Couple of Random Questions 2

[MegaStructures]

1) Effective Length

What is a real example of a column that is fixed at it's base and at it's top is free to translate, but fixed against rotation? Would a sign post be considered in this category, or would it be considered fixed at base and free to rotate and translate at the top?

2) Wind Load Distribution

For a one-story building with a horizontal diaphragm at roof level, is the force in the diaphragm equal to the wind pressure applied over the area of the entire wall, or wind pressure applied over half height of the wall (half of the force goes straight to slab, half goes to the roof diaphragm)

“The most successful people in life are the ones who ask questions. They’re always learning. They’re always growing. They’re always pushing.” Robert Kiyosaki

 

[phamENG]

1) No - that sign is not an example. As the sign head tries to twist, it will load the column in torsion and it will twist. Only thing I can think of would be a cantilevered column with moment connections at the top. The column is unable to rotate due to the fixity at the top, but it is free to translate horizontally because there are no other members to prevent it - it has to rely on its own stiffness to prevent translation.

2) Depends on how the wall is constructed, but typically that's how it works. Wind blows on vertical studs, reaction at the floor diaphragm and at the roof diaphragm going to be equal if there's no continuous parapet. You could have rigid frames and girts, in which case the wind load would be carried horizontally and load the side of the frames (which is why PEMBs can get away with just a few dinky rods in the roof - very little wind load has to go up there to get to the frames).

 

[KootK]

What is a real example of a column that is fixed at it's base and at it's top is free to translate, but fixed against rotation?

A moment frame column with a fixed base and a very stiff beam can get close. A braced frame stacked over a moment frame with continuous columns is sort of an extreme version of this.

Would a sign post be considered in this category, or would it be considered fixed at base and free to rotate and translate at the top?

Definitely free to rotate and translate.

For a one-story building with a horizontal diaphragm at roof level, is the force in the diaphragm equal to the wind pressure applied over the area of the entire wall, or wind pressure applied over half height of the wall (half of the force goes straight to slab, half goes to the roof diaphragm)

Most folks will do the half height thing.