Chapter 2 -Engineering Concepts ( soil, materials, air and fluid, electricity) Flashcards
this term refers to hte granular material, typically sand, gravel, and crushed stone, used in a variety of construction applications
aggregate
What two groups are aggregates divided into?
fine aggregates and coarse aggregates
Numbered (No.) sieve sizes are based on the number of square openings per linear inch of sieve. For example, No. 30 sieve has 30 openings per ______ or 900 square openings per _______
linear inch
square inch
what three ingredients is concrete made of?
aggregate, water, and hydraulic cement
What is the most common type of hydraulic cement
cement
ASTM (American Society for Testing and Materials) designates 8 types of portland cement:
Type 1 Type 1A Type 2 Type 2A Type 3 Type 3A Type 4 Type 5
Type of portland cement that is normal; general-purpose cement
Type 1
Type of portland cement that is normal, Air-Entraining and improved resistance to freeze-thaw cycles
Type 1A
Type of portland cement that is moderate sulfate resistance; used when in contact with water that has higher than normal, but not severe, sulfate concentrations
Type 2
Type of portland cement that is moderate sulfate resistance, Air-entraining with improved resistance to freeze-thaw cycles
Type 2A
Type of portland cement that is high early strength and provides high strength at an early period, usually one week or less
Type 3
Type of portland cement that is that is high early strength, air-entraining with improved resistance to freeze-thaw cycles
Type 3A
Type of portland cement that is low heat of hydration; used when rate and amount of heat during hydration must be minimized
Type 4
Type of portland cement that is that is high sulfate resistance and is used when in contact with water that has severe sulfate concentrations
Type 5
Other ingredients often added to concrete to alter the properties of concrete in various ways
admixtures
Type of admixture that improves concrete’s ability to resist freeze-thaw cycles and increase work ability of wet concrete. Commonly used in cold-weather climates that are subject to freeze thaw cycles
Air-entraining admixtures
Type of admixture that increases the workability of wet concrete without the additon of water. Commonly used in concrete overlays and patching
Water-reducing admixtures
Type of admixture that slows the curing time of concrete. Commonly used in hot weather to reduce the effects of high temperatures on curing
Retarding admixtures
Type of admixture that decreases the curing time of concrete. Commonly used to reduce setting time in cold-weather applications and to increase rate of strength development in tilt-wall construction
accelerating admixtures
Type of admixture that increases the fluidity of concrete without adding additional water. Commonly used for applications requiring very high slump, such as heavily reinforced structures.
Superplasticizers
What is the compressive strength of concrete generally expressed in? (units)
PSI
General use concrete compressive strength
3,000-5,000 psi
high-strength concrete compressive strength
6,000-20,000 psi
The specific formula and selection of materials that make up a concrete mixture
concrete mix design
concrete that is placed in its fluid state and allowed to cure (harden) and its permanent location on the jobsite
Cast-in-place concrete
This concrete mix is typically delivered by large specialty concrete trucks that slowly rotate the concrete mix to keep it from hardening during delivery
ready mix
Cast-in place concrete is commonly used for:
foundations, structural walls, slabs, sidewalks, lightweight floors, and roof deckin
Concrete that has been cast prior to placement on the job site
precast concrete
A place where concrete is cast off-site
precast plant (precast manufacturing facility)
RCP (an application for precast concrete)
reinforced concrete pipe
Applications for precast concrete
RCP, manhole structures, equipment pads, vaults, septic tanks, piles, columns, beams, parking decks, load bearing and veneer walls, planks, and lintels
uses a series of high-strength site-cast concrete wall panels that are cast atop a smooth casting slab. Once the panels have cured to approved strength, they are tilted (lifted) into place and become part of the buildings structure
tilt-wall construction
Most common forms of concrete reinforcement
Reinforcing steel bars or rebar
Welded wire fabric
Fiber reinforcement
Pre and post-tensioned concrete
Type of concrete reinforcement that is hot rolled, ribbed, round rods of steel that typically shipped in 60-ft lengths
Reinforcing steel bars or rebar
Type of concrete reinforcement that is grids of wire spaces 2in to 12 in apart, welded together, and fabricated into sheets or rolls for ease of use
Welded wire fabric
in rebar, 6 × 6 W1.4/1.4 has a grid spacing of 6 in. and a wire cross-sectional area of 1.4 hundredths of a square inch.
