According to Goodchild (1997), floor plates which chiefly means slabs account for 85% of superstructure costs. In the effort to cut construction costs of buildings, it is necessary to make a choice of the most effective and affordable slab type in construction. This consideration can be first by an in-depth knowledge of the advantages and disadvantages of different types of slabs. This is the purpose of this article.
A. One-way Solid Slab
Advantages
1. Simple.
2. Holes cause a few structural problems.
Disadvantages
1. Associated downstand beams may require greater storey height, deter fast formwork cycles and compromise flexibility of partition location and horizontal service distribution.
B. One-way Slab with Wide Beams
Advantages
1. Medium range spans.
2. Simple.
3. Large and small holes can be accommodated.
4. Fast.
5. Amenable to the simple distribution of horizontal services.
Disadvantages
Same as for one-way solid slab.
C. Ribbed Slab (one-way joists)
Advantages
1.Medium to long spans.
2. Lightweight.
3. Holes in topping are easily accommodated.
4. Large holes can be accommodated.
5. Profile may be expressed architecturally, or used for heat transfer in passive cooling.
Disadvantages
1. Higher formwork costs than for other slab systems.
2. Slightly greater floor thicknesses.
3. Slower.
D. Ribbed Slabs (one-way joists with wider beams)
Advantages
1. Medium to long spans .
2. Lightweight.
3. Holes in topping are easily accommodated (but avoid beams).
4. Large holes can be accommodated.
Disadvantages
1. Higher formwork costs than for other slab systems.
2. Slightly greater floor heights.
3. Slower.
E. Troughed Slabs
Advantages
1. Longer spans than one-way solid or flat slabs.
2. Lightweight.
3. Level soffit.
4.The profile may be expressed architecturally, or used for heat transfer.
5. Holes in ribbed slab areas cause little or no problems.
Disadvantages
1. Higher formwork costs than plain soffits.
F. Two-way Solid Slabs
Advantages
1. Economical for longer spans and high loads.
Disadvantages
1. Presence of beams may require greater storey height.
2. Requires a regular column layout.
3. Grid of downstand beams deters fast formwork recycling.
4. Flexibility of partition location and horizontal service distribution may be compromised.
G. Waffle Slab (usually designed as two-way slab using standard or bespoke mould)
Advantages
1. Medium to long spans.
2. Lightweight.
3. Profiles may be expressed architecturally, or used for heat transfer.
Disadvantages
1. Higher formwork costs than for other slab systems.
2. Slightly deeper members result in greater floor heights.
3. Slow.
4. Difficult to prefabricate reinforcement.
H. Waffle and Beam Slabs
Advantages
1. Medium spans
2. Lightweight
3. Level soffit
4.Profile may be expressed architecturally, or used for heat transfer.
Disadvantages
1. Higher formwork costs than for plain soffits.
2. Slow.
3. Difficult to prefabricate reinforcement.
I. Flat Slabs
Advantages
1. Simple and fast formwork and construction.
2. Absence of beams allows lower storey heights.
3. Flexibility of partition location and horizontal service distribution.
4. Architectural finish can be applied directly to the underside of slabs.
Disadvantages
1. Holes can prove difficult, especially large holes near columns.
2. Shear provision around columns may need to be resolved using larger columns. column heads, drop panels or proprietary systems.
3. Deflections, especially of edges supporting cladding, may cause concern.
J. Flat Slabs with Drops
Advantages
1. Relatively simple and fast formwork and construction.
2. Absence of beams allows lower storey heights.
3. Flexibility of partition location and horizontal service distribution.
Disdvantages
1. Holes can prove difficult, especially large holes near columns.
2. Shear provision around columns may be considered a complication.
3. Deflections, especially at edges supporting cladding, may cause concern.
4.Drops may cause some disruption to formwork.
K. Flat Slab with Column Drops
Advantages
1. Relatively simple and fast formwork and construction.
2. Absence of beams allows lower storey heights.
3. Flexibility of partition location and horizontal service distribution.
Disadvantages
1. Holes can prove difficult, especially large holes near columns.
2. Shear provision around columns may be considered difficult.
3. Deflections, especially at edges supporting cladding, may cause concern.
4. Column heads can disrupt cycle times.
L. Flat Slab with Edge Beams
Advantages
1. Relatively simple and fast formwork and construction.
2. Architectural finish can be applied directly to the underside of the slab.
3. Absence of internal beams allows lower storey heights.
4. Flexibility of partition location and horizontal service distribution.
Perimeter holes present a few problems.
Disadvantages
1. Perimeter downstand beams may hinder the use of table form.
M. Waffle Slabs designed as Flat Slabs
Advantages
1. Profile may be expressed architecturally.
2. Flexibility of partition location and horizontal service distribution.
3. Lightweight.
Disadvantages
1. Higher formwork costs than for other slab systems.
2. Slightly deeper members result in greater floor heights.
3. Difficult to prefabricate, therefore reinforcement may be slow to fix.
Further Reading
Goodchild, C.H. (1997). Economic Concrete Frame Elements. British Cement Association Century House, Telford Avenue, Crowthorne, Berkshire RG45 6YS
