Commercial Foundations He who has not first laid his foundations may be able with great ability to lay them afterwards, but they will be laid with trouble

  • View
    218

  • Download
    1

Embed Size (px)

Text of Commercial Foundations He who has not first laid his foundations may be able with great ability to...

  • Slide 1
  • Commercial Foundations He who has not first laid his foundations may be able with great ability to lay them afterwards, but they will be laid with trouble to the architect and danger to the building. Niccolo Machiavelli (1469 - 1527), The Prince Niccolo Machiavelli
  • Slide 2
  • Foundations Purpose Considerations Types of Foundations Shallow Foundations Spread Footings Strip Foundations Slab-on-Grade and Thickened Slabs Mat Foundation Deep Foundations Piles Cast-in-Situ Piles Why Do Foundations Fail?
  • Slide 3
  • Purpose of Foundations Provide a level, stable surface to safely support a building Transfer building loads to soil Anchor the building from wind, flood, and seismic loads
  • Slide 4
  • Design Considerations Loads from the structure Allowable soil bearing pressure Frost depth Flood elevation Drainage Costs
  • Slide 5
  • Loads from the Structure Foundations must resist Dead Load Live Load Lateral Loads -- Wind -- Seismic activity -- Flood SOIL REACTIONS
  • Slide 6
  • Allowable Soil Bearing Pressure Indicates the maximum pressure that a soil may be designed to support Includes a factor of safety Dictates the size, depth, and type of foundation Typically presented in pounds per square foot (psf) Different types of soils have different allowable soil bearing pressures
  • Slide 7
  • Soil Information Local Building Department, Codes and Regulations Preliminary info: USDA Web Soil Survey http://websoilsurvey.nrcs.usda.gov http://websoilsurvey.nrcs.usda.gov Local or State Building Codes Soil testing/analysis Site inspection and simple soil testing Soil borings taken at proposed foundation locations
  • Slide 8
  • Estimated Allowable Soil Bearing Pressure Soil TypeAllowable Bearing (lb/ft 2) Drainage BEDROCK 4,000 to 12,000Poor GRAVELS 3,000Good GRAVELS w/ FINES 3,000Good SAND 2,000Good SAND W/ FINES 2,000Good SILT 1,500Medium CLAYS 1,500Medium ORGANICS 0 to 400Poor
  • Slide 9
  • Frost Depth Freezing of soil can cause heaving of foundations Silt or clay soils with a high water table are highly susceptible to frost Defense Build base of foundation below frost depth or Provide frost protection for foundation
  • Slide 10
  • Frost Heave
  • Slide 11
  • Flood Elevation Inundation by flood waters should be avoided Damage to structure Damage to contents Height of floors and/or flood proofing is dictated by building codes Courtesy Federal Emergency Management Agency. Photographer Dave Saville.
  • Slide 12
  • Flood Zones A Zone Areas with a 1% annual chance of flooding V Zone Coastal areas with a 1% or greater chance of flooding and an additional hazard associated with storm waves BFE (Base Flood Elevation) The elevation shown on the Flood Insurance Rate Map that indicates the water surface elevation resulting from a flood with a 1% chance of equaling or exceeding that level in any given year
  • Slide 13
  • Flood Insurance Rate Maps Note: V29 indicates V-zone and BFE = 29 ft
  • Slide 14
  • A Zone Residential buildings - lowest floor (including basement) elevated at or above the BFE Non-residential buildings Lowest floor (including basement) elevated at or above the BFE OR Dry-floodproofed to the BFE Dry floodproofing: Building must be designed and constructed to be watertight to floodwaters
  • Slide 15
  • V Zone All Buildings (residential and non- residential) Elevated on piles and columns Lowest horizontal structural member of lowest floor at or above the BFE Anchored to resist flotation, collapse, and lateral movement The area below the lowest floor must be Used only for the parking of vehicles, building access, or storage, Free of obstruction, OR Any enclosure must be constructed of breakaway walls
  • Slide 16
  • V Zone Break-away walls: non- supporting and non-load bearing walls that easily break away from the structure when subjected to lateral flood forces.
  • Slide 17
  • Types of Foundations Shallow Foundation: Transfers loads to the soil very near the surface Spread footing or strip footing Mat or raft foundation Slab-on-grade Deep Foundation: Transfers loads to deeper soil layers Piles Cast-in-Situ Piles
  • Slide 18
  • Shallow Foundations
  • Slide 19
  • Shallow Foundation The load from the footing spreads out so that the soil bearing pressure diminishes with depth. The soil directly under the footing takes the greatest load. LOAD Critical Load Area Bearing Pressure (decreases with depth)
  • Slide 20
  • Spread (Column) Footing A footing that spreads the load over a broad area which supports one (or a few) load(s) USES Usually used in low-rise buildings PIER (Concrete or Masonry) SPREAD FOOTING (Concrete) COLUMN LOAD
  • Slide 21
  • Continuous (Strip) Footing A wide strip of reinforced concrete that supports loads from a bearing wall USES Light frame construction Under foundation walls FOUNDATION WALL (Concrete or Masonry) STRIP FOOTING (Concrete) LOAD
  • Slide 22
  • THICKENED SLAB WALL SLAB-ON- GRADE Slab-on-Grade and Thickened Slab Slab-on-Grade Reinforced concrete floor supported by soil Thickened Slab A slab on grade with an integral footing created by thickening the slab USES Residential or light commercial construction Shallow frost depth or when frost protection is used (instead of strip footing)
  • Slide 23
  • Mat Foundation A large, heavily reinforced concrete slab placed under the entire building to support loads from several points USES Heavy loads on weak soil MAT FOUNDATION CONCRETE PIER
  • Slide 24
  • Deep Foundations
  • Slide 25
  • Deep Foundation PILES LOAD Friction Force (Resisting Force) Bearing Force (Resisting Force) PILE CAP The building LOAD is transferred through friction on the sides of the piles and/or bearing on the end of the piles Top Soil Weak Soil Strong Soil
  • Slide 26
  • Pile Foundation Pile Vertical structural member that is driven, jetted, or drilled into the ground in order to gain support from deeper soil layers PILE PILE CAP (CONCRETE) USES Weak shallow soil with deep satisfactory soils PIER (CONCRETE) LOAD
  • Slide 27
  • Cast-in-Situ Piles A large diameter cast-in-place concrete pile USES Weak shallow soil with satisfactory soils at intermediate depth CAST-IN-SITU PILE BELL can improve bearing capacity GRADE BEAM LOAD
  • Slide 28
  • Why Do Foundations Fail? Bending Failure Foundation fractures due to bending moment Shear Failure Foundation breaks due to excessive shear Punch Through Structural member punches through concrete foundation Foundation Failure SECTION PLAN Bending Failure Punch Through
  • Slide 29
  • Why Do Foundations Fail? Settlement Foundation moves Weak or compressible soil Expansion/contraction of soil (moisture) Frost heave Soil Failure Illustrations courtesy U. S. Marine Corp.
  • Slide 30
  • Foundations Purpose Considerations Types of Foundations Shallow Foundations Spread Footings Strip Foundations Slab-on-Grade and Thickened Slabs Mat Foundation Deep Foundations Piles Cast-in-Situ Piles Why Do Foundations Fail?