Foundation Systems: Concrete and Masonry Flashcards
The structural system of
any building must be
designed to support both….
…static and dynamic
loads.
Static Loads
Loads that are applied slowly (typically downward), do not fluctuate rapidly, and must reach maximum peak before structure reacts.
Live (Occupancy) Loads
People, Furniture, snow, standing water, etc….
Dead Loads
Structure, non moving fixtures and equipment…
Ground Pressure
Loads caused by the horizontal force of soil on a vertical foundation (retaining) wall
Settlement Loads
Loads caused by the differential settlement of soil
Water Pressure
Hydrostatic (wall) or hydraulic (floor) force on a foundation wall or slab
Thermal Stresses
Movement due to expansion and contraction
Dynamic Loads
Loads that are applied suddenly and with rapid changes in magnitude and location
Wind Loads
Forces exerted by kinetic energy of moving air from any direction
Earthquake Loads
Longitudinal and transverse forces affecting lateral loading on a building’s horizontal surfaces
Columns
Rigid, slender,
designed to support axial
compressive loads,
subject to crushing or
buckling depending on
size, length and condition
Beams
Rigid members designed to carry and transfer transverse loads subject to bending and deflection
Trusses
Structural frame based on the rigidity of a triangle, top and bottom chord, web and panels, subject to axial tension and compression
Frame and Walls
Beam
supported by two columns
that are braced to resist
lateral forces, the frame
may be fixed or hinged
Concrete (cast in place**)
- Cement + Aggregate + Water = Concrete
- Strong in compression
- Weak in resisting tension and shearing
forces - Typically requires reinforcing
Advantages in Concrete
- Plastic
- Versatile
- Low cost (relatively)
- Fire-resistant
Disadvantages in concrete
- Weight (150 pcf)
- Requires forming
- Requires reinforcing
- Curing time
Cement (portland)
- AKA Hydraulic Cement
- Fine powder made of pulverized “clinkers”
- Clinkers result from burning clay/limestone mix
Type 1 cement
Normal for general construction
Type 2 cement
Resistant to heat buildup
Type 3 cement
High early strength
Type 4 cement
Low heat
Type 5 cement
Sulfite resisting
Water
Must be potable (no organics, fit to drink)
Cement paste
Cement + Water
Aggregate
- Inert mineral materials (i.e.
sand, gravel, etc.) - Represents 60-80% of
concrete volume - Critical to strength, weight,
fire resistance - Must be hard, dimensionally
stable, free of organics
Aggregate - Fine
Sand < 1/4”
Aggregate - Coarse
Crushed stone, gravel, etc. > 1/4” - 1.5” (through sieve)
Admixtures
Added to alter properties of concrete mix..
- Increasing workability
- Speeding/slowing setting
- Increasing strength
- Altering/controlling color
Water-cement Ratio
Ratio of mixing water to cement
- Controls strength, durability, watertightness
Too much - weak & porous
Too little - dense and difficult to work
Concrete Specifications
Specified according to compressive strength
28 days standard
7 days (high early strength)
Slump Test
Determines consistency and workability
Compression Test
Determines compressive strength
Steel bars, strands, and wire
Absorbs tensile, shearing, and
compressive stresses
Ties vertical and horizontal elements
together
Reinforcing Bars (Rebar)
Hot rolled with ribs or deformations
Welded Wire Fabric (WWF)
Grid of steel wire or bars
Typically used in floor slabs
Concrete Masonry Units
Manufactured product with
standard dimensions
Many shapes and sizes
CMU (concrete masonry units)
Precast Portland cement + fine
aggregate + water
Concrete Block
Hollow CMU with compressive
strength of 600 – 1,500 psi
Normal-weight > 125 pcf
Medium-weight 105-125 pcf
Lightweight > 105 pcf
50
Concrete block dimensions
Nominal dimensions – 8” x 8” x
16”
Actual dimensions – 7-5/8” x 7-
5/8” x 15-5/8”
CMU Grade N
Grade N – Loadbearing CMU for
use below or above grade
CMU Grade S
Grade S – Loadbearing CMU for
above grade use
CMU Type 1
Type I – Specified limit to
moisture content (minizes
cracking)
CMU Type 2
Type II – No specified limit
Basement
Below grade (whole or part)
Requires continuous foundation wall
Crawl Space
Below grade
Requires continuous foundation wall
Slab-on-Grade
(AKA Grade slab)
Supported directly by earth
Requires continuous foundation wall, trench footing or thickened edge slab
Shallow foundations
Foundation wall rests on a spread footing
Distributes load laterally over earth
Designed based on allowable bearing capacity
Strip Footings
Continuous spread footings supporting foundation walls
Isolated Footings
Concrete pads supporting columns or other bearing points
Sloped grade requires….
stepped footings
5 Foundation Wall Types (for this unit)
Cast-In-Place Concrete
Concrete Masonry (Block)
Treated Wood
Precast Concrete (i.e. Superior Walls, etc.)
Insulated Concrete Forms (Amvic, etc. )
Treated Foundation Wall and its pros:
AKA Permanent Wood Foundations
(PWFs)
Pros – Simple, quick, cheap, easy finishing,
better insulating values…
Treated Wood supported by a 2 x
footing plate and compacted
gravel.
What is a con for a treated wall foundation?
Prone to dampness, interior and
exterior decay, foundation leaking, bowing
and buckling…
Precast foundation wall and pros:
AKA Superior Walls
Pros:
No footings required
Pre-insulated
Fast installation (trucked to site and placed with a
crane)
What are the cons to precast foundation walls?
Cons:
Requires specialized equipment (crane)
Specialized drainage system required
Insulation prone to termite infestation
ICF (Insulated Concrete Forms) Pros:
Pros:
Well insulated
Easy construction
Air-tightness
Uses recycled materials
What are the cons for ICF Foundation Walls?
Cons:
Cost
Best suited to moderate or hot climates
