CA1105228A - Wooden i-beam - Google Patents
Wooden i-beamInfo
- Publication number
- CA1105228A CA1105228A CA327,204A CA327204A CA1105228A CA 1105228 A CA1105228 A CA 1105228A CA 327204 A CA327204 A CA 327204A CA 1105228 A CA1105228 A CA 1105228A
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- Canada
- Prior art keywords
- web
- flange
- web member
- plane
- ribs
- Prior art date
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Abstract
WOODEN I-BEAM
Abstract of the Disclosure A wooden I-beam suitable for use as a joist or a rafter, comprising solid wooden flange members of rec-tangular cross section joined to opposite sides of a ply-wood web member by an adhesively fastened joint. Large joint contact surface area, and a small amount of wood removal from flange members to form the joint, co-operate to create a strong joint without unnecessary weakening of the flange members, thus producing wooden I-beam members of consistently high strength.
Abstract of the Disclosure A wooden I-beam suitable for use as a joist or a rafter, comprising solid wooden flange members of rec-tangular cross section joined to opposite sides of a ply-wood web member by an adhesively fastened joint. Large joint contact surface area, and a small amount of wood removal from flange members to form the joint, co-operate to create a strong joint without unnecessary weakening of the flange members, thus producing wooden I-beam members of consistently high strength.
Description
. _ . ~ . ....... .. __ . . _ .. _.. .. _ Bac~grouna of the Invent; on ~ . ~
~
This inYention relates to wooden I-beams suitable for use as joists and rafters in construction of ~rame buildings, and particularly to wooden I-beams having solid lumber fla~ges and plywood webs.
Where strength is required to support loads applied primarily in one direction, considerable sa~ing o weight and material cos~ may be accomplished by usi~g a - .
beam.arranged in a fo~m having a cross seçtion resembli~g the capital letter "I" and called an I-beam. This gen-. eral design pro~ides required strength to support com-pressive and tension loads generated by application of load to the top of such an ~-beam resting on supporting Z5 s~ructure, as when such a beam is used as a rafter or joist.
~ hen a downw~rd load is applied to the top of a beam so constructed, with the ends of the I-beam supported ~k 5 Z Z ~
from below and the "I" cross section in an upright orien-tation, the stresses generated are distributed as com-- pression along a top flange portion of the I-beam and tension in a bottom flange~, The width of the top and bottom flanges gives required lateral stiffness, all~win~
the use of a narrow vertical web c~nnecting the ~langes.
Thus for a gi~en load supporting capacityS an ~-beam is lighter than a solid beam ha~ing a rectangular cross section.
10Altho~gh metal I-beams have long bèen used, within their strength range woode~ I-beams are often s~-perior. They cost less, are more easily cut to fi~, and since Shey don7t Tequire special fasteners, are better adapted to wood frame construction such as houses and small office buildings.
Typically~ to economically manufacture such beams ha~ing reliably consistent and uni~orm strength, clear, straight-grained lumber is used for the flange mem-bers, and the ~eb is made from plywood and glued to both flanges.
Various adhesiYe-joint a}rangements have b~en used in prior art wooden I-beams wlth some success, but with the disadvantage in some designs that assembly of the beam produces residual stresses in the composi~e heam member. In other design~ the sizable amount of wood cut from n ange members, in the m~kin~ of the jointJ tends *o weaken the flanges, reducing oYerall bea~. strength.
In one prior design, aisd ose~i in Troutner Patent No. 3,490,1~8, opposite margins of the web members are ... .. ....... ..
S22~
pressed to a tapered shape and adhesively fastene~ in a tapered groove in each flange. As the web absorbs adhesive, when it is inserted into the groo~e of the flange, the wood therein swells and thus the web tends to resume its original shape. This swelling causes a residual stress ~
in the completed I-beam tending to split the flange.
Another prior means of connecting the ~eb to the flanges o a wooden I-beam involves ~orcing a web mem-ber, having two thin parallel ~ibs on its edge, into 10 diverging gTooves in the flange members, thus creating Tesidual stresses tending to separate the laminations of the plywood web.
Summary o the Invention The present inYention is directed to a novel means for attachin~ the flanges to the web in a wooden I-beam so as to overcome the disadvantages of prior art designs. By using.a joint of novel construction between the flange and web members, comprising ~o parallel tapered grooves in one face of each flange member and corresponding tapered ribs on mating edges o the plywood web member, the invention produces an I-beam assembly which has a minimum of included or residual stress in the 1ange-to-web joint, an increased surface area avail-able for adhesive contact in the joint, and a reducedloss of cross section from the flange members in the fabrication of the joint.
