Slab Strengthening for Compactus Loading

[asixth]

Hi guys

I have an existing reinforced concrete that I need to design for a compactus loading which exceeds the design strength of the slab.

The compactus will be position roughly midspan of the middle span of the slab (between grids 13 and 14).

The slab is one way spanning onto the beams, I have gone through and done some calculations of this slab and I am not happy with the design of the slab in general. I do not believe that it has sufficient negative moment reinforcement over the beams (for the design load prior to the compactus).

However, I need to look at methods to strengthen this slab. Firstly I think of FRP strengthening. Primarily the slab needs to be strengthened at negative moments regions of the beams, deflections won't be excessive and the slab will be covered so any additional cracking will not be visual.

What would be other strengthening methods and how would the cost compare to that of FRP strengthening.

All help will be appreciated.

 

[ishvaaag]

As long as the main beams stay good and ample enough you can reinforce with steel for composite or noncomposite action. Main question is in what degree the load is dynamic, if scarcely so maybe just hilti anchors to the sides of the beams is enough.

 

[RHTPE]

asixth - By "compactus" are referring to a trash compactor of sorts?

You don't indicate the size of the "compactus" relative to the slab's span - this might help to provide additional insight.

You say "I do not believe that it (the slab) has sufficient negative moment reinforcement over the beams (for the design load prior to the compactus)." Then you say "...the slab needs to be strengthened at negative moments regions of the beams, ..." - don't you mean slabs?

Obviously it will be least costly if you can keep all remedial work on top of the floor structure and not have to do anything to the underside.



Ralph
Structures Consulting
Northeast USA

 

[rowingengineer]

A compactus is a large filling (paper) system, asixth, what type do you have?

What is the positive reo like? Can you redistribute to the bottom reo some of the loading?

If the strengthening is for the compactus and not the original possibly inadequate design, I would look at providing beams under the wheel runs. I normally like to see if they can accept a small setup into the filling system first, if not I would either put the beams under the slab, and play with the stiffness and back jacking, to get the beam to take the loading.



Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[asixth]

That is correct, the slab needs strengthening at negative moment regions, I am happy with the design of the beams except that shear reinforcement looks like it terminates to close to the support.

Unsure of the type of compactus but the max loading weight is 12t (120kN/26kips).

The bottom reinforcement is okay because there is unbalanced moment from the end-spans trying to hog the middle span.

 

[hokie66]

I agree with adding steel beams under the slabs, spanning between the existing concrete beams.

 

[rowingengineer]

I would try to find out the structure of the compactus instead of using a kPa, this is due to run of the machine. Generally they have wheels on tracks or a mechanical moving system (I always hope for the tracks), this will make a difference to your design because if you have too much deflection and the compactus can't role easily.



Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it