Bridges – Deck
Reexamination Certificate
1995-04-28
2004-03-23
Dang, Hoang (Department: 3672)
Bridges
Deck
C404S070000, C404S082000
Reexamination Certificate
active
06708362
ABSTRACT:
BACKGROUND OF THE INVENTION
a.) Field of the Invention
The present invention relates generally to static structures. More specifically, it relates to concrete panel structures in a form which is useful for trusses, structural floors, or for use in bridge decks. The present invention also relates to methods of producing concrete panels for use in trusses, structural floors and bridge deck structures.
b.) Description of the Prior Art
Typically, traffic bearing floors on bridges are constructed using concrete bridge deck panels supported by a specifically designed substructure. Such concrete panels are normally at least six inches thick, and are continuous over at least a pair of separated support members, such as beams, which beams extend longitudinally in the same direction as what is defined herein as the length of the panels bridge span. State-of-the-art concrete bridge deck panel construction has traditionally been comprised of a slab constructed of one layer or more than one layer of concrete having a “flexural reinforcing structure” distributed throughout the concrete layer. Such a “flexural reinforcing structure” is generally in the form of a matrix of overlapping steel reinforcing bars (re-bars) or steel strands, which are spaced from both the upper surface and the lower surface of the concrete deck panel. In accordance with traditional practice, this flexural reinforcing structure is included in the concrete for the purpose of carrying bending moment tension stresses which are placed on the concrete panel due to loading and unloading of the top surface, for example, by the passage of vehicles on, or adjacent to, the top surface of the panel.
It has traditionally been believed that structural flexural reinforcing material such as steel reinforcing bars (re-bars), are required throughout the concrete of such a panel, and especially in groups in the top and bottom halves of the panel near both the top surface and bottom surface of the panel. In the current state-of-the-art, it is believed to be necessary to use both top and bottom structural flexural reinforcing material re-bars in order to restrain cracking of the top surface and of the bottom surface due to applied loads. The traditional art of bridge deck design and construction has been governed by AASHTO (American Association of State Highway and Transportation Officials). The 1989 Edition of the AASHTO Standard Specification for Highway Bridges specifies the minimum thickness of bridge deck 6.5 inches.
The lower group of flexural reinforcing material in the bottom half of a bridge deck panel normally consists of a first plurality of re-bars which form a layer. This first plurality of re-bars are transverse to both the length dimension of the panel and to the load-carrying beams on which the panel is supported. For structural purposes, this lower layer of transverse flexural materials (re-bar) carries the positive moment tensile stresses which are applied to the panel. A second lower layer of flexural reinforcing material, normally consisting of a second plurality of re-bars which are parallel to both the length dimension of the panel and to the load-carrying, support beams (and transverse to the first lower layer of re-bars) is located directly above the first lower layer of re-bars. For structural purposes this second lower layer of flexural reinforcing material re-bars distributes the bending moment loads which are applied to the panel longitudinally. Both lower layers of flexural reinforcing material re-bars provide control of temperature and shrinkage cracking at the lower surface of the panel as the minimum amount required for temperature and shrinkage reinforcement is less than the minimum required amount of flexural reinforcing for reinforced concrete. Under current codes, for most support beam spacings, which are up to about eleven feet apart, the longitudinal bottom group of flexural reinforcing material constitutes from about one-half to about two-thirds of the main reinforcement of the panel. The two lower layers of flexural reinforcing material are usually joined together, for example with wire, to form a mat or matrix.
Further, in accordance with current practice, another group of main flexural reinforcing material is located in the top half of the panel near the upper surface of the concrete panel. It normally consists of a first upper layer comprised of a plurality of flexural reinforcing materials, normally re-bar, which are designed to carry the negative moment tensile stresses which are applied to the panel, and a second upper layer normally immediately below the first upper layer and oriented transversely to the first upper layer comprised of a plurality of flexural reinforcing material which are intended for control of temperature change and concrete volume shrinkage cracking and to hold the uppermost flexural reinforcing materials in position during concrete placement. Both upper layers of flexural reinforcing material re-bars are intended to provide control of temperature shrinkage cracking at the upper surface of the panel. In addition to their function as flexural reinforcing, the first upper layer of re-bars is intended to provide control of temperature and shrinkage cracking at the upper surface of the panel. The upper group of flexural reinforcing materials is also usually in the form of a mat or matrix, which matrix is sized and oriented substantially identical to, and also parallel to, the flexural reinforcing matrix group in the lower half of the concrete panel.
Flexural reinforcing materials composed of steel re-bars, which re-bars are not coated or connected to a sacrificial anode, corrode readily when exposed to thawing salts and other corrosive elements, and even to ordinary water.
Despite the above described traditional flexural reinforcing of concrete bridge deck panel structures, concrete bridge deck panels have been found to deteriorate rapidly and to require costly rehabilitation or replacement from time-to-time. It has been recently estimated, for example, that the use of thawing salts on bridges in the United States causes $1.6 billion dollars worth of damage annually. Similar problems exist outside of the United States. Thus, there is a world-wide need to reduce the deterioration of concrete bridge deck panels without reducing the ability of the bridge deck panels to resist moment stresses imposed thereon by traffic loads.
It has been determined that much of the deterioration of concrete bridge deck panels is actually attributable to the corrosion of the traditional flexural reinforcing bars in the upper half of such bridge deck panels. It had been the common practice, until the late 1960's, to construct most concrete bridge deck panels over girder bridges with the bottom flexural reinforcing bars bent up over the supporting elements, such as beams or girders. Because of their shape, such bent flexural strength reinforcing bars are sometimes referred to as “crank bars,” because they resemble crankshafts. In the late 1960's the use of thawing salts on roads became quite prevalent. Subsequently the use of a greater amount of continuous straight flexural reinforcing re-bars in the top half of the concrete panel replaced the use of crank bars, because it was found to be more cost efficient to use more flexural reinforcing bars in the top half, than to bend and place crank bars in the lower half. This practice also helped maintain the proper position of the bars in the top mat. As a result, this practice substantially increased the amount of corrodible steel re-bar material in the top of the deck panel. Bridge deck panels of this era were also constructed with only about 1.5 inches (3.8 cm) of protective concrete cover over the continuous straight top bars or re-bars.
During the early 1970's, the protective concrete cover over the top re-bars was generally increased to greater than about 2 inches (5.1 cm). At the same time, construction practices were improved so that reduction of the thickness of the top cover during panel placement, was avoided. It was believed t
Dang Hoang
Sheridan & Ross P.C.
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