How Engineers Solve the Problem of Punching Shear Failure
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- čas přidán 5. 09. 2024
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A lot of you are asking "How do we fix the problem?" presented in this video. That will be in a future video so stay tuned and thank you always for watching!
My question answered in the future. Thank you.
Sad. So we have to tune into the future to know the answer to the question you started the video with.
OK. I will jump ahead, and say if it costs money, it is a serious problem.
It is painfully simple, we just tear down the existing building, substitute for the proper size stud rails, then repour the floors and rebuild the building the way it was meant to be built to begin with. Surely nobody would object to this solution! 😂
Though in reality, I am guessing you would do something like an epoxy floor covering to seal the concrete on the top surface so that they are not continually exposed to new moisture.
Epoxy patch product
@@deconteesawyer5758 the question he started the video with was "how do engineers solve the problem of punching shear failure," which was clearly explained. The question he is pointing out is "how do we fix the problem of corrosion of the stud heads when exposed to the elements," which is to be covered, for free, in a later video.
I was a structural designer for 41 years. I'been retired for 8 years now. I didn't do a lot of concrete design; mostly steel design but I find these types of topics fascinating. Thanks for your videos and keep on teaching.
Thank you so much for watching and commenting.
Greg.. similar history.. glad we have a place to meet.. virtually.
@@BuildingIntegrity Appreciate your channel.. Thank you.
The instruction and explanations on this channel impress me as being CLEAR and uncomplicated. That's a sign of someone who understands his subject well enough to make it seem simple. I know nothing about ergs and joules and newtons and force vector this and force vector that, but I'm getting glimmers of understanding from watching the videos. Hey! A glimmer is a glimmer!
Agreed, these videos are fascinating. As a Bay Area native the Millennium Tower caught my attention but it'd be fun to see deep dives on other engineering challenges. The Bay Area has so many to choose from: the new Bay Bridge, the new Transbay Terminal (right near the Millennium Tower), 33 Tehama, or even older stuff like the San Onofre nuclear plant.
Why does a 72 year old retired grandma find your videos so fascinating? It’s because you explain everything so well. It is not boring. I really learn from you. You have a true calling for explaining things, so we all can understand and find interesting.
You have such a way of gluing people to the screen, and really paying attention and learning. If I was a kid again, I’d seriously consider this for a career path, based solely off your videos.
Thanks, that means a lot to hear.
I'm not a kid, and I'm considering it. (Wild imagination, heh!)
I definatly agree, I have always loved building design but this has changed how I look at everything around me.
Agreed. I' m not even a kid and considering a career path change. A friend of mine works in building inspection and now her and I nerd out on this stuff. I love your content!
Please more of this type of content, as an architect it help me to better communicate with engineers and better understand their needs.
I second that. As an electrical engineer in switchyard construction, I have to look outside of my box and at foundations and steel constructions. That concerns, for example, wind forces and forces from short-circuit loads.
Josh's videos help me a lot to understand those trades, too. A deeper insight into reinforcements would be highly appreciated.
This is such an interesting technology. Thank you for explaining it in a way non-structural engineers can understand. Well done. Love your videos!
Thanks for kind words!
Lifelong learners appreciate how your teaching style conveys a total version of the concept without requiring the burden of mathematical proof. Competence over mastery allows me the freedom to observe and graze more knowledge. Subscribed, Thanks.
My guess: it's serious because now that moisture has access to the rebar, the corrosion will accelerate weakening the joint. The rebar will swell from the corrosion causing more spalling of the concrete, which turns into a feedback loop that accelerates everything. 🤔
As a mechatronics & robotics engineer that works on weapons systems I want to give all you structural and civil engineers a shout out - thank you for designing all these targets for me! 😁
LOL...aim for the weakest; so we can replace them better !
Wow, you got me! At the beginning I didn't know what they were. After you started to explain I realized that I've been carrying one in my tool bag for almost 15 years. I picked up one of the spare studs off a jobsite and have been using it as a "Banger" to hammer things all this time. The narrow end sits on an anchor inside a box or some other narrow area and you can pound on the head with a hammer to set the anchor. The wide head helps to cordinate my hammer blows as I've never been the most cordinated with my hammer. I even lost my first Stud after a few years and found a new one on another jobsite. I consider it a very useful tool even though it's not the original intended purpose.
