Tag Archives: wind exposure

Free Post Frame Foundation Building Calculator

Free Post-Frame Building Foundation Engineering Calculator

No, such a thing as a free post-frame building foundation engineering calculator does not exist. However there always seems to be someone out there who is in search of “engineering for free”.

Reader KELLY writes:

“Guru,

Do you have a link to a pole foundation engineering calculator?

Looking for column depth / diameter for:

40x60x14

10 ft column spacing

35 PFS load

115 wind load.

No floor for constraint.

thanks.”

Mike the Pole Barn Guru responds:

There is no such thing as a “pole foundation engineering calculator” therefore, there is also no link to one. The design of post frame (pole) building foundations is one which is best left in the hands of RDPs (Registered Design Professionals – architects or engineers). When provided with all the pertinent information about your proposed building, they can design not only a structurally sound column embedment, but also your entire structure (which I whole heartedly recommend).

You’ve provided some of the information a RDP would require, but I will expand upon it:

Will the building have adequate sheathing (which could be roll formed steel roofing and siding) to transfer wind loads from roof to ground through endwalls? And will the sheathing be adequately fastened to underlying frame to take advantage of sheathing stiffness? If yes, diaphragm design can be utilized in your building design.

The difference in forces carried by sidewall columns with and without an adequate diaphragm is a factor of 4! If diaphragm design cannot be utilized, expect significantly larger columns, deeper holes and more concrete around columns.

What type of soil is at building site? Strength and stiffness of your soil will impact both depth and diameter of holes.

How are you measuring your 14′? It should be from bottom of pressure preservative treated splash plank, to underside of roofing at sidewalls. It does make a difference.

Does your building have overhangs?

What is the roof slope?

What is wind exposure at your site? The difference in force against columns between Exposure B and Exposure C is roughly 20%.

In the event you are not interested in procuring services of a RDP, the NFBA (National Frame Building Association) has available a Post-Frame Design Manual and you could attempt to do calculations yourself. For more information please see: https://www.hansenpolebuildings.com/2015/03/post-frame-building-3/.

Of course you could always invest in a fully engineered post frame building kit package. Besides engineer sealed blueprints and calculations, you would also get materials delivered to your site and a multi-hundred page Construction Manual to guide you through to a successful completion.

 

500 Year Storm and Wind Exposure

500 Year Storm and wind exposure.

Allstate® Insurance has a TV commercial featuring actor Dennis Haysbert. Haysbert sits in an open field and questions why there have been 26 “once in 500 years storms” in last decade, when term alone implies they should only happen every 500 years.

View Allstate® commercial here: https://video.search.yahoo.com/search/video?fr=crmas&p=Allstate+once+in+500+years+storm+commercial#id=1&vid=b134fa05aba0ff046debaea22891c23d&action=click

IBC (International Building Code) in Chapter 16 (https://codes.iccsafe.org/public/document/IBC2018/chapter-16-structural-design) Table 1604.5 lists Risk Category of Buildings and Other Structures.

Risk Category I includes buildings representing a low hazard to human life in event of failure – agricultural buildings and most detached residential accessory buildings fit into this category.

Risk Category II would be most homes and many low risk commercial, industrial and manufacturing buildings.

Risk Categories III and IV cover buildings with high occupancies or are essential to fire, life and safety (like fire stations).

IBC offers Minimum Design Loads modified by a given factor depending upon Risk Category. For a previous article about this subject please see: https://www.hansenpolebuildings.com/2018/08/minimum-design-loads-and-risk/.

Reflect, if you will, back upon paragraph one above and a 500 year storm.

wind damageRisk Category I buildings are based upon a once in 25 year probability of minimum design loads being exceeded. Risk Category II once in 50 years, while Categories III and IV are once in 100 years.

So, what does one do to protect against a once in 500 years storm?

When planning your new post frame building, this becomes relatively easy – have it designed for greater loads than bare Code required minimums. While this sounds simple, very few clients consider asking for it and even fewer post frame building sales people offer it!

Why would it not be offered?

Price

People are selling buildings using price rather than value.  Most are afraid to suggest increasing building price by a few percentage points, because they think it will cost them a sale!

I know there are numerous members in our post frame industry who are reading this article. To you I offer this challenge – as an option start offering to every potential client an ability to have their building designed for an extra even five or 10 psf (pounds per square foot) of snow load (in snow country of course). And, give them an option of withstanding greater wind speeds than Code minimums. Even upgrading wind Exposure B sites to Exposure C will increase ability to resist wind loads by about 20%.

A short wind exposure story can be found here: https://www.hansenpolebuildings.com/2011/11/wind_exposure/.

