design stress for vinyl sheet pile

Design Stress for Vinyl Sheet Pile

A Whitepaper by:

Ben Brown

2011 Crane Materials International4501 Circle 75 Parkway, Suite E-5370 Atlanta, GA 30339 USA Phone 866-867-3762 Fax 770-933-8363 International 00+1+770+933+8166

Physical properties are defined by ASTM testing standards, The Aluminum Association Design Manual, The Naval Facilities Design Manual DM 7.2, The US Army Corps of Engineers General Design Guide: PVC Sheet Pile and/or standard engineering practice. The values shown are nominal and may vary. The information found in this document is believed to be true and accurate. No warranties of any kind are made as to the suitability of any CMI product for particular applications or the results obtained there from. Crane Materials International is a Crane Building Products company. ShoreGuard, The ShoreGuard Seawall SystemTM, C-Loc, TimberGuard, GeoGuard, Dura Dock, Shore-All, GatorGates, GatorDock EliteTM, ArmorWareTM, ArmorRodTM, Box ProfileTM, UltraCompositeTM, Elite WallTM, Elite PanelTM, Elite Fascia PanelTM, Flat PanelTM, XCRTM, XCR TechnologyTM, XCR VinylTM, GatorBridgeTM, Gator AluminumTM, Gator Sheet PilingTM, GatorDockTM, I-Beam LockTM, Textured SlateTM, Crane Materials InternationalTM logo, CMI Sheet Piling SolutionsTM, Aqua Terra SystemTM, EnduranceTM, Endurance CSPTM, PolarisTM, EclipseTM, GridSpineTM, 21 PolyTM, PileClawTM, SheerScapeTM, SheerScape Retaining Wall SystemsTM, Sheer PanelTM and CMI Waterfront SolutionsTM are trademarks, service marks or trade names of Crane Materials International. United States and International Patent numbers 4,674,921; 4,690,588; 5,292,208; 5,145,287; 6,000,883; 6,033,155; 6,053,666; D420,154; 6,575,667; 7,059,807; 7,056,066; 7,025,539; 7,393,482; 5,503,503; 5,803,672; 6,231,271; 1,245,061CA and other patents pending. 2011 Crane Materials International. All Rights Reserved.

CRANE MATERIALS INTERNATIONAL

2|D e s i g n S t r e s s f o r V i n y l S h e e t P i l e

Vinylhasbeen a staple in the construction industry forover 50 years. Due to its strength, light weight, andcorrosionresistance,Vinylhas longbeenaclearfavoriteforpipingapplications.Itisnowseeingincreasinguseinstructuralapplications. Butunlike steel,aluminum,andwood,nostandardstructuraldesigncodescurrentlyexist.This lack of a governing design body has led toinconsistent design methods, general confusion, andmanipulation in the industry. Vinyl is not a mysticalmaterial.Vinylsheetpilingstructuresshouldbedesignedwith the same methodology used for any constructioncomponent.In the vinyl sheet piling industry, the topics of safetyfactor inproductselection,anddesignstress ingeneral,areoftenoverlooked.Currently,manypeoplearerelyingonmanufacturers togive themadesign stressvalue,orworse yet, simply the overall bending capacity of thesheet itself. Whileseekingadvicefrommanufacturers isencouraged, some manufacturers take this opportunitytomanipulate the design stress value to best suit theirinterestsattheexpenseofthedesignerorenduserwhois unaware. Many times high design stress values areused, minimizing the factor of safety, to give theperceptionofincreasedstrengthwithnophysicalchange.Other times, different design stress values are used forthe samematerial to give the appearanceof abroaderproduct range. When these things occur, the designstressvaluesmaybehiddenorhard to find. Thispaperwill aid the designer in establishing the proper designstress.Oncethisvaluehasbeenestablished,itshouldbeusedforallproductsbeingevaluated.FactorofSafetyandDesignStressWhendesigninganysheetpilewall,twoqualities,shapeproperties and material characteristics, are used tocalculate an appropriate sheet for a project. A sheetsvarious shape properties are determined solely by thegeometry of the profile and combined into one designvalue,SectionModulus.Materialpropertiescanbemore

challenging to quantify due to their inevitableinconsistencies.UnlikeSectionModulus,whichisentirelyobjective, design stress is determined by taking themaximum stressamaterial canwithstandbefore failureandapplyingachosenlevelofsafety.