Since the joint surfaces are matchingly.cut into the flange and web members 7 instead of being pressed ll~S2;~:~
.
to shape as are the edges of the web members described by the prior art Troutner design, there is practically no residual stress in the joint caused by swelling o the edge of the web. Therefore, the I~be~m construction of the inventlon is able to absorb greater amounts of lateral loading without failure of the flange along the web-to-flange joint, and results in beams of a conslsten*ly high strength.
It is therefore a principal objective o~ the present invention to provide a wooden I-beam which may be -mass produced to have a consistently high strength.
It is ano*her objective of the present invention to provide a wooden I-beam having a minimum amount o residual stTess in the joints between flange members ~nd web members.
It is a feature of the present inYention that the joint beh~een flange members and web members has a large amount of surface area, yet in its fabrication results in a minimal reduction in the flange member cross-sectional area.
It is a further feature of the present invention that the joint between the flanges and the web member, because of its inherent strength ana inte~ritr, is not the critical load-limiting portion of the I-beam.
The foregoing and other objectives, features, and advantages of the invention will be ~ore readily understood upon consideration of the following detailed description o~ the invention, taken in conjunction with the accompanying drawings.
~1~5228 Brief Description of the Drawin~s FIG. 1 is a partially cut-away perspective view of an embodiment of the wooden I-beam member of the present invention.
. .
S . FIG. 2 is a partially cut-away sectional v;ew .-of the I-beam taken at line 2-2 of PIG~ 1.
FIG. 3 is a detail of the jol~t cons~ructian .
- ' between web and fl.ange members of the I-beam.
- .. FIG. 4 is a diagrammatic view of the I-beam in use.
FIG. 5 is a perspective partially exploded, view --showing the use of stiffeners and bracing at the enas of t~e I-beam. .
- . .
'Detailed Des'cr'ipti'on o'f't~'e Invent'ion As seen in FIG. 1, the I-beam of the present invention in a preferred embodiment comprises a pair of .
elongate, parallel wooden flange members 20, of rectangular cross section and longitudinal gra~n structure, interconnectec by a plywood web member 22. Flange members 20 may be made, exemplarily, from nominal 2~' X 4" or 2" X 3'~ s~ruc-: tural grade lumber or a laminated wood product, and web member 22 ~ay be made of 3/8 inch thick, three-ply plywood joined to flange members 20 by continuous adhesive joints 24.
. In the preferred embodiment, web member 22 is composed of structural grade 1 plywood, arranged with the ; grain of a face veneer 27 perpendicular to the length o the flange members and tbe grain of a core Yeneer 29 parallel to the length of flange members 20. The web member 22 may be composed of a plurality of segments~
11~522~3 each having a length corresponding to the width of the sheet of plywood from which it was cut, commonly 4S inches~
Indi~idual ~eb segments are joined to one another adlles-ively at web segment joints 26, which may be simple butt joints, or~may be of interlocking cross section.
The web member sections may be cut to var;ous widths to form I-beams of different depth 33 as measured from top to bottom of the "I" shape. Within the strength limits of the materials used, increased depth of the I-beam provides increased I-beam strength. Using web - member material having a thickness 21 o f 3J8 inch, I-beam dep~hs from 10 inches to 24 inches have been successfully -used in structural applications.
Flange members 20 may be solid lengths of nom-inal 2" X 4" or 2" X 3" lumber corresponding to the entirelength of the finished I-beam, or may be made up of shorter lengths o~ such lumber connected end-to-end by a glued scar~ joint as shown at 28.
~l~ preferred materials for flange members are Douglas Fir, Larch, Hem-Pir, or Southern Pine wood haYing surface moist~re content less than 19%.
Preferably, the plywood should have a moistu~e content of from 7% to 16% at the time of web member I-.
beam assembly. To avoid residual stress in the web-to-flange joints the difference in moisture between web and flange materials should preferably be less than 5% at time of assembly.
As shown in FIG. 2, the glued joints 24 between flange members 20 and web member 2Z com~rise t~o elongate, .
l~SZZ~3 tapered, parallel ribs 23 extending along opposite edges 25 of each section of web member 22, and closely fitting - within corresponding groo~es 42 of flange members 20.
Grooves 42 are centrally located on one of the wider faces 44 of flange member 20, and extend parallel to the lengt~
S of each flange member.