That's what I love about construction. When tools get used for their unintended purpose to make another task easier. Thanks for sharing!
Perhaps this is a sign that the concrete surface needed some protective coating to reduce or prevent surface water ingress. Not an immediate problem but a maintenance topic to follow. Can you do a segment on concrete surface protection ethics and one on rebar coating methods to reduce rust impact? Different climate zones also important. A winter location where salt is used on roads will impact concrete parking spaces as salt water drips off parked cars. This might be similar to or slightly different to salt air conditions in coastal areas.
Typically worse I think since road salt is harsher and more concentrated than salt from ocean moisture
Hot dipped galvanized and other forms of highly corrosion resistant rebar is widely available and costs roughly twice as much as black rebar. ln the overall cost of a major project, that additional expense would be negligible and would go a long way towards mitigating these sorts of issues. Why isn't corrosion resistant rebar required or used more commonly in US construction? To quote Randy Newman: "lt's money that matters, ln the USA."
@@frankmiller95 Most projects are designed assuming a roughly 100 years max lifespan, for which standard rebar is certainly more than adequate provided proper construction techniques are observed. That might sound short sighted, but it really isn't as most buildings become functionally obsolete after 50-75 years and wind up being abandoned or replaced with new structures anyways. On a separate note, if you've ever seen a large slab under construction, the life of a bar can be pretty brutal, and there is zero probability that the bars will not have massive and unpredictable damage of that protective coating. The type of long-lasting construction you're suggesting works much better on civil structures like roads and bridges, in which the budgets are much bigger, construction timelines are longer, reinforcement placement is more uniform and organized, and the laborers are usually of much higher skill and proficiency, so laying down bar in a "clean" fashion is much more practical.
Most salt put on roads is not regular salt. Its a less corrosive substance and often times corrosion inhibitors are added. Its unlikely there would be a significant impact from dripping as a result of road salts.
@@ajr993 Have you never seen what road salt does to the undercarriage of cars? It eats it rather quickly.
civil and structural engineering channels that actually explain things well and cover interesting and realistic situations are so few and far between so glad I found your channel.
I first became acquainted with your channel after the Champlain Towers tragedy, and I found your excellent explanations very enlightening. I'm a cinema technician, so I know nothing about structural engineering. After watching your videos, I still know nothing, but I understand it better. (PS> I live in San Francisco, where the Millennium Tower building continues to slowly tilt off center. I used to enjoy lunch at an outdoor plaza almost just across the street from it, but I just cant eat there any more because being anywhere near that building makes me really nervous. Now there's a structural engineering problem I wish you or someone could solve, for the sake of the residents and my lunch hour! )
@18:15 and if the T head is gone as well, the stud rail is like a series of nail ends without any holding power.
I learned in engineering school theres no such thing as a "minor" structural problem. There are structural issues that will become major problems down the road.
minor issues are ones that can be corrected
How is this issue fixed?
@@Mj-CWO4 Accounting says there are can be no problems with the cheaper concrete mix. Procurement agrees with accounting.
@@Mj-CWO4 rust protection. the only reason metal has to be covered by concrete is that the ph level keeps the metal from rusting. but you can also use protective coatings- so get rid of the rust and paint it.
For the next video, tell us how to fix the one where the stud heads were not sufficiently covered.
Will do. I am waiting on footage that we will get when it gets fixed so we can visually walk you through the whole process.
@@BuildingIntegrity Nice.
Ooh! I like that this feels like an educational course rather than a commentary on a topic. Very informative and great graphics, thank you!
Seems to me that the "upside down" orientation (connecting rail on top) is the better one, as the rail between the studs is then on the tension side, and will transfer the bending moment even farther out on the top skin of the slab.
better yet why not make it like a ladder 2 rails connected by rungs?
@@ThunderClawShocktrix I had the same thought later. Cost? But how cost sensitive are these sorts of parts? Probably not at all, when you account for the whole building's materials. Maybe the nail-heads isolate fracture points better than a defined edge? (I'm just making things up now.)
d00dEEE I too wondered about that. I suspect (based on no knowledge of construction techniques, I freely admit) that the problem with having them "upside down" is that when the concrete is poured it will NOT flow like water and fill ALL of the area underneath the connecting rail. It will leave air gaps, and those air gaps will compromise the integrity of the slab. As my old man used to say "opinions are like a*s-holes. Everybody has got one and some are more smelly than others". This idea of mine may be a stinker !
