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Thread: Bolt shear strength

  1. #1
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    Default Bolt shear strength

    Iím trying to work up how many bolts I need to hold up a ledger board (actually angle iron) for a landing.

    As far as I can figure, a Grade 8 bolt, 1/2 inch, has a tensile strength of 150,000* and a shear strength of 60% of 150,000=90,000 per square inch.

    With a surface area of 0.196349541 square inches, that comes to a shear strength of 17,671 pounds.

    Can that be right? Seems way too high but I admit this is not my area. I may need to dial back my planned 12 bolts.

    Thanks

    Tom

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    Default Re: Bolt shear strength


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    Default Re: Bolt shear strength

    What is it bolting to? What material is the angle iron to be bolted to?
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Bolt shear strength

    Quote Originally Posted by Peerie Maa View Post
    What is it bolting to? What material is the angle iron to be bolted to?
    It will be directly through-bolted to a 10 inch thick, 6000 psi, concrete wall with 5/8 rebar at 12 inch on center. I may end up using graded threaded rod given the thickness. I have not checked with the bolt supplier yet on pricing.

    The landing will be 12 feet up so I am very interested in not making a mistake. The angle iron will be galvanized 4x4 inch, quarter inch thick. The other side of the landing will be supported by posts on piers.

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    Default Re: Bolt shear strength

    Quote Originally Posted by eggman918 View Post
    Nice chart. Thanks!

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    Default Re: Bolt shear strength

    Building codes are very picky nowadays regarding decks. If this is a consideration where you're at, you should check with your local building permit office. Otherwise, the Simpson Strong-Tie website has a lot of useful information re. decks and their connections.

    Jeff

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    Default Re: Bolt shear strength

    Quote Originally Posted by bluedog225 View Post
    It will be directly through-bolted to a 10 inch thick, 6000 psi, concrete wall with 5/8 rebar at 12 inch on center. I may end up using graded threaded rod given the thickness. I have not checked with the bolt supplier yet on pricing.

    The landing will be 12 feet up so I am very interested in not making a mistake. The angle iron will be galvanized 4x4 inch, quarter inch thick. The other side of the landing will be supported by posts on piers.
    Check the compressive strength of the concrete where it is applying the shear load on the bolts. Should be OK but that is the other important part of the joint.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Bolt shear strength

    Threaded rod, and incorrectly sized bolts will have a shear strength based on the minor diameter.

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    Default Re: Bolt shear strength

    Agreed. I will probably end up checking with the engineer before I have it mounted. Iíd like to have a plan before I go to keep the fees down.

    Itís a landing from an old airport skyway, and associated stairs. Pretty robust, fireproof, galvanized, and heavy as heck. And the stairs adjust to height.

    Pless will be along shortly....

    4B716F40-CDBA-48C5-8DFE-7AE03EFC11E1.jpg

    123FCDB0-EA65-4020-B30F-02D2E3B2C6AA.jpg

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    Default Re: Bolt shear strength

    Quote Originally Posted by Canoeyawl View Post
    Threaded rod, and incorrectly sized bolts will have a shear strength based on the minor diameter.
    Ok. Got it. Thanks

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    Default Re: Bolt shear strength

    Quote Originally Posted by Peerie Maa View Post
    Check the compressive strength of the concrete where it is applying the shear load on the bolts. Should be OK but that is the other important part of the joint.

    Ok. Thanks

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    Default Re: Bolt shear strength

    Quote Originally Posted by jpatrick View Post
    Building codes are very picky nowadays regarding decks. If this is a consideration where you're at, you should check with your local building permit office. Otherwise, the Simpson Strong-Tie website has a lot of useful information re. decks and their connections.

    Jeff
    18 months ago, I had to deal with stoopid code on the cantilever of my deck. It's 11 ft. out from the wall, 2x8 joists on 12" centers, with hangers on the inner end which is a 2x10 lagged every 2 ft. into the plate at the end of the the floor joists of the house. They told me it could have no more than 2 ft. of overhang so my posts had to be 9 ft. from the side of the house instead of the 8 I wanted.
    "If it ain't broke, you're not trying." - Red Green

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    Default Re: Bolt shear strength

    I researched cantilever once. It was pretty stringent. My engineer just said “don’t”

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    Default Re: Bolt shear strength

    Quote Originally Posted by bluedog225 View Post
    I’m trying to work up how many bolts I need to hold up a ledger board (actually angle iron) for a landing.

    As far as I can figure, a Grade 8 bolt, 1/2 inch, has a tensile strength of 150,000* and a shear strength of 60% of 150,000=90,000 per square inch.

    With a surface area of 0.196349541 square inches, that comes to a shear strength of 17,671 pounds.

    Can that be right? Seems way too high but I admit this is not my area. I may need to dial back my planned 12 bolts.

    Thanks

    Tom
    Will the bolts be loaded in shear, or will they be loaded in tension and the resulting shear loads carried by the friction between the ledger and sustrate?
    Creationists aren't mad - they're possessed of demons.

