Quakes Happen: How Engineers Ensure Seismic Safety
Back in late June, an earthquake occurred near Oaxaca, Mexico. Thousands of homes were damaged and 10 deaths were reported. This earthquake had a personal tie as my website designer and graphics guru lives in that area. Thankfully, she was fine.
This got me thinking about earthquakes and the responsibly and privilege that structural engineers have to mitigate negative effects of earthquakes. Civil Engineers (Structural Engineers are a subset of Civil Engineering) must adhere to the American Society of Civil Engineers (ASCE) Code of Ethics. Our first Cannon states that we “shall hold paramount the safety, health and welfare of the public…” And we do not take this responsibility lightly. This is always top of mind for us, making sure that the public is SAFE. In fact, this is the main reason that many of us got into this profession, to help people.
Earthquakes happen around the world on a daily basis, and are more common and typically more intense at the intersection of the earth’s tectonic plates. It is our job as structural engineers to predict the way that a structure will perform under these earthquakes so that the buildings that we design safely protect the public during these events. Here is a great resource on earthquakes if you’re looking to learn more.
Structural engineers, even in Iowa, have to design for earthquakes. Earthquakes moving through soil translate into a horizontal force at the base of the structure. This force causes reactionary horizontal forces throughout the building structure that cause the building to oscillate and results in a building base shear. It is our job to take these reactionary forces and transfer them down to the soil below.
Based on geographical location and soil conditions, we are able to find design values to plug into our equations. We use these design values and combine them with the weight of the levels of the forces to arrive at story forces and ultimately a building base shear. The heavier the structure, the higher the base shear. The more historically active an area is, the higher the base shear. Each building is classified into a Building Design Category and each Building Design Category has a different set of Code-stipulated requirements that have to be met such as methods of dissipating seismic loads and material ductility requirements. This is why when you look up at an exposed structure in California, it likely looks different than one in Iowa.
As structural engineers, we use data to predict how buildings will perform under certain loading conditions. We take material properties from the materials used in construction (concrete, masonry, wood, steel) and compare hypothetical loads to the material properties of each structural element within a building. These loads are generated by Building Code requirements and based on knowledge gained to date. We use mathematical equations to predict how these elements will perform. Then we instruct contractors, via structural plans, how to build a structure based on architectural constraints and our mad-scientist calculation findings. Our goal is to get all of the forces and loads of the building safely down to the ground.
Structural engineers are required to give earthquakes adequate attention and consideration when designing buildings. Earthquake engineering is just one way that we ensure the safety of the public.