Referring to FIG. 3, showing a detail of jolnt 24 in end view, it is seen that the edge ZS of web member 22 is cut to the shape of a pair of parallel ~ibs 23 with , an included groove 40 therebetween. A shallcw cut creating a 10 ledge 30 is made at a base plane 31 to in5ure that slight irregularities and variations in the thickness of pl~ood web material a~ailable do not cause a lac~ of sur~ace contact between flange members 20 and web members 22 with-in the joint. A pair of long sloping outer sides 32 extend from ledge 30 toward rib edge surfaces 34 which are aligned perpendicular to *he principal plane of web members 22. A pair of short sloping inner sides 36 ex~end toward a groove bottom surface 38 and, along with said surface 38~ cooperatively define the groove 4~ between 20 ribs 23 o the edge 25 of web member 22.
Grooves 42, extending ~edially along a wiaer face 44 of flange me~ber 20, correspond closely in profile to the sur~aces of ri~s 23, to proYide mating contact surfaces for adhesively fastening the joints between l~eb ~ember 22 and flange members 20. Thus long sloping groove walls 46 correspond to long sloping outer sides 32, 1at surfaces 48 correspond to rib edge surfaces 34, short sloping groove walls 50 correspond to short sloping inner sides 36, and an upper sur~ace 52 of rib 43 corresponds SZ2l3 to bottom surface 38 of groove 40.
A minimum width 53 of said rib edge surfaces 34 and said rib upper surface 52 is determined by the ability of the wooden material of the 1ange and web members to resist damage in being handled. From emperical-studies it has been found that about 0.035 inch is the minimum usable width and that 0.055 inch is the preferred minimum width for use ith 3/8 inch thickness plywood web material.
The depth 55 of groove 40 is preferably less than the distance 57, by which ribs 23 extend from base plane 31, defining a separation distance 58 between joint horizontal surface 38 and base plane 31; This separation distance 58 defines the oblique planes, or shear lines, 54 within web 22 wherein failure would occur if the l-beam should fail at the joint. By providing, through design, sufficient length to the shear lines 54 the web-to-flange joint is made strong enough to result in the structurally critical axis of the I-beam being located at a neutral plane 56, located in the web member 22, which is substantially parallel to and between flange members 20.
For required structural integrity, the minimum design length for each such oblique shear line 54 is proportional to the maximum web-strength required in the web-to-flange joint. More particularly, since the web member 22 itself carries part of the load stresses gen-erated in ~he beam as a whole, only the stresses generated in the flange members 20, and the small portion o~ the web further than the oblique shear line from the neutral a~is of the I-beam, must be carried by the web material 5~2~3 along the oblique shear line 54. Accordingly, the total thickness of web material along the two sections of obli~ue shear line 54 can be made proportionally less than the total thickness of the web material at a point medially be~ween the flange members. - ~
This critical proportion, affecting the mini-mum design length for the oblique shear lines 54, can be mathematically determined by di~riding (a? the statical moment of the cross-sectional area of the I-beam further from the neutral plane 56 *han the oblique shear lines ~4 by (b) the statical moment of the cross section of the complete I-beam, taking into account in the above calcu-lation the relati~e strengths of the flange and web mater-ials. -The shape of the joint cross section, having tapered ribs and sorresponding grooves, provides sufficien*
contacting surface area for good adhesion between the ribs and grooves to ensure that the joint between the flanges ... . . . . .
and the web is not the load limiting portion of the I-beam.
A rib side and groove wall slope within the range of about 5 to about 20 relati~e to the principal plane of the web member, with a range pf from 5 to 10 being preferred, has been ound satisfactory for ensuring that pressing the flanges onto the web members provides satisfactory contact.
Since the web material is plywood, laminated layers of veneer cut from a rotating solid of circular cross section, the particular weaknesses of plywood in a glued joint must be considered. This is called 5 ~ ~
the rolling shear strenoth of the plywood. To compensate for this weaXness, the surface area of an adhesive joint must be multiplied in comparison to adhesive joint between surfaces of solid wood pieces.
In the web-to-~lange joint of the I-beam con-struction.of the present invention, the area of the sloping . faces of ribs and gTooves forming the adhesi~ely joined stress-carrying surfa-ces of the web-to-flange joint is at : least 3-1/3 times the area which would be exposed by a cut made.perpendicularly to the plane of the web material, thus overcoming the weakness of rolling shear strength of plywood.
The two-rib design of the web portion o~ the joint cross section also reduces the amount of wood nec-15 essarily removed from flange 22 to receive-the.web edge in the ioint. Thus the cross-sectional area of material removed from flange 22 approadles t~e minimum required to provide both sufficient shear-resistive cross section of .
