Civil Engineering Reference
In-Depth Information
Problem 2.6
Rank the components circled below (Figure 2.52) according to overstrength factors Ω
d
to render
the structure ductile (higher energy dissipation capacity):
• Beam, Ω
d,bf
;
• Column, Ω
d,cf
;
• Beam - column joint, Ω
d,js
.
Ω
Ω
d
i
R
=
(2.33)
The seismic performance of structural systems is satisfactory if the
R
- factors supply exceed the
R
-factor demands, discussed in Section 3.4.4 .
Ω
d,bf
: Overstrength factor for beam flexural strength
Ω
d,js
: Overstrength factor for beam-column joint shear strength
Ω
d,cf
: Overstrength factor for column flexural strength
Figure 2.52
Overstrength factors employed for the design of multi-storey moment-resisting frames
Problem 2.7
The inelastic behaviour of two medium-rise steel moment resisting frames (MRFs) is assessed by
the pushover curves provided in Figure 2.53. Response parameters of these frames are summarized
in Table 2.10. Determine yield and ultimate deformations according to Section 2.3.3.1 , as appropri-
ate. Compare the computed values of
Δ
u
and
Δ
y
with those in Table 2.10. Determine observed
Ω
d
and inherent
Ω
i
overstrength factors for the frames. Compute also
R
- factors supply and translation
ductility
μ
δ
. Comment on the results.
Table 2.10
Response parameters of assessed frames.
Frame (label)
Period (seconds)
V
d
/
W
(%)
V
y
/
W
(%)
V
u
/
W
(%)
Δ
u
/ Δ
y
( - )
MRF_1
2.53
4.04
10.18
14.28
4.10
MRF_2
3.63
1.51
7.53
8.02
1.52
Key
:
V
d
= base design shear;
V
y
= base actual shear;
V
u
= base shear at collapse;
W
= seismic weight; Δ
y
= roof
drift at yield; Δ
u
= roof drift at collapse.
