Safety factor for structural elements subjected to impulsive blast loads

Safety factor forstructural elements subjected to impulsive blast loads

Pierluigi Olmati^1a*, Dimitrios Vamvatsikos^2b, Mark G. Stewart^3c

¹ Department of Architecture and Wind Engineering, Tokyo Polytechnic University, Japan.

² School of Civil Engineering, National Technical University of Athens, Greece.

³ Centre for Infrastructure Performance and Reliability, The University of Newcastle, Australia.

^a Researcher, fellow of the Japanese Society for the Promotion of Science JSPS.

^b Assistant Professor.

^c Professor and Director.

^* Corresponding author; e-mail: pierluigi.olmati@gmail.com  

Abstract

Design of blast loaded structures is usually carried out following a deterministic rather than a probabilistic approach. The design load scenario would cover the plausible load conditions (typically some conservative estimate) that a structure would experience if an explosion occurs but the probability that the structure will satisfy the design performances for the considered scenario remains unknown. Applying a performance-based design framework typically requires arduous Monte Carlo simulations, but a probabilistic design could also be achieved by a single structural analysis when consistent safety factors are applied to the load and the structural resistance. Such a factor is proposed herein for the case of components subjected to impulsive blast loads. The dependence of the safety factor on the amount of explosive, stand-off distance and their variability is estimated numerically and provided by means of regression formulas. A design example using the proposed safety factor is carried out and Monte Carlo simulation is used for verification. The results confirm the validity of the proposed safety factor approach and its applicability for the performance-based design of blast loaded structures using the current design practice methods.

Keywords: performance-based design; probabilistic analysis; safety factor; blast design; terroristic explosions; blast load; vehicle borne improvised explosive devices.

Figure 16: Probability of exceeding the limit state P(ϴ>θ) calculated using a Monte Carlo simulation compared with the APE used in the design carried out with the proposed safety factor λ. The structural uncertainties have been considered as well for comparison purpose.  Furthermore the reinforcement percentage is plotted too as design output for the RC panel. The proposed approach is accurate enough for APEs<15% while for higher APEs (not suitable for design purposes) it gives a conservative design.

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