Explosions in urban environments: Modelling of gas explosions and risk of premature shear failure in reinforced concrete structures

Licentiate thesis, 2023

The risk for accidental gas explosions in urban environments has increased in Sweden in recent years. This is due to densification of existing urban centres and the rise of vehicles powered by alternative fuels. Because of this, blast-resistant design of reinforced concrete (RC) structures may eventually become a common aspect of urban development and structural engineering.

This thesis aims at expanding the knowledge concerning explosion and blast loads in urban environments and the response of RC structures subjected to it. Two key research areas were identified. The first one deals with the strength of vapour cloud explosions (VCEs) on urban roads. The strength of the blast source is a necessary input to predict the blast load generated by VCEs. However, there is much subjectivity and inconsistency today in the determination of the explosion strength, particularly for the conditions on urban roads. This work used computational fluid dynamics (CFD) calculations in combination with the principles of factorial design to determine the expected strength for several explosion scenarios on urban roads and identify the most significant parameters affecting the resulting strength. For the studied scenarios, the explosion strength varied approximately from 2 kPa to 100 kPa. Moreover, the number of vehicles in the transversal direction (i.e., vehicles standing side by side) was found to have the most significant effect on the explosion pressure.

The other area is concerned with the uncertainties related to the failure modes of blast-loaded RC one-way slabs. The motivation behind this research area is the need to prevent brittle shear failure in blast-loaded RC elements. The Monte Carlo method was used to determine the probability of premature shear failure of the blast-loaded slabs considering the uncertainties associated with the materials, geometry, and resistance models. The slabs were initially designed to have a balanced failure (i.e., the resistance to shear and bending failure are theoretically equal). Bending failure was found to be the expected failure mode for the studied cases. However, the likelihood of shear failure (particularly for slabs without stirrups) may still be considered relatively high, depending on the risk tolerability of a given design. Thus, an additional partial factor to enhance the confidence level regarding the preferred failure mode was put forward.