. web member-material in the joint and the adhesive con-.tact area ~equired.by rolling shear strength of the web . member, and the original s*rength of flange members 22 is reduced only slightly by loss of material. Additionally, .. . . .
since all material removed is replaced by wood of the plywood web member Z2, loss of flange member strength because of material removal for the joint is further minimized.
In the fabrication o~ wooaen I-beams according to the present invention the use of graded materials for 11~52~8 flange and l~eb members has been found to result in pre-dictable and consistent I-beam strengths~ Each flange member is preferably visually examined and mechanîcally tested to determine its modulus of elasticity and bending resistance, and thereafter a resulting grade is assigned _ reflecting the maximum bending stress to which the parti-cular piece should.be subjected.
With more consistent material, it has been ..established that beams can be produced accoraing to the present design which have a more reliable strength, there-:by allol~ing the use of lighter weight beams for a givendesigned load, with no sacri~ice of safety factor.
In constTuction of an I-beam of the invention7 a properly prepared adhesive, preferably a waterproof ex~erior type adhesive such as one having a phenol, resorcinol~ or - -melamine base, is applied to one or both o~ the surfaces to be joined. The flange grooves 42 are located in register with the web ribs 23 and the I-beam ls then pressed together to provide good surface contact. In this manner ledge 30 is brought into contact with flange surface 44, and any excess adhesive is squeezed out between flange members 20 and web member 22 forming a small fillet.
The I-beam is then held together in proper dimensional relationship until the glue cures. This may be accomplished by clamping or by insertion of nails 59,.
as seen in FIG. 2, at intervals along the joint after assembly and pressing, and before the I-beam is removed from the pressing means.
Use of sloping sides of grooves and ribs aids .. . ... . ... .. . . . .. ~
assembly of the pieces of the I-beam and insures tight surface contact between flange and web members. However, since these sloping sides are formed by cutting away excess wood rather than by pressing the web margins, in ~ contrast to the joint design employed in the Troutner - 5 patent, there is no ~esidual stress created by swelling of the wood within the joint to split flange members 20 after the glue joint has curea. Thus more of the original strength of flange member 20 remains tQ absorb lateral stresses before such would cause this mode of failure in the I-beam.
Referring to FIG. 4, a typical installation of I-beams of the present invention is shown diagrammatically.
The normal direction of the application of loads to the beam is shown by arrow 60 and the resulting downward elastic deformation is indicated by arrows ~2. A neu*ral piane 56, loca*ed in the web 22, di~ides areas of com-pressive loading in the upper portion of the I-beam from areas of tension loading below the neutral plane.
FIG. 5 shows a perspective, partially exploded view of a pair of I-beams constructed accoraing to the invention, including wooden stiffeners 64 used to provide additional support to web member 22 at the point where the I~beam is supported, and bracing used there to maintain proper orientation of the I-beams in structural use.
A sill member 66 suppoTts the ends of the joists, and for lateral bracing of *he I-beams a blocking panel 68, comprised of a short section of I-beam inserted between adjacent stiffened I-beams may be usea. Alternati~ely, metal strap bracing well-known in the art may be used.
~
This inYention relates to wooden I-beams suitable for use as joists and rafters in construction of ~rame buildings, and particularly to wooden I-beams having solid lumber fla~ges and plywood webs.
Where strength is required to support loads applied primarily in one direction, considerable sa~ing o weight and material cos~ may be accomplished by usi~g a - .
beam.arranged in a fo~m having a cross seçtion resembli~g the capital letter "I" and called an I-beam. This gen-. eral design pro~ides required strength to support com-pressive and tension loads generated by application of load to the top of such an ~-beam resting on supporting Z5 s~ructure, as when such a beam is used as a rafter or joist.
~ hen a downw~rd load is applied to the top of a beam so constructed, with the ends of the I-beam supported ~k 5 Z Z ~
from below and the "I" cross section in an upright orien-tation, the stresses generated are distributed as com-- pression along a top flange portion of the I-beam and tension in a bottom flange~, The width of the top and bottom flanges gives required lateral stiffness, all~win~
the use of a narrow vertical web c~nnecting the ~langes.
Thus for a gi~en load supporting capacityS an ~-beam is lighter than a solid beam ha~ing a rectangular cross section.
10Altho~gh metal I-beams have long bèen used, within their strength range woode~ I-beams are often s~-perior. They cost less, are more easily cut to fi~, and since Shey don7t Tequire special fasteners, are better adapted to wood frame construction such as houses and small office buildings.