@@ThunderClawShocktrix You can't get the ladder rails trough a rebar 'net', but you can poke the studs trough. You could put the ladders in first, but then you'd have to weave dozens of rebar bars trough.
Some rebar could be fitted under the stud heads rather easily, or a piece of flat iron with slots cut for the studs...
@@Timoohz Aha, it all becomes clear! Mystery solved.
I had very short spell as a structural engineer designing mostly in reinforced concrete. I can remember being asked by heating and ventilation engineers whether it would be possible to have holes in the concrete next to the columns and doing calculations within the code of practice current at the time and giving them a yes or no on that basis. At that time these studs had not been invented or introduced. You have now made me rather nervous about some of my working. I am happy to say that these buildings are still standing after 52 years so so far so good.
I’m an electrical engineer and love all types of engineering. I find it interesting how nature repeats itself. Solder cracks in a very similar fashion but due to heating/cooling; creating a cold solder joint. Also when lightning hits an Integrated Circuit, the core looks like a shear punch head. I had guessed not serious now but will if left unmonitored in the future. Great Topic!
The question that the conclusion of this video raises to me is what form remedial work would take. The solution that immediately springs to mind is to seal the the slab over the stud rails with a millimetre or two of a suitable epoxy coating. This then raises another question of whether it is necessary to remove the existing small amount of corrosion before coating the slab.
If there isnt a significant loss of section by corrosion, i think that you could use the typical procedure for corroded armature repair, treating it to remove rust then coat with an epoxy bonding layer and a thicker layer of concrete on top, or on the worst case casting a capital or drop panel under the slab anchored to the column.
It would seem possible to remove the heads if they are severely damaged and remove the concrete from around the rust affected area and weld new heads slightly lower on the shafts. Then epoxy coat and replace the concrete layer covering them as mentioned above.
Though the previous post would probably be preferred provided the damage is not severe since there's less liability involved .
@@alexlail7481 The heat from welding will cause moisture in the existing concrete to form steam bubbles and cause more spalling. Then you have the problem of adhesion of new concrete to the old existing concrete. Little patches tend to just flake off.
@@brnmcc01 I think we may have different ideas as to the scope of the work...
@@brnmcc01 use epoxy it’s stronger than concrete and bonds with surrounding concrete, used it to repair warehouse floors and loading docks. A lot stronger than actual concrete
Since watching your channel, I’m inclined to think that any rusted steel is potentially a major problem! It never occurred to me to look at these things before, I’ve learned so much from your channel, thanks. The last multi-story garage I parked in I looked around, there wasn’t a spot of rust anywhere, looks like they did a great job.
If you're interested in this topic you should take a look at Practical Engineering as he recently did a while series about corrosion which is pretty interesting!
As a retired private building inspector, I can tell you if it was built that way, it likely violates code. All steel must be a certain distance from the surface of concrete, 2" if I recall correctly. This (code) is an attempt to prevent spalling. No Idea if this is a big or little deal. Did the contractor put the column (or the connecting steel in the slab) in the wrong place??!
Edit - Oh, I see now that I finished your vid.
Question 2 - wouldn't it be stronger to have the steel go across the column, maybe be welded to the column reinforcing steel? I usually see the horizontal and vertical steel tied together on construction sites.
Question 3 - How can reinforcing steel be prevented from damage due to "rising damp", moisture rising due to capillary action of porous masonry/concrete? Seems to me every building built with it sits on the ground, which is varying levels of damp/wet. What about pier or bridge columns that are in water?
Comment - State of California spent billions after the '71 and '94 earthquakes reinforcing the columns holding up the freeways as they punched right through. Interstate 10 was severely damaged in places.
6 cm in Germany if I recall correctly. I am no civil engineer, only mechanic engineer.
This channel fascinates me, fills a need I did not know I had. Every now and then I come across a gem like this on CZcams. Another was a online series teaching the Python programing language to Google employees. Always hated school, guess it was just that I experienced the wrong instructors for me.
