Existing Suspended Slab Rectifications

[engoaus]

Hi All,

Would love any thoughts/better ideas on this predicament, especially if anyone has dealt with a similar situation in the past:

Existing Scenario:

• 100mm thick suspended slab (combination of open balcony/partial kitchen above, low head-height garage below)
• Simply supported 3.7m span to single-leaf brick walls without any slip joints,
• Unknown f’c, reo and footings (however engaged brick piers in garage level below)
• Significant full-depth shrinkage cracking in secondary direction (unsure if due to lack of secondary direction reo or slip joints or both), which leaks through in the rain
• Lack of falls
• Unsound prop added at some stage under kitchen to SOG below (has noticeably settled here); assume due to excessive deflections with large SDL

Concerns:

• Strength/deflection concerns – obviously even with heavy reo, running this to current code doesn’t work as is, and the prop is not good
• External slab falls – needs to drain
• Waterproofing to garage below – electrical appliances in there!
• Rectification options are limited as removing half the kitchen or having an internal step with a new slab isn’t an option and limited existing head-room in garage below

Options:

• To achieve falls:
  • Lightweight tiles on stilts, less intensive stiffening/strengthening below but waterproofing issues difficult to solidly resolve (water would still end up getting to slab under and pond etc)
  • Topping slab to achieve falls, adding in waterproofed control joints, but heavy load increases so more intensive stiffening/strengthening
• To stiffen/strengthen:
  • Sika CarboDur strips (CFRP) to soffit, maintaining current slab schematic and enabling toppings without too much extra load onto existing footings, less intrusive on head room in garage below but very expensive,
  • Add steel beams under the slab to span between engaged piers, thus flipping the slab span direction, gaining the benefit of continuity but potentially won’t work if no reo in this direction and with the full-depth cracks – would need to have slab scanning performed to get a better idea? Also more intrusive into headroom below

Cheers all!