Joist Floor Systems: General Framing Layout and SNI Requirements
1. Joist Floor System
Joist Floor Systems
General framing layout of
the pan joist system.
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2. One-Way Joist
Construction
Definition: Pan joist floor
systems are series of closely
spaced cast-in-place T-beams
or joists used for long-span
floors with relatively light
loads. Typically removable
metal forms (fillers or pans)
are used to form joists.
MacGregor, Fig. 10-28
One-Way Joist Construction
Details of ribbed floor with
removable steel pans.
Ribbed-floor cross sections.
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3. One-Way Joist
Construction
The design of a ribbed floor
with steel pan forms and
average weight of the floor.
One-Way Joist Construction
The design of a ribbed floor with steel pan forms and
average weight of the floor.
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4. One-Way Joist Construction
Joist Details
Joist Floor Systems
• SNI Requirements for Joist Construction
(Sec. 10.11, SNI 2847)
– Slabs and ribs must be cast monolithically.
– Ribs must be spaced consistently
– Ribs may not be less than 100 mm in width
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5. Joist Floor Systems
• SNI Requirements for Joist Construction (cont.)
(Sec. 10.11, SNI 2847)
– Depth of ribs may not be more than 3.5 times
the minimum rib width
– Clear spacing between ribs shall not exceed 750
mm.
** Ribbed slabs not meeting these requirements
are designed as slabs and beams. **
Joist Floor Systems
• Slab Thickness
– (SNI Sec. 10.11.6.1)
t ≥ 50 mm for joist formed with 500 mm wide pans
t ≥ 62,5 mm for joist formed with 750 mm wide pans
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6. Joist Floor Systems
• Slab Thickness (cont.)
– Building codes give minimum fire resistance rating:
1-hour fire rating: 20 mm. cover, 75-90 mm slab
thickness
2-hour fire rating: 25 mm. cover, 110 mm slab
thickness
Joist Floor
Systems
• Standard Removable
Form Dimensions
– Note the shapes
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7. Joist Floor Systems
• Standard Removable Form Dimensions
– Standard Widths: 500 mm. & 750 mm.
(measured at bottom of ribs)
– Standard Depths: 150, 200, 250, 300, 350, 400
or 500 mm.
Joist Floor Systems
• Standard Removable Form Dimensions (cont.)
– End Forms: one end is closed (built-in) to form
the supporting beam
– Tapered End Forms: provide additional shear
capacity at ends of joists by tapering ends to
increase rib width.
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8. Joist Slabs
Standard Pan Joist Form
Dimensions
Ref. CECO Concrete Construction
Catalog
Joist Slabs
Standard Pan Joist Form
Dimensions
Ref. CECO Concrete Construction
Catalog
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9. Joist Floor Systems
• Laying Out Pan Joist Floors
– Rib/slab thickness
• Governed by strength, fire rating, available space
– Overall depth and rib thickness
• Governed by deflections and shear
Joist Floor Systems
• Laying Out Pan Joist Floors (cont.)
– Typically no stirrups are used in joists
– Reducing Forming Costs:
• Use constant joist depth for entire floor
• Use same depth for joists and beams (not
always possible)
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10. Joist Floor Systems
• Distribution Ribs
–Placed perpendicular to joists*
–Spans < 6m.: None
–Spans 6-9 m.: Provided a midspan
–Spans > 9 m.: Provided at third-points
–At least one continuous 13mm bar is provided
at top and bottom of distribution rib.
*Note: not required by the Code, but typically
used in construction
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