HEC TDF02-038: Performance of Confined Dry Block Masonry Against Blast Loading

The protection of human lives and building infrastructure against the terrorist explosions, remained always a challenge for engineers. The terrorist’s activities during the last two decades attracted the attention of scientists towards the blast resistant structures. The literature study revealed that the conventional masonry is showing a weak performance against shock waves and the behavioral deficiency of this material is corelated with the failure of mortar joints. In this research study, an effort has been made to cope with the challenges by introducing the Dry Stacked Masonry (DSM), composed of self-interlocking compressed earth blocks as made exclusively by Eco Enterprises, Islamabad as a masonry unit, against blast loading. To assess the performance of the DSM against blast loading, four confined masonry walls, two restrengthened walls, and a typical full-scale building were fabricated and tested with the incremental amount of explosive, in a controlled environment. The confined DSM walls were provided with different arrangements and detailing of reinforcement in the confining elements. For strengthening of the DSM walls, ferro-cement overlay, and Carbon Fiber Reinforced Polymers (CFRP) were applied on both faces of the walls. To record the various parameters of the shock waves, a high-speed camera and pressure sensors were mounted at different locations. In order to get a reflected form of shock waves, the explosive material was placed at a height of 3 ft (0.915 m) from the ground level.

The DSM wall strengthened with ferro-cement overlay sustained the shock waves of scale distance of 1.31 m/kg1/3 however large number of fast moving fragments were observed which made it more hazardous. The DSM wall provided with 90º hooks and widened spaced stirrups was fully damaged at a scale distance of 1.41 (m/kg1/3). The provision of 135º hooks with the same spacing increased the capacity of the DSM wall and damaged at a scale distance of 1.31 m/kg1/3. The DSM walls with closely spaced stirrups and 135º hooks incurred severe damages and hinges were developed at the bottom joints of the vertical confining elements at a scale distance of 1.13

m/kg1/3. The provision of diagonal reinforcement at the joints enhanced the performance of the DSM wall and only hair line cracks were observed at a scale distance of 1.31 m/kg1/3. The DSM wall strengthened with CFRP performed well against the blast loading in terms of capacity and mitigate fragmentation. The full-scale DSM building experienced no structural damages and withstand against 33 Kg of TNT at a distance of 20 ft (6.09 m). The maximum pressure recorded inside the building was 5.98 psi (41.23 kPa), which is slightly greater than the threshold limit of human ear i.e., 5 psi (34.47 kPa). The material is recommended for the development of infrastructures for Law Enforcing Agencies (LEA) and other vulnerable buildings against blast loadings throughout the worldwide.

PhD Scholar: Engr. Azmat Ullah

Supervisor: Prof. Dr. Khan Shahzada
Professor, Department of Civil Engineering
University of Engineering and Technology, Peshawar

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