cool stuff man wow
Type of concrete reinforcement that is steel, fiberglass, synthetic, or natural fibers added in the concrete mix to increase strength, control cracking, and/or improve freeze-thaw resistance in concrete
Fiber reinforcement
Type of concrete reinforcement that uses tendons (typically cables in plastic sleeves) to strengthen the concrete by putting the concrete member under a compression load
Pre and post-tensioned concrete
concrete tendons are stressed at anchorage points before the concrete is placed
pretensioned concrete
tendons are stressed after the concrete has set
post-tensioned concrete
Term refers to building materials consisting of brick, block, stone, or other masonry units held together with mortar
Masonry
Two most common types of man-made masonry units
CMU (concrete masonry units)
clay bricks
Type of CMU strength that is placed at horizontal joints to help control shrinkage cracks
Joint reinforcement (look up picture)
Type of CMU strength that that is a highly fluid mixture of cement, sand, and water used to solid fill CMU cores and bond anchorage and reinforcement to surrounding masonry
Grout (look up picture)
Type of CMU strength that is used for horizontal reinforcement to incerase shear strength and distribute lateral loads. Typically laid one or more rows of rebar. commonly plaed at the top of walls, floor levels, openings, and as required for additional shear strength
bond beam (look up picture)
Type of CMU strength that is typically steel or precast concrete installed above openings and used to transfer lateral loads around openings
lintels (look up picture)
Type of CMU strength that is used to increase the thermal properties of the CMU wall. Three commonly used types are rigid foam inserts, expandable foam insualtion, and loose fill insualtion
core insualtion
Brick walls can be manufactured as:
solid, cored, hollowed, or frogged
Brick walls can be:
load bearing or non-load bearing
the thickness of brick walls are designated in terms of ______ a vertical layer of masonry units one unit thick
wythe
an exterior non-load bearing brick wall, typically used for aesthetic purposes that is anchored to a structural wall by metal ties or other anchoring methods
brick veneer wall
Masonry walls with multiple wythes of different types of masonry units. Ex) a brick veneer over a CMU wall assembly
composite walls
Conventional mortar has which 4 ingredients
sand, water, portland cement, and hydrated lime
Type of masonry mortar that is high-strength- mortar, typically used in high load areas and masonry below grade
Type M
Type of masonry mortar that is medium-high strength mortar, typically used in severe weather exposure areas with normal compressive loads
Type S
Type of masonry mortar that is medium-strength mortar, most commonly used as mortar above grade
Type N
Type of masonry mortar that is medium-low-strength mortar, typically used only for non-load-bearing interior walls and partitions
Type O
A material composed mainly of iron and less than 2% of carbon
steel
what does high carbon steel content result in?
steel that is hard and brittle
what does low carbon steel content result in?
