Page 230 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Steel Frame Building With Masonry Infill Walls Chapter 4 223

it is conservatively assumed that the frame connections in the example building
is pin, hence R 1 ¼0.5. It is worth mentioning that the wall in the axis B-1-3 can-
not be regarded as the infill panel, because it does not meet the requirements of
the position of the opening according to ICERIFB; however, by reducing the
size of the opening in this wall, it is possible to consider this wall as an infill
panel. The infill panels and the effective width of their equivalent struts are pre-
sented in Table 4.9.
Thickness. Because the infill panels in the example building are completely
located inside the frames, their whole thickness is considered in calculations.
However, it is necessary to install steel plates at the corners of the infill in order
to improve the connection between the infill panels and the surrounding frame.
The details of this plate are presented in Section “Evaluation of the Frame
Connections.”
Expected Shear Strength. According to ASCE 41 [1], the shear behavior in
infill panels is considered a deformation-controlled action. The expected shear
strength of infill panels shall be computed in accordance with Eq. (4.15).
a t inf f me cosθ
Q CE ¼ (4.15)
2:5
where:
a ¼effective width of infill panels which is computed in accordance with Eq.
(4.9);
t inf ¼thickness of infill panel and equivalent strut;
f me ¼expected compressive strength of infill material which is assumed to be
5.0MPa in this example; and
θ ¼angle whose tangent is the infill height-to-length aspect ratio (radians).
The expected shear strengths of infill panels in the transverse direction are pre-
sented in Table 4.10.

4.4.2.5 Analysis of the Building
In the presented example, the linear static procedure (LP) is utilized to analyze
the building under seismic demands.

Natural Period of the Building
According to ICERIFB [2], the natural period of the building can be determined
according to Eq. (4.16).
3
T ¼ 1:25 0:05 H 4 (4.16)

where H is the total height of the building.
3
H ¼ 9:8m ! T ¼ 1:25 0:05 9:8 4 ¼ 0:346 s