Variability and probabilistic modeling of external blast loads on cylindrical shells

Deterministic load models adopted by current blast-resistant design codes struggle to quantify the load variability arising from inherent uncertainties in the explosive source, propagation path, and the models themselves, thus hindering reliability-based blast design. This paper presents a systematic investigation into the variability of external blast loads on cylindrical shells through 20 repeated tests and tests with varying charge orientations, complemented by numerical simulations thoroughly validated against multi-physics experimental data. For the first time, the contributions of repeatability errors and charge orientation errors to the overall variability are decoupled and quantified, revealing that ignoring charge orientation increases the total load variability by over 120%. Statistical tests indicate that peak overpressure and maximum impulse follow a Normal distribution, while positive phase duration follows a Lognormal distribution. This study develops spatial distribution models for the coefficient of variation, showing that charge orientation deviation and structural obstruction effects amplify blast load variability in the near-field and far-field, respectively. Through extensive parametric numerical analyses, a deterministic load model considering charge size, distance, and orientation is established. Furthermore, a probabilistic load model guided by the 95% fractile value is proposed. This model can be directly integrated with the partial factor system of current structural reliability design codes, providing a practical tool for the probabilistic blast-resistant design and safety assessment of cylindrical shell structures.