Strengthening of braced unreinforced brick masonry wall with (i) C-FRP wrapping, and (ii) steel angle-strip system under blast loading

Abstract

Accidental detonations, and explosions made by extremists are major threats to human life and building structures. The vulnerability of the load-bearing masonry structures is more as compared to the reinforced concrete structures against explosion-induced loadings. Such events weaken the socio-economic stability and therefore necessitates the evaluation and effective strengthening strategies of masonry structures to improve their blast performance. Unreinforced masonry (URM) walls have little flexural resistance against out-of-plane loadings and exhibit a brittle mode of failure. In this research work, the clay brick masonry wall braced with two transverse walls one at each end, tested experimentally under the explosive loads of 4.34 and 7.49 kg-TNT equivalent at scaled distances 2.19 and 1.83 m/kg1/3, has been numerically analyzed using a high-fidelity commercial FEM-based dynamic computer program, ABAQUS/Explicit-v.6.15 considering micro-modeling technique and concrete-damaged-plasticity (CDP) model with strain rate effect. Damage in the exposed masonry wall in the form of (i) vertical mortar joint cracks at the center and next to the bracing transverse walls, (ii) flexural cracks near the ground; and diagonal cracking in the lower part of the bracing walls, is observed at a scaled distance, Z = 2.19 m/kg1/3. For Z = 1.83 m/kg1/3, out-of-plane catastrophic collapse of the walls occurs. The computed damage patterns are found quite similar to the experimental ones in the open literature. A novel strategy other than commonly used carbon fiber reinforced polymer (C-FRP) wrapping technique, consisting of steel angle-strip system has been devised and used to strengthen the wall against the considered blast levels. CFRP wrapping of 2mm thickness, and steel strip mesh of thickness (a) 3mm, and (b) 5mm with angles along the edges of the walls, are considered to improve the wall response and analyses are carried out. The blast load-carrying mechanisms of the walls strengthened with the two techniques are explained.