Wednesday, 21 June 2017

Basic Principles and Classifications of Pile Foundations

Introduction

Shallow and deep foundations signify the relative depth of the soil on which buildings are founded. When the depth of a foundation is less than the width of the footing and is less than ten feet deep, it is a shallow foundation. Shallow foundations are used when surface soils are strong enough to support the imposed loads. If the depth of a foundation is more than the width of the building foundation, it is a deep foundation. Deep foundations are often used to transfer building loads deeper into the ground. 

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Conditions where deep foundations are used

· Soil near the surface that has relatively weak bearing capacities (700 pounds per square foot or less)
· Soils near the surface that contain expansive clays (shrink/swell soils) 
· Surface soils that are vulnerable to being removed by erosion or scour

Classification of deep foundations 

Deep foundations are classified into three categories:
· Pile foundations
· Well foundations
· Caisson foundations

Types of foundations and basic mechanisms involved in the classification of deep foundations are reviewed in our FE Civil exam review course for those preparing to become an engineer in training.

Pile foundations

A pile foundation is defined as a series of columns constructed or inserted into the ground to transmit loads to a lower level of subsoil. A pile is a long cylinder made up of a strong material, such as concrete. Piles are pushed into the ground to act as a steady support for structures built on top of them. Piles transfer the loads from structures to hard strata, rocks, or soil with high bearing capacity. The piles support the structure by remaining solidly placed in the soil. As pile foundations are set in the soil, they are more tolerant to erosion and scour.

Installation of pile foundations 

Piles are first cast at ground level and then hammered or driven into the ground using a pile driver. A pile driver is a machine that holds the pile vertical and hammers it into the ground. Blows are repeated by lifting a heavy weight and dropping it on top of the pile. Piles should be hammered into the ground until the refusal point is reached, which is the point where a pile cannot be driven into the soil any farther. The method of installing a pile is a major consideration in the structural integrity of pile foundations. The driven-pile method is an ideal option because it least disturbs the supporting soil around the pile and results in the highest bearing capacity for each pile. Since every pile has a zone of influence on the soil around it, piles must be spaced far enough apart from each other so that the loads are distributed evenly.

Categories of piles

· Depending on their function, piles are classified as bearing piles, friction piles, friction-cum-bearing piles, batter piles, guide piles, and sheet piles.

· Based on the composition of materials, piles are classified as timber piles, concrete piles, sand piles, or steel piles. 

1)Bearing piles are driven into the ground until a hard stratum is reached. Bearing piles rest on hard strata and act as pillars to support the structure. Bearing piles allow vertical loads and transfer the building load to the hard stratum underneath. 

2)Friction piles are used when the soil is soft and there are no hard strata available. These piles are long, and the surfaces are roughened to increase surface area and increase frictional resistance. They bear on frictional resistance between their outer surface and the soil in contact. Friction piles do not rest on hard strata. 

3)Batter piles are driven inclined to resist inclined loads.

4)Guide piles are used in the formation of cofferdams to provide stable foundations for under-water construction.

Basic principles of pile foundations and their classifications are recommended topics to review prior to taking the FE Civil exam. 

Types of piles based on shape and composition


Wednesday, 14 June 2017

The Conduction Process and its Importance in Mechanical Engineering Applications

Introduction

Regions with greater molecular kinetic energy pass their thermal energy into regions with less molecular energy through direct molecular collisions. This process is known as conduction. In metals, a significant portion of the transported thermal energy is carried by conduction-band electrons.

Definition of Conduction

Conduction is the transfer of thermal energy that does not have any flow of material medium and is the main process by which thermal energy is transferred from one solid to another. Our PE Mechanical course reviews the physical properties of heat.

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Importance of Heat Transfer Conduction

· Sticking a metal pole into a fire is an example of heat transfer conduction. Particles at the heated end vibrate vigorously. They collide with the neighboring particles and transfer their energy. Eventually, the particles at the cooler end are set into vigorous vibration, which causes the entire metal pole to become hot.

