STRUCTURAL PLATE

Technical Field The present invention relates generally to structural plates,

Background Art Structural plates are used to span over plane areas and support their own weight as well as additional loads. Under the applied loads the plates deform into a concave shape while developing internal tensile, compressive and shear stresses. A structural plate performs well as long as the internal stresses remain below specified threshold values which are characteristic properties of the material or materials, which the plate is made of, and, as long as the deformation remains small. For different environments and uses, codes of practice normally define the maximum allowable deformation that renders the plate serviceable. As the dimensions of the area to be covered increase, it becomes increasingly more difficult to satisfy the performance requirements. Sometimes the only reasonable solution is to introduce different structural members such as linear beams which interfere with the plate action as well as with the free space that is covered.

The stiffness of the plate, or in other words its deflection due to a given unit load and its weight effects the frequency of free oscillations. In many applications, such as in providing a support

to vibration-sensitive equipment, it is highly desirable to raise the magnitude of the natural frequencies. Since the increase of thickness is accompanied by an increase of weight, it is sometimes very difficult, if at all possible, to achieve the desired frequency level.

Disclosure of the Invention

Accordingly, it is an object of the present invention to provide a structural plate which avoids the disadvantages of the prior art. In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a structural plate, which has a main plate part with two opposite surfaces and at least one ring-shaped peripherally closed uninterrupted member provided on at least one of the opposite surfaces and fixed to the latter. The ring-shaped members can also be provided on both opposite surfaces of the main plate part. On the other hand, it can be fixed either on the upper surface, or on the lower surface of the plate part, if the structural plate extends in a horizontal plane. The ring-shaped member can be formed as a cylindrical ring, or a ring of another shape. Its peripheral wall can extend exactly perpendicularly relative to the main plate part or somewhat inclined relative to the latter. When the structural plate is designed in accordance with the present invention, the ring- shaped member or members which are fixed to the main plate part, force the plate to develop intermediate

SUBSTITUTESHEET

inflection lines, i.e. lines along which the slope of the deflected shape is zero. In doing so, the maximum deflection of the plate is greatly reduced, thus increasing its stiffness with only a slight increase in overall weight. The novel features of the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its manner of operation will be best understood from the following description of preferred embodiments which is accompanied by the following drawings.

Description of Drawings

FIG. 1 is a view showing a structural plate in accordance with the present invention, with a main plate part provided with an upper ring-shaped member; FIG. 2 is a view showing a radial cross-section of the structural plate of FIG. 1 in a deflected condition; FIG. 3 is a view substantially corresponding to the view of FIG. 2, but showing the structural plate with a lower ring-shaped member; FIG. 4 is a view showing compression stresses in the ring-shaped member of FIG. 1; FIG. 5 is a view showing tensile stresses in the ring-shaped member of FIG. 3; and FIG. 6 is a view showing ring-shaped members of different shapes.

Best Mode for Carrying Out the Invention

A structural plate in accordance with the present invention has a main plate part 1 with two opposite surfaces 2 and 3, and a ring-shaped uninterrupted peripherally closed member 4 attached to at least one of the surfaces 2 and 3 of the main plate part 1. As can be seen from FIG. 1, more than one ring-shaped member can be attached to the same surface, for example to the surface 2. In the shown example, two ring-shaped members 4 and 5 are attached to the surface 2 of the main plate part 1. The ring-shaped members can be spaced from one another on the same surface. For example, they can be arranged one inside the other and concentrically relative to one another as shown in FIG. 1 and 2 for the ring members 4 and 5. The ring-shaped member in FIGS. 1 and 2 extend transversely to the surface 2 and particularly perpendicularly to the latter. However, it can be somewhat inclined to this surface as well as at a desired angle. The ring-shaped members 4 and 5 can be of different heights relative to the surface 2. In FIG. 3 a ring-shaped member 6 is attached, to the contrary to the lower surface 3 of the main plate part 1. In accordance with the present invention, it is also possible that the ring-shaped members are arranged on opposite sides 2 and 3 of the main plate part 1. The ring-shaped members on the opposite surfaces can have different shapes. On the other hand, the ring-shaped members 4 and 5 provided on the same surface and arranged concentrically in one another. The ring-shaped member 7 is cylindrical, the ring-shaped member 8 is

formed by a plurality of concave walls, the ring- shaped member 9 is formed by a plurality of convex walls. In the inventive structural plate as the plate part begins to deflect under the action of applied load the contour of the ring-shaped member stretches for the member located below the plate part, or compresses for the member located above the plate part. These predominantly membrane stresses act along the circumference of the ring-shaped member maintains its verticality as the plate deflects. Because the ring-shaped member is fixed to the plate part, the horizontal line in the plate part must remain horizontal in the deformed shape. Since the deflection of the plate part is the analytic integral of the slope, the maximum deflection of the main plate - ring-shaped member system will be smaller as compared with the deflection of a purely flat plate. The ring-shaped members can be attached to the main plate part by conventional methods, for example welding, gluing, etc. The invention is not limited to the details shown, since various modifications and structural changes are possible without departing in any way from the spirit of the invention. What is desired to be protected by Letter Patent is set forth in particular in the appended claims.

SUBSTITUTE