ASTM D2899-2012 Standard Practice for Establishing Allowable Stresses for Round Timber Piles 《确定圆木桩允许应力的标准操作规程》.pdf

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1、Designation: D2899 12Standard Practice forEstablishing Allowable Stresses for Round Timber Piles1This standard is issued under the fixed designation D2899; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.

2、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 stresses for round timber piles starting with clear woodstrength proper

3、ties.1.2 Stresses established under this practice are applicable topiles conforming to the quality, straightness, spiral grain, knot,check, shake, and split provisions of Specification D25.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is

4、 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 PilesD245 Practice for Establishing Structural G

5、rades and Re-lated Allowable Properties for Visually Graded LumberD2555 Practice for Establishing Clear Wood Strength Val-ues3. Terminology3.1 Definitions:3.1.1 allowable stressthe numeric value of pile strengththat is appropriate for use in structural analysis.3.1.2 end-bearingcompression-parallel-

6、to-the-grainstress resulting when pile load is not carried to the soil throughskin friction.3.1.3 load sharingthe distribution of load in proportion topile stiffness. This results in piles that perform as a groupreducing effects of between-pile variability and increasingsystem reliability over that

7、of piles which perform indepen-dently.3.1.4 skin frictionthe interaction between the pile surfaceand the soil which serves to distribute load either away from orinto a pile. A positive skin friction refers to pile loadsdistributed to the soil. Negative skin friction distributes load tothe pile when

8、soil strata subside or consolidate.3.2 Symbols:Ccp= adjustment for small clear compression perp for an-nual ring orientation (1/1.67)Cct= conditioning factorCdol= adjustment for duration of load and factor of safetyCd= adjustment for density applied for Douglas fir andSouthern pine onlyCfs= combined

9、 adjustment for form and size (= 0.97)Cg= adjustment for grade characteristics applied to allspecies including bending (0.75), compression (0.93), andshear (0.50)Ch= adjustment for height in the tree (= 0.96 if softwoodsand = 1.0 for hardwoods)Chv= adjustment for height and for reduced variability(M

10、OR = 0.91 for softwoods, 1.05 for hardwoods, C/ = 0.91 forsoftwoods, 1.05 for hardwoods, Shear = 0.99 for softwoods,1.03 for hardwoods)Cls= load sharing adjustment (structural engineers option)Cs= size adjustmentCv= adjustment for shear deflection in calculation for bend-ing modulus of elasticity (=

11、 1.06)D = diameter of a round timber pileE = clear wood unseasoned average modulus of elasticityfrom Test Methods D2555MOE = modulus of elasticity (average)Fb= allowable stress for stress designated by the subscript bFc= allowable compression stress for pile tips1This practice is under the jurisdict

12、ion of ASTM Committee D07 on Wood andis the direct responsibility of Subcommittee D07.04 on Pole and Pile Products.Current edition approved April 1, 2012. Published April 2012. Originallyapproved in 1970 as D2899 70 T. Last previous edition approved in 2011 asD2899 11. DOI: 10.1520/D2899-12.2For ref

13、erenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, We

14、st Conshohocken, PA 19428-2959, United States.fc05= small clear lower 5 % exclusion compression strengthin accordance with Test Methods D2555fi05= lower 5 % exclusion value for stress “x” determinedusing the green, small clear strength and standard deviationvalues reported in Test Methods D2555b = s

15、tress value subscripts, c = compression parallel,cp = compression perpendicular, b = bending, v = shear4. Significance and Use4.1 This practice is intended for use by associations, tech-nical societies and other groups that develop national designstandards and use recommendations for round timber pi

16、les.4.2 In using allowable stresses established under this prac-tice, factors specific to each end use which may affect theperformance of the pile system shall be considered. Suchfactors include the location of the critical section, the bearingcapacity of the soil, the ability of the pile to withsta

17、nd drivingforces and conditions of service.PRINCIPLES INVOLVED IN ESTABLISHINGALLOWABLE STRESSES5. Species5.1 This practice applies to any species of piles for whichclear wood strength values are given in Test Methods D2555.5.2 Where pile allowable stress is to be established for acombination of spe

18、cies and or regions, clear wood valuesassigned to such combinations are based on the groupingcriteria given in Section 5 of Test Methods D2555.6. Clear Wood Properties6.1 Information on average properties and their variationgiven in Test Methods D2555 apply to small, clear, straight-grained wood in

