Page 229 - Advanced Design Examples of Seismic Retrofit of Structures

222 Advanced Design Examples of Seismic Retrofit of Structures

The thickness of the strut and the modulus of elasticity of the material assigned
to struts are the same as those in the real infill panels in the example building.
The effective width of these struts is determined based on the method presented
in this section, which is based on ASCE 41. It is noteworthy that the proposed
relations in ASCE 41 are based on solid infill panels inside frames with rigid
connections. As a result, these relations should be modified to be used in this
example building, as some of the infill panels have openings and all the frame
connections are simple. Also, in order to capture better the demands from the
infill walls on the frame members, several multi-strut models have been pro-
posed which can be alternatively used for simulation of the effects of infill walls
[17, 18].
Effective Width. According to ASCE 41 [1], the effective width of the infill
(a) is determined based on Eq. (4.12).
0:4
a ¼ 0:254 λ l h col Þ r inf R 1 R 2 (4.12)
ð
where:
0:25
10E me t inf Sin 2θÞ
ð
λ l ¼
E fe I col h inf
h col ¼column height between centerlines of beams;
h inf ¼height of infill panel;
E fe ¼expected modulus of elasticity of frame material;
E me ¼expected modulus of elasticity of infill material;
I col ¼moment of inertia of column;
r inf ¼diagonal length of infill panel;
t inf ¼thickness of infill panel and equivalent strut;
θ ¼angle whose tangent is the infill height-to-length aspect ratio (radians);
λ l ¼coefficient used to determine equivalent width of infill strut; and
R 1 ¼the reduction coefficient for frame connections according to ICERIFB
[2]; if the connection is rigid or pin, the coefficient is unity and 0.5, respec-
tively. For other cases, this coefficient is determined according to Eq. (4.13).

R 1 ¼ 0:51 + CRð Þ (4.13)
where CR¼the rigidity of the connection, with CR¼1 as the rigid connection
and CR¼0 as the pin connection, and R 2 ¼the reduction coefficient for infill
panels having opening according to ICERIFB [2] which is determined accord-
ing to Eq. (4.14):

2
A Opening A Opening
R 2 ¼ 0:6 1:6 + 1 (4.14)
A Panel A Panel
where A Opening ¼the area of the opening and A Panel ¼the area of the panel.
According to Karami [15], the cradle-type connections are semi rigid; how-
ever, due to lack of sufficient data about the rigidity of this type of connection,