Final Exam Study Guide Flashcards
What is a force that tends to cause a rotation or twist about a point?
Moment
What is a moment?
a force that tends to cause a rotation or twist about a point
Moment Equation is M= ? * ?
M=F*(perp dist to origin)
What are the units of a moment?
Force times distance
Name 2 examples of a moment unit
kip-ft, kip-in, lb-ft, lb-in
What is the difference between a dead and a superimposed dead load?
dead– only the structural weight
superimposed– all permanent loads (flooring, roofing, permanent equipment, MEP)
Name some types of superimposed dead loads
flooring, roofing, permanent equipment, MEP
Name some types of dead loads
this is me being silly & tricky,,, it’s just the self-weight
What is the load on a structure that is temporary or transient?
Live load
What is a live load?
A load on a structure that is transient or temporart
What are some examples of live loads?
People, vehicles, partitions, furniture, moveable equipment, snow
What are the units of inertia?
(unit of length)^4
What is a mathematical expression that describes the relative location of material in a cross section?
Moment of Inertia
What is a moment of inertia?
Relative location of material in a cross-section. It resists bending stress and deflection
What is another name for moment of inertia?
Second moment
What is moment of inertia a measure of?
Cross-sectional stiffness
How would one find the Moment of Inertia of Hollow Shapes?
If the centroids of two shapes coincide, you may subtract the moment of inertia of the void from the moment of inertia of the overall body. THIS IS CALLED THE NEGATIVE AREA METHOD
What is the manner in which loads travel throughout the structure?
Load Path
What is a Load Path
the manner in which loads travel throughout the structure
What concept considers the area that a member must support as being halfway between the adjacent similar members?
Tributary area
What is tributary area?
concept that the area that a member must support as being halfway between the adjacent similar members
Beams are classified based on ____
support conditions
What is a simply supported beam?
2 supports, 1 on each end
What is a continuous supported beam?
3 or more supports
What is a cantilever beam
1 end supported rigidly
What is an overhang beam?
2 supports but 1 or both are not located at the end
What is a propped beam??
2 supports, 1 end is fixed
What is a restrained or fixed beam
both supports are fixed, allowing no rotation
What is the mathematical relationship between nominal and actual dimensioning?
1 nominal inch=3/4 actual inch
2-6 n”= -.5” actual
8+” n= -3/4” actual
What concept is represented by the equation I/C, where I is the moment of inertia and c is the distance from the centroidal axis to the extreme fiber
section modulus S
What is the variable S?
Section modulus, a ratio that can be standardized for materials of given size/makeup & found in tables
What is the equation for section modulus S?
I/C
Where C is the distance from the centroidal axis to the extreme fiber
and I is the moment of inertia
This equation is not usually used for standard shapes bc S is in tables
What is the variable fb?
fb is the bending stress at the extreme fiber, top or bottom
What is the formula for bending stress or flexure?
fb= Mc/I or M/S since S=I/C
M is the bending moment in the beam, usually Mmax and found through the shear & moment diagrams
S is the section modulus, found in a table
What equation could be used to determine the required section modulus when designing a wood beam?
Sreq=M/Fb
where Fb is the allowable bending stress
M is the maximum bending moment in the beam (shear&stressgraphs)
What is a load in which the resultant concentrat4ed load passes through the centroids of all resisting sections
Axial load
What is a load in which the loads are applied transversely to the longitudinal axis of the member.
Flexural or bending load
What is an axial load?
a load in which the resultant concentrated load passes through the centroids of all resisting sections
What is a flexural load?
load in which the loads are applied transversely to the longitudinal axis of the member. also known as bending load
Stress flexural
What is the quantity of force that acts on a unit of area
stress
What is normal or axial stress
force per unit area. Stress acts perp. to the cross-section
What is the average value of the axial stress?
f = σ = P / A
where P is axial force
and A is perp. resisting area
What is shear stress?
quantity of tangential force acting over an area parallel to the direction of the applied load. Acts parallel or tangential to the cross-section
What is the formula for shear stress?f
fv = τ = V / A
Where V is shearing force
A is cross-sectional area parallel to load direction
What type of stress is the primary concern when designing beams?
flexural or bending stress
What is the formula for bending stress
σb = M * c / I
where σb is bending stress
M is bending moment
c is distance from centroid to extreme top & bottom fibers
I is moment of inertia
Is bending stress for unsymmetrical cross-sections determined by the the smaller or larger of the distances from the centroid line to the extreme top/bottom?
larger of the 2. distance c.