Types of conduction

There are two types of conduction:
1)Molecular vibration
2)Free electron diffusion

Molecular Vibration

· When heat is supplied to one end of an object, the molecules at that end start to vibrate vigorously. During this process, they bump into their neighboring molecules, which transfers some energy. The receiving neighbor molecule gains energy and starts to vibrate more vigorously. The cycle continues.

Free Electron Diffusion

· This form of conduction takes place only in metals because only metals have free electrons. Electrons are freed from a molecule when heat is applied, which forces the electrons to travel toward the colder end of the metal. At the colder end, the electrons collide into many molecules, and therefore, pass energy to the molecules at the other side.

Conduction in Metals

· In solids, thermal energy is transferred through the vibration and collision of particles. However, in metals, due to the presence of free electrons, thermal energy is spread through electron diffusion. Electrons gain kinetic energy and move rapidly and collide with the atoms in the cooler parts of the metal to pass on their energy.

The process of conduction in metals is important for engineers to understand when preparing to pass the PE Mechanical exam.

Fourier’s Law of Heat Conduction

The law of heat conduction, or Fourier’s law, states that the time rate of the heat transfer through the material is proportional to the negative gradient in the temperature and to the area.

Q = -kA(dT/dx)
‘Q’ - heat flow rate by conduction (W)

‘k’ - thermal conductivity of body material (W m-1 K-1)

‘A’- cross-sectional area normal to direction of heat flow (m2) and ‘dT/dx’ is the temperature gradient (k-m-1)

· The negative sign in Fourier’s equation indicates that the heat flow is in the direction of negative gradient temperature, which makes the heat flow positive

· The thermal conductivity “k” refers to the transport properties 

· Thermal conductivity “k” provides indication of the rate at which heat energy is transferred through the medium by the conduction process 

Applications of Conduction Phenomena in Engineering

· Mechanical Engineering Equipment
· Home Appliances
· Boilers

Wednesday, 7 June 2017

Types and Sources of Air Pollution

Introduction

Air pollution is defined as the presence of any particle or gas found in the air that is not part of the original composition. Air pollution is a change in the physical, chemical, and biological characteristics of the air surrounding us. The substances that cause air pollution are called air pollutants, and they may be in the form of a gas, liquid, or solid.

PE Environmental Exam Course

Air pollutants are transboundary in nature as they travel and affect areas far away from their point of origin. Air pollution causes adverse effects on humans and other living organisms. Our PE Environmental exam review course thoroughly reviews the types and sources of air pollution for those preparing for the PE Environmental exam.

Air Quality Index

Air quality index (AQI) indicates whether pollutant levels in the air may cause health concerns. AQI ranges from 0 to 500, with a higher number meaning a lower air quality.

The table below provides the AQI limits for human health.


Air Quality Index
Air Quality
Air Quality Index Range
Good
0-50
Moderate
51-100
Unhealthy for sensitive groups
101-150
Unhealthy
151-200
Very unhealthy - ALERT
201-500

The air quality index table is a useful reference for environmental engineers preparing to take the PE exam.

Types of Air Pollutants

Air pollutants may be natural, such as wildfires, or may be synthetic (manmade). Air pollutants are classified as primary pollutants and secondary pollutants. 

· Primary air pollutants are emitted directly into the atmosphere by the original source
· Secondary air pollutants are formed because of reactions between primary pollutants and other elements in the atmosphere, such as the ozone.

The common air pollutants are discussed below:
· Carbon Monoxide - Carbon monoxide is a colorless, odorless gas. Carbon monoxide can be present in car exhaust and smoke. Carbon monoxide deprives humans of their oxygen supply, which causes headaches, fatigue, impaired vision, and even death.

· Sulfur Dioxide - Sulfur dioxide is produced when coal and fuel oils are burned and is also present in power plant exhaust. Exposure to sulfur dioxide narrows the airways in the respiratory system, which causes wheezing and shortness of breath. 

