V. Wind On Open Structure

Validate the calculated member loads for an open structure subject to wind loading.

Details

A structure is subjected to wind loading from +X direction. The members are rectangular members with 500 mm × 500 mm in dimension. The diagonal member is also of same dimension but rotated at a beta angle value of 45°. Thus, the wind facing area of that member will be different than that of the other members.

Table 1. Variation of wind intensity over structure height
Height (m)	Intensity of wind load (kN/m²)
≤5	1.5
5 - 10	2
10 - 20	3

Validation

When open structures are subjected to wind load, wind load incident on the structure is applied as uniformly distributed loads on the members along the projected axis (i.e., in PX/PY/PZ direction). Wind intensity multiplied by the effective area of the member facing the wind load gives the uniformly distributed member load on the member.

Wind Load on Members 1,3, 6 & 8

Wind intensity varies between the length of the member, so different parts of the member will be subjected to uniformly distributed loads of different magnitudes.

Let the midpoint of member 1 be K. So, AK = CK = 5 m

Up to Height 5 m (part AK)

Intensity of wind load = 1.5 kN/m²
Area of the member facing the wind = 0.5 m
w_AK = 1.5 × 0.5 = 0.75 kN/m

Up to Height 10 m (part KB)

Intensity of Wind load = 2 kN/m²
Area of the member facing the wind = 0.5 m
w_KB = 2 × 0.5 = 1 kN/m

Due to same orientation, member load on member 3, 6, and 8 will also be same as that of member 1.

Wind Load on Member 9, 10, 11 & 12

Intensity of wind load = 3 kN/m²

Area of the member facing the wind = 0.5 m

w = 3 × 0.5 = 1.5 kN/m

Due to same orientation, member load on member 10, 11, and 12 will also be same as that of member 9.

Wind Load on Member 4 & 5

Intensity of wind load = 2 kN/m²

Area of the member facing the wind = 0.5 m

w = 2 × 0.5 = 1.0 kN/m

Due to same orientation, member load on member 5 will also be same as that of member 4.

Wind Load on Member 14 & 15

Intensity of wind load = 3 kN/m²

Area of the member facing the wind = 0.5 m

w = 3 × 0.5 = 1.5 kN/m

Due to same orientation, member load on member 15 will also be same as that of member 14.

Wind Load on Member 2, 7, 13, & 16

These members are aligned along the +X axis. Since the structure is subjected to wind load from +X direction only, the area of those members facing the wind is zero. So, there will be no load due to wind on these members.

Wind Load on Member 17

Since the member is rotated at a beta angle of 45°, the area of the member faceing the wind = 0.5 m/cos45° = 0.707 m

Wind intensity varies between the length of the member, so different parts of the member will be subjected to uniformly distributed loads of different magnitudes.

Up to heigh 5m

Wind intensity = 1.5 kN/m²
w = 1.5 × 0.707 = 1.061 kN/m

Up to height 10m

Wind intensity = 2 kN/m²
w = 2 × 0.707 = 1.414 kN/m

Results

Table 2. Comparison of uniformly distributed load due to wind from +X on each member (kN/m)
Member No	Hand Calculation	STAAD.Pro	Difference
1, 3, 6 & 8	Up to 5m: 0.75 5m - 10m: 1	Up to 5m: 0.75 5m - 10m: 1	none
4 & 5	1	1	none
9, 10, 11, 12, 14, & 15	1.5	1.5	none
17	Up to 5m: 1.061 5m - 10m: 1.414	Up to 5m: 1.0607 5m - 10m: 1.4142	negligible

Note: Members with no loading under this load condition are not displayed.

STAAD.Pro Input File

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\06 Loading\Wind Load\Wind On Open Structure.STD is typically installed with the program.

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 30-Aug-18
END JOB INFORMATION
*******************************************************************************
* This problem is created to determine the uniformly distributed load
* on the members when the structure is subjected to wind load
*******************************************************************************
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 0; 2 0 10 0; 3 10 10 0; 4 10 0 0; 5 0 0 10; 6 0 10 10; 7 10 10 10;
8 10 0 10; 9 0 20 0; 10 10 20 0; 11 0 20 10; 12 10 20 10;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4; 4 2 6; 5 3 7; 6 5 6; 7 6 7; 8 7 8; 9 2 9; 10 3 10;
11 6 11; 12 7 12; 13 9 10; 14 9 11; 15 10 12; 16 11 12; 17 2 5;
DEFINE MATERIAL START
ISOTROPIC CONCRETE
E 2.17185e+07
POISSON 0.17
DENSITY 23.5616
ALPHA 1e-05
DAMP 0.05
TYPE CONCRETE
STRENGTH FCU 27579
END DEFINE MATERIAL
MEMBER PROPERTY AMERICAN
1 TO 17 PRIS YD 0.5 ZD 0.5
CONSTANTS
BETA 45 MEMB 17
MATERIAL CONCRETE ALL
SUPPORTS
1 4 5 8 FIXED
DEFINE WIND LOAD
TYPE 1 WIND 1
INT 1.5 2 3 HEIG  5  10  20
EXP 1 JOINT 1 TO 12
LOAD 1 LOADTYPE Wind  TITLE LOAD CASE 1
WIND LOAD X 1 TYPE 1 OPEN
PERFORM ANALYSIS PRINT LOAD DATA
FINISH

STAAD.Pro Output

   LOADING     1  LOADTYPE WIND  TITLE LOAD CASE 1                            
   -----------
   MEMBER LOAD - UNIT KN   METE
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
      1     0.7500 PX   0.00    5.00
      1     1.0000 PX   5.00   10.00
      3     0.7500 PX   5.00   10.00
      3     1.0000 PX   0.00    5.00
      4     1.0000 PX   0.00   10.00
      5     1.0000 PX   0.00   10.00
      6     0.7500 PX   0.00    5.00
      6     1.0000 PX   5.00   10.00
      8     0.7500 PX   5.00   10.00
      8     1.0000 PX   0.00    5.00
      9     1.5000 PX   0.00   10.00
     10     1.5000 PX   0.00   10.00
     11     1.5000 PX   0.00   10.00
     12     1.5000 PX   0.00   10.00
     14     1.5000 PX   0.00   10.00
     15     1.5000 PX   0.00   10.00
     17     1.0607 PX   7.07   14.14
     17     1.4142 PX   0.00    7.07