Steel Truss Calculation - The easy formulas you need to use
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- เผยแพร่เมื่อ 1 มิ.ย. 2024
- I show you the simple formulas you need to do a steel truss calculation for a long span roof truss. Learn to design a roof truss including how to select a size, finding the force in the top and bottom chord, and allowable deflection calculation.
#truss, #how-to, #structures
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Helo sir, do you have a simplified book for designing steel and concrete the easiest way of calculation?
Thank you for taking the time to make this video.
It's the "step by step formula" that I've been looking for for ages.
You are literally a million times better than my college tutor Thankyou
Brilliant way to understand anyone who got basic physics.
Thanks and god bless you.❤
Wonderfully simple to understand. Thank you.
Thanks I appreciate it!
Thank you so much for the shared knowledge.
Thank's for the video.
Great video!
Thanks For Teaching Sir
This is amazingly useful thank you for producing this! Do you know if any of these equations are in the Eurocodes or national annexes?
How you consider the thickness and sizes of the angle bars in your computation?
Love this guy.
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If you take I req = wL^3 you can leave w at the value per meter. This prevent you from not using the total length w and errors.
very nice i join it.thank you.
Sorry, I understood your deduction and it's correct, congratulations!
Can you combine trusses with arches? Would that increase the load capacity of the arch? (Not talking about suspension bridges)
Hi, how do we calculate the maximum load/maximum vertical deflection the truss can take with no intermediate supports, a free effective length of 1.5m , maximum load applied at the center 5kg.
Do you have a process you could share to do the same with regular Douglas fir wood? I would really appreciate it. Thanks!
Based on your calculation what is the deflection in mm?Do we need to put some amount of camber for such long span beam?
Can you post a video with the complete steel truss design with size selection, defelctions, etc....?
Excellent!
Finally I found a technical video easy to understand being a non engineer myself
thang you very much
Hi. When working with smaller trusses for machines i found that the equation I=A*d^2/2 gives 4-10 times bigger moment of inertia than the real one (that was my statistics, the situation may be even worse). My trusses were mostly ~2 m long and ~300-400 mm deep, i needed really small deflections (l/40000)
Thank you for the amazing video, here is my dilemma. I have a 30 feet span residential floor project and have a hard time to find the stell bar joist criterias using the formula and second the distance in between trusses!? You don't mind giving me more info please. Thank you
Why is this so hard to find?!
This is excellent!
Totally like your tutorial. And could you please guide me how to calculate the inclined and vertical member between the two main chord? Thank You so much.
Thanks - I'll put it on my list
OMGOSH! Where have you been all my life? This has given me new reason to live...LOVE doing these calcs! Why couldn’t my Statics and Dynamics Professors in engineering school explain things this way?!
I’m a little confused about the Moment, in school they taugh that it was Force times direction (F x Cosine or Sine theta) so if you could differentiate that for me I’d be grateful.
Do you do Free Body Diagrams where you show the forces acting on a body from x, y, and z? I’d love to see that.
How come academia fails to explain things this way?
THANK YOU! THANK YOU!!! THANK YOU!!!
Hi Carmen. Thanks for the compliment! Moment in a beam is basically a force couple, so you have an equal and opposite force in each chord, top and bottom.
Can you do a video showing how to find all reaction forces in an arch?
For the configuration you drew the top chord force will be 562.5 but the bottom chord force will be less because of the diagonal web members framing into the bottom chord at midpoint.
True but for a quick approximation it will get you in the right ball park.
Hello sir Do you have a simplified book for designing the easiest way?
Hello, your videos have really helped me, thank you. I have a question, from your example, Irequired was 605,000cm4, so does that mean when picking a steel section to use we have to pick one with an Ix value greater than that? Like 1016x305x249 universal beam? And lastly, can universal beams like that be used to construct trusses? Sorry for the many questions, your answers would be appreciated.
Once you have the required I value, you then derive the I value for the truss using the next part of the calculation in the video. I may need to clarify that in a future video.
@@RobindeJongh Thank you. Also, is there a way to calculate the bending moment in a specific truss member to be able to carry out a bending resistance check?
