Wood Engineering Blog

CM and CF and Fb ... all tangled up!

2012-01-27T22:32:00.000-08:00

... note that C_F and C_M are all tangled up. I mean that to get C_M for flexure (for Dimension Lumber) ... you also need to know C_F (and F_b). Look at the table on the left side of page 30 in the NDS SUPP about half way down. The table gives a value for C_M on F_b, but the problem is ... there is a little " * " thing. As we look below it indicates that C_M actually depends on what C_F times F_b is. Wild.

Attached is a page from my solution to Problem 1, Part a) of our Assignment 6 ... that shows how I deal with it (and the other Adjustment factors for bending for that part of the problem).

Note: jus cuz I show the 2 x 8 in the calcs above - it does NOT mean 2 x 8 is the final answer ... I'm just checking the 2 x 8 to see if it works!

...

Assignment 2 SOLUTION - Board Foot Measure

2012-01-26T15:23:00.000-08:00

... here, for your convenience, is the solution to Assignment 2 ... my cell phone being the scanner!

... may have a better scan somewhere ... but this gets you going.

Doc

Bending Check - Dim Lumber Joist (Assn 5)

2012-01-26T10:20:00.000-08:00

Design Checks for Sawn Lumber Joist ...

2012-01-25T14:16:00.000-08:00

... here they are! ... (NOTE SOME CORRECTIONS)

Bending Design Check - Example from Lecture

2012-01-23T20:12:00.000-08:00

... here is the bending check for the example we did in class today ... for the 2 x 8 and 2 x 6 sizes:

(Note I include some page numbers.)

So, for the assignment (see Schedule) ... you'll do Grade No. 2 and Grade No.1 ... (smallest 2 x depths).

Doc

Cross-Plate Shrinkage ... (Assn 4)

2012-01-23T19:41:00.000-08:00

So, here is my solution for Assignment 4 ... if we consider just the shrinkage across the PLATES ... I get about 3/8 in. total.

Recall that in this assignment we are assuming manufactured lumber floor systems (rim and other joists) ... with minimal shrinkage (across the floor depths).

... this amount of shrinkage is probably quite manageable. Follow the sheathing and wall covering Manufacturers' installation requirements and recommendations.

Doc

CLT

2012-01-20T22:20:00.000-08:00

Today a former student sent me an email asking what I thought about Cross Laminated Timber (CLT). I was mulling a response when, just a bit later, an email came in from APA ... happening to be an announcement of their New Standard for Cross-Laminated Timber. (Is that wild, or what!!!)

You can download the Standard from APA (probably you'll need to register): http://www.apawood.org/level_b.cfm?content=pub_PubUpdate_January2012

I also found this clip on youtube: http://www.youtube.com/watch?v=rLqiwBL28v4

The youtube clip talks about some things we have been talking about a bit in class:

1) the `heavy timber' fire rating ... these are SOLID WOOD PANELS. They do NOT `burst into flames'!!! Solid wood is actually quite fire safe.

2) use of wood is net carbon negative ... the effect on global carbon is WAY better than use of steel or concrete.

The video also talks about sustainability ... use of the CLT in high-end structures in Europe ... and good life cycle performance.

GOOD STUFF!!!

scan

2012-01-19T13:08:00.000-08:00

... here's a cool scan ... shows No. 1 Grade lumber (in this case DF-L) of different widths and knot sizes.

For our purposes ... Species or Species Group lumber are sorted into Stress Grades.

The most apparent factor in Stress Grades are `knots'.

Knots are considered a strength reducing characteristic. Thus, within each Grade there are limits on knot sizes.

We'll talk more about this in class.

Scan is from the WWPA literature (Western Wood Products Association).

NOTE: as a designer you will generally NOT be `grading' wood products ... but you will be SPECIFYING wood products.

(So this is what they look like! ...)
Grading of wood products is done by people who are trained and certified to do so.

On occasion I need to make a `field judgement' (opinion) on a certain grade of lumber ... stuff like this (above) helps.

Doc

Board Foot Measure

2012-01-07T14:58:00.000-08:00

...

Board foot measure is used to communicate wood volume in the manufacture and wholesale of sawn lumber wood products and products derived from sawn lumber such as glued laminated timbers. In short, one board foot of lumber is equivalent to one 1 x 12 (12 square inches) that is one foot (ft) long. The `1' and the `12' are in inches. So, one 2 x 6 one foot long is also one `board foot' of volume measure (2 times 6 equals 12). Easy enough! A 2 x 6 that is 10 ft long has a board foot volume of 10 (10 B.F. or 10 BF). One hundred of such 2 x 6's have a volume of 1000 B.F., or 1 `thousand board feet' (1 MBF). And, in fact, lumber is sawn, sold, distributed, etc. in such volumes that the common unit in communicating such is `thousand board feet', or, actually, often just `thousand', with the `board feet' part implied. So, for example, when discussing the price of thousands of board feet of 2 x 6s it would be common to state a dollar price `per thousand'.

Let us now consider the `board feet' of lumber joists that will go into a floor that is framed with 2 x 12s spaced 16 inches (in.) on center (o.c.) spanning 16 ft across a floor that is 30 ft long. One way to go about this would be to calculate the total length of the floor in inches, in this case 30 ft times 12 in. per ft = 360 inches. Then, to get the number of joists we could divide 360 in. by 16 in. per joist to get 22.5 joists. Well, we really wouldn't use half (.5) of a joist; we would probably use just 22, and the last space at one end would be half of 16 or 8 in. These are the joists that span between the ends. If we have a joists at the start and ends also, then we would have 24 joists total. Each individual joist is 2 x 12 divided by 12 equals 2 board foot per foot of length. And since each joist is 16 ft long, each joist is 2 board feet per foot times 16 feet equals 32 board feet. Thus, to frame the floor, 24 joists times 32 board feet per joist gives 768 BF (almost a `thousand'). If these 2 x 12s are part of a large project (including wood volumes for other floors, walls, roof, etc.) their volume might be ordered and priced in terms of (thousands of) board feet. Or, they might be ordered and priced by `linear feet'. This floor, for example, would have 24 times 16 equals 384 linear feet of 2 x 12s. Indeed, if we go into the local building supply store and order just one or several 2 x 12s they will be priced by (linear) foot, and the price will vary by wood species, grade, how long, and maybe how many if the `several' is enough to motivate a discount. The `how long' comes into play as the longer length lumber pieces (longer than 12 ft or 16 ft) generally cost a bit more per foot.

The conversation could end here, except that mention has also been made of glued laminated timber (glulam) products. But to deal with glulam we must also first be clear on what a 1 x 12 (or 2 x 6, or 2 x 4, etc.) really is. In the lumber industry these dimensions are `nominal', which literally means `in name only'. Thus a 2 x 6 is not really 2 in. x 6 in.; it is actually 1.5 in. x 5.5 in. A single 1 x 12 board is actually ¾ in. x 11-1/4 in. A single 2 x 12 is 1-1/2 in. x 11-1/4 in. People who deal often with lumber products either have the actual dimensions (of nominal sizes) memorized, or, have at their fingertips the information quickly available in tabular form.

And now for glulam. Glued laminated timbers are made from sawn lumber pieces (or laminations, or `lams'). For example, a 5-1/8 in. x 12 in. glulam will be manufactured using eight 2 x 6s. The actual dimensions of the 2 x 6s are 1.5 in. times 5.5 in. Eight of these `layed up' (laminated) wide face to wide face gives a product that is 5.5 in. wide and 8 times 1.5 in. equals 12 in. deep. The 5.5 in. width is planed down to 5-1/8 in. The board feet measure of glulam is based on the input laminations; so, the 5-1/8 by 12 is 8 times 2 times 6 divided by 12 or 8 board feet (per foot of beam). If the beam is 18 ft long, it has a board foot measure of 8 times 18 equals 144 BF. Or, since we already said that a 2 x 6 is one BF per foot, and since there are 8 of them in the beam layup, we have 8 BF per foot of beam; 8 BF per foot times 18 ft gives 144 BF total.

Now let's wrap this up with one more example. Let's determine the board feet volume of a glulam beam that is 14-3/8 in. wide x 58.5 in. deep and is 72 feet long. The beam will be manufactured using 2 in. thick laminations that are actually 1.5 in. thick, and each lam (or layer) is made of a 2 x 6 and a 2 x 10 laid side by side (with the joints between the two staggered layer to layer). (This is referred to in the industry as a `composite' beam in that each lamination or layer is `composed' of more than one piece of lumber.) So, a single lam has 2 x 6 plus 2 x 10 equals 32 divided by 12 equals 2.667 board feet (per foot). There will be 58.5 divided by 1.5 equals 39 such laminations. Thus the whole beam will have 39 times 2.667 equals 104 board feet per foot. The entire 72-ft long beam will thus measure 72 times 104 giving 7488 BF. Whoa! ... this beam has a board foot volume of over 7000 (board feet) ... a 1 x 12 board 7000 ft (a mile and a half) long. Yeah, this is a big beam!

