1、Designation: D7746 11Standard Practice forCalculating the Superimposed Load on Wood-frame Floor-Ceiling Assemblies for Standard Fire-Resistance Tests1This standard is issued under the fixed designation D7746; the number immediately following the designation indicates the year oforiginal adoption or,
2、 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 covers procedures for calculating thesuperimposed load required to
3、 be applied to load-bearingwood-frame floor-ceiling assemblies throughout standard fire-resistance tests.1.2 These calculations determine the maximum superim-posed load to be applied to the floor-ceiling assembly duringthe fire resistance test. The maximum superimposed load,calculated in accordance
4、with nationally-recognized structuraldesign criteria, shall be designed to induce the maximumallowable stress in the wood floor-ceiling fire test configurationbeing tested.1.3 This practice is only applicable to those wood-framefloor-ceiling assemblies for which the nationally recognizedstructural d
5、esign criteria are the NDS (National Design Speci-fication for Wood Construction).1.4 The text of this standard references notes and footnoteswhich provide explanatory material. These notes and footnotes(excluding those in tables and figures) shall not be consideredas requirements of the standard.1.
6、5 The values stated in inch-pound units are to be regardedas standard. No other units of measurement are included in thisstandard.1.6 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 establis
7、h appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D9 Terminology Relating to Wood and Wood-Based Prod-uctsD6513 Practice for Calculating the Superimposed Load onWood-frame Walls for Standard F
8、ire-Resistance TestsE119 Test Methods for Fire Tests of Building Constructionand MaterialsE176 Terminology of Fire StandardsE1529 Test Methods for Determining Effects of LargeHydrocarbon Pool Fires on Structural Members and As-semblies2.2 Other Standards:3NDS National Design Specification for Wood C
9、onstructionNDS Supplement Design Values for Wood Construction3. Terminology3.1 DefinitionsDefinitions used in this practice are inaccordance with Terminology D9 and Terminology E176,unless otherwise indicated.3.2 Definitions of Terms Specific to This Standard:3.2.1 gross area, nsection area calculat
10、ed from overallactual dimensions of member.3.2.2 net section area, nsection area calculated by deduct-ing from the gross section area the projected area of allmaterials removed by boring, grooving, dapping, notching, orother means.3.2.3 superimposed load, nthe additional external loadneeded to be ap
11、plied to the assembly to result in the calculatedstresses within the assembly when any dead load of theassembly itself is accounted for in the calculations.4. Significance and Use4.1 Test Methods E119, E1529, and other standard fireresistance test methods specify that throughout the fire-resistance
12、test, a constant superimposed load shall be applied toa load-bearing test specimen to simulate a maximum loadcondition. This superimposed load shall be the maximum loadallowed by design under nationally recognized structuraldesign criteria for the tested floor configuration (that is, joistselection,
13、 spacing, and span).4.1.1 For this Practice, the nationally recognized structuraldesign criteria to be used to determine the maximum load1This practice is under the jurisdiction of ASTM Committee D07 on Wood andis the direct responsibility of Subcommittee D07.05 on Wood Assemblies.Current edition ap
14、proved Nov. 15, 2011. Published March 2012. DOI: 10.1520/D774611.2For 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 standards Document Summary page onthe ASTM webs
15、ite.3Available from American Wood Council (AWC), 803 Sycolin Road, Suite 201,Leesburg, VA 20175, http:/www.awc.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.condition are those for allowable stress design in the NDS(National De
16、sign Specification for Wood Construction).4.1.2 Alternatively, the standard fire resistance test methodsshall be permitted to be conducted by applying a load less thanthe maximum allowable load in 4.1.1 for the tested configura-tion; however, these tests shall be identified in the test report asbein
17、g conducted under restricted loading conditions.4.2 This practice describes procedures for calculating thesuperimposed load to be applied in standard fire resistance testsof wood floor-ceiling assemblies. Practice D6513 provides asimilar methodology for calculating the superimposed load onwood-frame
18、 walls.4.3 Statements in either the fire resistance test methodstandard or the nationally recognized structural design standardsupersede any procedures described by this practice.4.4 The NDS shall be reviewed to ensure calculations are incompliance with all applicable provisions of that standard.5.
