Transcript Foundation Design - Civil-Engineering

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FOUNDATION DESIGN
Foundation- Design
Considerations
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Factors to be taken into consideration when
determining the type of the building foundations:
Function of the structure
Loads from the structure
Bearing capacity of foundation material
Total and differential settlement of foundation
Uplift forces acting on the foundation
Costs
Soil Bearing Capacity
The soil bearing capacity needs to be
determined. This can be done by:
• Local or State Building Codes
• Uniform Building Code (UBC)
• Soil testing/analysis
– Site inspection and simple soil testing
– Soil borings taken at proposed foundation
locations
Foundations- Shallow
• Shallow Footings- in Rochester, NY the base of
the footing must be 48” below ground surface.
– Spread footing ( square or rectangular)- footing is
spread out over a broad area. Usually in low-rise
buildings
– Strip Footing – with load bearing walls, an example
would be basement walls, in which the building loads
are carried by the foundation walls with continuous
footings.
– Grade Beams - as the name implies , these are beams
at grade. It may be built integral with the floor slab or
may be used for Pile caps.
Foundations - Deep
– Pile Foundations - vertical structural
members that are forced into the ground by
pile drivers (similar to driving nails into wood)
– Caissons – similar to pile foundations, but
are created by auguring (drilling ) a deep hole
into the ground and then filling the hole with
concrete. Caissons may be belled at the
base. Steel reinforcement may also be used.
Caissons can extend to bedrock.
Foundations
– Mat or raft foundations – the entire
building is placed on one large continuous
footing. Typically used in locations where
the soil is weak/poor and bedrock is too
deep.
– Mat foundations with caissons or piles –
a combination of a mat foundation with
piles or caissons.
Soil Bearing Pressure
Spread Footings
Calculated Soil Bearing =
Load (pounds)
Area of Footing (sq.ft)
Compare to Allowable Soil
Bearing Capacity
Diminishing Soil Pressure
Critical zone for
compaction
Soil pressure
cut by ½ at
this level
Soil pressure
cut by 2/3 at
this level
W=footing
width
W
W
Building Type Guide
• Short Span Buildings
– 10 to 40 feet bays
• Flexible plan
– Structural elements (columns) can determine spatial
relationships
• Moderate Long-Span Buildings
– 40 to 140 feet bays
– Need to consider structural depth of floor and roof in
the spatial planning
Building Type
• Long-Span Buildings (> 150 feet )
– Structural system determines the building's
image or visual statement
Reference Sources
– Jefferis, A., & Madsen, D. A. (2001). Architectural Drafting
and Design. Albany, NY: Delmar, a division of Thomson
Learning.
– Kane, K., & Onouye, B., (2002). Statics and Strength of
Materials for Architecture and Building Construction.(2nd
ed.). Saddle River, NJ: Pearson Education, Inc
– Shaeffer, R. E., (2002). Elementary Structures for
Architects and Builders (4th ed.). Columbus, OH: Prentice
Hall.
– http://www.concretenetwork.com/concrete/footing_fundam
entals/why_soils_matter.htm
– http://www.emporis.com/en/
– http://www.pbs.org/wgbh/buildingbig/lab/forces.html