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Theoretical analysis and design of joints in a representative sofa frame constructed of plywood and oriented strandboard.

Abstract

Increasingly, plywood and oriented strandboard (OSB) are being used in the construction of upholstered furniture frames. There is little information available, however, concerning the strength of frames constructed with these materials. The rational use of plywood and OSB in furniture frames requires reliable information concerning the strength of the joints that can be constructed with them and, indirectly, how frames constructed of these materials behave as compared to solid wood. The procedures needed for the sound engineering of joints used in upholstered flames constructed of plywood and OSB were developed by the authors in previous studies. A representative sofa frame constructed of either plywood (HPLY, SPLY) or OSB was analyzed in order to demonstrate the use of simplified methods of structural analysis in the engineering of such frames. As a result of the study, it was concluded that simplified methods may be used to analyze and design sofa frames constructed of plywood and OSB, and that these materials may be used in construction of upholstered furniture frames to meet specific design loads.

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The analysis and design of joints is an important process in the product engineering of sofa frames. The strength properties of joints in a structure depend upon their geometry and the mechanical and physical properties of the material used in their construction. Joint design is particularly important since a joint in a frame may fail at a fraction of the load capacity of the members it joins together--as was shown by Lin (1997).

Even though a sofa frame can be analyzed by applying the principles of structural mechanics in the same manner they are applied to any other engineering structure, practical design considerations usually dictate the use of simplified methods of analysis. Several simplified techniques may be used as long as the crucial requirements of design are not neglected. Eckelman (1993), for example, showed that exact analyses of upholstered furniture frames are rarely necessary because many of the forces involved are of such small magnitude that they can be neglected.

The purpose of this study was to examine whether the joints used in representative plywood and oriented strandboard (OSB) sofa frames, based on the design information and expressions obtained from past joint and fastener tests carried out on plywood and OSB, had sufficient capacity to resist three sets of specified design loads.

Design loads and construction of the representative sofa frame

The general configuration of the representative sofa frame used in this study is shown in Figure 1. Three sets of design loads, corresponding to the service requirements for light, medium, and heavy duty service as outlined in General Services Administration (GSA) Specification FNAE-80-214 (Eckelman 1978, Eckelman and Erdil 2001) are given in Table 1. This specification was established for performance testing of upholstered furniture frames and provides, perhaps, the best estimates of design loads since it is known that this specification was based on a wide range of experimental data. These requirements are based on cyclic performance. Since cyclic joint strength is equal to about half of static joint strength, light, medium, and heavy level service loads were doubled for each joint in order to obtain comparable static loads--as shown in Table 1.

[FIGURE 1 OMITTED]

Construction of frame

The representative frame (Fig. 1) is assumed to be constructed of 3/4 inch thick OSB (EN 300, 1997), Douglas-fir (Pseudotsuga menziesii) plywood (SPLY), and Sweetgum (Liquidambar styraciflua) plywood (HPLY). Some physical and mechanical properties of the these materials are given in Table 2 (Erdil 1998). Joints were constructed with 3/8 inch yellow birch (Betula alleghaniensis) dowels and aliphatic resin glue (PVAc). All of the members were conditioned to 7 percent equilibrium moisture content (MC) before gluing. Construction of the joints in the representative frame is essentially the same as in previous studies (Erdil 1998, Eckelman and Erdil 2000, Erdil and Eckelman 2001, Eckelman et al. 2002, Zhang et al. 2002a, 2002b) in order to provide the means for a close comparison of results. Dowel spacing in the front rail to stump joint was 2 inches.

Test methods

Subsystems were identified and the estimated loads acting on these subsystems were then determined. These included the seat, side frame, back, and center rail subsystems. The internal forces acting on the joints of these subsystems were then calculated using basic structural analysis techniques. A static analysis of each joint was made under the light, medium, and heavy level of service conditions indicated in Table 1.

Types of loading for the joints are given in Table 3. The joints were first analyzed and their static strength capacities estimated--based on the results reported in previous studies (Erdil 1998, Eckelman and Erdil 2000, Erdil and Eckelman 2001, Eckelman et al. 2002, Zhang et al. 2002a, 2002b). These joint strengths were then compared to the calculated forces and moments imposed on the joints by the allowable light, medium, and heavy design loads given in Table 1.

Results and discussion

Results were evaluated for each of the following structural subsystems.