For the learning engineers out there I have 2 clarifying points. 1) The roughly 45 deg fracture plane corresponds to the max tension principal stress of the cross section. It's not exactly the bending that causes it but a far off load causes bending and shear stress together. Bending moment is the integral of shear
2) The pull thru shear area is not the top view area he cross hatched. It is the effective perimeter times the thickness. That perimeter could be something like a diamond shape between the 4 corners, or it could be more circular if more radial ties are installed.
Overall very good explanation for non-engineers :)
i get involved in a lot of flat slab design in the UK and recently really did a deep dive into punching shear design and shear rails and comparing different codes of practice and found it really interesting how the control perimeter varies between various countries coded of practice, along with the minimum requirements and allowable contribution from the shear strength of the concrete itself, and influence of bars passing straight through the column. found a particularly funny article from the 90's talking about "shear hoops" which looked ridiculous but at the time seemed promising, and stud rails were just sort of a foot note (and called "shear combs"!)
great video definitely a great starting point for learning about punching shear and how to visualise it.
this video was fantastic - a technical explanation that I think most people can understand, whether structural engineers or not
An excellent video. A good starter for students. These stud rails are a simpler form of ligature which converts the beam/stab into a truss member. The studs take tension forces and the concrete takes the compressive forces at an inclined angle from top to bottom. Another similarity are the vertical web stiffeners on large steel I beams. The web stiffeners take the compressive forces and the flat web inbetween takes the tensile forces. This is to prevent web buckling. So in essence the forces are distributed to those components best suited for the preferred type of stress condition. In concrete ----tension is bad, compression is good. In steel --- tension is good, tension may be bad if buckling can occur. Cheers.
The stud rail should be replaced by a welded ladder design - as if you joined all the stud heads together. That would provide better ancorage and increased tensional resistance to the upper edge of the slab.
I love your explanations, so clear and concise. I didn't even bother guessing at what the problem was initially - had no idea. This is the first I've ever heard of stud rails, and it was most enlightening. Overall, however, I'm getting the disturbing message that a poured concrete building's safety is being compromised by cheaper construction methods, the stud rails are further evidence that attempts to correct the safety deficiencies are being tried, and, sometimes, ineffectively used. This is equivalent to not placing X-bar reinforcing in buildings in earthquake zones because it costs more and looks unattractive, but would you rather be in an ugly safe building in an earthquake zone, or an unsafe, attractive building, when the ground starts shaking? We all know which developers and realtors choose, but they're placing the occupant's lives at risk. I'll take safe and ugly anytime!
Interesting. Never having heard of stud rails, when you initially asked "major or minor", my answer was "no opinion".
Once you explained what they were, my assessment changed to "major problem". Not a major problem _now_, but knowing what human nature is, when told something will be a major problem in the future, the response is almost always "well, let whoever owns the property then worry about it, I don't have to spend any money now".
Anyone that suggests that it doesn't work that way for buildings should go back and look at the FIU bridge or Champlain Towers South.
The distinction between important and urgent is crucial. This problem with the stud heads in my opinion is very important, since it may cause the collapse of the building if not taken care of, but not urgent (for now) since the corrosion is still small and limited. No need to evacuate the building, for example
I retired from my construction engineering job 25 years ago. My tallest building is in Chicago at 67 floors.. I'm a Civil Engineer and a PE. I never heard of studrails before this video.. Thanx for explaining their use.
Fascinating. Thank you for presenting this in such a 'lay-friendly' manner. Would have been interested in the required treatment for the exposed stud rails.
Question- is it inevitable we will find that reinforced concrete will not stand the test of time. Wood and/or steel structures can decay however if is more or less simple to repair or replace, you can expose the problem area and repair. However reinforced concrete the rebar can deteriorate, concrete can spall. It is harder to repair, you can’t just cut out a section and replace because it is designed as a monolithic structure with engineered overlapping steel rebar. Seems to me most concrete repairs only patch and retard or cosmetically cover the problem, after the patch it isn’t really better than before.
With proper maintenance concrete structures can stand much more time than wood. Repairs, if the problem is addressed in reasonable time, can be made with the addition of more reinforcing elements on top of the existing ones generally. I think thats exactly the opposite in this aspect, as wooden and steel structures depending on the type , you'd have to replace entire pre-made elements, as on concrete structures its possible to even cast new beams and colums in extreme cases, provided the correct shoring and other procedures.
