PPD Equations Flashcards
What equation do you use to determine a material’s R-Value using K?
K= in/R
solve for R
The k-factor of a material is a measure of thermal conductivity and not thermal resistance. Thermal resistance is measured by a material’s R-value. The higher the R-value, the better the thermal insulation. The K-factor can be determined by taking the thickness of the insulation and dividing it by the R-value.
In this example, K-factor = 10
10=8 inches/R
10R=8
R=.8
Exit corridors shall be designed such that no corridor results in a dead end longer than 20 ft.
In certain occupancies, if the building is equipped with an automatic sprinkler system, the length of the dead-end corridor can be extended to ____ ft.
According to IBC 2015 Section 1020.4, Exception 2, in occupancies B, E, F, I-1, M, R-2, R-4, S, and U that are sprinkled, a dead-end corridor is allowed to be extended to 50 ft.
How many SF are in an Acre?
43,560 SF
An architect is reviewing the ventilation requirements for an enclosed attic space of 3,000 square feet. The ceiling of the attic is applied directly to the underside of the roof framing members and includes fiberglass bat insulation along with a Class I vapor barrier.
What is the minimum allowable area of ventilation for this space?
Based on the requirements of International Building Code (IBC, 2015) Section 1203.2, 1/150 of the roof's area is required for ventilation. (1/150)*3000 square feet = 20 square feet. In order to reduce the ventialtion requirement to 1/300, the architect would have to meet both exceptions 1 & 2 of IBC (2015) 1203.2. Even though the question states that a class I vapor barrier is being used it doesn't state what climate zone the project is in.
Given a 300-Hz sound traveling in a solid concrete structure at a 10,500 ft / sec speed, find the distance within which a complete cycle of disturbance takes place.
The distance a sound travels in one cycle is the wavelength of the sound. The speed c is the product between frequency f and wavelength.
λ (c = f λ), so the distance λ is 10,500
ft / sec divided by 300 Hz, which is 35 ft.
A structural engineer has told an architect that the total pressure on a retaining wall cannot exceed 1,500 plf. The concrete wall has a total length of 40 feet and is adjacent to a parking lot.
How high can the architect make the wall? Assume the pressure is 30 lbs/ft^3.
the answer is 10
We will use the formula P= 0.5 (p) h^2, where the variables are defined as follows:
P = total pressure (1500 plf) p = media pressure (30 lbs/ft^3) h = height
Plugging in the numbers that are known, we get:
1500 plf = 0.5 (30 lbs/ft^3) (h^2)
Using algebra to solve for h, we find the answer:
h = 10 ft.
What is the equation for Deflection?
Deflection = 5wL4 / 384EI
Wd = Dead Load Weight L = Length in inches E = modulus of Elasticity I = moment of Inertia
- Correct: By increasing “I”, moment of inertia, the deflection value will decrease.
- Incorrect: By decreasing “I”, the deflection value will increase; thereby exceeding
allowable deflection. - Correct: By increasing “E”, modulus of elasticity, the deflection value will decrease.
- Incorrect: By decreasing “E”, the deflection value will increase; thereby exceeding
allowable deflection. - Incorrect: By increasing the beam length, L, the deflection value will increase, thereby
exceeding allowable deflection. - Correct: By decreasing the beam length, L, the deflection value will decrease.
Resource: Simplified Engineering for Architects and Builders, Parker, Ambrose, Chapter 3, pp. 86-156
Section Modulus (S) is used in equation….?
Section Modulus (S) is used in equation F = M/S,
Allowable bending stress = Maximum Moment divided by Section Modulus or to find the Maximum stress (F) divide the force trying to bend the beam (M) by how strong the beam is (S).
The greater the weight (steel beam), the stronger, but also more expensive since there is more material (steel) in the beam. Therefore, a W10x60 is stronger than a W12x14, but is more expensive. One might use it in order to reduce the floor to ceiling height, since it is 10-inches tall versus 12-inches tall.
Resource: Fundamentals of Building Construction, Materials and Methods, Allen, Iano, Chapter 11: Steel Frame Construction, p. 430
Drift of one story relative to an adjacent story may not exceed 0.0025 times the story height. IBC If the story height is 13 ft, what is the maximum drift?
