Thursday, 24 November 2022

Determinacy and Stability on the FE Civil Exam

For those taking the FE Civil exam, one of the structural topics one should be familiar with is determinacy and stability. This blog post will provide a brief overview of these concepts, review how basic structures can be evaluated for determinacy, and briefly discuss some of the basic methods for solving the reactions of indeterminate structures.

Determinacy and Stability on the FE Civil Exam


1. Statically Determinate and Statically Indeterminate Structural Systems

In structural analysis, there are considered to be two different types of stable structural systems: statically determinate and statically indeterminate. A stable structure is one whose forces are in equilibrium (as opposed, for example, to one which is in motion). Those stable structures which are determinate can be solved by statics using the three familiar equations of equilibrium. Namely, these are: The sum of forces in the vertical (or y-axis) direction is equal to zero; the sum of forces in the horizontal (or x-axis) direction is equal to zero; and the sum of moments is equal to zero. Again, such structural problems which can be solved using only these equations are known as statically determinate structures. Statically indeterminate structures, by contrast, are those which cannot be solved by these equations alone. These are also sometimes referred to as redundant structures.

The simple method by which one can determine whether a structure is statically determinate or indeterminate (and if indeterminate, by what degree) is the following: Determine the number of support reactions to solve for, and then compare them to the number of static equilibrium equations, which is three. If the number of support reactions is less than or equal to three, then it is a statically determinate structure. If it contains more than three support reactions to solve for, then it is statically indeterminate. The degree to which a structure is indeterminate is equal to the support reactions minus three.

For example, if a simple beam is supported on one end by a pin support and on the other end by a roller support, the structure can be evaluated for determinacy as follows. The pin support, since it prevents translation in the horizontal and vertical directions (but allows for rotation) has two unknown reaction forces, that of the x-direction and the y-direction. The roller support, since it prevents translation in the vertical direction (but allows for translation in the horizontal direction and for rotation), has one unknown reaction force, that of the y-direction. With a total of three unknown support reactions, which is equal to the number of static equilibrium equations, the structure is statically determinate, and (whatever the loading conditions on the beam) the reactions can consequently be solved for utilizing those three equations alone.

If, however, one were to take the example of a beam which is supported with two pins and a roller, it would be evaluated as follows. Each of the two pin supports would have two unknowns (again, the vertical and horizontal reaction force components), and the roller would have one (again, the vertical reaction force). The total number of the support reaction forces, therefore, is five. As this is in excess of the number of static equilibrium equations by two, the system is statically indeterminate by a degree of two.

Taking one further example - a cantilevered beam with a fixed support connection at one end and a roller at the center, it can be evaluated for determinacy as follows. The fixed support, as it prevents translation in the vertical and horizontal directions and, additionally, as it prevents rotation at the support, is found to have three unknown reaction forces (x-direction, y-direction, and moment about the connection point). Adding these three unknowns to the one unknown of the roller support yields a total of four, and thus the structure is found to be indeterminate to the degree of one.

It should be noted that the above examples relate to what is known as external determinacy (or indeterminacy, as the case may be), but it is also possible to have structures which are internally indeterminate (even if they are externally determinate). One example of an internally indeterminate structure is that of a truss with an excess of members such that the forces within them cannot be calculated using the static equilibrium equations alone.

2. Trusses

In evaluating a truss (within a two-dimensional plan) for internal determinacy, the following method can be used. Count the number of truss members and add this number to the number of support reactions. If this number is greater than the number of joints in the truss multiplied by two, then the structure is indeterminate. If this is the case, the degree to which it is indeterminate would be the difference then between the two numbers.

3. Stability

In terms of stability, while statically determinate structures are stable, a failure at any restraint of any of the supports results in instability of the system. By contrast, indeterminate structures, by virtue of the fact that there are more restraints than necessary for stability, are considered to be redundant systems. That is to say, the overall structure has greater potential to remain stable if a local failure were to occur within the system.

4. General Approaches to Problem-Solving

While exam-takers of the FE exam are unlikely to need to solve for reactions in a full analysis problem of an indeterminate structure, it is worth having knowledge of the general approaches to solving for these types of problems. These include the general force (or unit load) method, Castigliano's method, the moment distribution method, and the slope deflection method. For indeterminate building frames, there are still other methods, including the portal method and the cantilever method. As the general force method is one of the more common basic approaches, a brief overview of the method is provided below.

