Year

2012

Degree Name

Doctor of Philosophy

Department

School of Civil, Mining and Environmental Engineering

Abstract

This study investigates the response of axially restrained non-composite steel-concrete-steel (SCS) panels under static, impact and blast loading conditions. This type of panels shows promising economic and technological characteristics as protective barriers for critical infrastructure protection. Axially restrained non-composite SCS panels have high strength and ductility, which enable them to withstand extreme loading such as impact and blast. The concrete core mass provides inertial characteristics which are beneficial for resisting impulsive loads. The primary resisting mechanism in this type of panels is based on dissipation of imparted energy by axial stretching of the steel faceplates (membrane resistance) and crushing of the concrete core. No hazardous projectiles will be generated since the concrete core is confined by the steel faceplates. The overall cost of construction is reduced by not providing shear connectors between the steel faceplates.

Comprehensive experimental investigations have been carried out on axially restrained non-composite SCS panels under static and impact loading conditions. The experimental results have demonstrated that the panel resistance combines the flexural resistance at the initial stage, followed by the tensile membrane resistance of the steel faceplates under large deformation. The tensile membrane resistance of steel faceplates at large deformation could be significantly higher than the flexural capacity of non-composite SCS panels, and it is the main energy dissipation mechanism in this type of panels. The static resistance function of axially restrained non-composite SCS panels has been derived from the results of quasi-static monotonic loading tests. The finite element (FE) modelling techniques for the non-composite SCS panels have been developed and validated against the impact test results of the panels.

Using the validated FE modelling techniques, the response of axially restrained non-composite SCS panels subjected to blast loading has been investigated. It is observed that the response of non-composite SCS panels under blast loading can be simulated by simplified model of the thin steel sheet catcher systems. During blast loading, the front faceplate is separated from the concrete core and bounces back before the panel reaches its maximum displacement. Therefore, the energy dissipation by the front faceplate can be neglected, while the rear faceplate dissipates about 80% of the kinetic energy in the panel through membrane stretching. A simplified engineering-level model of the panel has been proposed that considers only the rear faceplate as a catcher system for resisting the impulse delivered by the fragmented concrete core.

The response of a barrier composed of non-composite SCS panels and steel posts subjected to blast loading has been studied using numerical simulations. It is found that a certain amount of kinetic energy in the panels is transferred and dissipated by the steel posts due to panel-post interaction. The failure modes observed from the simulations are bending failure of the posts and fracture failure of the rear faceplate of the non-composite SCS panel. From the comparison between the response of a reinforced concrete blast wall and the barrier utilising non-composite SCS panels, it is found that the barrier with non-composite SCS panels could reduce the wall thickness by about 60% when similar amount of steel is used in the construction of both walls. Therefore, the barrier utilising non-composite SCS panels is an economical alternative to the reinforced concrete blast walls in resisting close-range detonation of high explosives.

As part of this study, an instrumented falling weight impact (IFWI) test rig is developed to investigate medium strain rate effects on stainless steel. The test results of the stainless steel specimens in this study are significantly lower than the theoretical prediction using the existing Cowper-Symonds coefficients. From comprehensive literature reviews, it is found that the stress level, prior work hardening, heat treatment condition and microstructure of the stainless steel will affect the strain rate effects. Therefore, the Cowper-Symonds coefficients should be used with care. Improved Cowper-Symonds coefficients have been proposed for the stainless steel Grade 304 used in this study.

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