Page 180 - Advanced Design Examples of Seismic Retrofit of Structures

172 Advanced Design Examples of Seismic Retrofit of Structures

3.5.2.3 Connections
Diaphragms-to-Shear Walls
To control the diaphragm’s shear capacity at the connection to the shear walls,
the force-controlled shear demand (from the model) at CP performance level at
the most critical loads combination for each wall is considered. These forces are
compared with the friction shear capacity of the diaphragms by assuming the
yield strength of the reinforcement of 300MPa. The controls are made in
Tables 3.15 and 3.16 for the existing and the new shear walls, respectively,
which indicate the adequacy of shear capacity in all the shear walls. The friction
shear capacities of the diaphragms are based on Eq. (3.13).

V s ¼ 0:9A s f y =S (3.13)
It is noteworthy that extra shear reinforcements are needed at the connection
of the diaphragms to some of the new shear walls. These extra shear reinforce-
ments are shown in bold in Table 3.16.

New Shear Walls-to-Existing Shear Walls
Similar to the previous section, the shear forces demand at the connection of the
new shear walls to the old ones are compared with the friction shear capacity of
the shear walls. For the connections in which the shear capacity is not adequate,
additional shear reinforcements (stitching) are used. For example, for the shear
wall W2 with φ16@20 cm, we have:

0:9A s f y
V n ¼
S
2
π 16 300
¼ 2 0:9 ¼ 541 kN=m
4 200
V n 0:2f A c ¼ 0:2 14:5 350 1000 ¼ 1015 kN=mOK
0
c
The shear forces in the shear wall under most critical loads combination are
shown in Fig. 3.36. As can be seen, the forces are smaller than the calculated
capacity.

3.5.2.4 Foundation Control and Design
The results of the evaluations indicate there is no concern for the soil pressure
and settlement; however, at the vicinity of the RC shear walls, the foundation
requires retrofitting. The related actions are as follows.

Control of the Structural Adequacy of the Foundation Under
Gravitational Loads
In this part, the controls of soil pressure, settlement, and flexural and shear ade-
quacy of the foundation under the factored gravitational loads are made. The