Large concrete floor plate to scheme - opninion please?
Large concrete floor plate to scheme - opninion please?
(OP)
Hello,
I have a large concrete retail building to design - basement plus 3 storeys. the building footprint is approx. 40,000 m sq so a significant size. Basement and Ground floor will be car parks with retail usage on the upper floors. The column grid is locked in at 8m x 16m (client request) so a banded post tensioned slab is out as 16m is too far to span for the slab. I'm thinking in-situ beams spanning 8m supporting precast hollow core slabs spanning the 16m.
Does anyone have an opinion on this system? Apart for the obvious constraints with hollow core slabs - floor void restrictions, cantilevers etc, is there anything else I should be concerned about..?
Any advice would be appreciated.
Thanks
I have a large concrete retail building to design - basement plus 3 storeys. the building footprint is approx. 40,000 m sq so a significant size. Basement and Ground floor will be car parks with retail usage on the upper floors. The column grid is locked in at 8m x 16m (client request) so a banded post tensioned slab is out as 16m is too far to span for the slab. I'm thinking in-situ beams spanning 8m supporting precast hollow core slabs spanning the 16m.
Does anyone have an opinion on this system? Apart for the obvious constraints with hollow core slabs - floor void restrictions, cantilevers etc, is there anything else I should be concerned about..?
Any advice would be appreciated.
Thanks






RE: Large concrete floor plate to scheme - opninion please?
There's a system by Peikko called delta beam where they send steel beams (with or without fire rating) that are flush framed into the hollow-core. You end up with a completely flat floor. It's a pre-eng product too. Minimal shoring compared to cst-in place beams.
RE: Large concrete floor plate to scheme - opninion please?
are there any general issues with hollow core slabs that would make them disadvantageous for a floor plate of this size? the building will be in the middle east so I will need movement joints every 30 - 40m. something is telling me this might cause some issues with the slab layout? i'm not sure you can achieve articulation in a hollow core slab to insitu beam connection..?
RE: Large concrete floor plate to scheme - opninion please?
Don't know where the project is located, but here in the U.S. this might be done with precast double tees spanning the 16m direction bearing on precast inverted T-beams.
I'm not that familiar with the design load capabilities of the double tees and their ability to meet the required design loads for retail spaces, but these spans are quite common for parking garages.
Ralph
Structures Consulting
Northeast USA
RE: Large concrete floor plate to scheme - opninion please?
The upper-most storey I would frame with hollow-core as double tees are too thick for that i think.
RE: Large concrete floor plate to scheme - opninion please?
Play with your beam width to optimize your slab spans.
RE: Large concrete floor plate to scheme - opninion please?
RE: Large concrete floor plate to scheme - opninion please?
16m for an insitu PT beam seems excessive, i usually try to keep spans to 10-11m max for commercial use loads. i can always deepen the beams however.
the building will be subject to 50 degree celcius in summer so the requirements for movement joints are more strict than australia or the US.
RE: Large concrete floor plate to scheme - opninion please?
Most experienced PT designers would suggest that they be designed purely as a one way system rather than analysing and designing them in a plate style FEM program however. And make sure for those sort of spans you are using a proper cracked long term deflection calculation, not a long term deflection fudge factor which should never be used for PT members.
RE: Large concrete floor plate to scheme - opninion please?
previously, when designing PT I used the program Rapt (for a preliminary design, PT contractor carried out detailed design). for that case I simply analysed each band beam and slab run individually.
however for this project i need to use the frames as moment resisting for stability as the cores will not be sufficient. normally I would analyse the frame in Staad Pro and then design the beams and columns for the critical moments etc. Can i use this same approach if the frame is PT, i.e analyse the frame in staad for the gravity and lateral loads and then simply design the beams in Raapt using the results of the analysis?
RE: Large concrete floor plate to scheme - opninion please?
Do the lateral load analysis in your frame software.
The results of this can be input into RAPT for each design strip as a moment/shear diagram/envelope as a wind load or earthquake load case.
For the gravity load and PT cases analyse them in RAPT. You could compare the gravity load results to the frame program results if you are unsure.
But make sure that the PT subcontractor designs the same way. Beam and slab structures often give weird results in FEM design programs. And make sure they do not include the slab tendons parallel to the beams in the beam design. Some designers in the Middle East and other areas have a bad habit of doing this.
RE: Large concrete floor plate to scheme - opninion please?