Static structures (e.g. – buildings) – Machine or implement
Reexamination Certificate
1999-02-15
2001-01-16
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
Machine or implement
C052S749100, C052S749100, C052S749100, C052S749100
Reexamination Certificate
active
06173550
ABSTRACT:
TECHNICAL FIELD
The present invention relates to wood structural members and, in particular, to improved wood I-beams.
BACKGROUND OF THE INVENTION
Beams, trusses, joists, and columns are the typical structural members that support the weight or loads of structures, including buildings and bridges. Structural members may be manufactured from a variety of materials, including steel, concrete, and wood, according to the structure design, environment, and cost.
Wood structural members are now typically manufactured from multiple wood segments that are bonded together, such as in glue-laminated members, laminated veneer, parallel strand wood and I-beams. These manufactured wood structural members have replaced sawn lumber or timbers because the former have higher design limits resulting from better inspection and manufacturing controls. Wood is a desirable material for use in many structural members because of its various characteristics, including strength for a given weight, appearance, cyclic load response, and fire resistance.
Wood I-beams can be manufactured with a wide variety of structural components. Generally, wood I-beams include a pair of parallel wood or manufactured wood flanges that are secured along their lengths to a transverse web material that can be formed of wood, manufactured wood, or steel.
FIG. 1
is an exploded side elevation of a conventional steel web wood I-beam
10
of a type widely used as beams, floor joists, and roof joists. Steel web wood I-beam
10
includes an opposed pair of elongated wood flanges
12
and
14
that have positioned between them multiple straight steel tubes
16
arranged in a zig zag pattern as a substantially continuous tubular steel web
18
. Wood flanges
12
and
14
typically are formed of multiple wood sections
20
that are joined at their ends by finger joints
22
.
In this embodiment, the web members
16
are formed from steel tubes
16
having ends
24
that are flattened parallel to the plane of web
18
to fit within either slots
26
in top surface
28
of wood flange
12
or similar slots (not shown) in bottom surface
32
of wood flange
14
. Pins
34
made of metal, wood, or plastic pass through the sides of wood flanges
12
and
14
and flattened ends
24
of the steel tubes
16
so that tubular steel web
18
is secured to flanges
12
and
14
.
Conventional manufacturing practices provide steel web wood I-beams that are of generally high quality and have generally high design limits that include having adequate stiffness to meet application deflection criteria. These manufacturing practices typically specify the grade of wood used to form flanges
12
and
14
, the type and size of steel tubes
16
, the pitch of the zig zag pattern formed by steel web
18
, the size and placement of pins
34
and
54
, and the size and form of flanges
12
and
14
.
In conventional manufacturing practices, wood flanges
12
and
14
are formed of high grade wood so that flanges
12
and
14
can withstand the tensile and compressive forces applied to the I-beam, the shearing forces exerted by pins
34
and
54
, and the pressure in flanges
12
and
14
adjacent pins
34
. Finger joints
18
have a strength that is typically at least about
60
percent of the strength of the wood that is joined together. High grade wood is also required so that finger joints
18
have at least a minimum strength to prevent a localized failure that could lead to total failure or collapse of the beam.
Knots and slope of grain variations are typically avoided in flanges
12
and
14
because they can initiate localized failure under compression. The limited availability of affordable high quality wood can greatly increase the cost of steel web wood I-beams or require use of oversized flanges of lower quality wood. Moreover, conventional steel web wood I-beams suffer from the disadvantage of failing completely whenever tension flange failure occurs.
Furthermore, stiffness is a major consideration in the design of wood I-beams. The flange construction and material of the reinforcement panel all contribute to beam stiffness.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to provide wood I-beams with wood or wood composite flanges having fiber reinforcement.
Another object of this invention is to provide metal or wood web wood I-beams with improved capability of bearing shearing forces and pressures exerted on the flanges by pins securing the web.
A further object of this invention is to provide web wood I-beams with reduced susceptibility to total beam failure resulting from flange failure.
Still a further object of this invention is to provide a wood I-beam with improved flange stiffness.
The present invention includes wood I-beams with fiber reinforcement. In a preferred embodiment, a steel web wood I-beam includes an opposed pair of elongated wood flanges, which include wood composite flanges, and a substantially continuous tubular metal (e.g., steel) web positioned between them. The tubular steel web includes multiple metal tubes that extend between the wood flanges and form a zig zag pattern. The ends of the metal tubes are flattened parallel to the plane of the metal web so the ends can fit within either slots in the top surface of the bottom wood flange or slots in the bottom surface of the top wood flange.
Metal pins pass through the sides of the wood flanges and the flattened ends of the metal tubes to secure the tubular metal web to the flanges. Reinforcements are adhered to the wood flanges so that the pins also pass through the reinforcements. The reinforcements preferably include multiple fiber strands held within a resin matrix. The wood flanges preferably include multiple elongate wood segments are bonded together with their lengths generally aligned with the length of the I-beam and the reinforcements are bonded either between elongate woods segments or on another surface of one of the flanges.
Failure in conventional steel web wood I-beams typically occurs in a flange, in cleavage, compression, or tension, in the vicinity of the pins coupling the flanges and metal web. Lateral buckling of the compression flange also occurs. The reinforcements provide the wood flanges of this invention with enhanced resistance to these failure modes, as well as to failure in the vicinity of finger joints where portions of the wood flanges are joined end-to-end and to failure in the vicinity of local defects in the flanges (e.g., knots in compression-side flange). As a result, metal web wood I-beams of this invention can be manufactured with flanges of lower grades of wood and have comparable or greater strength than conventional steel web wood I-beams. Also, the reinforcements function to increase the ductility ratio (i.e., the ultimate load over the yield point load) of wood I-beams and to prevent the wood flanges from completely failing, thereby providing improved safety characteristics.
In another preferred embodiment, reinforcement according to the present invention is employed with wood I-beams having other web materials such as, for example, a wood web and oriented strand board. Such reinforced wood I-beams also have improved load bearing capabilities and failure characteristics. Various other wood materials are also suitable for the flanges of wood I-beams, including laminated veneer wood, parallel strand wood, and solid sawn lumber. The wood flanges and/or the solid wood web may additionally be made from reconstituted wood, such as wood particles held together in a resin matrix. Additionally, the wood flanges and/or the solid wood web my be made of plywood, oriented strand board, laminated veneer, or parallel strand lumber.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceeds with reference to the accompanying drawings.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceeds with reference to the accompanying draw
A Phi Dieu Tran
Friedman Carl D.
Stoel Rives LLP
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