steel that is soft and relatively weak
What does W8x18 mean
W designates the shape as wide flange
8 indicates a nominal depth of 8 inches
18 is the weight per foot of length in pounds
Two main classifications of wood
hardwoods and softwoods
wood harvested from broad-leafed deciduous trees
hardwoods
wood harvested from narrow, needle-leafed coniferous trees
softwoods
T/F: Softwoods are more abundant, less expensive, and typically used for most structural framing and sheathing, and hardwoods are used for furniture and high-end interior finishes
Treu
T/F: Wood is strong in compression in tension parallel to the grain but weak when applied perpendicular to the grain
True
The five most common types of wood products used in construction:
lumber, wood panel products, laminated wood, structural composite lumber, and wood manufactured building components
solid wood product cut directly from the log of a felled tree
lumber
boards are cut from the log to achieve maximum yield. Structural wood framing is typically cut like this
plain-sawn
boards are cut so that the grain runs perpendicular to the face of the board
quarter-saw lumber (look up picture)
T/F: Common grades of structural lumber, rated in decreasing order, are select Structural No.1, No.2, and No.3. The lower the number the better
True
Most structural lumber is cut S4S meaning
surfaced four sides
Wood product that is manufactured by adhering wood venners, strands, particles, and/or fibers together
Wood Panel products
Type of wood panel product that is made up of thin layers of wood veneers adhered together in alternating directions; typically used in floor, wall, and roof sheathing
plywood (look up picture)
Type of wood panel product that is made up of large strands of wood adhered together in layers of strands in alternating directions; typically used in floor, wall, and roof sheathing. Less expensive than plywood
OSB Oriented Strand Board (look up picture)
Type of wood panel product that is made up of wood fibers adhered together and sandwiched between outlside layers of wood veneers; typically used in cabinent construction and other none structural appliactions
Composite panels (look up picture)
Type of wood panel product thatis made of wood particles smaller than OSB adhered together; typically used in shelving, plastic laminte countertops, and other nonstructural applications
Particle Board (look up picture)
Type of wood panel product that is made up of wood fibers adhered together with resin; typically used in cabinents and moldings
Medium-density fiberboard (MDF) (look up picture)
Wood product that is manufactured by adhering strips of wood to cerate large structural members. Laminated wood members are commonly referred to as:
glue-laminated wood or glulam (look up picture)
Wood product that is manufactured by adhering wood veneers or strands to create structural members
Structural Composite Lumber (look up picture)
Type of structural composite lumber that is manufactured by using sheets of wood veneers; looks similar to thick plywood
Laminated veneer lumber (LVL) (look up picture)
Type of structural composite lumber that is manufactured by using narrow strips of wood veneers
Parallel strand lumber (PSL) (look up picture) (look up picture)
Type of structural composite lumber that is manufactured by using large strands of lumber; looks similar to thick OSB
Laminated strand lumber (LSL) (look up picture)
Wood product that is manufactured by combining and/or configuring standard lumber and/or wood panel products together to create efficient structural components
Wood Manufactured structural components (look up picture)
Type of Wood Manufactured structural component that is typically manufactured with 2x4s or 2xs joined together by metal plate connectors; use less wood, span greater distances, and allow for faster installation that stick built roof framing
Wood Roof Trusses (look up picture)
Type of Wood Manufactured structural component that is commonly manufactured with 2x4 or 2x6s top and bottom chords and same sized webbing joined together with metal plate connectors or smaller sized webbing finger joined and adhered together span greater distances an allow for ease of mechanical and electrical installation compared to conventional floor framing
Wood floor Trusses (look up picture)
Type of Wood Manufactured structural component that is an I-shaped member typically manufactured using solid lumber, LVL, or LSL top and bottom flanges with solid plywood or OSB webs; span greater distances, can come in long lengths, and are lighter than conventional floor framing
Wood I-joists (look up picture)
Type of Wood Manufactured structural component that is prefabricated floor, wall, or roof components constructed of dimensional lumber and/or wood panel products
Wood panel components (look up picture)
Which material isporne to fire damage and deterioration by moisture and insects?
wood
Concrete is strongest in:
compressive strength
Which of the following is a type of aggregate? A. gravel B. topsoil C. water D. cement
Gravel
Approximately what percentage (by volume) does aggregate make up in general-purpose concrete?
C. 75%
75%
What does a sieve size of No.4 mean?
The sieve has four openings per linear inch
The 10 in a W10 × 30 steel beam indicates what?
the nominal depth of the beam in inches
Which of the following mortar types has the highest strength?
Type M
Which 3 components does soil contain?
