Numerical and analytical study of overpressures and impulses inside a masonry box subjected to external blast loading

Blast loads have attracted considerable attention in recent years due to accidental or intentional events involving important structures, which have occurred around the world. The activities related to terrorist attacks have increased and, unfortunately, the current trend suggests that they will continue to rise in the future. In relation to the design of structures subjected to blast loadings, there are still many uncertainties in the specialized technical literature. Particularly, the overpressures and impulses inside constructions are difficult to estimate due to many reflections of the shock wave. The main objective of this work is to study the propagation of the blast wave inside constructions subjected to external loadings. An experimental study was performed using a masonry box with reinforced concrete beams and columns and a typical window. The results were previously presented. In this article, numerical models are developed in order to compare results and to obtain design guidelines. Explosive charges of equivalent 1–5 kg of TNT and elevated 1 m above the ground were detonated at different distances from the window, and overpressures and impulses were obtained at five points inside and outside the room. However, empirical–analytical results using a well-known technical manual are also obtained and compared. The obtained results are useful to evaluate numerical codes and empirical formulas.

Using Explicit Finite Element Analysis to Simulate the Structural Damage Associated With an Internal Detonation in a Heat Exchanger

Developing the realistic blast loading associated with an internal detonation occurring within a pressure vessel or heat exchanger is challenging. Unlike evaluation of external blast loading on structures due to far-field explosions, where typical overpressure-time histories can be reasonably defined based on empirical data, investigating confined detonations presents additional complications. The subsequent impulsive peak reflected overpressure from confined detonations acting on a structure can be extremely high due to the close proximity of the blast source to the vessel wall or pressure boundary. This establishes the possibility of significant structural damage for process equipment subjected to an internal detonation, even for relatively modest amounts of concentrated explosive products. This paper discusses the underlying theory of blast analysis and examines the practical application of non-linear, finite element based, explicit computational techniques for simulating the load acting on a structure due to internal and external blasts. The investigation of a recent, real-life industry failure of a heat exchanger due to a suspected internal detonation is discussed. Explicit, three-dimensional blast analysis is performed on the heat exchanger in question, and an internal detonation is simulated to reasonably replicate the considerable damage actually observed in the field. This analysis permits the determination of an approximate amount of concentrated product that caused the accidental explosion; that is, the plausible equivalent amount of explosives is back-calculated based on the predicted damage to the finite element model of the equipment in question. Computational iterations of varying charge amounts are performed and the predicted amount of permanent damage is documented so sensitivity to the hypothesized charge amount can be quantified. Furthermore, explicit blast analysis of nearby equipment is performed. In this investigation, computational results for both the heat exchanger (subjected to internal blast loading) and surrounding equipment (subjected to external blast loading) are in good agreement with the measured plastic deformations and failure modes that were actually observed in the field. Commentary on the likely detonation event that caused the significant damage observed is provided. Additionally, an advanced finite element failure criterion that is driven by plastic yielding is employed where portions of the computational model are removed from the simulation once a user-defined strain threshold is reached. This approach facilitates simulation of the gross heat exchanger pressure boundary failure actually observed in this case. The explicit finite element based analyses discussed in this study reasonably predict the structural response and damage characteristics corresponding to a recent, real-life industry failure.

BlastWall: An Integrated Wall and Window Retrofit System

Exterior wall infill panels of non-loadbearing masonry, often with window openings, are commonly used in buildings around the world. While the structural frame may possess a good level of resistance to explosion loading the masonry wall panels are often relatively weak and liable to sudden, brittle failure when subjected to blast loads with the result that hazardous debris is thrown into the interior of the building. Blast resistant windows can be set into openings in the masonry wall panels; however failure of the wall may occur at a lower load than that against which the window would survive if it was adequately supported. The BlastWall research project was carried out by a consortium of industry partners and research institutions with the aim of developing a practical integrated wall and window retrofit system to mitigate the hazards to building occupants and critical equipment from the failure of masonry wall infill panels under external blast loading. Utilising elements of Tecdur® technology, the BlastWall system proved successful under loading at EXV15, with since-proven potential for even higher performance. The system is supported by a software tool that allows its components to be tailored to suit a wide range of existing materials, dimensions and loading conditions. This paper describes the project objectives, the BlastWall system and its components, including the software tool, and the trials carried during system development resulting in overall proof of concept.