Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SEISMIC RESISTANT EQUIPMENT RACK
FIELD
The present invention relates to an equipment rack typically used
for telephone relays which have been made resistant to damage from seismic
5 disturbances.
BACKGROUND
Telephone companies typically have several sites around a major
metropolitan area where racks of relays are stored together with other
10 equipment. The purpose of these sites known as central offices, is to operate as
switching centers for telecommunication within a region of subscribers. The
relays located at these sites are critically important to the maintenance of
telephone communications within the area and with other areas. One of the
main potential causes of damage is due to seismic disturbances, particularly in
15 regions of high earthquake activity. In such areas as well as other areas it is
important to design racks for holding these relays which are resistant to damagefrom seismic disturbances. Typically such racks have been made from
aluminum formed into a rectangular frame with a cross bar at the top and bolted
and/or welded to a common base. Dynamic testing of such racks has disclosed
20 them to be unable to withstand even relatively small earthquakes when
subjected to lateral vibrations. Often the upstanding frame elements twisted
dramatically.
Known telephone racks include that disclosed in U.S. Patent No.
25 4,715,502 issued to Salmon. The Salmon rack is made up of a pair of U-
shaped upright members joined at the top by a U-shaped cross member and
bolted at the bottom to base plates transverse to the plane defined by the
upright and cross members. The base plates are described as the means by
which the upright members are prevented from tilting forward or backwards.
30 The U-shaped channels are inherently stronger than a flat plate but not
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sufficiently strong to prevent twisting and/or bending when strong seismic forces
are imposed.
U.S. Patent No. 5,566,836 issued to Lerman also discloses a
5 telecommunication rack having a pair of U-shaped channel uprights joined at
the bottom by plates extending across the bottom of the uprights and bolted to
the latter with the ends bent transverse to the plates so as to provide some
stiffening to the plates. It is doubtful that the base bolts which affix the uprights
to the base plates or the U-shaped uprights could withstand any significant
10 seismic activity.
U.S. Patent No. 4,493,422 issued to Kaegebein discloses a rack
having a pair of U-shaped channel members as uprights, a U-shaped cross
member and a pair of base plates the extend transversely to the plane defined
15 by the uprights and cross member and a pair of oppositely disposed stiffening members affixed to each base plate and associated upright. Kaegebein
discloses no cross member joining the base of the uprights. Although the
stiffening members would assist in resisting vibrations transverse to the plane of
the uprights and cross member, the bolts between the base plate and the
20 stiffeners would be subject to shear. Also horizontal vibration forces parallel to
the latter plane would be resisted only by the bolts between the stiffeners and
the base of the uprights. The latter bolts are also in shear.
Accordingly, it is an object to provide an improved rack for holding
25 equipment that provides improved resistance to seismic vibrations.
SUMMARY OF THE INVENTION
According to the invention there is provided a seismic resistant
equipment rack which has a pair of hollow tubular uprights having a rectangular
3 o cross section and a hollow tubular cross member extending across the top of
the uprights from one of the pair to another and welded to the uprights around a
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perimeter of each end of the cross member. A stiffening device is mounted in
each of the uprights proximate a top thereof for stiffening the top of the rack. A
pair of gusset plates extends from a base of one of the uprights to another. Thegusset plates are welded to the uprights along a top and bottom thereof. A pair
5 of stiffening elements are welded at each side of the rack to each of the gusset
plates and extend transversely to the plates. The above rack is simpler than
known racks, much lighter and less expensive. Utilizing gusset plates together
with stiffeners for the gusset plates and welding the uprights to the gusset plates
provides hitherto unachieved stability. Added to this is the strength of
10 rectangular tubular steel frame members and cross members.
A pair of stiffening plates may be aligned with top and bottom
surfaces of the cross member and welded in an interior of each of the uprights
proximate a top thereof. The stiffening plates provide continuity of material from
15 an outside surface on one side of the rack to an outside surface of the other side. This makes any deformation of the upper end of the rack much more
difficult.
The tubular uprights and cross bar are preferably made of steel.
2 0 However, other metal alloys which are as strong or stronger than steel may be
used.
The uprights may have a cross section with dimensions of 2
inches by 4 inches by 1/8 inch. The gusset plate may be 1/2 inch thick and also
25 may be made of steel.
Advantageously, the natural frequency of the rack in either a
direction parallel to a plane of the uprights or transverse thereto preferably
exceeds 6 Hertz.
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BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages will be apparent from the
following detailed description, given by way of example, of a preferred
embodiment taken in conjunction with the accompanying drawings, wherein:
Fig. 1 is a perspective view of the seismic resistant equipment
rack;
Fig. 2 is a front elevation view of the equipment rack;
Fig. 3 is a detail diagram of an upper corner of the rack;
Fig. 4 is a partial section of the upper corner of the rack; and
Fig. 5 is a side elevation view of a bottom portion of the rack.
DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS
Referring to Figures 1 and 2 the equipment rack 10 has two
upright parallel tubular members 12 and 14 of rectangular cross section.
These uprights are 4 inch by 2 inch by 1/8 inch hollow structural steel sections.
Metal such as aluminum is too soft to provide sufficient strength. A cross
member 18 joins upright members 12 and 14 at the top and is welded around
the perimeter of the ends of cross bar 18. The cross member 18 is of the same
cross sectional dimensions and the same material as uprights 12 and 14. In
addition, as seen in Figures 3 and 4 two stiffening plates 30 and 32 are
positioned to align with the top and bottom surfaces of cross bar 32 when the
latter is in position to be welded to the uprights. The stiffening plates 30 and 32
have welds 34 and 36, respectively, extending around their perimeter which
bond them to the inside of the respective uprights 12 and 14. Thus, there is a
3 o continuity of material all across the top through to the outside surfaces of
uprights 12 and 14.
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The bottom of the two uprights 12 and 14 are welded to two right
angle 1/2 inch thick steel gusset plates 16 and 26 with welds 44 and 42
formed along the top and bottom, respectively, of each plate at each upright 12
and 14 and by welds 41 and 43 along the sides of each upright at each of
plates 16 and 26. In addition, steel stiffeners 20 are welded at each end on
each side of the rack 10. The stiffeners 20 have welds 41 and 43 along each
side of their line of contact with the plates 16 and 26. They provide resistanceto vibrational motion perpendicular to the plane of the rack. Welds 44 and 42
10 of the plates 16 and 26 to the bottom of the uprights 12 and 14 serve to resist
shear due to vibrations in the plane of the rack 10. The bottom portion 24 of
base plates 26 and 16 is anchored to a base support (not shown) which is
usually a thick reinforced concrete slab. Heavy plate washers 38 and
seismically rated anchors 40 are used to fasten the rack base to a concrete
15 floor through slots 22.
Utilizing strong steel members of rectangular cross section
improves the resistance of the rack to fracture of these members and twisting.
Ordinarily, shelving and equipment is screwed to the front of the uprights
20 through with self-tapping screws engaging screw holes which pass through the
front of the uprights.
Such units were subjected to test protocols in accordance with the
Generic Requirements document (GR-63-CORE of 1 October 1995) published
25 by Bell Communications Research, Inc.(Bellcore) and titled: Network
Equipment-Building System (NEBS) Requirements: Physical Protection. It was
found that full compliance was achieved with static testing, with the
requirements for natural mechanical frequency and all of the dynamic tests that
were run.
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Accordingly, while this invention has been described with
reference to illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications of the illustrative
embodiments, as well as other embodiments of the invention, will be apparent
5 to persons skilled in the art upon reference to this description. It is therefore
contemplated that the appended claims will cover any such modifications or
embodiments as fall within the true scope of the invention.
