Applied Knowledge

Blast Testing of Unbonded Post-tensioned Concrete Slabs

Given the large number of existing post-tensioned concrete structures and the number of new post-tensioned structures anticipated in the U.S. and worldwide, there is a critical need to determine how they respond to blast loads and to develop practical guidelines for their design when blast resistance is required.

Currently, there is a lack of data on the blast performance of post-tensioned structures.  As a result, end users and designers are typically conservative in their assumptions and tend to underestimate the blast resistance of structural components with un-bonded post-tensioned reinforcement.  Information on the blast behavior of these structures and structural components would be beneficial for vendors, designers, regulators, and standards development organizations worldwide.

Stone Security Engineering and Stone-OBL, in conjunction with Structural Technologies/ VSL, have lead an investigative effort to conduct open-air blast testing on an un-bonded Post-tensioned slab reinforced with Structural Technologies’ proprietary systems.  The slab was specifically detailed by Structural Technologies to withstand blast loading and was tested at the Stone-OBL blast testing site outside of Bend, Oregon.

The 16-ft by 16-ft by 8- inch thick concrete slab was mounted in the Stone-OBL concrete reaction structure using a stiffened steel frame.  This configuration was subjected to two seperate blast tests using different weights of ammonium nitrate/fuel oil (ANFO) at different standoff distances.   Table 1 summarizes the ANFO weights and standoffs used for the testing program.

Table 1.  Testing Matrix

Test

ANFO Charge Weight

(lb)

Standoff

(ft)

1 500 45
2 700

35

 

The slab performed extremely well in both tests with support rotations of less than 2 degrees and minimal cracking.

The results were recorded using sensors and high speed cameras.  The measured responses out-performed initial analytical predictions and exceeded current blast response criteria for un-bonded PT systems.  Table 2 provides an overall summary of the test results and the photos below show post-blast test photos of the un-bonded PT slab specimen.

Table 2.  Test Results Summary

Test

Maximum Deflection (in) Support Rotation (degrees) Maximum Strain (in/in) Response Type Peak Pressure  (psi) Positive Phase Impulse           (psi-ms)
1 0.76 0.5 0.0037 Elastic Deformation 64-120 84-175
2 2.24 1.4 0.0131 Permanent Deformation 170-260

220-350

Unbonded PT

Post-Blast Test Photos of the VSL un-bonded PT Slab Specimen

The remarkable results obtained during these tests warrants further investigation and research to define parameters that affect the performance of these structures and to develop practical design provisions for un-bonded pre-stressed concrete elements.

For more information, please contact us at Info-DC@StoneSecurityEngineering.com or info@Stone-Obl.com.

 

Presenting: StoneSmart Solutions

New York, USA May 23, 2017-  Stone Security Engineering is pleased to announce the launch of StoneSmart Solutions, a research and development company dedicated to developing new and innovative products and services for the protective design community. StoneSmart’s first efforts toward this goal have been the creation of two joint venture companies: Stone-OBL and Stone Protective Solutions. In addition to these joint ventures, StoneSmart has teamed with ProtectiFlex, which provides a versatile, cost-effective, and practical construction material solution for all of our clients’ ballistic, forced entry, and blast resistant needs.

Stone-OBL specializes in testing building products against extreme loadings such as blast, ballistics, forced entry, and fire. Stone-OBL combines the engineering expertise of Stone Security Engineering and the testing, instrumentation, and research expertise of Oregon Ballistic Laboratories (OBL). The combination of these skills makes this joint venture a one-stop shop for extreme load testing, product research and development, and product certifications. The Stone-OBL blast test range is able to accommodate a wide variety of test specimen configurations, explosive materials and weights, and standoffs in order to meet the varying needs of the security, safety, and industrial sectors.

Stone Protective Solutions is developing a line of modular building products which are engineered to meet security and safety requirements. Our Extreme-Woodlam Panel is a patent pending technology whose blast resistance capabilities exceed those of other materials of the same weight, such as steel and concrete.   Other benefits of this technology, compared to traditional steel modular buildings, are that it is created from renewable materials, uses less energy to manufacture, and is less expensive to ship.  Additionally, structures that have our Extreme-Woodlam Panels inherently provide enhanced insulation, and quieter interior environments.

ProtectiFlex is an innovative single material solution that protects against extreme loading. The proprietary technology, consisting of recycled rubber chips and fibers in a concrete mix, closely resembles typical masonry blocks and precast concrete panels. ProtectiFlex provides advantages over conventional masonry and precast concrete due to its impressive energy absorption characteristics, making it an excellent choice for a ballistic, forced entry, and blast resistant material, which can easily be integrated within a traditional structural steel or concrete structure.

We are thrilled by the launch of our new ventures,” said Hollice Stone, General Manager of StoneSmart Solutions. “The Stone team has always had the attitude that if we see a hole in the industry, we want to fill it – and that is exactly what we are doing. We look forward to expanding our ability to provide high quality products and services which fit the needs of our industry.”

Throughout the coming weeks, StoneSmart Solutions will be profiling their recent projects and detailing the various offerings across the StoneSmart portfolio. If you would like to receive this information, sign up for their newsletter today.

 

StoneSmart Solutions, LLC is a small business and New York based company established by the primary engineers of Stone Security Engineering.

Stone Security Engineering Turns 8 This Week!

Stone Security Engineering, PC will be 8 years-young on July 2nd, and what a wonderful 8-years it has been.  I am so proud and excited about what we have accomplished.    Among other things, we have

  • Opened offices in NY and the Washington DC Metro area;
  • Become employee-owned;
  • Performed research and development for the US Army Corps of Engineers, the US Department of State, and private manufacturers developing new products for the safety and security industry.
  • Developed (with our partner firm Stone-OBL) an open-air blast testing facility in the high desert of Oregon.
  • Performed vulnerability assessments and mitigation designs for facilities in high threat environments such as Somalia, Yemen, Iraq, Afghanistan, Algiers, and Egypt.
  • Created Security Design Criteria and Blast Resistant Designs for Iconic High-Rises in places like New York City and Dubai.
  • Written the GSA’s blast resistant design requirements.
  • Developed and presented classes for engineers, architects, contractors, developers, and security professionals to help educate the industry and lift all of us to a higher level.
  • Continued to work with the design community working with the US Government to analyze and design new buildings and major renovations projects to meet blast and progressive collapse requirements.
  • Created iStandoff, an app to help design teams make early phase decisions regarding standoff distances for DoD projects.
  • Developed new software for the US government;
  • And so much more!

I look forward to the next 8 years to see what new mountains we can climb while continuing to provide customized and quality service for our clients and team members.

Thanks to all of you for being part of our family.