ASTM D2899-2012(2017) Standard Practice for Establishing Allowable Stresses for Round Timber Piles《用于确定圆木桩许用应力的标准实施规程》.pdf

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1、Designation: D2899 12 (Reapproved 2017)Standard 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

2、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 stresses for round timber piles starting with clear w

3、oodstrength properties.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 w

4、ith its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized

5、 principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D25 Specification for Roun

6、d Timber PilesD245 Practice for Establishing Structural Grades and Re-lated Allowable Properties for Visually Graded LumberD2555 Practice for Establishing Clear Wood Strength Values3. Terminology3.1 Definitions:3.1.1 allowable stressthe numeric value of pile strengththat is appropriate for use in st

7、ructural analysis.3.1.2 end-bearingcompression-parallel-to-the-grain stressresulting when pile load is not carried to the soil through skinfriction.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

8、 variability and increasingsystem reliability over that 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.

9、Negative skin friction distributes load tothe pile when soil strata subside or consolidate.3.2 Symbols: Ccp= adjustment for small clear compressionperp for annual ring orientation (1/1.67)Cct= conditioning factorCdol= adjustment for duration of load and factor of safetyCd= adjustment for density app

10、lied for Douglas fir andSouthern pine onlyCfs= combined 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)C

11、hv= adjustment for height and for reduced variability(MOR = 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 deflecti

12、on in calculation for bend-ing modulus of elasticity (= 1.06)D = diameter of a round timber pileE = clear wood unseasoned average modulus of elasticityfrom Test Methods D2555MOE = modulus of elasticity (average)F= allowable stress for stress designated by the subscript Fc= allowable compression stre

13、ss for pile tipsfc05= 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 D2555 = stress value subscripts, c = com

14、pression parallel,cp = compression perpendicular, b = bending, v = shear1This 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 Oct. 1, 2017. Published October 2017. Originallyapp

15、roved in 1970 as D2899 70 T. Last previous edition approved in 2012 asD2899 12. DOI: 10.1520/D2899-12R17.2For referenced 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 standar

16、ds Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decisi

17、on on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14. Significance and Use4.1 This practice is intended for use by associations, tech-nical societies and other groups that deve

18、lop national designstandards and use recommendations for round timber piles.4.2 In using allowable stresses established under thispractice, factors specific to each end use which may affect theperformance of the pile system shall be considered. Suchfactors include the location of the critical sectio

19、n, the bearingcapacity of the soil, the ability of the pile to withstand 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 Wh

20、ere pile allowable stress is to be established for acombination of species 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

21、in Test Methods D2555 apply to small, clear, straight-grained wood in 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 establishallowa

22、ble stress for such timbers under Practice D245 also areapplied to piles.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

23、adjustmentfactors given in Table 10 of Practice D245 to obtain basicvalues 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 modu

24、lus of elasticity and compres-sion perpendicular to grain at 0.04-in. 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

25、also are established. The modulus ofelasticity factor is a shear deflection 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 value

26、s include both variabilityin properties between trees and variability 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 ar

27、e adjusted to account for this reducedvariability.8. Minimum Tip and Critical 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 an

28、d 16 ft. For softwood species,clear wood strength properties generally 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 se

29、ction of thepile is assumed to occur at a point 10 ft above the pile tip. 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 o

30、btained from TestMethods D2555 must be reduced to account for this heighteffect when establishing compression parallel to grain,bending, shear and modulus of elasticity design stresses forpiles made with softwood species.9. Density9.1 Specification D25 requires the outer 50 % of the radiusat the pil

31、e tip to have an average rate of growth of at least 6rings per inch 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 t

32、he classification of Douglasfir and southern pine sawn lumber meeting 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

33、limiting the occurrence of lowdensity material.9.3 Increases for density 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 f

34、or the inner core of the pile tip that is notrequired to meet the density 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.

35、18) than that of a square beam ofequivalent area by approximately the same ratio as the strengthof 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

36、 circular cross section is used.D2899 12 (2017)210.2 Clear wood bending stresses 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

37、 having an area equal to that of a squaresection, the equivalent depth adjustment 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

38、 the 1/9 power equation. The same practice is employedwith round timber piles. 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. G

39、rade11.1 Knots in round piles reduce compression parallel tograin and bending 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 contain

40、ing various knotsizes. Regression analyses of compression strength againstknot 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 b

41、y theratio of the section modulus of a wedge section occupied by theknot to 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 dis

42、tribution ofstrength ratio, (2) a normal clear wood distribution, and (3)linear 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 a

43、s that on the shearstrength of sawn timber.12. Duration of Load12.1 Wood strength 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 aresh

44、ort-term test values reduced to a normal load duration basis.Normal load duration 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 t

45、en years, pile allowable stressfor bending, compression parallel to grain and 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-b

46、orne salts.12.3 Duration of load adjustments are not applied to pileallowable 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 co

47、ntinuously exposed tothe weather.13.2 No increase in properties for material 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 rou

48、nd timber piles established in this practice.14.2 Conditioning of piles by 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

49、based on compression parallel to grain testsof end-matched conditioned and 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 Grain15.1 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 t