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Design and construction of school work tables for developing countries.

Abstract

Cyclic tests were conducted to determine the strength and durability of two types of school work tables designed for use in developing countries which were constructed with round mortise and tenon joints. The frames were constructed largely of material that is often discarded as waste, such as sawmill edgings or discarded building materials or from material cut from the stems of small-diameter plantation thinnings. The tops were constructed of medium density fiberboard. Initial frame designs were first analyzed under the action of representative static service loads to determine the forces and moments acting on the joints, and the joints and members were then designed accordingly. The resulting frames were then subjected to cyclic front-to-back loads and cyclic side-thrust loads to determine their resistance to representative repeated in-service loading. Results indicated that the tables could be classified as medium duty when compared to tables used in university libraries.

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In many parts of the world, there is a need for well-designed school furniture that may be easily constructed from local materials either by cottage industries or through factory production. Such furniture includes student and teacher chairs, desks, cabinets, and work tables. In previous papers, the design, construction, and testing of chairs, desks, bookcases, and cabinets has been reported (Haviarova et al. 2001a, 2001b; Eckelman et al. 2003; Tankut et al. 2003, 2007; Eckelman and Haviarova 2006). In this paper, the design, construction, and testing of two types of tables are described that are suitable for use as work tables by students or teachers.

Table frames can be constructed of material that is often discarded as waste, such as sawmill edgings or discarded building materials or from material cut from the stems of small-diameter plantation thinnings. In particular, the first type of table described was constructed from material ripped from salvage 2 by 4s left behind at a building site. The table tops were constructed of medium density fiberboard (MDF) but relatively thin panel materials can also be used. Because of their simplicity, inherent ease of quality control, and durability, round mortise and tenon joints were used in the construction of both tables.

Table design and construction

The design and construction of the two types of tables are shown in Figures 1 and 2. Two tables of the first type were constructed of southern pine (Pinus sp.) in order to evaluate what is often available as scrap material. Likewise, two tables of the second type were constructed of yellow-poplar (Liriodendron tulipifera) in order to evaluate a lower strength hardwood species. All of the wood was visually inspected to eliminate severe defects. The wood was maintained at 7 percent moisture content (MC).

Round mortise and tenon joints were used in the construction of the tables. Mortises were drilled to a diameter slightly less than that of the tenons in order to obtain a "force" fit. (In general, a tenon could be freely inserted two-thirds of its length into the mortise before significant force was required to seat it further.) The walls of the mortises were liberally coated with a 42 percent solids polyvinyl acetate (PVA) resin adhesive, and the tenons were inserted into the mortises. Pipe clamps were used to pull the assemblies together. Following assembly, the frames were maintained at 7 percent MC.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The first type of table, shown in Figure 1, was constructed of southern yellow pine. The flame measured 42 inches long by 24 inches wide by 24 inches high. All of the members measured 1.5 by 1.5 inches in cross section except for the two cross rails that support the top. These two members measured 1.5 by 2.25 inches in cross section; their purpose was to provide support for the relatively thin tops, or tops that are prone to "creep" under load. Other member sizes could be used in the construction of this type of table, but it was specifically designed to make use of nominal 2 by 4 scraps left behind at building sites. In addition, the table can be constructed with other dimensions to meet specific classroom needs since only the lengths of the legs, longitudinal rails, and stretchers are affected.

Tenons were cut with a 0.875-inch deep hole saw and measured 0.72 inches in diameter by 1.5 inches long. This diameter was chosen because it was estimated that smaller diameter tenons would lack sufficient moment capacity, whereas mortises for larger diameter tenons would unduly weaken the legs.

The top was constructed of 0.75-inch-thick MDF that measured 48 inches long by 28 inches wide. It was attached to the flame by means of four flat-head carriage bolts as shown in Figure 1. Only two cross braces were used in the table tested, but additional cross-brace supports could be added if the top were to be constructed of another relatively thin panel material, such as plywood left behind at a work site.

