IMPACT LOADING ON PRESTRESSED CONCRETE PLATES

Abstract

A civil structure has to sustain different types of loads throughout its service life. Broadly, loads can be classified as static or dynamic. Static loads are easy to deal with, as their effects on the structure is well understood and easily computable. Unlike static loads, impact loading, a special case of dynamic loading, lasts a few milliseconds, and therefore, is of a complex nature. Nuclear containment structures and protective structures are prone to impact loading by either human induced cause such as missiles and bullet attacks, accidental impact events such as aircraft crash on the structure or a naturally induced event such as debris generated during earthquake or tornado episodes. The behavior of such structures is of critical importance both from national security as well as public health standpoint. Localized damage is a response of concrete structures towards impact loading and is quantified in terms of crack distribution, penetration, spalling, scabbing and perforation. Present experimental work tried to explore the response of prestressed concrete slab in comparison to reinforced concrete slab when subjected to projectile impact loading by a 10 kg projectile. Prestressed concrete slab and reinforced concrete slab of 1000×1000 mm plan dimensions and 150 mm depth were casted along with reinforcing the slabs in double layers by 10 mm diameter steel reinforcement bars at a spacing of 165 mm center to center. The prestressing force of 15% of unconfined compressive strength of concrete was induced in prestressed concrete slab by pretensioning using a hydraulic jack. An initial trial run revealed the velocity achieved by the projectile is at 104 m/s operated at full capacity. A pneumatic gun setup for the projectile impact loading was opted for the experimental tests. Due to the spread of pandemic, the prepared specimens of slabs could not be tested so the response of the reinforced concrete slab were predicted using empirical formulae available in literatures. Among the various empirical formulae present in the literature, four were selected as they were claimed to be valid in a configuration similar to this experimental configuration. Among the four empirical formulae, three of them predicted that the reinforced concrete slab would undergo perforation damage as well as scabbing damage. Modified Petry formulae was found to underestimate the prediction of limit thicknesses in comparison to other empirical formulae. No empirical formulae were found in the literatures for the damage predictions in prestressed concrete slabs.