Civil Engineering Reference
In-Depth Information
4.4
SHEAR IN TWO-WAY SLAB SYSTEMS
When two-way slab systems are supported by beams or walls, the shear capacity of the slab is seldom a critical
factor in design, as the shear force due to the factored loads is generally well below the capacity of the concrete.
In contrast, when two-way slabs are supported directly by columns (as in flat plates and flat slabs), shear
near the columns is of critical importance. Shear strength at an exterior slab-column connection (without
spandrel beams) is especially critical because the total exterior negative slab moment must be transferred
directly to the column. This aspect of two-way slab design should not be taken lightly by the designer.
Two-way slab systems will normally be found to be fairly “forgiving” if an error in the distribution or even
in the amount of flexural reinforcement is made, but there will be no forgiveness if a critical lapse occurs in
providing the required shear strength.
For slab systems supported directly by columns, it is advisable at an early stage in the design to check the shear
strength of the slab in the vicinity of columns as illustrated in Fig. 4-11.
Corner
column
Interior
column
C panel
L
Critical shear
perimeter
Edge
column
Effective area for direct
shear force
Figure 4-11 Critical Locations for Slab Shear Strength
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