Suppose the beam is priced at $800.00 `a thousand' (not a real price; just used for the example); this beam would be priced at $800 per thousand times 104/1000 thousand board feet per linear foot of beam equals $83.20 per linear feet of beam. The entire beam would be $83.20 per foot times 72 ft equals $5990.40. Alternately, the price of the entire beam could be calculated by 7488/1000 thousand board feet times $800.00 `per thousand' giving (the same) $5990.40.

If we want some equations for this `Board Foot' stuff,

BFPF = n x b x h / 12,

where

BFPF = Board Foot measure per foot of member (BF/ft),

n = number of input pieces (lams),

b = nominal width of piece(s) (in inches)

h = nominal depth of piece(s) (in inches).

Total BF = BFPF x L

where

L = length of member in feet.

For the 5-1/8 x 12 Glulam,

BFPF = 8 x 2 x 6 / 12 = 8.

The 5-1/8 x 12 glulam timber (itself) is considered to have a nominal (overall member section) dimension of 5 x 12 (or sometimes 6 x 12). A 5 x 12 sawn timber is a `single' piece (of actual dimension 4.5 x 11.5). The 5 x 12 timber, if given BF measure, is thus,

BFPF = 5 x 12 / 12 = 5 ... or the 6 x 12 ... 6 BF per foot ... (way less than the similar size Glulam ... interesting, or not).

References

Timber Construction Manual, 5th ed., American Institute of Timber Construction, 7012 S. Revere Parkway, Suite 140, Centennial, Colorado, 2005 (pages 3-5).

Deck ledger ... Simpson Connector News

2011-10-20T14:40:00.000-07:00

The October 2011 Simpson Strong-Tie NEWS features wood screws that can be used for ledger construciton:

News: http://www.strongtie.com/news/literature.html?source=topnav

Product line: http://www.strongtie.com/products/connectors/SDWS-SDWH.asp?newsletter=Oct11

I recently specified use of these screws for the attachment of a ledger carrying a loft (heavy storage) to existing studs. Use of conventional screws would have mutilated the studs; use of nails ... well, just couldn't get the capacities needed with nails.

What is Wrong with this Wall?

2011-07-12T13:46:00.000-07:00

...

Well, some would say, “Nothing.” (Apparently all those who went before me thought so.) The wall is framed with 2 x 4 @ 16 in. o.c. DF-L `Stud’ grade studs. The studs themselves are 84 in. long (tall). The openings have 2 x 4 headers and are about 38 in. wide (clear). The wall supports continuous floor joists that span 10 ft one direction and 14 ft the other. The floor is light frame wood construction, and the use is `office’ or `commercial’ of some sort or another (or perhaps light manufacturing or storage).
I assume that the wall was intended to be a bearing wall. (The span would be too large for the joists for even the lightest use otherwise.) Intended or not – once framed tight, and loaded, the wall will take on load.

The situation is this: the wall shown does not have any sheathing or wall covering. Thus, the studs are not braced laterally in either direction – most importantly – their `weak’ direction. For `2 x’ studs that are 84 in. tall the `weak direction’ slenderness ratio is 84 divided by 1.5 (2 in. nominal is 1.5 in. actual, remember) = 56. The maximum slenderness ratio for wood compression members (that’s what a stud in a wall is) ... is ... 50. This is addressed, for example, in the International Building Code Sec 2308.9.9 Bridging. It is also addressed in the National Design Specification for Wood Construction (NDS). The NDS allows a slenderness ratio of up to 75 during construction ... but once the building is finished, and ready for occupancy, something must be done to keep the ratio down to or below 50. This is typically (and simply) done with the application of wall covering or sheathing. It may also be accomplished by `bridging’.

From a structural standpoint – studs unbraced in their weak direction have a greater potential of buckling (becoming unstable). Why is the wall still standing? Well, because the supported area above has only been recently occupied ... and thus loaded only `lightly’.

GET SOME SHEETROCK OR WOOD PANEL SHEATHING ON AT LEAST ONE SIDE OF THIS WALL!!! (That’s what I communicated to my client – though in a different tone.)

WHAT ELSE !!! ...???

The 2 x 4 headers, silly!!!

Under design loads I calculate that this wall will have to service a total load of over 2000 lb per linear foot (of wall). That’s over 6000 lb over a 3 ft opening.

AND GET SOME DOUBLE 2 X 10 HEADERS IN THERE OVER THOSE OPENINGS!!!

(Also communicated to my client, and also in different tone.)

It’s fun!!!

...

Holes in Joists, Beams, and ... Diaphragms!

2011-06-27T12:36:00.000-07:00

"Where do the stairs go? In the middle, silly!"

I love it when things come together and make sense on a big scale. Here is such a case.

As a consultant I sometimes have to deal with holes drilled in glulam beams that are `not okay’, or at least feared not okay. Generally I turn to the American Institute of Timber Construction (AITC) Technical Note (TN) 19, “Guidelines for the Evaluation of Drilled Holes and Notches in Glued Laminated Timber Beams.” Figure 1 of that TN is shown below (with permission).

Manufacturers of engineered wood trusses publish similar ... showing where, and where not to put holes, or notches.

Sec. 2308.8.2 of the International Building Code intimates similar for sawn wood joists.

In summary:

... you can have notches as long as they are not too large, and are not along the edges mid-span (or ends mid-depth) ...

... they may be in the corners, if small, except ...

... they may not be at load or bearing points (bearing critical zone of a beam) ...

... holes may not be too large, and they must not be near bottom or top edges, especially midspan, or ends, mid-depth.

Holes may-should be (if required) in the MIDDLE!

Sweet!

So why does the title include `diaphragms’???

Well, a diaphragm is just like a (big, flat) beam, isn't it!???

And so here is the situation: my clients, and students (architects, and architect majors) like to put holes in floor (diaphragms) ALONG THE EDGES! ... and not just small holes, BIG ones ... STAIRS!!!

Some may not even know clearly what I diaphragm is, or does ... so I’ll just say `FLOOR’!!!

The building codes, and engineers, know what a diaphragm is, and generally require floors (and roofs) to function as such.

They (my architects, practicing and aspiring) argue that stairs mess up `space’ when they are in the middle of a floor.

Well they mess up STRUCTURE if they are at the edges!!!

Okay – you can put in a small hole – shoot for a corner.

And it needs to be small.

No long stair runs parallel-alongside a wall (boundary to the diaphragm)!

The boundaries of the diaphragms – at the walls – are where load is transferred in/out.

AND, ... if the floor (diaphragm) is intended to provide lateral support for a basement retaining wall – serious load comes in along the edge! And then goes back out at the sides!

In (re-)summary, then, keep holes and notches small. Keep them away from the edges mid-span, and ends mid-depth. If they must be along edges – put them at the unloaded corners.

MY PREFERENCE IS TO PUT THEM IN THE MIDDLE !!! (of the joist, beam, diaphragm) ... and then I might even let you make them be non-small!

JRF ...

Cantilever Beam Diagrams ...

2011-06-25T16:10:00.000-07:00

So, here are a couple Cantilever Beam Diagrams ... courtesy of AITC (Am. Inst. of Timber Construction) ... on their way to the 6th ed. Timber Construction Manual (2011).

A real life example of this type of framing is pictured in an earlier post (sorry the photo isn't so good): http://woodengineering.blogspot.com/2011/06/beam-framing.html

Theoretically, the hinge can be placed to balance out the negative and positive moments in the `main' beam, and or make the moments smaller in the main beam (both beams, for that matter). And, in fact, the `smaller' end beam(s) may be smaller both in length and section.

Notice that the hinge connections are (necessarily) at the locations of zero moment.

In fact, strictly for kicks and giggles, we could put a hinge at every location of zero moment.

In the words of the Director of Tech Services, AITC, ... "[But] the system would be unstable and impossible to install. Otherwise nothing would change."

:) :) :) I love it !!!

And, not only that! ... we would have twice, or three times the hardware, for the same amount of beam!

It's fun!

Beam Stability Running Away ...

2011-06-14T20:54:00.000-07:00

I just did the coolest problem. Actually, it was frustrating in the process. I gave my students an assignment of determining the required beam size for a problem we did in class. In class the beam was fully braced laterally. Their homework problem was to determine the size if unbraced along its entire length. In class we solved for the fully braced case in glulam (24F-V4 DF), and also steel W shape (A992, 50 ksi). Here are the conditions:

SL 60 psf
DL 15 psf
Span 30 ft
Spacing (trib width) 12 ft
Deflection limits: L/240 for SL and L/180 for TL (excl creep)
An additional 5 psf area load was assumed to accommodate the beam self weight.

Here is what we got for a fully braced beam:

5-1/8 x 25.5 24F-V4 DF
6-3/4 x 22.5 24F-V4 DF

and

W 16 x 26 A992 Gr. 50 ksi

We were able to use the AITC Span Tables (after getting line load from area load, of course) for the glulam.

For the W shape we did LRFD plastic hinge design, compact section, etc., blah, blah ...

Then in class we released the top of the STEEL beam from lateral support ... the example being, perhaps, of a wall coming down on a beam without some kind of ceiling or something at beam level to prevent lateral movement.

