Engineering Misconceptions, Part 3 - Earthquake Magnitude and Intensity

Wrong: I designed your building to withstand an earthquake with a magnitude of 7.0 and intensity 10.

Right: I designed your building according to the minimum safety requirements of the building code which aims to protect life and limb from harm due to a 475-year return period earthquake. I also designed the foundations as appropriate. The intensity depends on the expected level of damage. If all buildings were designed properly, the intensity scale (expected level of damage) would go down for the area around your building.

Facts:

Engineering Misconceptions, Part 2 - Design Wind Speeds

Wrong: A wind speed of 60 m/s has been recorded recently in this area.  Therefore the 55 m/s design wind speed (50-year return period) shown in the Building Code is now wrong.

Right: A wind speed of 60 m/s has been recorded recently in this area.  The basic wind speed for this area as shown in the Building Code is only 55 m/s. I should convert 55 m/s to the actual design wind speed for this area based on the height, topography, and surface roughness to see if the recorded 60 m/s is over and above the actual design wind speed for this specific area. I should also read books to find out what exactly are return periods to better understand them.

Facts:

Engineering Misconceptions, Part 1 - Return Periods

Wrong: The 50-year return period wind speed of 55 m/s occurs once every 50 years.

Wrong: A wind speed of 60 m/s has been recorded recently in this area. Therefore the 55 m/s 50-year return period wind speed is now wrong.*

Right: The 50-year return period wind speed of 55 m/s has a 63% chance or probability of occuring or being exceeded at least once in the next 50 years.

Facts: