Failure Modes And Damage Assessment Of Reactive Powder Concrete Columns Subjected To Blast Loading

Due to the global political situation and the requirements of national strategic development,there is an urgent need to improve the blast resistance of building structures under the effect of blast loading.Reactive Powder Concrete（RPC）has the characteristics of high strength,high toughness and high strength-to-weight ratio.It has a promising application in bridge engineering,hydraulic structures and protection engineering.Under the blast loading,building structures often occur collapses due to column damage.The dynamic response pattern and damage mode of RPC columns under blast loading are not clear,and the damage assessment method of RPC columns based on P-I curve is rarely reported.To address the above issues,the following work has been carried out in this paper.（1）Based on the Equivalent Single-Degree-of-Freedom（ESDOF）method,a numerical model for dynamic response analysis considering the bending-shear coupling effect of the RPC columns was developed.The study shows that RPC columns are susceptible to shear damage in the impulsive load region,to bending damage in the quasi-static load region and to bending-shear damage in the dynamic load region.（2）To address the problem of complex damage patterns of RPC columns under the blast loading,the dynamic damage of RPC columns was classified into four classes:no damage,mild damage,moderate damage and failure.The damage assessment criteria for bending-shear response of RPC columns were determined.The degree of bending damage was assessed using the maximum angle of rotationθ_max at the end of the RPC columns,and the assessment criteria for mild damage,moderate damage and failure were 1.4°,3.4°and 7.1°respectively.The shear damage was assessed using the average shear strainγat the RPC column support,and the three damage degrees were assessed at 1%,2%and 3%respectively.Using the bending-shear damage assessment criteria,six bending-shear response overpressure-impulse（P-I）curves were obtained for a typical RPC column and compared with the dynamic response of the reinforced concrete（RC）column under the same cross-sectional dimension and reinforcement.The results show that the overpressure asymptote increases by approximately 3.5 times and the impulse asymptote increases by approximately 1.84 times for the RPC columns in bending response compared to the RC columns,while the overpressure asymptote increases by approximately 34.9%and the impulse asymptote increases by approximately 19.6%for the RPC columns in shear response.（3）Five key parameters（slenderness ratio,cross-sectional dimension,RPC strength,longitudinal reinforcement ratio and axial compression ratio）were studied on the shape of the P-I curve and its asymptote.Based on the parametric analysis,a practical calculation formula for the P-I curve of RPC columns considering the bending-shear response was established.The results show that:the RPC column damage degree with the slenderness ratio,axial compression ratio（bending response）is directly proportional,and the cross-sectional dimension,RPC strength and axial compression ratio（shear response）is inversely proportional.For the RPC column longitudinal reinforcement ratio,its change for the RPC column comprehensive blast resistance effect is weak,only to meet the reinforcement requirements in actual engineering.Among the five key parameters,the axial compression ratio and cross-sectional dimension have the greatest influence on the value of the P-I curve asymptote,with the increase in cross-sectional dimension and axial compression ratio,the RPC column bending response overpressure asymptote increases by approximately 5.08times or decreases by approximately 59.3%respectively.In the analysis of the RPC column P-I curve equation,the main parameters affecting the shape of the P-I curve are the RPC column slenderness ratio,cross-sectional dimension and axial compression ratio.（4）A method of converting blast loading to TNT equivalent is proposed for the difference between a terrorist attack blast loading and conventional blast loading,and the eight categories of blast conditions were designed.A method for determining the damage probability based on RPC column P-I curve damage assessment levels is proposed for the different blast conditions.The results shown that the damage probability of the RPC columns increased by 26.4%when the slenderness ratio increased from 8.66 to 17.32,the damage probability of the RPC columns decreased by 41.9%when the cross-sectional dimension increased from 200×200mm to600×600mm.In addition,the damage probability of the RPC columns decreased by14.3%when the material strength increasing from 90 MPa to 210MPa.When the longitudinal reinforcement ratio of the RPC columns increased from 0.97%to 4.02%,the probability of failure of the RPC columns decreased by 6.3%.Finally,when the axial compression ratio of the RPC columns increased from 0.1 to 0.8,the probability of failure of the RPC columns increased by 11.5%.In summary,the parameters influencing the damage probability of the RPC columns are,in descending order of magnitude:cross-sectional dimension>slenderness ratio>RPC material strength>axial compression ratio>longitudinal reinforcement ratio.