**3. Buildings connected to nearby walls at deep cuts**

Often in mountainous terrains, a building is constructed at the foot of an excavated hill, and a high "facing wall" is constructed to support the excavation. The idea of connecting the building, at floor levels, to the "facing wall" by reinforced concrete beams attracts the designer. The author prefers to call it a facing wall rather than a retaining wall because, in fact, the wall is never designed as a retaining wall. The fact is that it is usually a reinforced concrete thin wall with constant thickness and very narrow base. Connecting such a wall to the highly stiff diaphragms of the building by beams seems to convince designers that the wall is provided with a high factor of safety against sliding and overturning. According to the geometry of the excavated hill, the building slabs may be connected to the "facing wall" in two directions (see **Figures 8**–**10**).

The structural seismic analysis of a complex a multistory building connected to a wall as described has in general a completely different structural response than the bare building alone. Shear, moment, and torsional forces prove through seismic analysis to be different from the values of the isolated building. The number of the linking beams as well as their distribution on the facades of the building have a great effect on the response. The choice of the number and distribution of linking beams at the level of each floor, that is to say, their configuration on the building elevation is in fact more arbitrary than studied by practicing engineers. As such, the response of the structural complex of the building, linking beams, and facing wall may reveal a non-safe seismic performance. Ground shaking may be imparted to the building at the base level and at all floor levels, which are connected to the wall **Figure 8**.

This will be more evident and may be very unsafe when the building is connected to the wall in two directions.

Time history seismic analysis of a 10-story 3-D building connected to a nearby facing wall 0.35 m thick, is carried out using the well-known El Centro acceleration recording in two directions, **Figures 9** and **10**. The X direction is that of the linking beams, and Y direction is perpendicular to it. The analyzed model includes the foundation soil below the building and the soil behind the facing wall attempting

#### **Figure 8.**

*Section of a multi-story building connected to an adjacent wall by beams.*

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

**Figure 10.** *A building connected to a nearby wall by several beams at different floor levels, Amman, Jordan.*

to include soil-structure interaction. Below foundation soil and the deep-cut soil are modeled as solid elements in SAP200. Soil properties are modulus of elasticity E = 2x105 MPa, Poissons ratio = 0.2, and shear modulus G = 77 MPa. The facing wall or beams can be connected to the cut soil by Gap links according to SAP 200 modeling techniques. While the foundation of the column can be connected to the underlying soil by springs with suitable spring constants depending on the soil stiffness. The analysis results show that the behavior of the connected building with the linking beams is completely different from that of the isolated building. Behavior differences are evident in displacements, member response forces, periods of vibration, and mode shapes. **Figures 11a** and **12a** show analysis plots of SAP2000 output for the shear, moment and torsional forces of the building with the linking beams and soil, while **Figures 11b** and **12b** show the output of the isolated building. The differences between the results can not be overstressed. These are only examples to show the complete change of the structure behavior when the building is linked to a nearby wall.

Based on the analysis results, the following general notes can be drawn:


#### **Figure 11.**

*Comparison between shear and moment values of the isolated building B, and the building connected with linking beams to the wall and soil masses below and adjacent to the wall a. values are taken at 1.0 second from the application of El Centro excitation in the direction perpendicular to the linking beams.*

#### **Figure 12.**

*Comparison between torsional force values of the isolated building (12-B), and the building connected with linking beams to the wall and soil masses below and adjacent to the wall (12-a). Values are taken at 1.0 seconds from the application of El Centro excitation in the direction perpendicular to the linking beams.*

4.The shear, torsional forces, and moments in the building beams and columns as well as the linking beams and the "facing" wall may have excessive values beyond their original design capacities and could be unsafe.
