A 20-meter-high square-plan five-storey building with flat roof and 4m-high floors, located in Makati CBD, has sides of 10 meters length each, and a large open front door on the first floor that is 2m x 2m in dimension. Assuming that G = 0.85 and that torsion is negligible,
- Show how this maybe is an open, partially enclosed, or enclosed building.
- Determine the internal pressure coefficients.
- Determine the external pressure coefficients for the design of main girders and shear walls.
- Determine the base reactions due to along-wind loads acting on the front wall of the building.
1. The building satisfies all definitions of a partially enclosed building (NSCP 2010 Section 207.2).
2. The internal pressure coefficients for a partially enclosed building (GCpi) are +/- 0.55 (NSCP Figure 207-5).
3. The external pressure coefficients on MWFRS (from NSCP 2010 Figure 207-6) are as follows:
- windward wall, Cp = 0.8
- leeward wall, Cp = -0.5 since L = 10m, B = 10m, and L/B = 1
- side walls, Cp = -0.7
- whole roof, Cp = -1.04 or -0.18 since h = 20m, h/L = 2, L <= h/2 = 10m, and Roof Area = 100 sq.m > 93 sq.m
4. The base reactions can be calculated after we calculate the design wind force at each level. However, taking x = along-wind direction, y = across-wind direction, z = vertical direction, we already can deduce that Vy = 0, and Mx = 0. Additionally, Mz is given as zero. We only need to estimate Vx, Vz, and My.
To calculate the design wind force at each level, we need to multiply net design wind pressures at each level with tributary areas. To get net design wind pressures, we calculate pressures on both windward and leeward faces. On each face, we need to calculate the net of external and internal pressures. To get external and internal pressures, we need first to calculate the velocity pressures at each level. To calculate by hand, it is easiest to do this in table form but with a computer, a spreadsheet makes it much easier:
| Assume: Exposure Terrain Category B Case 2, Iw = 1.0, Kd = 0.85, Kzt = 1.0, V = 200 kph | ||||||
| Windward wall pz (kPa) | Leeward wall pz (kPa) | |||||
| z (m) | Kz | qz (kPa) | with +Gcpi | with -Gcpi | with +Gcpi | with -Gcpi |
| 20 | 0.88 | 1.42 | 0.18 | 1.75 | -1.38 | 0.18 |
| 16 | 0.82 | 1.32 | 0.12 | 1.68 | -1.38 | 0.18 |
| 12 | 0.76 | 1.22 | 0.05 | 1.61 | -1.38 | 0.18 |
| 8 | 0.67 | 1.08 | -0.05 | 1.52 | -1.38 | 0.18 |
| 4 | 0.57 | 0.92 | -0.16 | 1.41 | -1.38 | 0.18 |
| 0 | 0.57 | 0.92 | -0.16 | 1.41 | -1.38 | 0.18 |
Net
along wind pressures pz (kPa)
|
Afz (sqm)
|
Net
along wind loads Fz (kN)
|
Base
bending moment contribution My,z (kNm)
|
|||
with +Gcpi
|
with -Gcpi
|
with +Gcpi
|
with -Gcpi
|
with +Gcpi
|
with -Gcpi
|
|
1.56
|
1.57
|
20
|
31
|
31
|
620
|
620
|
1.5
|
1.5
|
40
|
60
|
60
|
960
|
960
|
1.43
|
1.43
|
40
|
57
|
57
|
684
|
684
|
1.33
|
1.34
|
40
|
53
|
54
|
424
|
432
|
1.22
|
1.23
|
40
|
49
|
49
|
196
|
196
|
1.22
|
1.23
|
20
|
24
|
25
|
0
|
0
|
Vx (kN) =
|
274 | 276 | 2884 | 2892 | ||
My (kNm) =
|
||||||
| Af,roof (sqm) | Roof loads 1, p (kPa) | Roof loads 2, p (kPa) | Vz = Roof loads 1 (kN) | Vz = Roof loads 2 (kN) | ||||
| with +Gcpi | with -Gcpi | with +Gcpi | with -Gcpi | with +Gcpi | with -Gcpi | with +Gcpi | with -Gcpi | |
| 100 | -2.04 | -0.47 | -1 | 0.56 | -204 | -47 | -100 | 56 |
| Vz (kN) = | -204 | 56 | ||||||
Spot any errors? Sound out in the comments. :)
