Term
| What is the section modulus of a beam that is 12" wide and 24" deep? |
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Definition
s = b * d * d / 6
s = 1152 inches-cubed |
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Term
| What is the formula for moment of inertia of a rectangular section? |
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Definition
I = b * d * d * d / 12 also, I = s * c |
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Term
| Where does a beam have "positive moment"? |
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Definition
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Term
| Where does a beam have "negative moment"? |
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Definition
| (generally) directly over the supports. |
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Term
| what is the difference between a long column and short column? |
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Definition
a short column fails by either crushing (i.e. concrete) or plastifying (i.e. steel). a long column is governed by BUCKLING (think of pushing on both ends of a straw until the straw suddenly bends). |
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Term
| For the purposes of the ARE exam, there are only two types of structural entities: |
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Definition
* 1-dimensional members (beams and columns) * 2-dimensional members (plates) <- think of a slab or a plate of glass |
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Term
| What 3 kinds of forces are applied to 1-dimensional members such as beams and columns? |
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Definition
- compression (pushing on both ends, think of a column) - flexure (bending - think of a beam ... flexure causes both bending moment and shear) - torsion (twisting) |
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Term
| If a beam is attached at one end (imagine a rod is hanging from the ceiling), and you heat it with a blow torch, what happends? |
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Definition
It gets longer at the tip, but it stays attached to the ceiling. (If you made the rod cooler, it would shrink.) |
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Term
| If a beam is clamped at both ends (imagine a rod embedded in concrete at both ends) and is heated with a blow torch, what happens? |
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Definition
Since neither end can expand, the material is subjected to compression stress because it wants to expand, but is stopped by the concrete. (if you made the rod cooler, it would be subjected to tension stresses) |
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Term
| In a truss, members are typically subjected to what 2 types of forces? |
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Definition
- tension and compression (for the purposes of the ARE, not bending or flexure or shear or torsion) |
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Term
| What is a good estimate for the fundamental period of vibration for a 1-story building? |
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Definition
About 0.1 seconds. This is how long it takes to sway back into place if hit with a sudden lateral force. |
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Term
| If the question references "Euler", associate this with: |
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Definition
- elastic buckling of long columns (this is called "Euler Buckling" |
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Term
| What is the difference between strength and stiffness? |
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Definition
Strength: ability of the member to resist the forces. Stiffness: dictates how much deflection or displacement |
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Term
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Definition
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Term
| What is the definition of natural frequency and units? |
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Definition
Natural frequency is the INVERSE of natural period. It tells you how fast the structure tends to oscillate if hit with a sudden lateral force. Units are HERTZ; a Hertz (Hz.) = (1/second) |
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Term
| What are the 3 typical kinds of lateral-force resisting systems? |
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Definition
- moment frames - braced frames - shear walls (you can also have combinations of these, for example, a building could have both moment frames and braced frames) |
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Term
| what type of lateral-force resisting system do architects like to use at glass curtain walls? |
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Definition
moment frames typically (they don't want to see the big diagonal braces) |
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Term
what property relates STRESS to STRAIN? |
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Definition
modulus of elasticity represented by E each type of material has a specific modulus for example: Es = mod. of elasticity for steel Ec = mod. of elasticity for concrete |
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Term
define stress versus strain... what's the difference? |
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Definition
stress: what the member FEELS (it's related to strength). units: PSI strain: a measure of DISPLACEMENT (related to deflection). units: INCHES |
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Term
| what beams in a building are usually designed for torsion? |
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Definition
beams at the exterior wall the interior loadings make them tend to twist inwards under the weight |
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Term
| what are good and bad beam shapes for torsion? |
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Definition
good: circles, squares, pipes, tubes bad: w-shapes, plates, angles |
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Term
| what is the property of concrete that determines the strength? |
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Definition
water-cement ratio.
it's typically about 0.45 to 0.50. |
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Term
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Definition
stress equals force per area.
This basic equation applies to:
- members in tension
- compression of short columns
- footing design
**Careful, this definition never applies to:
- bending or flexure or shear |
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Term
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Definition
Camber usually only applies to steel beams.
The engineer checks the vertical deflection of the beam under the dead load. If the vertical deflection is large (typically over 3/4"), they will specify the beam to be swept at a radius so that the deflection is 3/4" in the middle. Therefore, when the beam is put in place, and the dead load applied, the beam deflects into a level position. |
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Term
| What is a standard factor of safety against overturning for a retaining wall? |
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Definition
| Usually varies from 1.5 to 2.0 |
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Term
| What 3 limit states need to be checked for a retaining wall? |
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Definition
- Sliding (need enough weight to generate friction between the footing and the soil)
- Overturning (need the base wide enough that it can't tip over)
- Member strength (sizing the rebar in the retaining wall to take the forces related to the earth pressure) |
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Term
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Definition
Little steel pegs about 4" long with a round cap. You weld them to the top of the steel beam. Then they are embedded in concrete when the slab is poured.
Shear studs allow the engineer to use a type of design called composite action. Since the slab is well-connected to the beam with the studs, you can use the concrete as part of the beam, and get more capacity. |
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Term
| What is the P-Delta effect? |
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Definition
Lateral loads on a building frame produce horizontal displacement called drift.
However, in this displaced state, the gravity loads are still pushing down through those columns to the foundation.
But now, those columns are loaded eccentrically due to the P-Delta effect. So in design, you have to account for loading your columns eccentrically so they are not overstressed when drift occurs. |
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Term
| If your building is sited on CLAY, what problems would you anticipate? |
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Definition
Some clays are expansive, meaning when they are wet they expand and push on your building and when they dry out they get smaller and develop lots of cracks.
For large buildings, if there's a lot of clay, you usually have to have deep foundations. (For small buildings sometimes you can get away with shallow foundations, but for the purposes of the ARE, when you see clay, think DEEP FOUNDATIONS) |
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Term
| What are some examples of deep foundations? |
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Definition
Caissons
Augers
Piles
they're all slight variations of the same thing: a long column underground that either goes all the way down to bedrock, or develops sufficient friction with the soil around it.
Some are driven (like driving a nail with a hammer), others drilled (think of a screw), others can be a hole dug out and then filled with concrete. |
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Term
| What are the four classifications of soils and their characteristics? |
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Definition
Gravel - best Sand - still pretty good Silt - worse Clay - worst Gravels and sands are cohesionless (they don't stick to each other and are relatively stable). Silts and clays are cohesive (tend to compress and deform under load) |
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