Foundation Design Example with Offset Column and Eccentric Moments
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- čas přidán 7. 08. 2024
- I go through a foundation design example with an offset column that induces eccentric moments.
#foundationdesign #structuralengineering #geotechnicalengineering
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hello there! just wanted to say thanks for doing this video. I'm a new engineer who just started working and has the exact problem in a project just like in this video. Thank you for teaching this, really helps me a lot !! cheers !!
Excellent video Dazz! More please
Great Explanation and walk through example!
Hi there! I really like your channel! One thing you should always check: is your total soil pressure equal to your vertical load? (244 + 200) / 2 = 222 x 3 x 3 = 1998. Something is wrong, your minimal soil pressure. It should be 111 - 22 - 111 = -22. Mean soil pressure = 111. 111 x 3 x 3 = 999 ~ 1000. Normally a foundation can’t handle tension. So you should make a different calculation. Your eccentricity is 600 / 1000 = 0.6 m. The distance from the work line of your load to the edge of your slab = 1,5 - 0,6 = 0,9 m. The length of your triangle pressure figure is 3 x 0,9 = 2,7 m. Your max soil pressure is 2 x 1000 / (3 x 2,7) = 247 kN/m2.
Agreed here. Thanks.
there is nothing wrong with university text, but you are talking about an actual design, if you want, this is the most accuarate one, Pressure, P1 + (P1 - P2) (Lenght of direction in question, L + Width of column)/L = 266KN/m2
Thanks for this video. It was really helpful
New to your channel and finding the content useful, thanks for taking the time to make it. Would be interested to see your method of assessmemt of an existing residential foundation relative to the effect of conversion works. For example, load bearing masonry wall removed and replaced with beam and posts and following through the effect to check suitability of existing found.
I think this style is perfect for better understanding the method. Would also be good to see how you formally produce in a calc pack also though. Keep up the good work 👍🏼thanks
I was gonna say exactly the same thing... Great video Dazz
Great, I really like your videos.
Thanks a lot 🙏
Should the additional moment due to shear and thickness of the foundation be added to the bearing stress check as well?
Loving these videos man! Do you have any advice for someone like myself who has been out of the engineering game for a year and is about to jump straight back into a design engineering position? These videos are a great referesher I must say! Thanks
Thanks! I’d say just get some practice in. You’ll pick it back up quite quickly I imagine.
Great Video. I am assuming that this foundation is at some depth(say 1.5m) from NGL. In some case when the load is not as high as this example and pad footing is to be rested on the ground and no Geotechnical data is available, how would you approach in the design?
Love it man! I love how you put everything together for every kind of structural designs, as done by industry. Learning from practicing engineers definitely more valuable for the workforce, than learning from uni inexperienced academics.
I totally agree
how did you get the shear force?
Hello there, a question regarding to your overturning check of the foundation why did not you add the additional moment due to eccentric load (column) you have calculated at the beginning of the video of 500 kN.m with the overturning moment ?
What about allowable soil pressure Mr Dazz ?
Moment on eccentric column will not act on centroid of the footing. So the MOI calculated is wrong...
What foundation book can you recommend
Could you do the similar type of example for us code
what is the software that your using to mark up
Do include some underground Pit design examples in your next Video 😀
Can you do a design also using ACI code please?
It would be very useful to show the reinforcement design of the foundation 👍
Something I’m going to do in the future 🙂
Great video, however I just have a simple question to ask, for the bearing pressure check, aren’t we supposed to check the calculated value vs the bearing capacity from the geotechnical report? (You didn’t include the bearing capacity) thanks.
Yes you would check against the allowable bearing pressure from the geo report. I just skipped it 😅
@@EverydayDazz okay then. So at 3:32 on your stress diagram, you indicated that the calculated values for the bearing pressure are 244kN/m2(highest) and 200kN/m2, my assumption is that the bearing capacity is greater than 244 in that case, what do you think 🤔? (Bearing capacity should bd greater than the bearing pressure)
Yeah so if the allowable was greater than 244 than it passes. But if it’s less then you would need to re-size your pad to spread the stress
are you using ACI CODE for the safety factor of 1.5 and reduction factor of 0.9?
I’m using euro codes.
What would you do if footing width and length is limited sir
Reduce the load if possible
Thank you sir
Question: According you the moment generated by the excentricity isnt reversable, as so, whenever there's a compression load with excentricity and no moment at the foot, there's an constant increase in the bearing pressure.
This doesnt feel correct! the pressure should vary and not be constant.
can you please clarify me??
If the column force is fixed in place then the eccentric moment generated is also fixed and doesn’t vary. So pressure cannot vary if the only moment generated is from eccentric axial loading.
@@EverydayDazz shouldn’t there be more pressure closer to the eccentric column position compared to away from the column?
czcams.com/video/3OkkiFicH2Y/video.html
hi i have a question. will eccentricity caused by column offset from the centre lead to greater bending moment?
czcams.com/video/m_ITdRW-wYI/video.html that’s a better eccentric pad foundation design
Big question. What do you do if your method shows the soil in tension. This can happen when the loading is outside the kern. The S changes - to what? You did it another way, but you passed over the real reason for using 1.5.
Do you mean when their is uplift? Soil can’t be in tension.
If there is uplift then you need to make the foundation bigger to increase the self weight so that there is no more uplift.
@@EverydayDazz That is my point. If you have tension in the soil, then the design does not work and the design is flawed. Stop and redesign. You did not check for tension. If you have the same problem using a tall steel pole with low axial load, high overturning, and low shear, you can see tension, which is not good because soil does not resist tension. If you have a situation with unsymetrical foundation or skewed lateral loads the problem is similar but more complex. A wind turbine foundation is somtimes octagonal.
So I work out the stress on the soil and it’s all in compression, so that is the check to see if there is uplift.
Also the overturning check is a check for uplift. Factor down the favourable forces and factor up the unfavourable forces.
High shear is unfavourable because you take moments about the foundation.
@@EverydayDazz To be quite honest, I don’t do these foundations by hand, I wrote an Excel spreadsheet with pictures and diagrams that would solve the problem and print the documentation. We also do not use the .9 on the weight for overturning; I wish I knew what code you are using. My perspective is from the electrical world (NESC) and the telecom world (EIA/TIA-222), not the building world. Bowels wrote a book that had very good examples of ths problem but it is very old.
Would this "fag packet calculation" be sufficient for a building control submission or is it more for preliminary sizing or for Seniors to do a quick check?
If you tidy up the calculation there’s no reason why you can’t use it for building regs.
Definitely a great tool to use for preliminary sizing too since it’s so quick.
@@EverydayDazz And by tidy up you mean copy and pasting the bearing pressure check, sliding check etc. in the correct sequence onto some calc paper?
Yeah basically. Maybe use a ruler for the sketches too just to neaten everything. But essentially the calculation as I’ve shown is good enough for build regs.
@@EverydayDazz Okay, good stuff. Thank you again!
You're probs getting sick of me saying thank you but your content is top quality mate fairplay.