Seat system

The seat system consists of the front rail, back rail, and the stretchers along with the side rails and stumps. This system is subjected to vertical loads resulting from user sitting actions along with out-of-plane loads arising from sinusoidal type springs used as part of the seat foundation system. The critical joints in the seat system are the front rail to stump and the stretcher to front and back rail joints.

Front rail to stump joints.--Ordinarily, the front rail to stump joints are subjected to three types of loads, namely, vertical loads, outward side thrust loads, and front-to-back out-of-plane loads, Figure 2. Estimated joint strength capacities along with design loads for the three stated levels of service are given in Table 4.

In the case of vertical loading, [F.sub.V(fr)], the bending moments acting on the front rail to stump joints are assumed to be sufficiently small to be neglected. Thus, the vertical shear strength of the joint is of primary concern. Estimated vertical shear capacities of two-dowel joints in 4-inch-wide OSB, SPLY, and HPLY rails in the edge position are 1,063, 1,394, and 1,312 pounds, respectively (Erdil 1998, Eckelman and Erdil 2000, Zhang et al. 2002a), whereas the calculated shear forces acting on the joint, Table 4, for light, medium, and heavy services are 900, 1,125, and 1,238 pounds, respectively, for this joint. Hence, the front rail to stump joints constructed of plywood would satisfy the stated design requirements for heavy service, whereas the joints constructed of OSB would satisfy the design requirements for light service.

Figure 2 also shows the front rail to stump joint under the action of an outward side thrust load, FH(a). In-plane bending moments act on this joint when users push outward on the arm or when someone pulls on the arm when attempting to move the sofa. The estimated bending moment capacities of the joint for OSB, HPLY, and SPLY, respectively, and the calculated bending moments acting on the joint for the three stated design levels are given in Table 4.

The calculated bending moments acting on this joint are 2,100, 4,200, and 5,600 inch-pounds for light, medium, and heavy service, respectively (Table 4). The estimated bending moment capacities of the OSB, SPLY, and HPLY joints when fabricated with 4-inch-wide rails are 1,356, 4,524, and 3,430 pound-inches, respectively, whereas the comparable estimated values for 6-inch-wide rails are 3,012, 7,668, and 5,900 pound-inches (Erdil 1998, Eckelman and Erdil 2000, Eckelman et al. 2002). Hence, joints fabricated with 4-inch-wide rails constructed of SPLY and HPLY would satisfy the stated light and medium service loads, whereas joints constructed with 6-inch-wide SPLY and HPLY rails would satisfy all of the stated design loads. Finally, in the case of OSB frames, 6-inch-wide rails would satisfy the requirements for light service.

Front rails of sofas fabricated with sinusoidal type seat springs are also subjected to out-of-plane loads, [F.sub.H(fr)], owing to the action of these springs as shown in Figure 2. Each of these springs can apply an out-of-plane force of approximately 50 pounds to the top of the front and back rail (Erdil 1998, Eckelman and Erdil 2000). The average number of springs attached to a 72-inch front rail is 15. Thus, the resulting bending moment acting on each front rail to stump joint amounts to (750/2) x 3, or 1,125 pound-inches, which is calculated by summing the forces about the lower dowel of the 4-inch-wide rail with 2-inch dowel spacing.

[FIGURE 2 OMITTED]

The estimated torsional capacities of a dowel joint constructed of OSB, SPLY, and HPLY with 4-inch wide rail in the flat position, Table 4, are 1,035, 1,436, and 1,480 inch-pounds, respectively (Erdil 1998, Eckelman and Erdil 2000, Zhang et al. 2002b). Thus, the joints constructed of HPLY and SPLY would satisfy the stated design loads, Table 4, but the joints constructed of OSB would need to be reinforced.

Stretcher to front or back rail joints.--Generally, two stretchers are used in three-seat sofa systems. They are joined to the front and back rails at the third points of the rails. Stretchers, in most cases, are not subjected to vertical loads since sinusoidal springs do not impose such loads and most coil spring systems are now self supporting. Stretchers are important structural elements in frames with sinusoidal springs, however, because they reinforce the front rail against the front to back forces applied to the top of the front rail by the seat springs. To effectively resist these forces, the ends of the stretchers should be braced to the front and back rails. Braces, or corner blocks, should extend from the top edge of the rails at an angle of at least 45 degrees (measured from the inside rail surface) to the top surface of the stretcher.

