b'Computer analysis of shaft buckling is therecommended method to achieve the most GRAPH 7 - CONSERVATIVE CRITICALaccurateresults.Manytimes,however, BUCKLING LOAD FOR BUDGET ESTIMATESonemusthavegeneralinformationtoprepareapreliminarydesignorbudget SPT "N" 1 SPT \'N" 2 SPT \'N" 4proposal.Table15belowprovides 170Conservative CriticalBuckling Load 160Estimatesforvariousshaftsizes thatare 150fixed at both ends and penetrating throughdifferent types of weak homogeneous soils. 140Graph 7 presents a visual representation of 130BUCKLING STRENGTH X 1,000 LBScriticalbucklingloadsthat willquickly 120identifyshaftconfigurationswithInsufficientBucklingStrengthwhen 110passingthroughsoftsoilsthatdonot 100adequately support the shaft. 90AllowableCompressiveLoads -Pilein 80Air: Graph8showsthereductionin 70allowableaxialcompressiveloadingrelative to the length of the pier shaft that 60isfixedatbothendsand withoutlateral 50support. Table 14 illustrates that the 4-1/2 40diameter tubular Torque Anchor providesan axial stiffness of more than five times 30that of a 2-7/8 diameter shaft.In addition, 20Graph8demonstratesthatthe4-1/2 10diameterpilehasanultimatecapacityof 0morethanfourtimesthatofthe2-7/8 1-1/2 1-3/4 2 2-7/8- 2-7/8- 3-1/2- 4-1/2-diameter shaft when each shaft has ten feet Sq. Sq. Sq. .203 .276 .300 .337ofexposedcolumnheightwithoutanylateralsupport.Whenonecomparesthe SHAFT CONFIGURATION IN CLAY SOILbucklingcapacityofthe4-1/2anddiameter shaft to the 1-3/4 solid square shaft, the 4-1/2 diameter tubular shaft has more than threetimes the capacity.The same comparison between the 3-1/2 diameter shaft and the 1-3/4 solid squareshaft, the 3-1/2 shaft has 1.6 times greater buckling capacity.Table 15 Working Loads Under Buckling Load ConditionsFor Budgetary Estimating(Factor of Safety = 2.0)Uniform Soil ConditionShaft Size Organics Very Soft Clay Soft Clay Loose SandN 1 N = 1 - 2 N = 2 - 4 N = 2 - 41-1/2 Square Bar 14,000 lb 16,000 lb 23,000 lb 18,000 lb1-3/4 Square Bar 20,000 lb 24,000 lb 34,000 lb 27,000 lb2 Square Bar 28,000 lb 35,000 lb 48,000 lb 43,000 lb2-7/8 Dia x 0.203 19,000 lb 22,000 lb 31,000 lb 25,000 lb2-7/8 Dia x 0.276 20,000 lb 24,000 lb 34,000 lb 28,000 lb3-1/2 Dia x 0.300 33,000 lb 39,000 lb 55,000 lb 45,000 lb4-1/2 Dia x 0.337 59,000 lb 69,000 lb 98,000 lb 80,000 lbECP Helical Torque Anchors Technical Service Manual2021 Earth Contact Products, L.L.C.2021-09 Chapter 1 - Page 34 All rights reserve'