Static Bending Moment Capacity of T-Type Gusset-Plate Joints in Oriented Strandboard

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1 ORAL PRESENTATION Static Bending Moment Capacity of T-Type Gusset-Plate Joints in Oriented Strandboard Samet Demirel 1, and Jilei Zhang 2 1 Res. Asst. Dr., Karadeniz Technical University, Trabzon Turkey; 2 Prof., Mississippi State University, Starkville, Mississippi, USA. sdemirel@ktu.edu.tr Abstract: This study evaluated and compared static bending momentcapacities of T-type, stapled, one-side, two gusset-plate joints constructed of three different OSB materials. To estimate the static moment resistances of T-type joints, a mechanical analysis models for T-type gusset-plate joints were developed. Results demonstrated the ultimate static bending moment resistance loads of T-type joints ranged between 220 and 706 lb. The ratios of estimated to observed loads of T-type joints are ranking between with an average Therefore, the mechanical analysis model is plausible to estimate static moment resistance capacity of T-type joints. In general, the moment resistance capacities of T-type joints are significantly different among three different OSB panels. Keywords: T-Joint bending moment, multi-staples-connected joints, oriented strand board, mechanical model, estimation equation. Introduction: A gusset-plate joint can be defined as a place in a frame structure where two members assemble edge-to-edge and are attached with plates fastened to the member sides with fasteners driven perpendicularly through the plates into the member faces. Gusset plates can classified as metal or wood and woodbased composites such as plywood. Plywood is one of the most popular wood gusset plate materials among others. Plywood is widely used as gusset-plate due to its good tensile strength and split-resistance (APA 1997). the staple is one of the most commonly used fasteners for joining structural members in upholstery furniture because power-driven staples are fast and easy to assemble gussetplate joints in upholstered furniture frames, (Zhang et al. 2002). A gusset-plate can be attached to two jointed members using staples alone or staples with glue applied on the surfaces of members and gusset-plates. Since staple-connected gusset-plate joints yield high bending moment resistance capacity, gusset-plates connect highly stressed joints in upholstery furniture frame construction. Staples withstand face lateral shear forces rather than direct withdrawal forces when the joint is subjected to an in-plane bending moment (Zhang 2005). Therefore, the bending moment resistance capacity of a stapleconnected gusset-plate joint in wood-based composites such as OSB materials might be governed by the resistance capacity of the OSB materials to face lateral shear withdrawal load of staples. Not many studies have been found about development of mechanical models in estimating bending moment capacities of staple-connected gusset-plate joints constructed of OSB materials, especially for the joints connected with two narrower gussetplates located on the upper and lower part of the same side of two jointed members. Developing these models can yield moment capacity predicting equations as a function of relevant variables, such as face lateral shear resistances of staples in OSB materials and joint member width. Such quantitative information can help furniture manufacturers conduct a rational strength design of furniture frames. Eckelman (1971) found the bending moment resistance capacity of T-type, staple-glued gusset-plates joints in solid wood Douglas fir. The two joint members were connected with two plywood gusset-plates symmetrically located on both side of the joint, respectively. Experimental results indicated that the joint moment resistance capacity was not particularly sensitive to construction variables such as the number of staples used. The moment resistance capacity of the evaluated joints improved considerably when width and 924 I n t e r n a t i o n a l C a u c a s i a n F o r e s t r y S y m p o s i u m

2 Samet Demirel, and Jilei Zhang length of gusset-plates were increased. The average ultimate moment resistance reported was from 294 to 14,724 lb.-in. with the coefficients of variation (COV) ranging from 4.2 to 19.0 %. Zhang et al. (2001) worked on the bending moment resistance capacity of T-type, stapleglued gusset-plates joints constructed of woodbased composites. Two joint members were also connected with two plywood gusset-plates symmetrically located on each side of the joint, respectively. Wood-based composites used as joint members were southern yellow pine plywood, aspen Timber strand laminated strand lumber (LSL), and aspen engineered strand lumber (ESL). Test results showed that the joint moment resistance was significantly affected by gusset-plate thickness, width, and length, and among these parameters plate width affected joint moment resistance the most. Joint member material type and the number of staples used had no effect on the moment resistance capacity, and all joint failures happened at gusset plates. The average ultimate moment resistance capacity ranged from 6,073 to 18,528 lb.