Side frame system

The side frame system may be analyzed as a two-dimensional frame; generally, it consists of a stump, back post, arm, side rail, and side slat. Side frames are subjected to vertical forces owing to a user sitting on the arm and to horizontal forces owing to a user leaning against the backrest. Side frames are also subjected to side forces acting perpendicular to the frame that act largely on the stump to front rail connections, as previously discussed. Aside from the stump to front rail joint, the most critical joints in side frame systems are the arm to stump and arm to back post joints and the side rail to stump and side rail to back post joints.

Backpost to arm joints.--In general, the back post to arm joints in the side frame system must resist both vertical forces and horizontal forces, [F.sub.V(a)] and [F.sub.H(a)]. Vertical forces occur, for example, when a user sits on an arm. To satisfy the light, medium, and heavy levels of service, Table 1, the arms should resist estimated loads of 600, 750, or 825 pounds. Usually, these joints are flexible and thus the bending moments acting on the ends of the arm owing to the action of a vertical load may be neglected.

The lateral holding strengths of dowel joints in 4-inch wide sofa rails constructed of OSB, HPLY, and SPLY supported in the flat position are estimated to be 600, 881, and 961 pounds, respectively (Erdil 1998, Eckelman and Erdil 2000, Zhang et al. 2002a). Thus, the back post to arm joints of the representative sofa frames constructed of HPLY and SPLY could resist all of the stated vertical design loads given in Table 5, and the joints constructed of OSB could satisfy the light design load.

The back post to arm joints must also resist front to back loading. As a first approximation, the axial force acting on the end of the arm may be expressed by the equation:

f = ([h.sub.1]/[h.sub.2]) x (3[F.sub.H(tr)]/2) [1]

where f is the internal tensile force (pounds), [h.sub.1] is the height of the back post (30 inches), [h.sub.2] is the distance from center of the side rail to back post joint to the arm to back post joint (16 inches), and 3[F.sub.H(tr)] is the total horizontal front to back load acting on the top rail. According to Table 1, light, medium, and heavy cyclic loads acting on the backrest frame test correspond to 150, 200, and 300 pounds, respectively. Equation [1] estimates that the corresponding tensile forces acting on the arm to back post joint amount to 422,563, and 844 pounds, respectively. Assuming that the arm is joined to the back post with two dowels, the withdrawal force acting on each dowel for each load case would be 211, 282, and 422 pounds, respectively.

Previous research has shown that the withdrawal capacities of 3/8-inch dowel pins from 3/4 inch-thick OSB, HPLY, and SPLY are 766,759, and 610 pounds, respectively (Erdil 1998, Eckelman and Erdil 2000, Erdil and Eckelman 2001, Eckelman et al. 2002). Since two dowels were used in the construction of the frame joints, the total estimated withdrawal capacities of the OSB, HPLY, and SPLY joints amount to 1,532, 1,518, and 1,220 pounds, respectively. Thus, the joints should be able to carry the stated light, medium, and heavy design loads. Table 5 provides a comparison of estimated back post to arm joint capacities to design load requirements.

Side rails to back post or stump joints.--The side rail to back post joints in a sofa frame are subjected to high in-plane bending moments. These moments occur at the side rail to back post and side rail to stump joints when horizontal front to back loads are transferred from the ends of the top rail to the back post. In order to analyze these joints, the entire side system is treated as a two dimensional frame. As a first approximation, it may be assumed that the arm joints and side slat joints in this frame are flexible, i.e., hinged, so that the side rail to back post joint and the side rail to stump joint provide the internal moment resistance to external front to back loads applied to the top rail of the sofa. The bending moment acting on either of these joints, [f.sub.b], may be estimated by the equation

[f.sub.b] = (3[F.sub.H(tr)]/2) x ([h.sub.1]/2]) in-lb. [2]

Estimated bending moments acting on these joints for back loads, [F.sub.h], corresponding to 150, 200, and 250 pounds amount to 3,375, 4,500, and 6,750 in-lb, respectively. The estimated bending moment capacities of 4-inch-wide OSB, HPLY, and SPLY rails with two dowels may be found from the expression presented by Eckelman (1991), i.e.,

