Note: Descriptions are shown in the official language in which they were submitted.
~10~)7:t4
The present invention relates primarily to an im-
provement in bearings of the type described and claimed in
U.S. Patents 3,806,975 and 3,921,240. The bearings described
in these patents are primarily intended for the support of the
decks of bridges or piers and abutments wherein rotational and/or
translational motion takes place between the bridge deck and the
pier or abutment. However, the present invention also provides
an improvement which is useful with bearings of somewhat similar
general construction wherein there may be no rotation or trans-
lational movement between the bridge deck and the pier or abutment.
The invention also is useful with bearings which support other
structures such as buildings. The principal objective of the
invention is to assure that the bearing will have the capabilility
of sustaining very heavy loads and that the load carrying capability
will be stabilized.
In bearings of the aforesaid type, an elastomeric pad,
generally 1/4 to 5 inches thick is fitted between two flat plates
which in turn are secured between the bridge deck or some other
structure and the pier, abutment or some other foundation. In the
type of bearings described in the aforesaid patents, a third plate
is mounted for sliding movement relative to one of the plates and
anchored to the structure or the foundation to accommodate trans-
lational movement, and means are provided to minimize shearing
strains in the elastomer without interfering with necessary rota-
tion between the first and second plates and compression ofthe elastomer by the weight of the structure. The preferred type
of elastomer pad is circular, and the lateral edge of the pad
preferably is concave. In practice, the elastomer pads which
have been used in this type of bearing have been biconical
(i.e., they resemble a pair of conical sections, one
inverted over the other).
Variations have been encountered in the load capa-
, . .
bilities of the elastomer pad. This is evidenced by the load-
deflection curve for the bearings wherein the deflection of
a bearing under load is greater in some instances than in
others. It now has been discovered that these variations can
be attributed to variations in the bonding of the elastomer
pad to the aforesaid plates above and below it, which is
believed to have allowed the upper and lower surfaces of the
biconical pad to spread laterally under load, to some extent
irreversably. The present invention provides a structural
means for preventing lateral spreading of the outer surfaces of
the elastomer pad and therefore maximizing and stabilizing the
load carrying capability of the bearings.
In a preferred form the invention also provides a
safety element which protects the bearing pad from the hazard
of overload and from separation from the aforesaid plates
during rotation. Briefly, the structural means comprises means
secured to the plate which provides a mechanical interlock with
the elastomer pad so as to exert a force opposed to lateral
growth of the upper and lower surfaces of the biconical or similar
pad when it is compressed.
The invention will be better understood by reference
to the following detailed description of preferred embodiments,
reference being made to the drawing, in which:
11~0714
FIGURE l is a cross section through a preferred
form of the new bearing;
- FIGURE 2 is a plan view of a plate used in the
bearing of FIGURE l;
FIGURE 3 is a side elevation of the bearing pad of
the bearing of FIGURE 1, when partly compressed;
FIGURE 4 is a side elevation of the bearing pad of
the bearing of FIGURE l, when further compressed; and
FIGURES 5-10 are cross sections through the bearing
pad and ac'joining plates of other embodiments of the bearing
of the present invention.
As shown in Figure 1, the bearing comprises three
steel components, a square .op plate, a square middle plate
2 and a base plate 3. A circular bearing pad 4 is positioned
( 15 between the middle plate 2 and the base plate 3 and a low
friction plastic sheet 5 is positioned in a recess 6 in the top
of middle plate 2 to r`educe friction between middle plate 2 and
top plate 1. The top plate 1 and the base plate 3 are fitted
with concrete anchors 7 and 7' to secure them respectively to a
bridge pier 8 and a bridge deck 9 although it will be understood
that the bearings can be used in other kinds of constructio~.
The top plate l is provided with depending side plates lO and il
which extend along opposite sides of the middle plate 2 to sub-
stantially confine relative sliding movement between the bridge deck
9 and the pier8 to a single direction. However, it will be
understood that other arrangements can be used, for example, to
allow sliding movement in all directions, by omitting plates 10
14
and 11 or to substantially prevent sliding move~ent in
all directions, depending upon the requirements of the
structure.
The bearing is equipped with a pin 12, which is
integral with the base plate 3 and which is engaged in a
cylindrical collar 13 as described in U.S. Patents 3,306,975
and 3,921,240 in connection with Figure 3 thereof.
The bearing pad 4 is made from polyurethane elastomer,
preferably 85 to 95 durometer, Shore A and is of biconical
shape. The dimensions of the pad 4 depend on the weight the
pad is expected to support, but typically the exte-nal diameter
is 4 to 60 inches and the diameter at the midpoint 14 is typically
1/8 to 2 inches less than the diameter of the pad.
