Exterior Climbing Walls - Wind Load

[vmirat]

I'm analyzing the effects of attaching two climbing walls to the sides of an existing old open framed radar tower. The climbing walls will be attached to two adjacent sides of the tower. The tower is square, 24 feet along each side and 26 feet high.

My concern is the wind pressure that will develop on the inside corner as the wind blows through the tower frame. ASCE 7 doesn't really address inside corners very well. The load diagram in Figure 6-9, Case 3, indicates a reduced pressure value for wind attacking a building at an angle to an outside corner. This makes sense since the air will flow aerodynamically from the corner as opposed to creating a stagnation pressure as it would if it was blowing normal to the wall. However, I'm thinking the pressure on an inside corner would be the full force of Pwx and Pwy applied simultaneously. Does this make sense?

 

[ishvaaag]

Table 5.2 of former loads code in Spain NBE AE-88, for zones concaves to the wind, all the surface takes the frontal pressure, normally to the surface. It stated it at 0.8 of the dynamic pressure on a surface normal to the wind, but you need to add suction from the other side, stated at 0.4 suction on dynamic pressure. Hence it would be a total by such code of 1.2w normally to the surfaces, from inwards to outwards, for the inner concave part of corners.

 

[ishvaaag]

Due to the proportion of the supporting structure, if close support is provided against it, I don't see necessary the further increments out of slenderness. From a more modern viewpoint, however, the rims etc should take more wind load on fractional areas, both by itself the strength of the climbing wall and its fasteners to the supporting structure and even from the secondary structure to the main structure.

 

[wannabeSE]

Is there a problem with using Figure 20 and assuming it is similar to be a solid freestanding wall or solid freestanding sign.

 

[MiketheEngineer]

I agree - treat it like a sign.


But also make sure you check for wind at 45 degrees hitting both walls?? That may be the worst condition.

 

[csd72]

Agreed,

If there is a significant gap between the two signs then there will be a greater wind at 45 degrees than flat on.

 

[vmirat]

Perhaps I didn't make myself clear. The wind pressure on the two walls as the wind approaches the front (45 degrees on to the point of the corner) will be less than the wind pressure approaching the back of the walls and stagnating in the inside corner. My question is, how do you calculate the wind pressure approaching the back of the walls?

 

[wannabeSE]

I don't know if it helps. But Figure 20 has case C for oblique winds. This case also has reductions when there is a return at the corner. However, they do not have data for cases when B/s<2. The commentary reference wind tunnel testing.

 

[ishvaaag]

As you see, like per the spanish quoted code, a "hydrostatic" viepoint is applied: you apply to the 45º inner corners the same wind (pressure+suction) than at 90º attack, only that normally to the walls.

 

[csd72]

vmirat,

You are wrong with that assmption, just because it forms a scoop does not necesarily mean that it is the highest wind pressure.

For hoardings and walls the highest pressure is when the wind blows at 45 degrees to the end as this creates fluctuating wind gusts.