[f.sub.b] = F([d.sub.1] + [d.sub.2]/2) [3]

where [f.sub.b] is the bending moment at the joint (in-lb), F is the withdrawal force of a 3/8-inch dowel from face of OSB, HPLY, and SPLY panels, [d.sub.1] is the dowel spacing (2 inches), and [d.sub.2] is the dowel to edge spacing (1 inch). For withdrawal capacities of 766, 759, and 610 pounds, respectively (Erdil 1998, Eckelman and Erdil 2000, Erdil and Eckelman 2001 Eckelman et al. 2002), the corresponding moment capacities amount to 1,915, 1,898, and 1,525 pound-inches, respectively. Comparison of estimated joint capacity with calculated moment levels for each design load level are given in Table 5. Results indicate that the estimated capacities of the side rail to back post and side rail to stump joints of the all sofa frames are less than the calculated values at each design load level. Overall, it is advantageous to reinforce the joints in order to have sufficient capacity. Specifically, the arm to from and back post joints should be reinforced with substantial braces in order to redistribute a part of the moments acting on the side rail to post joints to the arm to post joints. Ideally, an equal distribution of moments should be obtained.

Back system

The back system consists of the back rail, top rail and the interior uprights. The top rail and back rail are the most stressed members in the system while the interior uprights are more lightly stressed since they transfer the forces to the other members. The top rail to back post joints are especially critical joints in the back system.

Top rail to back post joints.--These joints are similar to the front rail to stump joints in the seat system. In the case of vertical loads, [F.sub.V(tr)], top rails are stressed both from users sitting on the rail and from normal sitting loads transferred to the rail via the interior uprights and the back springs attached to the rail. The corresponding vertical- shear forces (corresponding to the three stated design loads) acting on each of the top rail to back post joints are 900, 1,125, and 1,238 pounds, respectively (Eckelman and Erdil 2001). The estimated lateral shear capacity of joints fabricated with two dowels in 4-inch-wide rails constructed of OSB, SPLY, and HPLY are 1,063, 1,394, and 1,312 pounds, respectively (Erdil 1998, Eckelman and Erdil 2000, Zhang et al. 2002a). Thus, the estimated capacity of the top rail to back post joints constructed of HPLY and SPLY exceeds the calculated forces imposed by the heavy design load, whereas the estimated capacity of the top rail to back post joints constructed of OSB exceed the calculated internal force generated by only the light design load (Table 5).

The back post to top rail joints (Fig. 2) are also subjected to horizontal lateral shear forces, [F.sub.H(tr)]/2, when users lean backward in a sofa. The calculated lateral shear forces acting on each joint would be 225, 300, and 450 pounds for light, medium, and heavy design loads, Table 1. The estimated lateral shear strengths of this joint when fabricated with 4-inch-wide OSB, HPLY, and SPLY rails with two 3/8-inch dowels are 325, 450, and 480 pounds (Erdil 1998, Eckelman and Erdil 2000, Zhang et al. 2002a). Hence, the analysis (Table 5) indicates that the estimated capacity of the top rail to back post joints constructed of HPLY and SPLY exceed the calculated internal forces arising from the heavy (back) design loads, and the estimated capacity of joints constructed of OSB exceed calculated internal forces arising from both the light and medium design loads.

Center rail system

The center rail system consists of the center rail, which is connected at each end to the side slats, and the braces that connect the center rail to the interior uprights. The center rail is usually constructed of a single member placed in the flat position. Normally, the function of the center rail is to provide seat level points of attachment for backrest springs and upholstery material and to define the back tilt angle. However, the center rail together with the braces helps to hold the frame together should the back post to arm joints fail. Generally two types of joints occur in center rail systems, namely, the center rail to side slat joint and the center rail brace to interior upright connections.

Conclusions

The purpose of this study was to demonstrate the use of simplified structural analyses in the product engineering of a representative sofa frame constructed of oriented strandboard, hardwood plywood, or softwood plywood based on information and expressions obtained from previous research. Results of this study indicate that simplified analytical methods may be used to rationally analyze and design sofa frames. It was also found that strong reliable joints could be constructed with both plywood and OSB. Sufficient information exists to reliably estimate the strengths of several of these joints so that frames can be rationally designed based on information generated in previous studies.