Now, sell your potential client benefits of having last building standing when Mr. Haysbert’s storm rolls through.

Sold itself, didn’t it?

 

It Is Exactly the Same Building Part I

Well, maybe not exactly the same building.

In April of this year we had a client invest in a brand new 36 foot wide by 60 foot long post frame building kit package with a 16 foot eave height. Three months later, the building has been delivered, and one of the group which ordered the building sends us a quote on “exactly the same building” from a worthy competitor. And, of course, the competitor’s quote is way less expensive!

Now the competitor’s sales person advised the client the quotes were exactly the same, other than he had quoted a 25 psf (pounds per square foot) roof snow load, whereas we provided a 40 psf load, which is 60% more snow carrying capacity!

Turns out there were maybe a couple of other differences as well……

Things we have and they do not:

4/12 roof slope vs. 3/12 The steeper roof slope will look less industrial as well as more readily will shed snow.

C wind exposure vs. B wind exposure (for a detailed explanation of wind exposure please read here: https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/).  The benefit of an Exposure C wind load is it makes the building roughly 20% stronger in resisting wind forces, than the B exposure.

12″ enclosed overhangs vs. 18″ open overhangs. Not only are enclosed overhangs far more attractive, they provide ventilation and eliminate the wonderful nesting locations for flying critters which are provided by open overhangs.

12’x14′ residential overhead door vs. 14’x12′ commercial overhead door. If the client wants to get something taller than 12 foot through the other guy’s door, it just isn’t going to fit no matter how big a run one gets at it. Residential overhead doors come with “dog eared” openings and a far more attractive in a residential setting. Here I discuss why 14 foot wide doors are not what they are cracked up to be: https://www.hansenpolebuildings.com/2016/05/14-foot-wide-doors/.

One more entry door. Insulated commercial steel entry doors with steel jambs do not come cheap, especially when they are four foot wide!

Integrated J Channel on windows. So much easier to install than having to cut four pieces of steel trim to fit around a window and have them not leak!

The reflective radiant barrier with pull strip attached adhesive tab on one side vs. Metal Building Insulation (MBI) under the roof steel to minimize condensation challenges. My personal horrors of installing MBI can be visited here: https://www.hansenpolebuildings.com/2011/11/metal-building-insulation-in-pole-buildings-part-i/.

Lifetime paint warranty on steel vs. 40 year pro-rated. Your post frame building is going to be around for a long time, might as well have the best paint warranty available to minimize the effects of fade and chalk.

Base trim – keeps those creepy crawling critters from entering the building through the high ribs of the wall steel.

Top of wall trims – Even though roll formed steel siding lengths are controlled by a computer, they do vary slightly from panel to panel. The bottom of the panels should be kept at the same height as “stair steps” at the base of the walls is quite noticeable. Easiest way to hide any variants is to place the top edge into a piece of trim which covers any fluctuations.

Jamb trim on Overhead Door– exposed wood overhead door jambs are very popular in some parts of the country, however they do turn grey and then eventually black if not kept painted.  The idea of a steel covered post frame building is to minimize future maintenance. Having to paint raw exposed wood does not meet with this criteria.

Heard enough? No? Then come back tomorrow for Part II. You won’t be disappointed!

Airplane Hangar Exposure C

Why Your Airplane Hangar is Probably Exposure C

I had the joy of growing up “hanging out” (pun intended) at airplane hangars and doing a lot of flying including having my hands on the controls of a Cessna 182 for many hours before I became a teen. One thing for certain about airplane hangars – they are always built with the idea of being able to take off and land the airplanes which are housed inside, somewhere in the general vicinity of the hangar!

Yes, I know this reads like a mission for Captain Obvious.

After all, what would be the use of a hangar if not to be able to fly the plane?

Airplanes do require a certain amount of space to be able to land and the runway better be fairly flat, as well as not obstructed by things like other buildings and trees. Those tall things generally tend to make the life of a pilot miserable.

A Hansen Pole Buildings client recently ordered a new post frame hangar with an Exposure B for wind. This is the short version of the definition of a B exposure:

Wind Exposure B is a site protected from the wind in all four directions, within ¼ mile, by trees, hills or other buildings. This would include building sites in residential neighborhoods and wooded areas.

Whereas, Wind Exposure C is a site where there is open terrain with scattered obstructions having heights generally less than 30 feet high. (Commonly associated with flat open country and grasslands).

If you are curious and want to know all there is to know about Wind Exposure here is some good late night reading: https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/.

Being a fairly simple guy, I am scratching my head at this wondering how the plane is going to takeoff through all of this protection.

Hansen Pole Buildings’ Managing Partner Eric did a quick Google search of the site and let me know it is in the middle of a field!

