Science of Simple Spans of Floor Joists
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- Опубликовано: 27 июн 2024
- Learn about simple spans of floor joists, including load, bearing, span, height and width of joists, bridge blocking, and the code. Subscribe for new video uploads at ruclips.net/user/BenGromi...
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Simple, clear and well structured.
Each relevant section is presented and can thus be further researched. Thank you.
Thanks, Alex.
This is simply an EXCELLENT summary for the layman, who is not a structural engineer. Thanks so much!
Glad it was helpful!
Fair play that was extremely well presented and explained. I’m in the UK and, although, we have our own building regs, this made complete sense. Well done! 👍🙂🏴
Thank you. I love the UK. Can't wait to come back and visit.
VERY WELL done! I didn’t learn much by way of practice (observation and mimicry have made sure all my DIY projects have been safe and compliant); but, now I understand WHY many requirements are what they are, and WHY certain practices seem ‘right’ and others seem ‘wrong’. In particular, I have a much better appreciation of the role of joist hangers and blocking. THANKS!
Thank you! Cheers! That information is from Glenn Mathewson from buildingcodecollege.com/. Check him out.
So much info jam packed in this video. Gonna have to throw it on repeat. Great work!
Awesome, thank you! Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
During the pandemic there has been a significant increase in DIY'ers. So, your presentation is very much appreciated. I just had a brief discussion with a structural engineer this past week. I have since been researching more and more about forces on trusses and joists. All this is to help with an extension project and attic conversion in the future, after the supply chain issue and lumber prices hopefully will decline. Thank you. I also really appreciate the images and drawings. The more the merrier because visual presentations add so much more clarity and depth to any presentation, and yours was really important💯👍🇨🇦
Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
@@BenGromicko Thank you. I have viewed a few more of your vids. The long one on inspecting cracks trusses was really informative. Keep up the good work. I will check out the link you sent. 👍🇨🇦😉
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Lumber prices won’t be going down for a long time. Local lumber prices are going up every week!
@@revolution6133 Here in Canada I am hoping that the Bank of Canada measures with their slow increase in interest rate hikes will somewhat curve the lumber prices amongst other pricing issues. Yes, patience is key. In the meantime I continue to save money, investing it in trading with solid companies that have a long history of increasing and sustaining their dividend. So, no rush because I get paid as I wait and keep reassessing the construction industry situation here in Atlantic Canada, East coast. Stay strong, keep safe.💯🇨🇦🍁
Good stuff: I really liked your explanation of joists wanting to lay flat in the middle of a span and how that ties in to blocking reduces deflection. I've always heard that blocking doesn't make a floor "stronger", while experience has taught me that midspan blocking makes it "better" Your video clarified my thinking on this. Thanks!
I've always heard that about blocking as well, but like you, I've always had a different opinion. It is just common sense that mid-span blocking will help distribute the load evenly across more of the joists at the point of maximum deflection.
What it doing is bracing against lateral torsional buckling. That’s what this “flopping” that he talked about is. Bracing the top flange by nailing the subfloor to it and bracing the bottom flange by nailing a drywall ceiling to it does the same thing.
Glad it was helpful! Thank for watching the video about simple spans of floor joists. The content was provided by Glenn Mathewson at buildingcodecollege.com/.
This is a great video. No nonsense and very well explained.
Thank you very much 👍
Glad it was helpful! The content was provided by Glenn at buildingcodecollege.com/.
Straight forward to the point. No stupid commentary. Also, the formulas are a plus. 👍
Thank you.
Interesting information. I learned a few things today. Thank you for taking the time to share and teach.
Glad it was helpful! Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
WOW THANK YOU. I recently bought my first house and have been working on repairing the sag in the middle of the floor. I've been sistering a bunch of the joists with new wood and its taking me a lifetime due to the incredible amount of work. Also I wasn't sure if I was taking the best approach from an engineering stand point and this helps a lot. I'm going to to utilize these bridge blocks to significantly reduce the amount of work I will need to successfully complete my DIY job. Thanks again for this knowledge, it's very valuable to me
Solid bridging will strengthen a great deal as once tied together function as a whole unit…if over eight ft. in length install two rows I did it to my house and I have 2x8s that span a bit over 12 ft, …I put in two rows of blocking and it work very well…much cheaper then sistering especially these days…good luck…
Thank for watching.
