Soils & Foundations Flashcards
1
Q
Spread Footing
A
Spread the load from the structure over a large area - conservative on the load-carrying capacity of soil, minimizes settlement
2
Q
Pile & Caisson foundation
A
- Pier foundation system
- Distribute load from buildings to piles, which typically bear on bedrock or to surround soil
3
Q
Wall Footing
A
- Typical T or L shaped foundation under bearing wall
- Reinforced, keyed joint
4
Q
Independent Column Footing
A
- Similar to wall footing, dedicated to one column
5
Q
Combined Footings
A
- One spread footing captures 2 or more closely located columns
6
Q
Strap footing
A
- AKA Cantilever footing
- Concrete strap beam to distribute column loads from one column to another to equalize soil pressures on each footing
- Beam itself is poured on compressible material so it doesn’t bear on the soil
6
Q
Mat Foundation
A
- AKA raft foundation
- ## One two-way slab of concrete under all the structural elements
6
Q
Pile Foundations
A
- Driven or drilled
- Driven - timber, steel or precast placed with pile-driving hammers
- Driled - hole is drilled to required depth into which concrete is poured
- Drilled hole may receive metal lining if surrounding soil is too soft to hold concrete on its own
7
Q
Grade Beam
A
- Continuous beam designed to transfer loads from building walls to piles
- Used where expansive soils are near the surface. Poured so upward pressure from soil expansion are not transmitted to concrete
8
Q
Footing Design Factors
A
- Unit Loading
- Shear
- Bending
9
Q
How footings fail in shear
A
- Punching (2-way shear): column load punches through footing
- Flexural shear (diagonal tension): same as regular beams
10
Q
Spread footing loads
A
- Load on the column
- Weight of the column itself
- Soil of top the footing
- In addition to the loads, the footing needs to be designed for shear/moment/other loads and reinforced accordingly
11
Q
Foundation Load Formula
A
U = 1.2D+1.6L
U: required ultimate strength load
D: actual dead load
L: actual live load
12
Q
Effective Depth
A
- Distance from top of footing to centroid of reinforcing steel along bottom of spread footing
- The concrete below the bottom reinforcing steel doesn’t contribute to the structural performance of the footing, just provides coverage for the rebar
13
Q
Unreinforced footings at light loads
A
- Concrete is cheaper than steel - generally prefer to just do it all with concrete if possible
- Thicker, wider unreinforced is preferred where loads are light
- Some steel is still required even for wall loads, parallel to length of wall, for temperature reinforcing & footing span over shitty soils
14
Q
Footings at heavy loads
A
- Footing widths may grow to the point they require tension reinforcement
- Max allowable shear governs depth of wall footings
15
Q
A
