Investigations On The Blast Resistance Of Corroded Reinforced Concrete Columns

Chloride-induced corrosion is one of the key factors affecting the lifecycle performance and loading capacity of reinforced concrete(RC)structures.The corrosion degrades the mechanical properties of reinforcement and the bonding ability between reinforcement and concrete,leading to cracking in concrete.When analyzing reinforced concrete structures that may be exposed to explosion hazards,considering the influences of chloride-induced corrosion of reinforcement can provide quantitative insight into the structure’s lifecycle performance against blast loads.In this study,the dynamic bond-slip relation of reinforced concrete was quantitatively investigated by performing dynamic pull out tests of corroded and uncorroded reinforcement in concrete.A dynamic bond and slip model was proposed.Considering the bond degradation of reinforced concrete,the blast resistance of corroded RC columns was analyzed,and the fragilities of RC columns with different levels of corrosion damage were established for assessing the lifecycle blast resistance capacities of RC columns.This study conducted numerical simulations on the blast response of corroded reinforced concrete columns using the verified numerical models against available test results.In particular,this research consists of the following main tasks and achievements:(1)The dynamic pull-out test of rebars from concrete was carried out in the strain rate range up to 100/s.The influence of strain rate on the bond-slip behaviour between reinforcement and concrete was observed from the tests.Based on the test results,the dynamic bond-slip relation as a function of strain rate was obtained,and the dynamic bond-slip model was proposed and applied to the numerical model established in LS-DYNA.The accuracy of the numerical model was verified against the testing data.Using the verified numerical model,numerical studies were carried out to investigate the influences of various parameters on the dynamic pull-out of rebars from concrete,and an empirical formula of dynamic increase factor(DIF)of bond strength as a function concrete strength,concrete cover thickness,reinforcement diameter and strain rate was derived from the numerical and testing results.The formula can be used to simulate the response of RC members under dynamic load.(2)Dynamic pull-out tests on electrochemical accelerated corroded rebars in concrete specimens were carried out.The dynamic pull-out behaviours of corroded rebars with different corrosion levels were analyzed.Through dynamic pull-out tests,the ultimate bond load and bond-slip relation corresponding to different strain rates and corrosion degrees were obtained.The bond reduction coefficient was defined to simulate the bond degradation between corroded steel bars and concrete,and the empirical formula of dynamic growth factor of ultimate bond strength under different corrosion rates and strain rates was proposed.It can be used to better simulate and predict the response of corroded reinforced concrete structures under dynamic load.(3)Based on the proposed dynamic bond-slip model,the response of RC columns under blast load was predicted.The effectiveness of the model was verified by the field blast test available in open literature.Using the verified numerical model and taking different blast load conditions as examples,the influence of perfect bond assumption and bond-slip on the response prediction of RC columns was studied.A simulation method for predicting the dynamic load response of corroded reinforced concrete members was proposed.The applicability of the model was verified by the drop hammer test for simulating corroded RC beams.The effects of corrosion rate,detonation face and concrete strength on the blast response of RC columns were studied by using verified numerical models.(4)Considering the chloride-induced corrosion of reinforcement,the blast failure probability was calculated by Monte Carlo simulation based on two corrosion models,i.e.,general corrosion and pitting corrosion.The mean and standard deviation of diameter degradation and yield stress degradation of reinforced concrete columns after 90 years of corrosion are established and incorporated into the empirical formula of the pressure-impulse(P-I)curve for RC columns to predict the degradation of blast resistance with the number of years in service.In the analysis,the scaled distance was used as the demand intensity measure(IM),and the random fluctuation of peak reflection pressure,positive duration,concrete compressive strength,concrete cover thickness,diameter and yield stress of rebar were considered in the simulation.According to the damage degree of a typical reinforced concrete column with different corrosion initial times,the explosion fragility curves were obtained.The influences of the size,reinforcement ratio and corrosion rate of RC columns were discussed.