Ben you did a great job explaining that hidden life of a joist...thanks dude
Glad it was helpful! Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
Excellent delivery of the information. Thank you.
Thank you, Mike.
Allowable deflection. I used to design I-joist floors in their beginning. Most people thought I-joists were designed to span super far, but the fact is, they were designed to be super predictable. I always designed floors to over perform, because most home owners expected better performance. Most home owners would be surprised to know, at the time, 9 1/2" I-joist DID NOT out perform 2x10s in a simple span. As a designer, I was always thankful that 'unacceptable deflection' was a long way from failure.
Good comment. Thank you for watching. And I love your brother's movie.
Fantastic video! Clear and concise.
Well done sir, I had thought that what you explained was common sense until I became involved in a rebuilding project. The carpenter didn’t understand the superior strength of the 100 year old true dimensional hardwood joists, the contractor disputed the interior walls as supporting walls. I am showing them this lecture to support my positions, although today’s professionals only want to work with new materials.
If the joists are bearing on the interior walls, then they are “supporting walls”.
Thank for watching the video about simple spans of floor joists. The content was provided by Glenn Mathewson at buildingcodecollege.com/.
Lots of good info here! I'm building my own barndominium and I'm at the joist stage. I appreciate it
You're welcome.
I have so much appreciation for this presentation I love this practical application of science!
Glad it was helpful!
As an engineer, I think codes are really cool. They take a lot of research and experience and produce simple guides.
So true, and yet, people dread and fear codes.
Thanks, Austin. I agree with you.
In our world there seems to be no end to rules and regulations, many which are based upon uneducated opinions and wild guesses that haven't had much thought put into them and are effectively useless. But when it comes to this subject, there is relatively precise data available from actual tests, so the results are predictable and can be measured. I wish all builders were aware of this. Start with your design needs, error toward the heavy side if unsure, and calculate what you need to achieve that. That's a much better approach than taking a wold guess and seeing how it turns out. And, it's always better to go a little heavier duty than needed to go a little cheaper and try to compensate some other way for marginal or sub-par performance. You never hear anyone say they wish their floor or roof wasn't so strong. Along this line, you might even find out that you can use a smaller framing member than your hunch and still meet the design goals.
@@G53X0Y0Z0
I have a very different opinion of codes versus requirements. People should not be building anything unless they know enough to use codes, but I think codes should be more like certifications rather than requirements. Requirements are often discriminatory and political whereas codes are just standards.
For instance, bars/clubs have much less regulations to meet than churches (at least where I live). We saw this firsthand when bureaucrats decided which establishments were essential, closing outdoor dining of small restaurants while allowing massive gatherings of corporate establishments. Non-sensical (and anti-science) requirements were placed on stores that actually facilitated viral spread rather than reducing it, in the name of science of course. Many of these destructive and financially burdening requirements are still in place across the world. It was a perfect extreme to illustrate why requiring anything, even if the reasoning sounded good at first, is a violation of freedom which should never be allowed.
@@Austin1990 wrong soapbox.
Thanks for the Info, The Outline how it was explained was great
Glad it was helpful! Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
So good, rebuilding a deck inside a warehouse, you put all my worries to rest. Thank you
Thank you for watching.
Excellent assemblage of information and great presentation. I enjoyed watching it.
Thank you, Steevo.
Thank you. This explained a lot of questions I had about why stick frames are built the way they are.
Thanks for watching, Cindy.
Thank you for putting this together Ben. I’m in the process of building a torsion box for a CNC table, and your presentation helped me with a few terms and concepts. :)
Glad it was helpful!
douglas
What's a torsion box?
And what does that CNC machine do?
We have a small Woodwork factory.
Well explained, visual aids, photos, etc, would also help tremendously.
Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
Good to the point, helpful information! Liked it a lot! Thank you!
Thank you, Nico.
This is fantastic information. Thank you!
Glad it was helpful! The info came from Glenn at buildingcodecollege.com/
I live in a 16' wide row home ( actually closer to 15' wide when you subtract the 10" poured concrete basement walls. While I was drilling 4 or 5 holes thru each basement joists noticed the two doubled up ones that provide extra support I guess for where stairwell is took a lot longer to drill my 3/4" diameter holes. While pulling wire noticed the doubled up joust were 3 by 12 and a different guess stronger species of wood. Bet contractors have not did this use in many years. While an electrical apprentice we were taught to avoid the middle third of all joists whenever possible. Also believed it was better to drill two 3/4" holes at least two inches apart then a big 1.25" hole for wires.
Thanks for watching.
Great info Ben! Thank you.
My pleasure! The info came from Glenn at buildingcodecollege.com/
Just stumbled across this vid and WOW!! Awesome! Thank you for sharing this information!!
Glad it was helpful!
My house was built in 1935. Over the living room are 6x8 joists (exposed, no blocking). True measurements are 5-1/2 x 7-1/4. They are on 32” centers, 15 foot spans. Walls are concrete block with open cells. I don’t know how much they bear. The first joist is on the edge of the stairwell and has the bedroom wall sitting on it, it is visibly deflected or curved downwards and has cracks along roughly the middle sides. The rest of the joists look good, straight, no cracks. The sub floor above is 1x12 knotty pine panelling with Douglas fir floor on top.
Good to hear, David. Thanks for watching.
Thankyou for the help you've given in this presentation . . . Chris . . . Norwich, England
Thank for watching the video about simple spans of floor joists. The content was provided by Glenn Mathewson at buildingcodecollege.com/.
One of the better explanations I've watched
Thanks.
Love this!!! About to take the residential contractor exam.
Nice. Best wishes to you. Post how it goes.
I agree with Douglas, thanks for the knowledge.
Thank you.
Same I learned a bit more then expected. I love learning the why of things.
The content was provided by Glenn at buildingcodecollege.com/.
Beautiful explanation- concise
Glad it was helpful!
Very good informative video. Try to find a span table for your jurisdiction and you will find that the allowable span increases with the addition of solid blocking, cross bridging, cross bridging with strapping under the joist and also with construction adhesive with the subfloor. I believe in our area the max span for 2x10 ss spf on 16" oc is 16' 1" with 2 rows of crossbridging with strapping and glued 5/8" subfloor as opposed to about 13' 5' with just subfloor and one row of strapping which is the bare minimum.
Thank you.
Thanks Ben, learnt something and enjoyed your presentation. I know that seasoned and unseasoned timber have different ratings as well.
Thank for watching the video about simple spans of floor joists. The content was provided by Glenn Mathewson at buildingcodecollege.com/.
Very helpful video! Thank you!
Thank you for watching. That information is from Glenn Mathewson from buildingcodecollege.com/. Check him out.
Excellent video!
I am certain to refer to it in coming project.
Please do!
floor decks people perceive to be "unacceptable" is really due to the deck weight per sq ft being "light". a "light" deck produces a lot of vibrations when people walk across the deck and describe this as "bouncing". if you would have placed 1-1/2" of of gypsum leveler on top of that same deck configuration, hence increasing its weight per sq ft, the deck would produce less vibrations and be perceived to perform better. vibration reduction is also done with blocking/ bridging along the joists, sheathing the underside of decks and perpendicular partitions to the floor joist direction. these items mostly dampen vibrations by connecting all the diaphragm/ floor elements together at more "points" to absorb vibrations induced by loads/ people walking- good video!!
Bingo !
Thanks for watching and commenting, Brett.
Thank you very much. This all makes sense to me now. My attic build will be better for it. Cheers
Great to hear! That info comes from Glenn Mathewson of buildingcodecollege.com/.
Thank you. Much appreciated. Now I know more about what I don't know.
Happy to help!
