emergency exits and critical mechanical/electrical systems. Through effective structural design, the overall damage levels may be reduced to make it easier it is for occupants to get out and emergency responders to safely enter.

Beyond the issues of preventing collapse, and facilitating evacuation/ rescue the objective is to reduce flying debris generated by failed exterior walls, windows and other components to reduce the severity of injuries and the risk of fatalities. This may be accomplished through selection of appropriate materials and use of capacity-design methods to proportion elements and connections. A well designed system will provide predictable damage modes, selected to minimize injuries. Finally, good anti-terrorist design is a multidisciplinary effort requiring the concerted efforts of the architect, structural engineer, security professional, and the other design team members. It is also critical for security design to be incorporated as early as possible in the design process to ensure a cost-effective, attractive solution.