Take a look at Building integrity's "Reinforced Concrete's Number 1 Enemy" video.
Could be a sign of rusting concrete reinforcement. So I would say a serious problem.
Always interesting, always presented clearly.
Man I don't have enough data to make a firm judgement but it's definitely something I'd want looked at.
It's obvious from the photo that corrosion of the stud rails is present - eventually, the corrosion can progress to the point where the entire shear head could fail because of the severe expansion of corroded steel inside the concrete causing loss of structural integrity of the entire shear head itself.
You make engineering so interesting! If I were 50 years younger I’d consider it as a career.
a lot of work, sacrifice and lack of appreciation
@@TheLuminousOne I’m sure that is true, but, my brother is still an actively working civil engineer at age 85 and loves what he does. His wife finally convinced him to cut back to 4 days a week.
@@ohmcintyre2067 that's really impressive!
I have, in my retirement in a lndoChina country, built 2 small hotels, a house and workshop with an apartment above.
I find this series fascinating and informative. Thank you.
I spent my life as a contractor, inspector and facility director. Your videos are excellent. I watched this video and then watched it again with my son, who owns 3 construction companies. Very well done, thank you for sharing your expertise.
I'm less than a minute into your video and I have absolutely no idea whether this is a little problem or a big problem but either way it should be properly looked at by a structural engineer who knows about concrete as you can't see what's going on underneath.
An intensely unique channel. The ratio of comments to views says it all, approximately 1:100. Your videos have a become a legitimate reference source for the Engineering world.
This is so thorough and understandable. Many thanks.
No scientific/engineering background: I think they are part of the rebar for the top of the foundation piling cap where it ties into the column. I guess that it should not be close to the surface, the concrete slab has been poured too thin and it is rusting withing and will cause spalling which could continue to erode and weaken the structural integrity of the foundation and columns. I also guess this is from water ingress due to a high water table or poor drainage. Will update comment after watching video.
Finished watching. I was wrong and won't give up my nursing job! Have still learned plenty!
The stud rail is a minimal number component as compared with rebar. As such it would be advantageous to use stainless steel. My preference would be capitals where loads are high or moving; i.e. parking garage.
Excellent as always. They do this with steel decking ,by welding the studs to the decking and to the beam below the decking ,anchoring it all together.
This channel has a way of explaining things so clearly that I finish the video feeling that I have always known about the subject! Simply brilliant.
In my country we mostly do solid slab with the beams. Less weight and labor costs are lower so it becomes cheaper than flat slab
You are such an excellent communicator. Thank you for your videos!
After all your analysis coverage of the tower and this keeps me constantly looking up now in every parking structure here in salty NovaScotia
As always... excellent information from you. We know how to 'not build' columns, those that pose Punching Shear Failure. The recent condo collapse is still a great classroom where ideas can be shared,
Newtons third law for every action theres an equal and opposite reaction.Gravity is the action steel and concrete are the reaction.The more you try to cheapen the cost of construction the more you cheapen the construction.Surfside is an example.
As a retired civil inspector I am acutely aware of the need to assure compliance with plans and specifications. Cutting corners in construction can cause catastrophic if not deadly consequences.
In the heavy truck industry, "spalling" is generically called "rust jacking". You could add that to your repertoire for relating spalling to other crowds.
Rust jacking ruins trucks just like with concrete. When trucks have double frames, there are two channels tightly nested. But there's no way to ultimately prevent moisture, so rust forms and splits the beams from each other and ruins the frame.
People restoring or maintaining older equipment deal with rust more than any other problem and rust jacking presents varied and interesting results.
Mechanical engineering student here. Not going into structural, but this is still interesting to know about.
Thanks for watching. Good luck on your future in engineering. You'll love it.
