**Abstract**

Every building is designed according to its own structural system. Needs of making modifications to the structural systems of buildings may arise after the buildings are constructed. Any change in the structural components of the building by addition or omission will necessarily produce a change in its dynamic properties such as its stiffness, mass, and damping matrices, and modes of vibration. During earthquake actions, the new structural system will have different seismic responses than the original system. The new seismic responses such as shear, torsion, moment, and displacement may be reduced, or increased. Safety provisions require that before any changes in the structural system are carried out, a thorough seismic structural analysis of the new system be carried out. Linking two adjacent buildings with rigid or semi-rigid sky bridges is one example of such changes. Theoretical investigation of linking two buildings together by damping devices to mitigate seismic risks is finding its way into the literature. There have been numerous studies addressing the effects of connecting two buildings by rigid sky bridges on the seismic response of the new structural complex which comprises the two buildings and the linking beams and slabs. Dramatic changes in the seismic response of buildings are noted in most cases studied.

**Keywords:** structural system, seismic, dynamic properties, response, mode of vibration, damping device