Solid ( weathered rock and decayed vegetaion), liquid (water), and gas (air)
Three broad classifications of soil:
Cohesive soils, Cohesionless soils, and organic soils
Type of soil classification that has very small particles that stick together
Cohesive soils
Type of soil classification that that does not tend to stick together such as gravel, sand, and silt
Cohesionless soils
Type of soil classification that contains organic material, such as peat
Organic soils
Typically used to classify soil and rock deposits in excavations based on their stability. OSHA standards classify four of these.
Soil Type
Soil and rock deposit, soil type that is natural solid material that can be excavated with vertical sides and remains intact while exposed
Stable rock
Soil and rock deposit, soil type that is undisturbed cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (tsf) or greaterhow
Type A
Soil and rock, Soil Type deposit that is cohesive soils with unconfined compressive strength greater than .5 tsf but less that 1.5 tsf; also include stable, granular, cohesion less soils; previously disturbed soils; and unstable rock
Type B
Soil and rock deposit, soil type that is cohesive soils with an unconfined compressive strength of .5 tsf or less, unstable soils, and saturated soils and rock
Type C
how are grain sizes determined?
sieve analysis
Soilers finer than a No.____ sieve size are considered fine- grained soils
200
T/F: Cohesive soils have particles that are too small to be determined by sieve analysis
True
what analyzes particles by indirectly observing their settling velocities in a soil-water mixture
hydrometer
4 Atteberg limit states that define soil consistency
liquid, plastic, semisolid, and solid
3 transition limits between the the atteberg limits
Liquid limit: Transition between liquid and plastic states
Plastic Limit: transition between plastic and semisolid staes
Shrinkage limit: transition between semisolid and solid states
3 phenomea related to water within soil
Permeability: the movement of water in soil through voids. Soils with large voids such as gravel and sand generally have greater permeability than soils with smaller voids such as clay
Capillarity: the rise of water, against gravity, from a water source into the voids within a soil. Soils with high capillarity typically have smaller grain size and higher permeability, usch as silts and very fine-grained sands
Frost heave: the vertical expansion of soil due to the freezing of water within the soil
Subsurface soil exploration consist of:
Boring: drilling or digging a hole in the ground. Common types are auger borings, wash borings, test pits, and core borings
Sampling: removing the soil from the hole. Samples classified as disturbed (auger and wash borings) or undistrubed (test pits and core borings)
Testing: the process of determing the properties and characteristics in the soil
What is the final step in soil investigation
soil investigation report or geotechincal report
Two main types of fouindations:
shallow and deep
this type of foundation bear on suitable soil foind at hte base of the structure. Less expensive than deep foundations
Shallow foundations
this type of shallow foundation is a pad of concrete that spreads a concentrated load from the building above
Isolated, single column or pad footing
this type of shallow foundation is a continuous strip of concrete that supports a continuous load above, similar to load-bearing wall
Wall, strip, or continuous footing
this type of shallow foundation is a concrete slab with thickened edges at loads above. Least expensive type of foundation. Typically used in areas with little or no ground frost
Monlithic slab on grade
this type of shallow foundation is a foundation wall, usually concrete or masonry, set atop a concrete strip footing. Typically used in areas with deep ground frost, low water table, and/or grade changes
Crawl space or basement
this type of shallow foundation is large, often thick, foundation that supports the entire structure. Often used whe ncolumn footings become large enough that they overlap or are more economical to pour as one unit
Mat or Raft foundation
Type of foundation that is used to penetrate upper layers of unsatisfactory soils to allow the structrue to bear on satisfactory soils or rock deeper in the earth,
Deep foundations
Type of deep foundation that is drilled or dug cyindrical shaft with belled end and, if required, filled with concrete. used to transfer loads through layers of satisfactory soils or rock below
Cassion
Type of deep foundation that is a material, typically timber, steel, or concrete, driven into the ground through unsatisfactory soil until a firm bearing layer (end bearing pile) or sufficient friction resistance (friction pile) is encountered
Piles
OSHA requires one of the following tests to be used for the manual field soil analysis:
Plasticity test: requires the tester to mold a moist or wet sample into a ball and attempt to roll it into threads. If the soil sample does not tear or break when held by one end, it is considered cohesive soil
OSHA requires one of the following tests to be used for the manual field soil analysis:
Dry strength test: used to determine the amount of strength and the presence of fissures in dry soils. If the soil and dry and crumbles on its own or with moderate pressure into individual grains of fine powder, it is granular
if the soilis dry and falls into clumps that break up into smaller clumps, but the smaller clumps can be broken up only with difficulty, it may be clay in any combination with gravel, sand or silt
If the dry soil breaks into clumps that do not break into small clumps and can be broken only with difficulty and there is no visual indication the soil is fissured, the soil may be considered unfissured.