What is the sign convention for compression & tension?
compression is (-)
tension is (+)
What is strain?
deformation per unit length. results from stress or temperature change.
What is the symbol δ
deformation
What is the symbol ε
normal STRAIN
symbol γ?
shear strain
What is normal/axial strain?
deformation per unit length resultant from a normal load.
What is the formula for normal strain?
ε =δ/L
Where ε is strain
δ is the change in length
L is the original length
What is the modulus of elasticity
Also called young’s modulus
Measure of the material stiffness or how much stress it will take to cause a unit strain (contraction or elongaiton)
What is the equation for modulus of elasticity?
Hookes Law: E =σ/ε
modulus = stress / strain
What is shear strain?
deformation due to shear stress, which is stress acting parallel to the cross section, results in changes to shape but not volume. represented by γ
What is the formula for shear strain?
γ = δs/L = tanφ
where γ is shear strain
δ is shear deformation (distance one point of original side moves)
L is original length
φ is angle that the original side moves
What is bending strain?
deformation per unit length due to bending stress
What is the difference between ductile and brittle materials?
Ductile materials have molecular bonds that reform after exceeding the elastic limit that will result in permanent deformaiton while still remaining in one piece without a significant loss in strength.
Brittle materials when the elastic loimit is exceeded are unable to reform , causing cracks or seperation of material
Give examples of ductile materials
low-carbon steel, aluminum, copper, gold
give examples of brittle materials
cast iron, high-carbon steel, ceramics
What is lumber grading?
Lumber is graded according to its quality, strength, and appearance, with trained inspectors using standardized criteria such as knots, grain patterns, and defects to assign a grade. This classification ensures that lumber meets industry standards and facilitates its appropriate use in construction and manufacturing.
Do grades of lumber go up or down from 1 to 3?
1 is best quality, 3 is cheapest. select structural is highest. below 3 is stud, then construction.
What is allowable stress?
Stress that a member can hold. Allowable stress divided by failujre stress provides the factor of safety.
Section modulus rectangle?
S = bh^2/6
How is stiffness of material evaluated?
Young’s modulus or the modulus of elasticity, which is the slope of the straight-line portion of a stress-strain daigram.
E = f/ε
where f is stress and ε is strain
What is ultimate strength?
absolute highest stress magnitude on a stress-strain graph
A structural system that distributes loads to supports through a alinear arrangement of various-sized members in patterns of planar triangles
truss
What is a truss?
a structure that consists of members assembled such that they resist loads axially only
Truss members are connected by ____
smooth pins @ their joints
all loading is applied ____ of a truss
at the joints
since members are ____, their weight is ____ compared to joint loads.
slender, negligioble
What are the only forces oln truss members?
compression & tension
What is a zero force member?
An unloaded joint where 3 members frame together. if 2 members are in a straight line, then the 3rd is zero force.
What is deflection?
A stiffness requirement representing a change in vertical position of a beam due to the applied loads.
What is the equation to find actual deflection on a simple span with a uniform load?
deltamax=5wL^4/384EI
where delta is deflection
w is the applied loads
E is the elastic modulus
I is the moment of inertia
What is the shortcut formula form Maximum moment of a simply supported beam?
`wL^2/8
where w is the total load (dead+live)
L is the length of the beam
What is the shortcut for Vmax of a simply supported beam?
wL/2
where w is the total load on the beam
L is the length of the beam
What is the shortcut for cross-sectional area required of a simpy supported beam?
Areq=1.5Vmax/Fv
Where Vmax is the maximum shear on the loaded beam (found by wL/2)
Fv is the maximum shearing stress, may be given in the problem.
What is the formula for allowable deflection of a simply supported beam?
deltaallowable(DL+LL) = L/240
where L is the length of the beam
deltaallowable (LL) = L/360
***dont forget to multiply L by 12 if it is in feet and not inches