Introduction to shallow foundations- Design issues Flashcards
What is are foundations?
They constitute the part of the structure at the interface between the foundation soil and the structure itself.
What are the 5 roles of foundations?
- The foundation transfers vertical (e.g. the weight of the building) and horizontal (e.g. wind forces) forces to the ground.
- The foundation controls the amount of movement in the building due to changes in stress in the ground or changes in water level
- Prevents damage to adjacent structures.
- Transmits the load beneath zones affected by seasonal change.
- Prevents damage to structures due to subsequent changes in the use of the building
What is a steel column designed to operate at?
Working stress of 150 MPa
What is a concrete column designed to operate at?
10 MPa
What is the range at which soil strength varies?
5 kPa - 1000 kPa
What should we consider when designing a foundation in terms of settlement?
It should be kept within allowable limits
Define bearing capacity
Capacity of the ground to resist loads, such as: dead, live, wind, inclined thrusts and uplift, water table and earthquake forces
What can happen if a foundation is designed poorly?
The building could start to crack/tilt due to differential settlement of the foundations (fails serviceability limit criteria)
What is a differential settlement?
Non-uniform movement of the underlying soils
What are the two problems we need to investigate when designing a foundation?
- Settlement = Soil compressibility
- Failure = Shear strength
When a soil fails how does it fail?
Soils generally fail in shear
- At failure, shear stress along the failure surface reaches the soil shear strength.
Give two examples of soils failing in shear
- Excessive displacement causing building to collapse
- Land slide
