This paper describes a series of tests conducted at VTT Technical Research Centre (Finland) in order to assess the influence of pre-stressing on perforation capacity of concrete slabs under hard missile impact (impact with negligible missile deformations). The paper presents three tests along with their results having as a baseline specimen the reinforced concrete (RC) slab (2.1 m X 2.1 m X 0.25 m) with longitudinal reinforcement only. The following tests are: ? The baseline RC slab with longitudinal reinforcements only, ? RC slab unbounded Dywidag bars (placed in empty PVC sleeves to avoid the contact between the concrete and with Dywidag bars in order to simulate ungrouted tendons), ? RC slab with unbounded Dywidag under tension to introduce pre-stressing of 10 MPa in the concrete slab. The impact missile velocity was defined using empirical equations applicable to reinforced concrete slabs to achieve slab just-perforation. The goal of the tests is to assess the effect of pre-stressing on perforation capacity. This effect is complex due to the presence of pre-stressing bars (or cables) and the possibility that the missile hits the bars. In order to assess the effect it was necessary to decouple the influence of Dywidag bars as an additional reinforcement and the effect of pre-stressing (tensile stresses in Dywidag bars). The results show an increase of perforation resistance of concrete slabs due to pre-stressing. The overall damage of the slabs was assessed and compared in all cases as well.
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