19、the green condition under short-term loading.6.2 Round timber piles having minimum tip diameters of 5in. or larger are considered by this practice to be comparable tosawn timbers: General adjustment factors used to establishallowable stress for such timbers under Practice D245 also areapplied to pil

20、es.6.3 For the properties of bending strength (modulus ofrupture), compression strength parallel to the grain and hori-zontal shear strength, clear-wood 5 % -exclusion values calcu-lated from Test Methods D2555 are divided by the adjustmentfactors given in Table 10 of Practice D245 to obtain basicva

21、lues for these properties from which pile allowable stress isestablished. The adjustment factors for the three strengthproperties include a reduction for normal duration of load anda factor of safety.6.4 For the properties of modulus of elasticity and compres-sion perpendicular to grain at 0.04-in.

22、deformation, clear woodaverage values from Test Methods D2555 are divided by theadjustment factors for these properties given in Table 10 ofPractice D245 to obtain basic values from which pile allowablestress for these properties also are established. The modulus ofelasticity factor is a shear defle

23、ction adjustment. The compres-sion perpendicular to grain factor is an adjustment to accountfor limiting ring position.7. Pile Variability7.1 Standard deviations given in Test Methods D2555 andused to calculate 5 % exclusion values include both variabilityin properties between trees and variability

24、in properties occur-ring within the cross section and along the length of anindividual tree.7.2 For round timber piles, only the between tree compo-nent of variance is applicable. Clear wood 5 % exclusionvalues applied to piles are adjusted to account for this reducedvariability.8. Minimum Tip and C

25、ritical Section Properties8.1 Average clear wood properties given in Test MethodsD2555 represent volume weighted average whole tree valueswhere the average property is that associated with materialoccurring between heights of 8 and 16 ft. For softwood species,clear wood strength properties generally

26、 decrease as the heightlocation in the tree increases.8.2 For compression parallel to grain, the minimum strengthof the pile occurs at the pile tip, or at a minimum diameter of5 in. For bending and shear strengths, the critical section of thepile is assumed to occur at a point 10 ft above the pile t

27、ip. Interms of location in the tree, both of these sections occur atheights in the tree which are appreciably greater than theheights associated with the whole tree average property values.Therefore clear wood average properties obtained from TestMethods D2555 must be reduced to account for this hei

28、ghteffect when establishing compression parallel to grain, bend-ing, shear and modulus of elasticity design stresses for pilesmade with softwood species.9. Density9.1 Specification D25 requires the outer 50 % of the radiusat the pile tip to have an average rate of growth of at least 6rings per inch

29、and an average summerwood content of not lessthan 33.3 %. Piles with less than 6 rings per inch are acceptableif the average summerwood content in the outer 50 % of thepile tip radius is 50 % or more.9.2 Practice D245 provides for the classification of Douglasfir and southern pine sawn lumber meetin

30、g growth rate andsummerwood content requirements similar to those in Speci-fication D25 as dense material. The properties of such lumber,except shear, are increased to account for the increased strengthand stiffness associated with limiting the occurrence of lowdensity material.9.3 Increases for den

31、sity applicable to Douglas fir andsouthern pine lumber also are applicable to piles of the samespecies. The increase for density in compression parallel tograin applicable to lumber must be adjusted when applied topiles to account for the inner core of the pile tip that is notrequired to meet the de

32、nsity provisions.10. Form and Size10.1 The average bending strength of round wood sectionsbased on standard beam formulas is greater than that ofmatched rectangular sections. However, the section modulus ofa round beam is less (1/1.18) than that of a square beam ofequivalent area by approximately th

33、e same ratio as the strengthD2899 122of the round member is greater than that of the rectangularmember. Round members therefore are assigned a unit strengthequal to 1.18 times that based on rectangular sections when thesection modulus of the circular cross section is used.10.2 Clear wood bending str

34、esses in Test Methods D2555are based on tests of 2-in. deep rectangular sections. UnderPractice D245, such values are adjusted for depth (d) by thefactor (2/d)1/9when applied to sawn lumber members. Basedon a circular section having an area equal to that of a squaresection, the equivalent depth adju

35、stment for a round member is(2.2568/D)1/9.10.3 Under standard practice, bending allowable stress forbeams and stringers and post and timbers are given for a 12-in.beam depth. Values for beams exceeding 12 in. are reducedusing the 1/9 power equation. The same practice is employedwith round timber pil