-in. with COV ranging from 4.7 to 23.7%. Erdil et al. (2003) found the effects of the number of staples and glue on the bending moment resistance capacity of T-type, stapled glued gusset-plates joints constructed with ¾- inch-thick Douglas-fir plywood. The two joint members were connected with two 3/16-inchthick 3-ply Douglas-fir plywood gusset-plates symmetrically located on each side of the joint specimen. The numbers of staples evaluated on each plate were 6, 10, and 12, respectively. Test results showed that the larger gusset plate dimension and higher number of staples increase the overall moment resistance capacity of joints evaluated. The average ultimate moment value of the joints connected with stapled gusset-plates ranged from 1,183 to 2,728 lb.-in with COV ranging from 5 to 10 %. The average ultimate moment value of the joints connected with stapled glued gussetplates ranged from 3,763 to 4,500 lb.-in with COV ranging from 10 to 20 %. Wang et al. (2007) studied the static moment capacity of T-type joints connected with two OSB gusset-plates symmetrically attached on both sides of joint members using glue and staples. The mean ultimate moment resistance load values of the joints with staples only were from 670 to 1,032 lb. with COV ranging from 4.9 to 9.4 percent, while with staples and glue were from 680 to 1,270 lb. with COV ranging from 7.0 to 11.8 percent. The moment resistance capacity of the joint increased in proportion with the length of the gusset-plate until the strength of the plate exceeded that of the joint members. Application of glue to the connection surface increased the moment resistance capacity of the gusset-plate joints. The moment capacity of an unglued stapled gusset-plate joint in OSB can be reasonably estimated using analytical equations if the load capacity of a single staple is known. The main objective of this study was to evaluate and compare static performance of T- type, stapled, one-side, two gusset-plate joints in three different OSB materials. Therefore, the specific objectives of this study were to: 1) evaluate the static bending moment resistance of T-type joints in three different OSB materials; and 2) develop mechanical analysis models of T-type gusset-plate joints in OSB, and derive equations to estimate moment resistances of the joints in OSB. Material and Methods Specimen Configurations and Materials: Tworow vertically aligned multi staple joint: The configuration of two-row vertically aligned multi staple joint is illustrated in Figure 1. The specimen consisted of two main structural members, a fastened member and a fastening member, connected together by staples with their crowns oriented at an angle of 45 degrees to the loading direction. Three types of 23/32- inch-thick southern pine OSB materials (OSB-I, OSB-II, and OSB-III) with their face strands oriented in the direction parallel to the full-size panel (4 by 8 ft.) 8-foot direction were used as the fastening members. One type of furniture grade, ¾-inch-thick 5-ply southern yellow pine plywood was used as fastened members. The full-size sheet of plywood (4 by 8 ft.) was 925 I n t e r n a t i o n a l C a u c a s i a n F o r e s t r y S y m p o s i u m

3 Static Bending Moment Capacity of T-Type Gusset-Plate Joints in Oriented Strandboard constructed with one center ply aligned parallel to the face plies and two evennumbered plies aligned perpendicular to the face. The face plies were aligned parallel to the sheet 8-foot direction. The staples were SENCO 16-gage galvanized chisel-end-point types with a crown width of 7/16 inch and leg length of 1.5 inches. The leg width of staples was inch, and thickness was inch. The staples were coated with Sencote coating, a nitrocellulose-based plastic. All joints constructed of OSB-I, II, and III, and total 180 T-type specimens for bending test. The gusset-plate size is 2x6 inches, and staple numbers are 8 and 12. The same type staple was used for this type of joint. Each group has 10 replications. All cut members and gusset plates were conditioned in an equilibrium moisture content chamber at 65± 4ºF and 41±1 relative humidity. The staple were driven into the specimens with air staple guns with 70 psi pressure. Staple crown orientation at an angle of 45 degrees to gusset plate face grain was considered in all specimens. All tests were performed immediately after staples were driven into gusset plate joint members. Experimental Design Figure 1. Placement of staples in the