Two new standards from ASCE’s Structural Engineering Institute offer critical provisions for civil engineers planning, designing, constructing, or assessing buildings.
Donald Dusenberry, P.E., F.SEI, F.ASCE, is the man behind both standards, having chaired both committees. His reputation speaks for itself: helped lead ASCE’s Pentagon building investigation after 9/11; former president of SEI; 2021 Engineering News-Record newsmaker.
Dusenberry spoke recently with Civil Engineering Source about his work.
Civil Engineering Source: I know these two standards are wholly separate, but with them publishing at around the same time, do you connect them in any way? Do they almost work in conjunction?
Don Dusenberry: These standards have been developed independently. It is just a coincidence that they have finished at about the same time. That said, they have related content, and a user of one most probably would be a user of both.
The disproportionate collapse mitigation standard is written to be independent of the cause of initial damage to a structure. The first failure could be from a vehicle collision, storm effects, or even a localized design or construction flaw, among other things. But, of course, an explosion could be a cause of initial damage. Certainly, if an engineer is in the building security business, both standards would be essential references.
Source: This is the first revision for ASCE 59. What fundamental changes can engineers expect to find in this update?
Dusenberry: After several years in use, the committee that maintains the Blast Protection of Buildings standard (ASCE/SEI 59) saw the need for an update and revision. Issued in late 2022, the new edition of this important standard improves terminology, updates load combinations, now includes a detailed approach in the provisions for dealing with fragmentation (and still contains a more elaborate approach in the commentary), and provides new guidance about roofs and fenestration.
In addition, the standard has updated sections on concrete, steel, and composite structures. It is a modest update, but the revisions bring in essential new information, expand guidance on several critical issues, and add clarity.
Source: I gather that ASCE 59 dates back to September 11. Was there a similarly specific impetus for work on ASCE 76?
Dusenberry: Actually, the concept to prepare a standard on blast effects preceded 9/11. Talks were underway prior to, and actually had a meeting scheduled on the very day of, the attacks on Washington and New York in 2001. Similarly, professional discussion about the problem of disproportionate collapse and means to prevent it has been going on for decades – back as far as the 1970s at least. The series of extraordinary failures during the late 1990s and the early 2000s continued to justify discussions about why local failures sometimes lead to widespread collapses and how to design to mitigate the effects. Perhaps the sense of urgency increased following 9/11 but, in fact, our understanding of the phenomenon, our means to analyze collapse mechanisms, and data on structural performance under extreme deformations all evolved in recent years.
The profession is ready, and the timing is right to publish a standard to support engineers working to prevent disproportionate collapse.
Source: Can you highlight why the performance-based approach made the most sense for ASCE 76?
Dusenberry: The techniques we use to analyze and design for collapse prevention once there is an initial failure can be very different from the techniques we use to establish good performance during service conditions.
In addition, there are challenges associated with controlling costs and avoiding potential conflicts with performance for other conditions that must be considered – for example, seismic resistance in which strong column and weak beam balance is preferred vs. collapse prevention in which strong beams are a potential solution.
These influences demand creativity from engineers while they develop designs to efficiently resist all hazards, and all loading conditions from service and extraordinary. Constraints imposed by prescriptive designs are counterproductive.
This standard is a significant entry into performance-based design that allows engineers to explore innovative means to assess and economically raise the performance of structures for all hazards.
Learn more about ASCE 59-22.Learn more and pre-order ASCE 76-23.