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

joints shown, being one to the left and the other to the right, produce a story drift of 263 + 243 = 50.6 mm. Similarly, for the left building frame, it is 66.4 mm. Some code limitations require that inter-story drift not exceed 0.015–0.02 h where h = story height. 0.015x3000 = 45 mm. These values of inter-story drift could be detrimental

#### **Figure 4.**

*Shear forces in beams and columns and the sky bridges under seismic excitation, a case of three sky bridges, with permission of the author [15].*

#### **Figure 5.**

*Torsional forces in beams and columns and the sky bridges under seismic excitation, a case of three sky bridges, with permission of the author [15].*

to the whole structure unless they are designed for such high values [15]. The linking bridge or bridges as well as some of the beams and columns of the two buildings may attract very large torsional, shear and moments values, which may well exceed their design capacities, and might render the buildings unsafe, **Figures 4** and **5**, [15]. For example, in the structure with three sky bridges, **Figures 4** and **5**, the bending moment in columns 269–270 is 93.2 kN.m as compared to 35.4, 51.6, and 60.6 kN.m for other columns in the same floor in the same plane. The same column has a shear force of 51.7 kN as compared to 25.3, 31.2, and 38.1 kN for other columns on the same floor in the same plane (see **Figure 4**).

Another note-worthy example is for a column in the top short tower which shows a moment of 67.4 kN.m when it is part of the twin towers and connected to the sky

**Figure 6.** *Suggested method of connecting two building by a sky bridge.*

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

beam, but it shows a reversed moment of 63.7 kN.m when it is in the unconnected single short tower under the same load combination. Similarly, some of the linking beams may attract large torsional forces that exceed their design capacities. The same note can be observed in the beams closest to the sky beams, **Figure 5**.

Code and safety requirements warrant that seismic analysis and redesign of the complex should be considered by the designer before connecting the two buildings.

The author suggests the connection of the two buildings be designed by having the linking bridge rigidly connected to one building while the other end has a sliding support to allow some movements during earthquake excitations, **Figure 6**. One important requirement for this type of connection is that the distance of the linking bridge resting on the building floors (distance L in **Figure 6**) should be larger than the expected maximum sum of the two displacements of the two connected floors during the design earthquake by a suitable factor of safety. The two displacements comprising the distance L should be obtained from inelastic dynamic analysis of the buildings where nonlinear plastic properties of the materials are utilized. **Figure 7** shows another example of a multistory building linked to a car park building by steel I section long after the two buildings were constructed.
