Existing Building and IBC Chapter 34

[marinaman]

Here's an interesting problem that I am considering taking a position on.....

The client has an existing building. The existing building is essentially square in plan. It is a one-story building comprised of a roof structure of 2x10 joists at 16" o.c. spanning between steel joist girders. Joist girders are about 12' on center. Joist girders, and on the other two sides of the building 2x10 joists, bear upon perimeter, 10' tall, unreinforced masonry walls. The perimeter walls of the existing building are the shearwalls that provide lateral stability to the existing building. The building is about 100' x 100'.

Its just a big box.

The client wants to place a structurally independent building beside this existing building, but, he wants to be able to walk from the exiting building into the new building....thru a new punched opening thru the existing building's unreinforced perimeter masonry wall.

I'm having a hard time allowing him to punch openings thru his existing building's perimeter masonry wall.

IBC 3403.2 says that for any existing element modified, where the load will be increased on the remaining segment of element by more than 5%, the element must meet the requirements of the current code.

IBC 3403.2.3.2 says that if modifications increase seismic forces on any element by more than 10%, the whole building must meet the requirements of the current code.

That being said.....does that mean that for the one shearwall that I want to punch an opening thru, as long as my new opening is less than 10% wide (less than 10' wide), but greater than 5% (greater than 5' wide), I've only got to bring the element (the shearwall itself) up to the current code? So if I had a 100' long perimeter wall.....I could cut a 9'-4" opening into it, only strengthen the other 90' of wall to the current code, and go on?

That seems to be the way I interperete the code.

Any comments on this?

 

[DST148]

Try thread507-316624. Although the OP is about loading on existing steel beam, there is a good discussion about interpretation of Section 3403.2 of IBC.

 

[southard2]

I'm in Florida where we don't work with seismic at all but I think your interpretation is correct. You might find that the 90 foot wall you have left is OK for shear as is. That is a long wall. As for wind loads and gravity loads you could just insert some vertical rebar into cells adjacent to the new opening and you can meet code that way With this approach you would not be increasing the load on the rest of the wall except of course for the shear loads. Check your footing also but it doesn't sound like you've got a whole lot of roof load there if the girders lines are only 12 ft apart.

Before you tell you client anything contact your building official for your area and run by your thoughts with him or her. That way you don't get into an interpretation fight.

John Southard, M.S., P.E.

http://www.pdhlibrary.com/