Term
| a combined footing supports __________ |
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Definition
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| which allowable bearing pressure do you use: above or below the footing |
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Definition
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Term
| a spread footing supports a ____________ |
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Definition
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Term
| name 2 ways to combat uplift on a building's foundation? |
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Definition
1. provide anchor bolts and/or rebar btwn bldg + fndn.
2. ensure that ftg is heavy enough so it's not lifted up |
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Term
| when is a combined ftg req'd? |
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Definition
| when 2 isolated ftgs overlap |
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Term
| T/F: shallow fndns are used for mid-rise and high rise buildings |
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Definition
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Term
| T/F - Deep fndns are usually used for low rise buildings |
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Definition
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Term
| fill in the blanks: as a building's weight increases, the ________ capacity (i.e. sliding resistance) also increases. |
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Definition
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Term
| T/F Tall buildings usually have critical issues with uplift. |
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Definition
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Term
| if fb increases, then the footing size will [increase or decrease] |
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Definition
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Term
| when does "heaving" occur? |
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Definition
| when a ftg is founded above the frost line |
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Term
| T/F fb depends on the soil strength |
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Definition
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Term
| what is the fundamental equation for the width of a wall footing? |
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Definition
stress = force / area... which specializes to
width = line load / fb |
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Term
| T/F short buildings have more problems with uplift than tall buildings |
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Definition
| F (short buildings tend to slide, not overturn) |
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Term
footings must be loaded directly through their:
a. water table
b. frost line
c. centroid
d. area |
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Definition
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Term
| T/F The purpose of a retaining wall is to keep water from infiltrating a building |
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Definition
| F. purpose is to retain soil |
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Term
| when designing combined ftgs always note that the center of the ftg should be located at the center of _____ |
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Definition
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Term
| for heavy buildings, or when bedrock is near the surface, _____ are a good alternative to shallow fndns |
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Definition
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Term
| T/F as bldg wt increaes, friction capacity increases |
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Definition
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Term
| a wall with a lateral pressure load due t presence of soil is called a |
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Definition
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Term
| lateral pressure from soil is usually about what % of unit weight? |
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Definition
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Term
| when soils are so weak that conventional spread footings exceed ___ % of the building, a mat foundation is more economical. |
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Definition
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Term
| when do you need to provide foundation drainage? |
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Definition
| when water table is ABOVE the BOTTOM of the footing |
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Term
| T / F. design process for mat foundations is similar to a 2-way slab design. |
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Definition
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Definition
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Definition
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Definition
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Term
| what are the units of a line load, w |
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Definition
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Term
| what is the basic stress equation for footing design? |
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Definition
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Term
ensure that bottom of footing is below what:
a. centroid
b. frost line
c. water table |
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Definition
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Term
| what geometric technique is used to build shallow foundations on a sloping site? |
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Definition
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Term
| what is the primary material used in shallow fndns? |
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Definition
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Term
| how is the frost line determined? |
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Definition
| it's in the geotech report - depends on the climate. |
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Term
| why is concrete a good material for shallow fndns? |
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Definition
| durability! (won't rot or decay) |
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Term
| what is the purpose of clear cover for rebar in shallow fndns? |
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Definition
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Term
| in a column ftg, the center of area must correspond to the center of _________ |
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Definition
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Term
| when 2 cols are too close together for individual footings, what do you do? |
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Definition
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Term
is the area of a ftg measured in:
a. square feet
b. cubic feet
c. feet inches
d. meters |
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Definition
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Term
convert 7'-10" to decimal feet:
a. 7.1'
b. 7.83'
c. 7.5' |
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Definition
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Term
| A combined footing measures 18' x 28' and supports 2 columns. The columns are spaced 10' apart. fb = 2500 psf. What is the maximum load that EACH column can support? |
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Definition
A = 18' x 28' = 504 SF
fb = P/A => P = fb*A = 1260 k
P1 = P2 = 1260k/2 = 630 k/column
answer: 630 k |
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Term
| All foundation concrete is required to have: ________________ |
