Tower Cranes & Foundations The Interface & CIRIA C654 .

Tower Cranes & FoundationsThe Interface & CIRIA C654Stuart MarchandC.Eng. FICE FIStructEDirectorWentworth House PartnershipCreated and organised by

EXAMPLES OF TOWER CRANEFOUNDATION TYPESCreated and organised by

Rail mountedCreated and organised by

Pad BaseCreated and organised by

Piled BaseCreated and organised by

Piled BaseCreated and organised by

Grillage BaseCreated and organised by

Grillage BaseCreated and organised by

SELECTION OF FOUNDATION TYPEThis will depend on:The class of crane – Light, Medium or Heavy dutyandThe ground conditions – Very soft clay to RockandThe site constraints – open area or congestedinner cityCreated and organised by

The InterfaceMechanical‘Thou’ (μm)EN 13001-02Regular, Variable,& OccasionalLoadsCivil1/16 (mm)EN1990Permanent, QuasiPermanent, Variable,& AccidentalActionsCreated and organised by

Foundation designs are currentlycarried out in accordance withCIRIA C654 Tower Crane StabilityThis guide published in 2006anticipated that the information fromcrane owners would in future be moredetailed so as to align with EurocodesCreated and organised by

CIRIA C654 Tower Crane Stabilityis currently being re-written to align withEurocodesThis is proving challenging due to themisalignment of the product designcode with the general Eurocodes, andthe different information provided bydifferent manufacturers.Created and organised by

Typical Foundation LoadsIn OperationOut of OperationStorm from rearErectionStorm from 829581Created and organised by

Draft revision to C654 treatment of theabove loadsThe Self Weight of the tower crane andof the foundation is taken as aPermanent ActionAll other loads are taken as VariableActionsCreated and organised by

Design of a simple pad base foundationThere are 3 main aspects to the designa) Stability – the EQU limit stateb) Geotechnical Capacity – the GEO limit statesc) Structural Design – STR limit stateCreated and organised by

Example Design MethodProvisional – Still Under DevelopmentGravity Crane BaseCreated and organised by

In order to illustrate the above we will use loadingdata from the Liebherr 280 EC-H 12 Litronic at ahook height of 47.9m with a 75m jibGround conditions will be taken as acohesive material with shear strength of 200kN/m2Created and organised by

The EQU limit stateErection CaseWt of base 6.5m x 6.5m x 1.4m x 24 kN/m3 1420 kNWt of crane 581 kNTotal Stabilising Moment 2001 kN x 6.5m / 2 x 0.9γ2001 kN 5852 kNmDestabilising Moment (3488 29 kN x 1.4 m)x1.5γ 5292kNmStabilising Destabilising - OKCreated and organised by

Storm CaseWt of base 6.5m x 6.5m x 1.4m x 24 kN/m3 1420 kNWt of crane 912 kNTotal Stabilising Moment 2332 kN x 6.5m / 2 x 1.0γ2132 kN 7579 kNmDestabilising Moment (4270 87 kN x 1.4 m)x1.0γ 4391kNmStabilising Destabilising - OKCreated and organised by

The GEO limit statesThere are 2 Ultimate GEO limit states to check, one witha material factor of 1.0 on the soil properties, and theother with a capacity reduction factor – in this case 1/1.4on the soil strength.The maximum soil pressures occur with the jib at anangle to the base. Part of the base may not be incontact with the ground.Created and organised by

Contact areaNote that the ground capacity varies with the loaded shapeCreated and organised by

The pressure is calculated based on Meyerhof for anequivalent uniform pressure distribution over a reducedrectangular areaCreated and organised by

GEO limit state ULS Combination 1Bearing capacity – there are 2 cases to checkFactor the variable load (moment) by 1.5Factor the permanent load(Base and Crane wt.) byCase 11.35Case 21.0Calculate the area of ground under load for a variety ofjib angles for each case.Calculate the bearing pressure on the groundCalculate the bearing capacity of the ground for eachpressure and loaded areaCheck that Capacity Applied LoadCreated and organised by

GEO ULS Combination 1 Case 1ErectionStabilising Action 2001 kN x1.35γ 2701 kNDestabilising Moment (3488 29 kN x 1.4 m)x1.5γ 5292kNmEccentricity 5292kNm / 2701kN 1.95mWidth of soil loaded 6.5m – 2 x 1.95m 2.6mSoil Capacity A' (cud Nc bc sc ic q)Soil Capacity 9718 kN9718 kN 2701 OKCreated and organised by

GEO ULS Combination 1 Case 2ErectionStabilising Action 2001 kN x1.0γ 2001 kNDestabilising Moment (3488 29 kN x 1.4 m)x1.5γ 5292kNmEccentricity 5292kNm / 2001kN 2.64mWidth of soil loaded 6.5m – 2 x 2.64m 1.22mSoil Capacity A' (cud Nc bc sc ic q')Soil Capacity 4350 kN4350 kN 2001 OKCreated and organised by