· Nitrogen Dioxide - Nitrogen dioxide is both a primary and secondary air pollutant. Nitrogen dioxide is created when nitrogen reacts with oxygen in the atmosphere. Nitrogen dioxide can cause respiratory infections and other respiratory problems.

· Particulate Matter - Particulate matter contains particles of different sizes that are released into the atmosphere from various sources, including fossil fuels, dust, smoke, and fog. Particulate matter can accumulate in the respiratory system, which can aggravate the heart and lungs and increase the risk of respiratory infections.

· Ground-Level Ozone – Ground-level ozone is formed from automobile, power, and chemical plant exhausts. Ground-level ozone irritates the respiratory system and causes asthma by reducing lung function.

· Smog - Smog is the combination of gases with water vapor and dust and forms when heat and sunlight react with gases, which is known as photochemical smog. 



Tuesday, 30 May 2017

FUNDAMENTALS OF KIRCHHOFF’S LAWS FOR ELECTRICAL ENGINEERS

Introduction

Kirchhoff’s laws are basic analytical tools used to obtain solutions for currents and voltages in an electrical circuit. Circuits may be from a direct-current system or from an alternating current system. The following diagram depicts a simple resistive network.
Figure: Simple Resistive Network

Kirchhoff’s laws of circuit analysis are reviewed in our FE Electrical exam review course. Kirchhoff’s Current Law (KCL) and Kirchhoff’s Voltage Law (KVL) are important for both DC and AC steady states, and they are important to understand for the FE exam.

fundamentals of kirchhoff's law

Parts of an Electrical Circuit

Node: In an electrical circuit, a node is the point where two or more components are connected. This point is usually marked with a dark circle or dot when being depicted on diagrams. The circuit in the diagram above includes nodes, which are labeled as “b” and “g.” A point, or a node in a circuit, specifies a certain voltage level with respect to a reference point or node.

Branch: A branch is a traversing path between any two nodes in a circuit that have electrical elements. The above diagram shows that the circuit has seven branches, of which four are resistive branches (a-c, a-b, b-c, and b-g), and the other three branches contain voltage and current sources (a-b, a-g, and c-g).

Loop: A loop is any closed path in an electrical circuit. A loop in a circuit consists of branches that have a beginning point and an end point for tracing the path of electricity. In the above diagram, loops/closed paths include a-b-g-a and a-c-b-a. Further, it may be noted that the outside closed paths are a-c-g-a and a-b-c-g-a.

Mesh: A mesh is a special loop that does not include any other loops within it. The above diagram indicates that the three loops (a-b-g-a, b-c-g-b and a-c-b-a) are also considered meshes, while the loops a-c-g-a and a-b-c-g-a are not considered meshes.

Kirchhoff’s Current Law:

KCL states that at any node in a circuit, the algebraic sum of currents entering and leaving a node at any instant of time must be equal to zero. Currents entering and currents exiting the node must be assigned opposite algebraic signs to assure the resultant equates to zero. Example: In the following figure, I1 – I2 + I3 – I4 + I5 – I6 = 0. 
Figure: Kirchhoff's Current Law

Kirchhoff’s Voltage Law

KVL states that in a closed circuit, the sum of all source voltages must be equal to the sum of all voltage drops. Voltage drops occur when the current flows from the higher potential terminal toward the lower potential terminal. Voltage rise occurs when current flows from a lower potential terminal toward the higher potential terminal or positive terminal of voltage source. 

Kirchhoff’s Voltage Law from the figure: in clockwise direction starting from the voltage source is: V1 – IR1 – IR2- V2 – IR3 – IR4 + V3 – IR5 – V4 = 0, V1 – V2 + V3 – V4 = IR1 + IR2 + IR3 + IR4 + IR5
Figure: Kirchhoff’s Voltage Law

Engineers preparing for the Fundamentals of Engineering Electrical and Computer exam should review Kirchhoff’s laws prior to the exam in order to be able to estimate currents and voltages in an electrical circuit.

