Battling Extreme Weather with Structural Engineering
Extreme weather events are happening more frequently these days and causing more costly damage than ever before, but what we don't often hear about is how buildings are designed to withstand incredible forces and in most cases, do exactly what they're designed to do when exposed to Mother Nature's fury.
Podcast: How Buildings Withstand General Weather and Extreme Weather
Top 3 Weather Factors to Consider During Structural Design
Weather touches every project during the entirety of its life. From design to construction and beyond, weather is a part of every step of the process. Structural Engineer Nate Schmidt says structural engineers think of three things when designing a building: the safety, health, and welfare of the public we serve.
As we know, Mother Nature's mood can change in an instant and sometimes we need to seek shelter to remain safe. Schmidt says there are three weather factors he keeps in mind for every project design to ensure people are safe: snow loads, wind loads, and seismic loads.
What are Snow Loads?
Essentially, snow loads can be translated to the weight of snow. Snow loads control several aspects of a project's design, but a large focus is put on making sure the roof is designed to hold the added weight of snowfall.
Codes for snow loads vary geographically. They go up for areas that see more snow, and they go down for areas that rarely see snow. The weight of snow also varies, as dry snow is much lighter than wet snow. That is also factored into snow loads.
Ways to combat heavy snow range from adding more support to changing the pitch of a roof. Have you ever gone to a ski resort and noticed that there are almost no flat roofs? That's because the pitch of the roof keeps too much snow from accumulating. It will simply slide off before the weight becomes an issue.
What are Wind Loads?
Wind load is the amount of force put on a building by the wind. If you're reading this from the Midwest, it's not in your head, outside of the coastal areas, we have some of the highest wind load ratings in the country.
Wind loads have several different forces they exert on a structure, but the main one to consider during design is the lateral force. The load-resisting system is an answer to lateral forces. The load-resisting system allows the structure to bend but limits the bending to keep the building materials from breaking. That sounds a little unnerving, but unless you're in an extremely tall building, you'll never notice any of that movement.
What are Seismic Loads?
Seismic Loads reference the amount of seismic activity in an area. Designing a building in Nebraska requires much less attention to seismic activity than a project in California. Schmidt describes seismic load as a forced displacement of the ground. He says it's the equivalent of someone knocking a person's feet from under them and then that person reacting to that displacement.
Another way of looking at it is to look at a building. If we move the bottom of the building, the top of it tries to stay where it is. It's that shifting that causes the seismic load. The same process of finding a balance of being sturdy but flexible so the building can bend without breaking is applied to combat earthquakes. When it comes to areas that see frequent earthquakes, some buildings are even designed to strategically fail in one area to keep the integrity of the structure intact. Again, that sounds strange, but it's designs like this that keep buildings standing even though the US experiences about 55 earthquakes per day and 20,000 per year.
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