And we got a beam of some DOUBLE the weight ...

W 10 x 54 ... W 12 x 53 ...

The W 10 x 54 barely cleared the deflection criteria.

The W 10 x 54 is a stinking stout beam ... as wide as it is tall ...

With this, then, I sent them home to find the unbraced glulam sizes ... with the suggestion they start with a `guess' on C_L of ... 0.50 ... (after all, we were needing twice the steel beam, unbraced).

Instead of getting some other work done - I decided to solve what I had asked my students to do.

Amazing ... the guess of C_L of 0.50 for the 5-1/8 in. wide beam undershoots ...

In other words, if we let f_b = F_b' with a guess of C_L of 0.50 and solve for the required section modulus, we get a section that is 33 in. deep and drives C_L to 0.414 (using the 2005 NDS provisions and the Emin's of AITC 117 2010).

Resolving using an even deeper beam ... C_L continues to drop Fb'.

The deeper section reduces f_b ... but not fast enough ...

We go off the charts ... looking for a 5-1/8 in. wide beam (depth) that will work. And we can't find one! At least in any reasonable depth.

FINE ... a tiny bit surprising ... certainly interesting

BUT WHAT I WOULD DISCOVER NEXT WAS EVEN MORE SO!

Turning to the 6-3/4 in. wide beam ...

The guess of C_L ... OVERSHOOTS!

It results in a depth of about 30 in.

But the 30 in. depth results in a C_L of 0.73.

So I tried a lesser depth ...

27 in. depth gives C_L of 0.788

Fb' = 2175 psi

And ... fb = 1580 psi ... STILL OVERSHOOTS.

Trying 25.5 in. ... STILL OVERSHOOTS.

Hmmmmm ... 24 in. ... STILL OVERSHOOTS.

W.T.F.!!!

Trying the 22.5 in. depth - the depth we got with full bracing ... it works for the unbraced condition.

I DID NOT EXPECT THAT!

Especially with what the unbraced length did to the other beam selections (5-1/8 wide glulam and W shapes) ...

The Volume Factor ...

For the 6-3/4 x 22.5 beam the C_L calcs out 0.866 for the unbraced length of 30 ft.

For the fully supported beam C_L is, of course, 1.00.

But in both cases C_V is 0.882.

So for the braced beam the 22.5 in. depth had a penalty due to volume nearly equivalent to what the stability effect would be when unbraced.

The Beam Stability factor took over with the release of the bracing, BUT NOT BY MUCH.

Answer:

                                      Braced                             Unbraced

24F-V4, 5-1/8 x ...        25-1/2                                 None

24F-V4, 6-3/4 x ...        22-1/2                                 22-1/2

W A992 50 ksi            W 16 x 26                          W 10 x 54??? or W 12 x 53

WILD!!!

jrf

(when I get the scanner working I may include the calcs ... maybe)

Update: here they are ...

...

Jump Start on Problem 5 ...

2011-06-03T21:20:00.000-07:00

... this is cool. Plus, you'll thank me for this!

...

Obviously I'll post the rest, later :).

Enjoy!

Assn 2 Prob 2

2011-06-03T17:23:00.000-07:00

This is sweet - take a look!

Note that I check using a spreadsheet. Sweet. But one needs to crank a number of these out by hand before venturing into spreadsheet territory.

Problem 1 of Assignment 2 ... Summer Session 352

2011-06-03T17:14:00.000-07:00

So, everything is the same (as our example problem) except we are trying the 16.5 in. depth. I used the example as a template .. HERE!

(The 16.5 in. depth works also!)

Example Problem - Glulam Beam Design Checks

2011-06-03T17:08:00.000-07:00

... here is that example problem we did in class ... it's a sweet problem!

(Note: you can click on each page and then print out full sheet if you want to ...)

Beam Framing ...

2011-06-02T14:32:00.001-07:00

... while my date (at South Fork Pub) was talking on the phone (with her niece) I looked up to see this interesting roof beam framing. This kind of framing is not so common anymore, at least for new construction, that I know of. Anyway, note the big beam supported by the column (column on the right) ... and how it extends out past the column a bit, and another smaller beam frames to it. This type of framing takes advantage of the big beam cantilevering by, first, the cantilever taking out some of the positive moment in the main span, and, second, a shorter span for the beam on the left.

The picture isn't the greatest (using an older gen cell phone). Looks like we have a column cap (CC) welded to a square tube steel column ... and the connector for the smaller beam is what is called a Hinge Connector (at least in the latest Simpson StrongTie catalog).

Here's another shot ...

Beam Diagrams and Formulas for this type of framing are in Appendix A.2.2 of the 5e Timber Construction Manual.

jrf

Conventional and Engineered ...

2011-04-29T19:20:00.000-07:00

Pictured is the Logan Residence in Pullman. I think it is the largest residence in town - correct me if I'm wrong. The `structural' for this house is a mix of `Conventional Wood Frame Construction' (what I call Rx) and `Engineered'. Where bracing could not be accomplished using structural wood panel brace (or shear) walls - we incorporated tube steel frames (one pictured). These were especially necessary where there was a lot of `glass'.

Okay, well, maybe I should photoshop out the backhoe.

From the West

(Under Construction - Foundation to Roof Tube Steel Frame)

NOTE: in the Jemes Residence (earlier posts) ... behind Brian, Sharon, and Lacy are some walls where Simpson StrongWalls were employed to provide bracing ... another project involving a mix of engineered and conventional construction.

Jemes Glulam Trusses

2011-04-29T16:05:00.000-07:00

Brian and Sharon Jemes - happy residents of their new custom home in Latah County Idaho - invited us (the Design Team) out to look at their finished project. My role was to provide structural engineering. Eye-catching of course are the custom glulam timber trusses for their Great/Living Room. The trusses are made of nominal 6 x 6 and 6 x 12 Douglas fir 2400F-1.8E members (actual sizes 5-1/8 x 6 and 5-1/8 x 12) connected with steel bolts in double shear and metal side plates. The original configuration of the trusses called for a lower ridge beam passing through the truss joints and cantilever supporting the lower, outer roof. Subsequent design called for more of a self supporting outer (lower) roof and thus the lower ridge beam became non-structural and could itself be `jointed'. The knee-brace features of the truss are non-structural and were chosen to `bring down' the roof-ceiling. IMO the trusses are beautiful!!!

(Left to Right - LOL: Sharon and Brian Jemes)

The Team: Wendy, Myself, Pam, and Karen.

...

Jemes Deck

2011-04-29T16:03:00.000-07:00

And here is the deck. The design originally called for more posts ... but Why?!!! Using larger glulam support beams did several things: 1) reduced the NUMBER of support columns (and their foundation elements); 2) opened up the view from the daylight basement; and 3) the fewer but larger structural members better corresponds to the look of the trusses inside and the overall look of the building. (I mean why try to get into support beams made of dimensional lumber and 4 x 4 posts where the rest of the structure boasts 6 x 6 and 6 x 12 and speaks of strength!!!)

The deck had some cool angles to work with.

Note the decking pieces they chose. Notice anything in particular? Yeah, no deck screws. Actually, there are screws, they are just hidden in the spaces between. How fabulous! (Decking is by TimberTech.)

What a fun visit - thank you Brian (left), Sharon (hand in front of Brian), and Kacy.

Jemes Res ... couple more features

2011-04-29T16:02:00.000-07:00

Here are the Jemes Res. glulam trusses again ... The truss ends (heels) bear inside the walls and on glulam columns that reveal a little into the living space. Note that one column dimension is chosen to match the truss member(s) width, with the other determined either by structural requirements or (oversized) for `look'. For example, a bare-bones minimum size column might fit entirely within the wall - but would not `reveal' the look of supporting the structure above. Likewise smaller truss members might be possible - especially with the really deep truss geometry - but, again, might not give the `look' of supporting the load above (potentially a lot of snow on the roof).

And here is a closeup of a support column revealing a bit into the living space. And, aha! ... a finger joint in the glulam. The finger joint is what makes glulam so awesome! ... the ability to end joint short or modest length pieces into laminations (and thus beams) of essentially unlimited length.

Wet Use / Service Factor and Deck Design

2011-03-25T16:55:00.000-07:00

...

So, think this through with me ...

(Yes, there is a deck under here. The framing may or may not be wet - but it is certainly not warm.)

This deck (the one we have been looking at in class), intermountain Idaho, cold, high elevation, absolute humidity really low (even when snowing) ... for the design snow event I am going to judge the joists (and ledger) relatively dry (as long as they are allowed to breath). So, C_M = 1.00 for the gravity load design condition.

Now let’s think of the spring of the year, when there is less snow ... it has been melting, and everything is wet, and has been for weeks. Then the earthquake hits. I will do the design checks for the seismic event using the Wet Service Factor for wet service. For the anchor bolts ... C_M = 0.7. I could (and maybe should) check the joists ... the load will be less (and the Code will provide for `just how much’ less) ... the Load Duration factor will go up (C_D = 1.6) ... and the Wet Service Factor will drive the wood strength down. Probably we’ll be okay. (But it would be `fun’ to check.)