OSHA requires one of the following tests to be used for the manual field soil analysis:
thumb penetration test: used to estimate the unconfined compressive strength of cohesive soils based on depth of thumb penetration
OSHA requires one of the following tests to be used for the manual field soil analysis:
pocket pentetrometer: direct reading, spring operated instrumetns used to determine the unconfined compressive strength of saturated cohesiv soils .Once pushed into the soil, an indicator sleeve displays the reading in either ton per square foot (tsf) or kilograms per square centimeter (kPa). Typically used on trench face or a large clump of soil. Penetrometers have error rates of +/–20%–40%.
OSHA requires one of the following tests to be used for the manual field soil analysis:
Shear vane, or torvane: hand-operated instrument used to determine the unconfined compression strength of soil. Soil strength is taken by pressing the instrument’s blades into a level section of undisturbed soil and slowly turning a torsional knob until soil failure occurs. The direct instrument reading must then be multiplied by 2 to provide results in tons per square foot (tsf) or kilograms per square centimeter (kPa).
OSHA requires one of the following tests to be used for the manual field soil analysis:
Drying test: used to differentiate between cohesive material with fissures, unfissured cohesive material, and granular material. The drying test procedure involves drying a sample of soil that is approximately 1 in. (2.54 cm) thick and 6 in. (15.24 cm) in diameter until it is thoroughly dry. If the sample develops cracks as it dries, significant fissures are indicated. Samples that dry without cracking are to be broken by hand. If considerable force is necessary to break a sample, the soil has significant cohesive material content. The soil can be classified as an unfissured cohesive material and the unconfined compressive strength should be determined. If a sample breaks easily by hand, it is either a fissured cohesive material or a granular material. To distinguish between the two, pulverize the dried clumps of the sample by hand or by stepping on them. If the clumps do not pulverize easily, the material is cohesive with fissures. If they pulverize easily into very small fragments, the material is granular.
Methods of soil compression:
- Consolidation: the extrusion of water from voids within a soil as a result of increased loading. The grain size and permeability of a soil greatly affect the length of time the consolidation process takes to complete. In soils with high permeability (i.e., coarse-grain soils, such as gravel and sand), consolidation occurs within a short time period. In soils with low permeability (i.e., fine-grain soils, such as clay), consolidation occurs over a long period of time. In fine-grained soils, consolidation is the leading cause of settlement.
- Compaction: the tightly pressing together of soil particles by expelling air from void space. Soil compaction increases a soil’s density and shear strength and results in a decrease in a soil’s permeability and future settlement. Compaction can occur rapidly during construction and is most effective with unsaturated soils.
3 Soil conditions:
Bank: soil that is in its natural, undisturbed state
Loose: soil that has been distrubed
Compacted: soil that has been compressed
Common types of mechanical equipment used in soil compaction
- Tampers: hand-operated devices that compact soil by delivering a series of vertical blows. Commonly used in areas with limited space not accessible by other types of compaction equipment.
