Slipform pavers capable of inserting dowel bars as a strip of concrete is being laid down are well-known and are produced and widely distributed, for example, by the applicant and assignee of this patent application.
Such well-known slipform pavers are typically used for laying down long strips of concrete, used in the context of projects for forming highways, airport runways, and the like. The pavers are continuously supplied with fresh concrete as they travel in the direction of the strip. The pavers form the freshly supplied concrete into a rectangular, cross-sectional shape, and then properly finish the top surface of the strip, after which the strip of concrete is allowed to set and harden. After the concrete has hardened, contraction joints are normally sawed across the width of the strip to control the cracking. In order to maintain the integrity of the strip at such contraction joints, dowel bars are inserted into the fresh concrete at the location of the joint for the purposes of load transfer. Generally, the dowel bars are arranged parallel to the length of the strip and typically have diameters that range from about one to two inches (1-2 in.) and lengths from twelve to twenty-four inches (12-24 in.).
Dowel bar inserters place a line of dowel bars across the slab and parallel to the slab as the slab is being formed at the location of the transverse contraction joint at mid slab length and, in general, simultaneously insert from about twelve to thirty-six (12-36) or more dowel bars depending upon the width of the strip being paved. Center-to-center spacing between the dowel bars typically varies between about twelve to eighteen inches (12-18 in.). As will be further described below, the mechanism that simultaneously inserts the dowel bars must remain stationary with respect to the strip of concrete being laid down while the dowel bars are inserted. The dowel bar inserter must therefore be able to move relative to the remainder of the paver during the dowel bar insertion.
U.S. Pat. No. 6,579,037 discloses a paver with a widely used dowel bar inserter, relevant portions of which are reproduced herein to facilitate the reading and understanding of the present invention. U.S. Pat. No. 6,579,037, owned by the applicant and assignee of the present patent application, is herein incorporated by reference. For further background and understanding of dowel bar inserters, U.S. Pat. Nos. 8,382,396, 9,039,322, and 9,359,726, each also owned by the applicant and assignee of this patent application, are all herein incorporated by reference.
Known dowel bar inserter machines and modules have a maximum width of about thirty-four feet (34 ft.). This structural limitation prevents practical use of dowel bar inserters with various slipform pavers that have the capability to lay down concrete at widths wider than thirty-four feet, leading to a limitation in throughput and a time bottleneck for construction.
Other attempts at constructing dowel bar inserters with widths substantially greater than known machines in the industry have employed excessively complicated and bulky superstructures, trusses, beam connections, or exoskeletons built up on top of known dowel bar inserters or portions thereof to allow them to handle the increased span and to support the DBI confining pan in the middle of the span. Besides the additional complexity of secondary attachment, there are problems due to mismatches between existing machine components and structure and the added-on supplement. The additional bulk makes these structures harder to change width and transport. These structures also tend to add excessive weight, adding stress to the machine, increase the ground pressure of the machine's supporting crawler tracks, and potentially affecting underlying paved concrete strips. The added weight and complexity of such solutions also increases the amount of time required to actually change the width of the machine. With all of these problems, there is also scant (if any) evidence that such attempts are technically or commercially viable, let alone successful.
A further limitation of previously known dowel bar inserters is that many such machines are unable to account for the curvature or crown of the ground or underneath the vehicle. In such cases, the location and orientation of a dowel bar by the inserter module may be offset, misaligned, or otherwise flawed in insertion, reducing the quality of the concrete and road being laid down.
Moreover, prior dowel bar inserter vehicles that attempted to change widths were limited by the effect on insertion height by the width change, in that the structures lowering dowel bars would not have the capability to account for any resulting changes in height, underlying ground shape, or the like resulting from the broader vehicle base.
This operational width limitation of such known dowel bar inserters, and the corresponding specific limitation to wide-width paving applications, affects the entire slipform paver because of its limited use. This is highly undesirable because it increases overall concrete laying costs because of the cost of this very specialized equipment.