Wow, very well done. Thanks.
Thank you too! That's from buildingcodecollege.com/glennmathewson/
I learned more information, useful information, here than any other video designed to easily propogate as an ad-hoc, overly generalized, and otherwise useless answer my question. At least now I know how to mitigate my problem.
Thanks for watching.
Thank you for sharing!
My pleasure! The content was provided by Glenn at buildingcodecollege.com/.
I built a "pit" for servicing my trucks and searched for guidelines for the beams I used. I couldn't find anything that applied to what I was building so I erred on the side of safety. The pit was constructed outside between my deck and my garage so I don't have to worry about air quality like pits built in a garage floor. I started by building a 10 x 10 concrete pad with two sections of concrete filled block pillars 8" x 32" at the end (actually, these pillars are part of a concrete filled concrete block wall, so the pillars are effectively 16 x 32 also). Then 4 concrete filled concrete block pillars 16" x 32". I spanned the pillars with 2-2x12's and 4 2x10's to create each "beam" with added blocking and 2x10's for decking. The beams are about 14' long, supported by the 3 pillars on each side. My trucks weigh around 9500 lbs. and I was real nervous when I tested it the first time. I set up a tape measure at the middle of the longest span and was unable to detect any deflection whatsoever. Obviously I over engineered my project, but at least I know that I can change the oil in a semi without having to rebuild it bigger.
Great information and feedback, Hot Shot Truckin'. Thanks for watching and sharing that information.
My od carpenter rule of thumb, when using softwood framing lumber, was to divide the span, and, add 2, so for a 16 foot span, you would use a 2x10 for a normal load. Using structural fir, makes them stiffer, or switching from 16inch spacing to 12 inch spacing also increases strength, Adding blocking between joists stiffens floors because is limits deflection. Now we use a lot of structural lumber, or engineered floor systems, here we generally rely on the reccomendations of the supplier.
That's great stuff, Keith. Thank you for sharing.
Hi Keith. Here in Canada our code will allow a 2x10 to span approximately 13'-8" to 14' depending on bringing and strapping. 2x12's are 15'-6" or slightly better. These are @ 16" o.c.. it was an interesting talk.
@@warrenshalm550 I live in estreme north east Minnesota, our county does not enforce a building code on resedential structures. Most licensed contractors do use the national codes. Your spans sound about what I have used, of course if you specify structural grade fir, as opposed to just softwood lumber, you will get much stiffer floors. As I said, using 12 on centers will also allow for longer spans with a given joist. Also using bridging to avoid deflection also helps. Most of our floors are now down with TJI's or some other floor truss system. The TJI's are lighter, have knock outs for electrical and plumbing, and, can be ordered in long lenghts, so even if you use a center beam or wall you can use a continuous joist, we can get them up to 32 feet in lenght. They have also replaced solid wood rafters in a lot of roof framing.
You're absolutely correct Keith. The betyer grades of lumber have greater spans and of course engineered lumbere has become popular for reasons you state. What has driven the choice in the last year for us has been availability shortages. That is in everything related to construction.
Thanks for this video. I was worried that the floor spans in my Minecraft castle might be too long, but this helped me to understand why some of the historical floor plans I've seen had >10 m wide rooms with wooden floors -- medieval contractors probably didn't care about floor sag as much as we do today (and trusses probably helped too). Now I can build my 10 m wide wood floors without worrying about historical accuracy. I'll just have to remember not to put all my chests in the middle of the room.
Great to hear! That info comes from Glenn Mathewson of buildingcodecollege.com/.
I hope this video gets watch by those in trades who believes mid span blocking is not really necessary. No, it is a MUST for a wood floor joists. In my own build i blocked every joist tight and glued. The difference before and after is incredible. It doesn’t only help to stiffen the floors but it reduces vibrations.
Thank you for watching. That information is from Glenn Mathewson from buildingcodecollege.com/. Check him out.
The number of blocks and the spacing of the blocks often overlooked. Too often people put a single row of blocks in the middle and call it good. A block every 4 feet along the length of joist is a cheap investment and a huge improvement in structural integrity and strength. Structural screws instead of nails are actually faster to install and are by far stiffer and stronger than nails as well. No such thing as too many blocks.
@@briangc1972 Totally agree from my experience. Material doesn’t cost much to blocking but it is a little labour intense if it is done right. To me blocks needs to be a tight fit and glued and screwed. If you are nailing a loose block you are asking for squeks as the joists deflect.
I used 2x 6x 30' iron C purlin. I welded back to back to make into an "I " beam. For my
Floor joists. No squeeking here. I put the 3/4 inch plywood across two sections to see deflection in floor then I spaced out I beams until no floor deflection. I also put another 1/2" plywood glued to 3/4" layer opposite direction.
Very very strong floor.
Nice.
So your floor is 1 1/4" ?
What did you use for adhesive?
Awesome information & explanation!!
Glad it was helpful!
Thanks Ben Gromicko and InterNACHI
Our pleasure! Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
TY I actually learned some things from this video.
All homes should be inspected by an InterNACHI certified home inspector at www.nachi.org/certified-inspectors. Thanks for commenting. - Ben.
Wow. Right to the point. Thanks. :)
You're welcome!
Good video presentation. Thanks!
Thank for watching the video about simple spans of floor joists. The content was provided by Glenn Mathewson at buildingcodecollege.com/.
Pretty informative. Learn with each one.
Thank you.
I added blocking to a 1922 home we owned. It made a huge difference.
Glad to hear it.
Amazing job at explaining this concept
Thank you.
@@BenGromicko I hope you teach at a high school or college because you’ve got a gift
Great video..thank you
Thank you too! The content was provided by Glenn at buildingcodecollege.com/.
Thanks. Folks should know that a structural engineer can analyze issues for little money. I opened a ceiling and found one 2x4 holding a roof load. I knew I could use a simple 4x6 beam but couldn’t contact the clients to approve the design change. I went to a local structural engineer. He quickly entered the data of the existing structure in that area into his computer program. I was able to use three select structural 2x4’s laminated together and keep them hidden above the ceiling drywall. $200 well spent!
Thank you for watching our videos and commenting here.
Well presented for those who need to learn the basics.👍👍👌👌
Thanks a lot
Well done!
Thanks, Lon, for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
Very interesting and above all informative .. tone, voice and content are perfect … just wish you were able to provide us with drawings or pictures for each case it makes it way easier for your audience to understand faster or make sure we have the same idea in mind … I’m nonetheless very grateful for the great explanation you granted us with in this video!
Good comment and advice, Thomas. I'll do better next time.
I am a visual person so I have to see it so having a pictures or drawings illustrations that would be perfect that would be nice if could do part 2 with images would be amazing.
Just a thought.
Thank you so much.
Great info. Subscribed.
Thank you for subscribing.
New subscriber from Davenport Iowa USA 👍
Welcome aboard! The info of this video came from Glenn at buildingcodecollege.com/
Thank you! 👍
You're welcome!
I am currently restoring (not rebuilding) a home that is about 100 years old. They used 2x6s and 2x8 for the floor joists. Many have cracked on the sill plates. I am keeping with the same pattern but replacing joists of the same size using joist hangers, structural bolts for sistering, blocking, and post supports. it is a small house, 1300 sqft, so without over-engineering things, I think updated lumber and structural support should be enough to keep this house sitting for much longer. It is also grandfathered into our local building codes so I do not need to perform intense structural changes or have them inspected to modern codes.
Thanks for watching, Michael. And for commenting.
Thank you!
You're welcome!
I wonder if joist flop over is similar to when I was a little kid and decided to do a tight rope walk on the edge of the cat's litter box. I balanced myself so the plastic edge of the litter box was supporting my weight, but it tipped over at mid-point. I think it's because the plastic started to buckle causing a twist in my applied weight. There was a solid support for my weight at the box corner but when I got mid-point something like torsion was created. Of course, my mom was not happy about me using the cat box for stress testing.
