TRUSS JOISTS HAVING EDGE PIN CONNECTORS
United States Patent 3857218
A truss joist having wood chords, connectors mounted on said chords, sheet metal and a plurality of metal strut members arranged diagonally between said chords joined to said connectors by metal pins which are partially embedded in transverse semi-circular channels cut in the inner faces of the chords.
US Patent References:
Apparatus for connecting the webs to the chords in trusses
Findleton - September 1956 - 2764108
Composite trussjoist with end bearing clips
Troutner - August 1966 - 3268251
COMPOSITE TRUSS JOIST WITH OFFSET BEARING
Troutner - January 1969 - 3422591
TIMBER TRUSS PLATE-FASTENER AND SYSTEM
Couch - June 1969 - 3449997
Apparatus for connecting the webs to the chords in trusses
Findleton - September 1956 - 2764108
Composite trussjoist with end bearing clips
Troutner - August 1966 - 3268251
COMPOSITE TRUSS JOIST WITH OFFSET BEARING
Troutner - January 1969 - 3422591
TIMBER TRUSS PLATE-FASTENER AND SYSTEM
Couch - June 1969 - 3449997
Application Number:
05/380215
Publication Date:
12/31/1974
Filing Date:
07/18/1973
View Patent Images:
Export Citation:
Assignee:
Simpson Manufacturing Co., Inc. (San Leandro, CA)
Primary Class:
Other Classes:
52/692
International Classes:
E04C3/292; E04C3/29; E04C3/18
Field of Search:
52/693,694,692,690,721,586,696,639-644,753E,751,752,753R 85/11,13
Primary Examiner:
Abbott, Frank L.
Assistant Examiner:
Friedman, Carl D.
Attorney, Agent or Firm:
Cypher, James P.
Claims:
I claim
1. A truss joist comprising:
2. A truss joist as described in claim 1 comprising:
3. A truss joist as described in claim 2 comprising:
4. A truss joist as described in claim 1 comprising:
5. A truss joist as described in claim 1 comprising:
6. A truss joist as described in claim 5 comprising:
7. A truss joist as described in claim 1 comprising:
8. A truss joist as described in claim 1 comprising:
9. A truss joist comprising:
1. A truss joist comprising:
2. A truss joist as described in claim 1 comprising:
3. A truss joist as described in claim 2 comprising:
4. A truss joist as described in claim 1 comprising:
5. A truss joist as described in claim 1 comprising:
6. A truss joist as described in claim 5 comprising:
7. A truss joist as described in claim 1 comprising:
8. A truss joist as described in claim 1 comprising:
9. A truss joist comprising:
Description:
BACKGROUND OF THE INVENTION
All steel trusses date back well over 100 years. Connections between the chords and webs were located on the center lines of the chords. Except for the generally known "light trusses" no significant new all-steel truss joists have been forthcoming. The market, particularly in the western states where lumber-based construction is more prevalent, requires cheaper trusses.
About twelve years ago, a composite chord came onto the market having wood chords and steel webs. Like the all-steel truss joists, the composite chord truss followed the established design of placing the web and chord connection at the center line of the chord. The design criteria required boring of holes through the center of the wood chord, usually through the width of the chord, thereby considerably weakening the chord in tension. Moreover, the boring of the holes and encapsulating the joint pin rendered the joint the weakest part of the design and dependent upon the wood grades for strength values.
Rapidly rising prices of wood and the increasing scarcity of wood having thet required strength characteristics, together with the need to span ever greater distances, has brought the composite wood-steel truss industry to a serious impasse.
Several design solutions have been advanced including specially laminated wood chords and more sophisticated end-bearing hardware. Both of these solutions, while partially accomplishing the increasing design goals has resulted in an unacceptable increase in cost.
SUMMARY OF THE INVENTION
The goal of the present invention is to substantially increase the spans possible with composite wood chord and steel struts at significantly lower costs in materials and fabrication.
The gist of the present invention is the use of edge pin connectors with rotational restraint design rather than the customary center drilled chord and encapsulated pin design. By encapsulating the joint area of the wood chord with metal, the whole joint area becomes the strongest area of the chords rather than the weakest as inherently true of present systems.