The second, more conventional, type of table, shown in Figure 2, was constructed of yellow-poplar. The main frame measured 44 inches long by 32 inches wide by 24.5 inches high. The top was constructed of MDF that measured 48 inches long by 36 inches wide and was attached to the frame by means of four flat-head carriage bolts. It was supported at mid length by a single cross brace; additional cross braces could be added if needed.

The legs measured 2 by 2 inches in cross section, rails (aprons) were 2.25 inches deep by 1 inch thick, and stretchers were 1.5 inches deep by 1 inch thick. Tenons measured 0.72 inches in diameter by 1.5 inches long. Due to the greater cross section of the legs, a larger tenon diameter could have been used. But, it was anticipated that somewhat thinner rail and stretcher members might also be used in the table construction and therefore, it was useful to evaluate the suitability of the 0.72-inch-diameter tenons.

Tenons on the ends of the front and back stretchers along with the tenons on the ends of the side stretchers were located off-center, as shown in Figure 2, in order to allow for maximum leg room. Front and back rail tenons were centered on the ends of the rails so that the corresponding leg mortises could be located a slightly greater distance from the end of the leg (Fig. 2). Side-rail tenons were located off-center in order to avoid interference with the tenons of the front and back rails.

Product engineering

When in use tables are subjected to front-to-back as well as side-thrust forces exerted by users pushing against the top. Experience with university library tables indicates that medium-duty tables are able to resist repeated application of a 200-pound force in either direction (Eckelman 1977). Grade school and high school classroom service would be expected to be less severe than college library service. Thus, structural capacity, or near capacity, to resist repeated application of 200-pound loads should be an excellent predictor of satisfactory field performance in less demanding grade school environments.

When front-to-back forces are applied to the top of the first type of table, critical points of concern are the leg-to-side-stretcher connections, the leg-to-side-rail connections, and the center-post-to-side-rail connections. In the case of end-to-end loading, critical points of concern include the front- and back-rail-to-leg-connections and the upper- and lower-center-rail-to-center-post connections. To evaluate the capacity of the flame at these points, structural analyses of the table flame were conducted to determine the forces and moments acting at these points.

The first type of table frame, which was constructed of southern pine, was first analyzed under the action of two 100-pound loads applied in the front-to-back direction (similar to the manner shown in Fig. 3(a)); it was next analyzed under the action of two 100-pound loads applied in the end-to-end direction (Fig. 3(b)). Based on past experience, semirigid connection factors of 5.0 x [10.sup.-5] rad/in-lb were assumed for the connections.

Under the action of two front-to-back forces of 100 pounds each applied to the top of the table, the absolute values of the lateral shear forces acting on the tenons of the leg-to-side-rail and post-to-side-rail connections ranged from 90.7 to 98.0 pounds; the absolute values of the bending moments acting on these tenons ranged from 313 to 390 in-lb. Similarly, the shear and bending moments acting on the post-to-side-stretcher connections amounted to 98 pounds and 170 in-lb, respectively. The bending moments acting on the side-stretcher to leg connections ranged from 370 in-lb for the front leg connection to 482 in-lb for the rear leg connection. The axial and shear forces acting on the front side-stretcher connection amounted to 92.5 and 67.8 pounds, respectively. The axial and shear forces acting on the rear connection amounted to 191 and 83.1 pounds, respectively. Finally, the bending moments acting on the rear legs at the leg-to-side-stretcher connections amounted to 1,525 in-lb.

[FIGURE 3 OMITTED]

Under the action of two end-to-end side-thrust forces of 100 pounds each applied to the top of the second pine table tested (Fig. 3(b)), the absolute values of the bending moments acting on the tenons of the longitudinal rail-to-side-frame connections ranged from 263 in-lb for the front and rear edge-rail-to-side-rail tenons to 500 in-lb for the front- and back-rail-to-leg tenons. The absolute values of the largest shear force and bending moment acting on the post-to-side-rail connections were 194 pounds and 46 in-lb, respectively. Also, the bending moments acting on the legs at the right side of the table amounted to 1,525 in-lb at the leg-to-side-stretcher connection, 1,200 in-lb at the leg-to-front-rail connections, and 265 in-lb at the leg-to-side-rail connections. Finally, the axial forces acting on the front and back edge rails and the front and back rails were 98 and 156 pounds, respectively. The axial forces acting on the top and bottom center rail were 278 and 372 pounds, respectively. This result indicates that the center-post/center-rail frame functions effectively as a stiffener against end-to-end loads.