Thanks for watching. The info of this video came from Glenn at buildingcodecollege.com/
Topic very well explained! :) But in my opinion it would be even 100x better with ilustrations of what you are describing at the moment.
Great suggestion!
Well, I’m glad someone else out there is advocating for a minimum of L/360 TL deflection!
Yep. That info comes from Glenn Mathewson of buildingcodecollege.com/ who wrote that content.
A old school builder taught me years ago about spans.
Get your length and half it and plus one is the best I’ve ever heard.
So on a 20 ft Span half it plus one and it’s a 11 inch timber
That's a great tip. I like it.
Thanks, I am building a log cabin with 30 foot span however I am installing footing piers every 10 feet and was wondering about floor joist loads
Yes.
You need help buddy!
magnificent explanation..! Ben, You are an Engineer...! or better, a great engineering instructor..! simple, easy..!
Wow, thanks! Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
Very interesting!
I agree. The info of this video came from Glenn at buildingcodecollege.com/
Thank You Sir
Most welcome. Thanks for watching the video. The information about spans comes from Glenn at buildingcodecollege.com/.
Very informative. I wish someone would talk about the relationship between deflection and load. For example are the directly proportional - i.e. for a given span does twice the psf equate to twice the deflection? And what are the deflections before a joist actually falls from shear? I'd like to be able to calculate the actual weight a span can carry before failure if deflection is not a critical factor.
Good idea, R&R.
@Robert Swaine Thanks for that detailed answer! I had 2 years of general Engineering studies but switched to Comp Sci before picking an Engineering Major... but I still find structural and mechanical engineering fascinating. I get why the emphasis with joists is always on deflection... but sometimes I don't care about deflection or "bounce" and just want to know if a structure will carry the load with a reasonable margin of error baked in. These are usually just shelving or storage projects - never anything life critical btw. And yeah... I can see how testing wood for tensile strength could be real tricky!
Very helpful for aquarium keepers
Interesting.
wow...in simple terms....thanks...this video was just what I needed...all my beams are solid teak and I was worried about the span I am building....not anymore!
That info was provided by Glenn Mathewson from buildingcodecollege.com/.
One point I would like to add from the real world is the effect of knots in joists. During an inspection, I saw a garage ceiling with 2 x 8 joists. Three consecutive joists had a knot in the bottom edge about three inches deep. They had deflected about two inches and were starting to crack along their length from the top of the knot. I would say that the framer should have been hung from those joists for using those particular pieces, but he'd probably escape unharmed.
😅
You're correct. Good point about knots in solid lumber. They're like bored holes.
Thank you, very informative. It was a little to technical for a layman, though. Some illustrations could have helped, like at the beginning, to understand the industry specific terms.
Glad it was helpful! The content was provided by Glenn at buildingcodecollege.com/.
Great video
Thanks!
This is the side of RUclips for men, fathers, and builders of America.
Thanks for watching.
Very interesting and informative
Glad you think so!
awesome tutorial... just what I need to confirm the builder is doing it right ! :) I will sleep better cheers
Oh, good to hear, Rajiv.
wonderful
Thank you for watching.
Very helpful video. I want to lift my floor joists (in order to replace the center beam or main girder) so I would like to clarify with you that using a 4x6x10' piece of lumber supported by two jacks (of appropriate strength) would be better than say a 2x8x10' piece of lumber as it doesn't have the same amount of area for the jack to support the beam above. Each 4x6x10 will likely support 7 floor joists. (I will do a row of these to support 45ft length house.) With an estimated house weight of 150,000 lbs, I'm planning to use a series of 5 support beams (2 jacks each) for a total of 10 jacks on one side of the girder and the same set up on the other side of the girder) If my jacks hold 15000 lbs each then I have 150,000 lbs supported on just one side of the girder. I personally think a wider piece of lumber would be better than a narrow piece of lumber. Thoughts?
This is a comment section not free structural engineering. And you need to lift all ten jacks in synch with each other or you will damage your framing and sheet rock will crack all over.
