Math in the Workplace - Measurements/Geometry
MONROC
Precast Concrete Structures
Job Site Construction Supervisor
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Job Description: Responsible for coordinating subcontractors' work and arrival of materials. Insures work is done correctly, safely, and on time. |
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Problem:
How many cubic yards of concrete will it take to make a bridge girder, called a voided flat slab?
The girder is 48 inches wide, 26 inches tall, and 54 feet long.
There are four 16 inches in diameter voids within the slab. The voids are each 24 feet long.
On each side of the girder is a 1" by 6" keyway.
 MONROC
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Solution:
1. Figure the total possible volume of the voided flat slab.
W x H x L = volume
48" width x 26" height x (54' x 12") length = 808,704 in3
808,704 in3
12" x 12" x 12" |
= 468 ft3 (volume) |
2. Calculate the 1" x 6" keyways on each side of the girder.
3. Calculate the 16" diameter voids.
Volume of cylinder = pr2 x length
| 3.14 x (8" x 8") x 288" = |
57,876.48 in3
12" x 12" x 12" |
= 33.499 ft3 |
33.49 ft3 x 4 voids = 133.97 ft3
4. Subtract the volume of the keys and voids from the total volume of concrete.
| 468 ft3 - (4.5 + 138.47) ft3 = |
329.53 ft3
3' x 3' x 3' |
= 12.21 yd3 |
This is a common geometry problem for engineers and construction supervisors. It requires math and geometry as well as analytical thought.