Safety Calculaion And Assessment Of Reinforced Concrete Structures Subjected To Impact By Missiles

Reinforced concrete has been widely used in military and civil engineering (e.g. nuclear power plant). The understanding of response and failure of reinforced concrete structures subjected to projectile impact is of significance for design and assessment of protective structures. The main purpose of thesis is to formulate a strategy in predicting through-thickness cone cracking, scabbing and perforation of reinforced concrete slabs subjected to missile impact. The main contents of this thesis are as follows:The UMIST formulae are modified within unified framework on the basis of the analysis of existing impact experimental data for reinforced concrete structures under projectile impact. The modified UMIST formulae are applicable for flat-nosed projectiles, but also for non flat-nosed projectiles, such as ogive, conical and hemi-spherical projectiles; not only for low velocity impact, but also for high velocity impact; not only for low strength concrete, but also for high strength concrete. It is shown that the modified UMIST formulae are in good agreement with available test results.An engineering model is presented to predict the penetration of semi-infinite concrete targets struck normally by flat-nosed rigid projectiles. A flat-nosed projectile may be treated as a conical-nosed projectile with the same diameter on the basis of the experimental observation that a "dead zone" was created ahead of the flat-faced missile penetrating a semi-infinite concrete target. It is assumed that the mean pressure offered by the concrete target materials to resist the projectiles is decomposed into two parts:quasi-static resistive pressure and dynamic resistive pressure arising form instantaneous velocity. Equation is obtained for predicting the depth of penetration. It is shown that the model predictions are in good agreement with available experimental data for penetration of reinforced concrete slabs subjected to missile impact.A dimensionless new empirical equation is proposed to predict the punching shear strengths of reinforced concrete slabs without shear reinforcement loaded quasi-statically by flat-faced circular indentors. Various effects such as rebar quantity, rebar spacing and span-depth ratio are taken into consideration in the present formulation. Compared to experimental data and the existing empirical formulae, it is shown that the present equation is advantageous over the existing empirical formulae.A semi-analytical equation is suggested to predict the critical energy for the through-thickness cone cracking of reinforced concrete slabs struck normally by a flat-ended projectile based on experimental observation that the impact process can be described by two stages, i.e. penetration/indentation and cone cracking. The critical condition for the transition of modes from penetration to cone cracking is obtained by equating the penetration resistance to the dynamic punching shear load in an approximate way. It is demonstrated that the present model predictions are in good agreement with available test data that many simplifications and assumptions are introduced.Numerical simulations are conducted on the reinforced concrete targets struck by flat-ended projectiles at normally incidence. The constitutive model developed by Laboratory is adopted which considers the effects of pressure normally, strain rate hardening, Lode angle, shear damage and tensile damage softening. It transpires that the failure patterns of the reinforced concrete slabs obtained form the numerical simulations are in good agreement with experimental observations. It also transpires that the presence of curvature can indicate the performance of reinforced concrete structures. In other words, the modified UMIST formulae can be used for safety calculation and assessment in a conservative way. The effects of the target thickness rebar spacing and rebar diameter on the failure modes of reinforced concrete targets subjected to impact by flat-nosed projectiles are investigated by numerical simulation method. The containment shelter are mainly composed of cylindrical and spherical shell in the nuclear power plants, hence, numerical simulation on shell shelters subjected to flat-nosed projectiles are also investigated in order to illustrate the effects of the curvature on the impact performance of such structures.