Table legs can be weakened when the mortises are machined in the legs both in the front-to-back and in the side direction. The stress acting on the legs in the front-to-back direction at the leg-to-end-stretcher joints may be estimated by the following expression (Eckelman et al. 2002):

s = 6F/(w - d)([w.sup.2]) [1]

where:

F = the ultimate bending moment (in-lb),

w = the width of the leg (in.),

d = the diameter of the mortise (in.), and

s = the modulus of rupture (MOR) of the wood (psi).

For a floor reaction force of 100 pounds acting from back to front on the legs, Figure 3(b), the stress developed in the legs at these joints is:

s = 6 x 1525/(1.5 - 0.72)([1.5.sup.2]) = 5,214 psi.

Similarly, for a lateral floor reaction force of 100 pounds acting sideways on the legs, the stress developed in the legs at this joint may be estimated by the expression:

s = 6F/([w.sup.3] - [wd.sup.2]) {2]

Thus, for a 100-pound lateral floor reaction force,

s = 6 x 100 x 15.25/([1.5.sup.3] - 1.5 x [0.72.sup.2]) = 3,523 psi.

The average MOR of shortleaf, loblolly, and longleaf pine at 12 percent MC is 13,466 psi, or, 16,160 psi at 7 percent MC. These results indicate that legs are highly stressed at these joints. Thus, the legs should be clear of defects at these points.

The bending moment capacities of the tenons themselves may be estimated by means of the following form of the flexure formula:

[F.sub.T] = 1.18 x ([pi] x [D.sup.3]/32) x s [3]

where:

[F.sub.T] = the bending moment capacity of the tenon (in-lb),

s = the MOR of the wood of which the tenon is constructed (psi),

D = the diameter of the tenon (in), and

1.18 = a form factor for round beams (Wangaard 1950).

Thus, the bending moment capacity of the tenons themselves is estimated to be:

[F.sub.T] = 1.18 x ([pi] x [(0.72).sup.3]/32) x 16,160 = 700 in-lb

All of the tenons have shoulders, however, which substantially increase their moment capacity. The bending moment capacities of joints with shouldered tenons may be determined by means of the expression:

[F.sub.J] = 0.934 x 2w/[D.sup.1.66] x [F.sub.T] [4]

where:

[F.sub.J] = the bending moment capacity of the joint and

w = the distance from the longitudinal axis of the tenon to the bearing edge of the shoulder (Eckelman et al. 2006).

Carrying out these operations gives:

[F.sub.J] = 0.934 X [(0.72).sup.1.66] x 700 = 1,692 in-lb

Thus, it can be seen that the bending moment capacity of both the tenon and the joint is greater than the maximum moment of 500 in-lb generated by the 100 pound front-to-back and side-thrust loads On the tenon connections.

Finally, the leg-to-side-rail joints pose a more complex problem because the centers of the mortises for the front and back stretchers are located only 1.5 inches below the tenon machined on the upper end of the leg. It must be assumed that the proximity of the mortise to the base of the tenon lessens both the moment capacity and the lateral shear resistance of the tenon; however, test data are lacking to quantify this effect. Hence, their adequacy must be determined by performance testing.

The front and back stretchers of the second type of table (constructed of yellow-poplar) along with the bottom stretchers of the side frames were located as high as possible in order to provide maximum leg room. As a result, the withdrawal forces acting on the tenons of the front- and back-rail-to-leg and side-rail-to-leg joints would be expected to be high so that the frames might be expected to fail at these points. Also, the bending moments acting on the legs at the front-and end-stretcher-to-leg connections are of concern.

