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— Typical heel configuration used in construction of trusses and heel support positions used in testing of trusses.
Source publication
Throughout the world, there is a need for simple, strong, yet inexpensive connectors that can be used to fabricate trusses from natural small-diameter tree stems as well as squared stems without extensive premachining of the joint area. A connector that might satisfy these requirements is the through-bolt with cross-pipe heel connector. Tests were...
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... configurations of the trusses that represented these two types of trusses are 1 Presumably, the load capacities of these cross pipes could be calculated (Seeley and Smith, 1952) for use in truss design calculations; however, the yield stress of the material must be known, which is both a function of the yield point of the material itself and of the forming operations used to fabricate the pipe (Karren, 1967). shown in Figure 4. Variations in heel construction and sup- port conditions are shown in Figure 5. All of the trusses had a 30 degree slope. ...
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... sets 1 to 3 were of essentially identical construction, Figure 4a, except for the species of the chords, namely, (1) eastern pine, (2) red pine, and (3) southern yellow pine. Cross- pipe joint connectors, Figure 6, were constructed of 2.375- inch diameter by 4-inch long schedule 80 pipe; these were located in the heels as shown in Figure 5a. ...
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... set 4a was constructed of nominal 3.5-by 3.5-inch no. 2 southern yellow pine with 1.90-inch diameter by 4-inch long schedule 80 cross pipes located in the heels as shown in Fig- ure 5a. Truss set 4b was identical to 4a except for the cross pipes, which were reinforced with two 1.469-inch by 0.1-inch (nominal 9/16-inch) washers, Figure 6c. ...
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... set 5a (6 specimens) was constructed with 2&B East- ern pine chords and 2.375-inch diameter by 4-inch long schedule 80 cross pipes that were centered at the intersection of the lower surface of the top chord with the upper surface of the bottom chord, Figure 5b. Truss set 5b differed only in that the cross pipes were reinforced with two 1.90-inch by 1.5- inch schedule 80 cross pipes, Figure 6b. ...
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... set 6 was constructed of 5.5-inch diameter round white ash members with 2.375-inch diameter by 6-inch long schedule 80 cross pipes and two 1.90-inch diameter by 2.5- inch long schedule 80 inserts (similar to Figure 6b) located in the heels as shown in Figure 5b. A half-inch thick slab was sawn off one side (the inside truss surfaces) of the members to provide a reference surface for alignment of the holes in the members. ...
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... set 7a was constructed of 4-by 6-inch yellow-poplar members with 4.0-inch outside (nominal 3.5-inch) diameter by 6-inch long schedule 40 cross pipes that were centered at the intersection of the lower surface of the top chord with the upper surface of the bottom chord (Fig. 5b). Truss set 7b dif- fered from 7a in that each cross pipe was reinforced with two 3.5-inch outside diameter by 0.117-inch thick (nominal 1-1/2-inch) washers in a manner similar to that shown in Fig- ure 6c. Truss set 7c differed from 7a in that each cross pipe was reinforced with two white ash disks that measured 3.5 inches in diameter ...
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... (nominal 1-1/2-inch) washers in a manner similar to that shown in Fig- ure 6c. Truss set 7c differed from 7a in that each cross pipe was reinforced with two white ash disks that measured 3.5 inches in diameter by 2 inches thick. These disks were inserted in each end of a cross pipe with their grain direction parallel to that of the top chord (Fig. ...
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... set 8a was constructed ( Fig. 4b) of nominal 3.5-by 3.5-inch no. 2 & better eastern pine with 2.375-inch diameter by 4-inch long schedule 80 cross pipes centered at the inter- section of the lower surface of the top chord with the upper surface of the bottom chord, Figure 5d. Truss set 8b was iden- tical except that the cross pipes were reinforced with two 1.90- inch diameter by 1.5-inch long inserts (Fig. 6b). ...
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... set 9 was constructed of 5.5-inch diameter white ash members with 2.375-inch diameter by 6-inch long schedule 80 cross pipes and two 1.90-inch diameter by 2.5-inch long schedule 80 inserts (similar to Figure 6b); these were located in the heels of the truss as shown in Figure 5f. ...
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... set 10a (1 truss) was constructed of nominal 4.5-inch diameter red elm members with 2.375-inch diameter by 6-inch long schedule 80 cross pipes located in the heels as shown in Figure 5g. This heel configuration was used to po- sition the bolt through the bottom chord at a greater distance from the end of the chord. ...
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... set 10b (1 truss) was con- structed of 3.5-inch diameter (average) red elm members with 2.375-inch diameter by 4-inch long schedule 80 cross pipes. Truss set 10c was constructed of nominal 3.5-inch square 2&B eastern pine with 2.375-inch by 4-inch schedule 80 cross pipes located in the heels as shown in Figure 5c. Truss set 10d was identical to truss set 10c except for the cross pipes, which were constructed of schedule 40 pipe. ...