In the event you are in need of a new airplane hangar and you are getting quotes from providers which do not specifically indicate on the Exposure C for wind, chances are good you are being quoted for Exposure B. The difference in design strength for resistance to wind loads is roughly 20%.

Think about it…..

Do you actually want your several hundred thousand dollar airplane to be parked in a building which is under designed for the actual wind conditions which could be applied to the building?

Wind Speed

Just Another Windy Conversation

Hansen Pole Buildings’ Designer Rick asked me this question today: “Mike, I got a guy who wants to compare an over wind rated building to a Quonset hut at 150 mph” (miles per hour).

Of course I jump right onto this one off the get go, “So the Quonset people have an engineer’s seal on a 150 mph building?” (Just call me a skeptic) “And even if they do – how functional is a Quonset hut?”

I’ve pointed out some Quonset challenges in a previous article: https://www.hansenpolebuildings.com/blog/2011/07/quonset-huts/

Rick, “I’ll check it, but for now I am about to call this guy back, the question is how high can I go up on the wind load and be reasonable?”

Hansen Pole Buildings has created a proprietary pole building design and pricing program which does some truly amazing things….but Rick had me stumped with this one!

WindFor this particular client’s building site the Code wind speed design would be for 90 mph. There is a nifty little formula to convert mph to wind pressure (.00256 X wind speed squared). This makes a 150 mph wind speed applying 277% of the load force of 90 mph.

On this particular 40’ x 60’ x 13’ pole building, the difference in investment for the 277% more force….?

Under 20% more!!

On many pole buildings, designing for extra wind resistance is minimal. For anyone considering a new building, I would certainly encourage them, at the least, to investigate an increase of 10 or 20 mph, at the least.

Next Rick decided to try a 200 mph wind speed (even though no Building Department anywhere in the United States has this requirement). We are now talking wind speeds only an EF-5 tornado would surpass!

Not surprising – our program would design the building…..at 200 mph!!

The sidebar to this story…..

The client wants to be able to pull a trailer out of his new building to live in if his house goes down!

Dear Guru: What is the Highest Wind Speed You Design For?

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: Hello, I am interested in this construction method, but I was wondering what is the maximum wind load that your buildings can take? Thank you for your time. WHISTLING IN THE WIND                                  

DEAR WHISTLING: We’ve designed pole buildings resist wind speeds up to 170 miles per hour. For all practical purposes, we could design for any wind speed and exposure condition desired.

DEAR POLE BARN GURU: What is the mil thickness of plastic to lay down in a

pole barn before the rock for moisture protection and do you carry the

product? MOIST IN MISSOURI

DEAR MOIST: If you are not intending to pour a concrete floor, then a black visqueen of at least 6 mil thickness should be used. For use under a concrete slab, the best product would be A2V insulation, which is available for direct purchase at:

www.buyreflectiveinsulation.com

There is an insulation calculator on the website to help you figure out how many rolls to purchase.

DEAR POLE BARN GURU: I am planning on constructing a 48’ x 48’ roof only pole barn. I would like to put a couple bags of sakcrete in the bottom of hole and then pour the rest when I pour the pad.  I am planning on putting rebar down into both sakcrete and have it stick up so it will connect to the other concrete.  Will this be ok?  If not, recommendations? STUCK ON SAKCRETE

DEAR STUCK: Sakcrete can be a great and practical solution to many problems, however this application is not any of those.

To begin with, a couple of bags of sakcrete will not provide an adequate footing under the columns. With your loading conditions, a 30 inch diameter by eight inch thick footing pad would be required. It would take eight 90 pound bags of sakcrete to pour each footing. It may not be practical to haul home almost four tons of sakcrete.

Even if you do pour adequate footings, you are quickly going to find out how challenging it is to work on a roof only structure, where the columns are not stabilized. Even with the columns braced in all four directions (which is going to require investing in a lot of extra material), there is going to be a significant amount of movement in the columns, as the roof system is framed and roofing installed.

Why fight it?

My recommendation would be to just concrete backfill the columns and footings monolithically in a single pour. It will take about nine yards of redi-mix, so it isn’t like there is going to be some big savings by waiting to pour the balance of the holes with the floor.

