Trends in building and infrastructure design have been underway to mitigate terrorist activities and threats for a number of years. September 11, 2001 shocked everyone and forced us into realizing the need to implement these standards in current design.
Terrorist Threat / Risk / Vulnerability
- Determination of Threat and Risk is primarily a function of where the building is located and what the building is going to be used for. This information is primarily collected from law enforcement agencies. Beyond law enforcement activities, there is not a lot that can be done to minimize threat and risk accepting that there is a need for a specific type building at a specific location.
Example: It probably does not make sense to locate a courthouse in a rural compound far removed from a city
- Vulnerability can be addressed by the A/E team and incorporated into the construction documents. Things to consider include sight selection and barriers, building security (physical and informational systems), and building performance.
Site Selection and Barriers that can be addressed by the Civil Engineer
- Set-backs – minimizes bomb blast effects, provides detection zone for intrusions
- Blast resistant walls – deflects blast originating from vehicles or pedestrians.
Warning: could deflect blast onto adjacent property
- Impact resistant bollards – prevents vehicles from ramming into the building and transporting blast agents closer to the building
- Perimeter fencing – prevents pedestrians from transporting blast agents closer to the building
Building Security is best addressed by the Architect
Building Performance that can be addressed by the Structural Engineer
- Global Blast effects on building
- Internal and External Blast Effects on building
- Progressive Collapse
- Global evaluation is just that, looking at the entire building to see how it will perform given a blast at a certain location inside or outside of the building. Global blast effects can be evaluated by various methods including equating equivalent blast forces and effects to static forces such as those used in wind analysis and design, or dynamic forces used to design buildings for resisting earthquakes.
- Assessment of blast effects on building components or cladding addresses the parts of a building when a charge is detonated near a column or beam. The performance of that beam or column may be critical to the protection of critical area within the building or critical to the stability of the building.
- The level of progressive collapse design for a structure is correlated to the occupancy category of the structure. The three levels of resistance to progressive collapse include the Tie Force Method, Alternate Path Method and Enhanced Local Resistance.