5. General Force Method

In the general force method, a loaded indeterminate structure is examined such that all support reaction components are identified. Then the structure is reimagined as one in which all redundant support components are removed so that a determinate stable structure remains (that is to say, one with only three support reaction components supporting the structure). This imagined version of the structure is sometimes referred to as the "primary structure" for the method. The primary structure is analyzed under the given loading conditions to determine the displacements which occur at the locations of the redundant support components of the original structure. The next step is to remove the original loading conditions and analyze a "secondary structure" which corresponds to the primary structure along with a unit force load applied at the location of the redundant support of the original structure. The displacement which occurs for this secondary structure is then solved for under this unit force load. This is done individually for each of the structure's redundant support restraints. Finally, through setting up equations in which the sums of the displacements are set to zero, the unknown reaction components of the structure's redundant supports can be solved for.

Conclusion

In summary, exam-takers of the FE Civil exam should be familiar with the concepts of determinacy and stability and be able to determine whether a particular two-dimensional structure is statically determinate or indeterminate and, if indeterminate, by what degree. The above examples describe the approach. While support reactions of determinate structures can be solved for using only the static equations of equilibrium, solving for indeterminate structures is a more involved process. There are a number of methods which have been developed for solving problems involving indeterminate structures. While exam-takers will not be calculating reactions for indeterminate structures on the exam, a general understanding of the most common methods, such as the general force method, aids in an understanding of the general approach to solving for indeterminate structures.

Do you want to pursue a career in civil engineering? Consider partnering with School of PE, one of the leading exam prep providers, to help you succeed with confidence!

About the Author: Adam Castelli

Adam Castelli is a licensed architect and engineer currently practicing in the Pittsburgh area. He holds a master's degree in architecture from the University of Massachusetts Amherst and a bachelor's degree in civil engineering from Villanova University.

Thursday, 17 November 2022

7 PE Exam Success Habits

When I look back on my Principles and Practice of Engineering (PE) exam experience, I sometimes reflect on achieving this milestone. There were seven (7) PE exam success habits that I utilized in my exam preparation. I am writing these habits for the PE exam because the process was more challenging than the Fundamentals of Engineering (FE) exam. The FE exam application is simpler than the PE exam, so the FE process was overall easier. Now let's get to it!


7 PE Exam Success Habits

1. Success Habit #1: Find the Right Motivation

I originally started looking into the PE exam as just the next step. Graduate school was my focus for a while, since my schedule was the workplace on weekdays, class on weeknights, and homework on weekends. That may sound mundane, but graduate school was good for both my personal and professional growth. And I was also continuing to gain practical engineering experience at my job. So, it was productive all-around.

This growth and enrichment became my motivation. There was much knowledge circulating around me, and I realized that if I could learn more, I could become better, both personally and professionally. My recommendation is to find your own motivation, something other than just more money or some other kind of bonus. Yes, I received a small bonus for passing the PE exam, but there was so much more that I had gained than just the dollar amount.

2. Success Habit #2: Get Off to a Hot Start with Every Morning

Preparation is the most critical element needed to pass the PE exam. It is interesting how you spend hours on end studying for just the one exam day, but all the preparation is key when you truly need it the most. I am more of a morning person, so this is how the idea first came to me. I realized that oversleeping did not really benefit me, since I was wasting extra time by either just lying in bed or trying to fall back asleep.

When I first started waking up earlier and accomplishing tasks, I was feeling better about the day ahead. Everyone else is just waking up, but you have already set the tone for a good day. I would recommend completing errands first thing in the morning, then you have the rest of the day ahead for PE exam preparation. And since you have already completed your other checklist items, you are already a couple steps ahead of everyone else. As I write this blog post, I can tell you that I got off to a hot start this morning!

3. Success Habit #3: Select a Pre-Recorded Online Review Course

I would recommend a review course to help with your studying preparation. I am suggesting a pre-recorded online review course since this allows yourself the time to study and learn at your own pace. I took the PE Mechanical (Thermal and Fluids Systems) exam, and the pre-recorded course option offered by School of PE was instrumental towards my success. I was able to start and end the review sessions depending on my schedule and did not have to abide by the predetermined webinar schedule for taking breaks.

You should not rush yourself in trying to study a certain amount of content in a limited amount of time; rather, you should use the time that you need. You will probably find that some subjects require more studying than others. The PE exam format lists a range of a certain number of questions, so you must be sufficiently prepared in all the core subjects. I will say that I am not too big on studying in groups or live webinars. When studying in groups, I find that you can become distracted too easily and you may try to adopt another person's study habits which may not suit your own.

4. Success Habit #4: Enjoy Other Hobbies/Interests

Preparation for the PE exam requires time. I will be honest here; you will probably have less time for a social life and other activities (but I can also assure you that pursuing a PE license is certainly worthwhile). But you should still try to allocate some time for other hobbies and interests. Diversions are good since they can help you stay fresh, so you are not just staring at textbooks and notes all day. Also, if you dedicate ALL your spare time to passing the PE exam, you are placing excessive pressure on yourself. I had a friend that did not pass the PE exam on the first try and felt even worse because he was too lopsided on study time, neglecting other activities altogether. I studied much during summer 2018, but was still attending yoga classes, volunteering with my church, and improving my cooking skills (eating healthy helps with a hot start, and of course breakfast is the most important meal of the day!).

5. Success Habit #5: Close Your Mind to All Criticism and Self-Doubt

I do feel that one of the success habits should be about facing past moments that were not your best. We have all experienced failure at some point; maybe you did not receive approval to sit for the PE exam on your first application attempt, or maybe you did not pass the first time. But it is important to eliminate that self-doubt and close your mind to all criticisms. Usually, I would recommend keeping your eyes open to new activities and expanding your scope. But in the case of passing the PE exam, I would suggest having more of a "tunnel vision" where you have laser focus on the passing goal.

Do not worry about past workplace mistakes either. I have certainly made mistakes myself; it is okay to make mistakes, as you should always keep moving yourself forward. Even if you do not feel ready for the PE exam, you should still pursue it anyways. I only had the minimum four years work experience and briefly contemplated waiting another year. But I decided to go for it (and got it).

6. Success Habit #6: Exercise then Relax Before Exam Day

I took the PE exam on Friday but made sure to attend my martial arts class the night before. As I mentioned earlier, you should still engage in other interests to keep yourself fresh and in a healthy, positive mindset. Passing the PE exam is not a sprint; the preparation is a journey to success. It certainly does not happen overnight. But it is important to clear your head the night before, so you feel that final preparation overnight.

Exercising at my martial arts class was the final puzzle piece to get into that healthy mindset so I would be truly ready. The exercise helps you to destress so you have that Exam mentality. Knowing myself, I may have psyched myself out trying to review every topic last minute the night before. I would have probably stayed up later and missed out on the rest needed for a proper hot start.

7. Success Habit #7: Confront the Exam Head-On

The seventh and final success habit comes on exam day. You are going to feel different emotions; I was feeling mostly a combination of excitement and anxiety. There was some fear, but I was already in a positive mindset from exercising the night before (Habit #6). And I also got off to a hot start that morning with a healthy breakfast (Habit #2). You can see that I was putting it all together. When you arrive to your exam location, you will find that everyone else is feeling that same atmosphere (pressure will probably be 1 atm!). This is a good reason why you should not panic or lose composure.

When you first receive the PE exam, look through the test. I seldom do this, but I checked ahead this time. Some questions will require longer methodologies than other questions, so you should identify early on which questions are shorter than others. Remember, the PE exam is not a sprint. You have the time to take a few moments to assess the entire exam. It is okay to revisit questions later and certainly okay to answer some questions wrong (just not too many). During the exam break (after the morning session), I overheard other examination candidates voicing similar concerns. Never quit; keep pushing ahead and tackle that exam!

Conclusion

I do not believe you should assign a certain number of hours for studying and preparation. Everyone has different study habits. I am providing my own insights and observations, but you must ultimately decide on your best strategy. There is no true universal equation for success on the PE exam (I have already checked the different NCEES Reference Handbooks), so you may need to identify your own success habits. But you can certainly use these seven (7) success habits as a guide. And of course, be sure to check back with School of PE for more blog posts.

