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Adam Hapij Lectures on "Blast Effects on Buildings"
By Ivan Durbak

On May 26th, 2005, the Ukrainian Engineers' Society of NYC presented a lecture by Adam W. Hapij, P.E., civil engineer at Weidlinger Associates, Inc., NYC, on "Blast Effects on Buildings".

Mr. Hapij began with a broad overview of terrorist attacks in recent history, categorizing the 2,667 explosive incidents in the U.S between 2000 and 2003. He then described the blast threats from explosive weapons (mortars, hand grenades, improvised explosive devices, vehicle bombs, bulk high explosives) as well as non-explosive blast threats (from aircraft impact, car impact, and gas explosions).

Mr. Hapij next detailed the general features of explosion phenomena: detonation, afterburning, flash, and fragmentation. He explained the mathematical models and empirical relationships that are used to approximate these explosion phenomena, in particular the Friedlander Decay Equation that characterizes the temporal variation of pressure, using Kingery Bulmash Relationships to determine peak incident pressure and decay parameters. Graphical techniques were used to illustrate attenuation of blast effects with distance, reflected pressure, effects of burst position, and air blast damage criteria.

Mr. Hapij reviewed various construction materials - steel, concrete, timber, and unreinforced masonry - comparing their strengths and weaknesses in withstanding blast effects. He examined the consequences of blasts on structural and architectural building components, highlighting the propensity for loss of structural integrity, propagation of failure front, and response of conventional glass to blast.

Mr. Hapij then explored in detail design issues in mitigating blast effects, including hardening, perimeter protection, and protective design with curtain walls. He explained that, while the U.S. does not have Building Code requirements for blast resistance, there are many federal design guidelines and manuals that provide important design recommendations; one such recent example is FEMA 452 " Risk Assessment: a How-To Guide to Mitigate Potential Terrorist Attacks Against Buildings" (2005).

Mr. Hapij outlined various blast response simulation methodologies used to study blast phenomena and their effects on buildings, especially the Single Degree of Freedom (SDOF) analysis used by the majority of structural design industry. Other more involved simulation techniques include: (1) nonlinear dynamic finite element analysis, including large deformations and inelastic constitutive models; (2) decoupled simulation of air-structure interaction, and (3) more sophisticated fully-coupled approach using the computationally demanding ALE (Arbitrary Lagrangian Eulerian) or Standard Coupler Interface (SCI) methods.

Finally, Mr. Hapij offered a design philosophy based on a balanced, practical approach to protect against specific threat locations, to protect against ill-defined loads, to utilize increased redundancy to redistribute extreme loads, to allow for load reversals, and to eliminate threats both within and adjacent to a building.

Throughout the presentation Mr. Hapij used vivid imagery and animations to demonstrate, with startling clarity and in slow motion, blast phenomena and effects. He kept the audience engaged and involved with a balance of technical material and practical real-world problems.

After the formal presentation, the audience participated in a spirited collegial debate over questions such as "could the WTC structural building collapse on 9/11 been anticipated and prevented?"

The evening finished with informal and convivial discussions over food and drinks.

The lecture counted towards NYS continuing education credit for licensed professional engineers.

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