Page 171 - Advanced Design Examples of Seismic Retrofit of Structures

Example of an RC Building Retrofitted by RC Shear Walls Chapter 3 163

(F) Checking satisfaction of Eq. (3.9). This equation shall be checked for four
. The eight load combina-
possible cases: M CE x+ , M CE x , M CE y+ , and M CE y
tions lead to 32 possible cases for each section in each shear wall for each
seismic hazard (Earthquake-1 and Earthquake-2). Finally, the most critical
load case is considered for the design of each section. For the walls that
cannot satisfy Eq. (3.9), steel plates are used to increase their flexural
capacity. These plates are connected to the foundation and embedded in
an RC section with a thickness of 70cm.
Examples of construction stages of the shear walls P 5 and P 6 are shown in
Figs. 3.24–3.26. Some retrofitting stages of the vulnerable shear walls P 3 and
P 4 are presented in Figs. 3.27–3.31.

Shear Design
The algorithm for design of the shear walls under shear demands is as follows;
(A) Classification of the shear walls including their added legs (if any) into
segments in North-South and West-East directions.
(B) Determination of the length, thickness, concrete compressive strength,
and steel yield strength, number and size of the shear reinforcements in
each shear wall segment.
(C) Determination of the shear capacity of each segment under two condi-
tions of the expected and the lower-bound capacity.
(D) Control of smaller shear strength of reinforcement than four times of
that of the concrete. In segments for which this control does not satisfy,
the shear strength of reinforcement is assumed to be four times of that of
the concrete.
(E) Determination of the ratio of the shear force resulted from the flexural
capacity of the shear wall to the lower-bound shear strength of the seg-
ment. Also, determination of the ratio of the shear force in deformation-
controlled action to the expected shear capacity of the segment.
(F) Comparison of the values of the ratios in the previous step and determi-
nation of the most critical ratio.
(G) In segments in which the shear capacity is smaller than the shear force in
the segment, horizontal steel strips (with 1cm or 2cm in thickness and
10cm or 15cm in width) are used to compensate the shear capacity
inadequacy.
(H) The connection of the added steel plates to the RC shear walls are made
by M25 and M20 bolts made of AIII steel which are drilled into the wall
at 40cm distance. The number of required bolts is determined based on
the shear capacity of each steel strip and the shear capacity of each bolt.
The shear capacity of each bolt is based on Eq. (3.10).
F v ¼ 0:45F u A g (3.10)