Integrated Excel workbook for Wood Structure Design 3

[AELLC]

I have seen many Excel worksheets that do individual design tasks and I wanted to start a discussion regarding integrating all that into one large workbook to streamline the entire design process.

I have my own workbook that I have improved over about 18 years and wanted to share ideas, etc.

It is Excel 2010 but can be saved as 2003-2007 with minor loss of functionality. It has no macros, UDF, or VBA etc., just basic Excel formulas, and nothing iterative.

I don't want to get into VBA discussions because not everyone is familiar with that.

 

[AELLC]

jeff-

We need to run a test problem, see what deflection results.

 

[AELLC]

Look at this

I hope no one perceives this as student posting hehe

 

[AELLC]

Here are results -

The AELLC BH method is that crude method I use for my 116 labels because it is very concise

But I was surprised because it gave such good results this time.

The Beamanal results are slightly off because that one is not capable of single span/cantilever - I had to "trick" the input

Where I wrote in black for Beamanal results I goofed - the location was correctly written in red above.

 

[jeffhed]

Yes. I was wondering if you would ask about that when I was attaching the file. I have it split into a ton of segments, but when I was first creating it I wanted to make sure there was extremely low rounding error with whatever programs I was checking it against, so I just made extra sure by providing 1000 segments for each cantilever and span. I ran it in my steel beam spreadsheet and I get the same as Beamanal. I have attached a printout from my steel beam spreadsheet that shows the reaction in the upper right and the deflections are shown down at the bottom.

Ra = 1159 k
Rb = 1021 k
Midspan deflection = 1.201" @ 8.96'
Cantilever deflection = -0.542" @ 24'

 

[AELLC]

I do so much tract home and used to do so much multi-family, there is a lot of what we would call routine little headers.

We always did those by standard chart or load tables (plf vs span) methods in the past, but Excel offered us a new opportunity to make design more quick and efficient - like occasionally you get a short header with a huge girder truss point load on the span. It also was useful that the trimmer or post was designed right there too.

So to make the sheet productive, almost all intermediate stuff was hidden, where there is input that frequently does niot occur, we put those cells just off the print boundaries.

So I came up with what I have been calling BH, which is a total of 116 labels, 4 to a printed page.

Another feature is frequently you input a header, and you had forgotten that you had previously just done a "worser-case"...the spreadsheet automatically shows the label code do you can lump the 2 into one design label.

So every "subroutine" had to made very compact (the deflection calc especially)

See attached

 

[AELLC]

OIC my LDM sheet gave the exact correct defl on the s.s. span, but the location was off just a tad because the beam was split into only 36 segments.

 

[AELLC]

jeff

How does your steel beam design sheet pick the correct size out of all those AISC shapes, and does it "filter" out beams too wide, etc with pre-set criteria?

The above was a big headache but I got help from the gurus over in engineering spreadsheets

 

[jeffhed]

The steel manual used to come wich a cd with a spreadsheet with all if the section properties on it. Now you can just download it from the AISC website. It's not 100% accurate since I had to estimate a beam weight as a percentage of dead load. They are really more like starting points for the beam size. And it finds the lightest weight section for the input loading just based on what section you select and what Ix, Zx, and Sx are needed. It usually is a section or to lighter than what you need.

 

[AELLC]

OK I went with the old ASD because it usually gives the same answer as LRFD for the simple load cases I use here, and use ASD for all my wood design - just makes load bookkeeping easier for me.

I know how to do LRFD but don't see a need for it unless I was doing major commercial work. I believe ASD is no longer legal for steel but all the plans checker allow it because it will give basically the same answer . The only time I saw a big difference is when it is a steel composite with concrete deck.

 

[AELLC]

Back on topic, I think for now I am going to use that method in 20 Mar 14 18:18 because that will give all the reactions, shears, moments, and deflections accurately albeit fairly awkward because only one copy of Beamanal is being used.

I can't think of a method to do all that for each of my 116 design labels because the Excel file would be too large to run, and if I had a pared-down flexibility matrix solver for each beam label, I would still have to have at least 36 beam segments per span, multiplied by load cases.

