Shake table tests and analytical studies on the gravity load collapse of reinforced concrete frames

While the collapse vulnerability of reinforced concrete building frames constructed prior to the introduction of modern seismic codes has been well documented by earthquake reconnaissance, the mechanisms that lead to collapse are not well understood. Collapse of a structure can only occur if the structure looses its ability to support gravity loads. Among other causes, this loss of gravity load capacity could result from column buckling, unseating of the supported beam, P-δ instability, or degradation of axial capacity due to column shear failure. The final cause listed, and the effect of the axial load failure on the rest of the building frame, is the focus of the study presented in this report.; An empirical model, based on the evaluation of results from an experimental database, is developed to estimate the drift at shear failure for existing reinforced concrete building columns. A shear-friction model is also developed to represent the general observation from experimental tests that the drift at axial failure of a shear-damaged column is directly proportional to the amount of transverse reinforcement and inversely proportional to the magnitude of the axial load. The two drift capacity models are incorporated in a non-linear uniaxial constitutive model implemented in a structural analysis platform to allow for evaluation of the influence of shear and axial load column failures on the response of a building.; Shake table tests were designed to observe the process of dynamic shear and axial load failures in reinforced concrete columns when an alternative load path is provided for load redistribution. The results from these tests provide data on the dynamic shear strength and the hysteretic behavior of columns failing in shear, the loss of axial load capacity after shear failure, the redistribution of loads in a frame after shear and axial failure of a single column, and the influence of axial load on each of the above mentioned variables. An analytical model of the shake table specimens, incorporating the proposed drift capacity models to capture the observed shear and axial load failures, provides a good estimate of the measured response of the specimens.