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For cohesion: Nc = ( - l) x cot(fd) = 28.4 For self-weight: N^ = 2(Nq - l) x tan(fd) = 17.8

Shiape factors

Bearing resistance

Partial factor from Set R2: yrv = 1

From overburden qu|t = Nq x sq x ct' b = 196.9 kPa From cohesion qu|t = Ncx scx c'd = 0kPa

From self-weight qu|t = N^ x s^ x Yk x — = 197.5 kPa

Total resistance qult = qult = 394.4

kPa qult

Design resistance q^d =-= 394.4kPa

Verification of bearing resistance

Verification of bearing resistance

Utilization factor

Design is unacceptable if utilization factor is > 100%

Utilization factor

Design is unacceptable if utilization factor is > 100%

© The calculated utilization factor is 75% which would indicate that according to DA2 the footing is potentially over-designed.

& Design Approach 3 applies partial factors to both actions and material properties at the same time.

© The resultant utilization factor is 123% thus the DA3 calculation suggests the design is unsafe and re-design would be required.

The three Design Approaches give different assessments of the suitability of the proposed foundation for the design loading. Of the three approaches, DA1 suggests the footing is only just satisfactory whilst DA3 suggests redesign would be required and DA2 may indicate that the footing is overdesigned!

Which approach is the most appropriate cannot be determined although DA3 would appear unnecessarily conservative by providing significant partial factors on both actions and material properties.

10.10.2 Eccentric pad footing on dry sand

Example 10.2 considers the design of a pad footing on dry sand, in which the imposed vertical load from the superstructure is eccentric to the centre of the foundation, as shown in Figure 10.10.

Because the load is eccentric, the foundation's design is based on its effective area. The foundation's self weight (which acts through the centre of the footing) helps to reduce the eccentricity of the total load. Eccentric loads should be avoided whenever possible since they make the footing inefficient.

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