Thank you, Lizanne, for watching. I appreciate it. And your comments.
@@BenGromicko Way to completely ignore their questions.
An old joiner once told me half span plus 1, so a span of 10 feet/2=5+1=6, joist required=6x2
I was taught the same.
I love those old-timer rule of thumbs.
@@BenGromicko Dont use a screw when a nail will do, Geof Hirst RIP
@@georgeliquor2931 Nice.
Excellent video my friend
Thank you! Cheers! That information is from Glenn Mathewson from buildingcodecollege.com/. Check him out.
This is really helpful but can you please have visuals for those that Learn with visual presentations.
Yes. The content was provided by Glenn at buildingcodecollege.com/.
great! thanks
You're welcome!
Good video. Thanks. Shear failure is interesting. I saw this at my sister's house. Her teenage sons had a few wild parties and one of the joist cracked and was 'bouncy'. The crack wasn't a horizontal line, however it did start near the middle of the joist along the grain and then followed that grain as it curved downward to the bottom of the joist where it left an open gap. (2x10 to 2x4) Joist span, construction, etc were all standard. I think this problem was caused by unusual stress, not ideal grain structure in the wrong place, and there was no blocking any of which would probably have been enough to stop it from happening. And the fix was simple (I'd flown cross country so I didn't have the tools to do it), lift the broken joist with a 2x4, sister up the joist and install blocking. I think this failure speaks to the robustness of standard joist construction. I've seen other failures in very old houses, undersized members, too large or too many utilities holes drilled, very old, very dry lumber, or rot/termites. (This Old House runs into this all the time)
I've often told people (something that might not be true - please correct me) "a standard floor in house construction built to code can hold 2000 pounds per square foot." I would use this as an argument for why a staircase should be built following code, or why a garden deck needs beefing up. I think it's clear how useful the statement is - if it's true. What would be a better way of expressing this thought to an inexperienced DIYer? (I think porches and decks are where the most code violations occur. I've done it myself. The only one I'll admit to is a foot off the ground - I can't imagine any building inspector even bothering to look at it.)
Forty pounds per square foot is typical of a basic residential floor design load, a house floor capable of adequately supporting 2,000 lbs. per square foot would be pretty stout. Could park your truck on it.
Thanks for watching and your comments.
@@G53X0Y0Z0 It has to hold more than 40lbs ft^2, I weigh 166 my feet are less than a foot long, so each foot exerts 83 pounds in less than a square foot. Even in my ratty 70 year old house no sag or squeaks. I also remember standing underneath the main level of my in-laws house on a steep hill in Silverlake (Los Angeles, California) and realizing I was below their two car garage. 2 x12" (maybe 14") 16 OC, a two-car garage is at least 18' x 20' span, blocking? (I guess I could find my photo.) Light weight concrete , but that floor has to be much much stronger than 40lbs ft^2. And after 40 years no cracks. My Tesla weighs 4400 lbs, that's 1100lbs/tire. I don't think it would put any sag in that floor - or there'd be articles on collapsing hillside garages. (I googled and found a few items, mostly due to water seepage.)
@@G53X0Y0Z0 But that design load is for an L/240 or better deflection ratio typically - which doesn't address actual failure limits. I understand that the code tables have a lot of built in safety... but sometimes it'd be nice to know where the failure limit actually is - but I suspect that they're worried if they actually published that, some would abuse the information.
@@WillN2Go1 - loads can be calculated and expressed in different ways. I think that the way terms are expressed and understood may be what is causing the question. Also, just a couple of inches of joist depth or a few inches of span increase or decrease can alter it's load bearing capacity significantly.
You in-law's garage was likely stronger than a 40 lbs. per square foot. Concrete actually has some flexibility and a slab can bend or deflect some without cracking. There are different strengths of concrete and much depends on how it was cured too. Concrete is not very strong in tensile loads, and most cracks are from shrinking. Of course there are limits of how far a concrete slab can be bent before it cracks. And, a concrete slab or other thick sheeting can help spread out loads. There also concrete slabs that are "pre-stressed", they are made usually in a factory setting and then delivered to the installation site. They are made to function as a load bearing structure such as a roof, wall, or floor. So it's perhaps possible the slab was something like that?
