Structures built next to each other in congested cities are likely to pound on each other during strong ground shaking caused by earthquakes. The main objective of this study is to examine the problem of mutual structural pounding to identify its effect on structures and then propose solutions to mitigate its effects. Mutual pounding of structural systems with varying mass, stiffness, and seismic joint gaps, subjected to several different input motions are examined. To evaluate the effects of pounding, the numerical results with and without pounding have been considered. The resilience between two impacting masses is represented by linear springs and also nonlinear Hertz model contact stiffness. Pounding causes a large increase in the shear force in the stories higher than the top pounding story, a large increase in the accelerations of the pounding floors and also large overturning effects on both structures. The parametric study of pounding of structures in series showed that in most cases the corner structures are penalized more than the interior structures. The study of the effect of foundation flexibility on the structural pounding response showed that a proper consideration of this parameter must be included in the analysis.

To alleviate the pounding effects to avoid damage to structural elements and supported secondary equipment, it was found necessary to join the structures by rigid links and brace all the stories of at least the taller structure. Joining of the floors is required to reduce the excessive floor accelerations caused by impact, whereas the story bracings are required to reduce the excessive story shears or bending moments in the higher stories caused by pounding of the lower floors. It is observed that except for very soft soils, the proposed pounding mitigation scheme will increase the shear force transmitted to the foundation, thus requiring a strengthening of the foundation as well. Since the forces in the rigid links connecting the two structures were observed to be reasonable, the joining of the two structures does not pose any special problem; it can be easily accomplished by using large-size steel rods hooked properly with both structures. In the case of column pounding where the floors of one structure pound on the columns of the other structure, the pounding mitigation strategy is to provide K-bracings on all pounding columns and diagonal bracing in the other stories to reduce high bending moment in the column, and to rigidly join them to avoid high pounding acceleration.