6 Foundations Flashcards
Strata
Identifiable layers of different soils
Soil type affects the type of building that can be built. Allowable foundation pressure for sandy clay is
1,500 lbs/ft2
For bedrock, allowable foundation pressure
12,000 lbs ft2
Approximate depth of test soil pits
8 ft
Highrise may require a foundation depth of
100 ft
Foundations must resist these types of loads
Wind loads, lateral or uplifting forces Soil pressure Uplifting forces from ground water Thrusts from arch supports, domes or vaults. Seismic forces
Footing
Part of foundation that rests off bearing soil and is wider than wall of foundation.
Main contributors to type of foundation are structural config and soil conditions. Others are
Available work space
Environmental factors.
Impact on adjacent properties
Building code and regulations.
Foundations are divided into two types
Shallow and deep
Shallow foundation
Transfers the weight of the building to slim and base of building. For use when shallow soil can support weight of building.
Deep foundations.
Penetrate soil deeps to reach more stable soil beds
Shallow foundations usually make use of what to transmit load to soil
Footings
Wall footing
Counting pus strip of concrete that supports a wall
Wall footings can take several forms :
Monolithic floor, increased thickness of floor slab at edges
Widened strip of concrete under a wall that supports raised floor with crawl space.
Widened strip of concrete under full story high walls that create a full or partial basement.
Column footing
Square pad of concrete that supports a column
Grillage footing
Footing that consists of beams placed at right angles to each other and usually encased in concrete.
Mat foundation
Thick slab beneath the entire area of a building. Mat is different than slab in thickness and reinforcement.
Floating foundations
Volume of soil removed from foundation space is approximately equal to weight of building supported, minimizing settling. Used in some situations where soil strength is low.
Depending on composition and density of soil, and building construction, 1 story of soil can equal
5-8 stories of building
Piles
Used to support loads. Likes are driven into the ground and develop the load carrying ability either through friction, or being in contact with rock or load bearing soil.
Pier
Load supporting member constructed by drilling or digging shaft then filling with concrete.
Deep foundations take the form of either
Piles or piers
A pier designed with a footing is known as
A belled pier
Piers are sometimes referred to as caissons. A caisson is actually
The protective sleeve used to keep water out of excavation for pier.
On a hill, the foundation vertical elements are connected with
A tie beam. Intended to resist lateral force of building on the hill.
Cracks in concrete foundation walls often develop but are
Don’t usually affect the ability of the wall to support or distribute load. Cracks must be inspected however to ensure they don’t worsen.
For a foundation. Expanded polystyrene foam EPS can be used
Outside the foundation as insulation.
Building settlement may be minor or structurally severe. Moving the building in what directions
Downward, settling
Upward, heaving
Outward, lateral displacement.
Most frequent building movement
Settling
Settling can be two different types
Uniform or differential
Uniform settling
Parts of foundation settle at same rate and misalignment of structural members is minimal
Differential settling
Different parts of foundation settle by different amounts. Causing significant misalignment of structural members.
Differential settling can result from several factors.
Non uniforms soil conditions
Footings of different size
Footings at different elevations
Unequal load on footings
Underpinning
Process of strengthening an existing foundation
Underpinning is needed when there is
Excessive settlement because of inadequate foundation
Increase in load on foundation because of additions
Erosion of soil around foundation
Shoring
Process of temporarily holding up building until underpinning can be accomplished. Done with timber, hydraulic pneumatic or screw jacks. Also holds up sheeting in trenches. Shores, cross braces and struts.
Disruption in foundation integrity can cause
Compromise of building structural members
