Seismic Principles Exam and some Seismic Design

A few days ago I had an opportunity to sit down with a coworker during lunch and discuss the California Seismic Principles Exam.

The general consensus I have received from other people is that this test is HARD. The test is 2.5 hours long and contains 50 questions, leaving you around 3 minutes per question. The topics of the test are detailed HERE.

My coworker however, passed the entire PE including Seismic Principles on his first try in April 2011. It was nice to be able to sit down with him and work through a few example problems and talk about what materials he used and how he studied.

Here are a few notes on topics you will encounter on the exam.Seismic Design Questions

Seismic design questions for buildings are a significant portion of the test. These problems are always in word format and you have to glean several (a LOT) of variables from them in order to solve the problem. In many of these problems the end result design value is the seismic base shear ($$V_S$$ in the book we were lookign at).
$$! V_S = C_s * W $$

The equation is deceptively simple. W is easy enough, it is the weight of the building. However $$C_S$$ is a monster, it is a function of many variables.

$$!C_S = \dfrac{I*S_{DS}}{R}$$


$$!C_{Smax} = \dfrac{S_{D1}}{T\left(\frac{R}{1}\right)}$$

You use whichever of these is the governing one. For now, having not gone into the variables yet, remember that $$C_{Smax}$$ usually only governs for buildings over 100′ tall. Problems will often hint at this by saying “a four-story” building or a “skyscraper”. If you can deduce whether or not the max equation is applicable you can save some time.

$$S_{DS}$$ is derived from the location of the building (eventually). From the location of the building you can use a map in one of the seismic resources to determine the ground velocity and ground acceleration (Fv and Fa). Also from the location of the building you can locate the soil properties ($$S_s$$ or $$S_1$$). $$S_{DS}$$ is a function of the ground velocity and soil properties, both of which are from the location.

I represents the Importance Factor. This is deduced from the purpose of the building. There are four levels with one being the least important and four the most. A building with an Importance Factor of one could be a storage shed or a water tank in the middle of nowhere or other similer things. Common buildings like houses and light commercial are level two and are the most common. I am not sure of three yet. Level four is for emergency response buildings such as hospitals and fire stations. The Importance category corresponds to a number that is used in your equation. I -> 0.85, II -> 1.00, III -> 1.15, and IV -> 1.5 (this is from my notes for now so I may come back and correct it later.

R represents the building’s material and structure type. It is given from reading the problem and looking up a value in a table. For example a steel braced frame building may have an R-Value of 4.5 or so.

T is for period (remember Physics 1?). This is the time of one “sway” (back and forth) of the building during an earthquake or other seismic movement. Taller buildings sway longer and slower during ground movement so it doesn’t really apply to buildings shorter than 100′. There are formulas for T that are based on the height of the building for both buildings over 100′ tall and under 100′.

This is a lot of stuff to lookup and remember! However the actual math is simple, and the problems I looked at appear to be relatively straightforward. My suggestion is that you obtain good review material that has all of these tables and lookup values very readily available. My coworker had the CodeMasters seismic design laminated sheet with him and said he used it for some outrageous percentage of the Seismic Principles questions. I recommend picking one of those sheets up, I ordered one, they are cheap and can give you a huge leg up.

Seismic CodeMaster Laminated Sheet

Aside from some design problems there were also a lot of word prolems that challenge your common sense skills (masonry and earthquakes do NOT mix), some code-lookup problems, and also some other types of specific design questions that I will have to look into further.

About Conrad

I am a Civil Engineer. I work in San Diego and am preparing to take the PE Exam. I am interested in surfing, business, travelling, and spending time with my wife. Thanks!

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