BLAST DAMAGE MITIGATION IN SUBMERGED SYSTEMS. PHASE I: INTERNAL EXPLOSION

This thesis is focused on quantifying the dynamic performance of lightweight metal sandwich systems under confined explosions, where this effort represents the first of a multi-phase comprehensive research program that is focused on developing blast damage mitigation techniques in submerged structures. A confined explosion occurrence inside such facilities may lead to paralyzing all operations depending on the functions of the affected sections. Subsequently, using sacrificial cladding placed as a physical barrier over critical components that might be vulnerable to a potential explosion is considered to be an effective blast damage mitigation technique. Furthermore, sandwich panels can be an ideal system to be used as sacrificial cladding, as it can be manufactured to possess high stiffness-to-weight ratio and superior energy absorption capabilities. Consequently, an experimental program was performed to investigate the performance of lightweight cold-formed steel sandwich panels under both quasi-static loads and confined explosions, where a total of fifty-seven sandwich panels were tested, considering various core configurations, different core sheet thickness, and different blast load intensity levels. The American ASCE/SEI 59-11 and The Canadian CSA/ S850-12 blast design standards predict the dynamic response of a structure component based on the static resistance function by applying dynamic increase factors. Subsequently, the static resistance functions for the proposed panel configurations were investigated experimentally and compared with the introduced analytical model, in order to quantify accurately the inelastic panel response. The quasi-static test program was performed in two stages, where the first included eighteen single layer core sandwich panels, which represented longitudinal and transverse corrugated core configurations. The results of the first stage configurations demonstrated an efficient strength and stiffness, but showed a lack in energy absorption capabilities and ductility capacity. Therefore, in the second stage, different core configurations were developed, including twenty-one panels representing Bi-directional and X-core double layered core configurations and its counterpart Uni-directional single layer core configuration. The results of the second stage demonstrated an enhancement in the ductility and energy absorption capabilities compared to the configurations tested in the first stage. The residual deformations and failure modes demonstrated were assessed and discussed in details, where web crippling, local buckling and global buckling induced by shear or flexurewere determined. In general the static resistance functions for each tested panel were used to quantify the panels’ yield loads, ultimate capacities, and corresponding displacement levels. Moreover, the influences of both the core configuration and the core sheet thickness on the panels’ stiffness, ductility levels and energy absorption were quantified. Based on the conclusions of the static testing and considering the ductility, capability of energy absorption, and the behavior beyond the elastic zone, two different core configurations were chosen to be tested under confined explosions. Eighteen panels were tested in a cylindrical shape blast chamber representing a typical submerged structure under different scaled distances ranged from 2.82 to 1.09 m/kg1/3, in order to demonstrate different damage state levels in accordance with the blast design standards (ASCE/SEI 59-11, CSA/ S850-12). In the blast testing results, the incident and reflected pressure time histories of the blast wave were measured, while the modified Friedlander equation was used to fit the first positive phase of the reflected pressure histories. In addition, the displacement response histories of the back face of the tested panels were recorded. The measured values of peak incident pressure, peak reflected pressure, incident impulse and the reflected impulse were compared to the predicted values using ConWep (Hyde 1990) considering the spherical explosion, and have shown a good agreement. Furthermore, the failure modes and the post blast damage were determined and compared to the static observations. In order to complement the experimental program, a nonlinear inelastic single degree of freedom model was developed in order to predict the dynamic response of the sandwich panels. The model used the recorded blast load and the static resistance while applying the dynamic increase factors recommended by the standards (ASCE/SEI 59-11, CSA/ S850-12). The model results were in a good agreement with the experimental data. Furthermore, the different ductility and support rotation values obtained experimentally and predicted analytically were related to the different damage levels specified by blast standards. Finally, the influence of sandwich panel core configuration on the dynamic blast response of the tested sandwich panels was discussed.

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