Summary

The rational design of joints in a furniture frame implies that the joints are designed to have sufficient strength to carry the loads that will be imposed upon them in service. Design loads have been developed for sofa frames in "GSA Test Method for Upholstered Sofas" (Eckelman 1978, Eckelman and Erdil 2001). Furthermore, the procedures needed for the sound engineering of joints used in upholstered frames constructed of plywood and OSB were developed by the authors in previous studies (Erdil 1998; Eckelman and Erdil 2000; Erdil and Eckelman 2001; Eckelman et al. 2002; Zhang et al. 2002a, 2002b). In this study, a representative sofa frame constructed of plywood (HPLY, SPLY) and OSB was analyzed in order to demonstrate the use of simplified methods of structural analysis in the engineering of such frames. The simplified structural analysis phases may be summarized as follows.

1. Analyze and design the seat system (which consists of the front rail, back rail, and the stretchers along with the side rails and stumps). The critical joints in the seat system are the "front rail to stump" and the "stretcher to front or back rail" joints.

a. Design the front rail to stump joint under vertical loads.

b. Design the front rail to stump joint under outward sidethrust loads.

c. Design the front rail to stump joint under front to back out of plane loads.

d. Design the stretcher to front or back rail joint under out of plane loads.

2. Analyze and design the side frame system (which consists of the stump, back post, arm, side rail, and side slat) as a two dimensional frame. The joints in the side frame system are the "back post to arm" and the "side rails to back post or stump" joints.

a. Design the back post to armjoint under vertical loads.

b. Design the back post to arm joint under horizontal front to back loads.

c. Design the side rail to back post or stump joint under horizontal front to back loads.

3. Analyze and design the back system (which consists of the back rail, top rail and the interior uprights). The "top rail to back post" joints are especially critical joints in the back system.

a. Design the top rail to back post joint under vertical loads.

b. Design the top rail to back post joint under horizontal loads.

4. Analyze and design the center rail system (which consists of the center rail and the and the rail to interior upright braces). Generally there are two joints in the center rail system, namely, the "center rail to side slat" joint and the "center rail brace to interior upright" joints.

a. Design the center rail to side slat joints under vertical/ horizontal loads.

b. Design the center rail brace to interior upright joints under vertical/horizontal loads.

Literature cited

Eckelman, C.A. 1978. Development of performance tests for upholstered furniture--Development of tests and results of test program. National Tech. Information Serv. Dept. of Commerce, Washington, D.C.

--. 1991. Textbook of Product Engineering and Strength Design of Furniture. Purdue Univ., West Lafayette, Indiana.

--. 1993. Design and Construction of Sofa and Lounge Furniture. Unpublished textbook. Purdue Univ., West Lafayette, Indiana.

-- and Y.Z. Erdil. 2000. Joint design manual for furniture frames constructed of plywood and oriented strand board. Extension Publication FNR-170. Purdue Univ., Dept. of Forestry and Natural Resources, West Lafayette, Indiana.

-- and --. 2001. General services administration upholstered furniture test method. FNAE 80-214: A description of the method with drawings. Extension Publication FNR 176. Purdue Univ., Dept. of Forestry and Natural Resources, West Lafayette, Indiana.

--, --, and J.L. Zhang. 2002. Withdrawal and bending strength of dowel joints constructed of plywood and oriented strandboard. Forest Prod. J. 52(9):66-74.

EN 300. 1997. Oriented strand boards (OSB)--Definitions, classification and specifications. European standard.

Erdil, Y.Z. 1998. Strength analysis and design of joints of furniture frames constructed of plywood and oriented strand-board. M.Sc. thesis, Purdue Univ., West Lafayette, Indiana.

-- and C.A. Eckelman. 2001. Withdrawal strength of dowels in plywood and oriented strand board. Turkish J. of Agriculture and Forestry 25:319-327.

Lin, F. 1997. Computer-aided design system for the product engineering of sofa frames. PhD. thesis. Purdue Univ., West Lafayette, Indiana.

Zhang, J.L., Y.Z. Erdil, and C.A. Eckelman. 2002a. Lateral holding strength of dowel joints constructed of plywood and oriented strandboard. Forest Prod. J. 52(7/8):83-89.

--, --, and --. 2002b. Torsional strength of dowel joints constructed of plywood and oriented strandboard. Forest Prod. J. 52(10):89-94.