Two frame analyses were conducted. The first analysis was carried out with two 100-pound loads applied in the front-to-back direction (similar to the manner shown in Fig. 3(a)); the second analysis was carried out with two 100-pound loads applied in the end-to-end direction (Fig. 3(b)). Based on, past experience, semi-rigid connection factors of 2.4 X [10.sup.-5] rad/ in-lb were used for the 2.25-inch rails with off-center tenons when the shoulder of a rail resists rotation (Fig. 4(a),) and 6.6 X [10.sup.-5] rad/in-lb when it does not (Fig. 4(b)); however, a semi-rigid connection factor of 4.4 x [10.sup.-5] rad/in-lb was used for 2.25-inch rails with centered tenons. Similarly, a semi-rigid connection factor of 4.4 x [10.sup.-5] rad/in-lb was used for the 1.5-inch stretchers (with off-center tenons) when a shoulder resists rotation and 6.6 X [10.sup.-5] rad/in-lb when it does not.

The bending moment acting on the legs at the side-stretcher-to-leg connection under the action of two front-to-back forces of 100 pounds each applied to the top of the table (Fig. 3(a)) is 100 lb X 18.375 inches, or, 1,838 in-lb. Under the simplifying assumption that the mortises extend completely through the leg, the ultimate moment capacity of the leg, F, may be estimated by means of the expression (Eckelman et al. 2002):

F = 2 x [(w - d/2).sup.2] (w + d/2)[s.sub.C]

where:

[s.sub.c] = the compressive strength of the wood parallel to the grain (psi), w = the width of the leg (in), and d = the diameter of the mortise (in).

[FIGURE 4 OMITTED]

Adjusting the Wood Handbook (USDA 1999) value for compression perpendicular to the grain of 5,540 psi at 12 percent MC to 7 percent MC gives 5,540 x 1.3 = 7,200 psi. Substituting the appropriate values into the above expression and solving gives:

F = 2 x [(2 - 0.72/2).sup.2](2 - 0.72/2) x 7,200 = 8,022 in-lb

Thus, the leg design would be satisfactory assuming there are no major defects in the leg.

The absolute value of the bending moments acting on the side-stretcher-to-leg tenons ranged from 529 in-lb for the front tenons to 433 in-lb for the rear tenons. The bending moments acting on the side-rail-to-leg tenons ranged from 1,020 in-lb for the front tenons to 464 in-lb for the rear tenons. The axial compressive force acting on the side stretcher was 321 pounds, whereas the axial tensile force acting on the side rail was 221 pounds. Previous research with essentially identical joints (Eckelman et al. 2004) indicates that the withdrawal capacity of the tenons should average 1,950 pounds. Hence, these joints should have an ample factor of safety with respect to axial forces.

The bending moment capacity of the tenons themselves is estimated to be:

[F.sub.T] = 1.18 x [([pi] x [(0.72).sup.3]/32) x 12,120 = 525 in-lb

which agrees closely with test values previously obtained (Eckelman et al. 2006). Thus, the estimated moment capacity of the rear side-stretcher and rear side side-rail tenons is greater than the calculated moments acting on them.

The moments acting on the front tenons of the end rails exceed this value, however, because of the greater stiffness of the joint owing to its shoulder. The bending capacity of this joint may be conservatively estimated based on a consideration of the withdrawal resistance of the tenon by means of the expression:

F = 0.894 X w X T

where:

F = the estimated bending moment capacity,

T = the withdrawal capacity of the tenon, and

w = the distance from the longitudinal axis of the tenon to the opposite bearing edge of the rail (Eckelman et al. 2006).

Carrying out this operation gives:

F = 0.894 x (2.25 - 0.375) X 1,950 = 3,269 in-lb

Similarly, the bending moment capacity of the end stretchers when loaded in a similar manner is:

F = 0.894 x (1.50 - 0.375) x 1,950 = 1,961 in-lb

Thus, both estimates exceed the moments imposed by the front-to-back loads.

