Blast load analysis of overpass columns with various cross-sections

Abstract

The column is one of the most important elements of the bridge because its destruction can cause a collapse of the entire bridge. The aim of the research is to analyse the blast behaviour of the overpass columns on Croatian roads and highways. Based on the archive documents of design plans the most common cross-sectional shapes of the reinforced concrete column were selected. The literature provides formulas for calculation of blast pressure that depends on the distance of the explosive from the target and the amount of explosive. However, the cross-sectional shape of the column plays a significant role in retaining the pressure and impulse on the column and its distribution by column height and width. This cannot be predicted by theoretical expressions, and therefore a numerical simulation that takes into account the column geometry is required. The columns were modelled in the Ansys Autodyn hydrocode software for a supposed scenario in which an auto bomb was placed below the bridge at a distance of 2 m from the column. Based on the numerical simulations it was concluded that the circular column had the lowest pressure on the surface directly exposed to the blast load. This is due to its roundness and the angles at which the pressure was reflected. In contrast, the back surface of the circular column has the highest pressure of all the analysed columns. Generally, rectangular cross-sections have a higher pressure on the directly loaded surface. For more detailed analysis and experimental testing, a rectangular column (P6) with recesses was selected due to its high pressures on both, the front and back surfaces. Selected overpass i.e. its column was designed using the old seismic regulations and as a part of further research, its blast behaviour will be compared to the column designed using modern seismic regulations.