I was told many years ago from an Engineer that the Concrete in structures is calculated as negative strength.
All of the strength comes from the reinforcing steel and the concrete just keeps the reinforcing steel in place.
This may be true for tensile strength, but it's not true for compressive strength. Concrete has excellent compressive strength but it lacks tensile strength. That's why pre-cast horizontal beams have all the re-bar at the bottom of the beam. When a horizontal beam flexes under a load, the top of the beam is under compression and the bottom is under tension and that's where the steel is needed.
Axis of orientation bears on this. We were doing a concrete building in California for the horizontal structural beams the rebar was tensioned before the pour. After the concrete had set the rebar was cut off leaving the concrete under compression. Of course this doesn't apply to the OPs photo.
Interesting. I did not know you could tension rebar. I knew cables were pre tensioned.
They do not used the Pretension cables as much as they use the Post Tension these days to my knowledge.
Most Post Tension cables are what they call non bonded.
They are in a greased sleeve that allows the cable to move with in the concrete a live loads change
They also use them where they have unstable ground and want to pull the concrete together to stabilize the concrete
(1) 1/2 inch cable from what I have been told equals a #11 bar that is a 1 1/8 inch bar,
Kinda crazy what technology can do.
I worked in an 6 level underground parking structure in down town Lost Angeles years ago shoring up damaged Columns with Steel Beams (the columns had small fractures non like the pic in the original post created by the North Ridge Quake) as the welders would get set up for the day I would walk around looking at stuff.
The walls to the underground structure had up to an 1 1/2 inch gap between the floors.
Now this was an underground Structure with the dirt pressing against the walls.
Then I noticed spawled out concrete concrete in the floor support beams overhead with rusted , very rusted bonded cables these are cables with out the greased sleeves they are like rebar that is connected directly to the concrete.
I would talk to my boss every day and I told him what I seen when walking around.
He came out to the project and I walked him around the project and pointed out what i found.
He was shocked as none of the Engineers mentioned anything about the Beams just the Columns.
He then asked what I thought should be done to fix the issues.
I told him that I was very happy that I was only the Welding Inspector on the project and that I did not have the License to do Concrete in the jurisdiction and that I did not have my Pre Tention/ Post Tension Certification.
He just looked at me funny.
Well they shut the project down for further investigation of the project.
Do not know if and when they ever started the project back up.
I am just happy that I was never called back on that project. It is a liability trap project for anyone involved.
Earthquakes can do strange things to structures.
The Engineers engineer building to with stand Earthquakes just long enough to get people to safety.
There is no such thing as an Earthquake Proof Structure
It looks to me that the Column in the 1st pic did what it needed to do.
It did fail but the structure did not collapses 100%.
They put a lot more Horizontal ties in these days that the use to do to hold the Columns together better when thing get to moving when they are not supposed to be moving.