Edge pin connectors were further searched at the Smithsonian with special emphasis on the 1810-1850 period when the earliest efforts were made to construct railroad bridges using wood and steel composite trusses. Two days intensive search disclosed no evidence of it although in retrospect, such a connector would have solved some of the serious connector problems they ran into at that time which eventually led to substantially all-wood truss bridges for the bulk of the railroad era.
An object of the present invention is to provide a single "wood to metal" connector which can be used in completely assemblying a truss and thereby avoid the numerous "bits and pieces" of assorted complex fittings presently used.
Another object is to provide identical connectors at all the joints whether they be end or intermediate joints so that modular trusses can be stocked and "cut" to the specific installation length required without undue trouble or disturbing the basic engineering assumptions of the truss.
Still another object is to provide a connector which will permit the use of lower grade woods for the chords, such as F-1000 or F-1450 common lumber as opposed to F-2400 machine graded lumber as used in drilled pin trusses.
Another object is to provide a connector which can be used in "light", "medium" and "heavy" type trusses.
An object is to provide a connector method which will provide high strength and reliability yet is relatively easy and inexpensive to fabricate without highly precise joint-control with consequent high costs and undesirable "unique" product controls required for specific jobs.
Another object is to increase ultimate tested load values by not less than one-third above pin non-encapsulated trusses, and to eleminate "explosive total failure" by chord splitting at the pin under ultimate load.
An object is to provide a system without splitting tendency so that certain species of wood with otherwise good characteristics for chords, but split-prone, can be used with the new system, and it is unnecessary to block the sides of the chords at the ends.
A further object is to provide a connector which is attached to the wood chord without nails.
Still another object is to avoid the hazard of knots and other wood imperfections far more effectively than drilled pin connections where imperfections in the wood must be kept well-away from any proximity to the drilled hole area.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of portions of a truss constructed in accordance with the present invention.
FIG. 2 is an enlarged detail of the connector taken at line 2--2 on FIG. 1.
FIG. 3 is an enlarged detail of the portion of the wood chord which accepts the connector.
FIG. 4 is a cross section of the chord portion taken along line 4--4 of FIG. 3.
FIG. 5 is a top plan view of the chord shown in FIG. 3.
FIG. 6 is a top plan view of the connector mounted on the chord.
FIG. 7 is a bottom plan view of the connector mounted on the chord.
FIG. 8 is a cross sectional view taken along line 8--8 of FIG. 6.
FIG. 9 is a cross section taken along line 9--9 of FIG. 8.
FIG. 10 is a plan view of the connector cut from a flat metal sheet before bending.
FIG. 11 is a side view of the connector shown in FIG. 10.
FIG. 12 is a front elevation view of the connector shown in FIG. 10.
FIG. 13 is a top plan view of the connector as viewed along line 13--13 of FIG. 12.
FIG. 14 is a perspective view of a pair of connectors shown in side by side relation as they would appear when assembled on the chord.
FIG. 15 is a side elelvation view of the end connector of the present invention shown in place on a bearing plate.
FIG. 16 is a side elevation view of the end connector of the present invention shown in an alternate end type bearing.
FIG. 17 is a side elevation view of the end connector of the present invention shown in another alternate end type bearing arrangement.
FIG. 18 is a perspective view of the connector of the present invention shown in a double truss arrangement.
FIG. 19 is a perspective view of the connector of the present invention shown in an alternate form connection with a chord wider than the connector.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The present invention consists briefly of a truss joist having an upper chord 1, a lower chord 2 and a plurality of identical connectors mounted on the chords and shown in FIG. 1 as connectors 3-8. A plurality of strut members 9-14 are arranged diagonally between the chords and means pivotally secure the ends of the struts to the connectors at pivot points 16-21 located inwardly of the center lines.