19、Test Assumptions5.1 Floor AssemblyFor design considerations, wood-frame floor-ceiling assemblies consist of horizontal structuralmembers (that is, joists), the floor decking or sheathing, and theperimeter rim boards.5.2 Loading ConditionsHorizontal framing members sup-port a vertical load that is un
20、iformly distributed on the floorassembly. It is assumed that load application system for the testdistributes load between and along framing members in amanner consistent with a uniform load assumption and pro-vides load distribution to members that is representative of theend-use application.NOTE 1T
21、he calculation procedure in this standard is not appropriatefor a test that uses a load application system that incorporates discretepoint load distribution beams or frames with spanning capabilities thatserve to artificially re-distribute load from a failing member to the adjacentframing. Such a sy
22、stem would require a higher load to be applied thatconsiders the enhanced load-sharing between members provided by theload frame and the departure from a uniform load condition. An exampleof a system that conforms to the calculation assumption would be one inwhich each discrete load element (that is
23、, dead weight pack, water barrel,hydraulic cylinder, pneumatic cylinder, etc.) is applied to the floor at notmore than two locations along the length of the framing by distributionbeams that span across not more than three framing members.5.3 Lateral or torsional end support, including but notlimite
24、d to bridging, blocking, or bracing, shall be provided atpoints of bearing to prevent rotation. When additional lateral ortorsional support is used away from the ends to enhanceperformance of the floor-ceiling assembly, description andlocations of the support shall be reported5.4 Where required to e
25、nsure that bearing capacity does notlimit the test load, stiffeners or an increased bearing lengthshall be permitted at the bearing locations to increase capacity.6. Design Load Calculations6.1 Design Values-Reference design values: Fb, Fv, Fc,E and Eminfor rectangular sections are given in the NDSS
26、upplement, product literature, or code evaluation report.Reference design values: M, V, Rr, EI, EImin, and K for I-joistsare given in the product literature, or code evaluation report.6.2 Design Value AdjustmentsReference design valuesshall be multiplied by all applicable adjustment factors todeterm
27、ine the adjusted design values. Additional adjustmentsmay be required to address special design considerations forthe specific member type. Not all factors may be applicable toall product types.6.2.1 BendingFbfor rectangular sections and M forI-joists shall be multiplied by all applicable NDS adjust
28、mentfactors including: CD, CM, Ct, CL, CF, CV, Cfu, Ci, Cr, Cc.6.2.2 Compression parallel to the grain, Fc, shall be multi-plied by all applicable NDS adjustment factors including: CD,CM, Ct, CF, Ci, and CP.6.2.3 Shear parallel to grainFvfor rectangular sectionsand V for I-joists shall be multiplied
29、 by all applicable NDSadjustment factors including: CD, CM, Ct, Ci.6.2.4 Tension parallel to grain, Ft, shall be multiplied by allapplicable NDS adjustment factors including: CD, CM, Ct, CF,Ci.6.2.5 Bearing:6.2.5.1 Compression perpendicular-to-grainFcfor rect-angular sections shall be multiplied by
30、all applicable NDSadjustment factors including: CM, Ct, Ci, Cb.6.2.5.2 I-joist Reference Design ReactionRr, shall bemultiplied by all applicable NDS adjustment factors including:CD, CM, Ct.6.2.6 Modulus of elasticityE or Eminfor rectangular sec-tions and EIand EIminfor I-joists shall be multiplied b
31、y allapplicable NDS adjustment factors including: CM, Ct, Ci, CT.6.3 Adjustment Factors for Design ValuesThe followingadjustment factors are to be assumed by default. If values lessthan those listed below are employed, then the appropriate loadrestriction shall be reported in the test report and use
32、d to adjustthe design bending and shear capacity in application:6.3.1 Load duration factor, CD, is 1.0.6.3.2 Wet service factor, CM, is 1.0.6.3.3 Temperature factor, Ct, is 1.0.6.3.4 Beam stability factor, CL, is 1.0 for a single span,sheathed fire test assembly.6.3.5 Size factor, CF, is the value t
33、aken from tables in theNDS Supplement for the sawn lumber joist material in the testassembly.6.3.6 Volume factor, CV, per NDS provisions for glued-laminated timber members. The value of Cvfor structuralcomposite lumber shall be defined by the product literature orcode evaluation report. The value of
34、 Cvused shall be the valuefor the joist material in the test assembly.6.3.7 Flat-use factor, Cfu, the value per NDS provisions forthe sawn lumber joist material in the test assembly.6.3.8 Incising factor, Ci, the value per NDS provisions forthe sawn lumber joist material in the test assembly.6.3.9 R
