An analytical model for dynamic response of beam-column frames to impulsive ground excitations

The response of building frames under impulsive ground excitations is complicated by the contributions from both global and local (member level) dynamic responses of the system, as evidenced in previous numerical simulation studies and laboratory tests. Therefore, a simplified analytical approach needs to accommodate both global and local dynamic responses in the model, as opposed to the well established single-degree-of-freedom representation in typical seismic response analyses. This paper proposes a simplified model incorporating a beam-column element with additional concentrated mass and springs at the member ends to facilitate the interaction between the global and local dynamic responses. To take into account the shear deformation and rotary inertia, the model is formulated using Timoshenko beam theory. It provides a general solution to this category of dynamic response analysis problems. With this model, the significance of the global and local dynamic responses for ground shocks with different frequency characteristics is evaluated. It is shown that with the decrease of the main pulse duration (or increase of the primary frequency), the dynamic response tends to be dominated by the member vibration, while the shear effect becomes increasingly significant. General recommendations are also given with regard to the determination of the concentrated mass and the spring constants in the analytical model and the sensitivity of the computed responses to these parameters.