The heart of the present invention is the sheet metal connector which is shown in detail in FIGS. 10-14. The preferred form of the invention consists of a seat 23 with an upstanding leg 24 connected at a fold line 26 to one side of the seat and an upstanding arm 27 connected at a fold line 28 to the other end of the seat. An opening 29 is formed in the leg and an opening 31 is formed in the arm for receipt of a pin 32 which is mounted transversely of the chords.
The arms and legs of the U-shaped connector are formed so as to make approximately an angle of 30° with a line 33 perpendicular to the axis 34 of the chord. Note that perpendicular line 36 falls approximately at the outside edge 37 of the seat and an outside edge of the opening 31 as shown in FIG. 11.
The form of the invention shown in FIGS. 10-14 has a flange 38 on the leading edge of the arm and a flange 39 on the trailing edge of the arm. Also shown is a cutting tooth 41 formed in leading relationship to the flange 38 and a tooth 42 formed in leading relationship to the flange 39.
The skewed U-shaped connectors are used in pairs as shown in FIG. 14 with the mirror image connector designated by the same numbers but differentiated by (') prime marks after each number.
In small chord members such as 2 × 4's, it has been found that 16 ga. metal having a hardness of about R-B 50 seems the most qualified. In some applications where the hardness of the metal is R-B 70, 18 ga. may be satisfactory.
In the present design, a tube or a pin will work. Since the pin or tube is placed on the outside of the chord rather than encapsulating it within the chord, various size pins are possible, even for the small 2 × 4 chords. It is no longer necessary to make the pin small enough so that there will be a sufficient amount of wood between the pin and the outside edge of the chord. Further, the limiting factor on an embedded pin is actually one-half the compressive value resolved as a splitting force, limited only by the member's resistance to split.
In standard truss design, the pins are designed as cylindrical beams to resist both bending and shear. Bending usually determines size. In the present design, since the pins are in metal to metal contact with the connectors at their ends and in the middle, a 1/2-inch pin shows good over-all characteristics. Pins of 3/8-inch and 5/8-inch size may be used even for small chord 2 × 4's.
The pins should be hardened or heat-treated rod or bolt material of approximately commercial "drillrod" grade-45,000 psi. The force-reactions of the connector impose only nominal forces along the axis of the pin. The retention force beteeen the pin and the outboard legs of the connectors is therefore only nominal. One means of retaining the pins is to make them about 1/8inch longer than the face of the outboard leg. Each pin end has a 1/16 inch taper 45° and a 1/16 × 1/16 inch maximum retainer ring. A clip-retainer is snapped into this ringed insert slot upon assembly.
Referring to FIGS. 3-9, the preparation of the wood chord at each joint and the interrelationship of the connector to the chord may be seen.
A major advantage of the present system over pin embedded truss systems is the fact that wood removal is much less than the wood removed by the pin-embedded pin systems. This, of course, results in increased tension value for the wood chord (bottom chord). The savings in cutting is attributable to the fact that a slot is made in the face of the chord for only one half of the diameter of the pin. Further, since the pin is at the face of the chord instead of the center line, the strut ends do not go as far into the wood to make the connection to the pin. Thus the slot required in the wood is limited to a one-half circle as opposed to the full circle slot required by embedded pins.
Referring to FIGS. 3-5, a transverse semi-circular channel 44 is cut in the face of the chord. For a 1/2-inch diameter pin, the groove is 1/4-inch deep. A half segment recess 46 of a 1 1/2 inch circle, 1/2 inch wide, is then cut in the chord for receiving the ends of the struts and to permit some pivoting movement of the struts about the pin.
A slot 47 is formed through the chord as shown in FIG. 4 from the top face 48 to the bottom face 49 with the edges of the slot 51 and 52 forming an angle of about 30 degrees with a line perpendicular to the axis of the chord. The slot is about 1 9/16 inches long by 3/16 inch wide and is within the recess and intersects the pin groove. Using the above cuts, in a chord of 11/2 inches × 31/2 inches and a 1/2-inch pin, there is approximately 4.00 sq. inches net chord section left for tension value as opposed to about 3.25 sq. inches in the standard embedded pin system; a 23 percent increase.