Using stud rails is like getting Tommy John surgery before you actually injure your elbow and need the Tommy John surgery. Funny be cause pitchers would wait until their elbow was compromised before getting Tommy John, now some will get it before injury to avoid injury. Sounds the same to me
I was wrong, but I automatically thought rust = spalling. This is something I learned just from watching your channel. My thought was that if it was NOT of immediate concern, that the rust issue MUST be addressed. First, to remove the rust and see how much deterioration had occurred. Second, if the deterioration wasn't bad to immediately cover with a rust/waterproof paint as a very short term solution. And then there would need to be an intervention scheduled with an appropriate maintenance crew to permanently (or as permanent as possible considering the life of the property) fix the issue.
My wild guess would be that is punching shear reinforcement.
I have a BSc Civil Engineering
And in The Russian building code SP 63:13330:2011
For design of reinforced concrete structures
It’s stated clearly that the girth or thickness of the concrete provides resistance to punching shear and there is a formula that compares the punching shear resistance of the concrete slab to the axial load from the column
If the axial load from the column is greater
Then punching shear reinforcement is necessary
At the first glance it’s so unintuitive that these stud rails can provide additional strength without being connected to the columns. Amazing video.
Went around your elbow, on that explanation. 'Punch failures' leave a perpendicular line, like a shear cliff face. You're reference is to Tension induced shear failures, aka tearing.
Concrete/stone has negligible tensile strength,
Excellent explanation! I'm a non-egingeer and this provides logic to follow.
At the never completed and demolished Harmon Tower condominiums City Center, here in Las Vegas, these are where were left out by accident during construction over about 8 floors. They were up to the 25th or so floor out of the planned 45 before this discovery. Lawsuits, fears about collapse during a seismic event, the economic crash of 2008. The building was demolished floor by floor and is now being replaced by imagine that, more retail on the Las Vegas Strip.
I have seen the concrete chipping away from the tops of stud rails before. I knew it had to be structural, but until today, had no idea what stud rails were and how they spread the load to greatly reduce the effect of punch shearing. Thanks for the great explanation.
Since there is only one potential source of rust in reinforced concrete - from the reinforcing rebar matrix - this deserves attention sooner than later.
Dude, you are so amazing in Eastbound and Down!
Rust is a sign that something could be wrong. Is it all big wrong or a little wrong? I have no idea, but questioning what is happening is the first and necessary step to finding out. Simply saying "Hmmmm," and letting someone else worry about it could be the start of a disaster that won't be prevented when it could have been. Congratulations to whoever is making the inquiry!
One of the best channel in civil engineering like practical engineering.
My Furst Guess: No idea but any change of characteristic says something, and orange indicates rusts indicates water equals check it out.
I don’t know, I’ve never seen those kinds of dots before. I’m a computer engineer not a structural engineer! I’ll just watch and learn…
You should be a teacher. Thank you for this interesting video.
Would have been interesting to see how the problem could be adressed
Future video. This project just came into my office a couple weeks ago and the repair has not been implemented yet. I will follow up when it does.
No problem. Its always better when you can directly inspect rusting rebar that is generally INSIDE concrete slabs and structural columns.
This is the best channel that's very interesting and very informative I am glued to this channel thanks
another great explaintion. look forward to your content.
Yes, I guessed correctly ... in Aerospace, we call them "Doublers" but serve the same purpose ... to spread load. But the calculations are very precise ... the Rivet diameters and spacing well thought out to prevent damage in the future. This situation is minor now but the "Lying, Cheating Contractors" did a lousy job on height of the Studs as you rightly point out. The "Repair" I'd guess would be to core out Studs, re-weld new ones with correct height and pour high strength repair material in ??? But in the immediate situation, the corrosion needs to be neutralized and Studs sealed with epoxy ??? Otherwise, it'll be like the building in Tiachung, Taiwan's 1999 Earthquake ... the Hotel I used when there (6 Story) fell over completely which exposed that "smooth" rebar had be used instead the required "ribbed" ... easy to pull 16 penny nail out from the tip if the head has been cut off.
Great video, as always
Nicely explained. As a mechanic I found this extremely interesting.
Rust + concrete always makes me nervous. I'm going to guess that this is a serious problem, now back to the video.
I think it's the start of a major problem. Fixed properly, before it becomes a major problem would be best. Learned a ton about stud rails and building in general. Thanks again.
Another informative video with a great explanation. I find them easy to understand and follow. You help make this subject very interesting and I look forward to the next one.