- Plate compactors: hand- or machine-operated devices consisting of a flat, heavy metal plate that is vibrated up and down to compact soil. Commonly used in small or narrow areas, such as patios, small driveways, and trenches.
- Smooth wheel rollers: compact soil by use of heavy smooth metal rollers. Range in size from small to large. Small rollers are typically pulled by another piece of equipment, and large rollers may be pulled but are more commonly self-propelled with two or three rollers. Smooth wheel rollers are commonly used in compacting paving courses or to provide a smooth ground surface and can cover large areas quickly.
- Sheepsfoot rollers: compact soil by use of a heavy metal drum with projecting metal feet. The feet create a kneading action that is more effective in compacting fine-grained soils, such as clay, than are smooth wheel rollers. Typically self-propelled and used to cover large areas.
- Pneumatic rollers: compact soil by use of several highly inflated rubber tires. Pneumatic rollers are typically pulled by another piece of equipment. Commonly used for compacting clay and silty materials or granular material containing small amounts of fines.
- Vibratory rollers: compact soil by vibrating a roller up and down as it moves across the soil. Typically self-propelled and used in compacting granular materials, such as clean sands and gravels.
2. Clay is what type of soil? A. solid rock B. cohesive soil C. cohesionless soil D. organic soil
Cohesive soil
3. Sand is what type of soil? A. solid rock B. cohesive soil C. cohesionless soil D. organic soil
Cohesionless
4. Soil that has been excavated and stockpiled is considered to be in a \_\_\_\_\_\_\_\_ state. A. natural B. bank C. loose D. compacted
loose
- What is the purpose of a visual field soil analysis?
A. see how much work has been completed
B. establish general soil classifications
C. check for the presence of worms in the soil
D. develop an excavation plan
B.
6. What is the correct order of subsurface soil exploration? A. boring, sampling, testing B. sampling, boring, testing C. sampling, testing, boring D. testing, sampling, boring
boring, sampling, testing
7. Fine-grained soils are soils finer than a \_\_\_\_\_\_\_\_\_\_\_. A. No. 60 sieve B. No. 100 sieve C. No. 200 sieve D. No. 400 sieve
No. 200 sieve
is used in concrete construction to mold and control concrete to attain a desired size, shape, placement, and/or finish of the cast concrete.
Formwork
Type of prefab form that is reusable forms comprising a system of panels, hardware, and ties. Panels are typically manufactured in modular sizes, often 2 ft or 4 ft wide and ranging in height from 2 ft to 8 ft. The most common panel forming systems are unframed plywood panels, all-metal panels, and metal-framed plywood panels.
Panel forms and systems
Type of prefab form that is single-use one-piece form. Forms can be easily cut by saw to desired length and commonly range in diameter from 6 in. to 48 in.
Tubular fiber column forms
Type of prefab form that is reusable one-piece form that bolts or clamps along a single joint to allow the form to be removed after concrete has cured. Common diameters range from 12 in. to 36 in.
Round glass fiber-reinforced plastic column forms
Type of prefab form that is reusable forms made up of sections connected by hardware with bracing built into the forms. Forms commonly range in diameters from 14 in. to 10 ft and vertically from 1 ft to 10 ft in height.
Round steel column forms
Type of prefab form that is single-use forms made up of interlocking modular units or panels of rigid insulation. Forms remain in place, becoming a permanent part of the structure with added R-value.
Insulated concrete forms (ICFs)
Type of prefab form that is le-use ribbed or corrugated sheets of steel that form, support, and reinforce cast concrete. Metal decking is most commonly used in concrete floor and roof slabs and comes in various gauges and styles. Once the concrete is placed, the metal decking becomes a permanent part of the structure.
Metal deck
The most common loads encountered in formwork are
vertical loads, lateral loads, and loads imposed by the lateral pressure of fresh concrete.
