Wind Load as per ASCE 7-16

 

Information of Example Model

This is an explanation how to input wind load data in the warehouse with gable hip roof(Two-way).

Information of the example model is given as follows.

Figure1. Warehouse Example Model

 

 

 Figure 2. Warehouse Roof Example Model

 

 

Table 1. Wind Load Data Informations

 

 

 

 

 

√ Table of Contents 

 

1. Calculation of Wind Load - Velocity Pressure

 

2. Calculation of Wind Load - External Wind Pressure

 

3. Calculation of Wind Load - Internal Wind Pressure

 

4. Wind Pressure Summary

 

5. Input a Wind Load

 

 

Calculation of Wind Load - Velocity Pressure

The velocity pressure should be calculated in order to get the value of the wind load.

• Velocity Pressure : q_z = 0.613K_zK_ztK_dK_eV²

It usually applies ' 1.0 ' on the Ground Elevation Factor, K_e, if there is no exceptional case caused.

Figure 3. Ground Elevation Factor

2) Determination of K_d (Wind Directionality Factor)

It applies ' 0.85 ' since the wind directionality factor is based on the structure.

Figure 4. Wind Directionality Factor

3) Determination of K_z (Velocity Pressure Exposure Coefficient)

 

4) Determination of K_zt (Topographic Effects)

• K_zt = (1+K₁K₂K₃)²

• Assumed ValuesHill Type : 2S Escarpment

  H = 20m, L_h = 40m, x = 40m  →  H/L_h = 20/40 = 0.5, x/L_h = 40/40 = 1.0

Figure 6. Determination of Topographic Effects

The following is a table that indicates the final value of the velocity pressure after calculating values for all variables. To calculate wind pressure, q_h value for the roof level is applied.

Applying the pressure value depending on levels is more exact, but, it is okay to put the load value by using only the value of q_h instead.

• Velocity Pressure : q_z = 0.613K_zK_ztK_dK_eV² ≈ 490N/㎡ =q_h

 

Calculation of Wind Load - External Wind Pressure

p = qGC_P - q_i(GC_pi)

Case 1) Wind Pressure = External Wind Pressure - Internal Wind Pressure (Positive)

Case 2) Wind Pressure = External Wind Pressure - Internal Wind Pressure (Negative)

Two coefficient values for external pressure and internal pressure are needed in order to satisfy the formula. Basically, wind pressure has two values depending on the direction of internal pressure. If internal pressure is larger than the external pressure, positive internal pressure is generated. In the opposite case, negative internal pressure is generated. 

Figure 7. Positive Internal Wind Pressure and Negative Internal Wind Pressure

1) External Wind Pressure for Gable Roof Direction

Wind ward wall, leeward wall, and side wall are needed to satisfy the calculation of external wind pressure.

The following is an explanation of the calculation for the x-direction and wall.

Figure 8. External Wind Pressure in X-Direction

• Wall Pressure Coefficients (C_p)

Figure 9. Wall Pressure Coefficients - 1

                                             * L/B =14.4/ 18.6 = 0.774

                    q_wind = q_zGC_P = 490 * 0.85 * 0.8 = 333.2 N/m²

Blue Box : Wind load for Leeward wall (Wx(+ or -)_Leeward)

                     q_lee = q_hGC_P = 490 * 0.85 * - 0.5 = -208.3 N/m²

Yellow Box : Wind load for Side wall (Wx(+ or -)_Side)

                         q_side = q_hGC_P = 490 * 0.85 * - 0.7 = -291.6 N/m²

The following is an example of the calculation for the roof in X-Direction.

• Gust Factor (G) = 0.85 (Assumed Value)

   * You can get the gust factor as per 26. 11. 4

Figure 11. External Wind Pressure for the Roof in X-Direction

• Roof Pressure Coefficients, C_p, for use  with q_h

Red Box : Wind load for windward roof (Wx(+ or -)_Windward)

                   q_wind = q_zGC_P = 490 * 0.85 * -0.392 = -163.27 N/m²

                   q_wind = q_zGC_P = 490 * 0.85 * -0.071 = -29.58 N/m²

Blue Box : Wind load for Leeward wall (Wx(+ or -)_Leeward)

                     q_lee = q_hGC_P =490 * 0.85 * - 0.6 = -249.94N/m²

The following is an example of the calculation for the roof in X-Direction for the side area.