Typically~ to economically manufacture such beams ha~ing reliably consistent and uni~orm strength, clear, straight-grained lumber is used for the flange mem-bers, and the ~eb is made from plywood and glued to both flanges.
Various adhesiYe-joint a}rangements have b~en used in prior art wooden I-beams wlth some success, but with the disadvantage in some designs that assembly of the beam produces residual stresses in the composi~e heam member. In other design~ the sizable amount of wood cut from n ange members, in the m~kin~ of the jointJ tends *o weaken the flanges, reducing oYerall bea~. strength.
In one prior design, aisd ose~i in Troutner Patent No. 3,490,1~8, opposite margins of the web members are ... .. ....... ..
S22~
pressed to a tapered shape and adhesively fastene~ in a tapered groove in each flange. As the web absorbs adhesive, when it is inserted into the groo~e of the flange, the wood therein swells and thus the web tends to resume its original shape. This swelling causes a residual stress ~
in the completed I-beam tending to split the flange.
Another prior means of connecting the ~eb to the flanges o a wooden I-beam involves ~orcing a web mem-ber, having two thin parallel ~ibs on its edge, into 10 diverging gTooves in the flange members, thus creating Tesidual stresses tending to separate the laminations of the plywood web.
Summary o the Invention The present inYention is directed to a novel means for attachin~ the flanges to the web in a wooden I-beam so as to overcome the disadvantages of prior art designs. By using.a joint of novel construction between the flange and web members, comprising ~o parallel tapered grooves in one face of each flange member and corresponding tapered ribs on mating edges o the plywood web member, the invention produces an I-beam assembly which has a minimum of included or residual stress in the 1ange-to-web joint, an increased surface area avail-able for adhesive contact in the joint, and a reducedloss of cross section from the flange members in the fabrication of the joint.
Since the joint surfaces are matchingly.cut into the flange and web members 7 instead of being pressed ll~S2;~:~
.
to shape as are the edges of the web members described by the prior art Troutner design, there is practically no residual stress in the joint caused by swelling o the edge of the web. Therefore, the I~be~m construction of the inventlon is able to absorb greater amounts of lateral loading without failure of the flange along the web-to-flange joint, and results in beams of a conslsten*ly high strength.
It is therefore a principal objective o~ the present invention to provide a wooden I-beam which may be -mass produced to have a consistently high strength.
It is ano*her objective of the present invention to provide a wooden I-beam having a minimum amount o residual stTess in the joints between flange members ~nd web members.
It is a feature of the present inYention that the joint beh~een flange members and web members has a large amount of surface area, yet in its fabrication results in a minimal reduction in the flange member cross-sectional area.
It is a further feature of the present invention that the joint between the flanges and the web member, because of its inherent strength ana inte~ritr, is not the critical load-limiting portion of the I-beam.
The foregoing and other objectives, features, and advantages of the invention will be ~ore readily understood upon consideration of the following detailed description o~ the invention, taken in conjunction with the accompanying drawings.
~1~5228 Brief Description of the Drawin~s FIG. 1 is a partially cut-away perspective view of an embodiment of the wooden I-beam member of the present invention.
. .
S . FIG. 2 is a partially cut-away sectional v;ew .-of the I-beam taken at line 2-2 of PIG~ 1.
FIG. 3 is a detail of the jol~t cons~ructian .
- ' between web and fl.ange members of the I-beam.
- .. FIG. 4 is a diagrammatic view of the I-beam in use.
FIG. 5 is a perspective partially exploded, view --showing the use of stiffeners and bracing at the enas of t~e I-beam. .
- . .
'Detailed Des'cr'ipti'on o'f't~'e Invent'ion As seen in FIG. 1, the I-beam of the present invention in a preferred embodiment comprises a pair of .
elongate, parallel wooden flange members 20, of rectangular cross section and longitudinal gra~n structure, interconnectec by a plywood web member 22. Flange members 20 may be made, exemplarily, from nominal 2~' X 4" or 2" X 3'~ s~ruc-: tural grade lumber or a laminated wood product, and web member 22 ~ay be made of 3/8 inch thick, three-ply plywood joined to flange members 20 by continuous adhesive joints 24.
. In the preferred embodiment, web member 22 is composed of structural grade 1 plywood, arranged with the ; grain of a face veneer 27 perpendicular to the length o the flange members and tbe grain of a core Yeneer 29 parallel to the length of flange members 20. The web member 22 may be composed of a plurality of segments~
11~522~3 each having a length corresponding to the width of the sheet of plywood from which it was cut, commonly 4S inches~
Indi~idual ~eb segments are joined to one another adlles-ively at web segment joints 26, which may be simple butt joints, or~may be of interlocking cross section.