Tornado! What We Didn’t Learn in Moore

Tornado! What We Didn’t Learn in Moore

Moore OK Tornado RadarOn the afternoon of May 20, 2013, an EF5 tornado, with peak winds estimated at 210 miles per hour (mph), struck Moore, Oklahoma, and adjacent areas, killing 23 and injuring 377 others. The tornado was part of a larger weather system which had produced several other tornadoes over the previous two days. The tornado touched down west of Newcastle, OK staying on the ground for 39 minutes over a 17-mile path, crossing through a heavily populated section of Moore. The tornado was 1.3 miles wide at its peak. Despite the tornado following a roughly similar track to the even deadlier 1999 Bridge Creek-Moore tornado, very few homes and neither of the stricken schools had purpose-built storm shelters

Between 12,000 and 13,000 homes were destroyed or damaged, and 33,000 people were affected. Most areas in the path of the storm suffered catastrophic damage. Entire subdivisions were obliterated, and houses were flattened in a large swath of the city. The majority of a neighborhood just west of the Moore Medical Center was destroyed. Witnesses said the tornado more closely resembled “a giant black wall of destruction” than a typical twister.

The Oklahoma Department of Insurance said the insurance claims for damage would likely be more than $1 billion. Total damage costs have been estimated as high as $2 billion.

How did all of this happen?

Home builders protest the estimated cost of $2,000 to $6,000 for home tornado shelters would make houses unaffordable.  How much is a human life worth? If it is one of my loved ones, a whole bunch more than this.

Some of the fault might be placed upon local government, as well as the Building Departments which provide recommendations for design wind loads for structures. The design wind speed for the Moore area, by Code? 90 mph or roughly 20.736 psf (pounds per square foot). Consider 210 mph is over 107 psf – more than FIVE TIMES the design wind load!!

Anyone wonder why the photos were as astonishing as they were?

Not trying to be confusing….the values we use for wood design are based upon 40% of a 5th percentile figure. As an example, if 100 random pieces of lumber were tested for strength, and the values plotted on a curve, take the 5th lowest value from the bottom, and use 40% of this value. This does afford a certain amount of cushion for safety in designing wood structures.

At the least, I’d recommend increasing the required design wind speed to something in the range of 150 mph (57.6 psf) to 170 mph (74 psf). While this would not eliminate all destruction, it would certainly tend to be better than what exists currently.

In examining a fairly significantly sized full enclosed pole building kit package (40 feet wide by 60 feet long and 14 foot tall), the price increase from 90 to 150 mph design wind speeds was just over 10% (not much more than $1200).

Post frame construction lends itself naturally to being resistant to extreme wind loads. With columns embedded in concrete backfill, there is no weak point at ground level, as found in conventional stick frame construction, or manufactured housing.

With a minimal number of mechanical (nails, etc.) connections, as compared to stud wall buildings, pole buildings run a far lower risk of compromising these crucial joints. Over the years when I have examined “why” buildings fail (either pole buildings or stick framed), it was most often the connections which failed.

Play it safe – play it in a post frame building designed to actually support the types of loads with which it could be hit.

Things You Never Wanted to Know About Snow Load

Yes I know, it is white (at least it starts out that way).

From a design standpoint there are lots of things to know about snow loads.

Cautionary Warning: The information contained herein is fairly technical in nature. We use ALL of this information in the design of your new Hansen Pole Building. Some clients will think this is all very cool, for others, it may cause your head to explode. I’ve been waiting three decades to pass along this information to a client, as I’ve always felt the understanding of it is pretty impressive.

1.  GROUND SNOW LOAD (otherwise known as Pg). This is based upon a once in fifty year (probability of event greater than design loads happening is 2% in any given year). The use of unrealistically high Pg values causes issues with the design for drifting snow.

The International Code specifies design snow loads are to be determined according to Section 7 of a document called ASCE 7. This document provides for all roof snow loads to be calculated from ground snow loads, however not every Building Department follows this procedure. When discussing snow load with anyone, it is crucial to have a clear understanding as to if the load is a ground or flat roof snow load.

Pf is FLAT ROOF SNOW LOAD – If, as a consumer, your concern is snowfall and you want to upgrade the ability of your building to carry it, THIS is the value to increase. Often changes of five or 10 pounds per square foot result in minimal differences in cost.

Pg is converted to Pf by this formula:

0.7 X Ce X Ct X Is X Pg = Pf

2. Ce is the wind exposure factor for roofs.

For an Exposure B or C for Wind; Fully Exposed = 0.9; Partially Exposed = 1.0; for fully sheltered (e.g. nestled in tightly amongst conifer trees as an example) Exposure B = 1.2, Exposure C = 1.1 (how you could have Exposure C and fully sheltered is beyond me)

We use partially Exposed (Ce = 1.0 as a default)

3. Ct is the effect of temperature (building heating), where:

Ct = 1.0 for heated structures (climate controlled)

Ct = 1.1 for Structures kept just above freezing and others with cold, ventilated roofs in which the thermal resistance (R-value) between the ventilated space and the heated space exceeds 25h – ft^2 – degreesF/Btu

Ct = 1.2 Unheated

We use Ct = 1.2 as the default value

Most truss designers will use a Ct value of 1.0 or 1.1 in their designs. This results in a decrease in the ability of the roof to carry snow loads. These values should only be used when appropriate.

