Blast analysis of reinforced concrete beam/column members considering bond-slip effect and loading history

Abstract

An improved numerical model that that can simulate the nonlinear behavior of RC members subjected to uniformly distributed blast loadings is introduced in this thesis. Both flexural and direct shear behavior are incorporated in the one-dimensional finite element numerical formulation on the basis of Timoshenko beam theory. The moment-curvature relationship of an reinforced concrete (RC) section is adopted to describe the flexural behavior. A dynamic increase factor (DIF), usually defined in the stress-strain relations of concrete and steel, is newly designed to be defined in the moment-curvature relation. The plastic hinge region is considered in the finite element (FE) idealization of RC members and a modification of the moment-curvature relation is also performed within the region in order to accurately reflect the effects of the plastic deformation concentrated at the mid-span or beam-column joint due to the bond-slip after yielding of the main reinforcement. The advantages of the proposed model, compared with the layered section approach, are reduced calculated time and memory space in application to large frame structures with many degrees of freedom. Upon the construction of monotonic moment-curvature relation, the hysteretic moment-curvature behaviors of unloading and reloading are defined on the basis of the hysteretic relation of steel. Moreover, direct shear behavior, which can be observed under very high amplitude and short duration blast loading, is taken into account through implementation of the shear stress-slip relation. Finally, the validity of the introduced numerical model is established by correlation studies between analytical results and experimental data, and the effect of the finite element mesh size is also discussed. Additionally, the pressure-impulse (P-I) diagrams are constructed and compared to review the change in the resisting capacity of an RC member according to the variation of the axial force and slenderness ratio.