The struts 9-14 which correspond to the web members of standard trusses are shorter because their ends are connected to pins mounted at the edges of the chords rather than to pins mounted at the center of the chords. The struts may be 1-inch pipe with flattened ends 54 and 55 as shown in FIG. 8 with round openings 56 and 57 for receiving the pin 32. As in normal construction there is a 1/2 inch edge distance from the whole opening to the edges of the strut.
The connector may be either a single member or a pair of U-shaped members as shown. The early designs of the connector were a single member and were concentric with the leg and arm members rising at 90° angles from the seat. Since in the edge mounted pin design, the forces impose rotational forces on the connector, the seat area forwardly of the pin is not resisting the forces and therefore the skewed U-shaped design resulted with a savings in metal and weight of the connector. It is this rotational force that is one of the major factors which locks the wood chord between the seat and the pin thereby resisting sliding of the connector axially along the chord. Tests of the connectors without the flanges 38 and 39 or the teeth 41 and 42 were very successful and gave satisfactory results for some trusses.
The flange elements 38 and 39 sometimes referred to as the "grip-groove" members provide additional reinforcement to the ability of the connector to withstand rotational and axial forces and provide a means for holding the connector to the chord during fabrication. Grooves may be routed from the chord to receive the flanges in a force fit, but preferably, the flanges are preceeded with teeth so that by rapid light pounding with a soft head, such as hard rubber the teeth cut their own way into the wood. A pressure system, while workable, tends to push and distort the wood grain rather than provide a clean cutting action. Assembly could also be by a light reciprocating air gun to drive the flanges into the wood.
As shown in FIG. 13, the seat area 23 is not rectangular but along the fold line 26, it is shorter than along fold line 28 so that sides 61 and 62 are at an angle. This construction permits the connectors to be cut from a metal strip at a substantial savings in wasted metal.
A major advantage of the present system is the fact that no special hardware is required for the end joint connectors where the loads are greatest. FIG. 15 shows a close up of the chord bearing upon plate member 64. The opposite end of the chord is carried in a like manner on plate 65 as shown in FIG. 1. Since the identical connector is used at the end joint, no further description is required. For purposes of identification, like parts in FIG. 15 carry the additional identification of the letter a with each number. Note that the seat 23'a overlaps the plate 64 by a considerable amount between the edge face 67 and a point 68. Thus no special end fittings for the chord are required nor is notching of the plate required.
Where additional end bearing or lateral restraint is required, the end of the truss may be positioned as shown in FIG. 16. Again, the same connector is used as before and like parts are identified by adding the letter b to the numbers. Suitable notches can be made in the plate 70 to accommodate the strut 14, the pin 32b and the portions of the connector that protrude below the face 71 of the chord. Note that the entire seat area 23'b is projected upon the plate member 70.
Still another end bearing design is shown in FIG. 17 using the identical type connector previously described. In this design, almost the total seat area projects onto the bearing plate 72 without notching any part of the plate. The above is accomplished by inserting a short member 73 beneath the chord 1c and joining the two wood members together with another connector which is identical in construction to the previously described connectors. The connector on the truss chord is identified by numbers followed by the letter c and the additional connector is described by numbers followed by the letter d. Note that pin 32c serves to connect all of the U-shaped connectors together. The only additional modification of the chord 1c required is the addition of slits to accommodate the ends of the legs and arms of the additional connector which protrude beyond the face 75 of the short member 73. Additionally slits are made in the short member 73 to accomodate the ends of the connectors which protrude beyond face 71 of the chord.
The connector of the present invention can be used without dimensional change in chords which are wider than the connector such as in 2 × 6's. In FIG. 19, the connector is shown in a 2 × 6 numbered 77. A connector constructed in identical manner to the connectors described above is used and the parts are identified only by adding the letter e to each number. The only modification is in the chord in which end recesses 85 and 86 are cut for receiving the ends of the connector legs, 24e and 24'e.
