A Study On Response And Size Effect Of Reinforced Concrete Structures Under Intense Dynamic Loadings

With excellent compressive properties of concrete material and good tensile properties of steel rebar,reinforced concrete(RC)structures have been widely used in civil engineering(i.e.bridges,tunnels,dams,nuclear power plants,etc.)and military installations(namely,command centers,underground bunkers,etc.).On the one hand,RC structures may suffer damages caused by intense dynamic loadings such as missile impact or explosive.Hence,an understanding of the response and failure of RC structures subjected to intense dynamic loadings(impact and blast)is essential in both safety calculations and safety assessment of such structures in various engineering.On the other hand,the size effect of concrete is also well known.However,most of researches have been focused on static/quasi-static and low-velocity impact behaviour of concrete,whilst the studies on explosive response of RC structures are seldom reported.Therefore,it is necessary to investigate the size effect of RC structures under explosive loadings.The main purpose of this thesis is to study the response and size effect of RC structures under intense dynamic loadings(impact or explosive loadings).The main contents and achievements are as follows:1.Numerical simulations have been carried out on the dynamic response of reinforced concrete(RC)beams under different dynamic loading conditions(constant velocity loading and drop-weight impact loading)using the newly developed dynamic computational constitutive model for concrete.(1)The finite element(FE)models of the RC beams under different dynamic loading conditions have been established;(2)The load-displacement curves and crack failure patterns obtained from the numerical simulations have been compared with the experimental data.It is found that the numerical results are in good agreement with the experimental observations;(3)Parametric studies have been conducted with emphasis being placed on the influences of various parameters(i.e.shear reinforcement ratio,bending reinforcement ratio,span to depth ratio,loading(impact)location)on the response and failure of RC beams under low velocity impact loading;(4)The transition of failure mode of RC beams under dynamic loadings has been theoretically studied.An analytical equation has been proposed which defines the critical condition for the transition of failure modes in RC beams from bending/flexure to shear.The equation is found be in good agreement with the experimental data.2.Numerical studies have been performed on the impact response of reinforced concrete(RC)beams by the recently developed computational dynamic constitutive model for concrete together with a newly proposed 3D meso-mechanical model.(1)It is shown that the time-histories of impact force and displacement from numerical results are in good agreement with the experimental observations;(2)It is also shown that the crack distribution and propagation at different time from numerical results are in good agreement with the experimental observations.3.An experimental investigation has been carried out to study the size effect of reinforced concrete(RC)structure under explosive loadings.(1)The RC specimens(RC beams,RC slabs and concrete columns)are designed strictly according to the scale factor of 1:2:3,and the explosive charge mass is set according to the ratio of 1:8:27;(2)Each experiment has 4 conditions for each RC structure,which corresponds to 4 scaled distances in the case of RC beams and RC slabs or relative explosive weights and explosion modes in the case of concrete columns;(3)The damage and failure of the specimens are compared and discussed.The measured dimensionless parameters are statistically analyzed,which can be used to assess the damage of RC structures;(4)The experimental results show that there exists significant size effect on RC structures under explosive loadings with the small sized structures having stronger load bearing capacities and less damages than the medium and large sized structures which have weaker load bearing capacities and suffer more damages.4.Numerical simulations have been conducted on the size effect of reinforced concrete(RC)structures under explosive loadings.(1)The damage areas and failure morphologies of the RC specimens obtained by numerical simulations are found to be in good agreement with the experimental observations;(2)The numerically predicted values of dimensionless parameters are in agreement with the experimental results;(3)Based on the comparisons between the experimental results and numerical results,further analysis reveals that the size effect of RC structures under explosive loadings are due to the different tensile strain rate effects of concrete.