Under the action of two end-to-end side-thrust forces of 100 pounds each applied to the top of the table (Fig. 3(b)), the bending moment acting on the legs at the front-stretcher-to-leg joints is 100 x 19.875 in-lb. This value is only 19.875/ 18.375, or 8 percent greater than the moment for front-to-back loading, and hence, the leg design is again satisfactory. The moments acting on the ends of the front and rear rail are 703 in-lb and 707 in-lb, respectively, whereas the moments acting on the ends of the front and rear stretchers are 561 and 478 in-lb, respectively. Also, the axial tension force acting on the front and rear rail is 229 pounds, whereas the axial compressive force acting on the front and rear stretcher is 329 pounds. Thus, these values are also less than the estimated joint capacities.

Overall, the results of the analyses indicate that both sets of table frames should be able to resist a 200-pound load applied to the top in either the front-to-back or end-to-end direction. A point of concern, however, was the nearness of the front- and back-rail to leg mortises to the root of the tenons on the legs.

Performance tests

Performance tests were conducted to further evaluate the strength and durability of the two designs as well as to discover weak points in the design. The method of test used was the cyclic stepped load test developed by Eckelman (1988). The two tests used were the cyclic front-to-back load test and the cyclic end-thrust test.

The front-to-back load test consists of pushing from front to back on the top of the table. This action produces internal resisting forces in the end frames of the table similar to those caused by the action of someone pushing on the table when seated at the table or when pushing the table across the floor. The table was mounted for testing as shown in Figure 3(a). Reaction brackets are placed behind each of the back legs to prevent the table from sliding backward. A strap is then passed over the top of the table from front to back and attached to a small clevis connected to the rod end of an air cylinder that applies loads to the top. The other end of the belt is dropped over the front edge of the table top, allowed to hang vertically, and attached to a floor fitting located directly below the front edge of the table top. As the table top is pulled to the rear, the table tends to tip over backward. As it begins to tilt slightly, however, its motion is resisted by that portion of the strap that hangs vertically from the front edge of the table top and is anchored below; the vertical portion of the strap always provides the exact force needed to keep the table from overturning. Horizontal loads are applied to the table at a rate of 20 cycles per minute. Tests are conducted until a frame suffers disabling damage. The horizontal side load (or end-thrust) test on tables, Figure 3(b), is identical to the front-to-back load test except that the load is applied to the table top in an end-to-end direction, and reaction brackets are placed at one end of the table rather than behind the table.

The tests began at the 50-pound load level. Loads were increased by 25 pounds after 25,000 cycles had been completed at each preceding load level. Tests were continued until a table suffered disabling damage. Results of the tests are presented in Table 1.

Results and discussion

The first style of table (southern pine) (Fig. 1) was subjected to front-to-back loading (in the [X.sub.1]-direction). Presumably, failure started with the splitting of the top end of a rear leg at the leg-to-end-rail joint after 615 cycles had been completed at the 2 x 125-pound load level (at the 250-1b load level). The estimated bending moment acting on the joint at this load level amounted to 648 in-lb; the estimated shear force amounted to 113.5 pounds. Once this occurred, the end-stretcher-to-back-leg joint failed at a bending moment level of 603 in-lb and a vertical shear level of 104 pounds. These results indicate that the end-rail-to-leg joint is essentially a "weak link" in the construction. Studies are needed to evaluate the lateral shear characteristics of such tenons, both with and without adjacent mortises, in order to determine how the joints may be constructed to minimize failures at this point.

The second southern pine table (first style) was subjected to end-to-end, or, side-thrust loading in the [X.sub.2]-direction (Fig. 3(b)). Testing was discontinued after 20,300 cycles had been completed at the 175-pound load level due to fracture of the post at the post-to-end-stretcher connection followed immediately by failure of the legs at the front and back rail connections. Basically, the lower end of the post split out laterally in the [X.sub.2]-direction as did the tenon on the end of the rear leg. The top of the front leg underwent a more general tension perpendicular to the grain failure, however, which originated at the top of the leg and terminated at a point just above the end-stretcher-to-leg connection.

