Open Wood Porch Deflection and Lateral Loading

[RareBugTX]

I would like to know what deflection limitations you have used for structures like rear yard open wood porches, say up to three stories high and a plan dimension of 20'x8'. these porches here in the midwest are mostly attached to masonry or wood frame houses. I tried looking for some code limitations regarding this issue, but found nothing.

Second question, what lateral loading do you usually apply to this in other places of the country??? Wind here is the controlling factor.


Regards
RareBug

 

[MotorCity]

RareBug,
When you say "attached to masonry", the deflection limitations really depend on whether you are supporting masonry or you mean to say that the structure is founded on masonry.

Most of the time, I use L/360 unless the structure supports a non-structural face brick. In that case I use L/480.

Good luck.

 

[RareBugTX]

Motorcity:

By attached to masonry I mean that they are open wood structures leaning on a principal building.

As you have done, I have designed and checked deflection of wood joists and wood girders for L/360 but sometimes is difficult to make the numbers work for open porches that were designed and built with the old standards and not the new local requirement of 100 psf.

These porches do not support any masonry, are made entirely of wood. By the way, my question arose about a week ago when I overheard and architect saying "if you do not have a ceiling, i.e. gypsum wallboard, you do not need to check deflection,.....!!!!??????

Any additional suggestions are welcome.

 

[MotorCity]

For a wood porch not supporting masonry, you could make a case to use L/240.

As for the architect,let us know what structures he/she worked on.

 

[dicksewerrat]

I'd look at the story about the posrch collapse in chicago before i went to L/240. Walk around on a floor with L/240. Creepy. one person moves and sets up a wave action in the floor members.

 

[zennis]

The International Residential Code uses L/360 for the span tables in the floor construction section and L/240 for the span tables in the roof/ceiling construction section. I am curious about the new local code for residential decks requiring 100 psf.

 

[RareBugTX]

Zennis:

Thanks for the reply, that means that it is right to check deflections limits for decks, I also remember seeing this L/240 for roof construction from the New York Building Code.

On the other hand, Chicago Building Code Table
16(13-52-090) requires Decks, patio and roofs, a design live load of 100 psf.

 

[vmirat]

I recently designed a pergola for an outdoor patio of a restaurant in Colorado that is about 10,000 square feet in covered area. It has 2x2 wood slats at 3 inches on center supported by 2x8 rafters at 24 inches on center. At first, I was just going to apply the wind load to the horizontal projected area of the rafters, which seemed inadequate. I did some research and found a European building code that requires wind load to be applied at a 10 degree angle of attack. This seemed logical since wind can't be counted on to blow horizontally. I applied a wind pressure to a portion of each of the 2x8 rafters. I figure this accounts for the drag the wind will have against the whole structure.