• Gust Factor (G) = 0.85 (Assumed Value)

   * You can get the gust factor as per 26. 11. 4

Figure 14. External Wind Pressure for the Side Roof in X-Direction

• Roof Pressure Coefficients, C_p, for use  with q_h

Red Box : Wind load for windward roof (Wx(+ or -)_Windward)

                   q_wind = q_zGC_P = 490 * 0.85 * -0.972(Apply Max.Cp)= -404.9 N/m²

                   q_wind = q_zGC_P = 490 * 0.85 * -0.18= -75.0 N/m²

Blue Box : Wind load for Leeward wall (Wx(+ or -)_Leeward)

                     q_lee = q_hGC_P =490 * 0.85 * - 0.6 = -249.94N/m²

2) External Wind Pressure for Gable Roof Orthogonal Direction

The following is an explanation of the calculation for the y-direction. The wall pressure for the y-direction can be calculated as the x-direction way. 

• Gust Factor (G) = 0.85 (Assumed Value)

   * You can get the gust factor as per 26. 11. 4

• Wall Pressure Coefficients (C_p)

Figure 19. Wall Pressure Coefficients - 2

Red Box : Wind load for windward wall

                    q_wind = q_zGC_P = 490* 0.85 * 0.8 = 340 N/m²

Blue Box : Wind load for Leeward wall

                    q_lee = q_hGC_P = 500 * 0.85 * -0.3 = -127.5N/m²

Yellow Box : Wind load for Side wall

                     q_side = q_hGC_P = 500* 0.85 * -0.7 = -297.5N/m²

The following is an example of the calculation for the roof in Y-Direction. 

• Gust Factor (G) = 0.85 (Assumed Value)

   * You can get the gust factor as per 26. 11. 4

Figure 20. External Wind Load in Y-Direction and Angle

 

* h = 8.5m, Lx = 18.6m → h/L = 0.457

 

Figure 21. Roof Pressure Coefficients

The following is an example of the calculation for the roof in Y-Direction for the side area. 

• Gust Factor (G) = 0.85 (Assumed Value)

   * You can get the gust factor as per 26. 11. 4

Figure 22. External Wind Load for Side Roof in Y-Direction and Angle 

 

* h = 8.5m, Lx = 18.6m → h/L = 0.457

 

Figure 23. Side Roof Pressure Coefficients

Calculation of Wind Load - Internal Wind Pressure

1) Internal Wind Pressure for Gable Roof Orthogonal Direction

Figure 24 Internal Wind Pressure for Gable Roof Orthogonal Direction

Partially enclosed buildings in enclosure classification would be applied in this example. Therefore, the value of the internal pressure coefficient can be assumed as +0.55 and -0.55.

Figure 25. Table for Internal Pressure Coefficient

2) Wind Pressure on Wall for Gable Roof Direction (along x-direction)

Wind pressure in the x-direction is given as follows. The values of each case in the wind pressure are calculated by applying the values of the external pressure and internal pressure.

Table 3. Wall Wind Pressure Values along X-Direction

3) Wind Pressure on Roof for Gable Hip Roof Direction (along x-direction)

Table 4. Roof Wind Pressure Values along X-Direction

4) Wind Pressure on Wall for Gable Hip Roof Orthogonal Direction (along y-direction)

Table 5. Wall Wind Pressure Values along Y-Direction

5) Wind Pressure on Roof for Gable Roof Orthogonal Direction (along y-direction)

Table 6.  Roof Wind Pressure Values along Y-Direction

Wind Pressure Summary

The final values for cases 1 & 2 are as follows.

Table 7. Values for Cases 1 and 2

• Sign (+) : Direction to the inside of the building

• Sign (-) : Direction to the outside of the building

Input a Wind Load

1) Create Load Cases for the Wind Load

Figure 27. Static Load Cases Dialog Box

* Tips : you can easily distinguish each case if you put the name above.

Considered Factors

- Case : Case 1 & Case 2

- Wind Direction : X-Direction & Y- Direction

- Wind Sign : (+) & (-)

2) Create a Floor Load Cases for Wind Load

Figure 28. Information of Floor Load Cases for Wind Load

3) Input Wind Load as a Floor Load

Figure 29. Floor Load Type Dialog Box for Case 1

Table 8. Case 1 Values of Wall and Roof

• Sign (+) : Direction to the inside of the building

• Sign (-) : Direction to the outside of the building

When inputting the wind load into the model,  the sign must be corrected according to the direction of the load.

It also creates a floor load type for the opposite direction.

Figure 31. Floor Load Type Dialog Box for Case 2

Table 9. Case 2 Values for Wall and Roof

• Sign (+) : Direction to the inside of the building

• Sign (-) : Direction to the outside of the building

When inputting the wind load into the model,  the sign must be corrected according to the direction of the load.

It also creates a floor load type for the opposite direction.

Figure 32. Case 2 Name List Dialog Box

4) Generate Load Combinations with a Wind Load

Before performing analysis and design, we recommend you make load combinations with a wind load. Even if it is not automatically generated, you can easily create it by using a table for the load combination or copying it from excel.

Figure 33. Load Combination Example - 1 

Figure 34. Load Combination Example - 2