Jwo0dSg(2002)48138-146 The Japan Wood Society ORIGINAL ARTICLE Kei Sawata.Motoi Yasumura Determination of embedding strength of wood for dowel-type fasteners Received:August 2100/Accepted:April 18001 Introduction bedding strength of wood for the design of dowel-type 16.and 20mm.Embe EN383.The embedding strength parallel to the grain ment of the fastener governs properties for determining evaluate d by the method eners.Numerous h close to n of the embedding tes heeaPdhcameaheeaor8eha prenth perpendicul hen the and end-distance on the bearing characteristic of glued hen the aminat d timber mber.These stud ated by a maximum load up to 5mm displacement ac cording to EN383,the ratio of embedding strength might include the effects of the fracture of wood. nhaddina s compreh harve inve increased. and tempered hardboard with nails and bolts:and Ehlbeck ·Compressive strength the basiso h to the grain. in dealt only with ultimate embedding strength;they did not look at the yield embedding strength pendicular to the relations be ter an g d l ureS Shizuoka nated timber and some engineered woods,respectively 428529,92 These studis were based ve tests with cube tests parallel and perpendicular to the grain according to EN3 to examine both yield and ultimate embedding f the houhumerous studies have been reported on the relations between the embedding strength of wood or
J Wood Sci (2002) 48:138-146 9 The Japan Wood Research Societ 3, 2002 Kei Sawata 9 Motoi Yasumura Determination of embedding strength of wood for dowel-type fasteners Received: August 21, 2000 / Accepted: April 18, 2001 Abstract Embedding tests parallel and perpendicular to the grain were conducted to produce a database of embedding strength of wood for the design of dowel-type joints. Dowel diameters were 8, 12, 16, and 20mm. Embedding strength was evaluated by the 5% off-set method and a maximum load up to 5mm displacement according to EN383. The embedding strength parallel to the grain evaluated by the former method showed values close to those obtained with the latter method, but they showed a significant difference in tests conducted perpendicular to the grain. The embedding strength parallel to the grain was 0.9 times as large as the compressive strength parallel to the grain regardless of the evaluation method. The embedding strength perpendicular to the grain evaluated by the 5% off-set method was four times as large as the compressive strength perpendicular to the grain. When the embedding strength perpendicular to the grain was evaluated by a maximum load up to 5mm displacement according to EN383, the ratio of embedding strength perpendicular to the grain to the compressive strength perpendicular to the grain decreased as the dowel diameter increased. Key words Embedding strength 9 Compressive strength 9 Density 9 5% Off-set method K. Sawata. M. Yasumura (EEl) Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422-8529, Japan Tel. +81-54-238-4863; Fax +81-54-237-3028 e-mail: afmyasu@agr.shizuoka.ac.jp Part of this paper was presented at the annual meeting of the Architectural Institute of Japan 1999, Hiroshima, September 1999; the 50 th annual meeting of the Japan Wood Research Society, Kyoto, April 2000; and the World Conference on Timber Engineering 2000, Whistler, Canada, July-August, 2000 Introduction Johansen's yield theory is widely used for estimating the yield strength of dowel-type joints. According to this theory, the embedding strength of wood and the yield moment of the fastener governs properties for determining the strength of joints with dowel-type fasteners. Numerous studies have been performed on embedding characteristics of wood and wood-based materials with dowel-type fasteners. Hirai 2'3 investigated the influence of the embedding test method and round bar diameter on embedding strength and stiffness. Fujita et al. 4 examined the effect of edge-distance and end-distance on the bearing characteristic of glued laminated timber and laminated veneer lumber. These studies were based on the embedding tests in tension, and the ultimate embedding strength obtained in these studies might include the effects of the fracture of wood. Whale et al. 5 conducted a comprehensive investigation of the embedding strength of softwood, hardwood, plywood. and tempered hardboard with nails and bolts: and Ehlbeck and Werner 6 carried out embedding tests on hardwood under various loading angles to the grain. These studies, being the basis of the design of dowel-type joints in Eurocode 5.- dealt only with ultimate embedding strength; they did not look at the yield embedding strength. Kawamoto et al. ~ carried out the embedding tests perpendicular to the grain of glued laminated timber: and Harada et al. 9 and Hwang and Komatsu ~ investigated the relations between the dowel diameter and the embedding properties obtained by the embedding tests of glued laminated timber and some engineered woods, respectively. These studies were based on compressive tests with cubeshaped specimens, and ultimate embedding strength was not considered. Therefore. we conducted the embedding tests parallel and perpendicular to the grain according to EN383 tl to examine both yield and ultimate embedding strengths. Although numerous studies 3-<s<~ have been reported on the relations between the embedding strength of wood or
139 wood-based materials and round bar diameter,few data R embedding strength have been one of the most efficien which was 1.5dand≤4d ing p The were cut near the embed was 32mm square in the loading section and 64mm in design.There height. to producein em design o ow Embedding tests type joint ing strength from the tests. of the wooden member and wer aralle Materials and methods th-0MP /mn tor the cEmbed. to the grain was to the grain were terminate hen the Specimens or when the load decreased to half the maximum load.The Embedding and compressive tests were conducted on embedding stress increment perpendicular to the grain was n to the elastic area.Em ding test 90.100.L110.L125) 1a9 grade tural Standard.Approximately 1000 specimens were cu crack reached the end of the wood. more than 300 Compressive tests nd cording to EN383 were 14d in length,6d in width,and Table 1.Number and density of embedding specimens Grade Parallel to the grain Perpendicular to the grain No.dnens Density Density Mean (kg/m) CV(% Mean (kg/m)CV(%) 8mm 744514 193 011 4514 110007 09 120660 1190023 000 dowel diameter CV. variation
wood-based materials and round bar diameter, few data on the variance of embedding strength have been sought. Reliability-based design is one of the most efficient methods for evaluating the mechanical performance of timber structures. A statistical approach when considering the variance of embedding strength might be required to adapt the yield theory to reliability-based design. Therefore, embedding tests were conducted on a thousand laminae with different grades, dowel diameters, and loading directions to produce a database for the design of doweltype j oints.~2'13 Estimating the embedding strength from the compressive strength of wood was also proposed by comparing the embedding test results with those of compressive tests. Materials and methods Specimens Embedding and compressive tests were conducted on ezomatsu (Picea jezoensis Carriere) and todomatsu (Abies sachalinensis Fr. Schmidt) laminae, which had four grades (L90, L100, Lll0, L125) according to the Japanese Agricultural Standard. TM Approximately 1000 specimens were cut from more than 300 laminae. Dowel diameters (d) were 8, 12, 16, and 20 mm. The number and densities of embedding specimens for each dowel diameter and grade are shown in Table 1. The dimensions of the embedding specimen according to EN383" were 14d in length, 6d in width, and 139 32 mm in thickness, as shown in Fig. 1. The thickness of our specimen was within the range of that defined in EN383, which was ->l.5d and -<4d. Compressive specimens were cut near the embedding specimens. The dimension of compressive specimens was 32mm square in the loading section and 64ram in height. Embedding tests Embedding tests according to EN383 were conducted as shown in Fig. 1. Steel side plates 12mm thick were placed on both sides of the wooden member and were connected with a dowel. There was no clearance between the steel plates and the specimen. The embedding stress increment parallel to the grain was 10-30 MPa/min for the elastic area. Embedding tests parallel to the grain were terminated when the embedding displacement was equal to the dowel diameter or when the load decreased to half the maximum load. The embedding stress increment perpendicular to the grain was 3-10 MPa/min for the elastic area. Embedding tests perpendicular to the grain were stopped when the embedding displacement was equal to the dowel diameter or when the crack reached the end of the wood. Compressive tests Compressive tests parallel and perpendicular to the grain were conducted on the specimens cut from the wood near Table 1. Number and density of embedding specimens Grade Parallel to the grain No. of Density specimens Mean (kg/m 3) CV (%) Perpendicular to the grain No. of Density specimens Mean (kg/m 3) CV (%) d = 8mm Total 57 391 11.4 L90 14 381 11.0 L100 14 369 8.36 Lll0 15 399 9.58 L125 14 414 12.3 d = 12mm Total 117 394 10.2 Lg0 30 359 6.47 L100 30 393 12.0 Lll0 30 394 6.05 L125 27 422 8.26 d = 16mm Total 212 399 11.1 Lg0 50 350 10.2 L100 56 389 4.99 Lll0 56 411 7.52 L125 50 448 5.33 d = 20mm Total 117 403 10.7 Lg0 29 372 7.05 L100 30 381 9.65 Ll10 30 419 5.63 L125 28 441 9.67 57 387 10.9 14 373 9.57 14 364 7.10 15 398 9.13 14 412 12.0 119 389 10.3 30 351 5.05 30 383 9.36 30 401 9.87 29 420 6.89 212 403 11.1 50 357 7.64 56 392 4.45 56 404 7.73 50 460 6.08 118 401 12.2 30 361 6.26 30 372 8.50 30 418 5.68 28 450 11.1 d, dowel diameter; CV coefficient of variation
140 Parallel to the grain Perpendicular to the grain Load cell 5●》● Dowe 3d "3d 32m 40 d=8mm 8mm d=12mm d=12mm =16mm (edW)ssans 3uppac d-20mm 30 d=20mm 30 20 d=16mm 10 Parallel to the grain Perpendicular to the grain 0 10 15 20 25 10 15 25 Displacement(mm) Displacement(mm) Fig.2.Relations bet displacemen the embedding specimen according to the Japanese Indus- almost constant after vielding regardless of the increase trial Standard. Approximately 500 specimens with a den- siy生 to that of the pto te Ylcldins of terminated after the maximum load was attained and thos ment ratio after yielding was smaller as the dowel diameter as shown i the yield embedding strength.With the former method the Results and discussion ine that goes through the points on the curves correspond Evaluation methods of embedding strength o the direction and embedding strength is defined as he tion o this the edding showed a linear increase up to the yielding of wood and was 5%embedding strength and 5mm embedding strength in
140 Fig. 1. Configuration of embedding test. d, dowel diameter (millimeters) 50 [ d=amm ] 40 [ d=amm d=lZmm ~" [ / d=12mm [ ~" / ~ /.~ d=16mm ,40t I i3~176 ~' 30 20 I 20 m 0 0 5 1 0 15 20 25 0 5 10 15 20 25 Displacement(ram) Displacement(ram) Fig. 2. Relations between embedding stress and displacement the embedding specimen according to the Japanese Industrial Standard. 15 Approximately 500 specimens with a density (+_10%) close to that of the embedding specimens were tested. Compressive tests parallel to the grain were terminated after the maximum load was attained, and those perpendicular to the grain were stopped when the displacement was >10% of the height of the specimen. Results and discussion Evaluation methods of embedding strength The typical embedding stress-displacement curves are shown in Fig. 2. The embedding stress parallel to the grain showed a linear increase up to the yielding of wood and was almost constant after yielding regardless of the increase in displacement. The embedding stress perpendicular to the grain showed a liner a increase up to the yielding of wood and a continuous increase after yielding. The increment ratio after yielding was smaller as the dowel diameter was increased. Embedding strengths were evaluated by the 5% off-set method and according to EN383, as shown in Fig. 3. The 5% off-set method was adopted to evaluate the yield embedding strength. With the former method the line that goes through the points on the curves corresponding to 10% and 40% of the maximum load up to 5mm displacement was moved 5% of the dowel diameter parallel to the X-direction, and embedding strength is defined as the intersection of this line and the load-displacement curve. The latter is defined as the maximum load up to 5mm displacement. The former and the latter are expressed as 5% embedding strength and 5mm embedding strength in
14 Embedding stres Parallel to the grain 0.05d f尼.5m 尼.5 20 0.4 fe.sm 0.1尼5n Perpendicular to the grain 5mm Displacement d=8mm d产l2mmd-16mmdk-20mm Fig3.Method for evaluating embedding strength (fe) r 10:1a红d 60 60 5% 5mm fe,0,5%=-0.188+36.64 e,0,5mm=-0.12836.85 (edW) 40 40 五 10 e,90,5%=-0.095d+15.52 f尼，90,5mm=-0.508d+25.66 8 12 16 20 24 Y 16 20 24 Dowel diameter(mm) Dowel diameter(mm) this paper,respectively.Embedding strength was calculated strength had a positive correlation with the density.The as follows rent with dowels ofs and 12mm diameter sho slight increase.The increase in the 5mm embedding the load,is the thickness of the specimen,and d is the endcnewasoeheahgetendeai dowel diameter. This might be caused by the fact that there wasitteffer ence in average Embedding strength average density was larger with higher lamina rade for dowels 16 or 20mm in diameter.The data from the various amina grades were c in this study to simplify the y inereased the faninm grade hhigher.as show The embedding strengths parallel and perpendicular to di
Embedding stress f~), 5mm ,fi?.5% 0.4 ,/i,, 5~m~ O. 1 ./b,Sm~ 0 5mm Displacement Fig. 3. Method for evaluating embedding strength (re) 141 tt~ ,< 50 40 3O ._,_-1 20 10 0 d=8mm Parallel t t the grain 'erpendicule d=121nm to the gra t d = 16mm d--20mm Fig. 4. Relations between 5 mm embedding strength and lamina grade. Diamonds, L90; squares, L100; triangles, Lll0; circles, L125 60 50 .q" 40 "" 30 Lz~ 20 10 5% .1~,0,5% = -0.188d+36< 64 60 50 4O 30 ,~ 20 .1e,90,5O/o = -0.095d+15.52 0 i i i i 0 4 8 12 16 20 24 4 Dowel diameter(mm) 10 5mm ./e,0, 5mm = -0.128d+36.85 .fe,9~ = -0 508d 25.66 I I I I 8 12 16 20 Dowel diameter(ram) 24 Fig. S. Embedding strength as a function of dowel diameter. Circles, parallel to the grain; squares, perpendicular to the grain; symbols and vertical bars denote the mean value and standard deviation, respectively this paper, respectively. Embedding strength was calculated as follows. P fe~,~ - td (1) where fe is the embedding strength, a is the loading angle to the grain, fl is the evaluation method (i.e., 5% or 5mm), P is the load, t is the thickness of the specimen, and d is the dowel diameter. Embedding strength Table 2 shows the mean values and the coefficient of variation of the embedding strength parallel and perpendicular to the grain for each dowel diameter and lamina grade. The density increased as the lamina grade was higher, as shown in Table 1. Some studies 3'8 reported that the embedding strength had a positive correlation with the density. The 5 mm embedding strength for each lamina grade are shown in Fig. 4. As the grade increased, the 5mm embedding strength with dowels of 8 and 12ram diameter showed a slight increase. The increase in the 5mm embedding strength due to lamina grade was more significant in the specimens with a 16 or 20mm diameter dowel. The same tendency was observed with the 5% embedding strength. This might be caused by the fact that there was little difference in average density among each lamina grade used for specimens with dowels 8 or 12 mm in diameter, whereas the average density was larger with higher lamina grade for dowels 16 or 20mm in diameter. The data from the various lamina grades were combined in this study to simplify the analysis. The embedding strengths parallel and perpendicular to the grain for each dowel diameter are shown in Fig. 5. Although yielding of the dowel does not occur with a slen-
142 Table 2.Results of embedding tes Evaluation method Parallel to the grain Perpendicular to the grain Mean (MPa) CV(%) Mean (MPa) Cv(%) 5%Embedding strength 飞级助1110 6500 289T9 edding strength 6068 防纸级k10 87889 was obtained from the experimental an ular to the grain regardless of dowel diameter for practical purposes.It was that obvious that the 5mm embedding strength perpendicular to he er ng strength m constant me the strengths parallel to the grain were almost constant regar grainpcpCndiCularoienrooeachdoNeldia less of dowel diameter.which agreed with the latter study. eter.The ratio for the 5%embedding strength was almost
142 Table 2. Results of embedding test Evaluation method Parallel to the grain Mean (MPa) CV (%) Perpendicular to the grain Mean (MPa) CV (%) 5% Embedding strength d = 8mm Total 26.7 17.1 14.6 17.7 L90 26.8 8.42 15.0 10.8 L100 25.1 11.6 13.5 14.7 Lll0 28.8 23.3 15.3 20.8 L125 25.9 15.1 14.4 19.4 d = 12mm Total 35.4 10.5 14.2 15.5 L90 36.4 9.81 14.1 8.84 L100 35.6 12.0 14.2 19.5 Lll0 33.6 7.43 14.0 15.1 L125 36.2 11.0 14.7 15.8 d = 16mm Total 32.6 13.2 14.3 17.3 L90 28.4 10.4 12.7 16.8 L100 31.3 7.81 14.5 13.6 Ll10 33.9 9.61 14.2 20.1 L125 36.7 9.74 15.9 10.7 d - 20mm Total 33.9 11.2 13.3 20.3 Lg0 31.9 8.18 12.5 14.6 L100 31.9 9.51 11.8 17.1 Lll0 35.1 7.18 13.3 12.3 L125 36.6 11.9 15.4 21.8 5 mm Embedding strength d = 8mm Total 34.2 10.8 22.4 16.9 L90 33.8 6.26 21.8 10.4 LI00 32.9 6.11 21.6 16.7 Lll0 35.3 14.1 23.6 18.7 L125 34.7 11.9 22.5 18.2 d = 12mm Total 37.1 10.6 18.6 17.4 L90 37.3 9.83 17.6 il.9 L100 37.0 12.8 18.7 19~0 Ll10 36.0 7.43 18.5 I6.9 L125 38.3 11.0 19.7 18.1 d = 16mm Total 33.8 12.9 17.9 16.1 L90 29.6 11.6 15.4 16.3 L100 32.4 6.98 18.1 10.1 Lll0 34.7 9.42 !7.9 116.1 L125 38.5 7.84 20.3 10.1 d = 20mm Total 34.3 11.1 15,3 20.9 Lg0 32.5 7.63 14.5 14.2 L100 32.5 9.61 13.7 17.7 Lll0 35.6 7.64 15.5 14.6 L125 37.0 12.0 17.7 22.9 derness ratio of 4, the effects of bending the dowel on the load-displacement curve cannot be ignored. The regression equation of the 5 % embedding strength parallel to the grain was obtained from the experimental results with dowels 12, 16, and 20mm in diameter, excluding those with dowels 8mm in diameter. Whale et al. 5 reported that the embedding strength parallel to the grain decreased as the dowel diameter increased. Hirai 3 and Harada et al. 9 reported that the embedding strength was almost constant regardless of dowel diameter. In our study, the 5 % and 5 mm embedding strengths parallel to the grain were almost constant regardless of dowel diameter, which agreed with the latter study. For conditions perpendicular to the grain, numerous studies 3'4'6'9 reported that embedding strength decreased as the dowel diameter increased, which may be caused by the effects of crack propagation. 3 The 5% embedding strength perpendicular to the grain decreased slightty as the dowel diameter increased but could be considered almost constant regardless of dowel diameter for practical purposes. It was obvious that the 5 mm embedding strength perpendicular to the grain decreased as the dowel diameter increased. Figure 6 shows the embedding strength parallel to the grain/perpendicular to the grain ratio for each dowel diameter. The ratio for the 5% embedding strength was almost
143 60 d-8mm =12mm f尼.0,5%Jfe,0,5%=2.385Mean） 40 2.5 -1 --0 2 △ (edW)%s'af 0 =16mn 20mm 1.5 △ e0,5mm/fe,90,5mm=0.041d41.301 8 12 16 20 3 200300400500200300400500600 Dowel diameter(mm) Density(kg/m) 60 d=8mm d12mm fe,0,5%0,5mm=0.968Mean) 20 -20mm 0.d e,0,5%/f,90,5mm=0.016d+0.555 0.4 8 12 16 20 200300400500200300400500600 Dowel diameter(mm) Density(kg/m3) neheomhgin2gm6mcdiagscnehandcnsy.syn bedding strengths decreased as the dowel diameter in constant,averaging 2.regardless of dowel diameter.The creased.The embedding strength parallel to the grain is not ause the ding strength perpendicular to the grain becomes close to erctylastic-lastic patter.However er evalua that parallel to he grain when the dowel diameter is sm tion method should be used to obtain the yield and ultimate edding strength for conditions perpendicular to the diameter,such as a nail fastener. Effect of density The relations between the 5%and 5mm embeddine most equal to the 5mm embedding strength.Perpendicular strengths and the density are shown in Figs.8 and 9.re to the grain,the difference between the 5%and 5mm em- spectively.The 5%and 5mm embedding strengths were
o (3x ,< o ,< 3 2.5 2 1.5 4 24 fe,o,5%/fe,9o,5% = 2.385 (Mean) -9 fe,o,smm/fe,9o,smm = 0.041d+1.301 I I E [ 8 12 16 20 Dowel diameter(ram) Fig. 6. Ratio of embedding strength parallel to the grain to that perpendicular to the grain for each dowel diameter. Diamonds, ratio for 5% embedding strength; triangles, ratio for 5 mm embedding strength 143 60 v 40 20 0 4O 20 0 2O0 d=8mm o 8 d = 16mm d=12mm o d=20mm o o F I I 300 400 500 200 300 400 500 600 Density(kg/m 3) Fig. 8. Relations between 5% embedding strength and density. Symbols are the same as in Fig. 5 ,< 1.2 0.8 0.6 0.4 fe,o,5%/fg,o,5mm = 0.968 (Mean) 4 24 fe,90,5%/fe,90,5mm = 0.016d+0.555 I I I I 8 12 16 20 Dowel diameter(ram) Fig. 7. Ratio of 5% embedding strength to 5mm embedding strength for each dowel diameter. Symbols and vertical bars are the same as in Fig. 5 constant, averaging 2.4, regardless of dowel diameter. The ratio for the 5mm embedding strength decreased as the dowel diameter decreased. This indicates that 5 mm embedding strength perpendicular to the grain becomes close to that parallel to the grain when the dowel diameter is small. This coincides the fact that there is no effect of the loading direction in the case of softwood with a round bar of small diameter, such as a nail fastener, s Figure 7 shows the ratio of the 5% embedding strength and the 5 mm embedding strength for each dowel diameter. The 5% embedding strength parallel to the grain was almost equal to the 5 mm embedding strength. Perpendicular to the grain, the difference between the 5% and 5mm em- 60 40 20 "-" 0 40 20 0 200 d=Smm 0i ~ d=16mm d=12mm B d=20mm O p ~ J 300 400 500 200 O O 1 I I 300 400 500 600 Density(kg/m 3) Fig. 9. Relations between 5 mm embedding strength and density. Symbols are the same as in Fig. 5 bedding strengths decreased as the dowel diameter increased. The embedding strength parallel to the grain is not affected by the evaluation method because the embedding stress-displacement curve parallel to the grain indicates a perfectly elastic-plastic pattern. However, a proper evaluation method should be used to obtain the yield and ultimate embedding strength for conditions perpendicular to the grain. Effect of density The relations between the 5% and 5mm embedding strengths and the density are shown in Figs. 8 and 9, respectively. The 5% and 5mm embedding strengths were
14e Loaded direction Evaluation method d(mm) b,(×10 5% 10 5m5wedias Pero the 5aihdine 2608260826 Coefficient of cnfdenc interval:e had a positive with density.The on unpublished data.In the Eurocode 5 standard,embed- ower limit of t the confidence inter ding strength is calculate as follows 0.0821-0.01dp f=e-叭 +1+-we (2) e(1.35 +0.015d)sin a+cosa the regression line. ue or t-a As is shown in the relations between the embedding number of specimens.is the density of wood.is the mean value o the residual variance.The followine owing btai .(2 others.When embedding strength was evaluated by the 5% fe febp+bap+b 3 od,the values tor p)paralle and perpen reement with those reported by Harada t al.and where fefe,and p are the same as in Eq.(2);and bb and econstant value Kawamotoetal This indicates that%embeddings wa woul stimated from dow maximum load up to smm displacement according the 5mm embedding strength and the density was larger EN383,the value sity The variance of the embedding strength can be esti- larger p)perpe h ha(). ma ted by the density from Table 3 by he() show the values of (fp)obtained by Harada et aand Kawamoto et al. num stress according to
144 Table 3. Coefficients of regression line and lower limit of 90% confidence interval between embedding strength and density Loaded direction Evaluation method d (mm) al a2 b~ (x 10 3) b2 b3 Parallel to the 5% Embedding 8 0.053 6.15 0.394 -0.308 grain strength 12 0.049 16.04 0.146 0.115 16 0.076 2.15 0.046 -0.037 20 0.073 4.26 0.054 -0.044 5 mm Embedding 8 0.057 11.79 0.181 -0.142 strength 12 0.068 10.21 0.115 -0.091 16 0.082 1.11 0.038 -0.031 20 0.074 4.55 0.054 -0.044 Perpendicular 5% Embedding 8 0.039 -0.53 0.112 -0.087 to the grain strength 12 0.032 1.98 0.048 -0.037 16 0.036 -0.20 0.023 -0.019 20 0.040 -2.80 0.033 -0.027 5 mm Embedding 8 0.049 3.35 0.283 -0~219 strength 12 0.055 -2.60 0.084 -0.065 16 0.047 -0.92 0.026 -0.021 20 0.047 -3.67 0 .048 -0.038 104166 50.34 26.95 20.72 48.16 39.63 22.20 20.72 28.13 16.4t l 3.56 14.86 71.27 28.65 15.19 21.31 Coefficient of regression line: fe = alp + a2 Lower limit of 90% confidence interval: feL = fe - (blp 2 Embedding strength (aCe), in MPa Density: [p(kg/m3)] p, density of the wood; al, a2, bl, b2, b3, constants + b2p + b 3 positivly correlated with the density regardless of the dowel diameter, the evaluation method, or the loading angle to the grain. These results agreed well with reports 3'8 that embedding strength had a positive correlation with density. The regression line and lower limit of the 90% confidence interval between embedding strength and density were calculated. The lower limit equation of the confidence interval was as follows, z6 sop J (2) where fe L is the lower limit of 90% confidence interval, fe is the regression line, t(~, (o) is the value of t-distribution with the degree of freedom (~0) and significance level (co), n is the number of specimens, p is the density of wood, u 0 is the mean value of the density, Spr is the sum of squares of the density, and Ve is the residual variance. The following equation was obtained by transformation of Eq. (2). fe L = fe - ~/b~p 2 + b2p + b3 (3) wherefeL, fe, and p are the same as in Eq. (2); and bl, b2, and b3 are constant values. The coefficients of regression line and Eq. (3) are shown in Table 3. The inclination of the regression line between the 5ram embedding strength and the density was larger than that between the 5% embedding strength and the density. The variance of the embedding strength can be estimated by the density from Table 3. The embedding strength divided by the density (re~p) for each dowel diameter is shown in Fig. 10. These figures also show the values of O~e/p) obtained by Harada et al. 9 and Kawamoto et al. 8 and the design values of embedding strength according to Eurocode 57 standard. For the values of (re~p) by Harada et al., the density of sugi (Cryptomeria japonica D. Don) and karamatsu (Larix Ieptolepis Gordon) were assumed to be 430 and 510kg/m ~, respectively based on unpublished data. In the Eurocode 5 standard, embedding strength is calculated from the dowel diameter and the density. The equation in the Eurocode 5 standard is defined as follows. 0.082(1 - 0.01d)p lea = (1.35 + 0.015d)sin2a + cos2a (4) where fe~ is the embedding strength (MPa), d is the dowel diameter (mm), p is the density (kg/m3), and a is the loading angle to the grain. As is shown in the relations between the embedding strength and the dowel diameter (Fig. 5), the slope of the regression line of the 5 mm embedding strength perpendicular to the grain divided by the density was smaller than others. When embedding strength was evaluated by the 5 % off-set method, the values for (re~p) parallel and perpendicular to the grain obtained by this study showed good agreement with those reported by Harada et al. and Kawamoto et al. This indicates that 5 % embedding strength of softwood would be estimated from dowel diameter and density. When embedding strength was evaluated for the maximum load up to 5ram displacement according to EN383, the values of Oee/p) parallel to the grain were 23%- 29% larger than that derived by Eq. (4). The values of (re/ p) perpendicular to the grain were ctose to that of Eq, (4), Relations between embedding strength and compressive strength Compressive strength parallel to the grain was evaluated with maximum stress according to the Japanese IndUstrial
0.15 015 59% 5mm ((wx/ed) e0,5/-0.0968(1-0.00791d 疤，0,5mm/p-0.0970(1-0.00653d0 0. Harada Parallel ((u3)/edW) 0. Parallel 90.05 Kawamoto dpaus'af 0.05 Perpendi EC5 cular 尼，90,5%/p-0.0413(1-0.00935d 0 e,0,5mm/p-0.0676(1-0.0219d 8 1216 2024 28 121620 2428 Dowel diameter(mm) Dowel diameter(mm) enEasgrcnghitdydknysaanianofdodldincderymobandatcadbsaetieneasifFe.5EG.dsgn 1.6 10 fe,90,5mme,90=-0.159d+7.454 fe,0,5mmlfc,o=0.898 (Mean) 8 1.2 6 0.8 4 0.4 fe0,5%,0=0.863Mean) fe,0,5%e,0=3.937Mean) Parallel to the grain Perpendicular to the grain 4 8 12 16 20 34 12 16 20 Dowel diameter(mm) Dowel diameter(mm) strain parallel toward X-direction,and the compressive about 0 times as large as the compressive strength paralle strength was defined as the intersection of this line and the Based on compressive tests,the re ession line through values of (fe/fc) constant regardless of dowel diameter.The5%embedding density was obtained as follow strength perpendicular to the grain was about four times a fe。=0.0973g fcm=0.00932p (5) grain was evaluated by the maximum load up to 5mm .the values of()per e grai amete (kg/m). ncreased strength (for eachde From the result described above.5%and 5mm embed pa eesinmae a
145 E % tr % 0.15 0.1 0.05 5% fe,o,5% / ,o=O. 0968(1-O. 00791d) Hara~a_ _~ Parallel Kawamoto cular fe, 9o, 5%/,o =0.0413 ( 1-0.00935d) Perpendi- 0.15 r "--" "a 0.1 0.05 ,< 5mm 0 I ~ ' I I 0 4 8 12 16 20 24 28 4 28 Dowel diameter(mm) f e , o, smm/ ,o =O. 09 7 0(1-O . OO6 5 3 d) - _ ...... Parallel C~ PerpendiE cular fe ,90,Smm/ ,O =0.0676(1-0.0219d) I I I i I 8 12 16 20 24 Dowel diameter(mm) Fig. 10. Embedding strength divided by density as a function of doweI diameter. Symbols and vertical bars are the same as in Fig. 5. ECS, design value in Eurocode 5 1.6 10 O C < 1.2 0.8 0.4 0 4 24 fe, O, Smm/fC, O = 0. 898 (Mean) fe, o,5%/fc, o = 0 863 (Mean) Parallel to the grain I I I I 8 12 16 20 Do~el diameter(mm) Fig. 11. Relations between the ratio of the embedding strength to compressive strength and dowel diameter. Diamonds, ratio for 5% embedding strength; triangles, ratio for 5mm embedding strength. Jce,90,5mm/fC,90 ----- -0.159d+7.454 < 6 g 4 2 fe,9o,5o/o/fC,9O = 3.937 (Mean) Perpendicular to the grain 0 i i i 4 8 12 16 20 24 Dowel diameter(mm) Symbols and vertical bars denote the mean value and standard deviation, respectively Standard. 15 That perpendicular to the grain was evaluated according to ENl193; 17 the elastic line was moved 0.01 strain parallel toward X-direction, and the compressive strength was defined as the intersection of this line and the stress-strain curve. Based on compressive tests, the regression line through the origin point between the compressive strength and the density was obtained as follows. 18 fCo = 0.0973/) fcgo = 0.00932p (5) where fco and fc9o are the compressive strengths (MPa) parallel and perpendicular to the grain, respectively, and p is the density (kg/m3). The embedding strength divided by the compressive strength (fie@) for each dowel diameter is shown in Fig. 11. The values of (fe/fc) parallel to the grain was almost constant regardless of dowel diameter or evaluation method. The embedding strength parallel to the grain was about 0.9 times as large as the compressive strength parallel to the grain. When the embedding strength perpendicular to the grain was evaluated by the 5% off-set method, the values of (fie@) perpendicular to the grain were almost constant regardless of dowel diameter. The 5% embedding strength perpendicular to the grain was about four times as large as the compressive strength perpendicular to the grain. When the embedding strength perpendicular to the grain was evaluated by the maximum load up to 5mm displacement according to EN383, the values of (r perpendicular to the grain decreased as the dowel diameter increased. From the result described above, 5% and 5mm embedding strengths can be estimated by the following equation using Eq. (5) and the equations in Fig. 11
146 Embedding strength parallel to the grain teral resi feosx=feusmm =0.9fco 3.T Embedding strength perpendicular to the grain: f5%=0.4f () 4.FujitaM K.Ka feai=(-0.016d+0.745)t (8) and the maximum load up to 5 to EN383,respectively,f and fe are those per 长m餐 buil Conclusions ese shiT.Karube M.Ko K(1999)Dowel-bea he d this stud re of t from all lamina grades varies from 10%to 17%and 15%to strength and density. The embedding strengths parallel to the grain evalu- t method ar mum load up to bythe oints b etmeth s littte innuenced by dowe 14. maximum load up to 5 mm displacement decreases as the The J dowel diameter increases 15. onhSggecompresivetesl eva 16. density of the wood.The design value of embedding uaShoten.Tokyo, 12 handbook (in Japanese) 18 a K.Ta ding 4.The embedding strength for the dowel-type fastener e).Su References
146 Embedding strength parallel to the grain: feo,5O/o = feO,Sm m = 0.9fc0 (6) Embedding strength perpendicular to the grain: fego,5o/o = 0.4fc 0 (7) fe90,Smm = (-0.0].6d q- 0.745)fc0 (8) where feo.5O/o and feo.sm~ are the embedding strengths (MPa) parallel to the grain evaluated by the 5% off-set method and the maximum load up to 5 mm displacement according to EN383, respectively, feto.so/o and fe90.Smm are those perpendicular to the grain, respectively, fc o is the compressive strength (MPa) parallel to the grain, and d is the dowel diameter (mm). Conclusions The following conclusions can be drawn from this study. 1. The coefficient of variation of the embedding strength from all lamina grades varies from 10% to 17% and 15% to 21%, respectively, in the parallel and perpendicular directions. There is a significant correlation between embedding strength and density. 2. The embedding strengths parallel to the grain evaluated by the 5% off-set method and the maximum load up to 5 mm displacement according to EN383 shows close values that are scarcely influenced by dowel diameter. The embedding strength perpendicular to the grain evaluated by the 5% off-set method is little influenced by dowel diameter as well. However, the embedding strength evaluated by the maximum load up to 5 mm displacement decreases as the dowel diameter increases. 3. Embedding strength evaluated by the 5% off-set method can be estimated from the dowel diameter and the density of the wood. The design value of embedding strength in the Eurocode 5 standard is useful for the embedding strength evaluated by the maximum load up to 5 mm displacement according to EN383. 4. The embedding strength for the dowel-type fastener can be estimated by Eqs. (6) to (8) using the compressive strength parallel to the grain of wood. 2. Hirai T / 1989 ] Rational tesdng methods for determination of basic lateral resistance of bolted wood-joints (in Japanese Res Bull Exp Hokkaido Univ 46:959-966 3. Hirai T (1989/ Basic properties of mechanical wood-joints. 2. Bearing properties of wood under a bolt (in Japanese). Res Bull Exp Hokkaido Univ 46:967-988 4. Fujita M. Komatsu K. Kawamoto N. Harada M (1995l Bearing characteristics of glued-laminated-timber and laminated-veneerlumber with a steel rod (in Japanese). Mokuzai Gakkaishi 41:261- 270 5. Whale LRJ. Smith I. Larsen HJ (19871 Design of nailed and bolted joints proposals for the revision of existing formulae tn draft Eurocode 5 and the CIB code. tn: Proceedings of the CIB-W18 meetings, Paper 20-7-1 6. Ehlbeck J. Werner H (1992] Softwood and hardwood embedding strength for dowel-type fasteners. In: Proceedings of the CIB-W18 meetings, Paper 25-%2 7. European Committee for Standardization (1993l Eurocode 5: design of timber structures, part t-l: general rules and rules for buildings, p 82 8. Kawamoto N_ Komatsu K Harada M (1993l Lateral strengths of drift-pin joints in perpendicular to the grain loadings. III Estimation of yield loads by European yield theory (in Japanese). Mokuzai Gakkaishi 39:1386-1392 9. Harada M. Hayashi T. Karube M. Komatsu K 19991 Dowel-bearing test of glued laminated timber with a drift-pin (in Japanese)~ Summary of technical paper, annual meeting, Architectural institute of Japan, pp 49-50 i0. Hwang KH. Komatsu K (t999~ Relationship between embedment parameters and dowel diameter for various engineered woods (EW) (in Japanese). Summary of technical paper of annual meeting, Architectural Institute of Japan, pp 51-52 11. European Committee for Standardization (I993~ EN383: timber structures - test methods - determination of embedding strength and foundation values for dowel type fasteners 12. Sawata K. Yasumura M (20001 Evaluation of yield strength of bolted timber joints by Monte-Carlo simulation. In: Proceedings of the WCTE 2000. Paper 1.4.4 13. Sawata K (2000] Study on yield strength of bolted timber ioints by probabilistic approach. Master's dissertation. Shizuoka University 14. Ministry of Agriculture. Forestry and Fisheries (19961 Japanese agricultural standard for structural glued laminated timber ~in Japanese). The Japan Plywood Inspection Corporation 15. Japanese Industrial Standard 11977) Method of compressive test for wood (in Japanese). JIS Z 2111-1977 16. Mutoh S (19951 Statistical anatvsis handbook (in JapaneseJ. Asakura Shoten. Tokyo. pp 198-201 17. European Committee for Standardization (1993~ ENl193: structural timber - structural glued laminated timber - determination of additional physical and mechanical properties 18. Sawata K. Yasumura M (2000) Evaluating the shear strength of bolted timber joints. Part 1. Embedding tests of wood and evaluation of embedding strength (in Japanese). Summary of technical paper of annual meeting, Architectural Institute of Japan, pp 321- 322 References 1. Johansen KW (1949) Theory of timber connections. Int Assoc Bridge and Struct Eng 9:249-262
