# ASTM D7381-07 (Reapproved 2013)

Designation: D7381 − 07 (Reapproved 2013)Standard Practice forEstablishing Allowable Stresses for Round Timbers for Pilesfrom Tests of Full-Size Material1This standard is issued under the fixed designation D7381; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice contains procedures for establishing allow-able compression parallel to grain and bending stresses forround timbers used for piling, based on results from full-sizetests.NOTE 1—Allowable stresses for compression perpendicular to grain andshear properties are established in accordance with the provisions ofPractice D2899.1.2 Stresses established under this practice are applicable topiles conforming to the size, quality, straightness, spiral grain,knot, shake and split provisions of Specification D25.1.3 A commentary on the practice is available from ASTMInternational.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D25 Specification for Round Timber PilesD198 Test Methods of Static Tests of Lumber in StructuralSizesD245 Practice for Establishing Structural Grades and Re-lated Allowable Properties for Visually Graded LumberD1036 Test Methods of Static Tests of Wood PolesD1990 Practice for Establishing Allowable Properties forVisually-Graded Dimension Lumber from In-Grade Testsof Full-Size SpecimensD2555 Practice for Establishing Clear Wood Strength ValuesD2899 Practice for Establishing Allowable Stresses forRound Timber PilesD2915 Practice for Sampling and Data-Analysis for Struc-tural Wood and Wood-Based ProductsD4761 Test Methods for Mechanical Properties of Lumberand Wood-Base Structural MaterialD6555 Guide for Evaluating System Effects in Repetitive-Member Wood Assemblies3. Terminology3.1 Definitions:3.1.1 allowable stress—the numeric value of pile strengthappropriate for use in design.3.1.2 end-bearing—compression parallel to grain stressused in design when the pile load is not carried to the soilthrough skin friction.3.1.3 load sharing—the distribution of load that occurs intwo or more piles which are capped with a load-distributingelement that assures the piles deform as a group. The loaddistributed to the piles in such a group is in proportion to thestiffness of each pile. This distribution of loads to the piles inthe group reduces the effect of between pile variability andincreases system reliability over that of piles which perform assingle members.3.1.4 skin friction—the interaction between the pile surfaceand the surrounding soil which serves to distribute load eitheraway from or into a pile. A positive skin friction refers to pileloads distributed to the soil. Negative skin friction refers toloads being distributed into the pile as a result of soilsubsidence or consolidation.3.2 Symbols:c = circumference of a round timber pileCcp= conditioning adjustmentCds= adjustment for duration of load and miscellaneousfactor of safetyCls= load sharing adjustmentCoc,Cob,Coe,Coeb, = adjustments to Fc, Fb, E and EMOEfor pile oversizing relative to Specification D25 specifiedminimum circumferences1This practice is under the jurisdiction of ASTM Committee D07 on Wood andis the direct responsibility of Subcommittee D07.04 on Pole and Pile Products.Current edition approved April 1, 2013. Published April 2013. Originallyapproved in 2007. Last previous edition approved in 2007 as D7381 – 07. DOI:10.1520/D7381-07R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Ct= adjustment of allowable compression parallel to grainstress at pile tip to critical section location LD = pile diameterEi= modulus of elasticity for individual member individualcompression parallel to grain specimenEa= average modulus of elasticity of butt and tip compres-sion parallel to grain specimens from the same pileE’ = sample mean modulus of elasticity in compressionE = allowable modulus of elasticity in compressionEMOEi= effective modulus of elasticity in bending for anindividual pileEMOE’ = sample mean effective modulus of elasticity inbendingEMOE = allowable effective modulus of elasticity in bend-ingFb= allowable stress in bendingFc= allowable stress in compression parallel to grainfcTL= compression parallel to grain 5 % tolerance limit with75 % confidence determined from test results for the tipspecimenfbTL= bending 5 % tolerance limit with 75 % confidencedetermined from test resultsL = distance from pile tip to critical section, ftLe= distance from top of butt compression parallel to graintest specimen to top of tip compression parallel to grain testspecimen, ftMORBP = modulus of rupture at breakpointk = number of random variables used in random productssimulationn = number of piles in a species or species group selected fortestingp = exponent of Leused to calculate pile length effect oncompression strengthr = radius of gyration = D/4UCS = ultimate compressive strengthz = number of piles in a cluster4. Significance and Use4.1 This practice is primarily intended for use byassociations, third-party grading agencies, technical societiesand other groups that develop national design standards anduse recommendations for round timber piles.4.2 This practice provides procedures for establishing com-pression parallel to grain and bending stresses for round timberpiles including: sampling of material for testing; methods oftest and property calculation procedures; distribution analysisof test data; procedures for determining adjustments for criticalsection location; pile oversize, load sharing and treatment; andprocedures for deriving allowable stresses.4.3 In using allowable stresses established under thispractice, factors specific to each end use which may affect theperformance of the pile system shall be considered by thedesigner. Such factors include the location of the criticalsection, the bearing capacity of the soil, the ability of the pileto withstand driving forces, the properties of the cap or loaddistributive element tying piles together and the loading andconditions of service.5. Sampling Full-Size Round Timbers5.1 The population to be sampled shall be round timbers ofa particular species or species group meeting the provisions ofSpecification D25. Only those species groups that do notexceed the variability, as measured by the criteria of Section 5of Practice D2555, of the major lumber species groups sampledin the In-Grade lumber testing program in the United Statesand Canada shall be considered as a single species for samplingand analysis purposes. For species groups exceeding thesevariability limits, the species composition should be changedsuch that the limits will be met by the remaining species in thegroup if sampling of the group as a single species is desired.NOTE 2—See X9.1 of Practice D1990 for discussion of in-gradesampling of species groups. Major species groups sampled in the In-Gradelumber testing program are given in Note 3 of Practice D1990.5.2 A representative sample (n) of all sizes (diameters) andlengths of timber piles as in Tables X1.2 or X1.3 andTables X1.4 or X1.5 of Specification D25 shall be selected forthe species or species group being evaluated. Sampling by size,length and class shall be in proportion to total production andshall be distributed across plants representative of the produc-ing region.NOTE 3—Specification D25 pile specifications provide for only onegrade and quality level.5.3 Individual piles selected as test material shall be greenand randomly chosen from inventory in the yard at each plant.5.4 Sample size shall be based on the principles of PracticeD2915 and shall be sufficient to provide reliable estimates ofthe distributions of bending and compression parallel to grainstrengths of timbers of the species or species group beingevaluated. Each pile selected for test shall be evaluated for bothbending and compression strength with compression speci-mens being cut from the butt and tip ends after the bending testis completed.6. Test Methods and Calculation Procedures6.1 All test members shall be maintained in a green condi-tion prior to test.6.2 Each member shall be tested in bending in accordancewith the procedures of Test Methods D1036. Modulus ofrupture at breakpoint (MORBP) and effective modulus ofelasticity in bending (EMOE) shall be calculated in accordancewith the formulas given in 19.4 of Test Methods D1036.Ifanalternative formula is used to calculate EMOE, its derivationand assumptions shall be documented.NOTE 4—The cross-section of round timbers varies from butt to tip asa result of taper. A linear taper between butt and tip is assumed in thederivation of the EMOE equation. As tree tapers may not be linear butparabolic, the moment of inertia of the resisting cross-section is underes-timated and the resulting bending EMOE value for the pile is typicallysubstantially higher than the average E based on compression parallel tograin tests.6.3 After completion of the bending test, compression testspecimens shall be cut from the butt and tip ends of themember. These specimens shall be prepared and tested inaccordance with Sections 12–19 of Test Methods D198. Thesame slenderness ratio, specimen length divided by the smallend radius of gyration (r), shall be used for the butt and tipD7381 − 07 (2013)2specimens but shall not exceed 17. Specific gravity disks shallbe cut from the bottom and top of each pile, immediately abovethe small end of the compression test specimens.6.4 To prevent