Civil Engineering Reference
In-Depth Information
Table 4.16
Distributed loads on beams.
Framing system
Dead load (kN/m)
Live load (kN/m)
External frames (F1)
20
10
Internal frames (F2)
30
15
Table 4.17
Concentrated loads at the beam - column connections.
Framing system
Load at external col. (kN)
Load at internal col. (kN)
Load at cut -off col. (kN)
External frames (F1)
80
100
10
Internal frames (F2)
125
180
n.a.
Key
: n.a. = not applicable.
hW
xx
F
=
V
(4.44)
i
n
∑
1
Wh
i
i
where
W
is the total load (dead load and 25% of the live load);
h
i
and
h
x
are the height from the foun-
dation level to fl oor
i
and
x; W
i
and
W
x
are the portion of the total gravity load
W
located at level
i
or
x
; and
n
is the total number of stories. The seismic base shear coeffi cient
C
is the spectral response
acceleration (expressed in ' g ' ) obtained from the 'design' spectrum multiplied by the importance factor
(
I
), which should be taken equal to 1.1 for this building.
It is required to:
1. Model the two lateral resisting systems in the X-direction (F1 and F2) using any fi nite element
program and distribute the gravity loads on the two frames.
2. Calculate the actions of frame F1 from gravity loads.
3. Calculate the total base shear and distribute it along the height for the two lateral resisting systems
F1 and F2.
4. Estimate the actions and deformations of frame F1 using the equivalent static force procedure.
Modulus of elasticity of concrete,
E
c
, is 26 KN/mm
2
and Young's modulus of steel
E
s
is 200 KN/
mm
2
. Use 50% and 70% of the un-cracked stiffness of beams and columns, respectively, to esti-
mate the effective fl exural stiffness.
5. Estimate the periods of vibration and plot the fi rst three mode shapes of frame F1.
6. Estimate the actions and deformations of frame F1 using the response spectrum analysis proce-
dure. The response modifi cation factor and the design PGA should be used to scale the elastic
spectrum given in Figure 4.48 to obtain the design spectrum employed for the structural
analysis.
7. Use the earthquake record relative to the horizontal component of the Loma Prieta earthquake
(Northern California at Saratoga 'Aloha Ave.', USA, 1989). Scale the record to the PGA derived
from the attenuation relationship for the construction site given in equation (4.40). Perform elastic
response history analysis for frame F1 using the scaled record. Modern seismic codes allow for
a reduction in base shear demand from elastic response history analysis by using the response
modifi cation factor (
q
- or
R
- factor).