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Definition
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Definition
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Definition
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Term
| Given fb = 4000 psf and a load of 200 kips, what area is required for a footing? |
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Definition
stress = P/A => A = P/fb
A = 200k / 4 ksf = 50 SF
answer: 50 square feet |
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Term
| A structure is partially buried below grade on ONE SIDE ONLY. Do you recommend cantilever retaining walls or conventional basement walls? |
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Definition
| Cantilever retaining wall, b/c site is unbalanced and you need to resist lateral pressure from soil. |
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Term
| A structure is partially buried below grade on BOTH SIDES. Do you recommend cantilever retaining walls or conventional basement walls? |
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Definition
| Use conventional basement walls because the site is balanced and the floor diaphragm can provide a horizontal reaction at the top of the walls. The lateral soil pressures are equal and opposite, so there is no issue with stability. |
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Term
| What is the difference between a cantilever retaining wall and a counterfort retaining wall? |
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Definition
| counterfort wall has addiitional rigidity and stiffness created by the FINS, which are tension elements that prevent or reduce lateral tilt of the top of the wall. |
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Term
| T/F. A gravity retaining wall is stable only if it is heavy enough to resist the overturning moment caused by the soil. |
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Definition
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Term
| What is the primary material used in "deadman" retaining wall construction? |
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Definition
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Term
| what type of reinforcement is present in a spread footing? |
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Definition
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Term
| what type of reinforcement is present in a slab-on-grade? |
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Definition
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Term
| what type of reinforcement is present in a mat foundation? |
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Definition
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Term
| T/F. It is recommended to provide steps in column footings, not wall footings. |
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Definition
| F (step wall ftgs, not column footings) |
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Term
| T/F. Sometimes you may provide air-entrainment in foundation concrete that may freeze over its lifetime. |
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Definition
| F. ALWAYS provide air-entrainment under those circumstances. |
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Term
| List the 3 components of concrete and their relative percentages |
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Definition
| 10% water, 20% cement, 70% aggregate |
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Term
| Two footings are spaced apart 10' and EACH support 420kips (dead + live loads). If fb = 3000 psf, can separate footings be built or is a combined footing required? |
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Definition
A = P / fb = 420k / 3 ksf = 140 SF
length = sqrt(140) = 11.8 feet
round UP to 12' minimum.
Since 12' length exceeds 10' spacing, a combined ftg is required. |
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Term
| A 10'x10' footing supports a column load comprised of 200k dead load and 200k live load. If fb=3ksf, is the footing large enough? |
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Definition
P = 200+200 = 400k
Aftg = 100 SF
stress = P/A = 4000 psf
Since the actual stress 4000 psf exceeds the allowable bearing stress 3000 psf, footing is NOT large enough. |
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Term
| When solving for the area of combined footings, do you solve for the length by taking the square root of the area? |
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Definition
| NO. You only take the square root for a square footing. Combined footings are rectangular. |
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Term
| What is the max. line load permitted on a 6' wide strip footing that is 100' long, given fb = 5000 psf? |
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Definition
width = w / fb
w = width * fb
w = 6' * 5000 psf = 30,000#/ft
aka 30 k/ft |
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Term
| If a site slopes high to low from left to right, and if you are building a cantilever retaining wall, is the HEEL on the left or right? |
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Definition
Heel is on the LEFT.
Heel is always located below the high soil. The toe is on the side with the shallow soil depth. |
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Term
| If you calculations tell you that your cantilever retaining wall is too flexible and the top of the wall is deflecting to the side too much, what is one good strategy for an upgrade? |
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Definition
| use a counterfort wall instead |
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Term
| when would you use "rock bolting" |
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Definition
| use rock bolting in order to connect a shallow foundation directly to bedrock. |
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Term
| describe rock bolting process. |
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Definition
| core holes in bedrock, place rebar dowels, fill with grout. After grout cures, pour footing on top w/conventional rebar. |
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Term
| a cube measures 12" x 12" x 12" and is subjected to a lateral force at the top of the cube. If the cube weights 840 pounds, what force at the top initiates tipping? |
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Definition
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Term
| a cube measures 12" x 12" x 12" and is subjected to a lateral force at the top of the cube. If the cube weights 840 pounds, what force at mid-height initiates tipping? |
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Definition
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Term
| a cube measures 12" x 12" x 12" and is subjected to a lateral force at 2" below the top of the cube. If the cube weights 840 pounds, what force at the top initiates tipping? |
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Definition
(P#*10")=(840#*6")
therefore P = 504#
tips at 504# |
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Term
| on a foundation plan, what does "CJ" or "CLJ" mean? |
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Definition
| control joint in the slab on grade |
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Term
| in what foundation elements would you find control joints? |
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Definition
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Term
| in a wall footing, is the primary tension reinforcement oriented parallel or perpendicular to the wall? |
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Definition
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Term
| what is the purpose of a layer of aggregate below a slab on grade? |
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Definition
it's probably there to reduce water entry via capillary action.