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    Default Re: Bolt shear strength

    My understanding of a ledger board it that the load is carried by the friction. But the shear strength of the bolt seems like a good fallback if there is a failure of the friction bond. E.g. wood shrinking or concrete cracking.

    But I don’t know how to factor this into an analysis.

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    Default Re: Bolt shear strength

    Bolts in tension through masonry often have large plates under the nuts to spread that load over a bigger area.
    Money may not buy happiness, but it can buy a boat that will pull right up next to it!

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    Default Re: Bolt shear strength

    I am not a building inspector. These are my opinions. If this was a wooden ledger board, I would not consider clamp load and friction, just shear strength in the fastener. When I think bout it, most old things I can remember bolted to concrete were not all that tight anymore. It looks like the codes want 1/2" bolts with spacing requirements based on the width of the deck and are not fussy about the grade of bolt.
    https://www.deckmagazine.com/design-construction/framing/ledgers-on-challenging-walls_o
    EDIT:
    For solid masonry, steel expansion anchors whose bolts are a minimum of 1/2 inch in diameter and penetrate the masonry by at least 2 1/2 inches can take the place of lag bolts. The anchor spacing would be as shown at right in the table "Ledger Fastener Spacing for Masonry Walls."

    Note that I'm talking about structural masonry here, and not masonry veneer. Attachment to masonry veneer is a bad idea, and the reason that's so is discussed on page 6.

    There is a potential problem with attaching a ledger to concrete, which Woeste says should trigger a building department to require an engineer's design: "Although the strength of some expansion anchor bolts is rated, the strength of the concrete into which they're placed is probably not known in practice."

    When attaching a ledger to hollow masonry block, use adhesive anchors, such as the Epcon A7 from ITW Red Head (800/348-3231, www.itw-redhead.com) or the Hilti HIT HY 20 system (866/445-8827, www.us.hilti.com). The threaded rod used with the anchors must be at least 1/2 inch in diameter and must penetrate the block by at least 3 1/2 inches.

    Figure 1. In most cases, deck ledgers can be bolted directly to poured concrete or concrete block walls. Expansion anchors — never lead shields — are used in solid masonry or filled block, and approved epoxy or acrylic anchors and bolts are used in hollow masonry.
    https://www.decks.com/how-to/26/ledg...lid-concrete-f

    Since I suspect that the code requirements are based on galvanized bolts, higher strength grades are overkill. Not bad, just stronger than needed. Since the number of low strength bolts is likely to be the basis for the requirements, the following pedantic information is a moot point. Strength in the threaded portion of the bolt is calculated using the stress area diameter, which is the average of the pitch diameter and the minor diameter. ASME B1.13M and ASME B1.1 cover metric and inch screw threads, respectively. For a 1/2 inch grade 8 bolt, that makes a small difference, 12,270 vs 13,270 pounds. The calculation of the shear strength of the unthreaded portion in the OP was correct insofar as I can determine.
    Last edited by MN Dave; 02-27-2020 at 01:31 PM.
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  18. #18
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    Default Re: Bolt shear strength

    There are some caveats...
    Try this; https://www.fastenal.com/en/84/load-calculator

    (1/2" gr 5 is rated at 9000 lbs)

    And we have cut threads vs rolled threads and etc.

  19. #19
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    Default Re: Bolt shear strength

    Quote Originally Posted by Canoeyawl View Post
    There are some caveats...
    Try this; https://www.fastenal.com/en/84/load-calculator

    (1/2" gr 5 is rated at 9000 lbs)

    And we have cut threads vs rolled threads and etc.
    That is strange. Fastenal is generally pretty good with their information, but their calculator comes in low. None of the numbers correspond to the basic diameter, pitch diameter, minor diameter, or stress area diameter and material properties. IIRC, Canoeyawl should have the background to weigh in with some authority, so I am not shooting my mouth, well keyboard, off without having some background myself.

    For the dimensional requirements, look here:
    http://www.carbidedepot.com/formulas...dard.htm  (effective diameter is same as pitch diameter)
    http://www.carbidedepot.com/formulas-tap-metric.htm

    The Nucor link in Post #2 had accurate material strength numbers. The metric class indicates the tensile and yield strength, e.g. 10.9 means 1000MPa tensile and 90% of that for yield.


    The original question was whether a grade 8 1/2-13 UNC bolt could really have a shear strength of 17,000 pounds, and the answer was yes, but not in the threads, where it will be around 10,000 lb. So put the nut on the back side of the wall where the threads won't be in shear.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  20. #20
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    Default Re: Bolt shear strength

    The shear strength of the installed bolt may be limited by the strength of the material into which it is installed. The bearing capacity of the wood or concrete against the side of the bolt may be less than the actual shear capacity of the steel bolt.

  21. #21
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    Default Re: Bolt shear strength

    There is a stress concentration associated with thread grooves, so using the min cross section area is not enough. If the threaded region is not where the load is carried through, that's a different story. There will always be combined loading for a threaded fastener (tension + shear) if the bolt needs to be tight (it will), so a Mohr's circle analysis should be performed. Is it in single- or double-shear (in single-shear, you have a bending moment too). Then there is safety factor. Are you designing for something that will involve safety of people? Is there any chance there will be a dynamic load, especially shock? What about weather exposure & corrosion? Thermal expansion? These things all lead to overdesign to make sure than the fasteners won't allow a failure, which means a generous FS. Not trying to solve your problem, but these are the things to consider.

