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5.4.2.1.3 (1)&(2) Figure 5.11 5.4.3.2.1(1) Eqn 53

Figure 5.1 Table 5.3

For straight bars a =1.0 and if s.req s,prov

'b,net = = 534 mm for T16 bars, say 550 mm. Curtail alternate bars as shown in Figure 4.20.

Alternate bars curtailed at 1 and 2

Alternate bars curtailed at 1 and 2

Figure 4.20 Curtailment diagram

Check that bars are anchored past relevant critical punching perimeter.

Earlier calculation required column strip reinforcement to extend beyond a perimeter 420 mm from column face i.e. 570 mm from grid. It is assumed sufficient to provide an anchorage / beyond this perimeter. Inspection of Figure 4.20 shows that this is satisfied.

4.2.1.2 Design example of a flat slab with column heads

The previous example will be used with column heads introduced at the internal columns to avoid the need for shear reinforcement.

The rest of the design is unaffected by the change.

4.2.1.2.1 Punching at column B/2 (300 mm x 300 mm internal column)

In the previous example it was found that vSd = vRd1 at 420 mm from the column face where u = 3845 mm.

Provide a column head such that/H = 1.5/ih (see Figure 4.21). Figure 4.22

Figure 4.21 Slab with column head

For a circular column head, assume that EC2 Equation 4.51 applies to the case 4.3.4.4(1) where ZH = 1.5hH.

Note:

It is suggested that EC2 Equation 4.55 should read d = 1.5dH + 0.5/., which reduces to the same as Equation 4.51 when /H = 1.5hH.

Assume an effective column diameter, I = 300 mm c

To avoid shear reinforcement: 2xd .. > 3845 mm cnt d , > 612 mm cnt lH > 612 - 1.5d - 0.5lc = 612 - 1.5(185) - 150 = 185 mm Eqn 4.51

Circular column head 125 mm below slab and 670 mm diameter is sufficient to avoid shear reinforcement

To avoid shear reinforcement d ., > 612 mm crit lH > ^ (612 - 1.5d - 0.56/J

Square column head 100 mm below slab and 600 mm wide is sufficient to avoid shear reinforcement

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