Interested in earning your professional engineering license? School of PE's comprehensive courses provide what you need to succeed when exam day arrives! Register today.
About the Author: Gregory Nicosia

Gregory Nicosia, PE is an engineer who has been practicing in the industry for eight years. His background includes natural gas, utilities, mechanical, and civil engineering. He earned his chemical engineering undergraduate degree at Drexel University (2014) and master's in business administration (MBA) from Penn State Harrisburg (2018). He received his EIT designation in 2014 and PE license in 2018. Mr. Nicosia firmly believes in continuing to grow his skillset to become a more well-rounded engineer and adapt to an ever-changing world.

Thursday, 10 November 2022

Phase Relationships of Soil

Those taking the FE Civil exam should be familiar with the basic concepts in soil mechanics related to the phase relationships of soil. Phase relationships are also covered on the PE exam, regardless of which depth version of the exam is taken. This blog aims to provide an overview of soil phase relationship concepts, terminology, and the basic calculations involved in solving for soil component volumes and weights.

Phase Relationships of Soil


1. Soil Phases

Soil can be understood to have three "phases." Specifically, these are the solids within a soil, the voids between these solids which are occupied by air, and the voids between the solids which are filled with water. The various proportions of these phases within a given soil contribute to its behavior and properties.

2. Specific Weight of Water and the Specific Gravity of Soil Solids

Before discussing concepts and calculations related to the soil phases themselves, it is necessary to understand the specific weight of water and the specific gravity of the solids portion of soils. The constant value known as the specific weight of water can be understood as the weight of water in pounds within a cubic foot of volume of water. Specifically, the value of water's specific weight is 62.4 lb/cubic ft. The constant value known as the specific gravity of soil solids is a dimensionless unit which can be understood as the ratio of the typical density of the soil solids within a soil to the density of water within a unit volume. It is not actually a consistent number but varies by the type of soil being considered, and it is also an average value based on the different types of particles within the soil (it being assumed that the soil is homogenous). It can be taken, however, as typically ranging between 2.6 and 2.85. For some organic soils, however, it can be substantially lower. The value for a particular soil can be determined by performing a specific gravity test on the soil. For the purposes of the exam, if a calculation problem involving soil phases is given, this value would likely be given so that some other value related to the soil composition can be determined.

3. Soil's Five Potential Variables

In terms of phase relationships, soil can be understood to involve five potential variables. Namely, these are the individual volumes of the solids, air (empty voids), and water (filled voids), as well as the weights of the solids and the water. Note that the weight of the air-filled voids is considered negligible. Given the information we have about the specific weight of water and the specific gravity of soil solids, any of the five variables could be solved for if three are given. The exam taker should therefore be familiar with how to solve for any of the variables by understanding the relationships between them, as follows.

4. Volume and Weight of Water and Solids

The volume of water can be calculated by dividing the weight of water by the specific weight of water. The volume of solids can be determined by dividing the weight of solids by the product of the specific gravity of soil solids and the specific weight of water. Likewise, the weight of water can be determined by multiplying the volume of water by the specific gravity of water. The weight of solids can be determined by multiplying the volume of solids by the product of the specific gravity of soil solids and the specific weight of water. Any of the volumes can be found by subtracting two other volume components from the overall volume. For example, the air volume is the difference between the overall volume and the sum of the soil and water volumes. Similarly, the weight of an unknown component (water or solid) can be found by subtracting the overall weight by the known component (water or solid). A phase diagram is a useful tool for visualizing the content of the soil (solids, empty voids, and water-filled voids) and their associated variables by separating them into different regions of the diagram. The above-described calculations can then be done as needed to determine the unknown variables of the diagram.

5. Other Terms to Know

There are a number of other terms related to soil content that the exam-taker should be familiar with which are all defined by particular ratios involving the above-described weights and volumes of a soil. A soil's degree of saturation is defined as the ratio of the volume of water to the overall volume of voids within a soil (filled or not). It is sometimes expressed as a percentage, with 100% being a fully saturated soil containing no air voids. A soil's porosity is defined as the ratio of its volume of voids (filled or not) to its total volume (including solids and voids). A soil's water content can be found by dividing the weight of a soil's water by the weight of its solids. Finally, what is known as a soil's void ratio can be found by dividing the total volume of voids (filled or not) by the volume of solids.