(it could also be used if soils are too weak) |
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Term
| what is the purpose of a layer of aggregate below a footing? |
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Definition
| it is there because the soils are not suitable strong |
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Term
| T/F spread footings have rebar on the bottom, not the top |
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Definition
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Term
| T/F mat foundations have rebar on the bottom, not the top |
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Definition
| F. they have rebar top and bottom b/c they act like a 2-way concrete slab. |
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Term
| T/F slabs-on-grade have rebar on the bottom, not the top |
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Definition
| F. Slabs on grade are generally reinforced with welded wire fabric |
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Term
| T/F wall footings have rebar on the bottom, not the top |
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Definition
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Term
| If the frost depth is 3' and the footing is 1' thick, what is the highest t/footing elevation that is acceptable? |
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Definition
| 2' below grade is the HIGHEST acceptable. anything lower is OK |
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Term
| If the top of slab-on-grade is 100', using our rule of thumb, what is the top elevation of INTERIOR column footings? |
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Definition
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Term
| If the top of slab-on-grade is 100', using our rule of thumb, what is the top elevation of EXTERIOR column footings? |
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Definition
| trick question: you have to know the frost depth in order to answer this question. |
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Term
| does the frost depth requirement impact both interior and exterior footings? |
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Definition
| exterior only. soils in the vicinity of the interior ones are heated by the building and don't freeze. |
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Term
| the _________________ equation must be used in order to size a combined footing. |
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Definition
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Term
| if spread ftgs exceed 50% of building footprint, a mat foundation is usually more economical. explain why. |
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Definition
| because it is less labor intensive to do one big excavation instead of numerous smaller excavation. you use more material, but the labor is greatly reduced and the mat foundation can be poured expediently. |
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Term
| if soils are too weak AND if bedrock is quite deep, the best type of foundation system is probably: |
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Definition
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Term
| If fb = 1000 psf, and columns are at 30' on center and each support 400 kips, do you recommend mat fndns or spread footings? |
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Definition
stress = P/A
A = P/stress
A = 400k/1ksf = 400 sf
L = sqrt(400)=20 feet
area of bay: 30'x30'=900 sf
therefore footing is:
400/900 or 44%. Therefore, using rule of thumb (50%), go with spread footings. |
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Term
| When designing a combined footing, don't forget to .................. |
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Definition
| include load for BOTH columns in the calculation |
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Term
| T/F. For a 8" CMU wall with a cavity and 4" brick veneer, the footing should be centered on the CMU. |
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Definition
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Term
| If a line load is equal to 2 k/ft, how much force is loaded to a 1' wide strip of the footing? |
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Definition
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Term
| If a line load is equal to 2 k/ft, how much force is loaded to a 2' wide strip of the footing? |
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Definition
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Term
| T/F - The thickness of a footing can be determined by using the stress=P/A equation |
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Definition
F. The area (in plan) is based off of stress = P/A.
The thickness is based on one-way shear and two-way shear. |
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Term
| What are the 2 functions of rebar in a shallow foundation? |
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Definition
(1) tension reinforcement
(2) control cracking |
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Term
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Definition
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Term
| what is the factor of safety between qult (failure) and fb (allowable, safe bearing pressure? |
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Definition
about 2.5
therefore fb = qult/2.5 |
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Term
| do we use ASD or LRFD design philosophy for foundation design? |
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Definition
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