Still another design using the identical connectors as above described is shown in FIG. 18. The truss of FIG. 18 contains a second upper and lower wood chord disposed in side by side relationship with an identical chord as previously described. The first chord 78f and connector is numbered in like manner to the previously described components and is followed by the letter f. The second cord 79f is fitted with an identical connector which is distinguished by the letter g after each similar part. The only modification is the fact that a single pin 81 is common to both connectors. Thus pin 81 is inserted through opening 29f in leg 24f and through the opening in arm 27f. The pin then passes through the opening in arm 27'f and then through opening 29'f in leg 24'f. The same pin then passes through the opening in leg 24g and then through the opening in arm 27g. Finally, the pin 81 passes through the opening in arm 27'g and then through opening 29'g in leg 24'g. The connectors throughout the truss are identical to the connectors as shown in FIG. 18. Struts 11f, 12f, 11g and 12g are illustrative of the type of strut used and are connected in the same manner as previously described.
The assembly of the connectors on the chords is generally shown in FIG. 1. The identical connectors are used on the top and bottom chords. Where "skewed" U-shape connectors are used it is only necessary to angle the connectors so that the seat will restrain the rotational forces imposed at the offset pin. In a Warren truss as shown, the connectors on the top chord should be placed as shown with the angle of the connector legs pointing toward the center of the truss. On the other hand, the connectors on the bottom chord are oriented just the opposite with the connector legs angled toward the outside ends of the truss.
It has been found that for purposes of calculation it may be assumed that the pin is at the center of the chord.
All steel trusses date back well over 100 years. Connections between the chords and webs were located on the center lines of the chords. Except for the generally known "light trusses" no significant new all-steel truss joists have been forthcoming. The market, particularly in the western states where lumber-based construction is more prevalent, requires cheaper trusses.
About twelve years ago, a composite chord came onto the market having wood chords and steel webs. Like the all-steel truss joists, the composite chord truss followed the established design of placing the web and chord connection at the center line of the chord. The design criteria required boring of holes through the center of the wood chord, usually through the width of the chord, thereby considerably weakening the chord in tension. Moreover, the boring of the holes and encapsulating the joint pin rendered the joint the weakest part of the design and dependent upon the wood grades for strength values.
Rapidly rising prices of wood and the increasing scarcity of wood having thet required strength characteristics, together with the need to span ever greater distances, has brought the composite wood-steel truss industry to a serious impasse.
Several design solutions have been advanced including specially laminated wood chords and more sophisticated end-bearing hardware. Both of these solutions, while partially accomplishing the increasing design goals has resulted in an unacceptable increase in cost.
SUMMARY OF THE INVENTION
The goal of the present invention is to substantially increase the spans possible with composite wood chord and steel struts at significantly lower costs in materials and fabrication.
The gist of the present invention is the use of edge pin connectors with rotational restraint design rather than the customary center drilled chord and encapsulated pin design. By encapsulating the joint area of the wood chord with metal, the whole joint area becomes the strongest area of the chords rather than the weakest as inherently true of present systems.
Edge pin connectors were further searched at the Smithsonian with special emphasis on the 1810-1850 period when the earliest efforts were made to construct railroad bridges using wood and steel composite trusses. Two days intensive search disclosed no evidence of it although in retrospect, such a connector would have solved some of the serious connector problems they ran into at that time which eventually led to substantially all-wood truss bridges for the bulk of the railroad era.
An object of the present invention is to provide a single "wood to metal" connector which can be used in completely assemblying a truss and thereby avoid the numerous "bits and pieces" of assorted complex fittings presently used.
Another object is to provide identical connectors at all the joints whether they be end or intermediate joints so that modular trusses can be stocked and "cut" to the specific installation length required without undue trouble or disturbing the basic engineering assumptions of the truss.
Still another object is to provide a connector which will permit the use of lower grade woods for the chords, such as F-1000 or F-1450 common lumber as opposed to F-2400 machine graded lumber as used in drilled pin trusses.
Another object is to provide a connector which can be used in "light", "medium" and "heavy" type trusses.
An object is to provide a connector method which will provide high strength and reliability yet is relatively easy and inexpensive to fabricate without highly precise joint-control with consequent high costs and undesirable "unique" product controls required for specific jobs.
Another object is to increase ultimate tested load values by not less than one-third above pin non-encapsulated trusses, and to eleminate "explosive total failure" by chord splitting at the pin under ultimate load.
An object is to provide a system without splitting tendency so that certain species of wood with otherwise good characteristics for chords, but split-prone, can be used with the new system, and it is unnecessary to block the sides of the chords at the ends.
A further object is to provide a connector which is attached to the wood chord without nails.
Still another object is to avoid the hazard of knots and other wood imperfections far more effectively than drilled pin connections where imperfections in the wood must be kept well-away from any proximity to the drilled hole area.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of portions of a truss constructed in accordance with the present invention.
FIG. 2 is an enlarged detail of the connector taken at line 2--2 on FIG. 1.
FIG. 3 is an enlarged detail of the portion of the wood chord which accepts the connector.
FIG. 4 is a cross section of the chord portion taken along line 4--4 of FIG. 3.
FIG. 5 is a top plan view of the chord shown in FIG. 3.
FIG. 6 is a top plan view of the connector mounted on the chord.
FIG. 7 is a bottom plan view of the connector mounted on the chord.
FIG. 8 is a cross sectional view taken along line 8--8 of FIG. 6.
FIG. 9 is a cross section taken along line 9--9 of FIG. 8.
FIG. 10 is a plan view of the connector cut from a flat metal sheet before bending.
FIG. 11 is a side view of the connector shown in FIG. 10.
FIG. 12 is a front elevation view of the connector shown in FIG. 10.
FIG. 13 is a top plan view of the connector as viewed along line 13--13 of FIG. 12.
FIG. 14 is a perspective view of a pair of connectors shown in side by side relation as they would appear when assembled on the chord.
FIG. 15 is a side elelvation view of the end connector of the present invention shown in place on a bearing plate.
FIG. 16 is a side elevation view of the end connector of the present invention shown in an alternate end type bearing.
FIG. 17 is a side elevation view of the end connector of the present invention shown in another alternate end type bearing arrangement.
FIG. 18 is a perspective view of the connector of the present invention shown in a double truss arrangement.
FIG. 19 is a perspective view of the connector of the present invention shown in an alternate form connection with a chord wider than the connector.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The present invention consists briefly of a truss joist having an upper chord 1, a lower chord 2 and a plurality of identical connectors mounted on the chords and shown in FIG. 1 as connectors 3-8. A plurality of strut members 9-14 are arranged diagonally between the chords and means pivotally secure the ends of the struts to the connectors at pivot points 16-21 located inwardly of the center lines.
The heart of the present invention is the sheet metal connector which is shown in detail in FIGS. 10-14. The preferred form of the invention consists of a seat 23 with an upstanding leg 24 connected at a fold line 26 to one side of the seat and an upstanding arm 27 connected at a fold line 28 to the other end of the seat. An opening 29 is formed in the leg and an opening 31 is formed in the arm for receipt of a pin 32 which is mounted transversely of the chords.
The arms and legs of the U-shaped connector are formed so as to make approximately an angle of 30° with a line 33 perpendicular to the axis 34 of the chord. Note that perpendicular line 36 falls approximately at the outside edge 37 of the seat and an outside edge of the opening 31 as shown in FIG. 11.
The form of the invention shown in FIGS. 10-14 has a flange 38 on the leading edge of the arm and a flange 39 on the trailing edge of the arm. Also shown is a cutting tooth 41 formed in leading relationship to the flange 38 and a tooth 42 formed in leading relationship to the flange 39.
The skewed U-shaped connectors are used in pairs as shown in FIG. 14 with the mirror image connector designated by the same numbers but differentiated by (') prime marks after each number.
In small chord members such as 2 × 4's, it has been found that 16 ga. metal having a hardness of about R-B 50 seems the most qualified. In some applications where the hardness of the metal is R-B 70, 18 ga. may be satisfactory.
