1. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : concrete
posttensioning:
- performed on site
- tension the steel tendons after the concrete is cast
CONSTRUCTION AND DETAILING 1

2. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : concrete
precast concrete systems:
- precast slabs, beams, tees, one-way spanning units
- cast and cured in a factory / plant
- transported as components to site
- set in place on site
prestressed for greater structural efficiency
- supported by
- walls: insitu concrete / precast concrete / masonry loadbearing
- frames: steel / insitu concrete / precast concrete
CONSTRUCTION AND DETAILING 1

3. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : concrete
- advantages
- less depth
- reduced weight
- longer spans
- disadvantages
- modular nature not suitable for irregular building shapes
- generally standard sizes
- all service opening must be predetermined
- cannot chase or core into slab
(unless first analysed by engineer although still risky)
CONSTRUCTION AND DETAILING 1

4. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : concrete
hollow core slabs:
- one-way spanning units
placed on in-situ or precast concrete beams /
steel beams / masonry
cast in the factory with
smooth finish for painting or floor finish
delivered so site
positioned with cranes
CONSTRUCTION AND DETAILING 1

5. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : concrete
precast ribs with infill blocks:
- ribs with blocks are one-way spanning units
- supported on
- in-situ or precast concrete beams
- steel beams
- masonry walls
- infill blocks
- made of concrete or clay
- hollow or solid
- cast in the factory
- delivered to site
- positioned without cranes
- reinforced concrete topping cast over
- forms part of the structure
CONSTRUCTION AND DETAILING 1

6. CONSTRUCTION AND DETAILING 1
steel
CONSTRUCTION AND DETAILING 1

7. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : steel
- steel beams or joists to support
- metal decking
- precast concrete slabs
- light-gauge steel joists
- light, stable, span long distances
- easily assembled
- lightweight, non-combustible
floor structure
- laid out at certain spacings
- depending on loads of floor
- spans:
- 150x40mm between 3m – 4,2m
- 300x65mm between 5.4m – 8m
- covered with
- rc concrete over metal decking
- timber subflooring
CONSTRUCTION AND DETAILING 1

8. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : steel
- metal decking
- corrugated
- increase stiffness and spanning
- acts as formwork for insitu concrete slab
- decking panels secured with studs
- welded or rivetted through to the beams
- panels fastened to each other with screws / welds / seams
  - types
- steel beam decking
- open web steel joist decking
- types of steel beam decking:
- form decking
- composite decking
- cellular decking
CONSTRUCTION AND DETAILING 1

9. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : steel
form decking:
- permanent formwork
- for reinforced concrete slab
- until slab can support itself and live load
composite decking:
- tensile reinforcement for concrete slab
- bonded to it with embossed rib patterns
- composite action achieved
- between slab and beams
- welding shear studs through decking
onto beam below
cellular decking:
- welding corrugated sheet to flat sheet
- series of concealed spaces formed for
- electrical and communication services through floor outlets
- acoustic ceiling when filled with glass fibre
CONSTRUCTION AND DETAILING 1

10. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : steel
open-web joist framing:
floor deck may span across joists
(spacing dependent on floor load)
- floor deck comprised of
- metal decking with concrete fill
- precast concrete panels
- plywood panels / timber planking
- horizontal bridging
- prevent lateral movement of joist chords
- spaced between 3m – 6m
CONSTRUCTION AND DETAILING 1

11. CONSTRUCTION AND DETAILING 1
timber
CONSTRUCTION AND DETAILING 1

12. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : timber
- joists / beams to support
- planking / decking
- subflooring
- joists / beams supported by
- posts
- loadbearing walls
- wood joist floors
- form a level platform with wood panel sheathing or sub-flooring
- combustible: rely on flooring and ceiling for fire resistance
- susceptible to decay and insects: drainage and ventilation
- may be exposed (without ceiling) or concealed (with ceiling)
- if exposed
- susceptible to sound transmission
- lacks concealed space for insulation, service reticulation
CONSTRUCTION AND DETAILING 1

13. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : timber
 - joists supported by
- wood stud framing
- wood or steel beams
- loadbearing masonry
- concrete wall
lateral support for joist ends
- rim joist or header
-     additional support
- double end joists
- stiffness of joist framing is more important than its strength
deeper joists spread further apart better stiffness THAN
shallower joists closer together
spans dependent on loads, joist size, type of timber
depth: span/16 (rule of thumb)
CONSTRUCTION AND DETAILING 1

14. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : timber
- spacing: approx. 400mm centres
- spacing cavities for piping, services, insulation
- sizes and span ranges: approx. 3 – 5m
- 150x50mm up to 3m
- 200x50mm between 2.4m – 3.6m
- 250x50mm between 3m – 4.2m
- 300x50mm between 3.6m– 5.4m
CONSTRUCTION AND DETAILING 1

15. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : timber
- finish to floor structure
- floor finish applied over timber plank sub-flooring
- underside may be left exposed
- ceiling applied directly to joist or suspended below
CONSTRUCTION AND DETAILING 1

16. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : timber
- types:
- subflooring
- decking
timber subflooring:
- closely spaced joists with timber panel subflooring over
- joists
- openings or cuts may be made for services
- supported on load-bearing walls
- wrapped in dpm, built into the corbelled brickwork wall
- fixed to steel brackets bolted onto concrete walls
- bridging between joists
- stiffen the floor construction
- metal or timber cross bracing OR
- full depth blocking at 2.4m intervals
- omitted if joist ends are supported laterally against rotation and edges restrained by subflooring
CONSTRUCTION AND DETAILING 1

17. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : timber
 - subflooring
- material that spans across floor joists
- working platform during construction
- provides a base for finish flooring
- typically plywood
- underlay and screeds
- impact (load) resistance
- sound insulation
- smooth surface
for flooring material
decking:
- types:
- timber planking
- plywood
- stressed-skin panels
CONSTRUCTION AND DETAILING 1

18. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : timber
timber planking:
- timber planks laid across spaced joists
- laid perpendicular to joists / beams
- solid or laminated strip flooring
plywood:
- 30mm thick over 1.2m span
- laid continuously over 2 spans
- tongue and groove edges
stressed-skin panels:
- plywood facing bonded to distribute loads
- with adhesive
- to solid timber stringers and cross bracings
- integrated into single component with:
- thermal insulation, vapour retarder, interior finish
CONSTRUCTION AND DETAILING 1

19. CONSTRUCTION AND DETAILING 1
SUSPENDED FLOORS : sources
Ching, F.D.K (2008) Building Construction Illustrated 4th edition, John Wiley & Sons: New York.
Chapter 4: Floor Systems
Chapter 5: Wall Systems
Grobbelaar, A (2010) Building Construction & Graphic Standards, Anglo-Rand Publications: South Africa.
CONSTRUCTION AND DETAILING 1