Upgrading wood columns in an old building 2

[dgf20]

I'm working on load rating an existing unreinforced masonry building with wood floor systems and interior wood columns. The owner would like to upgrade the floor capacities, which is governed by the lowest level of wood columns (this is an old 5 story factory building). I innitially checked building up the existing columns with additional wood members, but the member stresses were still pretty high. I'm thinking about sandwiching channels to the columns. Can anyone point me in the right direction?

Thanks.

 

[JAE]

I think the key would be the load path from the existing floor into whatever type of column steel upgrading you would provide, be it channels or something else.

At each floor, there is now some means of transferring the load from the floor into the column. So your final design would want to include consideration for:

1. How to get the floor load into the new steel shapes.
2. How to get the column loads in the upper stories into the steel shapes at the lower columns.

 

[connect2]

How are the foundation doing? Sounds like what you should do is based on what you can see, rate it and restrict it. If you plan to reinforce above grade structure to increase capacity then get a geotechnical component going.

 

[jike]

The old buildings usually have pintels (cast iron?) transfering the load from one column to the next. I do not how to rate these other then testing. Do you have to consider uplift in the top story?

 

[dgf20]

JAE: The load transfer from the floors to the channels has been a concern. The pintels protrude past the columns and make for a realy messy detail. The more we look at it, it seems the right thing to do will be to replace the wood columns with steel at the lower levels. Caps and bases could be easily fabricated to take the place of the pintels and provide a means for anchoring each column to the one below.

JIKE: Thanks for the reminder, all of the upper levels of wood columns will require straps to resist the uplift.

CONNECT2: There are ledge outcroppings throughout this basement, and i have not found any signs of settlement. I suspect everything is found on solid foundations, however we cannot tell for certain. The joists and beams max out at around 50-55 psf, and I don't intend to bump up this somewhat low rating.

The lowest level of columns appear to be too light for snow load coupled with the 55 psf on all the floors above. In order to get the stresses down, I'd have to vacate a couple of floors.

 

[msquared48]

Have you considered LLR?


Mike McCann
McCann Engineering

 

[dgf20]

MSQUARED48: I am using LLR in the design of replacement and/or reinforcing, but did not in the existing conditions since the floor member capacities were below the IBC 2006 loads for new structures. The way I read the LLR section was that it could only be applied to the values in Table 1607.1 (125psf if this was new construction)?

The reinforcement/replacement will be designed for current codes (125 psf with applicable LLR), although the floor members will still only be rated at the 50-55 psf.