6. Dry Unit Weight vs. Saturated Unit Rate

One should be familiar also with the concept of a soil's dry unit weight as well as its saturated unit weight. A soil's dry unit weight can be understood, in terms of phase relationships, as the unit weight of a soil when there is no water present within the void spaces of the soil. The dry weight can be determined by laboratory test after oven-drying the soil. A saturated unit weight, by contrast, is the unit weight of a soil when the void spaces are entirely occupied by water. Completely dry soil as well as completely saturated soil are sometimes referred to as "two-phased" soils since they are lacking in the water component and the air component, respectively. Because of the necessary arrangement of solids within soils, all soils have at least some number of voids within them. Therefore, it is not possible to have a single-phased soil.

Summary

In summary, FE exam-takers should be familiar with the basic concepts of soil mechanics including those related to phase relationships for soils, how various unknown variables may be solved for given particular information about the soil content, the various terminology related to the ratios of these variables, and the concepts of dry unit weight and saturated unit weight.

About the Author: Adam Castelli

Adam Castelli is a licensed architect and engineer currently practicing in the Pittsburgh area. He holds a master's degree in architecture from the University of Massachusetts Amherst and a bachelor's degree in civil engineering from Villanova University.

Thursday, 3 November 2022

Water Resources - Water Quality and Drinking Water Distribution and Treatment

Those planning to take the Water Resources and Environmental Depth version of the PE Civil exam need to be familiar with the topics of Water Quality and Drinking Water Treatment. This blog will provide an overview of the relevant subtopics with which the exam-taker should be familiar. My intention is not to cover these topics in depth but to provide an introduction to the items which you should study further for the exam.

Aspects of water quality determination and analysis covered on the exam include: stream degradation; oxygen dynamics; total maximum daily load; biological contaminants; and chemical contaminants, which includes the topic of bioaccumulation.

Water Quality and Drinking Water Distribution and Treatment


1. Steam Degradation

Stream degradation refers to reduced water quality in a stream as a result of various types of pollution, erosion, or environmental degradation. The quality of the water may be considered to be degraded based on measurements of water temperature, turbidity (the clarity of the water), low dissolved oxygen levels (potentially due to microorganisms), pH balance, and/or the amount of solids content, which includes total solids (TS), total suspended solids (TSS), and total dissolved solids (TDS). Chemicals, such as from agricultural or industrial sources, which may flow into streams through surface runoff, are also contributors to stream degradation.

2. Oxygen Dynamics

Exam-takers should be familiar with concepts related to the determination of saturated content of dissolved oxygen, which is based on Henry's law. In terms of oxygen dynamics, it is also necessary to understand biochemical oxygen demand (BOD) and chemical oxygen demand (COD) and how they are determined.

3. Total Maximum Daily Load

Total maximum daily load (TMDL) is a concept in water quality which refers to the maximum quantity of pollutant that could potentially flow into a body of water on a daily basis without the water exceeding set maximum pollution levels. It is calculated as the sum of allocated waste loads from point sources, allocated loads from non-point sources, and a safety margin.

4. Biological Contaminants

Contaminants of concern in water that are biological in nature include bacteria such as E. coli (and other coliforms), Legionella, Cryptosporidium, Giardia lamblia, as well as enteric viruses. These specific microorganisms of concern (with the exception of Legionella) are largely associated with human and animal fecal waste contamination of water. The overall concentration of bacteria in a water source can be measured with a heterotrophic plate count (HPC). It should be noted that bacteria are naturally present in water sources, but lower concentrations of bacteria (as measured by an HPC test) can indicate a higher quality of water.

5. Chemical Contaminants

Chemical contaminants of concern for drinking water include inorganic contaminants (IOCs), volatile organic contaminants (VOCs), and synthetic organic contaminants (SOCs). Common IOCs of concern include arsenic, nitrate, nitrite, asbestos, lead, and copper. Bioaccumulation is the accumulation of contaminants within an organism as a result of ingestion of the contaminants.

6. Water Distribution and Treatment

Aspects of drinking water distribution and treatment that are covered on the exam include: drinking water distribution systems, drinking water treatment processes, demands, storage, sedimentation, taste and odor control, rapid mixing (such as with coagulation), flocculation, filtration, disinfection (including the byproducts of disinfection), and water hardness and softening.