  22. #22
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    Default Re: Bolt shear strength

    Quote Originally Posted by bluedog225 View Post
    I’m trying to work up how many bolts I need to hold up a ledger board (actually angle iron) for a landing.

    As far as I can figure, a Grade 8 bolt, 1/2 inch, has a tensile strength of 150,000* and a shear strength of 60% of 150,000=90,000 per square inch.

    With a surface area of 0.196349541 square inches, that comes to a shear strength of 17,671 pounds.

    Can that be right? Seems way too high but I admit this is not my area. I may need to dial back my planned 12 bolts.

    Thanks

    Tom
    How many zombies are you expecting it to hold?
    One bolt would hold it up.
    Two would keep it from pivoting.
    Zombie live load,though undead, is the missing factor.
    R
    Sleep with one eye open.

  23. #23
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    Default Re: Bolt shear strength

    Quote Originally Posted by Garret View Post
    18 months ago, I had to deal with stoopid code on the cantilever of my deck.
    Building codes aren't stupid, they exist to keep people alive. That being said, they're written to be foolproof so they sometimes overdo it. In most states, you can build something that goes against code if you get a licensed engineer to stamp the drawings.
    I will beg you for advice, your reply will be concise, and I will listen very nicely and then go out and do exactly what I want! (Apologies to Lerner and Lowe.)

  24. #24
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    Default Re: Bolt shear strength

    Quote Originally Posted by alkorn View Post
    Building codes aren't stupid, they exist to keep people alive. That being said, they're written to be foolproof so they sometimes overdo it. In most states, you can build something that goes against code if you get a licensed engineer to stamp the drawings.
    Some codes are indeed stupid - but I get why they are there. Nevertheless, the calcs for my cantilever showed that I could've packed 20 people into the 3'x20' overhang & then stood 20 more on their shoulders & not come close to having issues with the deck. I get (& approve of) safety, but reality has a place as well.
    "If it ain't broke, you're not trying." - Red Green

  25. #25
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    Default Re: Bolt shear strength

    Quote Originally Posted by Ron Williamson View Post
    How many zombies are you expecting it to hold?
    One bolt would hold it up.
    Two would keep it from pivoting.
    Zombie live load,though undead, is the missing factor.
    R
    Thank you all for the input.

    Excellent point Ron. However, I have a newly acquired fear of falling. Maybe I’ll include a couple of extra bolts for the comfort factor.

    About the zombies, is it really a “live load”....


  26. #26
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    Default Re: Bolt shear strength

    A fear of falling is healthy. As is a fear of falling things...

    There has been a new emphasis on bolt shear since the Twin Towers collapsed.
    (the analysis I saw attributed the collapse to the sheared single bolts at the ends of each floor joist. As the fire heated the joists in the center they sagged, the angle changed, shear loading the bolts beyond the "calculated" stress, and the bolts failed (sheared). Once the first one came down it was a domino effect. Joists and their fastenings were not generally calculated for maximum tension loading)

  27. #27
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    Default Re: Bolt shear strength

    I would be more concerned about some numnum hitting and collapsing one of the outboard supports.
    What specs do you have for those?
    4x4x1/4" filled solid with concrete, is a good start.
    R
    Sleep with one eye open.

  28. #28
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    Default Re: Bolt shear strength

    4x4x1/4 galvanized was the plan. Had not thought to fill them with concrete but that seems wise. And some sort of barrier is smart. Thanks

  29. #29
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    Default Re: Bolt shear strength

    A guard should be alright without filling the posts.
    Hopefully the guilty party would stop before the catwalk fell on them.
    R
    Sleep with one eye open.

  30. #30
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    Default Re: Bolt shear strength

    Nothing too formal, just cut down a cedar tree and haul it over, since the guilty party will probably be me.

  31. #31
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    Default Re: Bolt shear strength

    Given the jet fuel fueled fire...there was no doubt the bolts/structure was going to fail...the same principle as forging...as the material get hot enough it softens...and failure.

    I remember watch 911 with a group of other consultants...people wondered what would happen...I remember thinking that when one floor collapsed...the impact (you should think about impact in your design...harder normally means more brittle) would cause the floor below to collapse and you have a cascading affect.

  32. #32
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    Default Re: Bolt shear strength

    If the concrete is 10" thick, why not use expansion anchors? Their capacities are tabulated by the manufacturer. Then you just have to find the loads and do the rest of the design (this is your engineer's job). See the performance tables: https://www.itwredhead.com/Portals/0...20Anchors.pdfv

  33. #33
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    Default Re: Bolt shear strength

    Good point. The engineer used a lot of Simpson titen 8" fasteners. But another 2" drilling is no big deal and I get through bolted instead of screwed on a mount that will see regular vibration from the stairs. But yes, either would work.

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