Dynamic elasto-plastic behavior of steel building sub-assemblage including CFRP retrofitting under impact load

Abstract

This dissertation presents the outcome of a theoretical and experimental study of the dynamic as well as the quasi-static elasto-plastic behavior of a steel building sub-assemblage including carbon fiber reinforced polymer (CFRP) retrofitting. The steel sub-assemblage consists of a beam-column attached to a pair of beams at its top end while its bottom end is fixed. An apparatus is constructed and used for conducting a series of experiments by applying a lateral impact load on the beam-column in the presence or absence of a static axial load. An innovative procedure for determining the shape of the forcing function caused by the impact load is then developed. A mathematical prediction model based on a partial differential equation of flexural dynamic equilibrium is formulated including new nonlinear terms to account for the elasto-plastic behavior of both a steel cantilever as well as a steel building sub-assemblage. To solve the materially nonlinear partial differential equation of equilibrium, an iterative finite-difference solution algorithm is formulated and is coupled with a tangent stiffness scheme to enforce cross-sectional axial force and flexural equilibrium conditions. The experimental results are found to be in good agreement with the predicted behavior for both non-retrofitted and CFRP-retrofitted steel building sub-assemblages. It is found that the maximum impact load to develop a dynamic plastic hinge in the beam-column of the sub-assemblage decreases in the presence of an axial load for non-retrofitted sub-assemblage. Also, for the CFRP-retrofitted sub-assemblage, the increase in the maximum impact load capacity is less than that found for the case of quasi-static loading.