“Times are changing” is a common phrase that throughout history has been used to describe evolution of thought, process, and development of new methods, means, and products. Times are indeed changing in the A/E/C (Architectural/Engineering / Construction) industry right now, especially in engineering. Horrific events of terrorism within our country from internal and external sources targeted and struck buildings in Oklahoma City in 1995, and the 9/11 attack of 2001 that hit both the Pentagon and World Trade Center. These actions have led, in part, to the evolution of a unique specialization within the structural engineering industry – that of Anti-Terrorism & Force Protection (ATFP) and its inclusive elements of Blast Mitigation and Progressive Collapse Resistance.
Originally, these design requirements were established by the Federal Government by both the Department of Defense and the GSA for use in buildings considered as targets of potential threats. Obvious candidates were/are: military installations, courts, offices and other building types that are of high strategic threat or where high occupancy populations dictated higher levels of building safety and security.
New methods of design with forward thinking forensic analysis has evolved. ATFP requirements are currently in their infancy. Because of this, many of the requirements have not been fully developed. This is due to the new and ever-changing nature of threats and relative infrequent occurrence of terrorist events in the United States. This newness causes the potential for misinterpretation of the requirements by those that have not gone through the process of having designs reviewed and approved by federal representatives. When there is a disagreement or confusion about various provisions, returning to the intent of the requirement provides a rational basis for prudent decision making. The source document for minimum requirements for ATFP is the federal specification Unified Facilities Criteria 4-010-01.
There are of course, other codes and regulations that make this an all encompassing program. Some elements of ATFP are not necessarily within the scope of the actual structure of the building. These include set-back from roads or other structures, non-line of sight of entrances from various directions, and the use of bollards or large landscaping features that prevent vehicles from coming within established proximity of the actual building. Elements of ATFP related to structural design requires attention in several specific areas.
- Progressive collapse resistant construction is required for buildings 3 stories and taller. This can be accomplished by expanding traditional seismic detailing and utilizing perimeter frames.
- Windows and skylights must have blast resistant glass and be anchored adequately to the structure. This requires close coordination of the window supports design.
- Hardening elements or portions of the building that don’t meet standoff distances or require additional protection.
Not limited to federal government buildings, this structural engineering design criteria is being incorporated into other critical projects in order to provide for the safety of not only the structure, but also for those that work in or visit the building. Other municipal, public works, and even private buildings are now looking at including ATFP features to ensure safety of their personnel and critical operations.
Ron Dunn and Dr. Paul McMullin
Ron Dunn, S.E. and Dr. Paul McMullin, S.E, of Salt Lake-based Dunn Associates, Inc. have been involved in ATFP, Blast Mitigation, and Progressive Collapse Resistant buildings for several years. They have consulted with government representatives on all structural aspects of the requirements and have completed several ATFP designs. Recognizing the value of these experiences and future opportunities, Dunn Associates has prepared its own formal ATFP Structural Design Criteria and Standards.