To calculate wind load for industrial steel structures and to apply it by using TSD

CHALLENGE 5

AIM:

To generate manual wind loading in the design report based IS code as per the following input

• Basic wind speed = 39m/s
• Terrain category 2

Introduction:

Wind load is a lateral load acting on the structure. This wind load depends upon the height, location, topography and category of the building. Wind load is obtained from IS 875 Part 3

Procedure:

• Given, basic wind speed , Vb = 39 m/s ; Terrain Category = 2
• Length of the building, l = 18 m
• Breadth of the building, w = 18 m
• Height of the building, h = 16.88 m

Step 1: Finding Design Wind Speed:

• Referring to IS 875 P3, Vz = Vb k1 k2 k3 k4 according to Cl 6.3
  • Where Vz – Design wind speed
  • K1 – probability factor
  • K2 – terrain roughness and height factor
  • K3 – topography factor
  • K4 – importance factor for cyclonic region
• From table 1, k1 = 1
• From table 2, for height of the building 16.88 m and terrain category 2 , k2 is obtained by interpolation.
  • For 15 m , k2 = 1.05
  • For 20 m , k2 = 1.07
  • Therefore, for 16.88 m , k2 = 1.057 = 1.06
• From Cl 6.3.3 , k3 = 1 since, theta < 3(flat terrain)
• From Cl 6.3.4, k4 = 1.15 for Industrial structures
• Substituting all the above values, Vz = 39 * 1 * 1.06 * 1 * 1.15 = 47.54 m/s

Step 2: Finding Design Wind Pressure:

• From Cl 7.2, wind pressure, pz = 0.6 Vz^2
  • pz = 0.6 * 47.54 ^ 2 = 1356.1 N/m2
  • pz = 1.356 kN/m2

Step 3: Design Wind Load:

Wind Load on Wall:

• From Cl 7.3.1, F = (Cpe – Cpi) A pz = Cp * pz
• Cpe is found from Table 5 of IS 875 P3 for h/w and l/w ratios
  • h/w = 16.88 / 18 = 0.94
  • l/w = 18/18 = 1

• Lets consider medium openings in which Cpi = + 0.5 / -0.5 according to Cl 7.3.2.2 of IS 875 part 3

Wind angle 0:

A – windward side , B – leeward side

• Lets consider the loading Wind + Y + Cpi , Wind + Y – Cpi and Wind – Y + Cpi , Wind – Y – Cpi for all four sides A, B, C and D

Wind angle 90:

C – windward side , D – leeward side

• Lets consider the loading Wind + X + Cpi , Wind + X – Cpi and Wind – X + Cpi , Wind – X – Cpi for all four sides A, B, C and D

Wind Load on Roof:

• For calculating wind load, h/w ratio and roof angle is required to find Cpe
• In our case, h/w = 0.94 , roof angle = tan ^-1 (3.88/9) = 23.32 deg

For a roof angle of 23.32 deg, we need to interpolate between 20 and 30

Wind angle 0, EF = -0.534 , GH = -0.6

Wind angle 90, EG = -0.8 , FH = -0.734

Result:

• Design wind speed and pressure are calculated initially
• Then using h/w values and l/w values, the Cpe values are found for wind angles 0 and 90 for all 4 sides
• Cpi values are assumed
• For + Cpi and – Cpi , the various values are worked out and design wind loads are found for walls and roofs

Thus we calculate wind loads on walls and roofs

2. Aim:

To apply the loadings on the model based on the above loadings

Introduction:

Based on the above generated loads, the load cases are created first viz,

• Wind + Y + Cpi ( A – windward, B – leeward)
• Wind + Y – Cpi
• Wind – Y + Cpi ( B – windward, A – leeward)
• Wind – Y – Cpi
• Wind + X + Cpi ( C – windward, D – leeward)
• Wind + X – Cpi
• Wind – X + Cpi ( D – windward, C – leeward)
• Wind – X – Cpi

Procedure:

• Go to Load – Load cases
• Add the various wind load cases as mentioned above

• Create wall panels/wind panels for grids 1 and 4
• Go to Model – Wall panels
• After creating the wall panels, apply positive loads as towards the buildng and negative loads away from the building

• Wind + Y + Cpi

• Wind + Y – Cpi

• Wind + X + Cpi:

• Wind + X – Cpi:

On Roof:

Wind angle 0(+Y) = EF – windward , GH – Leeward

Wind angle 90( +X)= EG – windward, FH – Leeward and vice versa for -X and -Y

• Wind + Y + Cpi:

Wind + Y – Cpi:

Wind + X + Cpi:

Wind + X – Cpi:

• Repeat the same procedure for -X and – Y directions too
• For -Y direction interchange A and B sides
• For -X direction interchange C and D sides
• Similarly for roofs interchange EF and GH for -Y and EG and FH for – X

Result:

The various load combinations +Y + Cpi, +Y – Cpi , + X +Cpi and +X – Cpi ; -Y + Cpi, -Y – Cpi, -X+Cpi, -X-Cpi are thus generated for walls and roofs

3. AIM:

To generate wind loading on a separate model using wind wizard

Introduction:

Wind wizard option is used to automatically generate various wind load combinations. The various data like building height,width,height, basic wind speed etc has to be entered

Procedure:

• Use ‘Save As’ option to save this file to a new name
• Go to Load – Load cases and delete the existing wind loads

• Under wind load, select Wind wizard and under options tick Consider Cyclonic effect. Click on Next

• Provide the basic data

• Thus the wind loads are generated in 4 directions 0, 90 , 180 and 270 degrees

• Click on Next and finally click Finish
• Under Wind load, select Wind load cases to add various wind loads

• Click on Add to add wind load cases for various directions 0, 90, 180 and 270 degrees with Cpi of +0.5 and -0.5

• Click on OK
• Hence the wind loads are generated

Result:

Thus the wind loads are generated using Wind Wizard option