# Reliability Assessment of Steel-Lined and Prestressed FRC Slabs against Projectile Impact
## 1 Introduction
Concrete having a compressive strength of 48 MPa was prestressed with 10% of its compressive strength. The experiments measured damage volume, spalling, scabbing, and ballistic resistance at impact speeds ranging from 65 to 220 m/s. Of the three concretes examined, prestressed concrete showed the best ballistic performance. Additionally, they observed that prestressing effects are more noticeable as target thickness increases. Using a 234 kg steel hammer for free fall, [PERSON] et al. examined 12 samples of prestressed and reinforced concrete slabs (80 cm \(\times\) 80 cm \(\times\) 10 cm) of 60 MPa compressive strength. There were two levels of prestressing: 10% and 20%. They found that when moving from reinforced concrete to 10% prestressing, peak displacement was reduced more than when moving from 10% to 20% prestressing. [PERSON] et al. [11] reviewed the state-of-the-art research on thick ultra-high-performance concrete (UHPC) targets subjected to high-velocity projectile impacts. The researchers also evaluated existing empirical and semi-empirical formulas that can be used to predict the depth of penetration in conventional concrete and assessed their suitability for UHPC. Post-tensioned slabs under impact loads were studied by [PERSON] et al. [12]. Concrete slabs were post-tensioned to 3% of their strength. A 605 kg impactor was dropped on the slabs from a height of 20 m. There was no difference between RC and post-tensioned slabs in terms of maximum deflection, but post-tensioned slabs had 35.2% more impact force, and RC slabs had 14.9% higher maximum deflection. In the literature, there are few studies assessing the reliability of structures that have been subjected to aircraft, missiles, and projectile impact loads. [PERSON] et al. [13] presented a method for assessing concrete targets' reliability to rigid missile impacts at specific depths. An expression for missile velocity at any depth in the soil was derived based on penetration depth. Following this, the First Order Reliability Method was employed for assessing concrete target reliability. Sensitivity analysis also revealed results of practical interest. The steel plates shielded with RC were tested against hard projectile strikes using a simple experiment designed by [PERSON] et al. [14]. A Monte Carlo Simulation (MCS) technique was used to estimate the reliability of RC-shielded steel plates for different impact velocities, and the outputs were correlated with failure scenarios. Furthermore, they extended their work [15] to investigate how well a containment structure having double walls holds up against an impact from a rigid projectile. A correlation was made between a containment's ballistic limit and its reliability indices and probability of failure. The reliability of containment structures was also examined through a number of parametric studies. Considering the uncertainties associated with material, geometric, and impact parameters, [PERSON] et al. [16] devised a probabilistic method for estimating HFRC slab reliability against hemispherical nose projectile impacts. Additionally, hybrid fibers were investigated for their effect on the reliability of RC slabs against projectile loads. A projectile impacting the HFRC slab above its ballistic limit caused the slab to perforate, resulting in failure. Various impact velocities for a given projectile were used to assess reliability for different impact loads. By analyzing the reliability of the HFRC slabs, they determined their safety level against projectile impact. The above literature review examines the various studies on RC/FRC/PC members' impact behavior. Although the impact response of concrete targets has been studied in sufficient detail, reliability aspects are not covered, which is the focus of this study.