Note: Descriptions are shown in the official language in which they were submitted.
CA 02278462 1999-07-16
Concrete Pillar
Description
The invention concerns a concrete pillar, in particular a
circular pillar made of reinforced concrete with a pillar
base connected with a foundation, with a pillar top
supporting a load, as well as, optionally, a steel
reinforcement fitted inside the pillar.
Pillars are vertical structural members, of which the
height or length is large in comparison to their cross-
sectional dimensions. The pillars serve as supports or
bearings for other structural elements, such as beams or
girders, and conduct their loads into the fundament.
Therein the application of compressive-loading is primarily
in the longitudinal direction of the pillar. In addition,
pillars can be caused to bend by application of horizontal
forces, such as wind forces, impact forces or seismic
movements. With slender pillars there is the further
danger of buckling. Depending on the type of manufacture,
minimum thicknesses have been prescribed for pillars
independently of the loads or the danger of buckling. For
the evaluation of pillars, regulations set forth in
DIN 1045 apply. However, in a case of a danger of high
impact forces and seismic movements these guidelines are
not adequate for a buckling resistant design of steel
reinforced pillars.
Beginning herewith the present invention is concerned with
the task of providing a pillar with high resistance to
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buckling, which can also tolerate large horizontal forces
and seismic movements.
For the solution of this task it is proposed in accordance
with a first alternative embodiment to provide a flat strip
in the form of a helix between the pillar base and pillar
top and having a composite structure consisting of a
plurality of substantially parallel-aligned reinforcing or
reinforcing fibers and a binder matrix which shear-
resistantly binds the reinforcing fibers to each other and
which is attached to the pillar surface by one of its broad
sides by means of an adhesive, wherein the lead of the flat
strip helix is greater than the width of the flat strip.
The bandwidth is so determined, that no closed interstitial
space can be formed between the flat strip and the pillar
outer surface from which any penetrating water could not
escape again. The pitch of the helix accordingly
corresponds approximately to 1.1 to 5 times, preferably 1.5
to 2.5 times, the width of the flat strip. On its ends the
flat strip is preferably fastened to the outer surface of
the pillar by at least one fastener element, so that it
cannot come lose at its ends.
According to a second embodiment, multiple flat strips
circumscribing the pillar in the manner of rings are
secured to the outer surface of the pillar via an adhesive
between the pillar base and pillar top, spaced apart from
each other, wherein the flat strips are comprised of a
plurality of reinforcing fibers oriented essentially
parallel to each other and a binder matrix which binds the
reinforcing fibers to each other in a shear-resistant
manner. Therein the flat strips have their overlapping
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ends connected to each other via the binder matrix. The
separation between the flat strips is so determined, that
no enclosed interstitial space can be formed between the
flat strips and the pillar outer surface from which any
penetrating water could no longer escape. The separation
between the flat strips corresponds therein to 0.1-4 times,
preferably the 0.5 to 1.5 multiple of the flat strip
breadth.
In the case of square or quadratic concrete pillars the
flat strips preferably exhibit a superimposed or impressed
bending in the intermediate areas between the pillar edges
or corners. This bending can be achieved thereby, that the
flat strips in the corresponding areas are freed of the
binder matrix with exposure of the reinforcing fibers, and
the binder matrix is replaced by a pasty hardenable plastic
resin.
A further improvement in the buckling resistance can be
thereby achieved in a preferred embodiment of the invention
when supplemental flat strips are provided which cross over
the helical shaped or ring shaped flat strips in spaced-
apart separation from each other and are adhered to the
pillar outer surface and/or those flat strips which are
present by means of an adhesive.
The reinforcing fibers of the flat strips are comprised
preferably of carbon fiber, which are characterized by a
high modulus of elasticity. In principle, it is also
possible to use aramid, glass or polypropylene fibers or a
mixture of the above mentioned fibers as the flat strips.
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As binder it is preferred to use a reaction resin, such as
an epoxy resin, polyurethane, acrylic resin or polyester
resin. In order to achieve a stable binding of the flat
strip to the outer surface of the pillar, the adhesive is
preferably also comprised of a reaction resin of the above
mentioned type.
