Existing concrete spandrel beam replacement

[Engin1]

Hello Everyone,
I am working on a job to replace an existing beam and maybe the columns. The building is five story and the beams at this corner are in very bad shape, they are about 20ft span. There is no floor at this corner but new floor will be installed. I need suggestions on new beam to existing column connections and existing beams to new column connections. Please advise!
thanks!!

 

[Greenalleycat]

I advise you to pretty please give us some better photos, that angle is making my brain hurt
Got any existing drawings? A plan view showing layout, beam and column sizes, etc?
Any idea of reinforcement content?
Have you got any ideas yourself that you could propose for our review - after all, you're way more familiar with what is going on here than us
Is this seismic or no?

 

[Engin1]

Hello Greenalleycat,
Sorry for the wrong angle photo. That photo shows the damage of the beam. I have attached more photos.
The building is more than 100 years old. I don't have much experience on concrete building, the previous engineer worked on this repair left. The column is L shape 2'8"x2'8"x1'6"on lower floor and 2'8"x2'8"x1'1" on upper floor. The spandrel beam is 2'3" x10" with brick face. No reinforcement info. It's in Seismic Design Category B. More pictures in the attachment. thanks

 

[SlideRuleEra]

The building is five story and the beams at this corner are in very bad shape...
The building is more than 100 years old.
No reinforcement info.
...the previous engineer worked on this repair left.

Condition of the entire building needs to be evaluated before beginning design, including tests. Concrete that is 100+ years old is different than modern concrete... even when it was new.

If you do proceed, I would look into creating full length stepped columns to support existing beams. Do this on each floor all the way down to the foundation.

The previous engineer likely made the best decision.

 

[Engin1]

Testing was done, the strength of the concrete is about 3500 psi by testing company. The entire building needs to be repaired, and this corner needs to be replaced. I am thinking to replace the two beams on each floor and the L shape column. I am thinking the beam will be precast because of the shape of the spandrel beam. The existing columns supporting the new beams will be repaired. I need advice on how to connect the new beam to the existing columns.
I know the previous engineer made the best decision, and I did not expect to stay so long to see the construction of this project after 5 years. Anyway, I have to solve the problem now. thanks

 

[Enable]

You need more than just compressive tests. You need to evaluate the in-situ condition of the reinforcing steel and figure out where it is in the column / surrounding elements. You also want to know what kind of reinforcing steel you are dealing with (condition, shape, grade, weldability, etc) as that will inform your design options. Also, durability properties of the concrete would be nice.

I'd be very hesitant to use pre-cast. Usually in the repair of structures we try to maintain as much ductility as possible to help us with the fact there are a lot of unknowns. Precast in lieu of an existing CIP elements seems like it's going in the opposite direction.

Given the condition I would be tempted to create a concrete encased steel structure (running from new footing to roof) inside the existing openings, if a reduced size would be viable. The existing column would be connected via ties that go through beam flange or something of the sort (maybe a collar). Alternatively, CIP beams with a shelf angle + key + dowels might work but this option needs a lot more care; and if CIP I'd seriously consider going the route of SlideRuleEra with new columns supporting new beams.

Before you design anything you need more information on the existing IMHO.

 

[Greenalleycat]

Not sure of how it works for you guys, but here you have to be quite careful with replacing old building elements in seismic zones
There's a lot of complexity to how the building performs and you really need to make sure you're factoring all of that in with your design
That would begin with understanding how the original structure was built (reinforcement etc) to work out capacities of the elements and so on

 

[Brad805]

you attached a .rar file. Where are you in the world? If you do not have experience with concrete can you advise them to hire someone that does?

 

[hokie66]

I'm not going to try to open that .rar file. But your first photo looks suspiciously like a steel building, some of it partially encased in concrete. What was the building used for, perhaps some type of factory building? Looks like corrosion is your main issue. What caused it?

 

[Engin1]

Enable, thanks for your suggestion.
We do not have much info regarding the existing reinforcing inside the concrete. The rebar has been tested.
Because it's historical building, we cannot change it's size. Here is what I think, please advise if this is feasible or makes sense:
1. Remove the concrete of the two beams (at each floor), but leave the rebar going into the columns, I know this is a lot of work for contractor.
2. same time, Remove the L shape column at the corner.
3. Remove several inches of concrete of the columns which the two beams connect to, do not cut the rebar. The reason is that, it already has crack and needs repair. Then add pins and rebar and pour new concrete against the existing columns floor to floor.
4. Install new rebar for the beams and pour the beams floor to floor with shelf for the floor.
5. Pour the floor using lightweight concrete and light gauge metal deck.

Please advise.
thanks

 

[Engin1]

It's a concrete building, old factory and abandoned for many years. Yes, rust is the problem. I think it's caused by lack of concrete cover and maintenance, and water.

instead of precast, I am thinking to replace with CIP. We can add more rebar after they remove the concrete beam, leaving the existing rebar connecting to the existing columns.

 

[dik]

As noted, I think you would be far futher ahead, redoing the structure in steel. It's too difficult to determine the existing steel and concrete strenght as well as the type and amount of reinforcing. There are too many unknowns about the existing to move forward. What is the environment? and with that large an elevator shaft, what sort of loading are you looking at?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Engin1]

Redo this portion with steel or redo the whole building with steel? Using steel beams with epoxy bolts? It's a historical building, it has to be encased if using steel columns and beams. It will be a hotel room, 40 psf live load. thanks

 

[NOLAscience]

It looks like there has already been a repair to the column. Am I seeing that right?

 

[Engin1]

It looks like there has already been a repair to the column. Am I seeing that right?

That was done by the previous owner, just concrete surface parging, nothing structural.