The absolute value of the bending moments acting on the tops of the legs at this load level was 232 in-lb, whereas the bending moment acting on the legs just above the front- and back-rail-to-leg joints was 617 in-lb. The lateral shear force acting on each leg-to-rail connection was 171 pounds. Similarly, the bending moment acting on the lower end of the post (at the post-to-end-stretcher connection) was 162 in-lb, whereas the bending moment acting on the post just below the lower center rail was 711 in-lb. The corresponding lateral shear forces acting at these locations were 244 pounds. This test again showed that the key joints are the post-to-end-stretcher connections and the top rail to leg joints.

The first (style 2) yellow-poplar table was subjected to a front-to-back load test in the negative [X.sub.1]-direction. Testing was discontinued after 860 cycles had been completed at the 200-pound load level due to sudden excessive deflection of the frame as a whole. Splitting of one end rail at the end-rail-to-rear-leg connection at a point just above the tenon was first observed. This was followed by withdrawal of the tenon on the other end of the rail from the front leg.

Subsequently failure of an end stretcher on the other end frame was observed. Splitting of the rail likely occurred because the top was bolted to the rail at a point about 2.5 inches from the end of the rail. This prevented the rail from moving and allowed the split to occur. The racking action of the frame caused the off-center end-rail-to-front-leg tenon to partially withdraw from the mortise. Both of these results indicate that, where possible, tenons should be symmetrically located on the end of a member rather than off center.

The structural analysis of the frame indicated that for the off-center tenon configuration used in these tests, with 100-pound loads acting in a front-to-back direction (negative [X.sub.1]-direction) on each end frame, the absolute bending moment acting on the front end of the end-rail was 1,020 in-lb, whereas the moment acting on the tenon on the rear end of the rail was only 464 in-lb. The moment acting on the front end-stretcher-to-leg joint was 529 in-lb, whereas the moment acting on the rear end of the stretcher was only 433 in-lb. These results indicate that use of off-center tenons resulted in a decidedly unequal distribution of moment.

Calculations previously given indicated that the bending moment capacity of the tenons themselves is 525 in-lb, which is only slightly greater than the moments acting on the tenons in the rear side-rail and side-stretcher to leg joints.

The withdrawal force acting on the tenon as a result of the 1,020 in-lb bending moment may be estimated by rearranging the terms of the expression used above to give T= F/(0.894 X w). Substituting the appropriate values gives:

T = 1,020/0.894 X (2.25 - 0.375) = 609 lb

Thus, the estimated withdrawal force is less than the withdrawal resistance of the tenon. Since the rails and stretchers were 1 inch thick and the legs were 2 inches square, larger diameter tenons could have been used, perhaps 0.875 or 0.938 inch, to take advantage of the material used in order to obtain a more robust construction.

The second (style 2) yellow-poplar table was subjected to repetitive side-thrust loading. Testing was terminated after 9,000 cycles had been completed at the 250-pound load level due to sudden excessive deflection caused by partial withdrawal of the tenons from the mortises in the front-rail-to-leg joints. Splitting of the front and back rails did not occur. For this case, the maximum estimated bending moment acting on the front- and back-rail-to-leg joints was 884 in-lb. The axial withdrawal force acting on the tenons of the rails was 286 pounds.

Likewise, the estimated moment for each front- and rear-stretcher-to-left-leg joint was 701 in-lb compared to 598 in-lb for the right leg joints. The compressive axial force acting on the stretcher was 411 pounds.

Overall, the first style of table was nearly able to meet the suggested repetitive load criteria for medium-duty university library tables. These tests indicate that this design has sufficient strength for grade school classrooms. The second style of table essentially met the requirements for medium-duty tables, and hence this table was also judged to be sufficiently robust for classroom use.

Conclusions

Results of the tests indicate that round mortise and tenon joints may be used to construct strong durable classroom work tables of both conventional and non-conventional design. Because of their simplicity, inherent ease of quality control, and durability, these joints are especially well-suited for construction of school furniture in underdeveloped regions of the world. Use of intermediate cross braces to support the tops allows the use of relatively thin table top materials, whereas the frames may be constructed of essentially discarded material left behind at building sites as well as from lower strength hardwood mill scrap.

