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ANSWERED on Wed 3 Mar 2010 - 5:34 pm UTC by redhoss

Question: Structural Support Design - Beams and Columns for floor and roof

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Mon 1 Mar 2010 - 4:19 pm UTC

Question

gnoto
Customer

Hello,


I am renovating a 125 year old brick 2-story house.

Over the years a 3" sag has developed in the center of the floor and the flat roof.

There is no load-bearing center foundation, and therefore the floors and roof have no support. 

All joists are 2"x10" 16" O.C.  They clear-span a 21 distance between exterior walls. 

Joist ends are built into the brick and mortar walls.  They appear to be in good shape. 
The foundation is stable. It is formed of rock and mortar.  There is a dirt crawsplace below the 1st floor.

The floor is rectangular 30'x21'.  The stucture has a roof sloping 1" per 1.5'.




I had a number of problems with an architect/engineer I hired to design a support
system for the floor and ceiling.  I wish to become more knowledgable before working with another engineer, and would very much appreciate suggestions on practical design ideas,
reasonable beam, post and pad sizes, and any alternative ideas for a support system.


The current design consists of 3 concrete pads with posts supporting a steel beam running perpendicular
to the foor joists for entire length of the structure.  The 2nd floor and Roof are supported by LVL beams supported by columns.  All columns line-up directly over eachother.



Spans between columns are 16' and 14'.   Column placement was determined by the floor plan layout. 

Floor and roof joists are 21' long - the width of the structure.   The long dimension from wall to column is 11'5", the short dimension is 9'5"

Due to limitations on access for installation, it appears we may need to install the steel beam as 2 sections. 

Design loads are 50psf for each surface - the 1st floor, 2nd floor and roof.  Soil bearing capacity is 3000PSF.



My questions:

1.  Is there a practical alternative to placing a beam under the joists for support?

2.  If using a steel beam, should the beam sections be spliced with plates?

3.  Should the beam splice be placed directly over the central column?  How should the beams be joined in this case?

4.  Should a treated engineered wood beam be considered as a more practical alterinative to the steel beam considering cost,
installation requirements, construction material requirements, ease of installation?

5.  What size beams, posts and pads should be used?



Thanks!

 
 

Mon 1 Mar 2010 - 5:50 pm UTC

Uclue Researcher Request for clarification

redhoss
Researcher

Hello gnoto, let me see if I understand you. There are 3 beam runs. One supports the roof joists, one supports the 2nd floor joists and one is in the crawl space and supports the first floor joists. Since the columns all line up and the design loads are the same for each floor/roof, each beam run has exactly the same loading. How do you plan to dig and pour footings in the crawl space. The only steel beam is the one in the crawl space. Are we talking about steel columns. If so, round or square.

Answers to questions 1,2,3 and 4:

1. Not that I know of.
2. Yes, but they are not moment connections if located at the center   column.
3. Yes, a simple bolted plate just to hold alignment.
4. I would use steel beams for all 3 runs.

You and I have something in common. I also have had problems with architects.

 

Tue 2 Mar 2010 - 8:30 pm UTC

Question clarification

gnoto
Customer

Hi Redhoss,

Thanks for taking my question.

Clarifications are as follows:

1.  Beam Runs:  The beam configuration description is correct - 3 beam runs as described.

2.  Loading/Point Loads:  The loading is correct.  40PSF live load + 10PSF dead load on each floor.  30PSF snow load + 10PSF ceiling load + 10PSF roof load for the roof.  All columns line-up so each beam will have the same loading.

3.  Footings:  As part of the renovation project, we will be removing all the exsiting wood floor planks to expose the joists above the crawl space. This will allow for some room (16" between joists) to excavate the soil required.  I have no experince with this (and haven't figured out what to do with the dug-up soil!) - that is why I wondered if there is an alternative to the beam/post/pad support configuration.  Someone suggested engineered joists capabable of spanning the 21' width between walls to replace the exising joists, but I suppose that would not solve the problem of support for the roof.

4.  Crawlspace Beams:  I expect the longest beam length we can get under the 1st floor must be less than the 21' - the distance between walls.  We can lower a 20' beam section down into the crawlspace parallel to the joists and rotate it in place, considering that the floor planks will be removed and joists/crawlspace exposed.

5.  Columns:  It was recommended we use 3" 0 Schedule 40 Adjustable Pipe Columns.  I would be very happy to know of a more practical alternative if you have a suggestion considering cost, ease of installation, etc.

6.  Beam Spices:  You suggest a simple bolted plate to hold the beam alignment.  I suppose that would apply where the splice is directly over the column.  I don't have experience with construction - I suppose the column would not include flanges or some other feature to facilitate the spice?

7.  Beam Types:  You suggested steel beams for all 3 runs.  Would you mind letting me know why you suggest this over LVL's?  Just to let you know why I ask - A builder friend of mine recommended we completely avoid steel,  another person suggested a practical solution may involve joining 2 2"x10"'s to form a beam, with maybe an additional pad and post to shorten the beam run.  I priced a steel beam at 9'/Ft


8.  Architect!:  My Architect miss-interpreted the project as one in which the 2006 IBC was the correct code reference, when in fact the structure is a 2-family dwelling unit and the 2006 IRC should actully apply.   He thought the IBC should apply since the lot is zoned R3 - commercial.  I'm not sure if that's why all the support system components in his design appear oversized by a factor of 2.


Please let me know if I can provide further information or clarification.


Thanks for your help.  It is greatly appreciated!

 

Wed 3 Mar 2010 - 1:20 am UTC

Comment

myoarin
User

Here is a site with a nice illustration of what you want to do:
http://www.sinking.com/column.html

You might consider opening holes in the brick foundation to insert the beams, allowing them to be better secured with the building when the holes are then closed. 

Could also be easier and more efficient than manhandling the beams into the house and between the joists.

 

Wed 3 Mar 2010 - 5:34 pm UTC

Uclue Researcher Answer

redhoss
Researcher

Using your numbers, here are choices for a steel beam:
W8x17
W10x11.5

I admit that I am partial to steel because I was a steel designer. It scares me to look at those LVL beams. I know that they are a proven product and I apoligise for my prejudice. I guess you can ask your LVL provider for an equivalent to the steel beams.

The vertical load on the center column under the 1st floor beam will be about 24,000#. According to the tables I have, the 3" sch40 pipe you propose will be okay.

Using 24,000#/3,000psf you will need a spread footing with 8 sq ft area. So, you need a 2'-10" square footing.

Normally a column will have a plate which bolts to the beam flange. I have no experience with those screw adjustable columns.

I think I have answered most of your questions, but please ask for a clarification to clear up any others. I hope you like my work better that your architect.

 
 

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