Hi, Robin, can you check this?
L=5.6 m, total load = 1.5Knm, sectional area (light gauge steel 2x4x0.85 = 1.27 cm2) . I=2.24*1.5*5.6^2=105 cm4. I need to find de "D" value. So for me 1.27 * 13^2 = 107. Then, I need a "D" value of 13 cm. That's correct?
What about the member size of internal chords ? How do we determine that ?
Robin - Can you do a similar video with easy calculation you need to use
to make a wood Truss for a flat roof. Please.
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Hello and thank you. I would like to ask, does the I required is for one cord only or for both cord (top and bottom) added? Thank you
And one more question if you wish to answer, does the w is included with truss member itself or only the external force?
So if I do this what metal should I ask for at the builders merchants?
Robin - the UK is crying out for a channel like this. Make a series of Rules of Thumbs for the IStructE exam
Thanks Liam. I'll take that on-board!
Can we use this formula if there is a triangular truss
Not sure if you read these, but I can't seem to find an engineer to help with a project. I just want a truss drawing with thickness of mild steel angle iron used for the web and chords, and of course, how many triangle webs need to be inside the truss. I want to use a parallel chord vaulted truss design spanning 40 feet. I am putting a roof between two shipping containers, and need a snow load capacity of 50 psf. The perlins (span between trusses, I think they are called perlins) will be 2/4 every 24 inches connected with U channel, and I hope to get away with fabricating 11 trusses total, so every 48 inches. I would happily pay for a drawing.
Hi Chris. Sure - let me know on the following contact form: docs.google.com/forms/d/e/1FAIpQLSdXAY1zbCizMIF5CbdSrSRF5dBG-H1nXEW2wBuCYdgdJk309Q/viewform?usp=sf_link
How do I choose the size of bottom and top chord after the calculation
thank you for your video! im studying also... can i email you to ask a few questions?
Hi Robin, thanks for this video. I think there is something wrong !
I have an objection regarding your formula: I = 2.24.W.L2
Look what I found:
Deflection = L/360 must be < or = 5.W.L4 / 384.E.I
I < or = 5.W.L4.360 / 384.E.L
I < or = 5.W.L3.360 / 384.21000
I < or = 2.23.W.L3
Could you explain me where is the problem ?
Thanks in advance
Hi. It's ^2 for total load, ^3 for a udl.
Hi Robin, want to build a platform for keeping 2000 Liters x 2 water tanks. Platform is approx 5 x 10 feet. Pillars will be in brick mortar and I want I beams on it to support load. What sizes of i beam and how many in numbers to use?
Is this for a standard thickness of stock. Like 1/4 inch think 2x2 angle iron? It seems like the measurements of the material your using would change the equation.
Hi Paul. Generally you would measure to centroid of the section, so the calculation doesn't change if you change steel size.
is depth the depth of the truss for the last equation?
Would you be so kind as to go through the same steps for a timber truss?
Thanks sir 💐💐💐💐💐💐💐
Most welcome!
How do I choose the size of angle section after calculation
Thank You Robin
Can we use this formulas if there is a triangular truss
I don't think the formula works for a triangular truss.
Hello Robin. Thank you for your time putting this together it is really helpful. I need to ask one thing when are you calculating "I required" how cm^4 came? thanks
Glad you're finding it helpful. The formula for Ireq is a simplification where I've taken the formula for deflection 5WL^3/384EI and substituted in all the units and the value L/360, which then gives me the shortcut formula.
@@RobindeJongh Got it. Thank you very much
@@RobindeJongh How did it come to 2.24 I used how you derived the formula and what I got is 4.68
@@RobindeJongh And is this applicable for short span also?
@@alfredfungo2155 Yes, it's applicable.
Are you using factored loads?
Thanks you very much but how will determine the sizes of the size of still iron bars to be used thanks
Hi Jon. I keep being asked this question and I keep meaning to do a video on it. Thanks for the reminder!
Ese método se conoce como analogía estructural de viga, el cortante brinda las fuerzas en las diagonales , el diagrama de momentos, se divide entre el peralte de la viga equivalente, y resulta para cada tramo las fuerzas en los cordones superior e inferior, los montantes( elementos verticales), con el cortante en cada tramo
How do you calculate roof load on the steel
when you say area of cord say using 2X4 nomimal so 8 in square X 2 for top and bottom cord ?
