Static structures (e.g. – buildings) – With component having discrete prestressing means – Axially loaded vertical structure
Reexamination Certificate
2000-07-20
2004-12-21
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
With component having discrete prestressing means
Axially loaded vertical structure
C052S223100, C052S749100, C052S749100, C052S749100, C052S749100, C052S745170
Reexamination Certificate
active
06832454
ABSTRACT:
BACKGROUND AND SUMMARY OF INVENTION
The present invention relates to beam construction and, more particularly, to a beam constructed of a tubular housing filled with a filler material such as concrete, a deck system using such beams, and a method of manufacturing the beams.
Timber-plank bridge decks are a popular type of bridge deck used in the Northeast and Northwest areas of the United States. By placing 2×10 or 2×12 joists side-by-side and introducing post-tensioning strands through the joists in the transverse direction, an economical bridge deck system can be built relatively quickly and easily. The problem with this type of bridge arises from the wood. The wood can exhibit substantial creep properties resulting in the continual loss of post-tensioning stress. In addition, when subjected to a moist climate, the wood can begin to rot, thus resulting in its required replacement.
The discovery of new construction materials for this type of civil engineering application has thus become an increasingly popular engagement. Materials such as fiberglass reinforced plastics (FRP) are strong, non-corrosive, and attractive. Fiberglass has a high strength-to-weight ratio and can be easily manufactured for many different types of applications. An FRP section alone will not work, however, because the modulus of an FRP section is insufficient to provide the required stiffness for construction applications such as a deck, and prestressing in the transverse direction is not possible as the wall thickness of the web is not strong enough to take the anticipated load. To strengthen the beam, fiberglass tubes can be filled with concrete, the most popular and economical construction material in the world, to form a solid beam capable of withstanding significant loads. With the introduction of prestressing to the concrete within the tubes, deflection and cracking of the concrete can be controlled. These filled tubes can be placed side-by-side, similar to the wood joists, and post-tensioned transversely for use in a bridge deck system or the like.
This invention addresses filling the tubes with concrete to increase the moment of inertia of the sections and addresses prestressing the stiffness for the sections. By filling the tube with concrete, the transverse prestressing force in the deck construction can be increased to provide a higher distribution width for the bridge deck compared to a wood deck system. This in turn yields a better, more efficient and cost effective deck system for bridges to meet stiffness and strength requirements.
The tube confines the concrete inside the tube due to the prestressing in the longitudinal direction, which creates an expansion of concrete in the lateral direction (Poisson's ratio effect) that is prevented by the tube, which has a Poisson's ratio less than that of the concrete. This confinement increases the strength of the concrete inside the tube to make this system much more attractive for structural applications such as bridges.
The system does not require the costly formwork for concrete decks, or curing of concrete. No steel reinforcements that develop corrosion are included, and hence, the beams are very durable compared to wood or reinforced concrete. The beams can be used for any construction previously using wood beams, concrete beams and even steel beams, such as temporary structures, scaffolding platforms and building floors where stiffness requirements may or may not be critical.
Internal and external spiral reinforcements in concrete provide varying degrees of confinement to concrete. Steel tubes/spiral reinforcements are used in concrete, but seldom achieve very high confinement. Using an FRP material (with proper Poisson's ratio) or like material provides very high confinement to increase the compressive (up to 10 times) and shear strength of confined concrete. An important consideration is to keep the Poisson's ratio of the tube less than concrete to provide the confinement to concrete. This increased strength depends on the fiber architecture and the thickness of the tube.
In accordance with an exemplary embodiment of the invention, a construction beam includes a tubular housing filled with a solid material, wherein a Poisson's ratio of the tubular housing is less than the solid material to thereby confine the solid material. The construction beam may further include at least one reinforcing rod in the tubular housing such that the solid material surrounds the reinforcing rod. Preferably, the reinforcing rod is prestressed in the tubular housing. In one embodiment, the solid material is concrete, which is formed in the tubular housing after placing the reinforcing rod. The housing itself is preferably formed of a fiber-reinforced polymer such as fiberglass, carbon, Kevlar and the like. The solid material may be one of concrete, fiber-reinforced concrete, polymer concrete, sand, structural foam and the like. Additionally, the reinforcing rod may be formed of steel, carbon, fiberglass, Kevlar and the like. The tubular housing generally may be formed with any geometrically-shaped cross section.
In accordance with another exemplary embodiment of the invention, a deck system includes a plurality of the construction beams of the invention secured side-to-side. In this context, each of the construction beams may further include at least one transverse aperture therein defining a corresponding at least one transverse channel. At least one reinforcing bar may be extended through the transverse channel. In one embodiment, the reinforcing bar extending through the transverse channel is secured under tension to provide a transverse post-stress in the deck system.
In accordance with still another embodiment of the invention, a method of forming a construction beam includes the step of filling a tubular housing with a solid material, wherein a Poisson's ratio of the tubular housing is less than the solid material to thereby confine the solid material.
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Friedman Carl D.
Nguyen Chi Q.
Nixon & Vanderhye P.C.
South Dakota School of Mines and Technology
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