Design for punching shear

Eurocode 2 provides specific guidance on the design of foundations for punching shear, and this varies from that given for slabs. In Eurocode 2 the shear perimeter has rounded corners and the forces directly resisted by the ground should be deducted (to avoid unnecessarily conservative designs). The critical perimeter should be found iteratively, but it is generally acceptable to check at d and 2d. Alternatively, a spreadsheet could be used (e.g. spreadsheet TCC81 from Spreadsheets for concrete design to BS 8110 and Eurocode 27). The procedure for determining the punching shear requirements is shown in Figure 4.

Table 6

vRd,c resistance of members without shear reinforcement, MPa

Table 6

vRd,c resistance of members without shear reinforcement, MPa

Ri

Effective depth, d (mm)

300

400

500

600

700

800

900

1000a

0.25%

0.47

0.43

0.40

0.38

0.36

0.35

0.35

0.34

0.50%

0.54

0.51

0.48

0.47

0.45

0.44

0.44

0.43

0.75%

0.62

0.58

0.55

0.53

0.52

0.51

0.50

0.49

1.00%

0.68

0.64

0.61

0.59

0.57

0.56

0.55

0.54

1.25%

0.73

0.69

0.66

0.63

0.62

0.60

0.59

0.58

1.50%

0.78

0.73

0.70

0.67

0.65

0.64

0.63

0.62

1.75%

0.82

0.77

0.73

0.71

0.69

0.67

0.66

0.65

>2.00%

0.85

0.80

0.77

0.74

0.72

0.70

0.69

0.68

k

1.816

1.707

1.632

1.577

1.535

1.500

1.471

1.447

Key a For depths greater than 1000 calculate vRd,c directly. Notes

1 Table derived from: vnc = 0.12 k (100ri fc,)M > 0.035 k15 f,0-5 where k = 1 + -/(200/d) < 2 and pi = V(pY +Riz) < 0.02,

2 This table has been prepared for fc, = 30;

Key a For depths greater than 1000 calculate vRd,c directly. Notes

1 Table derived from: vnc = 0.12 k (100ri fc,)M > 0.035 k15 f,0-5 where k = 1 + -/(200/d) < 2 and pi = V(pY +Riz) < 0.02,

2 This table has been prepared for fc, = 30;

fck

25

28

32

35

40

45

50

Factor

0.94

0.98

1.02

1.05

1.10

1.14

Shear checks for pad foundations

Figure 3

Shear checks for pad foundations

Pad Foundation Design
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