In the present design, a tube or a pin will work. Since the pin or tube is placed on the outside of the chord rather than encapsulating it within the chord, various size pins are possible, even for the small 2 × 4 chords. It is no longer necessary to make the pin small enough so that there will be a sufficient amount of wood between the pin and the outside edge of the chord. Further, the limiting factor on an embedded pin is actually one-half the compressive value resolved as a splitting force, limited only by the member's resistance to split.
In standard truss design, the pins are designed as cylindrical beams to resist both bending and shear. Bending usually determines size. In the present design, since the pins are in metal to metal contact with the connectors at their ends and in the middle, a 1/2-inch pin shows good over-all characteristics. Pins of 3/8-inch and 5/8-inch size may be used even for small chord 2 × 4's.
The pins should be hardened or heat-treated rod or bolt material of approximately commercial "drillrod" grade-45,000 psi. The force-reactions of the connector impose only nominal forces along the axis of the pin. The retention force beteeen the pin and the outboard legs of the connectors is therefore only nominal. One means of retaining the pins is to make them about 1/8inch longer than the face of the outboard leg. Each pin end has a 1/16 inch taper 45° and a 1/16 × 1/16 inch maximum retainer ring. A clip-retainer is snapped into this ringed insert slot upon assembly.
Referring to FIGS. 3-9, the preparation of the wood chord at each joint and the interrelationship of the connector to the chord may be seen.
A major advantage of the present system over pin embedded truss systems is the fact that wood removal is much less than the wood removed by the pin-embedded pin systems. This, of course, results in increased tension value for the wood chord (bottom chord). The savings in cutting is attributable to the fact that a slot is made in the face of the chord for only one half of the diameter of the pin. Further, since the pin is at the face of the chord instead of the center line, the strut ends do not go as far into the wood to make the connection to the pin. Thus the slot required in the wood is limited to a one-half circle as opposed to the full circle slot required by embedded pins.
Referring to FIGS. 3-5, a transverse semi-circular channel 44 is cut in the face of the chord. For a 1/2-inch diameter pin, the groove is 1/4-inch deep. A half segment recess 46 of a 1 1/2 inch circle, 1/2 inch wide, is then cut in the chord for receiving the ends of the struts and to permit some pivoting movement of the struts about the pin.
A slot 47 is formed through the chord as shown in FIG. 4 from the top face 48 to the bottom face 49 with the edges of the slot 51 and 52 forming an angle of about 30 degrees with a line perpendicular to the axis of the chord. The slot is about 1 9/16 inches long by 3/16 inch wide and is within the recess and intersects the pin groove. Using the above cuts, in a chord of 11/2 inches × 31/2 inches and a 1/2-inch pin, there is approximately 4.00 sq. inches net chord section left for tension value as opposed to about 3.25 sq. inches in the standard embedded pin system; a 23 percent increase.
The struts 9-14 which correspond to the web members of standard trusses are shorter because their ends are connected to pins mounted at the edges of the chords rather than to pins mounted at the center of the chords. The struts may be 1-inch pipe with flattened ends 54 and 55 as shown in FIG. 8 with round openings 56 and 57 for receiving the pin 32. As in normal construction there is a 1/2 inch edge distance from the whole opening to the edges of the strut.
The connector may be either a single member or a pair of U-shaped members as shown. The early designs of the connector were a single member and were concentric with the leg and arm members rising at 90° angles from the seat. Since in the edge mounted pin design, the forces impose rotational forces on the connector, the seat area forwardly of the pin is not resisting the forces and therefore the skewed U-shaped design resulted with a savings in metal and weight of the connector. It is this rotational force that is one of the major factors which locks the wood chord between the seat and the pin thereby resisting sliding of the connector axially along the chord. Tests of the connectors without the flanges 38 and 39 or the teeth 41 and 42 were very successful and gave satisfactory results for some trusses.
The flange elements 38 and 39 sometimes referred to as the "grip-groove" members provide additional reinforcement to the ability of the connector to withstand rotational and axial forces and provide a means for holding the connector to the chord during fabrication. Grooves may be routed from the chord to receive the flanges in a force fit, but preferably, the flanges are preceeded with teeth so that by rapid light pounding with a soft head, such as hard rubber the teeth cut their own way into the wood. A pressure system, while workable, tends to push and distort the wood grain rather than provide a clean cutting action. Assembly could also be by a light reciprocating air gun to drive the flanges into the wood.