The web member sections may be cut to var;ous widths to form I-beams of different depth 33 as measured from top to bottom of the "I" shape. Within the strength limits of the materials used, increased depth of the I-beam provides increased I-beam strength. Using web - member material having a thickness 21 o f 3J8 inch, I-beam dep~hs from 10 inches to 24 inches have been successfully -used in structural applications.
Flange members 20 may be solid lengths of nom-inal 2" X 4" or 2" X 3" lumber corresponding to the entirelength of the finished I-beam, or may be made up of shorter lengths o~ such lumber connected end-to-end by a glued scar~ joint as shown at 28.
~l~ preferred materials for flange members are Douglas Fir, Larch, Hem-Pir, or Southern Pine wood haYing surface moist~re content less than 19%.
Preferably, the plywood should have a moistu~e content of from 7% to 16% at the time of web member I-.
beam assembly. To avoid residual stress in the web-to-flange joints the difference in moisture between web and flange materials should preferably be less than 5% at time of assembly.
As shown in FIG. 2, the glued joints 24 between flange members 20 and web member 2Z com~rise t~o elongate, .
l~SZZ~3 tapered, parallel ribs 23 extending along opposite edges 25 of each section of web member 22, and closely fitting - within corresponding groo~es 42 of flange members 20.
Grooves 42 are centrally located on one of the wider faces 44 of flange member 20, and extend parallel to the lengt~
S of each flange member.
Referring to FIG. 3, showing a detail of jolnt 24 in end view, it is seen that the edge ZS of web member 22 is cut to the shape of a pair of parallel ~ibs 23 with , an included groove 40 therebetween. A shallcw cut creating a 10 ledge 30 is made at a base plane 31 to in5ure that slight irregularities and variations in the thickness of pl~ood web material a~ailable do not cause a lac~ of sur~ace contact between flange members 20 and web members 22 with-in the joint. A pair of long sloping outer sides 32 extend from ledge 30 toward rib edge surfaces 34 which are aligned perpendicular to *he principal plane of web members 22. A pair of short sloping inner sides 36 ex~end toward a groove bottom surface 38 and, along with said surface 38~ cooperatively define the groove 4~ between 20 ribs 23 o the edge 25 of web member 22.
Grooves 42, extending ~edially along a wiaer face 44 of flange me~ber 20, correspond closely in profile to the sur~aces of ri~s 23, to proYide mating contact surfaces for adhesively fastening the joints between l~eb ~ember 22 and flange members 20. Thus long sloping groove walls 46 correspond to long sloping outer sides 32, 1at surfaces 48 correspond to rib edge surfaces 34, short sloping groove walls 50 correspond to short sloping inner sides 36, and an upper sur~ace 52 of rib 43 corresponds SZ2l3 to bottom surface 38 of groove 40.
A minimum width 53 of said rib edge surfaces 34 and said rib upper surface 52 is determined by the ability of the wooden material of the 1ange and web members to resist damage in being handled. From emperical-studies it has been found that about 0.035 inch is the minimum usable width and that 0.055 inch is the preferred minimum width for use ith 3/8 inch thickness plywood web material.
The depth 55 of groove 40 is preferably less than the distance 57, by which ribs 23 extend from base plane 31, defining a separation distance 58 between joint horizontal surface 38 and base plane 31; This separation distance 58 defines the oblique planes, or shear lines, 54 within web 22 wherein failure would occur if the l-beam should fail at the joint. By providing, through design, sufficient length to the shear lines 54 the web-to-flange joint is made strong enough to result in the structurally critical axis of the I-beam being located at a neutral plane 56, located in the web member 22, which is substantially parallel to and between flange members 20.
For required structural integrity, the minimum design length for each such oblique shear line 54 is proportional to the maximum web-strength required in the web-to-flange joint. More particularly, since the web member 22 itself carries part of the load stresses gen-erated in ~he beam as a whole, only the stresses generated in the flange members 20, and the small portion o~ the web further than the oblique shear line from the neutral a~is of the I-beam, must be carried by the web material 5~2~3 along the oblique shear line 54. Accordingly, the total thickness of web material along the two sections of obli~ue shear line 54 can be made proportionally less than the total thickness of the web material at a point medially be~ween the flange members. - ~
This critical proportion, affecting the mini-mum design length for the oblique shear lines 54, can be mathematically determined by di~riding (a? the statical moment of the cross-sectional area of the I-beam further from the neutral plane 56 *han the oblique shear lines ~4 by (b) the statical moment of the cross section of the complete I-beam, taking into account in the above calcu-lation the relati~e strengths of the flange and web mater-ials. -The shape of the joint cross section, having tapered ribs and sorresponding grooves, provides sufficien*
contacting surface area for good adhesion between the ribs and grooves to ensure that the joint between the flanges ... . . . . .
and the web is not the load limiting portion of the I-beam.