In one for~ of the ~resent invention, the ~iddle
plate 2 is provided with a depending circular ring 15 which
extends around the bearing pad, but whose internal diameter is
slightly larger than the initial diameter of the bearing pad 4.
Preferably, a clearance of 1/32 to 3/8 inch is provided. Simi-
larly, the base plate 3 is provided with a raised ring 16 of the
same diameter and it allows the same clearance.
The arrangement is such that, as initially assem-
bled, the bearing pad does not contact either of the rings lS
and 16. However, as the bearing is compressed by the weight
of the structure, two phenomena are observed. First, as illus-
trated in FIGURF 3, the tapered sides of the pad bulge outwardly
and towards each other. Ultimately, if the bearing is compressed
sufficiently, the tapered sides of the pad 4 bulge outwardly ~o the
.
: , :
` 11~)0714
extent that they contact the rings 15 and 16. However, the
bearings are designed so that this does not occur at the design
load. Thus the ring provides a safety factor which comes into
effect if the bearing is overloaded. At that stage the shape
S factor of the pad is increased and it is substantially prevented
from undergoing further compression.
The second phenomenon which is observed is that
the diameter of the bearing pad 4 may increase slightly on its
top and bottom surfaces, as described above, but growth is
limited by the rings 15 and 16.
A third phenomenon is observed if the bearing is rotated
or tilted. In this situation, the bearing pad is compressed
more on one side than on the other side. When this occurs,
the outwardly bulging tapered sides may contact the rings 15
and 16 in the area of greatest compression. When that occurs,
further compression in that area is restricted in effect by
changing the shape factor of the pad.
A further advantage of the invention follows from
this arrangement. Because overcompression during tilting is
avoided, it is possible to use relatively softer elastomer than
otherwise would be possible. During rotational movements, soft
elastomers can stretch a little, if needed, in the area opposite
the compressed areas, and therefore, avoid separation from the
plates 2 and 3, which otherwise might occur. As a result, the
bearings can be rated for greater rotational movement than
otherwise might be allowed.
-- 6
11~)(~714
The overall effect of the invention is to increase
the rated loadings of the bearings. For example, it is presently
believed that bearing pads which were rated at 2500 psi can now
be rated at 3~00 psi.
Further improvements in the bearings can be provided
by other means which reduce the growth of the upper and lower
surfaces of the pad 4. This is provided by a variety of mechani-
cal interlock arrangements which provide an internally facing
vertical or inclined surface of the middle plate 2 and/or the
base plate 3 which abuts an outwardl~ facing vertical or inclined
surface of the bearing pad 4 internally of the perimeter of the
bearing pad. Several forms of abutting surfaces are illustrated
in Figures 5-10. ~
Thus in Figure 5, metal rings 120 and 121 are fastened
to the lower surface of plate 102 and the upper surface of plate
103. The metal rings 120 and 121 are formed with grooves 122
and 123 on their lower and upper surfaces respectively. The
bearing pad 104 ls forced into the grooves 122 and 123, thereby
providing a mechanical interlock. In Figure 6 there are rings
220 and 221 secured to the lower surface of plate 202 and the
upper surface of plate 203 respectively. These metal rings
220 and 221 are formed with ribs 222 and 223 on their lower
and upper surfaces respectively which press into the bearing
pad 204. Therefore, a mechanical interlock is provided. In
Figure 7, there are circular grooves 320 and 321 formed in the
lower and upper surfaces respectively of the plates 302 and
303. The bearing pad 304 is pressed into these grooves and
14
therefore a mechanical interlock is achieved. In Figure 8,
there are circular ribs 42Q extending downwardly ~rom the
lower surface of plate 402 and there is a circular groove
421 in the upper surface of lower plate 403. The ring 420
presses into the elastomer pad 404 and the pad is pressed
into the groove 421. Therefore a mechanical interlock is
accomplished. In Figure 9, there are circular rings 520 and
521 extending downwardly and upwardly respectively from the
plates 502 and 503. The rings 520 and 521 press into the
bearing pad 504 to provide a mechanical interlock. Figure 10
is quite similar to Figure 9 except that in this case there
are three rings 620, 620' and 620" extending down from the
lower surface of the plate 602. Similarly, rings 621, 621'
and 621" extend upwardly from the upper surface of plate 603.
These rings press into the elastomeric bearing pad 604 to
cause a mechanical interlock.
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