Tag Archives: dead load

An Oops from a Competitor’s Architect Part Two- Lateral Load

As the Architect Turns

In our previous episode, we left Dan tied to railroad tracks in front of a speeding train….

Well close, we left Dan with a post frame building designed by an architect, with some serious structural connection problems.  Now I am a guy who watches Science Channel’s “Engineering Catastrophes”. I would just as soon we do not view Dan’s barndominium as one of them.

Moving forward from our last article:

It will shred LVL and/or column – wood is your weak link

You need to calculate the area being carried by one beam end beam – on an 8′ beam with 18′ joists you would have 8’/2 X 18’/2 = 36 sft (square feet).

Minimum floor live load (other than for bedrooms) is 40 psf (pounds per square foot) live load and you should figure 10 psf dead load for a total of 50 psf.

36 sft X 50 psf = 1800 pounds at each end of 8′ in this example.

Dan writes:

So I have the table you referenced and I get the load calcs but what I am trying to figure out is how you got to the 7 ledgerlocks per post figure. What is the math to get from that table and the 3600 lbs per eight foot section to the amount of ledgerloks?

And since we have gone down this rabbit hole, should I start to get paranoid that one of my 3 truss carriers is affixed with 60d nails and that I need to do a lateral load calc on that in order to make sure it is properly connected?  My guess is that this design was based on shear as well…

Ugh  this is what goes on in the mind of a DIY builder who is a data analyst by day.”

Mike the Pole Barn Guru responds:

Let’s do a run-down of information from ESR-1078 for 5″ Ledgerlock Fasteners (for those playing along at home Google ESR-1078).

Table 1C specifies an overall length of 5″ and 3″ of thread length. Allowable fastener shear is 1235# which by Footnote 4, “Allowable shear strength values apply only to shearing in the unthreaded shank portion of the fastener”. This would be fastener failure itself. This however is not our limiting value.

Table 2 references withdrawal design values – LVL is not likely to be sucked away from column by wind, so not applicable.

Table 3 is head pull-through design values – these values limit numbers derived from Table 2, again not applicable.

Table 4 is for Lateral Design Values in single shear. It lists a 5″ ledgerlock with a minimum of 1-1/2″ side member thickness and 3-1/2″ minimum main member thickness. As your LVL is 1-3/4″ thick, lateral design values will need to be adjusted downward by X 0.929 to account for a lesser length into column. Most glu-laminated post frame building columns are Southern Yellow Pine (SYP).  SYP has a specific gravity of 0.55, so a RDP could possibly calculate out values approximately 10% greater.

In your case, load is perpendicular to side member, parallel to column grain. Using Z perpendicular to grain and Sg of 0.5, adjusted for lesser depth into main member would give a value of 280# X 0.929 or 260.12#. Assuming an RDP could gain 10% for greater Specific Gravity, value per Ledgerlock would still be only 286.13#

With an 1800# load / 286.13# = 6.29 fasteners.

You might want to invest in having a qualified engineer review your plans for adequacy. Yes, there will be a price however you may have recourse against original provider and/or their architect in the event of significant structural deficiencies.

Had our Building Designer not given Dan bad advice, all of this could have easily been avoided. Hansen Pole Buildings, in conjunction with our third-party engineers has developed a sophisticated proprietary software program called Instant Pricing™. Not only will this system provide required investment for a myriad of design parameters in real time, it also does a complete structural analysis of every component and connection – assuring situations such as Dan has, will not arise.

Dead Load, Sliding Barn Doors, and Truss Spacing

This weeks PBG discusses a bottom chord dead load, installing sliding barn doors, and truss spacing.

DEAR POLE BARN GURU: Ok, just to make sure I understand that 10lb psf dead load rating would cover the bottom chords supporting ducts either resting on or suspended from them inside the conditioned space? My thinking is if the vents are within the conditioned space I would need minimal insulation to prevent surface condensation. ROB in ANNAPOLIS

DEAR ROB: 10 psf dead load is primarily to cover weight of ceiling gypsum wallboard. Your relatively light duct could be placed anywhere within roof system without adverse effects. A down side to placing duct work within a conditioned attic – effectively insulating roof slope plane and endwall triangles. For practical purposes this can only be achieved with closed cell spray foam. While being highly effective as an insulator, about R-7 per inch of thickness, it comes with a price tag not for those who are faint of pocketbook – usually around a dollar per square foot per inch of thickness. If you go this route, you need to eliminate venting eaves and ridge.

DEAR POLE BARN GURU: Good morning,

Figure 27-5

I need to get some pricing on a (2) 6’-0” wide x 8’-0” high sliding barn style doors for an agricultural building in Ware county Ga.

 

I have never purchased, or installed a door like this, so I was hoping you could help me get started.

 

Thanks, DAVID in KENNESAW

DEAR DAVID: Thank you very much for your interest. Hansen Pole Buildings only provides doors along with an investment in a complete post frame building kit package, due to high incidence of damage when shipped independently. We do have installation instructions available online: https://www.hansenpolebuildings.com/2016/07/build-sliding-door/.

 

DEAR POLE BARN GURU: What would the truss spacing need to be in our area that has a 40lb snow load? RODNEY in REPUBLIC

joist hangersRODNEY: In most instances a true double truss (not two single trusses spaced apart by blocking) will be most cost effective, as well as adequate to carry applied loads (along with properly sized roof purlins). However, depending upon a myriad of other factors such as eave height, truss span, roof slope and building length some other spacing may result in cost savings.

This will be just one reason I recommend consulting with a post frame building kit supplier who has sophisticated design software able to do a near instantaneous analysis of multiple possibilities. This supplier should also be able to provide site specific plans for your building, sealed by a registered design professional.

 

 

What Size Truss Carriers?

What Size Truss Carriers?

It seems every day I am asked to do structural design of post frame buildings – for free. Today’s request comes from BOB in ARKDALE who writes:

“Yesterday I asked a question about a double header and single trusses being spaced every 4 feet with 8 foot spacing on posts. I don’t use the internet much but a reply to my son’s email address would be great. The question was what is a proper double header? We thought one underneath the other off entered or sandwiched off enter.”


Bob’s earlier request was somehow spun off into an internet abyss, as it did not make it successfully to us.

nailing trussesIn my humble opinion, an ideal design solution eliminates need for a header (aka truss carrier) entirely, by having trusses bear directly upon columns. Why would this be ideal? Trusses (in my ideal dream world) are placed into a field cut notch in each column. This transmits all roof loads directly onto posts, without reliance upon beams typically scabbed onto each side. This eliminates trusses being driven to earth in a catastrophic snowfall event.

Back to your question – size and number of required members for your headers, as well as their orientation) should be clearly denoted upon plans provided by RDP (Registered Design Professional – architect or engineer) who produced them. Headers and their connections need to be able to withstand all imposed loads – live (snow), dead (weight of headers themselves along with trusses, purlins, insulation, roof sheathing (if used), roofing, any ceiling, lighting, etc.), as well as wind loads (uplift being a factor). These headers must be adequate to support one-half of clearspan width of your building, plus any overhangs beyond sidewall.

All of this takes an involved series of calculations best performed by an experienced RDP. If you somehow do not have one involved in your project – go hire one right now. This small investment into correct structural design becomes inconsequential compared to pain of building loss should it fail, damaging or destroying valuables your building was meant to protect, as well as injuring or killing yourself or your loved ones who may be inside when the roof caves in.