Yusuf Ziya Erdil

Ali Kasal

Carl Eckelman *

The authors are, respectively, Associate Professor and Assistant Professor, Dept. of Wood Sci. and Furniture Design, Mugla Univ., Mugla, Turkey (yziya@mu.edu.tr, alikasal@mu.edu.tr); and Professor of Wood Sci., Dept. of Forestry and Natural Resources, Purdue Univ., West Lafayette, Indiana (eckelmac@purdue.edu). This paper was received for publication in October 2007. Article No. 10426.

* Forest Products Society Member.
Table 1.--Summary of performance acceptance levels of GSA.

 Light service acceptance level

 Test Cyclic Static

 (pounds per cylinder)

Seat load foundation 300 600
Backrest foundation 112.5 225
Backrest frame 75 150
Front to back load on back leg 150 300
Side load on arms 75 150
Side load on legs 200 400

 Medium service acceptance level

 Test Cyclic Static

 (pounds per cylinder)

Seat load foundation 375 750
Backrest foundation 125 250
Backrest frame 100 200
Front to back load on back leg 200 400
Side load on arms 150 300
Side load on legs 250 500

 Heavy service acceptance level

 Test Cyclic Static

 (pounds per cylinder)

Seat load foundation 412.5 825
Backrest foundation 150 300
Backrest frame 150 300
Front to back load on back leg 300 600
Side load on arms 200 400
Side load on legs 350 700

Table 2.--Some physical and mechanical properties
of the materials used in the hypothetical frames.

 Flatwise bending

 Parallel to the long dimension

Materials Density Bending moment MOR MOE

 (Pct) (in-lb) (psi)

OSB 46.90 2,745 4,343 873133
HPLY 36.30 5,607 7,353 1115508
SPLY 34.80 2,592 5,916 627317

 Flatwise bending

 Perpendicular to the long dimension

Materials Bending moment MOR MOE

 (in-lb) (psi)

OSB 1,728 2,737 312291
HPLY 2,853 5,429 513432
SPLY 2,583 4,991 721145

 Edgewise bending

 Parallel to the long dimension

Materials Bending moment MOR MOE

 (in-lb) (psi)

OSB 7,299 3,162 394660
HPLY 15,093 6,845 490243
SPLY 10,764 4,991 412963

Table 3.--The subsystems and joints analyzed in this study.

 Subsystems Joint type Loading direction

Seat system Front rail to stump Vertical
 Horizontal sidethrust
 Out of plane
 Stretcher to front rail Out of plane
 or back rail

Side frame system Back post to arm Vertical
 Horizontal front to
 back
 Side rail to back post Horizontal front to
 or stump back

Back system Top rail to back post Vertical
 Horizontal

Center rail system Center rail to side slat Vertical / horizontal
 Center rail brace to Vertical / horizontal
 interior upright

Table 4.--Estimated joint strength capacities along
with design loads for the three stated levels of service.

 Loading Estimated static
Materials direction Rail width joint strength
 (inches)

OSB Vertical 4 1,063 lbs
 Horizontal 4 1,356 in-lb
 6 3,012 in-lb
 Out of plane (a) 4 1,035 in-lb

HPLY Vertical 4 1,394 lbs
 Horizontal 4 4,524 in-lb
 6 7,668 in-lb
 Out of plane 4 1,436 in-lb

SPLY Vertical 4 1,312 lbs
 Horizontal 4 3,430 in-lb
 6 5,900 in-lb
 Out of plane 4 1,480 in-lb

 Calculated static
 load requirement

 Light service
 Loading
Materials direction Force/moment Result

OSB Vertical 900lbs Passed
 Horizontal 2,100 in-lb Failed
 2,100 in-lb Passed
 Out of plane (a) NA (b) NA

HPLY Vertical 900lbs Passed
 Horizontal 2,100 in-lb Passed
 2,100 in-lb Passed
 Out of plane NA NA

SPLY Vertical 900 lbs Passed
 Horizontal 2,100 in-lb Passed
 2,100 in-lb Passed
 Out of plane NA NA

 Calculated static
 load requirement

 Medium service
 Loading
Materials direction Force/moment Result

OSB Vertical 1,125 lbs Failed
 Horizontal 4,200 in-lb Failed
 4,200 in-lb Failed
 Out of plane (a) 1,125 in-lb Failed

