**5. Theoretical studies of buildings connected together by damping devices**

The three previous parts of this chapter show cases of connecting building together or to adjacent walls. The purposes of such connections are to make easy and fast circulation between connected buildings in the former case and produce strong lateral support for the walls in the latter case. Previous studies of those cases have not tried to investigate means of mitigating earthquake effects on the new structural complexes produced by the connections. Numerous new studies have been carried out adopting newly invented technical devices to control and alleviate seismic effects on buildings. These techniques could be suitable methods of balancing the risks arising from connecting buildings to each other or to nearby walls. The door is open for more theoretical and experimental research in this regard.

## *Some Risky Practices in Earthquake Engineering That Need More Research and Evaluation DOI: http://dx.doi.org/10.5772/intechopen.108445*

Newly developed techniques for changing the dynamic properties of buildings are linking two nearby buildings by damping devices. Previous sections of this chapter considered buildings rigidly connected to each other or to walls, without aiming at reducing seismic responses during earthquake excitations. This section considers previous theoretical studies conducted to enhance buildings' performance during seismic actions. The purpose was to reduce story drifts, member moments, shear, and torsional forces. This is done by connecting two adjacent buildings with damping devices to dissipate energy imparted to the buildings by ground acceleration.

The buildings were considered a few stories to more than 50 floors in height. Many types of damping devices were used. Friction pendulum bearings are seismic isolators used usually between the structure and its foundation. In one study [12], they are used between the sky bridge and the buildings on both sides of the sky bridge. Viscous, viscoelastic, and friction dampers were also used in another theoretical study [12] to connect two buildings at different heights to reduce the effects of earthquake actions. Viscous damper reduces the vibrations induced by earthquakes, while viscoelastic dampers dissipate the building's mechanical energy by converting it into heat. Friction dampers operate by dissipating kinetic energy through friction. Friction dampers are installed diagonally between floors to reduce the story drifts. In one study, they were used between two buildings to reduce the earthquake effects by dissipating energy through frictional forces as shown in **Figure 14**. A summary of these studies is included here.

Bhaskararao et al. [11] conducted a theoretical investigation of two adjacent buildings connected with various types of dampers namely *viscous, viscoelastic, and friction dampers*. With all types of dampers used, it was concluded that the earthquake response of the two buildings was reduced. It was also concluded that it was not necessary to connect the buildings at all floor levels to achieve such a reduction. Optimum location of dampers at specific floor heights can be obtained.

Xiaohan et al. [12] considered four similar towers, around 240 m high, connected with a sky corridor bridge 300 m long at the rooftop. SAP200 software was used in

**Figure 14.** *Friction dampers used to connect two buildings at floor levels.*

#### **Figure 15.**

*Pounding of two adjacent buildings and damage produced. Full article: Effects of pounding on adjacent buildings of varying heights during earthquake in Pakistan (tandfonline.com).*

the analysis. *Friction pendulum bearings* are installed on the buildings' tops to support the sky corridor bridge. Several damping devices connected the towers and the sky bridge. The purpose of the study is to reduce the earthquake response and the member forces using the used devices. The authors concluded that connecting towers with friction pendulums with tuned mass dampers reduced effectively the structure seismic responses. Best seismic reduction was obtained when the frequency of the dampers is close to the frequency of the primary structure. On the other hand, larger interaction forces between sky bridges and towers were noted when towers and bridges were rigidly connected, a finding consistent with other research conclusions [15].

Rouzbeh et al. presented a state-of-the-art review of buildings connected together by various types of links. The authors classified the buildings coupling as rigid, passive, semi-active, active, and hybrid connections. These coupling links proved to be effective in preventing the pounding of adjacent buildings and reducing their seismic response. Damage to buildings due to pounding is very common between nearby or adjacent buildings during earthquakes, **Figure 15**.

Uz et al. [14] used fluid viscous dampers to connect two buildings and concluded that they improve the response of buildings to earthquakes, **Figure 16**.

Huaxiao et al. [16] carried out a theoretical study of two unequal buildings connected together by varying number of passive control devices at different floor levels. These devices can be metal friction dampers or fluid viscous dampers. The buildings are 59 stories (268 m height) and 55 stories (210.2 m height). The buildings are connected by a corridor with rigid support at one terminal and sliding support at the other terminal, the same way as suggested by the writer. The study considered wind forces and earthquake excitation at the same time. Tuned Liquid Column Damper Inerter (TLCDI) and tuned mass damper with an inerter (TMDI) are used to connect the two buildings to mitigate the wind and earthquake responses. The authors

*Some Risky Practices in Earthquake Engineering That Need More Research and Evaluation DOI: http://dx.doi.org/10.5772/intechopen.108445*

**Figure 16.**

*Typical fluid viscous dampers. Viscous damper - an overview | ScienceDirect topics.*

concluded that these devices are effective in reducing the wind and earthquake responses, and they are more effective in the wind case than in the earthquake case.

Based on these and other studies concerning the earthquake mitigating devices linking two buildings, the flowing can be concluded:

