roof framing connections in conventional residential construction

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evaluation. Another goal was to explore the applicability and demonstrate the advantages ofcapacity-based design methods for analysis of wood connections.The testing program included three tasks that investigated the performance of paired systems ofnailed heel-joint connections (Task 1), full-scale systems of roof-to-wall connections (Task 2),and individual rafter-to-wall connections (Task 3), respectively. Each tasks is presented in a selfcontainedsection (Sections 4.1, 4.2, and 4.3). Material properties for all three tasks aresummarized in the following section.3.0 MATERIAL PROPERTIESTest specimens were fabricated from materials purchased from a local building supplier andtested inside the NAHB Research Center laboratory facility located in Upper Marlboro, MD.Moisture content of wood members was measured using an electric pin-type moisture meter.Specific gravity of wood members was determined according to Method B (Volume by WaterImmersion) of ASTM Test Method D2395 [29].Nail bending strength was measured experimentally according to the general provisions ofASTM F1575 [30]. Nails were randomly selected from the batch used in fabricating the testspecimens. A sample size of ten was used for each nail type. Dowel bending strength of nails, F b ,was calculated as follows:3 P sF b=3(5)2 dwhere:P = test load at 5 percent offset or ultimate limit state;s = spacing between the reaction supports;d = nail diameter.Two characteristic properties were determined for each nail type: dowel bending strength at 5percent nail diameter offset, F b,5% , and dowel bending strength at ultimate load, F b,ult . Load at 5percent offset limit state was determined as a load at an intersection of the load-deformationcurve and a line assigned the initial slope and offset from the origin by 5 percent of thecorresponding nail diameter. Ultimate load was defined as the maximum load recorded duringthe test.Dowel bearing strength of nails was estimated using empirical equations published in TechnicalReport 12 [2] based on specific gravity of selected wood members used to fabricate the testspecimens. Two characteristic properties were determined for each nail type: dowel bearingstrength at 5 percent nail diameter offset, F b,5% , and dowel bearing strength at ultimate load, F b,ult ,as follows:1.84F e , 5%= 16,600 G(6)where:GD1.07F e , ult= 0.8) 11,735 G /( D= average oven-dry specific gravity of wood;= nail diameter, inch.0.17(7)10
Table 3 summarizes specific gravity and moisture content of wood materials used in the testprogram. Tables 4, 5 and 6 summarize the average tested nail bending strength and estimatednail bearing strength for heel joint, full-scale roof system, and individual roof-to-wall connectiontests, respectively. The measured nail bending strength values were lower than the minimumrequired [1][2][31]. This difference can be in part associated with the longer spacings betweenthe reaction bearing points used in the tests (see footnote 2 in Tables 4, 5, and 6) than thosespecified in ASTM F1575 [30].TABLE 3SPECIFIC GRAVITY AND MOISTURE CONTENT OF WOOD TEST MEMBERSSPECIFIC GRAVITY MOISTURE CONTENT,(OVEN-DRY)%TEST PROGRAM COMPONENT SPECIES & GRADESample Avg Sample AvgSize (COV, %) Size (COV, %)14.82 x 4 top plate Stud Grade SPF 24(22)Rafter-to-Ceiling 2 x 6 ceiling joist11.4#2\STD&BTR Spruce 14 1 0.4456Joist Connection (side member)(6)(10)2 x 8 rafter12.4#2\STD&BTR Spruce56(main member)(12)2 x 4 top plate0.407.0#2\STD&BTR Spruce 3028System Roof-to- (main member)(13)(14)Wall Connection 2 x 4 bottom chord0.586.8#2 Southern Yellow Pine 1528(side member)(14)(19)2 x 4 top plate0.487.7Individual Roofto-WallStud Grade SPF 2020(main member)(12)(5)Connection#2 Southern Yellow Pine 20202 x 4 bottom chord(side member)1 Specific gravity samples from all three components were averaged due to small number of samples taken for each component andinadvertent mixing of the samples.FASTENER DESCRIPTION0.48(8)TABLE 4DOWEL BENDING AND BEARING STRENGTH PROPERTIESFOR RAFTER-TO-CEILING JOIST CONNECTION TESTSAVG SIZE 1DIAMETER, IN,X LENGTH, IN(COV OF D, %)8d bright common nails 4 0.131 x 2.5(0.4)10d bright common 0.149 x 3.0nails 4 (0.2)16d bright pneumatic 0.132 x 3.25nails 5 full round head(0.7)AVG 5% OFFSETNAIL BENDINGSTRESS 1,2 , F B,5% , PSI(COV, %)81,491(8.8)80,639(6.3)83,691(3.4)AVG ULTIMATENAIL BENDINGSTRESS 1,2 , F B,ULT ,psi(COV, %)108,772(6.2)108,357(4.2)118,300(3.2)AVG 5%OFFSET DOWELBEARINGSTRESS 3 , F E,5% ,psi7.3(3)AVG ULTIMATEDOWELBEARINGSTRESS 3 ,F E,ULT , psi3,665 5,5103,665 5,3903,665 5,5031 Average of 10 samples for each nail type.2 Nails were tested using the following spacings between the reaction points: 8d common – s = 1.75 in, 10d common – s = 2.25 in, 16d common –s = 2.75 in, and 16d pneumatic – s = 2.5.3 Calculated based on average measured specific gravity for main members and side members.4 Common nails (Brand: Grip-Rite Fas’ner) distributed by Primesource Building Products, Inc., Dallas, Texas.5 Pneumatic nails manufactured by Senco Products, Inc., Cincinnati, Ohio. The nails were coated with a plastic-polymer coating by the manufacturer.11
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