joint specimens connected with two-row multi-staples of: a) four and b) six. T-type joint: The general configuration of the T- type joint in this study is demonstrated in Figure 2.The two main members, a rail and a stump, comprised a T-type joint. A pair of gusset-plates attached these two members by one side of the joint. The gusset plates were constructed of one type of frame, ¾ inch thick 5-ply southern yellow pine plywood. The rails were 11.5 inches long, 7 inches wide. There were three different widths for stump which were 4.5, 6, and 7 inches and the length of the stump was 16 inches. Two-row vertically aligned multi-staple joints: Four and 6 staples two-row vertically aligned multi staple joint were arranged and tested to use their data to predict bending moment capacities of T-type joints. The factors were fastening member material type (OSB-I, OSB-II, and OSB-III), the number of staples (4 and 6 per gusset-plate). Therefore, a total of 60 joint specimens were tested. The multi-staple placement patterns for each staple number level are given in Figures 1. T-type joint: A complete factorial experiment with 10 replications per cell was carried out to evaluate significance of factors on moment capacity of the T-type, end-to-side, stapled, one-side, two gusset-plate joints. Factors are the number of staples (8 and 12), stump width (4.5, 6, 7 inches), and material type (OSB-I, OSB-II, and OSB-III). Model Development: Figure 3 indicates mechanical analysis models used for deriving prediction equation of the moment resistance load of T-type joints at proportional limit. The distance between the center line and the neutral axis named as e. Distributions of gusset-plate joint stresses along lower compression side are shown in Figure 3. Figure 2. Configuration of joint specimens for evaluating moment capacity of T-type with 12 staples per gussetplate joints in OSB. 926 I n t e r n a t i o n a l C a u c a s i a n F o r e s t r y S y m p o s i u m

4 Samet Demirel, and Jilei Zhang Σ M = 0 P= F T (d 1+d 2)/d (2) whered =distance between moment resistance load to neutral axis; d 1 = distance between tensile force to neutral axis; d 2 = distance between compression force to neutral axis (in.). Figure 3. Mechanical analysis model for deriving ultimate moment resistance loads of T-type, end-to-side joints. By summing the forces in the vertical direction as indicated in Figure 3, the force at lower compression side can be obtained: ΣF y = 0 F C = F T(1) wheref T= tensile force (lb.); F C= compression force (lb.) By summing the moments at point B as indicated in Figure 3, the ultimate moment resistance load prediction equation for T-type gusset-plate joints can be obtained: d 1= (W S-W G)/2 +e (3) d 2= (W S/2-e)/2 (4) wherew S=Stump width; W G= gusset plate width; Then, substituting Equations 3 and 4 into Equation 2 yielded Equation 5. ( 3Ws 2W G 2e) P F (5) T 4d e-value: The calculation of e value for T-type joint was based on the assumption of angle (θ) between center line of the stump and displacement of load-head. It is assumed that the same angle existed for multi-staple lateral joint displacement as shown in Figure 4. Figure 4. Diagram showing the θ displacement angle of T-type joints. The displacement of the load head at proportional limit and multi-staple joints at proportional limit yielded e-value. Accordingly, The similar triangles have the same angle θ, yielded Equation 7 for e calculation. R a d b W ( S W e G ) 2 2 (6) WS WG d R( ) e 2 2 (7) R where d= distance between load head to rail (in.); a= the displacement of load head at proportional limit(in.); b= the displacement of the multi-staple joint at proportional limit(in.); R= ratio of a to b. 927 I n t e r n a t i o n a l C a u c a s i a n F o r e s t r y S y m p o s i u m

5 Static Bending Moment Capacity of T-Type Gusset-Plate Joints in Oriented Strandboard Testing: Static bending test specimens were carried out on a hydraulic SATEC universal testing machine at a load rate of 0.10 in/min. The placement of T-type joint is shown in Figure 5. The joints were bolted to the metal apparatus to be fixed during the bending test. The load was calibrated to not leave a gap between the load head and specimen before initiation of loading specimens. The joints were vertically loaded on the stump 12 inches away from rails. Testing wascontinued until the joints were disabled, and the ultimate bending load, displacement, and failure modes were recorded. Results and Discussion T-type joint Mean Comparisons: Table 1listed the mean ultimate load of T-type gusset-plate joints and their COV. The ultimate moment resistance loads T-type, end-to-side, stapleconnected gusset-plate joints in OSB were statistically evaluated with 3 ways ANOVA table and checked whether there are interaction effects among factors which are material (OSB-I, OSB-II, OSB-III), staple number (8 and12), and stump (4.5, 6, and 7 in.). Figure 5. Set-up ofbending moment test for T-type joints. Table 1. Static bending moment resisting load capacities of T-type gusset-plate joints subjected to a testing load. Material Type Number of Staples OSB-I 220 (5) 314 (5) 386 (10) 301 (4) 445 (5) 562 (6) OSB-II 220 (6) 334 (9) 461 (10) 297 (8) 485 (7) 642 (7) OSB-III 297 (7) 460 (7) 534 (8) 373 (6) 609 (8) 706 (10) According to the results, the 3-way interaction (Material Type Number of Staples Stump Width) and the 2-way interaction, material type by number of staples, are not statically significant at 5 percent significance level. The other 2-way interactions, material type by stump width and number of staples by stump width, are significant. Therefore, these two interactions were analyzed. Number of Staples by Stump Width Interaction: Tables 2 and 3 show mean comparisons of ultimate bending loads of T- type joints for stump width for each of staple number and mean comparisons of ultimate bending loads of T-type joints for number of staples for each of stump width, respectively. The results were based on a one way classification with 6 treatments. The protected least significant difference (LSD) multiple comparisons procedure at the 5 % percent significance level was conducted to determine the mean difference of those treatments using the LSD value of 34 pounds. 928 I n t e r n a t i o n a l C a u c a s i a n F o r e s t r y S y m p o s i u m

6 Samet Demirel, and Jilei Zhang Table 2. Mean comparisons of ultimate moment resistance loads of T-typegusset-plate joints for stump width for each number of staples. Number of Staples (A) 369 (B) 460 (C) (A) 513 (B) 637 (C) Table 3. Mean comparisons of ultimate moment resistance loads of T-type gusset-plate joints for number of staples for each stump width. Number of Staples (A) 323 (B) (A) 513 (B) (A) 637 (B) Material Type by Stump Width Interaction: The results depended on a one way classification with 9 treatments. The least significant difference (LSD) multiple comparisons procedure at the 5 percent significance level was performed to determine the mean difference of those treatments using the LSD value of 49 pounds. Tables 4 and 5 Stump Width Effects: As can be seen in Table 2, the ultimate bending loads of T-type joints attached with 8 staples are significantly different among stump width 4.5, 6, and 7 inches. The same relationship is valid for the ultimate bending loads of T-type joints attached with 12 staples. The same relationship among three different size stump width can be seen in Table 4. Thus, T-type joints made by OSB-I, OSB-II, and OSB-III with 4.5, 6 and 7 inch stump width are significantly different from one another. Number of Staples Effects: According to Table 3, the ultimate bending resistances of 12 staples T-type joints are significantly higher Model Verification: As it formerly mentioned, the calculation of e value for T-type joints was based the displacement of load head T-type gusset-plate joint at proportional limit and displacement of the two-row vertically aligned multi-staple joints. Equations 7were used to calculate e value. Accordingly, For 8 staple 4.5 inch stump size T-type gussetplate joints made of OSB-I, a R 5.46in. b show mean comparisons of ultimate bending loads of T-type joints for stump width with respect to material type and mean comparisons of ultimate bending loads of T- type joints for material type with respect to stump width. Table 4. Mean comparisons of ultimate moment resistance loads of T-type gusset-plate joints for stump width for each material type. Material Type OSB-I 260 (A) 379 (B) 474 (C) OSB-II 258 (A) 409 (B) 551 (C) OSB-III 345 (A) 535 (B) 620 (C) Table 5. Mean comparisons of ultimate moment resistance loads of T-type gusset-plate joints for material type for each stump width. Material Type OSB-I OSB-II OSB-III (A) 258 (A) 345 (B) (A) 409 (A) 535 (B) (A) 551 (B) 620 (C) than that of 8 staple T-type joints in 4.5 inch stump. The same relationship exists for 6 and 7 inch stump width. Material Type Effects: As shown in Table 5, the ultimate mean loads of 4.5 inch stump T-type joints constructed of OSB-I and OSB-II are not significantly different, but they are significantly lower than those which were constructed of OSB-III. The same relationship exists among 6 inch width stump T-type joint in OSB-I, OSB-II, and OSB-III. However, the mean ultimate loads of 7 inch stump T-type joints in OSB-II is significantly higher than those in OSB-I and lower than those in OSB-III, respectively ( ) e e = 0.95 in. e value was used to calculate observed P value for T-type gusset-plate joints in Equation 5. F T value is the proportional limit load of two-row vertically aligned 4 and 6 staples joints for this test group. To calculate predicted P value for 8 staples 4.5 inch stump T-type joints made of OSB-I are W S = 4.5 in., W G = 2 in., d = 12 in., e = 0.95, and F T = 502 as included in Table 6. Then all the numbers were substituted to the Equation I n t e r n a t i o n a l C a u c a s i a n F o r e s t r y S y m p o s i u m

