New Wood Joists in Existing Brick Pockets

[Forensic74]

In old brick masonry construction, they often pocketed floor joists right into the masonry bearing walls (interior and exterior walls). When dealing with fire damage to these buildings, would you ever go back with new joists bearing in the existing masonry pockets, or would you come up with some other sort of connection? If so, what general approaches have you done to obtain better attachment?

 

[Ron]

Pockets are fine for gravity loads, but you need to consider uplift and lateral load transfer as well, depending on configuration. I remember doing analysis on buildings after Hurricane Andrew in Florida (1992). Found that many of the structures designed in the '60's were not designed for uplift. Interesting.

 

[abusementpark]

I agree with Ron. Uplift will be a problem if they are roof joists. Also, don’t forget about axial tension load from wind/seismic if it is an exterior wall. That and lateral load will depend on what type of deck connection you have to the wall.

 

[XR250]

I sometimes epoxy anchor a band to the wall and hang the joists from that. Ditto on the comments about outwards loads.

 

[msquared48]

Really depends where you are...

Where Ron is, yes, definitely uplift, but in the Pacific Northwest where I am, seismic forces are a far greater worry, with tension between the joists and the brick wall dominating the structural stability od the building.

If the joists tear away from the walls, there go the diaphragns, and there goes the building and the neighborhood. Hence the need to retrofit these older brick structures with thru the wall rods and rosettes, all hooked to the joists with holllown brackets.

Seattle has hundreds of these older buildings on a list identified to be retrofitted at some in the future.

The big one is no joke here...

Mike McCann, PE, SE (WA)

 

[BAretired]

It was common in those old brick masonry structures to include a horizontal steel bar through the joist or beam which engaged with the bricks on each side. As others have said, a connection between brick and joist is needed to resist lateral and uplift forces. It may be adequate to provide such a connection on every second or third joist. Floor joists should be fire cut and the connection must be such that each joist is free to collapse in a fire situation without causing collapse of the brick wall.

BA

 

[dhengr]

Forensic74:
First of all, we are trying to kill a bunch of birds with one stone here, and that probably won’t all fly and meet todays codes at the same time. There have been some good discussions on these issues, here on E-Tips a few years ago, you might want to search for them, for what they have to teach/say. The joists resting in pockets in the masonry walls, with fire cut ends was a common detail. They, along with the horiz. diaphragms, were recognized as being very important for the wall and bldg. stability. They were fire cut so they didn’t pull the wall down when they failed in a fire. Today, we are dealing with much more stringent code requirements than they faced when these bldgs. were originally built. You will most likely have to provide fire rated ceiling/floor system assemblies in today’s rebuilding, so the fire cut ends idea kinda goes away. The pockets/joist ends generally didn’t have much more than bearing friction holding them in place and providing support for the walls, and that generally seems to have been enough, given the age of many of these bldgs. Of course, today’s lateral loads, wind and EQ, and roof loads, will require much more elaborate fixings btwn. the walls and the jsts. and diaphs. for todays higher loads. There is also a real need to understand the makeup and physical condition of the existing walls to determine what you can do in the way of drilling, grouting, etc. without destroying the wall in the process. The walls are generally more than adequate for the gravity loads, but can tend to fall apart when you start drilling, hammer drilling, brick removal, etc. on them. As a min. they usually require some serious outer surface rework, like tuckpointing, brick and mortar bed replacement in some locations. It is important to match the old wall makeup with the new materials and mortars that are compatible with the old ones, etc. In some cases, you discover that you are attaching to only one wythe of brick in a multi-wythe wall and that can cause serious problems. The pockets may be adequate for the jst. bearings but you will still need a ledger or blocking btwn. the jsts. to tie everything together with the wall.