Now let’s think of preservative treatment and decay. The deck joists will be wet for short periods of time during (and after) rains ... when it’s (relatively) warm. But after the rain the humidity falls again and if the joists are allowed to reach equilibrium moisture content ... they will get pretty dry pretty fast. In fact, in any particular rain ... my guess is that the surface gets moist without the moisture content (MC) of the interior wood necessarily changing much. That’s for rain.

For the snow melt ... which may be occurring over months ... the joists are wet – but everything is still cool – and I am thinking there is little decay activity. So, all this to say, then, that I will probably not spec. P.T. joists unless there is some condition that will cause them to be wet or moist for prolonged periods when it is also warm.

Now let’s direct our attention to the ledger. The ledger is in contact with concrete. Typically in this type of construction the concrete will be of a quality that can transport moisture ... so, even if the air is dry ... the concrete can be bringing moisture up from the ground/foundation ... any time of year. Plus, the interface (for lack of better word) between the concrete wall and the ledger is one place that might indeed trap (again for lack of better) water or moisture. Thus! ... I will probably spec. a P.T. ledger.

Note: as said in class, if this deck were in the Coastal or Cascade Range, where the snow is heavy, wet, warm, and the air humid, ... I would carry Wet Use/Service Factor into all my calcs.

JRF

Wood Trusses ...

2011-02-23T22:07:00.000-08:00

... at some point our conversation will return to roof framing. Here is a cool thing that shows various kinds of (manufactured wood) trusses.

http://www.sbcindustry.com/images/publication_images/ttb%20truss%20configurations.pdf

Doc

...

COLUMN CAPACITY CALCULATOR - SAWN - COOL

2011-02-23T17:24:00.000-08:00

...

Here is a Column Capacity CALCULATOR ... http://courses.cit.cornell.edu/arch264/calculators/example7.1/index.html

Totally COOL! ... note the disclaimers.

Me thinketh that it is for CENTRIC loading ... in fact, IT IS ... here's a quick check.

If you put in a length of, say, 0.1 ft, the C_P should be essentially 1.00. Further, for Normal load duration, not hot, not wet, etc. ... we should get a column capacity of ...

(follow along!)

Let's consider a 6 x 6 `Post and Timber' column of dims 5.5 by 5.5 ...

A = 5.5 x 5.5 = 30.25 sq. in.

Trying DF-L No. 2 ... Fc = 700 psi

All the C's go to unity

So, Fc' = 700 psi times 1's ... = 700 psi.

P_allowable = Fc' A = Fc A ...

So, P_allow = 700 psi (30.25 sq. in.) = 21,175 lb.

Behold, that's what the `calculator' gives us.

Load is indeed assumed to be dead center.

If we allow the load to drift off center ... the capacity will be LESS!

Doc

Columns, continued ...

2011-02-22T17:05:00.000-08:00

So, tomorrow (Wednesday), we will continue our conversation on columns. Here is a table (glulam) that you will find handy - print it out and put in your notebooks! http://aitc-glulam.org/pdf/Column/DF-2-1_15.PDF (and bring to class!).

Also ... bring page 210 and 211 from your text. Similar information, for sawn, but also different! (We will discuss.)

Doc

Column Capacity ...

2011-02-18T13:21:00.000-08:00

So, let's say that the column for the example we looked at in class ... instead of being short, or fully braced, is non-short, and un-braced. An example might be a column that is framed into a wall ... the wall braces it in one direction, and not the other. Let's consider the 6-3/4 by 6 ... and since it is nearly square ... we will, for conservative sake, assume it is NOT braced in the weak (thinner) dimension. (Actually, assuming the beam frames perp. to wall, to align the sides of the column with the 6-3/4 in. width of the beam - the 6-3/4 in. width will be braced and the weaker 6 in. width will not. So our conservative assumption is good.)

... let's assume the length (height) of the column is 8'-0".

... now let's go to the AITC Column Capacity Table ... DF, Load Duration 1.0 ...

(website: http://aitc-glulam.org/column.asp)

The Table gives us a value of ... 31,510 lb.

The Table says `Capacity' ... more technically this is an `Allowable' (axial) load.

The axial load in our situation is/was 15,000 lb.

So, is the applied load = 15k less than or equal to the Allowable load of 31.5k? Yes, GOOD!

Still plenty of capacity.

Look at the footnotes ... slightly different design value used ... 1900, instead of 1950 from class today. (Something is out of date.)

Note the blurb on eccentricity. The capacities in this Table allow for b/6 or d/6 off-centered-ness.

Note as you go down the 6-3/4 by 6 `column' (no pun intended) how the numbers are getting smaller ... that's what `Cp' is doing.

Functionally Cp is reducing the Allowable stress to account for (prevent) buckling.

Other things equal, going from a 4 ft unbraced length to an 8 ft unbraced length dropped our capacity by 25%.

And ... (WATCH THIS!)

2011-02-17T11:48:00.000-08:00

(Oops ... should say 2.1 psf above)

Problem 5 ... Blow by Blow

2011-02-17T11:44:00.000-08:00

... here is the blow-by-blow solution to Problem 5. If you played with the span calculator you might have found that 2 x 10 joists work ... until you count their weight! Then you kick up to 2 x 12. Also, the 2 x 8 and the 2 x 10 and the 2 x 12 all have different Size factors ... and the 2 x 8 has a different Wet Service factor since the Size factor kicks it above the FbCF = 1150 psi thing.

Continued on next post ...

Hem-Fir Deck Joists ... (Prob 5) ... cont.

2011-02-17T11:43:00.000-08:00

... pages 6 - 9 ...

Code, and Creep ...

2011-02-15T17:03:00.000-08:00

... interestingly, the Code does not REQUIRE us to account for creep in our deflection calculations, per se. But, if we do account for creep, the Code references a way (e.g. the calcs we have been doing in class). It actually puts it back on the designer ... "If long term deflections are to be limited ... "

You, the architect, will need to judge the effects of long term deflection, and then design (or have us engineers, design) accordingly.

Unless there is a strong reason NOT to include the effect of creep - I generally include it.

Doc

Specific weight ...

2011-02-14T17:43:00.001-08:00

Ughhhhh ... you had to ask that question! The weight of wood varies with MC (Moisture Content). We have been using 35 pcf for DF-L ... which is probably an okay value - maybe a tiny bit heavy. For Hem-Fir let's use 29 or 30 pcf. I'll send out more info later. Doc

Open web steel joists ...

2011-02-13T12:09:00.001-08:00

I was on a photoshoot today in Lewiston, and while waiting around (at the Starbucks down there) I looked up, and behold! Open web steel joists. Holding up a steel deck roof thing. Looks like 2 steel angles for the bottom (tension) zone of the beam, and two up above for the compression zone, with the zig-zag bars carrying the shear between. Sometimes the deck above, particularly with concrete poured over, is `studded' to the top of the beam - causing the concrete deck and steel to act as a composite. I suspect in this case the deck is simply attached to the joists to keep the deck from blowing away, and to provide lateral stability to the top (compression zone).

Note how `skinny' steel structure is compared to wood. My personal take is that wood is far more natural, and intuitive. Steel looks more `skeleton-ish'.

Also note the cross (X) brace. Steel happens to be so strong ... we end up with a lot of bracing and stability issues. You will rely heavily on your engineers when dealing with steel. "It's so strong it's unstable!"

... well, we are getting a bit ahead of the schedule - but I just can't resist a good shot.

Doc

... another example!

2011-02-11T16:14:00.000-08:00

... for kicks and giggles (KAG) I worked up another example. As posed it is a bit `academic' - but then I elaborate a bit, and make it useful.

Check: let's look at the AITC Table DF-26 (Roof Beams subject to Snow Loads, Douglas Fir) ... for 5-1/8 x 13.5 for span of 18 ft it shows 884 plf. NICE! ... I have that same number! Note also the `B'. That means that `B'ending controls the value. If we did a similar calc ... we would find that for Shear, Snow load and Total load deflections, the capacity (in this case the allowable spacing) values would all be greater (than the 9.1 ft). This kind of contradicts what I said in an earlier post - about glulam being governed by deflection for long spans. But - 18 ft is not a very long span for glulam. Plus, if you look at the AITC table ... you only have to go out to 20 ft ... to get `D'eflection governing (the `D').

The AITC DF-26 table is ... here.

BABY!!!

...

Some observations ...

2011-02-11T15:04:00.000-08:00

... hmmmm ... so it seems there may be a trend. I don't know if this could be a rule of thumb, or not ... but it seems with our dimension lumber we are getting joist depths that are about 1/16th the span, and the design is governed by flexure (bending stress). For our glulam beams we were getting depths of about 1/20th (or so) the span, and deflection controlled.

Some thoughts: assuming we are using the same wood `resource', glulam is `more efficient'; we place the higher strenght pieces where they do more good, and put the lower strength where strength is not as much needed. The result is that our DF glulams are about twice (or more) as strong as the `sawn' ... but with near the same stiffness (E).