ACI
American Concrete Institute
Include dead loads - such as the weight of the concrete and live loads - the weight of the workers, equipment, and stored materials
Vertical loads
LOOK AT LIVE LOAD EXAMPLE ON PAGE 37 OF THE PDF
LOOK AT LIVE LOAD EXAMPLE ON PAGE 37 OF THE PDF
Type of load that includes wind, movement of concrete equipment, dumping od concrete, and inclined forms
Lateral loads
The ACI recommends a minimum lateral load for slab forms of ____ plf of slab edge, or _____ of the total dead load, whichever is greater.
100 ; 2%
The basic formula for calculating lateral pressure of freshly placed concrete is
Ccp = wh
where
CCP = lateral pressure in pounds per square foot
w = weight of fresh concrete in pounds per cubic foot
h = depth of the concrete in fee
perpendicular forces will cause shaer and bending in the beam
Shear: There are two common types of shear that may affect a beam: vertical shear and horizontal shear. Vertical shear is the tendency of one part of the beam to move vertically to an adjoining part of the beam, perpendicular to the beam’s axis. Horizontal shear is the tendency of a beam’s fibers to slide horizontally past one another, parallel to the beam’s axis.
• Bending: A beam will have a tendency to bend when forces/loads are applied to the beam. The bending of a beam results in deflection. Deflection is the amount a beam bends when a force/load is applied. Deflection is typically measured in inches.
1. Wood, steel, and rigid insulation are all used for\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. A. concrete finishing B. formwork shoring C. strengthening concrete D. concrete formwork
Concrete formwork
2. Deflection is a result of what type of stress? A. bending B. tensile C. shear D. axial
bending
3. Which of the following is a type of multiuse form? A. tubular fiber column forms B. insulated concrete forms (ICFs) C. panel forms D. form release
panel forms
4. Which of the following would be considered a dead load? A. workers B. equipment C. stored materials D. formwork
formwork
is the term used to describe the thermodynamic properties of air mixed with water vapor. In
Psychrometrics
7 properties of psuchometrics:
• Dry bulb temperature (DB) is the air temperature and is the measure of sensible heat.
q
• Wet bulb temperature (WB) is the air temperature measured with a thermometer with a wet cloth sock over it. As the water in the sock evaporates, the temperature on the thermometer is lowered through the latent heat of the evaporation process. Wet bulb and dry bulb temperatures are equal only when the air is 100% saturated (100% RH) and no evaporation can take place. When the air is not 100% saturated, the wet bulb temperature will always be lower than the dry bulb temperature. The wet bulb temperature is the lowest temperature that air can be cooled by the evaporation of water.
• Dew point temperature (DP) is the temperature at which the water vapor in the air begins to condense. At this point, the air is 100% saturated and cannot hold any more water vapor. Relative humidity (RH) is the ratio of moisture in the air compared to how much that same sample of air could hold and is expressed as a percentage. Air that is holding .008 lb of water but has the
capacity of holding 0.10 lb would have a relative humidity of 80%.
- Humidity ratio or absolute humidity (W) is the amount of water in 1 lb of dry air. It is expressed as either grains of moisture per pound of dry air (gr/lb) or pounds of water per pound of dry air (lb/lb). A grain of moisture is 1/7,000 lb. This is a measure of latent heat in the air.
- Specific volume (v) is the physical size or volume of 1 lb of dry air. As air is warmed and humidified it gets larger. As it cools and dehumidifies, the same mass of air gets smaller.
- Enthalpy (h) is the total amount of thermal energy (sensible and latent) in the air. It is measured in BTUs per pound of dry air.
A graphical representation fo the 7 properties of air described above
psychometric chart
Important terms
Sensible heat: heat added to the air without adding moisture. As sensible heat increases the points on the psychrometric chart move to the right.
- Latent heat: the hidden heat added to the air by adding moisture (approximately 1,000 BTUs/lb of water). As latent heat increases the points on the psychrometric chart move up.
