VWf = 115 x 620 = 713 kN For the unreinforced section
100 x 1582 „„,„, with = f)y = pz = 25QQ~^~3Q5 = 0.21%
thus from table 8.2, VRd.c = 0.47N/mm2; therefore
As Vf,d.eff is less than Vrj c the section is adequate, and shear reinforcement is not needed.
3. At the dropped panel the critical section is 2.0 x 205 = 410 mm from the panel with a perimeter given by u = (2a + 2b + 2tt x 2d) = (4 x 2500 + 2?r x 410) = 12 576 mm The area within the perimeter is given by (2.5 + 3d)2 - (4 - tt)(2.0 x 0.205)2 = (2.5 + 3 x 0.205)2 - (4 - 7r)(0.410)2 = 9.559 nr Ultimate shear force.
As VEd,cff is less than VRd,t the section is adequate.
[Note - in the above calculation p\ has been based on column strip reinforcement at the support. Since the critical zone will lie partially in the middle strip, this value will be a minor over-estimate but is not significant in this case.]
Span-effective depth ratios At the centre of the span IOOA,.feq _ 100 x 1605 _ bd ~ 4000 x 205 ~ ' From hgure 6.3 the limiting basic span-effective depth ratio is 32 for class C25 concrete and this is multiplied by a K factor of 1.2 for a llat slab (see table 6.10) giving 32 x 1.2 = 38.4.
actual span-effective depth ratio 6500/205 = 31.7
Hence the slab effective depth is acceptable. To take care of stability requirements, extra reinforcement may be necessary in the column strips to act as a tie between each pair of columns - see section 6.7, and the requirement for at least two bottom bars to pass through each column will be satisfied by the spacings calculated above and shown in figure 8.14.
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