Lecture 3

Question 1

Using the generic terms for loads (or actions), in Slides 3-4 to 3-6 state which are permanent, variable, accidental or seismic

Answer 1

• Permanent loads are gravity as they are always a force on the structure. It is the self-weight of the building.
• Gravity is also a variable load
• Accidental load will be a fire, explosion, impact, anything as a result of human error.
• Variable load can also be hydrostatic and soil pressure.
• Seismic load can be from an earthquake. They are a dynamic force that act on the structure during the ground motion.
• Variable Loads: These are loads that can change over time or with conditions. They may include live loads (e.g., occupants, furniture, snow, wind) and environmental loads (e.g., wind, snow, temperature changes) that vary in magnitude and location.

Question 2

8. What is the characteristic value in the statistical description of a load

Answer 2

• Fixed on a statistical basis they correspond to values that have a prescribed probability of exceedance in a reference period.
• A graph that plats load against time, can measure the mean, the different quartiles, median and mode

Question 3

9. In terms of direct stress () and direct strain (), give a definition for the Modulus of Elasticity (E) of a material. What is the yield stress (or yield strength) (y), and what is its association with E? What is the ultimate stress (or ultimate strength), and what must the material possess for it to be higher than y. What is the response of a material that gives a measure of its ductility

Answer 3

• Modulus of elasticity is the ratio of direct stress to direct strain. It will be the gradient of stress to strain.
• Yield stress/strength is the point after where the material becomes deformed and can not return to its original shape. Once it exceeds E the object cannot return to original shape.
• Material with a higher E has a higher yield strenght
• The ultimate strength is the stress that the material can withstand before it breaks. It is a measure of its strength of a material.
• For an object to have a higher yield stress it must also have a higher E
• To give a measure of ductility the material experience a higher level of stress and deviates from its original straight line on the graph, the strain becomes large as the material approaches failure. The material must deform plastically before deformation.

Question 4

10. Why do you think we find little, if anything, reported on a case study when the failure is by excessive deformation

Answer 4

• As when excessive deformation happens the material will fracture.
• Attention might be bought to the primary cause of failure instead. As there are other types of failures that might have been a factor that people will think more of.