HPLY Vertical 1,125 lbs Passed
 Horizontal 4,200 in-lb Passed
 4,200 in-lb Passed
 Out of plane 1,125 in-lb Passed

SPLY Vertical 1,125 lbs Passed
 Horizontal 4,200 in-lb Failed
 4,200 in-lb Passed
 Out of plane 1,125 in-lb Passed

 Calculated static
 load requirement

 Heavy service
 Loading
Materials direction Force/moment Result

OSB Vertical 1,238 lbs Failed
 Horizontal 5,600 in-lb Failed
 5,600 in-lb Failed
 Out of plane (a) NA NA

HPLY Vertical 1,238 lbs Passed
 Horizontal 5,600 in-lb Failed
 5,600 in-lb Passed
 Out of plane NA NA

SPLY Vertical 1,238 lbs Passed
 Horizontal 5,600 in-lb Failed
 5,600 in-lb Passed
 Out of plane NA NA

(a) There is no specified acceptance
level for this type of loading.

(b) NA = Not applicable.

Table 5.--Results for back post to arm, side rail to back post or
stump, top rail to back post joints under vertical, horizontal, and
in-plane bending loadings.

 Loading Estimated static
Joint type direction Materials joint strength

Back post Vertical OSB 650 lbs
 to arm HPLY 881 lbs
 SPLY 961 lbs

 Horizontal OSB 1,532 lbs
 HPLY 1,518 lbs
 SPLY 1,220 lbs

Side rail In plane OSB 1,915 in-lb
 to back HPLY 1,898 in-lb
 post SPLY 1,525 in-lb

Top rail to Vertical OSB 1,063 lbs
 back post HPLY 1,394 lbs
 SPLY 1,312 lbs

 Horizontal OSB 325 lbs
 HPLY 450 lbs
 SPLY 480 lbs

 Calculated static
 load requirement

 Light service
 Loading
Joint type direction Materials Force/moment Result

Back post Vertical OSB 600 lbs Passed
 to arm HPLY 600 lbs Passed
 SPLY 600 lbs Passed

 Horizontal OSB 482 lbs Passed
 HPLY 482 lbs Passed
 SPLY 482 lbs Passed

Side rail In plane OSB 3,375 in-lb Failed
 to back HPLY 3,375 in-lb Failed
 post SPLY 3,375 in-lb Failed

Top rail to Vertical OSB 900 lbs Passed
 back post HPLY 900 lbs Passed
 SPLY 900 lbs Passed

 Horizontal OSB 225 lbs Passed
 HPLY 225 lbs Passed
 SPLY 225 lbs Passed

 Calculated static
 load requirement

 Medium service
 Loading
Joint type direction Materials Force/moment Result

Back post Vertical OSB 750 lbs Failed
 to arm HPLY 750 lbs Passed
 SPLY 750 lbs Passed

 Horizontal OSB 643 lbs Passed
 HPLY 643 lbs Passed
 SPLY 643 lbs Passed

Side rail In plane OSB 4,500 in-lb Failed
 to back HPLY 4,500 in-lb Failed
 post SPLY 4,500 in-lb Failed

Top rail to Vertical OSB 1,125 lbs Failed
 back post HPLY 1,125 lbs Passed
 SPLY 1,125 lbs Passed

 Horizontal OSB 300 lbs Passed
 HPLY 300 lbs Passed
 SPLY 300 lbs Passed

 Calculated static
 load requirement

 Heavy service
 Loading
Joint type direction Materials Force/moment Result

Back post Vertical OSB 825 lbs Failed
 to arm HPLY 825 lbs Passed
 SPLY 825 lbs Passed

 Horizontal OSB 964 lbs Passed
 HPLY 964 lbs Passed
 SPLY 964 lbs Passed

Side rail In plane OSB 6,750 in-lb Failed
 to back HPLY 6,750 in-lb Failed
 post SPLY 6,750 in-lb Failed

Top rail to Vertical OSB 1,238 lbs Failed
 back post HPLY 1,238 lbs Passed
 SPLY 1,238 lbs Passed

 Horizontal OSB 480 lbs Failed
 HPLY 480 lbs Passed
 SPLY 480 lbs Passed
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Author:Erdil, Yusuf Ziya; Kasal, Ali; Eckelman, Carl
Publication:Forest Products Journal
Geographic Code:1USA
Date:Jul 1, 2008
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