- British Thermal Unit (BTU): a quantity of heat. It is the amount of heat needed to raise a pound of water 1º F. An MBH is 1,000 BTUs/hr.
1. Which property of air is the best measure for latent heat? A. dry bulb B. relative humidity C. enthalpy D. humidity ratio
humidity ratio
3. If you have an air sample with a dry bulb temperature of 60º F and an RH of 100%, what is its wet bulb temperature? A. 30º B. 60º C. 90º D. 120º
60 degrees
4. Using the psychrometric chart, if you have an air sample with a dry bulb temperature of 60º F and a humidity ratio of 23.0 gr/lb, what is its relative humidity? A. 10% B. 30% C. 50% D. 70%
30%
- Air sample A has a dry bulb temperature of 80º F and a relative humidity of 90%. Air sample B has a dry bulb temperature of 65º F and a relative humidity of 90%. Which of the following statements is true?
A. A has more sensible heat but the same latent heat as B.
B. A has less sensible heat but more latent heat as B.
C. A has more sensible and latent heat as B.
D. A has less sensible and latent heat as B.
A has more sensible and latent heat as B
the flow of electrons through a conductor
Electrical energy
the electromotive force (EMF) or potential difference that cause an electric current to flow
Voltage
the flow of electrons. 1 coulomb per second
current
the internal property of matter that resists the flow of current. The unit of measure is the ohm (R). Materials with low resistance are called conductors. Materials with high resistance are called insulators.
Resistance:
Ohm’s Law
Voltage = Current × Resistance (E = IR)
Cicuits can be in series or parallel. circuits in series are added how?
Rt = R1 + R2 + R3 + Rn
Cicuits can be in series or parallel. circuits in parallel are added how?
1/Rt = 1/R1+1/R2+1/R3+1/Rn
the flow of electrons in a single direction
Direct current
the electrons alternate the direction of the current
alternating current
The ________ _________ used is called real power or working power. The____________ _________ is a number from 0 to 1 and is a measure of how much of the available power is being used.
actual power ; power factor (PF)
The unit of measure for AC power is what?
watt
power available to use
apparent power
Single Phase apparent power formila
Papparent = Voltage (E) × Amperes (A)
Three Phase apparent power formila
Papparent = 1.73 × Voltage (E) × Amperes (A)
Single Phase real power formila
Preal(watt) = VAPF
Three Phase real power formila
Preal(watt) = 1.73 VA*PF
__________ is the rate of energy transfer. In a building, power is how much electricity is being used at any given point in time. A 60 W lightbulb is consuming 60 watts per second. It’s a rate of energy consumption.
Power
__________ is the ability to do work and is quantifiable. It’s the rate of consumption multiplied by time.
Energy
Energy = W × hr
Because the watt is relatively
1. If you have 10 Ω of resistance and a voltage of 20 V, how much current is going through the circuit? A. 0.5 A B. 2 A C. 10 A D. 200 A
2A
2. Which is the unit of measure for AC power? A. volt B. ampere C. watt D. coulomb
watt
3. If you have three resisters in series and they each have 4 Ω of resistance, what is the total resistance in the circuit? A. 0.75 Ω B. 1.33 Ω C. 4 Ω D. 12 Ω
1.33 ohms
4. If you have three resisters in parallel and they each have 4 Ω of resistance, what is the total resistance in the circuit? A. 0.75 Ω B. 1.33 Ω C. 4 Ω D. 12 Ω
1.33 ohms
5. In the United States, alternating current is provided by utility companies at \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ hertz or cycles per second. A. 1 B. 50 C. 60 D. 100
60
6. If a three-phase circuit has 240 V, using 100 A with a power factor of .5, what is the real power? A. 0.24 W B. 12,000 W C. 20,760 W D. 24,000 kW
20,760 W
7. If a single-phase circuit has 120 V, using 10 A with a power factor of .8, what is the apparent power? A. 12 W B. 1,200 W C. 1,661 W D. 2,076 W
1200 W
