Stochastic Fragment Velocity Analysis of Concrete Masonry Walls under Blast Loading with a Multi Degree of Freedom Model via the Monte Carlo Method

Abstract

The behavior of concrete masonry unit (CMU) walls under dynamic overpressure loading where dynamic fracture produces secondary fragments is quite complex. The response of a CMU wall is influenced by the material properties of the wall, which vary considerably inside and between individual walls. A computational methodology was developed that can incorporate material property variation into fragment hazard analysis of CMU walls under dynamic overpressure loading. A fast-running Multi Degree of Freedom (MDOF) model was developed to calculate the fragment hazard of a CMU wall. The low computational cost of the MDOF was leveraged inside a Monte Carlo (MC) framework to completely describe the hazard distribution resulting from material property variations. MDOF model development was detailed and comparisons were made between MDOF model results, explicit finite element results, and full-scale experiments. The MC property distributions were developed by using information about material property variation from literature. The hazard calculated by the MDOF MC model was higher than the hazard observed in either full-scale experiment. The model allows for the full hazard of a CMU wall to be calculated and accounts for inherent material property variations.

An experiment was developed to examine the influence of loading rate on the shear bond strength between CMUs and mortar joints. A novel experiment technique was developed using a shock tube and ram to load CMU triplets in dynamic shear. Numerical modeling and results from the experiments were used to conclude that the shear bond strength increases as strain rate increases.