Problem 1: Tributary lateral load.
The question is on a fictitious 1965 building in Albany, NY. It was designed using the 1964 State Building Construction Code, in which Allowable Stress Design was used.
This flat-roofed building has three stories: a 15 ft. tall ground story and two 12.5 ft. upper stories.
A typical floor plan is shown in Figure 1a. The floors can be assumed to be rigid diaphragms, which is very important when determining force distribution.
An elevation of an interior frame in the narrower, N-S direction is shown in Figure 1b.
The Wind Loads from the 1964 code are as follows:
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At height above grade (feet)
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Exterior Walls (psf)
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>500 to 600
|
34
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>400 to 500
|
33
|
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>300 to 400
|
32
|
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>200 to 300
|
30
|
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>100 to 200
|
28
|
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>60 to 100
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24
|
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>40 to 60
|
21
|
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>25 to 40
|
18
|
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>15 to 25
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15
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0 to 15
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12
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*Within a given height interval, the wind load pressure is constant.
Use exterior windward forces only. That is, assume that leeward and sidewall pressures = 0 psf, all interior pressures = 0 psf, and all roof pressures = 0 psf.
Within each story, half of the wind pressure is resisted by the upper floor and half of the wind pressure is resisted by the lower floor (which is the ground for the ground story).
What is the North-South diaphragm wind shear (in pounds per lineal foot, plf) that acts at the top of the ground story at elevation = 15'-0"? Calculate the service load.
Figure 1a. Typical Floor Plan
Figure 1b. Elevation of Gridline C and D
Problem 2.
For the building in Problem 1, the latest building code requires an increase in wind shear over the earlier code. The service load wind shear is 80.0 kips at the top of the Ground Story. If you distribute this load over the length of the long side of the building it becomes 80 kips/125 ft = 0.64 kips/ft or 640 pounds per lineal foot (PLF).
Assume that the stiffness of the lateral load resistance is the same along Lines A, C, D, and F. Yes, the Chevron braces used in Frames C and D are comparatively large. In the North-South direction, what is the distribution of the service load wind shear to the Ground Story frames that contain lateral load-resisting Chevron braces?
Remember the floors are considered rigid diaphragms. Choose one of the following:
A. VC = VD = 8.0 kips and VA = VF = 32.0 kips
B. VC = VD = 10.0 kips and VA = VF = 30.0 kips
C. VC = VD = 16.0 kips and VA = VF = 24.0 kips
D. VC = VD = 20.0 kips and VA = VF = 20.0 kips
E. VC = VD = 30.0 kips and VA = VF = 10.0 kips
3. Drift limit.
For the building in Problem 1, assume that the limiting drift index (limiting drift ratio) = 0.00235.
What is the maximum allowable drift (inches) at the top of the ground/first story?
4. Axial loaded compression members.