Page 260 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Steel Frame Building With Masonry Infill Walls Chapter 4 253

where:
a ¼effective width of the infill based on Eq. (4.12);
t inf ¼total thickness of infill wall including the masonry and shotcrete;
θ ¼angle of the diagonal of infill with respect to the horizontal; and
F me ¼average compressive strength of infill layers based on Eq. (4.39):

n
X
F me i t i
i¼1
F me ¼ (4.39)
n
X
t i
i¼1
where F me i is the average (expected value) of the compressive strength of the
ith layer of the infill wall.
The acceptance criteria and m-factors of shotcreted infill walls is the same
as those related to unretrofitted infill walls which were presented in
Section “Acceptance Criteria” and Table 4.12, respectively.
For more information about the various details of shotcrete and the consid-
erations during implementation of shotcrete, the reader may refer to Practical
Instruction for Shotcrete in Seismic Rehabilitation of Schools [20], Practical
Instruction for Shotcrete Connection in Seismic Rehabilitation of Schools
[21], and the Code of Practice for Design Specification Manufacturing and Con-
struction of 3D Panel Structures (Code 385) [22].
The results of evaluation of infill panels after shotcrete are presented in
Table 4.17. Based on the results in Table 4.13, all the infill walls are vulner-
able. These walls are shotcreted on both surfaces of the walls. The total shot-
crete layer thicknesses of the infill walls are 15cm and 10cm in the floor
story and other stories, respectively. All the retrofitted infill walls adequately
meet the requirements presented in Section “Acceptance Criteria” and
are not vulnerable. None of the thickness of the layers in the shotcreted infill
walls exceeds the flange width of the frame member; hence, no reduction
of the effective thickness of the infill is required in the design procedure.
Example details of shotcreting masonry infill walls are shown in
Figs. 4.19 and 4.20.

Evaluation of the Beam and Columns
The adequacy of beams and column with retrofitted infill walls is similar to the
procedure in Sections “Expected-Values of Strength” and “Lower-Bound
Values of Strength.” The internal forces and moments from the activation of
the ultimate strength of the infill wall against which the adequacy of frame
moments is checked is based on Eq. (4.40), which is 2.5 times of the expected
strength of the shotcreted masonry infill wall based on Eq. (4.38) [2]:
F U ¼ at inf F me cosθ (4.40)