Question
Asked Aug 28, 2019
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A corner of a flat roof system in a reinforced concrete building is shown in plan view (see attached image). The tops of the reinforced concrete columns are shown as rectangles along lines A, B, and C. Column A1 is a corner column at the exterior of the building. Columns B1, C1, A4, and A7 are exterior columns around the perimeter of the building. Columns B4, C4, B7 and C7 are interior columns. Reinforced concrete girders (12in wide by 20in deep) span 30ft between columns along lines A, B, and C. Reinforced concrete beams (8in wide by 14 in deep) span 25ft between girders (or occasionally between columns) along lines 1 through 7. The concrete roof is a slab 6in thick and is supported by the concrete beams and girders. The beams, griders and columns are normal weight reinforced concrete (unit weight=150lb/ft3). The roof is lightweight concrete (weight is 8lb/ft2 per inch of slab thickness). In addition to dead loads, the roof must also support a snow load of 30lb/ft2.

  • Provide a free body diagram (FBD) of a beam along line 1 and show dead loads (including beam self-weight) and the snow loads acting on the beam. Label the maximum magnitude of the distributed load.
  • Provide an FBD of a beam along line 3 (spanning between girders) and show the dead load (including beam self weight) and snow loads acting on the beam. Label maximum magnitude of the distributed load.
  • Provide an FBD of a girder along line B (spanning between columns) and show the dead loads (including girder self weight) and snow loads acting on the girder. Label the maximum magnitude of any distributed loads, and also the magnitude of any point loads.
  • Determine the total magnitude of (dead+snow) load acting on the top of the interior column at the intersection of line b and line 4 (column B4).
  • Determine the total magnitude of the (dead+snow) load acting at the top of the corner column, A1.
25 FT
25FT
A
10FT
10 FT
10 FT
10FT
10 FT
10FT
2
3
4
5
6
7
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25 FT 25FT A 10FT 10 FT 10 FT 10FT 10 FT 10FT 2 3 4 5 6 7

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Expert Answer

Step 1

As per the rule, we have solved the first three sub part for your question, if you need the answer for any specific sub part, kindly repost the question mentioning that sub parts.

Show the slab as shown in Figure below:

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O B-2 B-1 B-3 B-3 B-3 B-2 25 f B7 B4 25f7 A 10FT 10FT 10PT 10FT 10FT 10FT 2 3 4 7

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Step 2

Check whether the slab is one way slab

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25 Slab size 10 2.5> 2( one way slab)

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Step 3

Find the load acting...

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Dead load on the slab = 6"x 81b/ft2 /in -481b/ft2/in Snow load 30psf Live load on roof 20psf Total Factored load,w =1.2x48+1.6 x30 -105.6 psf 106 psf

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