Another thought is this: generally we are using glulam for the longer spans ... and deflection governs for longer spans, irrespective of strength.

(Short spans: shear or bearing; medium spans: flexure (or maybe deflection); long spans: deflection (sometimes flexure); really long spans: deflection.)

... flexure (F_b) is a `strength' issue ...

... deflection is a `stiffness' issue (E) ...

... flexure deals with `safety' ...

... deflection deals with `serviceability'.

...

inches, silly!

2011-02-11T12:57:00.001-08:00

Case sensitive

2011-02-10T11:47:00.000-08:00

...

ADJUSTMENT FACTORS ...

(Hey, sorry, but they are `case sensitive’.)

C_i ... Incising factor

C_I ... Stress Interaction factor (glulam; we might talk about)

C_t ... Temperature

C_T ... Web Buckling factor (don’t worry; we haven’t talked about, and won’t)

... there might be some others.

One more thing ...

2011-02-10T11:16:00.000-08:00

...

Finally, there is yet another reason I am comfy if I come up with an `extra lam': not seldom in the design and construction of a structure there will come questions that sound kind of like this: "The Owner wants to go with a clay tile roof instead." So, now all the sudden we have a greater Dead load. Will the beam I specified still work? It's nice if it does, especially if it's already in place.

Doc

...

... there is another reason.

2011-02-10T11:12:00.000-08:00

...

Another reason I don't generally deduct the camber is this: professionally I am an engineer (structural). Engineers are a particular subspecies of the human race. Since we deal with buildings, and safety, our way of thinking is NO FAILURE! NO RISK. We can't be like medical doctors and have people die on us. So, naturally, we don't design to the `knife edge'. While I don't intentionally `over-size' a structural member - I don't mind if the beam I come up with, upon scrutiny, `has an extra lam'.

You (architects) are different. You need to satisfy your client, the Owner. Part of your interest will be making sure your client doesn't spend money where he/she doesn't have to. You are less intuitively conscious of safety. Obviously you want the building `safe' - but the concept is usually only a (single) four-letter word.

If the beam in question is a single beam, an `extra lam' doesn't mean that much money.

If the beam is a repeated application then there is greater motivation to scrutinize that extra lam.

Sometimes I will determine the bare-bones (code) minimum size member for an application. And that is okay also, because I know that the design process still includes well-thought-out factors of safety.

...

Example - Revised - CONSIDERING CAMBER

2011-02-10T10:57:00.000-08:00

So, here is the example, revised to include camber. Deducting the camber for the stated camber radius we get that the 8-3/4 x 16.5 section WORKS! Yay! In my first run through the example I didn't consider it. Why? Well, for one I was going fast (caffeine, remember) ... but the other reason is that I don't generally consider it in real life. For stock beams - which is what I was aiming for in this example - I generally do not consider, nor specify, camber. I know a stock beam will probably come with camber - but different manufacturers use different amounts (radii). I don't want to lock in to a certain camber, or manufacturer.

For longer and longer beams and/or those with high dead loads and self weight ... investigating and specifying camber might be a good idea ...

... the BC brochure we are using does NOT include creep - but they also do not deduct camber.

Example, Pages 1 - 6

2011-02-09T17:05:00.000-08:00

So, here is an example that grinds though the calcs we have been doing in class.

(Continued on the next (older) post ...)

Example, Pages 7-12

2011-02-09T17:01:00.000-08:00

If you look at the BC span tables ... you can come up with smaller beams. "Why?" ... you ask. Cuz they don't include creep. It seems the practice of the glulam manufacturers to not include creep. It's not that they shouldn't - it's just that no one wants to be the first - since the first to publish span tables including creep will be showing deeper beams than their competition, and they'll lose market.

Example, pages 13-16

2011-02-09T16:50:00.000-08:00

Cantilever roof beams ...

2011-02-08T22:01:00.001-08:00

So here the roof beams cantiliever - going outside and carrying an eave.

There are some `issues' ...

1. weathering ... many structural wood products will do just fine outdoors - but just realize they will `weather' ... and look like other wood outside (though that can be mitigated somewhat). Some engineered wood products aren't made for outdoor exposure - check with the manufacturer.

2. note that as the beams approach the supports and extend beyond the exterior walls that the compression zone is now on the bottom of the beam, which is not supported laterally ... so you will have a C_L value that is less than unity.

3. deflections for a cantilever beam `grow fast' ... in other words, if you look at deflection equations, it takes a much shorter span (for the same load) to get excessive deflection. (And that should make sense, intuitively.)

4. for a roof CONSIDER (in snow country) that the overhang is most likely unheated, while the main span is (heated). Thus there will be more snow on the eave than on the main span - an unbalanced loading of sorts. (It's possible to have, in fact, snow only on the eave - I've seen it many times - esp. with poorly insulated roofs.)

5. across the support and for the overhang the compression zone is in tension, for which, if an unbalanced glulam is used, the reduced bending design value must be used in the calcs.

Doc

Incising ...

2011-02-08T10:00:00.001-08:00

So, here is that bridge again ... better pic of the `slits' in the curved glulam. The slits are `incising' ... used to allow preservative treatment to penetrate the member. The preservative treatment deemed necessary due to the wet service conditions and potential of decay (or they did it just cuz).

Note that for glulam (around here) the beam is made and then incised (pressure treated) ...

Generally preservative treatment (P.T.) is not considered to affect the strength ... BUT THE LITTLE SLITS SURE DO! ... and thus the incising factor, Ci.

... more span tables ... these from AITC!

2011-02-07T17:01:00.000-08:00

...

here are some more span tables - these provided by AITC. These `carry more weight' (so to speak, say with building officials) than those typically provided by manufacturers. If you find these easier to use than the other stuff - go for it!

http://aitc-glulam.org/capacity.asp

...

Some more wood houses in Malaysia ...

2011-02-07T14:16:00.000-08:00

I am told that the (true) Malaysians build (built) their houses above ground. The wood houses build on the ground - probably the Chinese. (Big Chinese and Indian populations in Malaysia. Also folks from India and other. I don't know how the others build/built.) The third photo depicts apparently traditional Malaysian architecture.

Remember - the current residential construction in Malaysia is CONCRETE! Maybe I'll put some pics of their concrete houses up on my concrete blog.

Calcs on 3-1/8 x 13.5 DF Beam ...

2011-02-07T14:03:00.000-08:00

So, here are the calcs on the 13.5 in. deep beam. It passes all the design checks without camber. There are some differences in the conditions for the BC Span Table ... note that the ratio of SL to TL in their calcs is 0.75 ... in ours 0.67. It was not clear (to me) how they dealt with creep. A couple things at the bottom of my calcs: 1) the total beam weight ... actually, it will weigh more since it will (should) be delivered long; 2) the 2.6 psf is the self weight of the beam as `spread out' over the whole roof area being supported ... and it is somewhat typical of wood framing ... adding several `psf' to the whole weight of the structure. If I get bored (not likely) ... maybe I'll add a third line ... `BF'.

...

Custom Residential Structure - Moscow Mountain

2011-02-05T15:20:00.000-08:00

...

You students are blessed to have professors that actually `do' what they teach. Here are some photos of a custom residence up on Moscow Mountain. (Your) Prof. Paul Hirzel is the Architect on this structure, and I the (structural) engineer. Aside from stunning, the structure is unique in that the structural wood you see is (not glulam, but) dimension (sawn) lumber. BABY!!!

photo (c) Art Grice

We have not talked about dimension lumber yet ... but the design principles are much the same as in our conversation (ongoing example) of glulam. You will notice, however, that the individual members in this structure are not particularly large - and that is where dimension lumber is limiting. For large members we need to use engineered lumber (glulam, etc.), or find large timbers in already existing structures (being demolished). Large trees for large timbers ... are (largely) extinct, or inaccessible.

(I should take more photos of the projects I have done ... but I always seem to be moving on to the next thing.)

wood house in Malaysia ...

2011-02-05T14:49:00.000-08:00

... here is a wood house in a bedroom community (of sorts) of KL. It is wood, and beautiful. But building new in wood has left the minds of modern Malaysians. My trip over there was part of a push to get wood (Timber) back into construction. The Malaysians are surrounded by beautiful tropical hardwoods. That which they harvest is all exported, and they build with concrete and steel (even residential). The only structural wood product they manufacture is plywood, which they use for concrete forms, and when used, burn. (WHAT'S WITH THAT!???)

...

Roof Beam Check (Calcs)

2011-02-05T13:00:00.000-08:00

... here are my calcs on the 3-1/8 x 12 ... I think in class we left out the self weight of the beam in our TL deflection calcs ...

TL deflection should go like ... defl due to SL + immediate defl due to DL and self weight + k ( immediate defl due to DL and self weight ) ...

where k is 0.5 for glulam ... (and 1.0 for green, and so on).

Enjoy: (click to enlarge)

...

Beam Camber and Sustained Loads - situation from Class.

2011-02-04T13:01:00.000-08:00

... (click on the image, silly, to enlarge it!)