As shown in FIG. 13, the seat area 23 is not rectangular but along the fold line 26, it is shorter than along fold line 28 so that sides 61 and 62 are at an angle. This construction permits the connectors to be cut from a metal strip at a substantial savings in wasted metal.
A major advantage of the present system is the fact that no special hardware is required for the end joint connectors where the loads are greatest. FIG. 15 shows a close up of the chord bearing upon plate member 64. The opposite end of the chord is carried in a like manner on plate 65 as shown in FIG. 1. Since the identical connector is used at the end joint, no further description is required. For purposes of identification, like parts in FIG. 15 carry the additional identification of the letter a with each number. Note that the seat 23'a overlaps the plate 64 by a considerable amount between the edge face 67 and a point 68. Thus no special end fittings for the chord are required nor is notching of the plate required.
Where additional end bearing or lateral restraint is required, the end of the truss may be positioned as shown in FIG. 16. Again, the same connector is used as before and like parts are identified by adding the letter b to the numbers. Suitable notches can be made in the plate 70 to accommodate the strut 14, the pin 32b and the portions of the connector that protrude below the face 71 of the chord. Note that the entire seat area 23'b is projected upon the plate member 70.
Still another end bearing design is shown in FIG. 17 using the identical type connector previously described. In this design, almost the total seat area projects onto the bearing plate 72 without notching any part of the plate. The above is accomplished by inserting a short member 73 beneath the chord 1c and joining the two wood members together with another connector which is identical in construction to the previously described connectors. The connector on the truss chord is identified by numbers followed by the letter c and the additional connector is described by numbers followed by the letter d. Note that pin 32c serves to connect all of the U-shaped connectors together. The only additional modification of the chord 1c required is the addition of slits to accommodate the ends of the legs and arms of the additional connector which protrude beyond the face 75 of the short member 73. Additionally slits are made in the short member 73 to accomodate the ends of the connectors which protrude beyond face 71 of the chord.
The connector of the present invention can be used without dimensional change in chords which are wider than the connector such as in 2 × 6's. In FIG. 19, the connector is shown in a 2 × 6 numbered 77. A connector constructed in identical manner to the connectors described above is used and the parts are identified only by adding the letter e to each number. The only modification is in the chord in which end recesses 85 and 86 are cut for receiving the ends of the connector legs, 24e and 24'e.
Still another design using the identical connectors as above described is shown in FIG. 18. The truss of FIG. 18 contains a second upper and lower wood chord disposed in side by side relationship with an identical chord as previously described. The first chord 78f and connector is numbered in like manner to the previously described components and is followed by the letter f. The second cord 79f is fitted with an identical connector which is distinguished by the letter g after each similar part. The only modification is the fact that a single pin 81 is common to both connectors. Thus pin 81 is inserted through opening 29f in leg 24f and through the opening in arm 27f. The pin then passes through the opening in arm 27'f and then through opening 29'f in leg 24'f. The same pin then passes through the opening in leg 24g and then through the opening in arm 27g. Finally, the pin 81 passes through the opening in arm 27'g and then through opening 29'g in leg 24'g. The connectors throughout the truss are identical to the connectors as shown in FIG. 18. Struts 11f, 12f, 11g and 12g are illustrative of the type of strut used and are connected in the same manner as previously described.
The assembly of the connectors on the chords is generally shown in FIG. 1. The identical connectors are used on the top and bottom chords. Where "skewed" U-shape connectors are used it is only necessary to angle the connectors so that the seat will restrain the rotational forces imposed at the offset pin. In a Warren truss as shown, the connectors on the top chord should be placed as shown with the angle of the connector legs pointing toward the center of the truss. On the other hand, the connectors on the bottom chord are oriented just the opposite with the connector legs angled toward the outside ends of the truss.
It has been found that for purposes of calculation it may be assumed that the pin is at the center of the chord.