Performance of reinforced concrete columns under shock tube induced shock wave loading

Abstract

Recent events including deliberate attacks and accidental explosions have highlighted the need for greater research in structural response to blast loading. One of the primary research focuses has been on the prevention of progressive collapse of structures. The response of vertical load transferring members, such as columns, is of particular importance to progressive collapse prevention. In order to understand and predict the behaviour of the global structure during and after a blast loading event, a greater understanding of column behaviour must be developed. Currently there is a limited amount of experimental test data available on the response of reinforced concrete columns exposed to blast loads. This thesis presents the results of experimental research involving tests of scaled reinforced concrete columns exposed to shock wave induced impulsive loads using the University of Ottawa Shock Tube. A total of 14 half scale reinforced concrete columns were constructed and tested under blast pressures. The columns were designed according to Canadian Standard Association (CSA) Standard A23.3 for the "Design of Concrete Structures" (2006) standard as first story columns for both seismic and non-seismic regions. Axial load was applied to levels similar to what can be expected in actual structures. The columns were exposed to various pressure-impulse combinations which resulted in a range of column response. Comparisons are made between seismically designed and detailed columns and those that represent non-seismic gravity load columns in terms of displacement under similar shockwave loading. In addition, numerical analyses were conducted using single degree of freedom dynamic analysis. The numerical analysis accounts for the loss of axial load observed with horizontal displacement, strain rate effects on material strengths, the formation of plastic hinges in the column near the supports and at mid-height and the corresponding change in resistance and the response mode shape. The numerical analysis is validated with the experimental results and proven to accurately predict displacement of reinforced concrete columns under shock wave loading. The results indicate that an equivalent single degree of freedom model may be used to determine the response of a column under air blast induced shock loading if proper displacement-resistance models that account for material strength increase factors and change in axial load are used.