...

two simple spans end-to-end vs. one 2-span continuous

2011-02-02T16:03:00.000-08:00

...

follow along ...

M_max = wL^2/8 occurs mid-span in each of the two simple spans, tension on bottom

M_max = wL^2/8 occurs across the interior support on the 2-span continuous, tension on TOP

where two simple beams end-to-end occur in a project, it might be an option (temptation) to span both with a single beam ... okay, fine, BUT ... Glulam ... big deal if V4 used ... since it’s manufactured to resist tension on bottom (primarily) ... if V4 is to be used, a reduced capacity of the beam must be considered (see other blog post)

however ... the continuous framing is nice in that the framing is better tied together ... and the deflection(s) associated with the continuous framing is(are) way less (with continuous framing).

See diagrams on p. 94 of Ambrose (10e) ...

And ...

http://reinforced-concrete.blogspot.com/2010/10/continuous-framing-beam-diagrams.html

And ...

http://reinforced-concrete.blogspot.com/2010/10/continuous-framing-continued.html

...

Note: the max shear force is greater in the continuous framing, and the reactions are different ...
...

(I’m trying to help you be smart! ... avoid `situations’ cropping up in real life projects.)

...

24F-V4 or V8 (Unbalanced or Balanced Layup) ...

2011-02-02T15:25:00.000-08:00

Remember, the `V4’ glulam beam is intended for `unbalanced’ use, namely (typically), a `simple’ beam supported at its ends carrying downward loads in the span between. The beam is `unbalanced’ in the sense that high strength `tension lam’ material is placed in the bottom zone of the beam only, where flexural tension is expected. If the V4 beam is used as a cantilever, or as a continuous beam (spanning continuously over interior supports) then flexural tension is experienced in the top zone of the beam where only compression was expected ... and the design value (allowable stress) must be reduced. (Same if the V4 is used for a simple beam but installed upside down.) The V4 can theoretically be used in such cases, with reduced capacity, as long as it is a `straight’ beam. (Often V4 `stock’ beams are cambered.)

The V8 beam has high grade `tension lam’ material both top and bottom, and thus can be used in cantilever and continuous span conditions. It can also be installed upside down – without reduced capacity. The V8 beam is also referred to as `reversible’ or `balanced’.

One could avoid the inappropriate use of the V4 by specifying V8 in all cases (and I know of one engineer who does) ... but the V8 is typically (a bit) more expensive, and may not be (quite as) available.

Consider instead language in the Construction Documents (CDs) such as:

Glued Laminated Timber (Glulam)

All simple span members (supported only at end) shall be 24F-V4 DF/DF

All continuous and cantilever members shall be 24F-V8 DF/DF (balanced layup)

Why am I telling you all this? ... Because you will be specifying beams ... and you need to `know what is going on'!

...

Upside down beams (Repeated)

2011-02-02T15:04:00.000-08:00

... here in USA the glulam (and other engineered wood products) industry has evolved into using what I call `highly optimized’ beams. We get every `psi’ out of our wood as possible ... and we arrange the wood (in our layups) as efficiently and economically as possible. It’s good – but sometimes backfires, e.g. when an unbalanced beam gets installed upside down. Generally when an unbalanced beam gets installed upside down you either install it right-side up, or call an engineer. When the beam has been installed upside down, and construction continued, the re-install option is practically gone, so the `call an engineer’ is probably the way to go. The engineer may find that there was excess capacity in the beam to begin with – yay! (But then to deal with if the beam is/was cambered.) If the beam is inadequate upside down – then it will need to be reinforced (or replaced). Reinforcement is another conversation.

Blurb on upside down beam investigation: http://www.associatedcontent.com/article/1497620/glulam_beam_installed_upside_down.html?cat=15

...

I-Joist Compatible (IJC)

2011-02-02T14:40:00.000-08:00

... if you have gone to the Boise Cascade link ... you’ll see the `I-joist compatible glulams’ thing. Recall that (western species) glulam is made from 1-1/2 in. thick laminations. This results in beam depths that don’t match common wood I-joist depths. So, to not lose market, the glulam manufacturers have started manufacturing glulams with compatible (same) depths. (Commonly this is an issue if you are hiding both joists and beams in the ceiling of a roof or floor above ... and you want the bottoms and tops of the joists and beams flush.) Understandably the capacities of these beams would be different (different section modulus, etc.), and thus the additional published information. I am told that such beams are typically manufactured by making one or several of the `inner’ laminations thinner.

Link: http://www.bc.com/wood/ewp/guides-resources/guides/Western-US-including-Alaska/BOISE-GLULAM-series.html

...

Green Bamboo House

2011-02-02T10:34:00.001-08:00

Stagg sent me this ... definitely cool!

http://www.ted.com/talks/john_hardy_my_green_school_dream.html

Doc

Glulam bridge in town ...

2011-02-01T16:45:00.001-08:00

I was on a bike ride and skidded to a stop when I realized we have our own glulam bridge here in Pullman.

I'll get better photos some time - or better yet - you go visit - with your camera ... (this shot with cell phone).

Our very own glulam bridge - across the creek downtown. Note the slits in the wood = incisings for preservative treatment. Necessary?

( ... incising maybe not noticeable in photo)

Timber Talk in Malaysia

2011-01-30T11:09:00.000-08:00

Glulam Timber Talk at University of Technology MARA (UiTM), Malaysia ...

Article here: http://thestar.com.my/news/story.asp?sec=central&file=/2011/1/29/central/7831295

(Gosh I look bald in this photo :) ...)
...

LTB ...

2011-01-28T16:26:00.000-08:00

So here are a pic and video of a reinforced concrete beam in Lateral Torsional Buckling. Note that the failure is catastrophic ... and without much warning!

pic: http://reinforced-concrete.blogspot.com/2010/10/ltb-better-pic.html ... notice how the beam buckles sideways even though the load is downward. (The blue thing is delivering a concentrated downward load.)

video: http://reinforced-concrete.blogspot.com/2010/10/ltb-beam-starting-to-buckle.html ... this isn't a concrete course - but in concrete we learn that concrete crushing is (more) catastrophic ... and to be avoided! ... In this case the LTB produces excessive compressive stresses in the concrete. And eventually it ends up (suddenly) on the floor below!

Enjoy!

Doc

SPECIFIER'S GUIDE ...

2011-01-26T22:35:00.000-08:00

Since we have jumped right in to our conversation on glulam (glued laminated timber) ... now would be a good time to download the Boise Cascade Specifier's Guide (and bring with to class) ... link is here: http://www.bc.com/wood/ewp/guides-resources/guides/Western-US-including-Alaska/BOISE-GLULAM-series.html

In particular download the `Specifier's Guide' ...

The Product Guide might also be interesting.

The I-Joist Compatible (IJC) link no doubt deals with glulam sizes that have depths equivalent to common I-joist sizes - so everything fits and/or is flush. Recall that our (western) glulam comes in depths of multiples of 1.5 in. (9.0 in., 10.5 in., 12 in., 13.5 in., and so on) ... but these don't match the common I-joist sizes .... so the IJC glulams are made a bit different to match the I-joist sizes (depths). Take a look.

Fireside Grill ...

2011-01-25T20:56:00.000-08:00

...

So, if you haven't been to the Fireside Grill (here in Pullman) ... you need to go there. The food is good - but even better - the view. Look up and see the fabulous glulam roof beams, exposed. The roof had to be supported in some way - by choosing glulam the designers were also able to `show' the structure in a very appealing way.

I didn't do this design ... but my dad's company (The Filler King Company) did manufacture the beams.

(I did take the pictures ... )

Glulam Truss

2011-01-25T20:40:00.000-08:00

...

Glued Laminated Timber (glulam) = (my def.) wood structural member made up of laminating (gluing) relatively small pieces of wood together (in layers) to make one much larger (and stronger) than the constituent pieces.

Bowstring Trusses with Glulam Top and Bottom Chords, Victoria British Columbia Int'l Airport, Canada ...

(my photo, but not my design :))

The (glulam) members can be used for:

substitution for big solid timbers that are unavailable (or too costly)
for timber sizes unachievable with solid sawn timbers
for timbers requiring greater strength and/or stiffness than solid timbers

For use in simple framing ... glulam can be used for ...

joists, beams, girders, rafters
posts or columns

The thing about glulam is that while providing support - it can also be very attractive, and thus we could categorize the use of glulam also in terms of ...

un-exposed
exposed

Glulam can also be made into curved shapes, and thus ...

cambered beams
curved beams (circular shape, S-shaped, whatever)

... and tapered, thus

tapered beams (single or double taper)
pitched and tapered curved beams
arches with tapers

And, pictured ... glulam may be used in truss members (straight, curved, etc.)

AITC 117 ... Standard Specification for Structual Glued Laminated Timber of Softwood Species

2011-01-25T20:11:00.000-08:00

Gang,

... here is a link to AITC 117 ... http://www.aitc-glulam.org/shopcart/Pdf/aitc_117-04-with%20_errata_incorporated.pdf ... it is the 2004 version.

The 2010 version is out - but - at least at the time of this post - is not on the site.