If you had a 20'x10' (200 square feet) room and the floor was engineered (properly) to hold 40 lbs. per square foot then you should be able to put 8,000 lbs. in that room if it was pretty evenly spread out. But if you had a 4,000 pound object that was 1 square foot in size and put in in the middle of the span, the load would be on on or two joists in their weakest place. That kind of load is called a point load, and needs to be calculated differently to find the appropriate joist (or beam) size, because the weight is not spread out. If that load is close to the end of the span, the joist can support it much easier than if the same load was in the middle.
So, just for simplicity if the 4,400 lb. car put 1,100 lbs. on each tire you would have four 1,100 lb. point loads. As it rolls into the garage the leading tires first put their load on the ends of the joists, and then the middle of the span, and as the leading tires get closer to the other ends of the joists the back tires roll onto the floor, and assuming the joist spans (distance between supports) are not very much longer than the car, the loads end up close to the joist supports where joists are strongest.
If you put 2,000 lbs. per square foot on every square foot of our 200 square foot room, and that adds up to a total 400,000 lbs. , which is quite a difference from 4,100 lbs, which is the weight of 20 or 30 adults.
What I see a LOT in houses I've worked on for restoration is holes for wiring and plumbing being drilled far too close to the tension portion of a joist, sometimes even notches cut right out of the bottom. Not only is this annoying because when cutting through or tearing down ceiling drywall you have a high risk of damaging electrical and plumbing (not to mention people who do that never put up nail guards), but it effectively reduces the strength of each joist by how much was cut or drilled out. What's more, if someone else goes in and drills additional holes in at the proper distance, now they're cutting though the new tension point that the first person created, further reducing the load the joist can handle.
Thank for watching the video about simple spans of floor joists. The content was provided by Glenn Mathewson at buildingcodecollege.com/.
If you want to increase the load bearing capabilities of your joists without too much of an additional expense, fasten a steel strap to the bottom of each joist (it can be every other joist depending on your load bearing requirements for the floor). Steel strapping comes in 25 foot lengths up to 16 gage with lots of holes the entire length. Use 2 to 3 inch deck screws every 4 to 6 inches. The result is that all "tension" is moved to the bottom of the joist with the "neutral plane at (or near) the bottom of the joist, leaving all of the joist as the "compression area". "Deflection" will be greatly reduced compared to a joist without the steel strap. "Weight bearing" capability will probably be at least double that of a joist without the steel straps. A good idea is to extend the ends of the strap around the ends of each joist a couple of inches and fasten with two deck screws. I use this idea on fence posts that always eventually rot right at ground level to keep them from being knocked over too easily!
Thanks for the feedback. The info of this video came from Glenn at buildingcodecollege.com/
Interesting comment, thanks.
Load sharing bridging is code in most places..
@@jamesrussell6870 Thanks! I didn't know it was called "load sharing bridging". I've never seen this done by anyone else, and for me it was just solving a problem using basic physics. I'm a DIY handyman type with no formal training in construction.
@@paparayg It's just called bridging. Primarily for sharing load with adjacent members...
does r301.7 apply to roof joists on a flat style roof ? I recently observed 5/8 inch deflection on a 20 foot span with 10.5 inch wide joists on 24 inch centers when the roof was loaded with a 1500 lb. piece of equipment in the center of the span. the center area had blocking added to help spread the load out over a larger area in the roof structure . This "dead load " would be added to the capacity of the roof when supporting snow and rain in winter .
pictures or animations (real life examples) would help this video alot
You're right. Thanks.
If you really want a lesson on wood strength get bowers bible #1 and #2 it explains grain strength compression and tension from ancient bows and arrows the different species and also teaches you primitive bow building!this is a very good video on the subject
What was the book title?
Very interesting information. Thank you! Almost couldn't see the speaker other than his arms and face... 🙂
Sorry about that.