Static structures (e.g. – buildings) – With component having discrete prestressing means
Reexamination Certificate
1999-10-12
2001-07-10
Kent, Christopher T. (Department: 3635)
Static structures (e.g., buildings)
With component having discrete prestressing means
C052S223900, C052S223800, C052S223700, C052S796100
Reexamination Certificate
active
06256949
ABSTRACT:
The invention relates to a load-bearing wooden panel element for ceiling structures or for bridge construction, comprising a plurality of individual layers of boards standing on edge perpendicular to the plane of the panel element and preferably running along the entire length thereof, which boards are joined together by screw fastenings, and it further relates to the use of a screw for joining boards as a panel element.
The oldest and most familiar way of fastening board stacks is by nailing. In nailing, the forces between the boards are transferred by shearing in the nails and by hole-widening pressure between nail and wood. This kind of joint is relatively compliant and therefore of only limited effectiveness. Heretofore, prior art applications of screwed board stacks have depended on a principle of action analogous to nailing, or in other words shearing and hole-widening pressure.
There have already been published load-bearing panel elements (U.S. Pat. No. 1,944,237) in which a plurality of boards standing on edge are joined together by tie rods passing through all boards. In addition, the individual boards are joined together by nailing so that they are temporarily held mutually together during construction of such a stack. In the so-called transversely prestressed board stacks, the forces between the individual boards are transferred by friction, which presupposes a steady contact pressure. The transverse prestress therefore must always be guaranteed up to a certain level. Since wood has a tendency to shrinkage and creep deformations, it must be constantly ensured that the tension rods can be retightened.
In such a load-bearing wooden panel element, it is essential that the individual layers of boards be mutually firmly braced or be mutually firmly pressed, in order that they can better absorb the load. It must be realized in this known embodiment that only a certain number of boards standing on edge can be joined together as a panel element by tension rods. Thus it is not possible to make arbitrary widths of such panel elements, for example for use in ceiling structures or in bridge construction, and so individual panel elements, which are no longer joined together, are then disposed next to each other.
There have also been published other design variants for nailed, beam-like wooden structural members (DE C 842709) and for board-stack elements (DE A 19513729), in which individual boards are joined together as one element by nailed and/or screwed joints.
The object of the present invention is now to provide a load-bearing wooden panel element of the type mentioned in the introduction, which can be made with arbitrary length and width, wherein the forces occurring on individual layers of boards during loading of this panel element can be transferred to the greatest possible width of the panel element
According to the invention, it is proposed for this purpose that the individual boards be joined together at least partly by screws driven at an acute angle to the surface thereof and disposed at least approximately in a plane running transverse to the longitudinal extent of the panel element, which screws pass through at least two successive boards.
By these features according to the invention, the situation is achieved that the occurring forces are transferred to a plurality of layers of boards disposed next to each other, even in the case of point-like or small-area loading of such a panel element, since the successive layers of boards are joined together in, so to speak, hook-like manner by the screws driven at an acute angle. Moreover, it is achieved by the use of screws that the successive layers of boards are effectively held and braced mutually. Thus, even in the case of possible shrinkage or expansion of the natural wood product, no change of the mutual fastening of the boards is necessary, since these always remain intimately and intensively joined to each other. By virtue of the special arrangement of the screws, these should be stressed primarily in longitudinal direction, or in other words by tension or compression, thus ensuring great effectiveness with respect to load-bearing capacity and stiffness.
It is further proposed that, in successive boards or in every second board, screws with crosswise directions be driven into successive planes separated by a spacing and disposed perpendicular to the boards. This feature offers the guarantee that in precisely these fastening zones, each layer of board is for practical purposes attached on both sides to the neighboring board by a hook-like arrangement, so that it can transfer large forces to a large area of a panel element.
In order to create even more fastenings between the individual boards in addition to this special mutual fastening for extensive transmission of forces, it is proposed that, in addition to the screws driven at an acute angle to the surface of the boards, further screws be used which are driven at right angles to the surface of the boards, each of which screws passes through at least three successive boards. By these additionally driven-in screws it is achieved that joining of the successive layers of boards takes place almost in the manner of a truss, specifically since the screws driven at an acute angle and at right angles complement each other.
In this connection it is advantageous for the screws driven at right angles to the surface of the boards to be driven alternately into every second board and to pass through three layers of boards. This creates the possibility of a repeatedly overlapping fastening between the individual boards since, for example, the screws driven at an acute angle pass through two boards and the screws driven at right angles each pass through three layers of boards. In this way optimal force transfer to large areas of the wooden panel element can be achieved.
In one advantageous embodiment is it provided that screws driven in pairs at an acute angle and at fight angles to the surface of the boards are disposed successively at a predetermined grid pitch and in two planes separated by a small spacing. Thereby pairs of successive fastener planes separated by a small spacing are then practically always created at specified spacings, in order in this way to achieve the optimum in mutual joining of the boards and in the capability of mutual force transfer.
In this connection, it is advantageous for the screws in one of the planes disposed at the grid pitch always to be driven to be inclined at an acute angle in one direction and those in the other plane to be inclined at an acute angle in the opposing direction, the two screws in each pair being driven crosswise relative to each other at the respective surfaces of boards fitting the grid pitch, but being disposed in successive planes separated by a small spacing. During construction of the panel element, therefore, two screws are practically always driven at an acute angle into planes disposed next to each other but separated by a small spacing, one directed obliquely from top to bottom and the other obliquely from bottom to top. In this case two fastening planes are always present next to each other in the manner of trusses, so to speak, thus ensuring optimal mutual joining of the individual boards as a panel element and optimal transfer of forces.
In this connection, it is advantageous precisely in the sense of forming truss-like fastening planes for screws inclined at an acute angle in the one direction to be provided in a plane fitting the corresponding grid pitch relative to the length of the panel element and, furthermore, for screws driven at right angles to the surface of the boards to be provided close to the top and bottom board edge. In this way, top and bottom tension or compression elements are formed practically transverse to the longitudinal extent of a panel element, and load-bearing elements are produced by screws inclined at an acute angle therebetween. Since the two screws driven at an acute angle are additionally disposed crosswise, two load-bearing zones interacting with each other are created in the imm
Kent Christopher T.
SFS Industrie Holding AG
Thissell Jennifer I.
Volpe and Koenig P.C.
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