Transverse direction;
Ct = 0.020
Shear wall system
Longitudinal direction;
Ct = 0.030
Reinforced concrete moment frame
Resisting 100% of seismic forces
hn = 33-ft (10.06m)
Height to highest level
Ta = 0.020(33' )3/4 = 0.28 sec
Therefore;
transverse
Ta = 0.030(33' )3/4 = 0.41 sec
longitudinal
B-2 Determine Dead Load ` '
W:
Note: For determining the base shear, the proportions of the moment frame elements are initially guessed.
This is judged to provide adequate results because most of the weight of the building is due to the shear
walls and the pre-cast concrete floor and roof framing thereby making the moment frames a relatively small
percentage of the total building weight. The reproportioning of the moment frame elements is judged to
have negligible effect on the base shear. The beams are proportioned first using a rule of thumb of one inch
(25.4mm) of depth for every foot (0.305m) of span with the width being conservatively taken as 3/4 of the
depth. The columns are then proportioned to have the same dimensions as the beams. The columns are
proportioned as such because, by inspection, they support very little axial load and function primarily in
flexure with a loading similar to that of the beams (pre-cast concrete planks spanning between bearing
walls provide the primary gravity support, and the concrete frames are left to support only their own self
weight).
Try a 24" (609.6mm) deep x 18" (457.2mm) wide floor beam and column, and 16" (406.4mm) deep x 18"
(457.2mm) wide roof beam;
Check proportion requirements of ACI 318-95 Section 21.3, and 21.4;
Floor & Roof Beams;
Clear span = 21.5' 4(24")(1'12") = 8'(2.44m)floor or >4(16")(1'12") = 5.33'(1.63m)roof
>
/
/
O.K.
b 18"
b 18"
=
= 0.75 > 0.3
=
= 1.13 > 0.3
O.K.
(floors)
(roof)
h 24"
h 16"
b = 18" > 10"
b = 18" > 10"
O.K.
(floors)
(roof)
(457.2mm > 254.0mm)
(457.2mm > 254.0mm)
3
3
b = 18" ≤W + h = 54" (floors)
b = 18" ≤W + h = 54" (roof)
O.K.
2
2
(1371.6mm)
(1371.6mm)
Column;
W 18"
=
= 0.75 > 0.4
O.K.
C 24"
W = 18" > 12" (457.2mm > 304.8mm)
O.K.
H2-16
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