A rib side and groove wall slope within the range of about 5 to about 20 relati~e to the principal plane of the web member, with a range pf from 5 to 10 being preferred, has been ound satisfactory for ensuring that pressing the flanges onto the web members provides satisfactory contact.
Since the web material is plywood, laminated layers of veneer cut from a rotating solid of circular cross section, the particular weaknesses of plywood in a glued joint must be considered. This is called 5 ~ ~
the rolling shear strenoth of the plywood. To compensate for this weaXness, the surface area of an adhesive joint must be multiplied in comparison to adhesive joint between surfaces of solid wood pieces.
In the web-to-~lange joint of the I-beam con-struction.of the present invention, the area of the sloping . faces of ribs and gTooves forming the adhesi~ely joined stress-carrying surfa-ces of the web-to-flange joint is at : least 3-1/3 times the area which would be exposed by a cut made.perpendicularly to the plane of the web material, thus overcoming the weakness of rolling shear strength of plywood.
The two-rib design of the web portion o~ the joint cross section also reduces the amount of wood nec-15 essarily removed from flange 22 to receive-the.web edge in the ioint. Thus the cross-sectional area of material removed from flange 22 approadles t~e minimum required to provide both sufficient shear-resistive cross section of .
. web member-material in the joint and the adhesive con-.tact area ~equired.by rolling shear strength of the web . member, and the original s*rength of flange members 22 is reduced only slightly by loss of material. Additionally, .. . . .
since all material removed is replaced by wood of the plywood web member Z2, loss of flange member strength because of material removal for the joint is further minimized.
In the fabrication o~ wooaen I-beams according to the present invention the use of graded materials for 11~52~8 flange and l~eb members has been found to result in pre-dictable and consistent I-beam strengths~ Each flange member is preferably visually examined and mechanîcally tested to determine its modulus of elasticity and bending resistance, and thereafter a resulting grade is assigned _ reflecting the maximum bending stress to which the parti-cular piece should.be subjected.
With more consistent material, it has been ..established that beams can be produced accoraing to the present design which have a more reliable strength, there-:by allol~ing the use of lighter weight beams for a givendesigned load, with no sacri~ice of safety factor.
In constTuction of an I-beam of the invention7 a properly prepared adhesive, preferably a waterproof ex~erior type adhesive such as one having a phenol, resorcinol~ or - -melamine base, is applied to one or both o~ the surfaces to be joined. The flange grooves 42 are located in register with the web ribs 23 and the I-beam ls then pressed together to provide good surface contact. In this manner ledge 30 is brought into contact with flange surface 44, and any excess adhesive is squeezed out between flange members 20 and web member 22 forming a small fillet.
The I-beam is then held together in proper dimensional relationship until the glue cures. This may be accomplished by clamping or by insertion of nails 59,.
as seen in FIG. 2, at intervals along the joint after assembly and pressing, and before the I-beam is removed from the pressing means.
Use of sloping sides of grooves and ribs aids .. . ... . ... .. . . . .. ~
assembly of the pieces of the I-beam and insures tight surface contact between flange and web members. However, since these sloping sides are formed by cutting away excess wood rather than by pressing the web margins, in ~ contrast to the joint design employed in the Troutner - 5 patent, there is no ~esidual stress created by swelling of the wood within the joint to split flange members 20 after the glue joint has curea. Thus more of the original strength of flange member 20 remains tQ absorb lateral stresses before such would cause this mode of failure in the I-beam.
Referring to FIG. 4, a typical installation of I-beams of the present invention is shown diagrammatically.
The normal direction of the application of loads to the beam is shown by arrow 60 and the resulting downward elastic deformation is indicated by arrows ~2. A neu*ral piane 56, loca*ed in the web 22, di~ides areas of com-pressive loading in the upper portion of the I-beam from areas of tension loading below the neutral plane.