Step 1: Convert to inches
13’ x 12”/ft = 156”
Step 2: Calculate drift
156” x 0.0025 = 0.39” maximum dri
Formula: Soil capacity or Pressure = P (force) / A (area)
Step 1: Calculate tributary area 30’ x 42.5’ = 1,275 sf Step 2: calculate total loads (LL + DL) 90 + 30 + 40 + 30 = 190 psf Step 3: 1275 sf x 190 psf = 242,250 lbs Step 4: Calculate area of footing Formula: Soil capacity or Pressure = P (force) / A (area) 4250 psf = 242,250 lb / Area Area = 242,250 lb / 4,250 lb/sf
SLENDERNESS RATIO – RADIUS OF GYRATION
Length of column in inches (so multiply feet x 12 in/ft) divided by Radius of gyration (in inches)
Using same example, what is radius of gyration, if column is 10.5’ and Slenderness Ratio is 100? L/r = SR 10.5’ x 12”ft = 126” 126”/r = 100 r = 126”/100 r = 1.26” Using same example, what is length of column if SR = 120” and radius of gyration = 1.4? L/r = SR L = 1.4 (120) L=168”or(168”/12”)=14’
What is size of footing? Soil capacity is 4000 psf.
Pressure = P (force) / A (area)
P= F/A
What is the equation for overturning moment?
OM = Force X Distance
OM = Force X Distance OM=30Kx(30’+3’) OM=30KX33’ OM = 900 Kip-ft
Linear Expansion/Elongation due to Temperature
∆L = C x ∆T x L
First thing to know: Steel has a linear coefficient of thermal expansion = 0.0000065 inches/inch/1°F Question should provide that value.
∆L = thermal expansion or elongation in inches
C = Coefficient of expansion for steel = 0.0000065 inches/inch/1°F
∆T = Temperature Differential = 120 °F
L=Lengthofbeam=55’ (needtoconverttoinches) 55’x12’/inch=660inches
Equation: ∆L = C x ∆T x L
∆L = 0.0000065 x 120 x 660
∆L = 0.5148 inches
Wind pressure is given by the equation P = 0.00256 x V^2 where V= Speed of wind in mph. Result is in PSF
Wind pressure is given by the equation P = 0.00256 x V^2 where V= Speed of wind in mph. Result is in PSF
Life cycle cost equation
Life-cycle cost in equation form is:
LCC = IC + MC + AC + OC
where, IC = investment cost (first cost minus salvage)
MC = maintenance & repair cost
AC = amortization cost (replacement)
OC = operating cost (including labor and energy)
An office building has a usable area of 29,150 sf and a base building efficiency of 0.78. If the building has a rentable area of 35,574 sf, what is the building’s load factor?
Load factor = Rentable area / Usable area
Load factor = 35,574 sf / 29,150 sf
Load factor = 1.22
How do you calculate rentable area of a bldg?
Rentable area = Usable area x Load factor
F=M/S
F = allowable bending stress M = maximum moment S= section modulus
(maximum stress is equal to the force trying to bend the beam divided by how strong the beam is)
Maximum Bending moment (M) is also know as the force trying to bend the beam. To solve for M use what two equations?
wl²/8 (simple beam with uniform load)
PL/4 (simple beam with point load mid span)
What is the Section Modulus?
strength of the beam due to its cross section due to the shape and how much material is in the beam
How to decrease stress?
decrease the moment or increase the section modulus
WL²/8 (simple beam with uniform load)
W=weight (pressure or weight x width of spread)
L=length of beam
W12 x 26 beam is appx how tall and how many lbs per linear foot does it have?
12” tall
26 lbs per linear foot
Vapor barriers go on what side of the wall?
warm side of the insulation over the sheathing
in the south-outside
in the north-inside
deflection formula
∆ = 5 WL^4 / 384 EI
W= weight L= length E= modulus of elasticity (higher is better) I= moment of inertia (higher is better)
-if you want to limit deflection either decrease the top half or increase the bottom half
What is the approximate modulus of elasticity for wood?
1.3 -2.0 million PSI (1.6 average)
What is the approximate modulus of elasticity for steel?
29 million PSI (constant)
