Applied Knowledge

Time Matters: Blast Loads Defined by their “Time History”

Blast loads are defined by their “time history,” which is the trace of over-pressure throughout the load duration.  An idealized blast time history is shown in the figure below (after UFC 3-340-01):

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The pressure (relative to ambient) is on the vertical axis and time is on the horizontal axis.  The blast duration is generally taken to be the amount of time it takes for the blast load to initially decay to ambient pressure with respect to its time of onset (typically assumed to be the time of peak pressure).  Another term that you will hear is ‘impulse’.   The impulse can be thought of as the amount of energy delivered during the blast load, and is calculated as the area under the pressure vs. time curve.  When performing a simplified dynamic analysis, there are two common simplifications made when using blast time histories.

  • Only positive phase of history taken.
  • Use equivalent right triangular shock load shape preserving impulse.

When speaking about the magnitude of blast forces that a building is subjected to, that a design should resist, or that a product needs to protect against, both the peak pressure and duration (or impulse) must be used.  This is because a load of 10 psi (for example) that lasts for 2 msecs can result in significantly less damage than the same 10 psi load that lasts for 20 msecs.

Time matters.

Khaled El-Domiaty and Arturo Montalva Become Principals and Co-Owners of Stone Security Engineering

New York, New York (Oct. 8, 2015 ) – Stone Security Engineering, P.C., the woman-owned small business specializing in protecting people and property from accidental and manmade hazards, announced today that Khaled El-Domiaty, P.E. and Arturo Montalva, P.E. are now Principals and co-owners of the company.

“I am thrilled that Arturo and Khaled are now co-owners of the business.  It is important to me that we all are deeply invested in the success of Stone Security Engineering because that will translate to the quality and professionalism we bring to our clients.  We are looking forward to continuing our record of excellence and creativity in all that we do.”  Hollice Stone, President and Founder

Mr. El-Domiaty received his Masters in Civil Engineering from the University of Missouri-Rolla in 2002. He joined Stone Security Engineering in September 2014 as an Associate Principal/Vice President and Director of DC office Operations. Mr. El-Domiaty brings a remarkable background in design, analysis, research, testing, and  leading-edge solutions. As a key member in the safety and security design fields for more than 14 years, he has played an instrumental role in developing, managing, and delivering a wide array of projects. Mr. El-Domiaty has provided risk assessment services to property owners (government, commercial or industrial) to mitigate potential risks associated with blast, fragmentation, progressive collapse, ATFP, fire and toxic hazards. Additionally, he has performed forensic investigation for litigation support, training, R&D, guideline development, structural design, and remedial and retrofit design for a variety of structures. Mr. El-Domiaty is a licensed professional engineer in DC, VA, MD and NY.

Mr. Montalva studied Industrial/Mechanical Engineering at the Universidad Politécnica de Valencia in Spain. In 2010, he joined Stone Security Engineering as Project Manager. He has been featured in a number of publications including, Structures Magazine and Structural Engineers World Congress.  Mr. Montalva is a specialist in the mitigation of seismic, blast and progressive collapse hazards, with 16 years professional experience in the engineering industry. He has in-depth expertise in linear and non-linear structural dynamics and finite element analysis. Past projects include US Federal Buildings and Courthouses, high threat environment facilities, historic building renovations, development of mandated federal design criteria and numerous US Department of Defense and General Service Administration facilities. Mr. Montalva has utilized his knowledge in numerical methods to develop in-house analytical tools to better support our clients’ needs and to help lead the firm into the future.

Stone Security Engineering remains a small woman-owned business, even with our expanded ownership structure.

Stone Security Engineering, P.C., is an internationally recognized specialty engineering consulting business with offices In New York City and Washington, DC with focus on blast resistance, security and safety engineering and design, predicting and mitigating hazards from explosions, fires and toxins; assessing security and blast vulnerability; research and development, testing and training. Our engineers have participated in multi-hazard vulnerability, threat, and risk assessments for more than 200 facilities around the world and abnormal loading design for more than 300 buildings and structures. The company’s web site (www.StoneSecurityEngineering.com) contains more information.

Six Steps to Specifying Blast Products

The world of blast protection has been rapidly expanding and there are now numerous products and approaches to provide protection from explosive attack. Where there used to be two solutions, there may now be ten. It is critical that security and design professionals understand the strengths and limitations of the various mitigation measures, and how to select products appropriate for their project.

For exterior explosions, the most fragile and vulnerable elements make up the façade of the building: walls, windows, doors, louvers, etc.  These elements are most often not critical for the structural integrity of the building (unless the façade consists of load-bearing walls), but they can represent significant hazards to occupants in the event of an explosion.  For very large or close-in exterior or interior explosions, the structure of the building can be damaged as well.

The process of specifying blast resistant products can be simplified into 6 basic steps.

The following narrative provides a very brief description of each step.

Step 1:  Is Blast Design Required?
While security consultants and blast engineers can make recommendations on this subject, it is the owner who must make the final determination.  Project types that may require blast protection include:

  • Government buildings.
  • Data centers.
  • Iconic buildings in urban environments.
  • Multi-national corporate headquarters.
  • Critical infrastructure.
  • Crowded spaces (shopping malls, movie theatres, sporting arenas, etc.).
  • Buildings located near any of the above.
  • NGO compounds in high threat environments.

The types of threats to be considered in the design should also be identified at this juncture.  This includes the delivery methods (vehicle, backpack, package, etc.).   These delivery methods will lead to the establishment of the locations of the threats.

Step 2:  Identify Vulnerable Elements
Based on the types and locations of the blast threats, the vulnerable building elements can be identified.  These elements may include:

  • Façade.
  • Perimeter structure.
  • Interior beams/columns/walls/slab systems (for internal or external threats).
  • Roof systems.
  • Emergency evacuation and rescue equipment.

Step 3:  Develop Blast Design Criteria
For each type of building element, blast design criteria must be developed.  The primary components of blast design criteria are:

  • Blast load to use for design/analysis.
  • Required response of the elements to the blast loads.
  • Confirmation of compliance methods and requirements.
  • Applicable existing blast design criteria documents (if any) to be used in the design.

Step 4:  Identify Other Design Criteria
Other design requirements may be incompatible with certain approaches to blast resistance, and in other cases they may reduce the number of available products appropriate for a specific project.  Other design criteria to consider may include:

  • LEED.
  • ADA accessibility.
  • Fire resistance/fire egress requirements.
  • Operability (e.g., with respect to windows).
  • Historic preservation.
  • Aesthetics.

Step 5: Supporting Structure Check
One of the critical things to remember when designing structures for blast resistance is that the individual building elements (e.g., door, window, wall, roof system) do not act alone.  All building elements are supported in some manner, and those supportive systems must be able to withstand the blast loads transferred from the original building elements.

Step 6: Develop Specifications
Whether part of an overall construction document package or as a standalone document for one-off procurements, a well-written and complete specification is key to getting the proper blast resistant products.  Specifications should include:

  • Blast design criteria for the element being specified.
  • Engineer/manufacturer/installer/testing facility qualification requirements.
  • Other design criteria (or reference to other specification sections).
  • Blast design guidelines/standards/testing standards.
  • Calculation/test report submittals.