Monday, 22 May 2017

The Importance of Geology in Structural Engineering

Introduction

Geology is the study of the earth, its origin, structure, composition, and history. There are many forms of geology, including economic geology, planetary geology, and engineering geology. Engineering geology is a very important topic for structural engineers to understand as it helps them properly plan a project when considering the design, location, and other important geological factors.

Structural Engineering Exam

Importance of Engineering Geology

Engineering geology helps ensure a safe and cost-effective design for construction projects. Gathering geological information for a project site is important in the planning, design, and construction phase of an engineering project. Conducting a detailed geological survey of an area before commencing a project will reduce the overall cost of the project. Common foundational problems in dams, bridges, and other buildings are typically directly related to the geology of the area where they were constructed. Our SE exam review course provides adequate geological information for engineers preparing for the SE exam.

The Need for an Understanding of Geology 

For quality control of construction materials, such as sand, gravel, or crushed rocks, an engineer with a geological background is needed. The knowledge of the nature of the rocks in a specific area is necessary for tunneling and determining the stability of cuts and slopes. Geological maps also help in planning projects. If geological features, such as faults, joints, beds, folds, or channels are encountered, suitable remedies should be incorporated. Geological maps provide information regarding the structural disposition of rock types in a proposed area. Topographical maps are essential for understanding the advantages and disadvantages of all possible sites. 

Hydrological maps provide information regarding the distribution of surface water channels and the occurrence and depth contour of ground water. Knowledge of ground water is necessary for excavation works. Understanding soil erosion transportation and deposition by surface water helps in soil conservation, river control, and coastal works. In geologically-sensitive areas, such as coastal belts and seismic zones, knowledge of the geological history of the area is very important. It is recommended that those preparing for one of the SE exams have a thorough understanding of geology and how to evaluate a site before a construction project.

Wednesday, 17 May 2017

Soil Erosion: Its Causes and Effects

Introduction

Soil is considered to be one of the most valuable natural resources. Soil is a combination of weathered rock, decayed organic matter, mineral fragments, water, and air. As degraded soil becomes loose and weak, it loses the ability to absorb and retain water, which leads to soil erosion. Ellison (1944) defines soil erosion as the process of detachment and transport of soil particles by erosive agents. 


Soil Erosion Factors

Factors that contribute to erosion include climate, topography, soil characteristics, vegetation, velocity of winds, rainfall intensity, and duration. Knowing the factors that cause erosion assists in identifying the source of erosion and developing a plan to control it. 

Erosion is classified into two major categories: geological erosion and man-made erosion. Geological erosion occurs naturally, while man-made erosion arises when humans alter the land. Soil classification and soil erosion factors are discussed in our FE Environmental exam review course to recap the fundamentals and factors of soil erosion.

Agents of Soil Erosion


Soil Erosion by Water

When a raindrop hits the soil, it destroys the granulation of soil (compaction) and causes a disruption of the soil surface (detachment). The exposed soil particles are dislodged, splashed into the air, and suspended in the rainwater. The rainwater that runs from a slope during heavy rains is referred to as a runoff. This runoff carries away soil particles and nutrient elements along with it.

There are three main types of erosion that occur due to water:

· Sheet erosion is the uniform movement of a thin layer of soil from unprotected land.

· Rill erosion forms when the rainfall is heavy and runoff volume increases. Runoff rain water creates many small, deep channels called rills.

· Gully erosion evolves from rill erosion over time. When runoff is in a single wide and deep channel, it is known as gully erosion. A gully is defined as a scoured-out area that is not crossable with tillage and grading equipment.

Soil erosion by water is thoroughly discussed in our FE Environmental exam refresher course.

Wind Erosion

Wind erosion occurs when land that is bare of vegetation is exposed to high-velocity winds. Soil movement is initiated when the forces of wind are exerted against the surface of the ground. 

For each soil type and surface condition, there is a minimum velocity required to move soil particles; this concept is known as threshold velocity. When wind threshold velocity overcomes the cohesive and gravitational forces of the soil particles, wind can move soil and carry it away in suspension.

