Experimental and analytical dynamic collapse study of a reinforced concrete frame with light transverse reinforcement

Post-earthquake investigations have shown that the primary cause of collapse in cast-in-place beam-column frames is failure of columns, beam-column joints, or both. As axial failure of one or more member in a frame structure does not necessarily constitute the collapse of that structure, understanding frame-system behavior and frame member interactions leading to collapse is essential in assessing the seismic collapse vulnerability of this type of structure.;This study investigates, both experimentally and analytically, the seismic collapse behavior of non-seismically detailed reinforced concrete frames. To accomplish this task, a 2D, three-bay, three-floor, third-scale reinforced concrete frame is built and dynamically tested to collapse. The test frame contains non-seismically detailed columns whose proportions and reinforcement details allow them to yield in flexure prior to initiating shear strength degradation and ultimately reaching axial collapse (hereafter referred to as flexure-shear critical columns). Experimental data is provided on the dynamic behavior of flexure-shear critical columns sustaining shear degradation and loss of axial load capacity and on load redistribution in a frame system after shear and axial failure of columns.;Analytical modeling of the test frame is undertaken up to collapse. Good agreement between analysis and experiment is achieved up to shear failure in columns. A new zero-length fiber-section implementation of bar-slip rotational effects is introduced. A new shear failure model is introduced that determines column rotations at which shear strength degradation in flexure-shear critical columns is initiated.;An analytical model of the test frame is subjected to several near-fault ground motions recorded during the 1994 Northridge earthquake. Variability of ground motions from site to site (so called intra-event variability) and directivity effects are found to play an important role in analytical prediction of structural collapse. A new ground motion intensity measure that relates well to frame damage is proposed.