7 Static Bending Moment Capacity of T-Type Gusset-Plate Joints in Oriented Strandboard (3* 4.5 2*2 2*0.9475) P lbs. 4*12 Accordingly, the ratio (R) between observed P and predicted P was calculated. R = Predicted P / Observed P (8) The ratio for this group R = 119/124 = 0.96 configuration of T-type joints at proportional limit and its ratio value of predicted P to observep loads. The ratios are between 0.64 and 1.16 with an average 0.88 which mean predicted P values and observed P values from the experiments are quite close one another. Therefore, the equation from themodel isremarkableto estimate P predicted load. Table 6 lists the variables to predict static bending moment resistance load of each Table 6. The ratio of predicted Pload value of the T type gusset-plate joints at proportional limit to observed P value of the T-type gusset-plate joints. Number of Staples 8 12 Material Type OSB-I OSB-II OSB-III OSB-I OSB-II OSB-III W S W G e F T d P pre. P obs. Ratio a W S= stump width; W G= gusset-plate width; F T =the lateral resistance load of two-row vertically-aligned 4 and 6 staple joint load at proportional limit point;d= distance between moment resistance load to rail; P pre. = the predicted P load of T-type stump-to-front-rail joints;p obs. = the observed moment resistance load of T-type end-to-side joints at proportional limit point. Conclusion: The ultimate bending moment resistance capacity of T-type end-to-side, one sided, two gusset-plate joints were evaluated. The ultimate bending moment resistance loads of T-type joints ranged from 220 to 706 lb. The stump width affected moment resistances of T- type joints. Accordingly, the mean ultimate bending loads of 6 inch stump T-type joints were averaged 54 percent higher thanthat of 4.5 inch stump T-type joints and averaged 25 percent lower thanthat of 7 inch stump T-type joints. The mean ultimate bending loads of 7 inch stump T-type joints were averaged 93 percent higher thanthat of 4.5 inch stump width T-type joints. Number of staples also affected moment resistance of T-type joints. In accordance with this, the mean ultimate bending loads of 12 staple T-type joints were averaged 37 percent higher than the mean ultimate bending loads of 8 staple T-type joints. Material type influenced the mean ultimate bending resistances of T-type joint. In general, the mean ultimate bending loads of OSB-III T-type joints were averaged 34 and 25 percent higher than the ones of OSB-I and OSB- II, respectively; however, the mean ultimate bending loads of OSB-I and OSB-II were not significantly different. 930 I n t e r n a t i o n a l C a u c a s i a n F o r e s t r y S y m p o s i u m

8 Samet Demirel, and Jilei Zhang The mechanical analysis model to predict bending moment resistance of T-type joints yielded the ratio of predicted to observed moment resistance of 8-staple T-type joints ranged from to 0.64 to 0.96, and the same ratio of 12-staple T-type joint ranged from 0.78 to Results pointed that using the mechanical model for prediction equation of static bending moment resistance capacity of T-type gusset-plate joint is remarkable. In general, the bending moment resistance capacities of T-type joints could be predicted by means of the Equation 5. References American Plywood Association (APA) Panel Handbook & Grade Glossary. Tacoma, Washington. Eckelman, C. A Designing joints with gusset plates. Furniture Design & Mfg. 43(9): Erdil, Y.Z., J. Zhang, and C. A. Eckelman Staple holding strength of furniture frame joints constructed of plywood and oriented standboard. Forest Prod. J. 53(1): Zhang.J., F. Quin, and B. Tackett Bending fatigue life of two-pin dowel joints constructed of wood and wood composites. Forest Prod. J. 51(10): Zhang, J., F. Quin, B. Tackett, and S. Parkt Direct withdrawal strength of singlestaple joints in pine plywood. Forest Prod. J. 52(2): Zhang, J., G. Li, and T. Seller, Jr Bending fatigue life of two-pin dowel joints in furniture grade pine plywood. Forest Prod. J. 53(9): Zhang, J. and M. Maupin Face lateral and withdrawal resistances of staple joints in furniture-grade pine-plywood. Forest Prod. J. 54(6): Zhang, J., Y. Yu, and F. Quin Bending fatigue life of metal-plate-connected joints in furniture-grade pine plywood. Forest Prod. J. 56(11/12): Wang, X., A. Salenikovich, M. Mohammad, C. Echavarriar, and J. Zhang Moment capacity of oriented strandboard gussetplate joints for upholstered furniture. Part 1: Static load. Forest Prod. J. 57 (7/8): I n t e r n a t i o n a l C a u c a s i a n F o r e s t r y S y m p o s i u m