StressDesignSafetyofFactorValueStressMax

Equation1DesignStressCalculation

psipsi 000,152

000,30 Example1

DesignStressCalculation

Safetyfactorsarealwaysapplied intheconstructionandengineering industry in this fashion to account for theunknownandtoprovideaddedsafetyinthedesign.Itisthesole responsibilityof thewalldesigner tochooseanappropriatesafetyfactorfortheproject.Althoughnoofficialgoverning codesexist, theUSArmyCorpsofEngineershaslongbeentheleaderinsheetpilewalldesignsandinstallations.Theydesignateaminimumsafety factorof2 forbendingcalculationsofsteelsheetpiling(seeUSACEPublicationEM111022504,DesignofSheetPileWalls,section63,Designofsheetpiling). Attheveryleast,thesamesafetyfactorisrecommendedforall vinyl sheet pile products. But again, this decisionshouldultimatelybemadebythewallsdesigner.EstablishingaDesignStressforVinylSheetPilingThe minimum tensile strength of Vinyl for use in abuilding product is designated by its ASTM cellclassification.Thisistheonlystressvaluethatshouldbeusedinthedesignofvinylsheetpiling.Vinylsheetpilingmaterials produced by CMI are designated with thestructuralcharacteristicsofcellclassification14244333,meaning they will meet or exceed a minimum tensilestrengthof6,500psi. FromEquation1 above,use this



value along with the recommended factor of safety toarriveatthedesignstressforvinylsheetpiling.

psipsi 200,32

500,6 Example2

VinylDesignStressCalculationAlthough raw materials may vary slightly frommanufacturer to manufacturer, vinyls strengthpropertiesremainconstantregardlessoftheblend.IftheASTM cell classification is not known, the same designstress must be used across the board for productcomparison. In fact, the US Army Corps of Engineersspecifies 3,200 psi, as well, for the design stress of allvinylsheetpiling,regardlessofthemanufacturer.DesigningforlonglifeAfter establishing the proper design stress, longtermeffects should be considered to determine if this valuewould yield an acceptable design life. There aremanyfactorsthatdecreaseamaterialsperformanceovertime:fatigue, corrosion, and physical deterioration, forexample. Another is creep, the tendency of a body tocontinuallydeformover timewhileheldunder constantload. While only a major concern at very hightemperatures formostmetals, creep can affect vinyl atroom temperature. This phenomenon is the drivingfactor in determining the longterm behavior of vinylsheet piling. Strain is themeasure of this deformationand is reportedasapercentagechange in length. Vinylformulated to withstand impact like that used in themanufacture of vinyl sheet piling can withstand amaximum strain before failure of 5%. Again, using themethodsapplied inEquation1,asafetyfactorshouldbeappliedtothismaximumvaluetoarriveatthemaximumallowablestrain.

%5.22%5 Example3

MaximumAllowableStrain

Fortunately,creephasbeenthoroughlystudiedandwelldocumented.In1962,WilliamFindleybeganresearchonthe longtermeffectsofcreeponVinyl. In1987,Findleypublished 26Year Creep and Recovery of Poly (VinylChloride) and Polyethylene. Findley included in hispublishinganequationtopredictstrainduetocreep,foranygivenstressand timeperiod,where isstrain, t istime,and o, +,andnareconstants.

no t Equation2

StrainDuetoCreepFindleysresearchisbyfarthemostcomprehensivedonein this area, andhismodelhasproven tobe extremelyaccurate. His findings are THE authority in the field ofcreepeffectsonplastics,andwith26yearsofvalidation,hiscorrelationshouldbeusedexclusivelytopredictlongtermcreepeffectsonVinyl.Usingan inputstressof3,200psiandamaximumstrainof2.5%,adesign lifeof justover100years ispredictedfor Vinyl, further validating the use of 3,200 psi. Thisrelationshipbetweenstressanddesignlifeisexponentialinnature,andaseeminglysmallincreaseindesignstresswill result in a significantly shorter expected life. Forexample, 3,200 psi results in a service life 30% longerthan 3,300 psi (a difference of only 100 psi) and 250%longerthan3,700psi.



ReviewVinylisastandardconstructionmaterialandshouldbedesignedwithassuch.Inanystructuralapplication,engineersanddesignersshouldunderstandandendorsedesignmethodology,factorsofsafety,anddesignvaluesnotonlyfortheoverallscopeoftheproject,butforproductselectionaswell.Retainingwallsconstructedwithsheetpile,vinylorotherwise,arenoexception.Whenallfactorsaretakenintoconsideration3,200psiisthemostresponsiblevaluetouseforthedesignstressofvinylsheetpile.CMIhasbeentheleaderinvinylsheetpilesinceitsinceptionover20yearsagoandhasproducedmillionsoffeetofinstalledsheetpileandover90%ofallvinylsheetpilepresentlyintheground.Theseproductsandprocesseshavebeencloselymonitoredovertheyearstoensureproperdesign,safety,andlongevity.Itisourhopethat,withtheinformationpresentedhere,thedesignerorenduserwillbeabletomakeamoreinformedandresponsibledecisionregardingtheselectionandapplicationofvinylsheetpiling.


Design Stress for Vinyl Sheet Piling-coverDesign Stress for Vinyl Sheet Piling

design stress for vinyl sheet pile

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