From a service viewpoint, the tables may be classified as essentially medium duty when compared to tables used in university libraries. Furthermore, the frames of these tables should require little maintenance since the joints would not be expected to loosen in service. Clear material should be used in the area of the leg-to-stretcher joints because of the high stresses at these points. The ends of the members should also be clear so that tenons cut on the ends of the member will be free of defects-the post-to-side-stretcher joint of the first style of frame is of particular concern along with the leg-to-end-rail connections. Axial withdrawal forces acting on the tenons of the front and back rail and the side-rail-to-leg joints of the second table style are high and thus need to be well glued.

The lateral shear strengths of the mortise and tenon connections are of concern and need to be determined. Of particular concern are members in which a secondary mortise is cut in the tenoned member near the root of the tenon.

Literature cited

Eckelman, C.A. 1988. Performance testing of furniture. Part II: A multipurpose universal structural performance test method. Forest Prod. J. 38(4):13-18.

--, Y.Z. Erdil, and E. Haviarova. 2002. Effect of cross holes on the bending strength of chair and table legs. Forest Prod. J. 52(5):67-70. --, -- and -- 2003. School chairs for developing countries: Designing for strength and durability, simplicity, and ease of construction. Forest Prod. J. 53(2):63-70.

Eckelman, C., Y. Erdil, and E. Haviarova. 2006. Effect of shoulders on the bending moment capacity of round mortise and tenon joints. Forest Prod. J. 56(1):82-86.

--, E. Haviarova, A. Tankut, N. Denizli, H. Akcay, and Y. Erdil. 2004. Withdrawal capacity of pinned and unpinned round mortise and tenon furniture Joints. Forest Prod. J. 54(12): 185-191.

Eckelman, C.A. and E. Haviarova. 2006. Performance tests of school chairs constructed with round mortise and tenon joints. Forest Prod. J. 56(3):5137.

Haviarova, E., C. Eckelman, and Y. Erdil. 2001a. Design and testing of wood school desk frames suitable for production by low tech nology methods from waste wood residues. Forest Prod. J. 51(5): 79-88.

--, --, and --. 2001b. Design and testing of environmentally friendly wood school chairs for developing countries. Forest Prod. J. 51 (3):58-64.

Tankut, A., C. Eckelman, and H. Gibson. 2003. Design and testing of bookcase frames constructed with round mortise and tenon joints. Forest Prod. J. 53(7/8):80-86.

Tankut, A.N., N. Tankut, and C.A. Eckelman. 2007. Design and testing of wall cabinet frames constructed with round mortise and tenon joints. Forest Prod. J. 57(3):18-22.

USDA Forest Serv. Forest Products Lab. 1999. Wood Handbook: Wood as an Engineering Material. GTR FPL-113. Forest Products Lab., Madison, Wisconsin. 463 pp.

Wangaard, F.F. 1950. The Mechanical Properties of Wood. John Wiley and Sons, New York. 377 pp.

Yusuf Erdil *

Carl Eckelman *

Eva Haviarova *

The authors are, respectively, Associate Professor, Dept. of Wood Sci. and Furniture Design, Mugla Univ., Mugla, Turkey (yziya@mu.edu.tr), and Professor and Assistant Professor, Dept. of Forestry and Natural Resources, Purdue Univ., West Lafayette, Indiana (eckelmac@purdue.edu, ehaviar@purdue.edu). This paper was received for publication in July 2008. Article No. 10506.

* Forest Products Society Member.
Table 1.--Results of performance tests.

Table Initial Load Ultimate
 no. Wood species Type of test load increment load

 (lb)

 1 Southern pine Front-to-back 50 25 250
 2 Southern pine Side-thrust 50 25 175
 3 Yellow-poplar Front-to-back 50 25 200
 4 Yellow-poplar Side-thrust 50 25 250

Table
 no. Cycles at last load level Total cycles

 1 615 200,615
 2 20,300 145,300
 3 860 150,860
 4 9,000 209,000
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Author:Erdil, Yusuf; Eckelman, Carl; Haviarova, Eva
Publication:Forest Products Journal
Geographic Code:4EUUK
Date:Jan 1, 2009
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