excessive end crushing, the compressionspecimens shall be banded or the ends air-dried prior to testing.Load-deformation data shall be obtained for both specimens. Inplace of the testing speeds specified in section 17.3 of TestMethods D198, a rate of straining (in./in. per min) such thatmaximum load is obtained between 1 and 5 min shall be usedand both butt and tip specimens shall be tested at the same rate.NOTE 5—A range of 1 to 5 min in failure times is within the range of10 s to 10 min specified for in-grade testing of lumber in section 34.4 ofTest Methods D4761.6.5 Ultimate compression strength (UCS) and modulus ofelasticity (Ei) shall be calculated for both the butt and tipspecimens using the area of the small end of each specimen.Values of Eishall be based on the linear portion of theload-deformation curves with suitable adjustment made for anynonlinearity occurring at the beginning of the test. The averageof the Eivalues for the butt and tip specimens shall becalculated as the Eaof the pile.7. Reporting Requirements for Sampling and Testing7.1 The following information shall be reported:7.1.1 The production volumes for the various sizes, lengthsand classes of piles building poles used to develop thesampling plan for each species or species group evaluated.7.1.2 The methods used to select the manufacturing facili-ties for sampling and the individual test piles from eachfacility.7.1.3 A complete description of each test specimen includ-ing length, butt and tip circumference, rings per inch, percentsummerwood, slope of spiral grain and the maximum indi-vidual knot size and the maximum sum of knot diameters inany one-foot of pile length.7.1.4 The diameters of the small and large ends of the buttand tip compression parallel to grain test specimens selectedfrom each pile and the maximum individual knot size and themaximum sum of knot diameters in any one-foot of length ineach of these specimens.7.1.5 Slenderness ratios, rate of load application, time tomaximum load, section properties, specific gravity, formulasused to calculate strength and stiffness properties and otherinformation as required by the provisions of Test MethodsD198 and D1036.7.1.6 A complete description of the analytical methods usedto develop the statistics and factors described in Sections 8-11.8. Analysis of Test Data8.1 The average of the individual pile EMOEiand Eavaluesshall be calculated as the sample mean values (EMOE’ and E’)for the species or species group evaluated.8.2 The distributions of UCS values for the tip compressionspecimens and the MORBP values for the n piles in the sampleshall be examined to determined what type of distribution(normal, lognormal or nonparametric) best describes each dataset, particularly the lower strength values in the sample.8.3 If a parametric distribution is to be used, the mean,standard deviation and 5 % tolerance limit with 75 % confi-dence (fcTLor fbTL) determined for the property and sampleusing the methods of sections 3.4.3.2, 4.5, and Table 1 ofPractice D2915.8.4 If a nonparametric distribution is to be used, the sampletest values shall be arranged in ascending order and the mthorder statistic selected as the sample 5 % tolerance limit with75 % confidence (fcTLor fbTL) in accordance with 4.5.4, 4.5.5,and Table 2 of Practice D2915.9. Critical Section Located Above the Pile Tip9.1 Paired butt and tip compression parallel to grain UCSvalues shall be used to establish an equation for adjusting tipcompression allowable design values (Fc) when the criticalsection is located above the tip as a result of skin friction.9.2 For each test pile, the difference between butt and tipUCS values shall be normalized using the following calcula-tion:Ri5 @~UCSbutt2 UCStip!/UCStip#/Lep(1)where:Ri= normalized individual pile length effect on compressionstrength p = 1.6.9.3 If the significance of the slope coefficient of the regres-sion of Rion Leis not less than a probability of 25 %, theaverage of the Rivalues for the sample (Ravg) shall be used toestablish the following equation for determining Cl:Cl5 ~Ravg3100!/Lp(2)where:Cl= percentage increase in pile compression strength atdistance L from the pile tip p = 1.69.4 If the significance of the slope coefficient is less than25 %, the value of the exponent p shall be changed so as tomeet this criterion. Individual Rivalues based on a buttcompression specimen containing a split that occurred duringthe bending test shall not be included in the regression analysisnor in the calculation of Ravgfor the sample.10. Effect of Pile Sizes Exceeding Specification D25 SizeClass Minimums10.1 Piles are marketed in accordance with circumference(diameter) and length spe