QB2 Calculating Stresses

Question 1

When calculating stresses using Bousinesq’s point load theory of superposition, what is the first step?

Answer 1

Convert the UDL into a point load, and divide the value by the number of sections you have split the section into

Question 2

When is bousinesq’s point load theory used?

Answer 2

To calculate the load at the centre of sections

Question 3

The influencing factor must be calculated after separating the point load into sections, how are the ‘r’ and ‘z’ values obtained?

Answer 3

z = vertical stress depth

‘r’ = the hypotenuse from the centre of the small section to the centre of the large section

Question 4

After the influencing factor has been calculated, how is the vertical stress at ‘A’ calculated?

Answer 4

Stress = influencing factor x (Point load / depth ^2)

Total stress = stress x no. of sections

Question 5

Using Fadum’s graphical solution, how are ‘n’ and ‘m’ obtained?

Answer 5

‘m’ = L/Z (length of section divided by depth)

‘n’ = B/Z (breadth of section divided by depth)

Question 6

How is the influencing factor obtained using Fadum’s graphical solution?

Answer 6

‘m’ and ‘n’ are plotted on the graph to find Iz

Question 7

Using Fadum’s, how is stress calculated?

Answer 7

Stress = influencing factor x UDL x no. of sections

Question 8

When is Fadum’s most suitable?

Answer 8

Considering UDL’s

Question 9

How can the stress be calculated at the edge of a shape, instead of the centre?

Answer 9

Fadum’s calculates the stress in a corner, using this, the shape can be split into a number of segments and the influencing factor calculated in each segment.

The total stress = total influencing factor x UDL

Question 10

How can Fadum’s be used to determine stress at a point outside the area?

Answer 10

A projection of the area can be made with the dimensions provided.

Influencing factors for the extended section calculated then have the hypothetical areas’ influencing factor subtracted

Then: stress = final influencing factor x UDL

Question 11

How is the influencing factor determined in consolidation settlement?

Answer 11

Area of foundation is divided into 4 segments, then ‘m’ and ‘n’ values are calculated and factored into the graph.

Question 12

What is different about the ‘z’ value in consolidation settlement?

Answer 12

It is equal to the depth of the foundation to material change + half of the thickness of the layer at the bottom

Question 13

How is stress calculated in consolidation settlement?

Answer 13

Stress = no. of sections x influencing factor x P (load per m^2)

Question 14

How is consolidation settlement (dH) calculated?

What units should the answer be in?

If calculated in meters, how is the answer converted?

Answer 14

Mvd (value of the material in MN) x 10^-3 x P x H (height of layer in question)

mm

x 10^3