Wind & Skyscrapers

When wind hits the left side of a normal building with corner colums the entire frame deforms (shear), to reduce the deformation we can strengthen the joints/corners or instead use diagonal bracing/beams to add more resistance to beding in the horizontal direction.

Beams and columns are stronger in tension and compression than they are with bending loads. So if we add diagonal bracing they can carry this horizontal load.

This means the beams act like springs and when they are compressed they push on the joints and when they are stretched they pull inwards.

With diagonal bracing the wind load compresses the left diagonal (facing inward) and stretches the right diagonal (facing outward). The left column pulls down in tension and the right column pushes up in compression.

Where the braces meet they both push the bottom beam to the right. This causes the bottom beam to stretch on the left side and compress on the right side.

If this layer was the top of the next chevron (layer of bracing below or above) then the lower section is carrying the force from the layer above it and the normal wind load from the side. This continues to happen at every chevron. So the wind load builds up as you go down the building.

However thebuilding can’t have corner columns where the corners meet because of the gravity load, so in the wind the entire triangle wants to rotate. To prevent that from happening, on a 4 sided bracing systemthe left chevron pulls down by going into tension and the right one (far one) pushes up in compression.

The top and bottom beams are forced into compression and tension. The wind loads end up wrapping around the entire building. So every chevron works to transfer the wind load to the section below.

Skyscrapers very important to understand wind. Building shear increases as you go down the building because the total force is carrying everything above it