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V. IS 875 (Pt 3) 2015 WL Generation on Rectangular Clad Bldg 2

Verify the calculated wind pressure on an edge node on a clad building per the IS 875 (Part 3): 2015 code.

Details

The following structure:



Not all members are displayed here for clarity.

  • Building length along wind when wind blow +X or -X direction, Lx = 11.5 m
  • Building length across wind when wind blow +X or -X direction, Lz = 21 m
  • Building length along wind when wind blow +Z or -Z direction, Lz = 21 m
  • Building length across wind when wind blow +Z or -Z direction, Lx = 11.5 m
  • Building Height, h = 30 m
  • Basic Wind Speed, Vb = 33 m/s (Location: Bengaluru; as per Annex A of IS 875 3:2015)
  • Terrain Category: Terrain Category 2 (Cl 6.3.2.1 as per IS 875 3:2015)
  • Risk Coefficient Factors, k1 = 1.05 (All general buildings from Table 1 of IS 875 3:2015 )
  • Topography Factor, k3 = 1.15 (Up wind slope (ϴ) below 3 degree from Cl 6.3.3.1 of IS 875 3:2015)
  • Importance Factor for Cyclonic Region, k4 = 1.0 (All other Structures from Cl 6.3.4 of IS 875 3:2015)
  • Wind Directionality Factor for Buildings, Kd = 1 (From Cl 7.2.1 of IS 875 3:2015)
  • Area Averaging Factor, Ka = 0.95 (From Table 4 of IS 875 3:2015)
  • Combination Factor, Kc = 0.9 (From Cl 7.3.3.13 of IS 875 3:2015)

Validation

Table 1. Calculation of Variation in Design Wind Speed & Pressure with Height
Height from Ground, m Terrain & Height Factor, k2 (from TABLE 2 of IS 875 Part 3:2015) Design Wind Speed, Vz = Vb × k1 × k2 × k3 × k4 m/s (from Cl 6.3 of IS 875 Part 3:2015) Wind Pressure at height z, Pz = 0.6 × Vz2 N/m2 (from Cl 7.2 of IS 875 Part 3:2015) Design Wind Pressure, Pd = Kd × Ka × Kc × Pz kN/m2 (from Cl 7.2 of IS 875 Part 3:2015) The Value of 0.7 × Pz kN/m2 (from Cl 7.2 of IS 875 Part 3:2015) Status of the Value of Pd ≥ 0.7 × Pz kN/m2 (from Cl 7.2 of IS 875 Part 3:2015)
≤ 10 1 39.85 952.7 0.815 0.667 OK
12 1.02 40.64 991.2 0.847 0.694 OK
15 1.05 41.84 1050.3 0.898 0.735 OK
18 1.062 42.32 1074.5 0.919 0.752 OK
21 1.075 42.84 1101.0 0.941 0.771 OK
24 1.09 43.43 1131.9 0.968 0.792 OK
27 1.105 44.03 1163.3 0.995 0.814 OK
30 1.12 44.63 1195.1 1.022 0.837 OK

Internal Pressure Coefficient per Cl 7. 3.2.2 of IS 875 3:2015 for buildings with openings between 5 and 20%:

  • Cpi = 0.5 (positive internal coefficient)
  • Cpi = -0.5 (negative internal coefficient)

Node 243 is at an elevation of 18 m, thus the average intensity of wind pressure in this area, Pd, z=18 = 0.919 kN/m2 .

Tributary Area of Node 243



For a given panel, draw straight lines from the center of gravity (CG) to the midpoint of the members. So, the panel region will now contain several quadrilaterals whose two sides are made of portions of the respective members (or the ground) and the other two sides are lines going from the CG to the midpoint of the corresponding members.

Points A and B are the midpoints of members 473 and 22, respectively. Points A and B for a closed panel with the CG. Further, point 243 is located along segment A-B, so in this case the quadrilateral reduced to a triangle. So, the influence area for joint 243 is A-243-B-CG, which has an area of:

A243 = (3 × 3) / 2 = 4.5 m2

Positive X Direction

The positive wind load is acting towards face A as per clause 7.3.1 of IS 875 (Part 3) : 2015 and the equivalent joint loads are calculated as follows:

External pressure coefficient for wind in the +X direction (from Table 5 of IS 875 3:2015):

3/2 < h/w = 30 / 11.5 = 2.6 < 6

3/2 < l /w = 21 / 11.5 = 1.8 < 4

  • External Pressure Coefficient wind along +X on face A, Cpe = 0.7
  • External Pressure Coefficient wind along +X on face B, Cpe = -0.4
  • External Pressure Coefficient wind along +X on face C, Cpe = -0.7
  • External Pressure Coefficient wind along +X on face D, Cpe = -0.7

The equivalent joint loads are:

  • For Positive Cpi , equivalent joint load = 4.5 m2× 0.919 kN/m2 × [0.7 – (+0.5)] = 0.83 kN
  • For Negative Cpi , equivalent joint load = 4.5 m2 × 0.919 kN/m2 × [0.7 – (-0.5)] = 4.96 kN

Negative X Direction

  • For Positive Cpi , equivalent joint load = 4.5 m2× 0.919 kN/m2 × [-0.4 – (+0.5)] = 3.72 kN
  • For Negative Cpi , equivalent joint load = 4.5 m2 × 0.919 kN/m2 × [-0.4 – (-0.5)] = 0.41 kN

Positive Z Direction

  • For Positive Cpi , equivalent joint load = 4.5 m2× 0.919 kN/m2 × [-0.5 - (+0.5)] = 4.13 kN
  • For Negative Cpi , equivalent joint load = 4.5 m2 × 0.919 kN/m2 × [-0.5 - (-0.5)] = 0 kN

Negative Z Direction

  • For Positive Cpi , equivalent joint load = 4.5 m2× 0.919 kN/m2 × [-0.5 – (+0.5)] = 4.13 kN
  • For Negative Cpi , equivalent joint load = 4.5 m2 × 0.919 kN/m2 × [-0.5 – (-0.5)] = 0 kN

Results

Table 2. Wind loads on Face A at Joint 243
Result Type Reference STAAD.Pro Difference Comments
Wind direction +X, positive internal pressure 0.83 0.83 none  
Wind direction +X, negative internal pressure 4.96 4.96 none  
Wind direction -X, positive internal pressure 3.72 3.72 none  
Wind direction -X, negative internal pressure 0.41 0.41 none  
Wind direction +Z, positive internal pressure 4.13 4.13 none  
Wind direction -Z, positive internal pressure 4.13 4.13 none  

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Parent topic: V. Wind Load