I Broke These Concrete Beams - Design Principles from Beam Failures

I constructed six reinforced concrete beams in the lab and then loaded them to failure. What can we learn about reinforced concrete behavior and good design principles from these tests?

Two of the beams exhibited flexural failures with lots of flexural cracking and ultimate crushing of the concrete in compression. Two beams had traditional shear failures, with a diagonal crack extending through the section. Finally, two beams had anchorage failures, where the ends of the bars pulled out at the support. Good beam design encourages flexural failures because of its ductility and predictability.

Chapters:
0:00 Beam Fabrication
0:49 Test Setup
1:23 Beam 1 Test
2:31 Beam 2 Test
3:28 Beam 3 Test
4:19 Beam 4 Test
5:31 Beam 5 Test
6:23 Beam 6 Test
7:03 Results
8:15 Lessons Learned

[jjalandoon]

You will have to repeat #5 and 6 beams with rebars extended outside the beam to prevent anchorage failiure.

[rinflin]

I used to had a fear of buildings falling, I used to believe buildings just crack, but this video made me aware that buildings bend and they show signs before falling. Now i can rest well looking at concrete ceiling. Thank you so much

[frantisekhladky]

This is very beautiful video. I work 15yaers like structural engineer but when you see it real it si much more better than read in books ! Thanks !

[cleisonarmandomanriqueagui]

best youtube channel for civil indsutry ever . experience is better than theory

[MuhammadYusuf-trxe]

This has to be the best video I've seen this year, so informative. Subscribing right away

[OGTennyson]

Appreciate this type of content. Keep up the good work sir 🙏🏾

[franciscomendoza]

I LOVED ur videos, especially this, it's kind of hard to find this kind of material with so much quality and professionalism, would like to see more domestic examples from other countries constructive processes and material, as in Mexico is used a pre fabricated steel elements called Armex, and see the pros and cons of confinement process, or called also load-bearing walls.

Greetings guys! Keep the quality <3

[petewilkinson]

Dang, I was excited for beam #6. Would love to see it’s potential after anchorage failure issue is addressed.

[ashishbavdane]

Appreciate your effort! Needs more such stuff!

[Tobiwan-ru]

Video like this are very resourceful, please make more vids like this sir.

[ravshanbekmavlonov]

Wonderful beam test and analysis! Thanks for the helpful information.

[ytrew]

Asked Claude 3.5 :
Let me explain why rebars are often placed at the bottom of beams:

Tension zone:
When a beam is loaded from the top, the bottom of the beam experiences tension.
Concrete is strong in compression but weak in tension.
Steel rebars are added to the bottom to handle these tensile forces.

Bending moment:
The maximum bending moment in a simply supported beam typically occurs at the middle of the span.
This creates the greatest tension at the bottom of the beam in this area.

Compression zone:
The top of the beam is typically in compression when loaded from above.
Concrete is already strong in compression, so it often doesn't need as much reinforcement there.

Testing to failure:
In tests, placing the rebar at the bottom allows researchers to observe how the beam behaves under typical loading conditions.
They can see how the concrete cracks and how the steel reinforcement performs.

However, it's important to note that in real-world applications, beams often do have some reinforcement at the top as well, especially for:
Negative bending moments over supports in continuous beams
Shrinkage and temperature control
Torsional resistance
Compression reinforcement in some designs

[lonewolf]

Fantastic video, and a question, if you were to bend the rebar ends to allow the ends of the beam to be connected to the bottom of the beam in that way wouldn't that be able to prevent the ancor failure?

[LTVoyager]

It appeared that your supports were at the end of the bottom rebar or even somewhat outside of them. You need the steel to extend well beyond the supports.

[Nick]

This experiment more related to a pre-cast design otherwise development length plays a big role here. Top and bottom extra bars are also play a big role in construction. Also at the L2 should have stirrups closer than in the mid section.

[msamadzad]

Thanks; please post concrete compressive strengths too.

[ChristianWagner]

What was the calculated load capacity of each beam compared to the observed load capacity at failure? In other words, how close do our calculations match reality?

[ulisesandrade]

I’m setting a huge HVAC EF heavy piece of equipment on a concrete roof, the roof underneath has concrete beams holding the weight… I’m worried now

[jaykay]

I have been searching for this for a very long time )

[samuelpaitich]

Good stuff. It looks like bearing failures for those last two. A horizontal U-bar or two at each end at the bottom should do the trick