36、es. Pile bending stresses are indexed tothe diameter of a circular section having an area equal to thatof a 12-in. square, or 13.5 in. Clear wood bending values areadjusted to a 13.5-in. pile diameter by the factor 0.82.11. Grade11.1 Knots in round piles reduce compression parallel tograin and bendi

37、ng strength properties. Limits on allowable sizeand spacing of knots along the pile length are given inSpecification D25.11.2 The effect of knots on pile tip strength is determinedfrom tests of full size pile sections containing various knotsizes. Regression analyses of compression strength againstk

38、not size and specific gravity establish the effect of allowableknots on compression parallel to grain strength.11.3 The effect of allowable knots on pile bending strengthis derived assuming load-carrying capacity is reduced by theratio of the section modulus of a wedge section occupied by theknot to

39、 the section modulus of the total circular section. Thecombined interaction of clear wood strength, knot size andknot location along the pile length is assessed through randomproducts simulation assuming (1) a rectangular distribution ofstrength ratio, (2) a normal clear wood distribution, and (3)li

40、near induced moment in 2-ft length segments over a 10-ftcantilever beam length from the top of the pile to the criticalsection.11.4 The effect of splits, checks, and shakes on pile shearstrength is considered to be the same as that on the shearstrength of sawn timber.12. Duration of Load12.1 Wood st

41、rength properties are affected by the durationof the maximum applied load: the shorter the duration thegreater the maximum load that can be carried. Allowable stressfor round timber piles established under this practice areshort-term test values reduced to a normal load duration basis.Normal load du

42、ration represents application of a load that fullystresses a member to its design stress for a cumulative durationof approximately 10 years.12.2 When the cumulative duration of the full maximumload is less than or more than ten years, pile allowable stressfor bending, compression parallel to grain a

43、nd horizontal shearshall be modified in accordance with the duration of loadadjustments shown in Fig. 6 of Practice D245. Load durationadjustments greater than 1.6 shall not apply to piles preserva-tively treated with water-borne salts.12.3 Duration of load adjustments are not applied to pileallowab

44、le stress for modulus of elasticity and compressionperpendicular to grain based on a deformation limit.13. Moisture Content13.1 Allowable stress established by this practice applies topiles that are continuously wet or are continuously exposed tothe weather.13.2 No increase in properties for materia

45、l that is partiallyabove ground and may be partially seasoned is recognized.14. Preservative Treatment14.1 Preservative treatment by approved processes andchemicals does not significantly affect allowable stress valuesfor round timber piles established in this practice.14.2 Conditioning of piles by

46、kiln drying, steaming orboiling in liquids prior to pressure treatment to facilitatepenetration of preservative chemicals does affect strengthproperties. Reduction of allowable stress (Table 2) to accountfor such effects are based on compression parallel to grain testsof end-matched conditioned and

47、unconditioned full-size pilesections.14.3 No adjustments are made for conditioning prior totreatment of allowable stress for modulus of elasticity (E) andcompression perpendicular to grain at 0.04-in. deformation(Fcp).DERIVATION OF ALLOWABLE STRESS FORUNTREATED PILES15. Compression Parallel to Grain

48、15.1 Calculate compression allowable stress for pile tipsusing the following equation:Fc5 fc05Cdol!Chv#Cd#Cg# (1)15.2 Where the critical section in compression parallel tograin, Fc, is located above the pile tip as a result of skin frictionfrom the soil through which the pile is driven, or otherTABL

49、E 1 Strength and Stiffness Adjustments for Density (d),Grade (g), and Combined Duration of Load andFactor of Safety (dol)Stress Factor Bending Shear CompressionParallel to grainCompressionPerpendicular to grainMOECdA1.17 1.00 1.13 1.17 1.05Cg0.75 0.50 0.93 1.00 1.00Cdol-Sftwd1/2.1 1/2.1 1/1.9 1.00 1.00Cdol-Hrdwd1/2.3 1/2.3 1/2.1 1.00 1.00ADensity adjustments apply only to Douglas fir and southern pine.TABLE 2 Conditioning Effects on the Strength of Round TimberConditioning AirDryingKilnDryingBoultonDryingSteaming(Normal)Steaming(Marine)Cct1.0 0.90 0.95 0.80 0.74D2899 12