Blast and progressive collapse analysis of reinforced concrete frames with multitudinous members

Abstract

An improved numerical model to simulate behavior of a reinforced concrete (RC) members and collapse of frame structures subjected to blast loading on the basis of the moment-curvature relation of an RC section is introduced. In order to consider the high strain rate effect in the moment-curvature relation of the section, the dynamic increase factor (DIF) is also newly designed as a function of the curvature rate through a section analysis with variation of the strain rate. The decrease in the bending stiffness of the member caused by bond-slip is taken into account by introducing equivalent bending stiffness. The dynamic hysteretic moment-curvature relation of an RC section is defined to exactly trace the post-peak structural response after experiencing the large nonlinear deformation, and to describe the direct shear failure, the dynamic shear stress-slip relation proposed by Krauthammer is considered in this dissertation. The validity of the introduced numerical model is verified through a comparison of the obtained numerical results with those from the experimental data. In order to compare the accuracy and efficiency of the proposed model, comparative studies are conducted between the proposed model and other numerical method such as the single-degree-of-freedom model and 3D simulation. Furthermore, the blast resistance of structural members is evaluated using pressure-impulse diagrams and factors affecting the resistance of members are identified. In addition, the catenary action and damage index are introduced into the numerical model in order to apply the proposed model to the frame structure, and the validity of the modified model is verified through simple frame cases. Finally, the collapse mechanism and influencing factors are identified through analysis for blast-induced progressive collapse with the proposed model, and a simple method for connecting member-level and structure-level analysis using P-I diagrams is introduced by modifying the alternate load path method.