Reinforced Concrete Pipe

1 Reinforced Concrete PipeHow to Assess the Transition from Indirect to DirectDesign Methods in Deep Cover InstallationsAdam Braun, , ManitobaCanada Introduction, Background, andHistory Indirect Design SIDD Installations and DirectDesign Transition from Indirect toDirect Design ConclusionRigid Rugged Resilient2 Introduction,Background &HistoryRigid Rugged Resilient3 Introduction Reinforced Concrete pipe (RCP) First produced in 1896 inFrance Brought to North America in1905 Rigid Rugged Resilient4 Introduction Indirect Design(Marston/Spangler Analysis) Developed in the 1920 s and 30 s Empirically derived Excellent performance record in lowto moderate soil covers Direct Design (Heger/Selig) Developed in the 1970 s and 80 s Reinforced Concrete design theory Limit states design principals Applicable for large diameter andhigh external load conditionsRigid Rugged Resilient5 While direct design hasbeen formally adoptedby industry it does notsee widespread useIowa Experiment Station Anson Marston began researchinto the behavior of buriedrigid pipe in 1910 Born out of the increased useof clay and non reinforcedconcrete pipe in sizes up to 36 as both drain tile and sewerpipe The large diameter pipe wasprone to failure shortly afterinstallation Began with investigation intofailuresRigid Rugged Resilient6At the time therewas no quantifiabledesign method forburied pipe !

2 Original Soil Load and PipeStrength ExperimentsRigid Rugged Resilient7 Evaluating Trench Loads12 pipe Test36 pipe TestOriginal Soil Load and PipeStrength ExperimentsRigid Rugged Resilient8 Testing of pipe up to 42 diameter Homebuilt sand bedding testing machines Evaluation of test results to actual supporting strengthfor various installation typesTypical InstallationConditionsTests in FlatBottom TrenchesTests in ShapedTrenchesRigid Rugged Resilient9 Evaluation of Testing MethodsThe Theory of Loads on Pipes in Ditchesand Tests of Cement and Clay Drain Tileand Sewer pipe Published in 1913 bythe Iowa State Collegeof Agriculture andMechanical Arts Authors: Anson Marston A. O. Anderson New theories forcalculating soil loadson buried pipes innarrow trenchesRigid Rugged Resilient10 The Supportive Strength of Sewer pipe inDitches and Methods of Testing SewerPipe in Laboratories to Determine TheirOrdinary Supportive Strength Published in 1917 by the IowaState College of Agriculture andMechanical Arts New theories for quantifyingthe external load capacity ofburied rigid pipe Authors: Anson Marston W.

3 J. Schilick H. F. ClemmerRigid Rugged Resilient11 Continued Further development was undertaken in the 1920 s and 30 s by: W. J. Schilick M. G. Spangler Resulted in numerous papers on an ever expanding knowledge ofsoil loads and pipe strengths Developed calculations for determining earth loads fromembankment (projection) and tunnel installations Load calculations were all empirically derived from experimentsundertaken at the Iowa Experiment StationRigid Rugged Resilient12 Indirect DesignRigid Rugged Resilient13 Indirect Design Matches estimated trench loads to the estimatedsupporting strength of the installed pipe Installed pipe strengths estimated through the use ofempirically derived factors pipe strengths assessed using three edge bearing(3EB) testsRigid Rugged Resilient14 Three Edge Bearing Tests Standards.

4 ASTM C497 - Standard Test Methods for Concrete pipe ,Manhole Sections, or Tile CSA A257 Quantifiable means of determining a pipe ability tosupport externally applied loadsRigid Rugged Resilient15 Three Edge Bearing Tests RCP is typically tested with the intent of determining thefollowing loads: Hairline Crack Service Cracking ( or mm) Ultimate Failure Typical QA/QC procedures only require testing up toservicing cracking limit with the rare test taken to ultimatefailure It should be noted that standard three edge bearing teststo do not check for diagonal tension (shear) or radialtension failure modes. Both are governing failure modes in high soil Rugged Resilient16 Traditional Installation Types andBedding Factors Bedding types developed to reflect pipe installationmethods at the beginning of the 1900 s Reflect installation efforts involving hand excavation Bedding factors were developed for each installationtype reflect the increase in load a pipe can supportwhen installed vs.

5 In the three edge bearing test The bedding factor each installation type reflects thelevel of load distribution provided Better soil support equals a higher bedding factor!Rigid Rugged Resilient17 Traditional Installation Types andBedding FactorsRigid Rugged Resilient18 Indirect Design Method Calculate live and deadloads Determine a bedding factor Determine the equivalentthree edge bearing load(divide the soil load by thebedding factor) Convert to equivalent D-Load (Divide by thediameter of the pipe ) Select appropriate pipe fromthe ASTM or CSAspecification or specifyrequired loadRigid Rugged Resilient19 Indirect Design Method Reinforcement requirements are stipulated in ASTMC76 or CSA A257 Empirically derived in order to meet required D-Loads Single factor of safety applied against ultimatefailure, ranging from and No differentiation between live and dead loads andtheir respective levels of uncertainty Adequate for low to moderate soil coversconsistent with those used to develop the empiricaldesign methodRigid Rugged Resilient20 SIDD Installations andDirect DesignRigid Rugged Resilient21 New Design Approach American Concrete pipe Association (ACPA)undertook a long term research project in the1970 s and 80 s to develop a new designapproach for Reinforced Concrete pipe Dr.

