Static structures (e.g. – buildings) – Assembled in situ-type anchor or tie – Socket type
Reexamination Certificate
2002-01-10
2004-07-06
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
Assembled in situ-type anchor or tie
Socket type
C052S585100, C052S583100
Reexamination Certificate
active
06758023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to expansion dowel systems. More particularly, the present invention relates to construction joints for transferring stresses across a joint between concrete constructions. More particularly, the present invention relates to the use of polymeric sleeves extending around a portion of a rigid dowel bar within the concrete construction.
2. Description of Related Art
Concrete responds to changes in temperature and moisture when movement associated with these changes (or for other reasons such as internal chemical reaction) is restrained. In these instances, stresses develop that can lead to cracking. To control cracking, joints are built at interval distances short enough to maintain stresses below critical values. Transverse joints are saw cut, placed through induced cracking, or formed at pre-determined spacings.
Concrete pavements for highways, airport runways and the like are generally placed in strips or lanes with a longitudinal joint formed between adjacent strips or lanes. Concrete is poured in the first strip and allowed to cure. Subsequently, concrete is poured and cured in the adjacent strip and so on until the concrete pavement is completed. A longitudinal joint is formed between adjacent strips to facilitate construction and to reduce stresses and control cracking caused by contraction or expansion of the concrete. Transverse or slug joints are also formed in concrete by cutting or sawing the concrete at a given location and to a given depth.
Similarly, joints are formed in concrete structural slabs, walls, footings and the like to minimize stresses and/or simplify construction methods. Of these joints, there are several types. For example, the expansion joint provides a space between slabs to allow for expansion or swelling of the slab as temperature and moisture increase or grow occurs. A construction joint provides a finished edge or end so that construction operations interrupted for some length of time may be continued or resumed without serious structural penalty.
Load is transferred across a joint principally by shear. Some bending moment may be transferred across the joints through tie joints. Good load transfer capability must be built into the joint or the load carrying ability of the concrete slab or structure will be reduced. The alternative is to strengthen the concrete by improving support or increasing depth to minimize the joint load transfer weakness.
Tie bars and dowels are often used in concrete design to improve load transfer at the joint between concrete slabs or structures. Such tie bars and dowels are embedded in the concrete and arranged across the joint in a direction substantially perpendicular to the axis defined by the joint. Various approaches, depending on the type of tie bar or dowel, have been suggested with respect to concrete construction joints.
In the construction of concrete slabs on grade, it is common practice to install continuous side forms with dowels for future adjacent slab concrete placement and to place concrete in long continuous strips. It is also known to place slab dowels and sleeves at specified distances across the strips to allow the strips to have a controlled plane to accommodate shrinkage of the concrete. The positions of these dowel locations are marked on the side forms and the concrete after placement and finishing is struck to provide a joint at these locations.
The functions of the tie bars and dowels are to keep contiguous sections of concrete in alignment during contraction and expansion, and to transfer shear stresses and bending moments across the joint between the two slabs.
FIG. 1
shows a typical dowel bar sleeve assembly which is used in a concrete structure. As depicted in
FIG. 1
, sleeve dowel bar assemblies are embedded in the first concrete slabs, and arranged across the transverse transfer joint
22
a
to
22
e
and
23
a
to
23
e
, in a direction substantially perpendicular to the axes defined by the transverse transfer joint. Similarly, dowel sleeves are embedded in the first concrete slabs and arranged across the joint in a direction substantially perpendicular to the axes defined by the longitudinal transfer joint
24
a
to
28
a
, etc. In a typical installation sleeve, dowel bar assembly
32
is positioned on the rebar-matrix and the concrete slab is poured. The concrete slab is allowed to harden in situ with the dowel bars and dowel sleeves embedded therein.
After the first concrete slab has undergone expansion or contraction from thermal or drying shrinkage, the second concrete slab is placed adjacent to the first concrete slab after the dowel bars are inserted into the sleeves previously placed in the prior concrete pour so that the dowel bars are also essentially embedded in the second concrete slabs. The second concrete slab will attempt to shrink during curing in a similar manner to the shrinkage of the first concrete slab.
In a conventional installation, the dowel bars arranged across longitudinal joints between the first and second concrete slabs will attempt to restrain the second concrete slabs from movement. The developed and internal stress in the second concrete slab can create an added stress which may cause cracking by itself or when added to an applied load upon the slabs. The cracks will often develop along a line near the ends of the dowels bars. Referring now to
FIG. 1
, an illustrative reinforced concrete slab section
10
is shown which includes two versions of the concrete dowel slab joint system in place of the conventional dowel bars previously discussed. In a first version, denoted
18
, a dowel bar
20
is positioned within a single sleeve body
32
. This first version is used to bridge longitudinal joints, for example, the joints formed between adjacent slab segments
12
a
,
14
a
,
16
a
, etc. In a second version, denoted
19
, a dowel bar
20
is positioned within the confines of a pair of sleeves
32
. The second version is employed to bridge transverse joints
22
a
,
22
b
,
22
c
, etc. A reinforced concrete slab section
10
comprises a concrete slab and may include an interconnected matrix of reinforcing re-bar rods (not shown). The matrix of reinforcing re-bar rods are arranged in a predetermined pattern according to known principals of structural engineering.
In the past, various U.S. patents have issued relating to such expansion dowel systems. In particular, U.S. Pat. No. 5,797,231, issued on Aug. 25, 1998 to D.R. Kramer, describes a concrete dowel slab joint system for maintaining adjacent sections of concrete, and alignment during contraction and expansion of the concrete, and for transferring shear stresses and bending moments across a joint formed between adjacent concrete slabs. This system includes a sleeve assembly for receiving and maintaining the dowel bar there within. As a result, the dowel bar will not transmit substantial shear stresses to the concrete during the contraction and expansion of the concrete. The sleeve assembly comprises an elongate sleeve body having an outer surface and an inner surface and defines a hollow interior compartment. The sleeve assembly uses a collapsible spacer member located within the hollow interior compartment.
U.S. Pat. No. 5,628,579, issued on May 13, 1997 to H. Forrester, describes an expansion dowel which includes an expansion sleeve and an expanding member. The expansion sleeve is provided with a bore tapering in the setting direction as well as with an open ended longitudinal slot. The expanding member has a blind bore open towards the setting side and has a lug projecting from the same at its opposite end. The cross-sections of the lug and the blind bore are matched to one another so that a rated break point or failure point is formed.
U.S. Pat. No. 5,931,619, issued Aug. 3, 1999 to M. Hartmann, describes an expansion dowel formed of an axially extending expansion sleeve with a through bore and an expansion region having at least one axially extending slot, and an expanding member axially displaceable by axially directed
Friedman Carl D.
Harrison & Egbert
Katcheves Basil
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