lateral anaylsis of balconey with wood columns 1

[dwaine]

Is there a method to achieve the needed lateral strength using a wood column or small frame column say 12" . I'm working with the UBC & IRC and the aspect ratios don't allow it?

 

[ishvaaag]

You can use foundations and complementary comtraptions that make the columns act as vertical cantilevers fixed at the bottom. Put enough of the columns of the required size and you will have enough lateral strength, without shear walls.

However a far more efficient way is to build stabilizing systems made of wood trusses set in vertical planes in order to sustain the lateral forces. Yet these as shear walls will be invasive to the space in that space between the necessary pairs of columns will be taken by braces.

 

[RockEngineer]

You need to clarify your definitions so you use the right loads from the code.

A balcony is cantilevered from the wall and is not supported by columns at the outer edge.

A deck is supported by columns at the outer edge.

There are two other common ways to get your lateral resistance for a deck.
1. Knee braces at the top of the columns attached to the deck girders to provide a fixed end at the top of the column. The bottom of the column is still treated as a pinned joint.
2. A stiff floor diaphragm on your deck that transfers the lateral loads back to the structure (assuming your deck is attached to a structure. If the edge of your deck along the structure is twice as long as the depth of your deck away from the structure it is usually fairly stable. You can't used spaced deck boards for the diaphragm though. It has to be a solid diaphragm (plywood or concrete or steel) or the boards must be at diagonal angles to transfer the shear loads.

 

[dwaine]

RockEngineer, Thanks I'm new and trying to figure out how best to comunicate/ ask questions / #1 knee braces creats moment that resists lateral ? So connection design could be nails straps? Plywood over joist system & down column allows calculations of nails in shear but still have aspect ratio violation? #2 diapham transfer works but is it acceptable to assume existing strucure is able to handle addition lateral

 

[ERV]

dwaine,

Generally a deck or balcony will create axial loads, uplift may be a concern (due to wind), however, lateral loads should be minimal if tranferred back to the existing structure. Your columns in this case are for axial load of the deck structure.

There may be other considerations, although with the limited information, we can not ascertain these considerations.

 

[RockEngineer]

dwaine
1. For the knee braces you need to consider the knee brace member size and the connection. If your knee braces are set at 45 degrees they take out 1.4 times the shear load at the base of the column in axial load. This axial load must be transferred to the knee braces from the column and back to the girder. The knee braces depending on your load can be as siple as a plywood gusset or a nailed on 2x4. Asthetics may make you get more fancy.

2. It is not good to "assume" the structure can take the additional loads from making your deck a shear diaphragm. You need to look at the structure. Where are your shear walls? How heavily are they already loaded due to wind and seismic? How much load is my deck adding? It may be obvious when you look at your layout or you may have to run the numbers.