Other Forms of Soil Erosion

Gravity erosion is the transfer of rock and soil down a slope due to the direct action of gravity; gravity erosion can cause a mass movement of soil, ice, and rock, which leads to landslides, avalanches, and rock fall. 

Glacier erosion occurs when a huge mass of ice slowly moves over the land. Glaciers erode the earth’s surface and wear down, pick up, and carry sediments that vary in size. 

Sedimentation control methods and the effects of soil erosion are important concepts to understand for the FE Environmental exam.

Wastewater Treatment Methods

Introduction

Water is an ideal solvent with a neutral pH value and is colorless, odorless, and tasteless in its purest form. Any physical or chemical change in water that affects the health of a living organism is known as water pollution. Water can become contaminated due to domestic, industrial, physical, chemical, and biological pollutants. 

Water pollution is a global problem affecting millions of lives.
· 1.8 billion people do not have access to clean water
· 70% of all industrial waste is dumped into bodies of water
· 2 million tons of sewage is disposed of into bodies of water each day throughout the world 
· 840,000 people die each year from water-related diseases

waste water treatment

Sources of Water Pollution

Water pollution comes in different forms and from different sources. 
· Point-source pollution: pollutants derived from a single-known source (pipe or sewer line)
· Nonpoint-source pollution: pollutants that come from many unknown sources (agricultural run-off)
· Trans-boundary pollution: pollutants that affect the environment hundreds of miles away from the source (nuclear incident)

Water pollution and the causes of water pollution are thoroughly reviewed in our PE Environmental exam review courses.

Wastewater Treatment 

The water used for industrial and domestic purposes is degraded with pollutants, and such water must be treated to remove pollutants before being released into bodies of water. The aim of wastewater treatment is to remove suspended solids, salts, nutrients, bacteria, and oxygen-demanding material. Wastewater treatment is a large industry that is worth $20 billion a year. Therefore, it is important to study wastewater treatment methods prior to taking the PE exam. 

Methods of Wastewater Treatment

Wastewater is treated by using different methods to remove pollutants before returning the water to the drinking supply.

Two methods of water treatment are employed based on the need: 
· Conventional method using sewage tanks
· Centralized wastewater treatment plants

Wastewater treatment involves three stages: 
· Primary stage
· Secondary stage 
· Tertiary stage 

The three stages involved in wastewater treatment are explained in the following flow charts:



Primary Treatment

Screening stage: Incoming raw sewage enters the treatment plant and passes through a series of screens to remove large, floating organic material.

Sedimentation stage: In the second stage, water enters the sedimentation tanks to remove sand, small stones, and grit. The particulate matter settles out to form a mud called sludge. In the next step, sludge is removed and transported to a digester. Primary treatment removes about 35% of biochemical oxygen demand (BOD) from the polluted water. 

Secondary Treatment

Secondary treatment is a biological process involving microorganisms. The wastewater is pumped into oxidation ponds where the microorganisms oxidize its organic matter, and then it is transferred from the primary sedimentation tank to the stabilization tank. The partly-treated water then enters the final sedimentation tank where the sludge settles. After the sludge is settled, it is transported to the digester.

Chlorination Stage

At this stage, the pH value of the water is near neutral. The BOD value of water is assessed, and the chlorination process is activated to kill harmful pathogens. After chlorination, water that is safe to use can be discharged. Secondary treatment removes about 90% of BOD. Secondary treatment does not remove all nutrients, heavy metals, solvents and pesticides. To be cautionary in regards to safety, water should be treated in an advanced stage that involves sophisticated methods and technology.

Tertiary Treatment

Tertiary treatment is a physicochemical process aimed to remove the turbidity of wastewater caused by nitrogen, phosphorus, dissolved organic matter, heavy metals, and pathogens. Tertiary treatment involves a chemical oxidation of wastewater using strong oxidizing agents, such as chlorine gas, perchlorate salts, ozone gas, and UV radiation. Tertiary treatment renders the water safe to be discharged back into the environment. 

Wastewater treatment topics are extensively discussed and emphasized in our PE exam review courses for both environmental engineers and water resources engineers.