Single Home ownership seems to be a less risky dwelling, in terms of height risks. I know nothing about construction, yet learned something about it with a touch of physics. Thank you.
Single home dwellings are also often built on columns. For basements or in coastal areas for flood reasons.
@@JCrook1028 The columns hold up massive beams, which support joists. The issues at play virtually never arise in SFR.
I think minor. It's probably spalling due to rust from water getting under the surface. But since it's the foundation floor, and not directly supporting columns, it's probably not structurally unsound. edit, had to add. I think I was half right. I figured it was rust, but I thought it was the bottom of the basement and not a slab with a level below. That's why I said it was not unsound. The slab is weaker but it would take negligence to make it a safety issue.
Not only is the shear strength reduced but it introduces another avenue for water to rust the rebar.
You are very intelligent and are great at describing engineering concepts. The answer to the collapse is in the lack of punch shear heads. CTS did not have punch shear heads but were pionts. The dynamic forces on the columns were extremely dynamic in CTS. I can duplicate the lack of shear heads by duplication of the real world forces on the pool deck slab.
Cause of the support right there it looks like a serious problem that needs resolved in a timely manner.
In Germany rebar is built like in cages - so at has 3 dimensional stability instead of only 2D compared with a rebar mat. Google for pictures with "Bewehrungskörbe" No studs needed - the vertical rebar in the cages provides support.
I'm no engineer and thank god I'm no architect, but I did pay attention in school.
Exposed rebar is always a serious problem. Rusting expands iron and steel's volume, pushing apart and cracking surrounding concrete. Cracked concrete, especially when it needs to take a lot of load, such as around pillars, is obviously a big problem. What's more is that cracks allow further oxygen and moisture into the concrete, accelerating the corrosion of the rebar. If in weather, water may also freeze in those cracks, again expanding and causing more damage.
I learned a lot by closely observing the demolition of old and not so old concrete structures, especially when it was carried out in a controlled manner. The conditions that the concrete had been exposed to, the positioning of reebar and not necessarily the age of the concrete all seemed to hold factors of condition.
Huge problem. Someone obviously spilled a whole plate of spaghetti near this column in early 1971, maybe '72 depending on the noodle quality.
I would assume its rebar rusting in the basement's floor. It must be ground water has penetrating the slab corroding the rebar and could also effected the piers. I would assume it requires investigation.
This channel is easily one of my favorite channels and this is another very good video.
Excellent presentation of a minor problem that will become a mojor one if not addressed properly. Thanks for your hard work and dedication.
Before seeing the video:
- Corrugated rebar mesh, or possibly the spiral pattern on very large rebar. Either way, too close to the surface and spalled.
- Problem depends on how much rebar is in the concrete, pattern, etc. Leaning toward, minor problem that needs fixing.
After edit:
-Never heard of a stud rail before, but does roughly what I though rebar was doing.
I enjoy listening to you talk. You are an amazing person. Keep up the good work.
Civil Engineering Terms website also mentions it can occur in foundations... "If the foundation is supported by fairly loose soil, the failure surface will not extend to the ground surface. Beyond the ultimate failure load, the load settlement plot will be steep and practically linear. This type of failure in soil is called punching shear failure."
Serious problem. The brown spots are rust from the rebar embedded in the concrete rusting. Since rust (FeO^2) occupies much more space than the original rebar, we get forces, internal to the concrete structure, which seeks to tear the concrete apart from the inside-out. This happened recently in Florida when this problem caused an apartment building to collapse.
"The New Science of Strong Materials" is a great primer book on these concepts. Technical, but also very readable for everyone.
Another fantastic video. I think that we are going to have to start referring to you as " The Professor ".
Immediately I’d say that somebody was probing to see if the piling had a footing, and if so, what were the dimensions of the footing. Perhaps they were considering adding some floors to the building, perhaps it was just to verify that it was built properly to begin with. Maybe some other retro-fits to the building were being considered.
I'm 30 seconds in. Not being an engineer, I don't know that it's a problem at all. I'm 2:40 in. What the hell do realtors have to do with engineering? Now I'm at the end of the video. I was right to say I couldn't have known, though any visual defect should raise red flags. Thank you. I learned something.
Great video. It's really inspiring to learn from a pro, subjects like this in the building industry to further ones knowledge. Thank you.