For those of you in my Structure II course ... the 2004 version has the Adjustment factors for glulam that we will be using in class (starting on p. 5, the 8th page of the document).

Doc

The Canyon House ...

2011-01-25T20:04:00.000-08:00

So, one day I decided to google myself (vain sounding, but I know you've done it also) ... and up came my name on some award-winner structure. At first I passed it off as some `other' Jeff Filler, but then I remembered that it (my name) is not so common, and that another engineer in the area of the same name would really be rare ... so I looked further. WT!!! ... it is me! It was an article on one of Paul Hirzel's (Prof here at WSU in ACM) houses (one he designed) ... and, yeah, I have done the structural engineering on a number of his designs.

The Canyon House ... (photo borrowed from one of the articles linked below)

it is built in a Canyon ... the unique thing is that if follows the hillside, instead of fighting it.

Paul's structures are awesome - but not easy to engineer ... he functions out of the ordinary.

...

... links http://www.residentialarchitect.com/Architects/simple-pleasure.aspx and http://researchnews.wsu.edu/arts/55.html and don't forget to look at the slideshow.

and also ...

https://www.aiaseattle.org/news_041109_honorawards04_creditscomments.htm ... scroll down to Canyon House.

Guys of Glulam! (Malaysia) ...

2011-01-22T03:19:00.000-08:00

... here are the main players (Guys of Glulam - Malaysia) ...

(left to right:) Shahriman Ibrahim, Director of Engineering, Iktisas Engineering, Wan Ahmad Nizar Zakaria, CEO of Iktisas, Jeff Filler (myself), and Ahmad Asmadi (`Muddy') Mohammed. We are embarking on the structural engineereing of the first glulam (custom) home in Malaysia.

... first calcs! ... banglo asmadi!

2011-01-19T04:20:00.000-08:00

...

Today we did the first design checks for the first glulam house in Malaysia (architect rendering pictured). The house has two portions, structurally: glulam arches front to back with cable bracing between the arches in front and left (cables not shown in this rendering), with the remaining portion post and beam (with wall bracing). The design checks were using the Meranti (hardwood) species, 40mm lamination thickness. Design checks were performed using MS 544 Part 3 (Malaysian Standard for Glued Laminated Timber). More info to follow ...

Glulam House designed by Encik Ahmad Asmadi (Arch.)

(It was actually fun doing the calcs!)

Engineered Wood Products

2011-01-16T06:14:00.000-08:00

... okay, People, this is a good thing to download and read and have in your stuff (APA's ... Guide to Engineered Wood Products):

http://www.apawood.org/level_b.cfm?content=pub_PubUpdate_January2011#C800

You will probably have to register with APA to download - but that's okay. If you are going to have a future as an architect (or engineer, or builder) ... APA and engineered wood will be big players. It will be worth them being your friend(s).

JRF

First Glulam Manufacturing Plant in Mmmmmmm ...

2011-01-14T23:26:00.000-08:00

… flew down to Johor Bahro today (from KL) to visit the first glulam manufacturing plant in Malaysia ... Woodsfield Glulam Manufacturing Plant … Cool! Eddie Ling, Managing Director, gave us a tour. Laminating glued laminated timber from tropical hardwoods.

The visting group ... (most of us, anyway)

Relatively short pieces used ...

Finger Joint Cutters

`First Round' of finger jointing.

short pieces finger jointed into longer ones ...

... and planed.

... And stacked.

`Second Round' of finger jointing.

The pieces are joined end to end to make laminations generally a bit longer than the finish end beam ... the laminations are then glued face-to-face and cured under pressure.

Cured beam ...

... ready for finishing (or maybe testing).

The Finger Joint

2011-01-13T00:42:00.000-08:00

I did not at first understand the importance of the finger joint in glued laminated timber (glulam) … to me they were just some `necessary evil’. After all – don’t we picture in our mind the end of a glulam beam where the horizontally placed laminations are betrayed, with the glue (face-to-face) joints between? However, without the finger joint – there would be no glulam altogether. The deal is this: we can only make glulam beams as long as the individual laminations. So, if we want a beam that is 50 ft long – we need 50-ft long lams. Easy. NO! Well, yes with the finger joint. Without it we would be searching for sawn lumber pieces 50 ft long each, continuous. We don’t find lumber pieces that long. in fact, if we go shopping for lumber input for glulam beams we will probably find it offered in lengths not over 16 ft. Longer lengths are available, but they will cost. In fact, the preferred sources of laminating stock will probably be `random lengths’ up to 16 ft. Herein comes the beauty (actually importance!) of the finger joint. The finger joint is used to join, end to end, individual wood pieces, into much longer laminating pieces. If we want to manufacture a beam that is 50 ft long, we will finger joint pieces of various lengths into continuous pieces of 50 ft each, and then laminate (glue them face to face with one another). The ability to `finger joint’ our input lumber allows us to use input material of, loosely speaking, `any’ lengths. And if suppliers are given the liberty to cut the lamination stock into the best lengths for them, they will come available to the (glulam) manufacturer more affordably.

Pictured is a finger joint in one of the glulam beams at the Fireside Grill in town. It is noticeable as two different color woods happened to be joined. (Most of the other finger joints in the beams at the `Fireside' are far less noticeable.)

The Wood Handbook ... 2010

2010-12-02T15:35:00.000-08:00

So, here it is, revised!

The Wood Handbook, 2010, Forest Products Laboratory, U.S. Dept of Agriculture, Forest Service, blah, blah ...

Chapter 1: Wood as a Sustainable Building Material ... here.

(No, I did not write this.)

More to follow.

Dr. Rahmani's Roof Beams ...

2010-10-11T17:29:00.000-07:00

Ayad allowed me to photograph some of the glulam beams in his beautiful house for illustration regarding glulam. Take a look. Note several things: 1) there are no (large) knots in the bottom lamination. The bottom lam is the `tension lam'. Knots are generally `strength reducing' - so if we want high strength wood in the extreme fiber tension zone - no big knots. 2) there are significant knots away from the tension zone - where lower strength wood may be used. 3) Notice the knots in the top lamination - suggesting the beam is `unbalanced' and may indeed only be used in simple span condition.

The view is upward from an angle - so both the bottom and side faces show in the photos.

We could argue, then, if we are looking at a beam and wondering if it is `balanced' (can handle tension on top) ... then we would look for similar quality top and bottom lams (no big knots on top lam if balanced).

Also notice that there is a small gouge just left of where I say "Bottom face." In places where beams may be subject to serious gouging (say a warehouse) it may be wise to add a sacrificial lam to the beam.

GREEN ...

2010-09-17T11:43:00.000-07:00

Talking `Green' with Dr. Wong, MTC ...

I love the new `GREEN' color scheme on (some of) the Alaska/Horizon Q400 fleet ... yumm! I was able to chat more with Wong (long cab ride together from downtown Victoria to Int'l Airport) ... and we talked `green'. In Malaysia they take two or three trees per acre harvesting, and as such open up a bit of canopy allowing adjacent trees to get `their chance'. (Seldom do they need to plant.) Wong explained, to my marvel, the effect of timber harvest on CO2 globally ... and it makes sense. When a forest comes to maturity it is basically in carbon equilibrium ... growth and decay. When a forest (or trees) is (are) harvested and then used for furniture, structural timber, whatever, the carbon in the wood is `tied up' then for another fifty or so years. The smaller trees in waiting thus can now grow are in growth mode and tie up more CO2. I mentioned how in the States we manage forests by letting them burn ... gargantuan releases of CO2 ... and that regrowth is slow, or nill (far more sterile environment). And we don't fight forest fires here (until they get big). He asked `Why?' There is big money in fighting big fires! Anyway ...

It was great chatting with Wong and learning about the Malaysian timber industry.

...

Dr. Wong ... MTC GDM

2010-09-17T11:29:00.000-07:00

I met with Dr. Wong Tuck Meng, Director of the Malaysian Timber Council, and Jeff Linville, Director of Technical Services, American Institute of Timber Construction, with regard to writing a Glulam Design Manual for the country of Malaysia. (Linville is also a former student of mine; and we and I are working together presently on the 6th edition Timber Construction Manual.) Wong and Linville were there for the ISO TC 165 meetings; I was there for to meet, and `for fun'. Malaysia exports timber to 150 countries across the globe but, strangely, builds with concrete (and steel) ... even their residential structures. Generations ago things were built with timber, but now timber structures are literally being removed and replaced with other. Wong wants to get the Malaysians using timber again, and thus the project.

After the (ISO) Banquet on Wednesday night ... some attendees lingering.

Seattle Coho (Ferry) coming into the inner harbor.

Meetings were at the Inn at Laurel Point, inner harbor, Victoria, B.C.

...

ESR 1539 / NER 272

2010-09-12T20:15:00.000-07:00

Here is a link to ESR 1539 ... replaces NER 272.