 

[AELLC]

jeff,

Are you considering most wood beams and headers as being subject to outside elevated temperatures, that reduction factor Ct?

 

[jeffhed]

No. Everything I have read has made reference to manufacturing processes and steam or extremely high temperatures that the beams are exposed to for prolonged periods of time. I would consider the headers as interior beams since there is usually foam and stucco on the exterior wall and climate control on the inside. I'm not in the office so I don't have my 2012 NDS, but I found a poriton of the 2005 NDS commentary online, it is attached. The 2005 NDS commentary states "Tabulated design values also are appropriate for use with wood members directly exposed to solar radiation but otherwise surrounded by ambient air, such as members used in bridges, exterior balconies and stairways, and exterior vertical and horizontal structural framing." In southern Utah, we do have elevated exterior temperatures, although not nearly as much as in the Phoenix area. Due to the sun exposure here, most beams on exterior back patio roofs or other similar structures are not exposed wood. Most times they are wrapped and stucco is applied to the beams like the rest of the home. The majority of exposed beams I deal with are for lattice type structures where the members are so overly sized for aesthetic reasons that the reduction in strength due to extreme heat wouldn't make any difference.

 

[AELLC]

jeff,

OK, thanks, I am going to think about this some more, not worry about the beams and headers that have inside air-conditioned on one side.

I think it is going to be a non-issue except for instance, major beams in the attic space, such as a flush beam that supports trusses, and framing in garages.

The attics here seem be at least 120 degrees 24 hrs a day for 6 months. Garages, not nearly as bad.

 

[jeffhed]

Yeah. I've thought a lot about attics too. It does say in that commentary that if they are ventilated per code that it isn't really a concern because the part of the truss chord in contact with the roof would be heated up but probably wouldn't be heated all the way through. I know none of the truss manufacturers here have done it, and I can't shine the trouble that would happen to start requiring that. Even commercial buildings that have plan check it has never come up once. However, you guys are typically 10 - 15 degrees hotter than we are and our lows are below 100 most times so you probably have a little more reason to think about it. What is typical down there?[tt][/tt]

 

[jeffhed]

I am reposting my last comment with some corrections.
Yeah. I've thought a lot about attics too. It does say in that commentary that if they are ventilated per code that it isn't really a concern because the part of the truss chord in contact with the roof would be heated up but probably wouldn't be heated all the way through. I know none of the truss manufacturers here have done it, and I can't imagine the trouble that would happen to start requiring that. Even commercial buildings that have plan check it has never come up once from the plan reviewer and the reviewers are structural engineers. However, you guys (Phoenix area) are typically 10 - 15 degrees hotter than we are and our lows are below 100 most times so you probably have a little more reason to think about it than we do up here. What is typical down there?

 

[AELLC]

The low can be 92-94 and the high 110-114 for weeks it seems

IMO the attics aren't ventilated enough and I can't go into them anymore, not even mornings.

 

[jeffhed]

I know weve been talking about beams and girder reactions up until now, but how do you determine if a continuous footing can support a point load or if you need a spot footing in the continuous footing? Our footing program models the continuous footing like a base plate and it determines how far the footing can bend with full bearing pressure on it. With our typical footings, it ends up being around a 6'-0" length of footing (3'-0" from the point load on each side). We then take that length of footing and multiply it by the width and the remaining bearing pressure to determine a maximum point load the footing can support without a spot footing. So if our footing is loaded to 800 psf out of 1500 psf allowable, we would have an allowable point load of 6300 lbs for an 18" wide footing. Of course you would need the full 3'-0" of footing in a straight run on either side. If the point load is at a corner we show a spot footing, if the point load is closer than 3'-0" from a corner we will prorate the maximum load.

 

[AELLC]

My method is low-tech - see attached

 

[AELLC]

OIC I neglected to account for the uniform wall load that exists in the cont wall ftg to begin with

 

[AELLC]

I could code (to make this very automatic) the above topic of conc load at wall ftg, but that would take a few days - I usually do my Excel tinkering 4PM to 6PM or so