Ground Motions and Structures - Earthquake Engineering for Structural Design - page 373

Ground Motions and Structures 373

Figure 8.66 Mass irregularity (Gioncu and Mazzolani, 2002)

actual weight of partitions and permanent equipments on each floor. UBC (1997)
defines as irregular a mass distribution when the effective story mass is greater than
150% of the mass of an adjacent story (Valmundsson and Nau, 1997, Magliulo et al,
2002). The study of Magliulo et al (2002) considers that this condition is too severe.
Pounding of adjacent buildings. When buildings are erected without sufficient
seismic separation between them and their interaction has not been considered, the
buildings may impact each other, or pound, during an earthquake. Building pounding
can alter the dynamic response of both buildings and impart additional inertial loads on
both structures. Buildings of the same height with matching floors will exhibit similar
dynamic behavior. When the buildings pound, floors will impact with other floors,
which means that the damage due to pounding usually will be limited to non-structural
elements. Contrary, when the floors of adjacent buildings are at different levels, the
floors will impact with the columns of the adjacent building, causing serious structural
damage (Fig. 8.67a). As buildings are not in general designed for undergoing these
conditions, there is a potential risk for extensive damage and possible collapse. The
solution to avoid pounding is to design a suitable seismic separation between adjacent
buildings (Fig. 8.67b,c).