Static structures (e.g. – buildings) – With component having discrete prestressing means – Slab or panel construction
Reexamination Certificate
2000-07-06
2003-04-01
Safavi, Michael (Department: 3673)
Static structures (e.g., buildings)
With component having discrete prestressing means
Slab or panel construction
C052S223120
Reexamination Certificate
active
06539679
ABSTRACT:
TECHNICAL FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a load-bearing structural member. The structural member includes one or more strength-reinforcing, tensioned steel straps adapted for transferring an intermediate lateral load acting on the member to its supported ends. The invention is applicable to standard light-gauge steel C-channels, U-channels, Z-purlins, I-beams, and girts, square tubing, and light-gauge prefabricated building sections, such as floor trusses, stud or curtain walls, and roof panels. The invention provides a lightweight structural member with an extended span reach, and which is less costly and more functional than existing structures of equivalent strength and span.
A principle object of the invention is to create a maximum supporting reaction force at a predetermined location between the ends of the structural member in a manner that will not significantly increase the weight and/or cost of the member. The invention will double the span of the structural member without reducing its load-bearing capacity. For example, a standard 24 foot beam has a maximum supporting reaction force at its supported ends and a minimum supporting reaction force at its center point 12 feet from either end. Longer beams have less strength at the center point, and must therefore be made of a heavier gauge steel or must include separately attached reinforcing structure which can substantially increase the overall weight and cost of the beam. The present invention adds cost, lightweight reaction support at the center point of the beam, thereby shifting the area of less strength to respective mid-points between the center and ends of the beam.
Attempts have been made in the past to strengthen conventional beams using one or more steel cable tendons attached to opposite ends of the beam in tension, and forced downwardly and attached at intermediate points of the beam. Cable tendons, however, are costly and generally too elastic to maintain proper tension over time. For example, for every {fraction (1/50)}th of an inch of relaxing tension on a steel cable under 2500 lbs. of tension, residual tension in the cable is reduced by 100 lbs. To control elongation, the cables are typically pretensioned and imbedded in relatively heavy cement-type material and held rigid the full length of the beam. This is not an option with light-gauge structural members.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to provide a lightweight structural member which can span twice the distance of a conventional member without reducing its load-bearing capacity.
It is another object of the invention to provide a structural member which has twice the load-bearing capacity of a conventional member of substantially equal length.
It is another object of the invention to provide a structural member which is relatively inexpensive to manufacture.
It is another object of the invention to provide a structural member which uses a strength-reinforcing, flat steel strap which resists stretching under lineal tension.
It is another object of the invention to provide a structural member including a tensioned flat steel strap which will maintain a predetermined degree of tension over time.
It is another object of the invention to provide a structural member including a tensioned flat steel strap with a tensile strength of between 100,000 and 140,000 psi.
It is another object of the invention to provide a structural member including a tensioned flat steel strap which is stress-proof.
It is another object of the invention to provide a structural member including a tensioned flat steel strap which is tension-tested.
It is another object of the invention to provide a structural member including a tensioned flat steel strap which is anchored at opposing ends of the member without penetrating the strap from one major surface to the other.
It is another object of the invention to provide a structural member which uses two or more strength-reinforcing flat steel straps.
It is another object of the invention to provide a structural member which can be quickly and easily assembled.
It is another object of the invention to provide a structural member which is clearly marked to indicate the horizontal and vertical tension pulled on the steel strap.
It is another object of the invention to provide a method of forming a load-bearing structural member.
These and other objects of the present invention are achieved in the preferred embodiments disclosed below by providing a load-bearing structural member including an elongate beam and a strength-reinforcing flat steel strap. The beam has a top and a bottom, and first and second opposing ends. The steel strap extends along the length of the beam from one end to the other, and is adapted for transferring an intermediate load acting on the beam outwardly to the opposing ends of the beam. Anchoring means located at respective opposing ends of the beam engage and hold the strap in tension.
According to one preferred embodiment of the invention, the strap is anchored to the opposing ends of the beam at the top of the beam. A vertical tensioning post located between the ends of the beam engages and holds the strap adjacent the bottom of the beam. The tensioning post and strap cooperate to create an increased supporting reaction force between the ends of the beam at the location of the post.
According to another preferred embodiment of the invention, the vertical tensioning post is centrally located between the ends of the beam.
According to yet another preferred embodiment of the invention, the strap is formed of light-gauge, stress-proof steel having a tensile strength of at least 100,000 psi.
According to yet another preferred embodiment of the invention, the beam is formed of light-gauge steel.
According to yet another preferred embodiment of the invention, the beam has a generally V-shaped or U-shaped cross-section with a bottom, opposing sides integrally formed with the bottom, and respective flanges integrally formed with the sides.
According to yet another preferred embodiment of the invention, each of the flanges includes a longitudinal fastener groove for receiving fasteners.
According to yet another preferred embodiment of the invention, at least one lateral spreader bar is located between the sides of the beam to maintain uniform spacing of the sides from one end of the beam to the other.
According to yet another preferred embodiment of the invention, the anchoring means includes cooperating top and bottom anchor plates attached to each end of the beam. The anchor plates engage opposing major surfaces of the flat steel strap to frictionally hold the strap in tension without penetrating the strap from one major surface to the other.
According to yet another preferred embodiment of the invention, the anchor plates include a series of mating, spaced-apart, lateral crimps.
According to yet another preferred embodiment of the invention, the depth of the crimps formed in the anchor plates increases from an inside edge of the plates to an outside edge of the plates.
According to yet another preferred embodiment of the invention, the width of the crimps formed in the anchor plates is no greater than 80% of the width of the strap.
According to yet another preferred embodiment of the invention, the anchor plates are attached to the beam by a plurality of fasteners extending through the beam and plates, and adjacent to opposing side edges of strap.
According to yet another preferred embodiment of the invention, the anchor plates extend at an angle from the top of the beam towards the bottom of the beam to define a sloping bed for holding the strap.
According to yet another preferred embodiment of the invention, the beam is a steel C-channel including a vertical web member and spaced-apart top and bottom flange members integrally formed with the web member.
According to yet another preferred embodiment of the invention, top and bottom support panels are attached to respective top and bottom flange members of the C-channel.
According to yet another pre
Adams, Schwartz & Evans P.A.
Safavi Michael
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