b'Table14illustrateshowTable 14Torque Anchor Shaft Stiffness Comparisonstubularpileshavesuperiorshaft stiffness when comparedCross Moment of Piertosolidsquarebars.Itis Torque AnchorShaft Section Inertia - in 4 Stiffnessinterestingtonotethatthe2- Configuration Area - in 2 (Stiffness) Relative to7/8diametertubularTorque TA-288Anchor with a wall thickness TA-150 (1-1/2 Square) 2.21 0.40 21%of0.276inchescosts TA-175 (1-3/4 Square) 3.00 0.74 39%approximatelythesameasa TA-200 (2 Square) 4.00 1.33 69%TorqueAnchorfabricated TA-288L (2-7/8 Dia x 0.203) 1.70 1.53 80%from1-3/4solidsquarebar TA-288 (2-7/8 Dia x 0.276) 2.25 1.92 100%stock.Pleasenotice in Table14 that the 1-3/4 solid square TA-350 (3-1/2 Dia x 0.300) 3.02 3.89 203%bar is only 40% as stiff as the TA-450 (4-1/2 Dia x 0.337) 4.41 9.61 501%2-7/8diametertubularproduct.Itisclearthatthe2-7/8tubular reduction in allowable capacity.productisthebetterchoicewhendesigning It should be noted that solid square shafts arefoundationpilesthataretobeloadedinaxial onlyrecommendedtobeinstalledthroughcompression.Another situation where shaft buckling should be soils having SPT, N values greater or equalconsiderediswheretherearebothaxial to five blows per foot.compressionandlateralforcesactinguponthe The reason for this is the shaft offers very littlepile.Normally when the pile terminates within a strengthagainstbucklingwhensubjectedsoilsfooting, this is not a problem.When the pile is with SPT blow less than five.When designingnotfixedatthesurface,theremaybefactors pilesinaxialcompressionthatmustpenetratepresentthataffectbuckling.Thesefactors weak soils, it is good practice to consider tubularincludeshaftdiameter,length,soildensityand products for the application.strength, and pile cap attachment. The most accurate way to determine the bucklingBucklingLoadsInWeakSoil: Whenevera loadofahelicalpileshaftinweaksoilisbyslender shaft does not have adequate lateral soil performingabucklinganalysisbyfinitesupport, the load carrying capacity of the shaft is differences.Thereareseveralspecializedreduced as shaft buckling becomes an issue.In computerprogramsthatcanperformthisthecaseoftubularTorqueAnchors ,thefull analysisandallowtheintroductionofshaft properties and soil conditions that can vary withultimatecapacityisavailableprovidedthesoil depth.Another,lessaccuratemethodofthroughwhichthepilepenetratesmaintainsa estimatingcriticalbucklingisbyDavissonvalue for N4 blows per foot or greater as Method, Estimating Buckling Loads for Pilesreported on a Standard Penetration Test for the (1963).Inthismethod,Davissonassumesentire lengthofthe pileembedment.Thepile variouscombinationsofpileheadandtipmustalsobesecuredtoasuitablefootingat boundary conditions with a constant modulus ofgrade level to prevent lateral forces transmitting sub-gradereaction,k H withdepth.Loadto the top of the pile. transfer to the soil due to skin friction is assumedWheneveroneencountersweaksoilssuchas to not occur and the pile is straight.Davissonspeatorotherorganicsoils,improperly formula is shown as Equation 10 below.consolidated soil, or where the pile may become Equation 10. P cr= U crE pI p/ Rfully exposed from the soil due to erosion; the 2pilewillnotbeabletosupportthefullrated Where:capacity listed in Table 2. P cr= Critical Buckling LoadlbU cr= Dimensionless ratio (Assume = 1)In addition to the amount of lateral soil support E p= Shaft Mod. of Elasticity = 30 x 10 6psion the shaft, both the length of the pile pipe that I p= Shaft Moment of Inertia = in 4is exposed to insufficient lateral support and the R = 4E pI p/ k Hdstiffnessoftheslendershaftwillaffectthe d = Shaft DiameterinECP Helical Torque Anchors Technical Service Manual2021 Earth Contact Products, L.L.C.2021-09 Chapter 1 - Page 33 All rights reserve'