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60 Cards in this Set
- Front
- Back
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Shears
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External force that acts parallel to a place, unlike compressive force and tensile force which act perpendicularly
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stress
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internal resistance to external force (psi)
P/A |
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strain
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deformation of a body due to external forces (inch)
delta/ L |
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Young's modulus
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modulus of elasticity
E = stress/strain E= (P/A) / (delta/L) E is a measure of material stiffness |
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centroid
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center of mass
all area of sections can be concentrated at centroid without impacting moment of area about any axis |
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positive & negative moment
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for a simply supported beam under a point load or uniform load, the beam will deflect/sag forcing the top area into compression, the bottom into tension
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bending stress
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the maximum tensile stress of compressive stress at a particular point on/in a beam at the extreme fibers of the beam
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flexural bending formula
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M y / I
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shear stress
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the maximum stress occurs at the neutral axis
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bending stress
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f = MC / I
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Truss
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framework of connected members which resist loading primarily in axial forces (compression or tension) but not in bending
Members are connected together at panel points, to which we can apply point loads. |
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truss types
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parallel chord, crescent, bowstring, king post, etc
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method of joints
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perform a series of of equilibrium equations. Easy but long
Determinte support reactions create a free body diagram at 1 of the supporting panel oints Determinte the vertial and horizontal components of each chord Repeat as needed for each point as you move through the truss *careful with +/- direction of forces |
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method of sections
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perform one set of equilibrium equations with pythagoras. Tricky but short
1. Determine support reactoins 2. create a free body diagram which cuts through the member you wish to analyze and cuts through the full frame 3. label each point. member names are the start and end panel point. 4. Translate forces in the member of importance along its line of action..... judgement call 5. Use equilibrium equations to determine the vertical components of the members 6. use pythagoras to determine the diagonal force in the member. |
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ASD
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Allowable stress design
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LRDF
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Load Resistance factored design. - pretend we have more load
causes more vibrations. cheaper buildings, but has other problems. |
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shear & beams
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steel beams rarely fail due to a shear failure mechanism. exceptions: very short beams, heavily loaded
Vn = 0.4 Fy Aw |
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radius of guration
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r = (I / A) ^1/2
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allowable compressive stress of a column
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Fcr / (omega)
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effective depth in concrete design
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total dimension of concrete - cover (space beyond rebar for protection) - half the rebar diameter
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concrete design dead load & live load factors
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1.2 x dead load, 1.6 x live load
code req's that the beam depth d be 1.5 the width |
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Concrete Ultimate moment capacity formula
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Mu = (reduction factor) As Fy (d - a/2)
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cylinder test
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test compressive strenght of concrete
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concrete mix
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non homogeneous mixture of coarse and fine aggregates bound by cementitious paste that includes portland cement, admixtures and water
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hardwood and softwood
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softwoods are evergreens
hardwood are bad for the environment |
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Wood moisture content (MC)
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wood swells with increased humidity. Lower MC is dryer wood, typically denser, and has better E value
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most commong structural wood in US
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Douglas Fir and Souther Pine
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Shear stress formula
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v = V Q / I b
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deflection uniformly supported beam formula
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(5/384) w L^4 / E I
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Notching of beams
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a type of connection. requires the beam to be checked for shear failure
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Wood moisture content (MC)
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wood swells with increased humidity. Lower MC is dryer wood, typically denser, and has better E value
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most commong structural wood in US
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Douglas Fir and Souther Pine
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Shear stress formula
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v = V Q / I b
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deflection uniformly supported beam formula
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(5/384) w L^4 / E I
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Notching of beams
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a type of connection. requires the beam to be checked for shear failure
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concrete T beam / double T beam
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precast members. used primarily in parking garages. typical span 60 ft. good for repetitive structures
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arch horizontal force formula
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H = w L^2 / 8h
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spread footing
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load is appplied to concrete footing, which distributes it evenly over teh area of the square footing.
Actual stress = P/A but not greater than the maximum allowable bearing stress provided by the geotechnical report, based on soil testing |
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wall footing
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aka strip footing, similar to spread footing, but along a wall, applying uniformly distribute load to the soild not exceeding the maximum allowable bearing stress
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cantilever footing
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addition of grade beam to support a perimeter comumn from above at the end of a cantilever. the cantilever is supported by a spread footing, the benefit is that the load is applied to the soil away from an obstruction / property line.
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combined footing
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2 column close together may have overlapping spread footings, can be designed as 2 footing supporting both columns, hence combined
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mat footing
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soil conditions may require a low bearing stress, resulting in many overlapping footings, more cost effective to create 1 mat footings under entire footprint of building. Tie in basement walls to create a bathtub and let building float
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pile foundations
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wood concrete or steel
piles can be drilled of hammered into place end bearing piles may have a cone shpae at bottom known as bell shape |
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caissons
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same as pile, but usually with a diamter of 36" thus allowing a worker to climb down into it
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pile bearing capacity
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P = 2 W H / (s + 1)
s = dimention of pile penetration into ground on the last blow of hammer W = weight of hammer used to drive piles H length of hammer drop |
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retaining wall factor of safery
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1.5
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soil pressure formula
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p soil = K w h
K = soil coefficient w = weight of soil (avg 100 psf) h = distance to top soil |
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primary concern of connections
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shear resistance
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lag screws (lag bolts)
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- wood screws whose heads are similar to a bolt, used with washers but without a but as it reste on the material
- high withdrawal resistance - shear resistacne is generalyy lower than bolts of the same diameter |
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wood screws
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most common types are flat head and round head, specified by diameter # and lenght
- thread measures about 2/3 lenth of screw - avoid withdrawal loads |
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steel bolts
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1. bearing type - members transfer load to a connector through bearing load, while connector resists load by shear, joint strentgh is determined by whichever is lower
2. slip ciritical - possible only with ASTM-conforming high-strength bolts. Connected parts are so tightly clamped together that the faces resist loads by frection while shearing or bearing stresses are at a minimum, but for convenience, alowable resistance is referred to as shear stress 3. failure can occur in shear or bearing |
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welds
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1. fillet - right angled joints; shear stress on the throat of the weld, regardless of directin of applied load. workd in shear
2. groove: butt joints; direct tensino or compression 4. tpes = lap, butt, etc |
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occupandy category of a building
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from IBC, based on building usage
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site class A - E
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based on soil type. A is best, E is softest
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Importance factor Ie
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based on occupandy category.
i.e. - catetory iV is emergency shelter, hospital, places that have to whitstand everything |
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equivalent laterlal force
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V = Cs V
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stuff on seismic
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for short buildings (stiff) the lad approximates to a triangular loa (hightes load at roof)
For tall slender buildings, the las is parabolic, which is responsible for a whip lash effect at top of structure. |
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punding
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2 buildings adjacent to each other, separated by expansion joint, differing period, thus buildings will get out of sequence when swaying and hit each other
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overturning
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horizontal forces x lever arm to each floor, is resisted bu % of dead load x width of building
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story drift
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building ( floors) deflect from earthquake
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