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... set 11a was constructed of nominal 1.5-by 3.5-inch southern yellow pine with 2.375-inch diameter by 2-inch long schedule 40 cross pipes centered at the midpoint along the length of the bottom chord heel taper as shown in Figure 5e. In addition, each heel cross pipe was attached to a second cross pipe (1.90-inch outside diameter by 2-inch long sched- ule 80), embedded in the bottom chord, by means of a length of threaded rod (Fig. 5e). ...
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... diameter by 2-inch long schedule 40 cross pipes centered at the midpoint along the length of the bottom chord heel taper as shown in Figure 5e. In addition, each heel cross pipe was attached to a second cross pipe (1.90-inch outside diameter by 2-inch long sched- ule 80), embedded in the bottom chord, by means of a length of threaded rod (Fig. 5e). Truss set 11b was constructed with schedule 80 instead of schedule 40 cross ...
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... were applied to a steel cylinder located in the peak of the truss. Trusses were supported at each end by 4-inch square by 6-inch long steel blocks as shown in Figure 5-normally centered directly below the cross pipes or at the ends of the bottom chord. Testing machine load-head move- ment-corresponding to gross deflection of the peak of a truss-was measured by means of an electronic digital gage. ...
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... the heel joints were constructed with 1.90 inch by 4-inch long cross pipes (truss set 4), positioned as shown in Figure 5a, (truss sets 4a & 4b) non-linear deformation was not observed below 10,500 pounds but was clearly observed at 11,500 pounds. Capacity of the cross pipes reinforced with washers was not determined owing to heel failures in the lower chord, but the washers exhibited linear behavior until the lower chords failed at an average of 12,233 pounds. ...
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... when the heel joints were constructed with 2.375 inch by 4-inch long schedule 40 cross pipes, the trusses de- flected linearly through 3,250 pounds. In contrast, when the heel joints were constructed with schedule 80 cross pipes (truss set 5) located as shown in Figure 5b, the trusses de- flected linearly through 7,500 pounds. When each cross pipe was reinforced with two 1.90-inch by 1.5-inch schedule 80 inserts, the trusses deflected linearly through 12,500 pounds. ...
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... when the heel joints were constructed with 4.0-inch diameter by 6-inch long schedule 40 cross pipes (truss set 7) as shown in Fig- ure 5b, the trusses deflected linearly through 7,000 pounds. When the pipes were reinforced with two wrought iron washers, the trusses deflected linearly through 21,500 pounds. ...
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... contrast, when the joints (truss set 11) were constructed as shown in Figure 5e with 2.375-inch by 2-inch long sched- ule 40 pipes, non-linear deformation occurred at about 4,500 pounds. In similar joints constructed with schedule 80 cross pipes, non-linear deformation occurred at about 7,500 pounds. ...
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... of the cross pipe occurs principally in the short arc formed between the top chord bolt and the lower chord through-bolt. Presumably, therefore, the through-bolt in the bottom chord contributes to the strength of this connec- tion by minimizing this arc and provides greater load capacity than the typical bolted heel connection shown in Figure 5d. ...
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... the heel joints (truss set 8c) were constructed as shown in Figure 5d, with 2.375 inch by 4-inch long schedule 40 cross pipes, non-linear deformation occurred above 2,100 pounds; testing was discontinued at 3,000 pounds owing to substantial ovalization of the cross pipes. Similarly, when the joints were constructed with 2.375-inch by 4-inch long sched- ule 80 cross pipes (truss set 8a), non-linear deformation oc- curred above 4,500 pounds; testing was stopped at an average load of 6,500 pounds. ...
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... white ash trusses (truss set 9) constructed as shown in Figure 5d with 2.375-inch diameter by 6-inch long schedule 80 cross pipes and two 1.90-inch diameter by 2.5-inch long schedule 80 inserts deflected linearly through 10,500 pounds. Testing was discontinued at an average peak load of 12,250 pounds owing to continued deformation of the cross pipes without increase in load. ...
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... the heel (truss set 10a, 10b) was constructed as shown in Figure 5c, tests were discontinued at the 10,000 and 6,000 pounds levels owing to deformation of the heels of the truss even though the cross pipes had not substantially deformed- presumably because the continuous length of threaded rod carried part of the load and reinforced the cross pipe. Like- wise, when the heel was constructed with 2.375-inch diameter by 4-inch long schedule 40 cross pipes (truss set 10c) and sup- ported as shown in Figure 5g, non-linear deformation oc- curred above 5,750 pounds; testing was discontinued at 6,250 pounds owing to substantial deformation without increase in load capacity. ...