This document is awesome. It expands on fastener sizes, requirements, etc., diaphragm and shear wall information ... and, what is really cool, is that it gives illustrations of, for example, the fasteners / connections spec'd in IBC Table 2304.9.1.

http://www.isanta.org/ESR-1539_corrected_Oct_09.pdf

So, when a Contractor asks about using one fastener over another (that I have spec'd) ... I simply say, " ... well, what does NER 272 (now ESR 1539) say?" "Oh, you don't have a copy? ... my goodness! ... what's your email address? Here."

Flat Use Factor ...

2009-09-02T18:26:00.000-07:00

Good stuff.

When we lay the 4 x 6 flat, our Cfu goes from 1.0 to 1.05. (You can see that in NDS Table 4A.)

What that means is that our unit strength, or design value, increases ... our `psi' value. (The strength of the material increases by 5%.)

BUT, the strength of the member, however, decreases.

Let's check ...

The reference resistance or reference capacity, for bending, is M = Fb S ... (it comes from the equation f = M/S and setting f = Fb).So, (and for the time being NOT showing the other adjustment factors, which are equal in the two orientations) ...

... for the 4 x 6 on edge ...

S = bh^2/6 = 3.5 (5.5)^2/6 = 17.65 in.^3M = 2540 psi x 17.65 in.^3 = 44,820 lb-in. = 3735 lb-ft.

... for the 4 x 6 on the flat ...

S = 5.5 in. (3.5 in.)^2/6 = 11.23 in.^3M = 2540 psi (1.05) x 11.23 in.^3 = 2667 psi x 11.23 in.^3 = 29,950 lb-in. = 2496 lb-ft.

So,... by laying the thing flat, the unit strength of the material went up (2667 psi vs. 2540 psi), but the capacity of the member went (way) down (29,950 lb-in. vs 44,820 lb-in.).

BABY!

NDS Commentary on Adjustment Factors ...

2009-08-29T23:03:00.000-07:00

NDS Commentary on Adjustment Factors ... here.

Note: the form factor, Cf, is no longer used.

Sink your teeth into this one ...

2009-08-06T16:47:00.000-07:00

Wood Column Design Using the 2005 NDS LRFD Provisions ...

http://www.associatedcontent.com/article/2031526/wood_column_design_using_the_2005_nds.html?cat=15

While the equations for design check and Column Stability Factor for axial loading of a wood column are the same for both ASD and LRFD in the 2005 Dual Format NDS, the `numbers’ certainly are not.

Dual ASD and LRFD Beam Stability Calc using 2005 Dual Format NDS

2009-08-04T10:50:00.000-07:00

Here is a calc of the Beam Stability Factor in both ASD and LRFD for a wood beam using the 2005 Dual Format NDS. Interestingly, the formula for CL is the same in both formats, but the `ingredients' are different, and so thus the end numbers.

Enjoy: (and note - this is a draft - comments welcome): http://www.associatedcontent.com/article/2021852/beam_stability_factor_using_2005_dual.html?cat=15

Another one ...

2009-07-31T08:47:00.000-07:00

Owner: "Does the fact that it is standing presently have any merit?

Consultant: "The structure is empty and it's summer. Put a couple layers of sandbags on the roof - to represent the design snow load plus overload, and a couple of layers of sandbags on the main floor system - to represent occupancy plus overload, and then we can talk. But I don't want to be inside while you're doing it."

Quote of the week ...

2009-07-29T19:27:00.001-07:00

"Jeff, on your plans it specs a 5-1/8 x 16.5 glulam. We put in a 4 x 12. Is that OK?"

ASD and LRFD Design Checks for a Wood Beam - Shear

2009-07-04T12:57:00.000-07:00

... here I do the design checks for shear for a wood beam using ASD and LRFD approaches.

http://www.associatedcontent.com/article/1834127/asd_and_lrfd_design_checks_for_a_wood.html?cat=15

Reduced Design Snow Load for a Metal Roof ...

2009-07-03T16:59:00.000-07:00

... inspired from a recent consulting job ... here.

Drifting Snow onto Lower Roof ...

2009-07-03T16:58:00.001-07:00

... recent piece on calculating the drift surcharge from snow drifting from an upper roof onto a lower ... here.

Comparison of Stability Equations for a Wood Beam

2009-06-16T13:23:00.000-07:00

In the linked article I compare the 2005 NDS Beam Stability Factor with that calculated using the AWC TR 14, for a particular beam example. In this example the two CL values come out quite close!

http://www.associatedcontent.com/article/1851309/comparison_of_beam_stability_equations.html?cat=4

Bending Check ...

2009-06-13T00:26:00.000-07:00

Okay, I just cranked out the flexure and deflection checks ...

http://www.associatedcontent.com/article/1840879/bending_check_of_a_pitched_roof_rafter.html?cat=4

TCM Revision ... 6e

2009-06-12T21:01:00.000-07:00

It's Revision time ... I will be working with AITC (American Institute of Timber Construction) on the 6th Edition of the Timber Construction Manual. To get the `juices flowing again' I did a design check of a beam in both ASD and LRFD. It derives from Examples 4.1 and 7.1 in the 5th Ed. Fun.

Here ... http://www.associatedcontent.com/article/1834127/asd_and_lrfd_design_checks_for_a_wood.html?cat=15

Note: the example covers shear only. And there's a disconnect between the shear design values and the shear strengths in the 5th ed.

Shear Design Check

2009-06-12T20:58:00.000-07:00

... here is the shear design check for a pitched roof joist (ASD).

http://www.associatedcontent.com/article/1840449/shear_design_check_for_a_pitched_roof.html?cat=4

Balanced and Unbalanced Snow on a Gable Roof

2009-06-12T20:55:00.001-07:00

Inspired by a recent consulting job ...

http://www.associatedcontent.com/article/1834691/balanced_and_unbalanced_snow_loads.html?cat=15

Upside Down Beam

2009-02-20T16:09:00.001-08:00

Article is here ... http://www.associatedcontent.com/article/1497620/glulam_beam_installed_upside_down.html?cat=15

Load Combinations ... ASD

2009-02-14T15:06:00.001-08:00

... in response to questions ... http://www.associatedcontent.com/article/1476848/load_combinations_and_load_factors.html?cat=4

Perforated Shear Walls

2009-01-19T15:17:00.000-08:00

I just did a Perf Shear Wall design for bracing a timber frame. It' intersting in that the shear wall is not in-plane with the timber frame - as is common with timber frames.

http://www.associatedcontent.com/article/1402292/perforated_shear_wall_bracing_for_a.html?cat=15

Span Calculator

2008-10-04T20:16:00.000-07:00

... here is a `calculator' that I have found useful (for wood joists and rafters) ... you don't need to download any software, or sign up for something - it's on an external site (American Wood Council).

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Douglas+Fir-Larch&size=2x10&grade=Select+Structural&member=Floor+Joists&deflectionlimit=L%2F360&spacing=16&wet=No&incised=No&liveload=50&snowload=-1&deadload=15&submit=Calculate+Maximum+Horizontal+Span

APA pub on checking ...

2008-10-01T14:43:00.000-07:00

... here is an APA publication on checking in glulam ... contains a few pics.

http://www.apawood.org/glu_level_b.cfm?content=prd_glu_gen_check&searching=evaluation%20checking

`Cracks' in (Wood) Beams ...

2008-10-01T14:29:00.000-07:00

Okay, in class today we approached rationally the effect of a `side crack' in a wood beam.

IRL we would want to investigate ...

1) is it a drying crack (drying `check' would be the more correct nomenclature)? ...

2) or is it a manufacturing defect? ... say, in a glulam beam, due to lack of adhesive coverage, occurrence of `wane' in a lamination, undersized lamination, or whatever.

3) other???

If the beam is a glulam, we have some specific guidance available ...

http://www.aitc-glulam.org/test/shopcart2/Pdf/aitc_tn_11.pdf

http://www.aitc-glulam.org/test/shopcart2/Pdf/aitc_tn_18-2004.pdf

... what you'll see is that some checking is expected in glulam, and design values (from which we get allowable stresses) take this into account.

If the checking is excessive, we have the above to help us in our evaluation of just `how bad' the checking is. The AITC Tech Note 18 is a rational approach, though simplified, conservative, and for some cases (some relative depths in the beam) ... way conservative.

The real issues is ... will the checking progress? ... or has the check reached some kind of equilibrium condition? And in this regard I always recommend that such situations be monitored into the future.

If the checking progresses, in concept, the beam could split completely, and then we would have two (or more) beams, on top of one another. And this could be a problem ... though I have never personally encountered such.

The situation of a glulam column completely splitting ... would be a problem.

Dedication ...

2008-09-29T21:05:00.000-07:00

... this blog is dedicated to the questions, findings, musings, discoveries, and perhaps even exploits ... related to structural wood engineering. We will tackle dimension lumber situations, glued-laminated timber, timber frame (with wood joinery), maybe even some log structure stuff. We'll probably also get into Structural Composite Lumber (SCL), wood I-joists, and structural panel issues - from the `engineering' side.

This blog is launched by `Pancho' (pen name for Jeff R. Filler, Ph.D., P.E., Owner of WoodEngineering.com).

Follow along as we discuss, wrestle with, and maybe even come to grips with ... cool stuff.