35、epetitive member factor, Cr, the value per the NDSprovisions for the joist material in the test assembly.6.3.10 Curvature factor, CC, the value per the NDS provi-sions for structural glued laminated timber.6.3.11 Column stability factor, CP, is calculated from equa-tions in the NDS.NOTE 2When a comp
36、ression member is supported throughout itslength to prevent lateral displacement in all directions, CP=1.6.3.12 Bearing area factor, Cb, is 1.0.6.3.13 Buckling stiffness factor, CT, is 1.0.D7746 1126.3.14 For lumber and structural glued laminated timberpressure-treated with fire-retardant chemicals,
37、 the allowabledesign values, including connection design values, shall beobtained from the company providing the treatment andredrying service.6.4 Dimensions:6.4.1 Gross cross-sectional areas are the section areas basedon the standard dressed size of the member as given in the NDSfor the nominal siz
38、e sawn lumber or glue laminated timbermember. The gross cross-sectional areas for I-joists and struc-tural composite lumber are given in the product literature orcode evaluation report.6.4.1.1 Net section area, A, is the gross area minus theprojected area of all materials that may be removed by bori
39、ng,grooving, dapping, notching, or other means.6.4.1.2 For nailed or screwed connections, the net sectionarea equals the gross section area.6.4.2 The span of the horizontal structural member is thedistance from face to face of supports, plus half of the requiredbearing length at each end.6.5 Test Lo
40、ad:6.5.1 The load to be applied in the test shall be calculated inaccordance with nationally recognized design criteria. Thesuperimposed load shall be the lesser of the load calculated inaccordance with 6.5.1.1 or 6.5.1.2.6.5.1.1 A superimposed load which induces a bendingmoment equal to the full de
41、sign capacity at the criticalcross-section along the length of the horizontal structuralmembers of the floor-ceiling configuration being tested.6.5.1.2 Asuperimposed load which induces a bending shearforce equal to the full design capacity at the critical cross-section along the length of the horizo
42、ntal structural members ofthe floor-ceiling configuration being tested. Any holes ornotches present in the test specimens shall be neglected for thepurpose of establishing the available shear capacity of thehorizontal structural members.6.5.2 A lower superimposed load than described by 6.5.1shall be
43、 permitted provided it corresponds to a stiffness limit,reaction limit, connection limit, or other alternative designcriteria. However, these tests shall be identified in the testreport as being conducted under restricted loading conditions.Where stiffness increases for partial composite action arep
44、ermitted by design and the load is governed by the systemstiffness, the maximum partial composite action between thehorizontal structural member and the floor decking or sheath-ing permitted in application shall be included in the calculationof the stiffness for the tested floor assembly.6.5.3 The s
45、uperimposed load, as well as the superimposedload expressed as a percentage of the maximum superimposedload from 6.5.1 or 6.5.2, shall be included in the test report.Where the maximum superimposed load based on flexure andthe maximum superimposed load based on shear are both lessthan 100 % of the fu
46、ll design capacity, the greater of the twopercentages shall be used to reduce the design shear andbending capacities in application.6.5.4 Actual stress in a member in 6.5.1 and 6.5.2 includesboth that due to the superimposed load applied to the assemblyand that due to the dead load or weight of the
47、componentsbeing supported by the member.6.5.5 Total superimposed load to be applied to the testassembly during the fire test is the sum of the maximumsuperimposed load of each of the structural horizontal flexuremembers in the assembly. Where the first and last horizontalfloor-ceiling members are fl
48、exural members spanning thefurnace, the load on these members is allowed to be reduced byhalf due to the reduced tributary area.7. Keywords7.1 fire resistance; floor assembly; superimposed load;woodAPPENDIX(Nonmandatory Information)X1. EXAMPLE CALCULATION (ALLOWABLE STRESS DESIGN METHOD)FIG. X1.1 Wo
49、od Joist Floor AssemblyD7746 113ConstructionJoists: S-P-F (North) No. 2, 1.5 in. x 9.25 in. (nominal 2x10) 16 in. o.c., 12.5 ft. spanSubfloor: in. thick plywoodCeiling: 5/8 in. Type X gypsum board 2 layers, directappliedCalculation of Test LoadAllowable bending moment of member, Ma, determined inaccordance with the NDS using Allowable Stress Design(ASD) for the conditions listed above:Bending Design:Fb= adjusted bending design value, psiFb5 FbCDCMCtCLCFCfuCiCr(Table 4.3.1, NDS)5 875!1.0!1.0!1.0!1.0!1.1!1.0!1.0!1.15!51107 lb/in2where:Fb, reference