Hi Robert. The "A" is the area of one chord, so you would typically use the same top and bottom chord. The area is area of steel, which takes into account wall thickness and so on.
Long span for hall 30m length the optimum flat structure and optimum steel type tube or angle section or c channel?
Angle or c-channel back to back can work well and is easy to bolt together or weld. Circular tube needs more welding and fabrication time.
Can you refer to design manuals
Sir, i have a doubt. How can we calculate the member forces (especially diagonal member) when udl is acting
on this kind of through truss?
Hi. Usually we take the maximum shear and use that as the force in the diagonals. Also you can ask further here: geni.us/askrobin
I want to build a lightweight trailer for my ultralight aircraft (350 lbs) , it has to be single axle and 24' long and be enclosed (arched covering). I was thinking about welding two lightweight trusses together as the main support instead of get a heavy rectangle or angle. They can't be very tall though, maybe 6" your calculation makes it 18" high and that would make the floor of the trailer too high. but two of them could be smaller maybe? what should I use, 1" square tube and flat bar maybe? I don't know if it's worth it.
Hi. Trusses are a lightweight solution at the expense of depth. Steel UC sections offer the opposite, a less deep solution at the expense of weight. If you have only 6" then you're limited to a UC section or Square hollow section.
@@RobindeJongh they incorporate the trusses into short side walls to make these long lightweight sailplane trailers.......that's the secret!
@@RobindeJongh how do we design such a truss other than simple triangles if we want to make it stronger but don't mind doing more cutting and welding?
Hi sir, is this still the same if we use triangular truss
Hi Rimar. This method is only for parallel chord trusses.
Using 40*40*1.6 mm pipe. Flat truss 40 * 1.6mm pipe * 10 inches is it enough for 30 feet shed without middle support.(pillar)
D30/15 for long span , if short span like 8feet/15?
Span / 15 is a preliminary sizing rule, to help you decide on the depth of the truss.
is there an easy formula to check for the web members too?
Yes there is - generally you can take the maximum shear force in the beam and check the web members for that.
Hello, is (I required) = 2.24 W L^2 or is it 2.24 W L^3. As in your video "How to do a steel beam calculation Part 4, you used the formula I required = 2.24 W L^3 so I am confused which one is correct. Please could you reply at your earliest convenience as I have a close deadline.
Hi. The difference is whether you use w for kN/m or W for kN, in other words total load. So ^2 if you use total load (big W) or ^3 if you use a UDL (kN per m).
@@RobindeJongh Thank you
@@RobindeJongh Is there a formula, to calculate the deflection of a truss, so It can be compared to the formula deflection has to be less than span/360? so the truss can be proven as satisfactory
@@rayrim-rukeh1967 Hi Ray. Yes, if I remember rightly that's covered in the video.
@@RobindeJongh hello, if you did I can’t figure out which one it is. Please could you help?
I am wondering what the Ac is? The overall area of top chord and bottom chord or just counting one chord?
Ac is the cross sectional area of one chord, if the chords are equal size.
@@RobindeJongh thx.. Got it
@@RobindeJongh and how does this work for ub's or uc's?
7:04 how to we get this Aₗ?
Is this specific for steel trusses? Or any type of truss?
Same kind of thing with timber trusses also. The deflection formula is different.
@@RobindeJongh Got it. Thank you!
Hi Robin . I need some help in truss building
Do you mean with calculations, or construction?
I didn't quite understand how the 2.24 came about. You stated l over 360. Is that 30 divided by 360? Because I get a complete different number than the 2.24?
It's a shortcut formula for deflection that has been developed taking into account youngs modulus and the allowable span to deflection ratio.
@@RobindeJongh but where does this 2.24 come from?
If look online I see L/360 and than see actually same number as me. Aslike 30/360, as the distance oenght is 30m
It’s literally a page full of calcs to get to it.
@@RobindeJongh ow I didn't get that. I'm sorry
can you derive how you get 2.24wl2?