4. “Is” is the IMPORTANCE FACTOR

ASCE I is a structure which is a low hazard to life in the event of a failure. Is = 0.87

ASCE II residences and frequently occupied commercial buildings (a warehouse or storage building is probably ASCE I) Is = 1.0

ASCE III Is = 1.1

ASCE IV Is = 1.2 (these are “essential” essential facilities – police/fire stations, hospitals)

5. There is also a Minimum Roof Live Load (known as Lr) of 20 psf (defined by Code) (psf = pounds per square foot) which accounts for weights such as construction loads, when Pg values are very low.

Lr is adjusted based upon the area the roof member supports and can be as low as 12 psf, in cases where a roof member supports over 600 square feet of area.

Doing the math, it would be unusual, using the laws of physics, for Pf to be greater than Pg – however, some jurisdictions have established Lr values which defy the laws of physics (e.g. State of Oregon, where most of the state has a minimum Lr of 25 psf – exceptions being some locations along the coast, where it is 20).

From Pf, Pr (Pressure on the roof) values are calculated depending upon whether the roof is a slippery surface or not, whether building is heated or not and the slope of the roof.

The Top Chord Live Load (TCLL) of any roof trusses will be the greater of Pr or Lr.

6. Duration of Load (DOL) for Snow is typically 1.15. DOL can play a part in some snow areas, where the Building Official (BO) has made the determination snow will remain upon the roof for extended time periods. Some Examples of this include Higher elevations in Utah and Kittitas County, WA where the BO has declared DOL = 1.0. In areas with little or no snowfall (where Lr > Pr) DOL = 1.25.

Yes, I know this is a lot of stuff to carry around in your head.  Trust me, I know all too well, and my character analysis consistently reads “does not like numbers”!  All these numbers and “code requirements” are why we not only ask, but insist you must take the page of our quote with the Design Criteria to your building department to get their blessing on it, and ask if there is anything else they require.  With over 7000 building departments in the U.S., it would be the greatest feat on earth if we could keep up with all of them, and which ones change on any given day. My last caution is to be careful when asking your building department about snow load.  Be sure you keep “roof” and “ground” snow loads separate.  Because when it comes to getting your building designed, priced and finally plans signed off by your building department, there is a difference! 

Building Codes: Wind Exposure C

We all know what Assume Means…

Bob is a builder in Northern California. He made a request for a quote on a building recently, via the Hansen Pole Buildings website.

The building he had in mind was to be 30’ wide x 80’ long. Bob told me the roof snow load was 100 pounds per square foot (psf) and wind speed 60 to 100 miles per hour (mph).

Bob called to discuss the project, which was to have one long sidewall open, so recreational vehicles, tractors and other equipment could be parked. I asked Bob how wide the openings between the sidewall columns would need to be – to which he replied 12’. Quickly doing the math, I suggested he might want to consider 84’ in length, as 12’ evenly divides into 84’. Bob liked that idea.

We discussed wind exposure. I asked Bob, “If you stand in the middle of the building site, with your arms parallel to the ground, and at 90 degrees to each other, and then turned in a circle, would the area between your arms ever be exposed to the wind?”  This would be Exposure C.   The alternative being a site which is protected from the wind on all sides, or Exposure B. Bob advised, once the three walls were up, it would be protected from the wind, because the “local winds never come from the open side”.

Somehow, I just do not think we were communicating.

For once, I listened to the little voice in my head and suggested to Bob that he give me the address of the site and I would call the Building Department to verify the loading requirements. While the building purchaser must ALWAYS confirm the code and loading information with their Building Department prior to placing a building order, I felt an ounce of prevention would be worth a pound of cure in this case.

Now Bob has been a registered contractor in California for over five years, in the area where the building will be constructed. The pleasant lady at the Building Department even guessed who he was, when I gave her the jobsite address. Obviously, he is known, and knows the area.

Well it turns out the design roof snow load was 60 psf, not 100. This will save Bob’s client thousands of dollars. The wind speed requirement is for 85 mph, however the entire county uses C for wind exposure.

There is a moral to all of this. Just because one hires an experienced registered contractor to construct a building, does not mean the contractor necessarily knows or understands the proper design criteria. Having the correct information on loads, saved the building owner thousands of dollars by using the correct snow load, and prevented a possible collapse from using an incorrect (and under designed) wind exposure.