Steel fiber reinforced concrete panels subjected to impact projectiles with different caliber sizes and muzzle energies

In special situations like terrorist attacks, concrete structures are occasionally subjected to impact loads such as firearms. Since concrete is brittle, it often shatters into several pieces under impact loadings. In order to alleviate this brittleness, fibers are generally incorporated into concrete. In this study, steel fiber reinforced concrete panels subjected to projectile impact loads with different geometries was investigated. The impactors in the form of bullets came in three different caliber sizes 9, 11, and 7.62 mm, providing muzzle energies of 468, 1972, and 3259 J, respectively. Hooked end type steel fibers were used at 3 vol fractions of 1–3%. The specimens were cast in square panels with dimensions of 400 × 400 mm and varying thickness from 10 to 100 mm. Each panel was subjected to a single impact at the center. Data in the form of velocity (prior to and after impact event), failure modes, and spalling diameters were collected. Results showed that four typical failure modes were commonly found in panels: perforation, scabbing, spalling, and cracking. For piercing type bullets, the thickness played an important role on the impact resistance of the panels. However, for large and blunt tip bullets, both thickness and fiber volume fraction must be considered together to provide sufficient impact resistance.