SlidingThe horizontal load is a variable load and hence factoredby 1.5The soil resistance is unfactored, but the friction factorbetween the concrete and soil needs to be incorporated.EC7 does not give any guidance, but BS8002 suggests0.75Horizontal Action 29 x 1.5γ 43.5 kNResistance 100 kN/m2 x 1.22m x 6.5m * 1.0γ * 0.75 594 kNCreated and organised by

GEO limit state ULS Combination 2Bearing CapacityFactor the variable load (moment) by 1.3Factor the permanent load (Base and Crane wt.) by 1.0Calculate the area of ground under load for a variety ofjib angles for each case.Calculate the bearing capacity of the ground for eachpressure and loaded areaCompare this with the failure capacity of the ground withstrength reduced by 1.4Created and organised by

GEO ULS Combination 2ErectionStabilising Action 2001 kN x1.0γ 2001 kNDestabilising Moment (3488 29 kN x 1.4 m)x1.3γ 4587kNmEccentricity 4587kNm / 2001kN 2.29mWidth of soil loaded 6.5m – 2 x 2.29m 1.92mSoil Capacity A' (cud Nc bc sc ic q')Soil Capacity 8221 kN8221 kN 2001kN OKCreated and organised by

SlidingThe horizontal load is a variable load and hence factoredby 1.3The soil resistance is factored by 1/1.4, and the frictionfactor between the concrete and soil is incorporated.Horizontal Action 29 x 1.3γ 37.7 kNResistance 100 kN/m2 x 1.92m x 6.5m * 0.75 / 1.4γ 668 kNCreated and organised by

GEO limit state SLSCalculate the settlement of the ground under SLS loadsand confirm this is acceptable with the Tower craneManufacturerORBased on UK custom and practice, calculate the bearingpressure on the ground under SLS loading, and if this is 1/3 of the failure capacity, deem that settlements willbe acceptableCreated and organised by

STR limit stateDesign with jib orthogonalTake the worst case from the GEO analysisCalculate the maximum momentwhich is at the point of zero shearCreated and organised by

GEO ULS Combination 1 Case 2Design the reinforcementThe base projects 2m beyond the tower crane leg (pointof zero shear)Ground Pressure 2001 kN / 1.22m / 6.5 m 252 kPaDesign moment 252 kPa * 1.22m *(3.25 m – 1.22m/2) – 33.6kPa *(2.25m)2/2 520 kNm/mCreated and organised by

Using 25/30 concrete fck 25 N/mm2Effective depth 1.4m – 50mm cover – 40mm bar allowance 1310mmK Med / (bd2fck) 520 x 106 / 1000/13102 / 25 0.012Lever arm Z d(0.5 Sqrt(0.25 – K / 0.9)) but 0.95 x dZ 0.95 x 1310 1245mmArea of reinforcement requiredAs M / fyd z 520 kNm / (500/1.15γ x1245mm) 960 mm2 /mCreated and organised by

Check minimum reinforcement 0.26 x (fctm/fyk)btd 0.0013btdwhere fctm 0.30fck0.666 0.30 x 250.666 2.56 MpaMinimum reinforcement 0.26 x (2.56/500) x 1000 x 1310 0.0013 x 1000 x 13101744 mm2 / m but 1703 mm2 / mHence minimum reinforcement governs – 1744 960 mm2 / mCreated and organised by

Check ShearDesign Shear at d from support252 kPa * 0.94m - 33.6kPa *0.94m 205 kN/mShear stress vEd 205 kN/m / 1310mm / 1m 0.16 kPavRd,c (0.18/γc)k(100rlfck)0.333 0.035k1.5fck0.5whereγ c 1.5k 1 (200/d)0.5 2.0: k 1 (200/1310)0.5 1.39rl Asl/bd 1744/(1000x 1310) 0.00133fck 25 MPavRd,c (0.18/1.5)x 1.39 x (100 x 0.00133 x 25)0.333 0.035 x1.381.5x 250.5 0.284 0.249 0.16 MPaCreated and organised by

Pull out/push through of the anchorsThe CIRIA guide states “If the manufacturer’srecommendations regarding shear reinforcement arefollowed, punching and pull out shear should be satisfactory”I have yet to see any manufacturer’s recommendationsregarding shear reinforcement, apart from sketchesindicating where it should go.Created and organised by

Foundation AnchorsCreated and organised by

This is fundamentally a punching shear issueWith some types of anchor it is clear where the failure conewill occurCreated and organised by

With others it is less clear, but Liebherr now suggestCreated and organised by

Discussion PointsStorm from front condition – should this be a generaldesign case or a special case?Why can we not have loadings which are Eurocodecompliant?What load factors are appropriate to the erection case?Are current expendable anchor designs sustainableand what can be done to improve them?Created and organised by

Created and organised by The Interface Mechanical Civil ‘Thou’ (μm) 1/16 (mm) EN 13001-02 Regular, Variable, & Occasional Loads