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... the heel (truss set 10a, 10b) was constructed as shown in Figure 5c, tests were discontinued at the 10,000 and 6,000 pounds levels owing to deformation of the heels of the truss even though the cross pipes had not substantially deformed- presumably because the continuous length of threaded rod carried part of the load and reinforced the cross pipe. Like- wise, when the heel was constructed with 2.375-inch diameter by 4-inch long schedule 40 cross pipes (truss set 10c) and sup- ported as shown in Figure 5g, non-linear deformation oc- curred above 5,750 pounds; testing was discontinued at 6,250 pounds owing to substantial deformation without increase in load capacity. In the case of identical joints constructed with schedule 80 pipe (truss set 10c), non-linear deformation oc- curred above 8,000 pounds, and testing was terminated at 9,000 pounds because of deformation without increase in load. ...
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... a 2.375-inch by 6-inch long schedule 80 cross pipe with two 1.90-inch by 2.5-inch long schedule 80 inserts has a linear load capacity of about 10,500 pounds. For the heel support detail shown in Figure 5g, a 2.375-inch diameter by 4-inch long schedule 40 cross pipe has a linear load capacity of about 5,250 pounds, whereas a comparable schedule 80 cross pipe has a linear load capacity of about 8,000 pounds. Finally, for the heel detail shown in Figure 5e, a 2.375-inch by 2-inch long schedule 40 cross pipe has an estimated load capacity of about 4,500 pounds, whereas a comparable schedule 80 cross pipe has an estimated load capacity of 7,500 pounds. ...
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... the heel support detail shown in Figure 5g, a 2.375-inch diameter by 4-inch long schedule 40 cross pipe has a linear load capacity of about 5,250 pounds, whereas a comparable schedule 80 cross pipe has a linear load capacity of about 8,000 pounds. Finally, for the heel detail shown in Figure 5e, a 2.375-inch by 2-inch long schedule 40 cross pipe has an estimated load capacity of about 4,500 pounds, whereas a comparable schedule 80 cross pipe has an estimated load capacity of 7,500 pounds. ...
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Citations
A traditional wooden beam and column joint was revised using an embedded threaded rod with the assistance of dowels, and the structural performance of the joint in resisting the bending moment was examined in the study. Beam and column members of Japanese cedar and southern pine timber with a size of 120×120 mm were used to construct a T-structure which was then subjected to a cantilever load. The results indicated that the joint tightened with a threaded rod with 150 mm of embedded length in the side beam member showed a higher bending moment compared to those with 120- and 180-mm embedded lengths. The bending moment resistance of a joint in which a threaded rod was embedded at the upper location of the cross-section on the beam member was 4 times that at the lower location while exhibiting only 25.3% of the moment-rotation coefficient value. The bending moment capacity of joints tightened with a 60×60-mm washer was 40.2 and 36.2% higher than values of joints with 50×50-and 60×80-mm washers, respectively. The critical failure of a joint tightened with an embedded rod may have been due to the weak compressive strength perpendicular to the grain on the column member. When epoxy reinforcement was applied to the joint, the bending moment resistance of the Japanese cedar member joint with 2 embedded threaded rods improved 39.5%, and the internal rotation angle and moment-rotation coefficient were reduced by 21.6 and 40.6%, respectively. Overall, similar bending resistance values of beam and column joints assembled with both Japanese cedar and southern pine members were found after epoxy reinforcement was applied. The results also demonstrated a reduction of 68.4% in the moment-rotation coefficient for the joint with additional epoxy reinforcement.
The hardwood species European oak, European chestnut and black locust are hardly used for engineering structures in their naturally grown shape, although such a use is generally possible. From forest thinnings these hardwoods are available as low-cost material to a certain extent and their durability and remarkable strength can fulfil the demands of robust timber structures. However, the irregular shape of naturally grown logs and the subsequent complexity of connections inhibit engineering applications. Thus, there is a gap between the potential of an available low-cost material and the possibility of a value-added application. In order to bridge this gap the present contribution aims first at giving basic ideas to make naturally grown logs more calculable and second at presenting a modular screw connection. Hence, compression tests on naturally grown logs, screw withdrawal tests and tests on screw connections were performed. Based on the experimental results, strength models for the compression capacity and the withdrawal resistance of screws were developed and a high strength and ductile connection type was designed. The findings of the work may widen the possibilities in the engineering design of timber structures made of naturally grown logs.
Tests were conducted to determine the withdrawal capacities of 10-mm (nominal 3 =8-in.) and 15.9-mm (nominal 5 =8-in.) through-bolts with Diameter Nominal (DN) 15-mm (nominal 1/2-in.) and DN 25-mm (nominal 1-in.) pipe-nut connectors intended for use in light-timber frame construction. The capacity of unreinforced 15.9-mm through-bolts with DN 25-mm pipe-nut connectors was approximately 31.1 kN; the capacity of comparable reinforced connectors was approximately 71.2 kN. Likewise, the withdrawal capacity of smaller unreinforced 10-mm through-bolts with DN 15-mm pipe-nut connectors was approximately 13.3 kN; comparable reinforced connectors had a capacity of 17.8 kN. Similar 10-mm through-bolts with DN 10-mm pipe couplings had a capacity of 26.7 kN. Overall, results indicate that high-capacity joints can be constructed with through-bolt and pipe-nut connectors.
