TIE BACKS FOR SHORING PARTY WALL - EACH JOIST TO BE TIED TO MASONRY 1

[PT999]

Construction Type: masonry walls with lumber floor joists

I am showing tie-back anchors for the building to remain, for EACH floor joist on each floor at the party wall. These buildings were built in the early 1900's.

The tie-back anchor is a 3/4" threaded rod with plate and nut on the exterior side connecting to an angle connected to the lumber floor joists with lag bolts to connect to the lumber.

I am getting resistance on doing this at every single floor or ceiling joist. Any comments on whether this is excessive.

 

[msquared48]

Normally at 32 or 48" OC, but your specific conditions could dictate that requirement, particularly if you are in a high seismic area with heavy floor dead loads.

What is your framing?

Mike McCann, PE, SE (WA)

 

[msquared48]

Depends also on local code requirements for unreinforced brick masonry that may be less than the IBC requirements.

Mike McCann, PE, SE (WA)

 

[jguid17]

Every joist does seem excessive if your joists are at 16" on center. As noted above, 32-48" on center is pretty typical.

 

[bookowski]

In my area up to 6ft is typical if there are no specific issues with the wall. If the wall has issues (leaning, bulging, deteriorating etc) then it depends.

 

[PEinc]

Be careful doing this. I have seen the party wall move away from the remaining building and pull its floors away from the next party wall back. If the far ends of the lumber floor joists are not attached to or mortared into the next party wall, they can be pulled out of the wall and the floors can drop down upon the lower floors. While what you are considering is often done, it is not a fool-proof method to protect the remaining building.

http://www.PeirceEngineering.com

 

[msquared48]

Good point PE. Never thought of that scenario.

Mike McCann, PE, SE (WA)

 

[PT999]

Thanks everybody, I'll will taking a second look at the far side also.

In terms of calculating lateral force on the tension anchor, I am just looking at wind force on the wall. The governing condition appears to be the capacity of the new lag bolts in the lumber - lumber also of unknown grade - before grading - before stamps - before Codes. Anything else in the analysis to consider. By the way, this wind force analysis supports 32" spacing with 2 lag bolts, but this also assumes good masonry in between.

In terms of analyzing the unreinforced brick masonry, I am analyzing this using old fashioned WSD design, adding bending stress fb and gravity (axial) stress fa to get a total actual stress.

The question is what is an allowable stress for this old building, of unknown mortar type and poor condition.
Type N mortar would allow 100 psi and for Type S 160 psi, but that is all for new construction. This is an old building. I am thinking 60 psi, but its just a convenient number

Your thoughts appreciated.

 

[bookowski]

What is going to control is showing that it works for zero net tension.

It is not uncommon for these walls to step down to two wythes at the upper floors. It's usually not possible to show that it works for out of plan wind.

 

[XR250]

Why not use thru bolts instead of lag screws?

 

[dhengr]

PT999:
I agree with Bookowski and PEinc and their comments on this situation. Bookowski seems to have made a bit of a career out of working on these types of bldgs. and has a good handle on some of the problems associated with them, and has seen a bunch of them, if I recall correctly. He and I have been involved in a number of threads on some of those issues. These bldgs. do have walls which vary in the number of brick wythes as you move up in story height. I’m not even sure they are always bonded. The walls are generally in pretty crumbly condition and were only built as gravity walls in the first place. The original designers and builders did understand that floor systems on both sides offered some lateral stability (mostly friction) to the walls and some diaphragm action, but I don’t know that you’ll find any old bldg. calcs. which show much attention to those conditions. They were really pushing the h/t ratios for the day with these bldg. walls. I don’t know what the wind loads were, if any. The floor beams/joists were most often fire cut, so they would fall out of their wall pockets rather than pull the walls down with them, in case of fire severing them in the middle. They did have experience with this happening, and figured out how to minimize this problem. They made no account of the fact that at some point in time the adjacent bldg. and floor framing might be removed, and what that would do to wall stability. It’s a shame if and when these old bldgs. can’t be saved and renovated, but it is a real bitch to try to make them meet today’s codes, stds. and requirements to the letter. Then, the new rich owners want amazing renovations and improvments. You really need an understanding AHJ and a city and bldg. dept. willing to work with you, and one wanting to save these communities of bldgs., and then allowing you to use the best engineering judgement, within reason, to meet the intent of the codes, but maybe not the current letter of the codes.