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Design Example_ Deep Mass Concrete Pad Base

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Design Example_ Deep Mass Concrete Pad Base

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  • 6/19/2015 DesignExample:DeepMassConcretePadBase.|Builder'sEngineer

    http://www.abuildersengineer.com/2013/01/designexampledeepmassconcretepad.html 1/5

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    Design Example: Deep Mass Concrete Pad Base.Twittear 0 0

    Asteelframedbuilding is tobebuilt onasiteadjoiningpreviously,wherevariablellextendsdowntothelevelofthebedrock.Aheavily loaded stanchion, carrying axialload only, is to be supported on a padfoundation.

    It has been decided to found the heavilyloaded base in the sandstone bedrock, inorder tominimize settlement.Thebase istobeconstructedasamassconcretepad.

    LoadingsThe superstructure working loads are asfollows:

    AllowablebearingpressureFromDesign Example, the sandstone has a net allowable bearing pressure of na = 2000kN/m2.SizeofbaseThe foundation surcharge due to the groundbearing slab is small and can be neglected.Therefore,

    Thereforea1.5m1.5mpadfoundationwillbeused,asshowninFig.11.15.

    The stanchion bases are set at a common depth of 300 mm below slab level, and theremainingdepthofexcavationdowntothesandstonerockistakenupbythemassconcretebase.

    Theminimumdepthofbaserequired,before itbecomesnecessaryforreinforcementtobeintroduced,is500mm(seedepthtoangleofloaddispersioninFig.11.15).Clearlyamassconcretebaseisadequateinthisinstance.

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  • 6/19/2015 DesignExample:DeepMassConcretePadBase.|Builder'sEngineer

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    Fig.11.15Massconcretepadbasedesignexample.

    The choice between the full sized mass concrete pad and the stub column solution isdeterminedfromeconomicconsiderations.

    The economic changeover point is where the crosssection required for groundbearingpurposesbecomesexcessivelywasteful intermsofthecostofconcretecomparedwiththecostofintroducingshutteringtoformthesmallercrosssection.Situationswherethiswouldapplyare:

    (1)Wherethepadsareverydeep,(2)Wheretheallowablegroundbearingpressuresareverylow,or(3)Where,duetothenatureoftheground,ashutteredpadisrequiredinanycase.

    The lower pad plan size is determined from the loading and the allowable groundbearingcapacity.Ifthesectionisreducedathigherlevel,thesizeatthepointwhereitisreducedisgenerallybasedupona45dispersionofloadthroughthemassconcrete(seeFig.11.16).

    Fig.11.16Stubcolumnpadbase.

    Theupperpedestal crosssection isdetermined from the load, theallowablebearing stressbelow the base plate and the allowable compressive stress on the mass concrete inconjunctionwithasuitablepracticalandeconomicsizeforconstruction.Forexample,thesizedetermined from stress considerations often needs to be rounded up to a larger practicalmass concrete crosssection particularly where the mass pier is relatively tall (see Fig.11.17).

    LabelsFOUNDATIONS (134) PILES (61)STRUCTURES (58) WATERPROOFING (58)SOILS(47)FOOTINGS(30)SITEEXPLORATION(30)BUILDING(29)PADFOUNDATIONS (18)STRIPFOUNDATIONS(18)CONCRETE(15)RAFTFOUNDATIONS(14) DRILLED PIER FOUNDATIONS (13) RETAININGWALLS (10) EXCAVATIONS (9) SURFACE SPREADFOUNDATIONS(9)

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  • 6/19/2015 DesignExample:DeepMassConcretePadBase.|Builder'sEngineer

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    Categories:CONCRETE,PADFOUNDATIONS

    Fig.11.17Masspiercriteria.

    Related Post:CONCRETE

    PADFOUNDATIONS

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