**4. Theoretical studies of buildings rigidly connected by sky bridges**

There has been a lot of theoretical research on nearby buildings linked together by steel or reinforced concrete sky bridges. Numerous adjacent world skyscrapers are connected by sky bridges. The Petronas Twin Towers in Malaysia is a typical example (**Figure 13**).

Esthetic and grand appearance of similar connected towers is one architectural purpose of the connection. The sky bridges can serve as fire escape routes in addition to ease of circulation and time-saving purposes [3]. Theoretical studies of the effects

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

#### **Figure 13.**

*Petronas twin towers in Malaysia connected together by a sky bridge. Petronas twin towers | buildings, Kuala Lumpur, Malaysia | Britannica.*

of inking on the seismic performance of connected buildings have been addressed by many authors [2–10]. The problem of buildings linked together by sky bridges has not found its way into building design codes due to the extreme complexity of the issue. Research has shown, in general, cases of increased seismic response of the buildings, and cases of reduced seismic performance. The heights of the connected buildings varied from few floors up to more than 250 m of height. The connection was, usually, modeled as rigid beams or slabs made up of reinforced concrete or steel. The position of linking sky bridges, as they are called by researchers, was shifted from floor to floor to investigate the effects of such positions on the performance of the buildings. In general, the findings of most of those theoretical studies indicated that such rigid connections of the two buildings often resulted in dramatic changes in the seismic performance of the two isolated buildings. The seismic response (mode shapes, frequency, shear, torsion, moment) of the complex of linked buildings and sky bridges are much different for each isolated building before connection. A summary of some theoretical work is presented next.

Sayed, M [2] studied 30-floor twin buildings with sky bridges connecting them at different heights utilizing ETABS software. The sky bridge connecting the towers is 33.6 m long built of reinforced concrete and resting on the buildings' columns on either side. As such, the connection to the towers is a rigid connection. The study did not aim at alleviating the buildings of any earthquake actions. The study conclusions described the effect of changing the height of the position of the sky bridge on the seismic response of the buildings. None of the findings of the research mentioned anything about reducing the forces or seismic responses of the buildings.

Abbood et al. [3] conducted a study on 40-floor twin buildings connected rigidly by 3 reinforced concrete links at the upper two stories. The links were 15 m long and modeled as a beam and slab. The results of the study showed that the seismic response of the two connected buildings increased or decreased compared to the single tower's response. The study did not aim at reducing the effect of earthquake actions on the structures.

Tse et al. [4] investigated the 3-D theoretical model of two 40-floor buildings with the links connecting them modeled as rigid beams with 3 degrees of freedom at each end. The study examined the effect of changing the location of the links on the periods of vibrations.

Sayed et al. [5] carried out a 3-D dynamic (time history) analysis of the Petronas Twin Towers in Malaysia connected with a linking reinforced concrete sky bridge. The analysis used an earthquake string record scaled to 0.15 g ground acceleration in the direction of the sky bridge as well as in the orthogonal; direction. The sky bridge was positioned at the following floor heights to investigate the effect of its position on the seismic response of the connected twin towers: 22nd, 44th, 66th, and 88th floors. The analysis results were compared to the results of the bare towers, which revealed that the seismic response in the sky bridge was amplified. It was also found that the location of the sky bridge on the upper floors had a detrimental effect on the seismic response of the twin towers when the earthquake excitation was in the direction of the sky bridge.

Hu et al. [7] theoretically investigated two linked buildings for the wind-induced response. The effects of the mass, stiffness, and location of the links on the acceleration of the linked buildings revealed that the torsional acceleration of the linked buildings was always larger than that of the unlinked buildings. This is in agreement with other research [15]. The author concluded that designers should be careful of this fact when designing linked buildings [7].

Based on the general findings of previous research, the following notes can be drawn:

