Analysis grid line C

Consider grid line C as a bay 6.0 m wide. (This may be conservative for grid line C but is correct for grid line D etc.)

Effective spans:

9600 - 2 x 400 / 2 + 2 x 300 / 2 = 9500 mm <5.3.2.2(1)>

8600 - 2 x 400 / 2 + 2 x 300 / 2 = 8500 mm Check applicability of moment coefficients:

8500 / 9500 = 0.89 .*. as spans differ by less than 15% of <Concise EC2 Tables 15.2, 15.3>

larger span, coefficients are applicable.

As two span, use table applicable to beams and slabs noting <Concise EC2 Table 15.3>

increased coefficients for central support moment and shear.

** The all-spans-loaded case with 20% redistribution of support moments would also have <5.3.1 & NA> been acceptable but would have involved some analysis. The use of Table 5.9 in BS EN 1992-1-2 (Fire resistance of solid flat slabs) is restricted to where redistribution does not exceed 15%: The coefficients presume 15% redistribution at supports. <Conc/se Table 15.3>

Design moments in bay Spans

MEd = (1.25 x 85 x 0.090 + 1.5 x 4.0 x 0.100)x 6.0 x 9.52 =842.7 kNm Support

<Concise EC2Table 15.3> <Concise EC2 Table 15.3>

Column Strip And Middle Strip

Figure 3.20

Column and middle strips

Figure 3.20

Column and middle strips

Apportionment of moments between column strips and middle strips:

Percentages

Column strip

Middle strip

-ve (hogging)

Long span = 70%se Short span = 75%

Long span = 30% Short span = 25%

+ve (sagging)

50%

50%

<Table I.1, CS Flat slab guide[29]> <Table I.1> <NA.3[1a], Fig. I.1>

Parallel to grid C, column strip is ly / 2 = 3 m wide. The middle strip is also 3 m wide. Long span moments:

Parallel to grid C, column strip is ly / 2 = 3 m wide. The middle strip is also 3 m wide. Long span moments:

<Table I.1, CS Flat slab guide[29]> <Table I.1> <NA.3[1a], Fig. I.1>

MEd

Column strip, 3 m wide

Middle strip, 3 m wide

-ve (hogging)

0.70 x 952.8 / 3.0 = 222.3 kNm / m

0.30 x 952.8 / 3.0 = 95.3 kNm / m

+ve (sagging)

0.50 x 842.7 / 3.0 = 140.5 kNm / m

0. 50 x 842.7 / 3.0 = 140.5 kNm / m

ยงยง The Concrete Society Guide[29] recommends a percentage, k1, based on Lx / Ly Assuming Lx / Ly = 1.5 the distribution of moments in the long span between column strips and middle strips is given as 70% and 30%.

Punching shear force, VEd At C2,

VEd = 16.6 x 6.0 x 9.6* x 0.63 x 2 = 1204.8 kN At C1 (and C3)

VEd = 16.6 x 60 x 9.6 x 0.45 + (10 + 0.2 x 03 x 25)"' x 1.25 x 6.0 = 516.5 kN

<Concise EC2 Table 15.3>

<Concise EC2 Table 15.3>

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