Help me identify this floor plate system? 1

[clarke1973]

I am currently tasked with doing design checks on an existing vacant shell building, which is to be fit out as a retail store. The single storey building is roughly 5 months old but there are no available structural as-built or design drawings available.

We have prepared a spec for some investigative work - exposing slab and column reinforcement, excavation to measure foundations, concrete core strength test etc. I have not visited the site yet, but from the attached photo, can anyone tell me what this floor plate system is? It looks like a series of band beams spanning across the columns (grid is 10.2m x 9.5m) with a 2 way slab in between, same depth as the bands. Or is a flat slab system? the orange rectangular strips on the under side of the slab are confusing me though.
Is there a possibility it could be pre-stressed?

Any advice would be much appreciated.
Thanks

 

[jdcollins]

I think the strips under the slab could possibly be forms that are unstripped (or foam forms meant to be left?) to create a pan joist system. The wide beams could potentially be post-tensioned. X-raying the side of the beam (if the orange "forms" can come out) may help you determine.

The big question is where is this building located that a 5 month old building has no existing design drawings available?

 

[Guest262653]

This looks like a waffle slab with band beams and hollow masonry units (the orange strips and sqaures) to reduce the slab weight.

 

[clarke1973]

Thanks for the responses. The building is in the middle east (Saudi). Client / contractor issues with payment so no drawings/calcs were handed over.

avscorreia - can you explain how the waffle slab works with the masonary units. is the the slab cast insitu around the units, with the bottom reinforcement in between the units spanning in the same direction?

 

[Guest262653]

Yes. The units are laid directly on top of the formwork, bottom rebar is installed in band beams and ribs (2 way or 1 way) formed by the space between the masonry units, top rebar is installed and then the whole thing is filled up with concrete. Usually there's a compression concrete layer between 3 to 6 cm above the masonry units. I've seen this also applied to post tensioned slabs, making the ribs wider to acommodate the post tension cables. In Portugal this system has been applied as a cheaper replacement for the recoverable plastic forms in the last 20 or 30 years. Although the final slab weight is a bit higher, you do get some advantages in terms of acoustic and thermal performance.

FERCA has been selling slab masonry units for a long time. You can check their system and a typical slab section at the following link:

FERCA-BLOCO

 

[hokie66]

The conclusions about the system seem correct, but for a new structure, the legal issues need to be sorted out before the building is used. I wouldn't accept a commission to do "design checks" on a new building without being able to access the design.

 

[SteelPE]

A 5 month old building without any design drawings. Something doesn't smell right, I would walk away from the project (something you probably can't do) and tell the client to call the original designer to do an investigation or get you the design documents.

 

[pappyirl]

I think I saw this building, is it in Riyadh? I would guess it is not post tensioned, there are no anchor voids visible on the mezzanine level, although it could be stressed from the other side. Grout tubes on the top or side of the slab would be a giveaway for a bonded system.

Similar to a waffle slab with bricks instead of voids. 2 way slab based on those dimensions, looks like middle strip would be lighter and have a reduced moment of inertia than a conventional solid slab. This seems to be a popular form of construction in continental Europe, particularly for residential buildings.

 

[clarke1973]

pappyirl - there was too much dirt and dust on top of the beams for me to check for grout tubes, although they could have been stressed from the beam face on the opposite side. we just received design reinforcement drawings from the building owner (schedule only, no details) and translated them from arabic. the reinforcement in the beams is minimal - maximum 6T16's top and bottom in a 1600w x 400d beam. if the drgs are correct this suggests to me that the beams are PT and the reinforcement drawing was prepared by a separate sub-contractor.
your thoughts?

SteelPE - agree with your concerns. initially we were promised full detailed drgs and calcs from the building owner. my client is only leasing the building for a 10 year period so the building owner should have been responsible for providing this info.

 

[pappyirl]

The reinforcement is so light it would suggest that the beams might be post tensioned, the depths would also suggest this to be the case. The schedule might indicate spirals or small but numerous U-bars or links for the PT anti-burst. It should also be possible to locate the stressing pocket and remove the packing to see what system was used and the number of strands. If an unbonded system was used there would not be any grout pipes but possibly larger stressing pockets. The profile will be difficult to ascertain, scanning will be of limited use, you really need the drawings.If people haven’t been paid it will obviously be difficult to get the information you need.