Concrete bearing pad remediation 1

[Temporaryworks]

I am detailing remediation for a bearing pad between concrete corbel and a metal-deck slab. See spalling in attached photos where you can see the top corner of the corbel is spalling.

My assumptions so far:
- Spalling is likely caused by inadequate bearing detail between corbel and metal-deck slab. The slab movement is "pulling" the corbel corner away rather than sliding on the plate as indented. Or it could be that the plate is not the full depth of the corbel seat and that the reuslting high bearing pressure is causing spalling.
- We need to remediate the corbel by introducing a suitable bearing detail - see attached snip. We will specify that the top 5mm of the corbel is to be cut back and a new pad inserted.

I would appreciate peoples thoughts on this? How would you detail this? Would a greased plate be sufficient or should I be specifying a durable non-slip coating to the plate?

Regards,

https://files.engineering.com/getfi...2e9-b2ab-084b8e50e7ba&file=Corbel_spalled.png

https://files.engineering.com/getfi...55-836c-faf15c6362cf&file=Corbel_spalled1.png

https://files.engineering.com/getfi...a458411b47&file=Bearing_plate_remediation.PNG

 

[Ingenuity]

Back in the day (decades ago) when I practiced in Sydney we used to specify HERCUSLIP COMPOSITE - manufactured by Hercules Engineering in Sydney metro area.

They are still around: Link

It is thin - 7mm thickness - and comes in various widths to accommodate your line load capacity.

It will be tough to replace the old jointing material and rout-out 5mm from the continuous corbel. You will have to stagger your joint replacement.

Do you know the make-up of the existing jointing material? If you don't, I suggest some invasive site investigation (concrete chipping and probing) to determine what was built and probable-cause of spalls.

You section does NOT seem to indicate metal-deck on the RHS of the continuous corbel. Is this a generic detail?

 

[HTURKAK]

I could not get the full picture.. Is the metal deck is for roof and is sloped towards concrete corbel? Will you pls provide the existing connection detail?

My first impression is, leak or condensation accumulation is the reason for the spalling of the concrete rather than slab pulling or bearing problem..

 

[Temporaryworks]

All, with regards to the photos - I have checked the three hyper-links in the body of the text and they work for me.

Ingenuity - the section doesn't but I have inspected the slab and it is definitely a metal-deck slab. Yes, we will stagger the joint replacement, unfortunately the floor above is a retail space which is in use throughout the day, 7 days a week. I don't have any more detail on the corbel, I have got up to the corbel and taken a look; it appears that they may have omitted the bearing detail all together as there is no gap between the metal deck and the corbel seat.

HTURKAK - It is not sloped. WE don't really have any details as the as-built drawings are lacking - if you can get onto those photo links that will aid your understanding? Why would leaking or condensation accumulation cause the issue?

Thanks all

 

[Ingenuity]

Temporaryworks:

As far as probable-cause, I think you have addressed the issues - the slab is pulling along its long axis, and the bearing joint was not detailed or constructed properly. Additionally, the concrete slab on metal-deck is an end-span, so there is angular rotation at the end - small, but present - and without an adequate bearing (or gap at the leading edge of the corbel) the metal-deck slab rotates and it tip-loads the corbel, resulting in spalling.

As far as repair execution, it will be challenging. You could consider 2 polished sheets of stainless steel to make a custom bearing (vertical) and slip (horizontal) interface, or go with a proprietary engineered system bearing strip like Hercules, or others. I would personally probably go with an pre-engineered system.

To install maybe select 1m lengths - staggered. Thin horizontal cuts will be difficult - there are sprinklers and attachments in the way. With thin horizontal concrete cuts you also have to install the selected bearing material in a thin space AND then fill in any voids such that it will be vertical bearing.

Therefore I would tend to concrete chip the tip of the corbel - 1 m lengths. As follows:

Repeat for adjacent 1 m lengths. Between each 1m length there will have to be a small gap WITHOUT a bearing strip (maybe 1 metal-deck profile width) to accommodate the grout dams-ends.

You have to be mindful of getting load into the new bearing strips uniformly, especially considering a staggered approach where stage 1 bearing strip will take load before stage 2 (adjacent) strips are installed. You will need to look at the magnitude of your loads to the corbel and consider shoring the metal-deck concrete slab ends to partially de-load the corbel so when all bearing strips are finally replaced there will be more uniform load distribution to the new bearing strips.

How old is the structure? More than 5 years where considerable creep displacements have occurred?

Make sure that your efforts here are not 'temporary works' Nothing worse that repairing the repair!

 

[Temporaryworks]

Ingenuity, that is a great post. I have already approached Hercule Engineering's supplier to ascertain which product is best suited. They have advised that 15-20mm is the minimum chase that I will need to detail because of the remedial plate thickness + grout for even bearing.

I will detail props at close centres at the hit-and-miss bays that are being cut and that the props should be hammer-tightened to provide a sort of preload.

The building is 10-15years old, it is a post-tensioned slab. I think that the main component of movement now is just long-term creep.

Yes, this will be very much a permanent solution, I have taken my "temporary works hat" off for this project!

The damming off on the side face of the hit-and-miss bays was something that I did not think about and so thanks for that.

 

[HTURKAK]

By looking the pictures , my first impression was, the metal deck is roof deck and sloped towards corbel and unheated space with cable racks etc.. The probable cold bridgings and heat loss from the roof will be the reason for condensation around corbel together with roof leaks and in long term,the result will be spalling of plaster and concrete.

However, now i learned that the floor above is a retail space which should have floor finish ( may be ceramic tiling ? ). The radical solution will be insertion of rubber or neoprene strip which requires lifting of composite deck to have a working height which will be costly..

It is pity that they did not provide pad or at least chamfering at corner of the corbel.

If you post top view , a picture of the corbel line at retail floor, we can guess the cost of repair.

IMO, if i were in your shoes, do nothing with small surface repair is an option or try to chamfer the corner and repair the surface.