I could but it would be pretty boring 🤣. Essentially, you take the formula for deflection, and then substitute in all the normal values, and then rearrange it. It uses the deflection as span/360, youngs modulus of 205,000.
what is meant with "Area of the chord" ?
Hi. It's the cross section area of the steel section that is used.
@@RobindeJongh So in this example the unit of 'A' would be square centimeter and the unit of 'D' would be centimeter in order to receive a value comaparable to the 'Ireq' from the previous formula which results in cm cubed, right?
How do we know load (w)
Check out part 1 of my steel beam tutorial.
hi there
can I get some help with calculating stress that steel can hold as horizontal and vertical load?
thank you very much if yes or no - would appreciate the yes :P
and how can I get in contact with u plz?
Hi. Check out my 4 part tutorial on beam design th-cam.com/play/PLJ7yQ-oWQGLRH8DjtJeq--2I1VKJFUQTq.html
I=2.24*wl3
wait how to find the total load? why did you multiply 30 by 10?
30 x 10 is the total load if the truss is 30m long and has 10kN/m on it.
What is ratio to get 15?
Span / 15 is just a rough guide to how deep a truss needs to be. Use it as a starting point, no more.
Things you need to do splice calcs
How to specify a conc beam and column
Preliminary calcs
Thanks Usman for these great suggestions 👍
@@RobindeJongh your welcome can you also do a video on general structural engineering formulas which are handy to know. Will you be running your course anytime soon
Where is the application of the value of M and F in this calculation?
Lástima, no hay traduccion en español
Hi sir i want help i am doing fabrication work in India i want steel structure idea
at 5:16 the general equation is I_cm^4= 5e8*f*wL^3/(384*E),hahaha
How to find Ac
Area of the chord
It's the cross-sectional area of the steel section, which you can find here: www.steelforlifebluebook.co.uk/hfshs/ec3-ukna/section-properties-dimensions-properties/
if the truss shape is triangular the depth should be measured at the center of the truss # 🇵🇰
good but U said depth formula is truss span devided by 15 or 18 ???? there should be one denominator either 15 or either 18 otherwise depth will be changed # 🇵🇰
Span/15 is not a formula, just a rule of thumb to help you decide what initial truss depth to try. The formula is later in the video.
👍😇🤗🙏
Why not splice it
the video is good, but the formula is wrong, the right Ireq=w.L³
Confusing
F=M/d, not M/L
Please, explain how to place such a beam-angle up, or down?
th-cam.com/users/shorts1xxh2YzwlU0?feature=share
Thank you!
As you described as a simply supported truss, it is subjected to the maximum moment of wL^2/8. The design max moment is located exactly at the center span. You considered the top and bottom chords at the center span as lone couple structural elements resisting the moment but strictly they are not. You disregarded the resistance to moment the diagonal member provides. This fact renders your entire design calculation inaccurate.
Good points but I respectfully disagree. This is an incredibly simple calculation that gets a 98% correct force in the top and bottom boom, and is slightly conservative. That's an amazing win if you don't have software to get you the final 2%.
It's not the cords that resist the moment, it's the beam, because the truss is just a beam, that is, an element subject to a binary of forces. The path of the forces constituting the binary along the beam is what matters for the truss...
CAN I USE OUR INDIAN COUNTRY ? IM FROM INDIA
Hi Pragati. It would be suitable in India or anywhere, as long as the local building control accepts your calculations. Local variations might be in steel grade (it's usually S355 or S275 here in the UK) and in the safety factors used.
Not sure why nut it is angering when you or anyone uses only metric or only imperial SAE etc.. mesuments. Do both. Yes we know KN in the US and occasionally use them. Butdam. It is in my opinion uncool not to include both even if KN or metric is better.
It's a good point, Jim, and one I have thought about a lot. It's a global audience watching these videos and here I am using only metric and alienating half my audience! To some extent I think metric is simply better and that people should learn to use it, but at the same time I realise that is not going to happen. I have actually never done calculations in imperial so that would also be totally alien to me. Any suggestions as to how I could be inclusive to those using imperial would be genuinely appreciated. 👍