7. Drinking Water Distribution Systems

The typical municipal systems for the distribution of public drinking water consist of a water source, treatment plant, storage tanks, and water mains and pipes which convey the water to the points at which the water can be consumed.

It should be noted that the enforced drinking water quality standards at the national level in the United States are set by the EPA in the National Primary Drinking Water Regulations (NPDWRs). These set maximum contaminant levels (MCLs). The water quality standards were first set in 1974 with the passage of the Safe Drinking Water Act (SDWA). The act has since been amended in 1986 and 1996 with updates to the list of contaminants which must be limited and the particular concentration levels which define those limits.

8. Drinking Water Treatment Processes

The treatment plants utilize processes of treatment that typically include a number of steps. These include rapid mixing (such as with coagulation), flocculation, sedimentation, filtration, and disinfection. The coagulation step aims to collect small and dissolved pollutants into larger particles resulting from their mixing and binding with chemicals, such as salts, which are introduced into the water. The flocculation step also involves the introduction of chemicals into the water, with the intention of forming "flocs," which are clusters of solids that can more easily be removed from the water than the smaller individual particles. These flocs settle to the bottom of a tank in the sedimentation step of the treatment process. Filtration involves the passage of the water (which has been separated from the flocs) through various filtering media, which may include charcoal, gravel, and sand. This step aims to remove any remaining sizable particulate matter from the water. Ultrafiltration is sometimes also done either as an additional step or as a substitution for the traditional filtration methods. This involves the use of a filter membrane with very small openings. The water is finally treated with disinfectants, such as chlorine, in order to prevent contamination by microorganisms both in the water leaving the treatment plant and in the water mains and pipes which carry the water from the plant to the points of use. Sometimes ultraviolet light is used for disinfection purposes either in addition to the chemical treatment or as a substitution.

9. Water Hardness

Water hardness refers to the total amount of dissolved minerals in water, typically calcium, magnesium, and iron. Though not typically a concern for health, it often leaves mineral buildup on pipes and fixtures. This buildup is also referred to as "scale." Because the particular elements contribute differently to the amount of hardness, they must be put into equivalent terms before adding them together to find the total hardness. The equivalent concentrations can be found by dividing the measured mineral concentrations by the equivalent weights of the elements. Water softness is, by contrast, a relatively low amount of dissolved minerals.

10. Unfavorable Taste and Smell

When it comes to unfavorable taste and smell of supplied drinking water, it can be caused by a number of factors. These often occur where secondary maximum contamination levels (SMCLs) are exceeded. These concentration levels are set in the National Secondary Drinking Water Regulations established by the EPA. These are guidelines are not required to be met by most jurisdictions but are recommendations for water quality that the agency sets. Where the concentrations of the contaminants exceed the recommended levels, though they are not understood to be risks to health, they can cause unpleasant taste, smell, or appearance, which can alarm consumers. These contaminants are also sometimes referred to as nuisance constituents. Contaminants negatively affecting taste or smell include chloride, iron, sulfates, and copper, among others. Those which may negatively affect appearance include aluminum, copper, and manganese, among others. The presence of silver in water can cause skin discoloration (though it is sometimes used for its antibacterial properties in home water treatment systems). Excess fluoride can cause tooth discoloration in children. The methods by which the odors, unpleasant tastes, and other negative effects can be controlled involve limiting the concentrations of these contaminants through processes at the water treatment plant.

Summary

Water quality and treatment is an important topic as it directly affects human health and well-being. For those taking the Water Resources and Environmental Depth version of the PE exam, it is especially important to have a thorough knowledge of the particular water quality contamination issues which water supply systems face and the processes by which the water is treated to resolve these issues and provide quality water to end users.

When you take one of School of PE's PE Civil exam review courses, our subject-matter expert instructors will guide you through each exam topic with respect to NCEES' exam specifications. Register for a course today!
About the Author: Adam Castelli

Adam Castelli is a licensed architect and engineer currently practicing in the Pittsburgh area. He holds a master's degree in architecture from the University of Massachusetts Amherst and a bachelor's degree in civil engineering from Villanova University.