The reinforced concrete pillar wrapped with the flat strips
can additionally be finished or provided with a protective
coating, so that the reinforcements are no longer visible
from the outside.
In the following the invention will be described in greater
detail on the basis of an illustrated embodiment shown in
schematic form in the drawings. There is shown
Fig. 1 a round pillar formed as a construction
support with helical shaped flat strip
wrapping;
Fig. 2a and b a top view and a side view of a flat strip
section;
Fig. 3 a construction pillar with ring or hoop like
flat strip wrapping;
Fig. 4a and b a section through a construction pillar
according to Fig. 3 formed as a square
pillar and as a round pillar;
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Fig. 5a and b a top view and a side view of a reinforcing
laminate or section with a binder free,
flexible intermediate area;
Fig. 6 a concrete pillar with cross-wise and
longitudinal running flat strip wrapping.
The concrete pillars 10 shown in Fig. 1, 3 and 5 have a
pillar base 12 imbedded in a fundament or foundation 11 and
a support head 16 formed as a bearing surface for a
construction element 14. The concrete pillar 10 can
include an internal steel reinforcement 17 (Fig. 4a and b).
The pillar is wrapped with a flat strip 18 (Fig. 1) or with
flat strips 18', 18 " for further strengthening against
bending or buckling.
In the case of Fig. 1 the flat strip 18 extends from the
pillar base 12 to the pillar top 16 in a helical manner
over the pillar outer surface and is secured thereto with
an epoxy resin adhesive 19. The free ends of the bands are
attached to the pillar via side-bar-like cover plates 20.
The pitch or axial spacing of the turns h of the flat strip
helix is therein larger than the band breadth b. This
corresponds in the shown embodiment to approximately 1.5
times the flat strip breadth b. The spaces 22 between the
flat strip ensure that no completely enclosed spaces are
formed between the flat strips and the pillar outer surface
in which water can collect.
In the embodiment shown in Fig. 3 a multitude of flat
strips 18' are provided which encircle the pillar in a
ring-like manner and are adhered to the outer surface of
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the pillar with an adhesive, and are provided with a
separation from each other which in the shown embodiment
corresponds to approximately 0.5 times the width of the
flat strip b. The spaces 22 between the flat strip rings
18' ensure that no associated closed hollow space can be
formed between the flat strip the pillar outer surface, in
which water can collect. The ring-shaped flat strips
encircle the support with ends 24 overlapping each other
(Fig. 3) .
In the embodiment shown in Fig. 6 there are provided, in
addition to the ring-like flat strips 18', flat strips 18 "
which cross these at an angle of 90°, which are provided
spaced apart from each other, so that also in this case
spaces 22 are maintained free for evaporation of water.
The flat strips are comprised of a composite of a plurality
of parallel oriented reinforcing fibers 26, preferably
carbon fibers, and a binder matrix 28, preferably of epoxy
resin, which binds the reinforcing fibers to each other in
a shear-resistant manner. As can be seen from Fig. 4a and
b, the pillars 10 can be either quadrilateral or round in
cross section. In the case of the quadrilateral cross
section according to Fig. 4a the flat strips are preferably
provided with an impressed bend 32 in the areas spanning
over the corners 30, which can be achieved thereby, that
the flat strip 18 is freed of its binder matrix 28 in the
appropriate area with exposure of the limp flexible
reinforcing fibers 26, and that after the wrapping of the
pillar the respective area is acted upon by a pasty,
hardenable plastic resin which can substitute for the
binder matrix (Fig. 5a and b).
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In summary the following is to be concluded: The invention
relates to a concrete pillar, in particular a circular
pillar made of reinforced concrete with a pillar base 12, a
pillar top 16 and, optionally, a steel reinforcement fitted
inside the pillar. In order to enhance flexural and
buckling resistance, a flat strip 18 in the form of a helix
is provided between the pillar base 12 and pillar top 16,
extending over the pillar surface, and having a composite
structure consisting of a plurality of substantially
parallel-aligned carbon fibers, and a binder matrix which
shear-resistantly binds the carbon fibers to each other.
The flat strip 18 is attached to the pillar surface by one
of its broad sides by means of an adhesive . The pitch h of
the flat strip helix is greater than the width b of the
flat strip 18.
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