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.
|
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 |
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.