FIG. 5 shows a perspective, partially exploded view of a pair of I-beams constructed accoraing to the invention, including wooden stiffeners 64 used to provide additional support to web member 22 at the point where the I~beam is supported, and bracing used there to maintain proper orientation of the I-beams in structural use.
A sill member 66 suppoTts the ends of the joists, and for lateral bracing of *he I-beams a blocking panel 68, comprised of a short section of I-beam inserted between adjacent stiffened I-beams may be usea. Alternati~ely, metal strap bracing well-known in the art may be used.
Claims (5)
1. A wooden I-beam, comprising:
(a) an elongate, generally planar web member of laminated wood having a longitudinal axis, a pair of opposite edges which are generally par-allel to said longitudinal axis, each one of said opposite edges having a base plane perpen-dicular to the plane of said web member and parallel to said one of said opposite edges and a pair of parallel ribs extending from said base plane and having sloping sides and an included groove therebetween, each said rib having a rib edge surface and said included groove having a bottom surface located closer to said rib edge surface than said base plane is located;
(b) a pair of elongate wooden flange members, said flange members being oppositely located along said opposite edges of said web member and each said flange member having a longitudinal surface comprising a pair of longitudinally-oriented parallel grooves located therein, said parallel grooves having shape and site closely corres-ponding to that of said ribs and included groove of said web member, and each said flange member being adhesively connected to said web member such that said ribs extend matingly into said parallel grooves with said base plane substan-tially aligned with said longitudinal surface, forming a joint defining a pair of oblique shear planes, each of said oblique shear planes extending through one of said ribs from the intersection of said longitudinal surface and said one of said ribs to the por-tion of said bottom surface of said included groove nearest to said intersection.
(a) an elongate, generally planar web member of laminated wood having a longitudinal axis, a pair of opposite edges which are generally par-allel to said longitudinal axis, each one of said opposite edges having a base plane perpen-dicular to the plane of said web member and parallel to said one of said opposite edges and a pair of parallel ribs extending from said base plane and having sloping sides and an included groove therebetween, each said rib having a rib edge surface and said included groove having a bottom surface located closer to said rib edge surface than said base plane is located;
(b) a pair of elongate wooden flange members, said flange members being oppositely located along said opposite edges of said web member and each said flange member having a longitudinal surface comprising a pair of longitudinally-oriented parallel grooves located therein, said parallel grooves having shape and site closely corres-ponding to that of said ribs and included groove of said web member, and each said flange member being adhesively connected to said web member such that said ribs extend matingly into said parallel grooves with said base plane substan-tially aligned with said longitudinal surface, forming a joint defining a pair of oblique shear planes, each of said oblique shear planes extending through one of said ribs from the intersection of said longitudinal surface and said one of said ribs to the por-tion of said bottom surface of said included groove nearest to said intersection.
2. The I-beam of claim l-wherein said sloping sides of said ribs have an included angle with respect to the plane of said web member lying within the range of 5° to 209.
3. The I-beam of claim 1 wherein said ribs extend from said base plane a distance no greater than the total thickness of said web member, and the total area of said sloping rib sides is at least three and one-third times the area of the intersection of said base plane with said web member.
4. The I-beam of claim 3 wherein the total area of said pair of oblique shear planes is at least as great as the area of the intersection of said base plane with said web mem-ber multiplied by the ratio of "a" to "b"; where "a" is the statical moment, about a neutral stress plane in the web of said I-beam, of the cross-sectional area of flange and web material further from said neutral stress plane of said I-beam than a line defined by said oblique shear planes and said bottom surface of said included groove; and "b" is the statical moment of the total cross-sectional area of said I-beam about said neutral stress plane.
5. The I-beam of claim 1 wherein said web member comprises a core veneer having its grain oriented longitudinally of said I-beam, the entire thickness of said core veneer ex-tending beyond said base palne into said flange member.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA327,204A CA1105228A (en) | 1979-05-08 | 1979-05-08 | Wooden i-beam |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA327,204A CA1105228A (en) | 1979-05-08 | 1979-05-08 | Wooden i-beam |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1105228A true CA1105228A (en) | 1981-07-21 |
Family
ID=4114166
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA327,204A Expired CA1105228A (en) | 1979-05-08 | 1979-05-08 | Wooden i-beam |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1105228A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6701690B2 (en) | 2001-07-17 | 2004-03-09 | Guildo Deschenes | I-shaped wooden beam |
-
1979
- 1979-05-08 CA CA327,204A patent/CA1105228A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6701690B2 (en) | 2001-07-17 | 2004-03-09 | Guildo Deschenes | I-shaped wooden beam |
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