6 Frank Heger was engaged to develop this newdesign method based on his knowledge ofreinforced Concrete design Continuation of Heger s post graduate work atMIT Dr. Ernest Selig was engaged to providedgeotechnical expertise in development of thepipe-soil interaction models Heger s other work Rugged Resilient22 New Design Theory Heger s 1962 PhD thesis ATheory for the StructuralBehavior of ReinforcedConcrete pipe strove todevelop a rational procedurefor predicting the structuralbehavior of reinforcedconcrete pipe Adapted Reinforced concretebeam theory to the circularpipe wallRigid Rugged Resilient23 New Design Theory Proposed design proceduresconsidered the following: Flexural strength Diagonal tension (shear) capacity Predicting and limiting in servicecrack widths Use of stirrups in controllingdiagonal tension Combined internal and externalloading conditions Assessed the development ofinternal wall forces under test(3EB) and in service conditionsRigid Rugged Resilient24(Heger 1962)Imparted Wall ForcesRigid Rugged Resilient25 Max bending moments develop at: Obvert Invert Springline Max wall thrust: Springline Max diagonal tension: 12 to 13 from invertBending MomentsRigid Rugged Resilient26 TensionCompressionTTTCCCSoil LoadDevelopment of BendingMoments during 3EB TestRigid Rugged Resilient27(Heger 1962)Diagonal and Radial Tension Radial Tension Failure.

7 Cause by tension forces withinthe radial reinforcement These tension forces act tostraighten out curved steel,causing it to pull away from thepipe wallRigid Rugged Resilient28 Radial Tension FailureDiagonal TensionFailureSoil Pressures and Wall Forces The interaction between buried pipe , the embedmentmaterial, and native soils is complex and dependent onmany factors Heger and Selig developed the computerized finiteelement program SPIDA (Soil- pipe Interaction Designand Analysis) to determine the distribution of soilpressures around the pipe and wall forces developed This lead to the development of four new installationtypes to reflect modern pipe installation Rugged Resilient29 Standard Installations DirectDesign (SIDD)Rigid Rugged Resilient30 Most IntensiveInstallationRequirementsLeast IntensiveInstallationRequirementsType 1 InstallationQuantitativevs.

8 QualitativeInstallationProcedureStandard Installations DirectDesign (SIDD)Rigid Rugged Resilient31 Visual Representationof Applied SoilPressuresHeger Positive Projection Load Heger and Selig developed a simplified load calculationmethod based on the new SIDD installation types Only positive projection conditions considered Load coefficients developed with SPIDA Applied load = Prism load x Vertical Arching Factor (VAF)Rigid Rugged Resilient32 Trench Widthsare Difficult toControl in theFieldEstimating Wall Forces Heger and Selig utilized SPIDA to assess and developload coefficients for the new SIDD installations typesRigid Rugged Resilient33 Direct Design Proposed in Heger s 1988 paper New InstallationDesigns for Buried Concrete pipe Incorporates SIDD Installations and SPIDA developedload coefficients Incorporates limit states design methodology Proposed steel reinforcement design methods tocounteract the following applied wall forces.

9 Bending moments Wall thrust Diagonal tension (shear) Radial tensionRigid Rugged Resilient34 ASCE 15 and PIPECAR ASCE 15 Standard Practice for DirectDesign of Buried Precast Concrete PipeUsing Standard Installations (SIDD) Originally published in 1993 subsequentlyupdated in 1998 and 2017 Outlines SIDD installation requirementsand direct design methodology Computerized design programPIPECARTM Developed by Frank Heger for the ACPA Direct design of RCP for a myriad ofdesign and installation conditions Direct design and SIDD installationshave now been adopted by bothAASTHO and CSAR igid Rugged Resilient35 Transition from Indirect to DirectDesignRigid Rugged Resilient36 Limits of Indirect Design Indirect design was developed based on empiricaltesting on small to intermediate diameter pipe (<36 )under loading conditions typical of the time (<15 ) Failure modes recognized at the time were limited toflexural failure Testing of unreinforced clay tile and Concrete pipe 3EB tests do not directly assess diagonal or radialtension failure modes which govern under largeexternal loading conditionsRigid Rugged Resilient37 Diagonal and Radial Tension Pipes designed to withstand applied flexural stressesmay not contain sufficient reinforcing to withstandimparted diagonal tension forces If not confirmed, mobilization of tensile steel underhigh loads may result in radial tension failureRigid Rugged Resilient38 Under 3EB test conditions largediameter pipes can fail underdiagonal or radial tension prior toexperiencing flexural failureReinforcing for Diagonal Tension Diagonal tension is resisted by.

10 Placement of additional radial reinforcing steel (to a point) Placement of stirrupsRigid Rugged Resilient39(Brzev et al 2006)Stirrups placed tointercept theshear planeHeavily Reinforced 10 diameter Concrete pipe ,designed using direct designmethodsReinforcing for Radial Tension Stirrups must be employed to overcome radial tensionforcesRigid Rugged Resilient40 Stirrups used toanchor the innerreinforcement intothe pipe wallTransitioning from Indirect toDirect Design Determine the transition from a flexural controlledfailure to diagonal and/or radial tension controlledfailure Requires the direct design methodologies ( handcalcs or PIPECARTMR igid Rugged Resilient41 Rigid Rugged Resilient42 Verification Governing failure modes Bending moment capacity Diagonal tension capacityRigid Rugged Resilient43 Diagonal Tension Failure -1050 mm Class V RCPV erificationRigid Rugged Resilient44 Radial Tension Failure -1650 mm Class V RCP Governing failure modes Bending moment capacity Diagonal tension capacityVerificationRigid)