Wrapping system for strengthening structural columns or walls

Details Wrapping system for strengthening structural columns or walls Wrapping system for strengthening structural columns or walls

1999-03-18

2001-04-24

Stephan, Beth A. (Department: 3635)

Static structures (e.g., buildings)

Machine or implement

C052S749100, C052S749100, C052S749100, C052S749100

Reexamination Certificate

active

06219988

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of structural engineering and, more particularly, reinforced concrete based structures, such as columns and walls, and wrapping methods and mechanisms for strengthening such structures. More specifically, the invention pertains to a wrapped structure and wrapping process for improving the structure's axial, flexural, and shear strength, as well as its ductility and stiffness.
2. Description of the Related Art
Conventional techniques for wrapping columns or walls involve winding fabric made of filament or fiber around at least a portion of the structure. The fiber fabric typically is made of glass fiber, carbon fiber, or aramids fiber. The amount of fiber wrapping applied to a column or wall depends upon the type and degree of strengthening that the specific structure requires.
Thin filament or fiber fabric wrapping, referred to hereinafter as fiber reinforced plastic (FRP) wrapping, is known in the art and described generally in U.S. Pat. No. 5,218,810, which is hereby incorporated by reference. When a circular column has FRP wrapping wound around it, the wrapping exerts a substantially uniform confining pressure around the entire circumference of the column because of the circumferential membrane (axial) stiffness of the wrapping system. As a result, the FRP confines the entire cross-section of the wrapped structure.
Conventional methodologies of applying FRP wrapping have been successful in improving the strength and ductility of circular columns. Considerations applicable to noncircular columns and walls, however, are different. This is because the axial stiffness of the filament or fiber winding in the transverse direction of the column or wall (i.e., in a direction perpendicular to the axis of the column or wall) cannot provide any significant confinement along the flat sides or planar surfaces of the noncircular structure. As such, most of the confining pressure falls on the corners of the column or wall. Thin FRP wrapping possesses negligible transverse flexural stiffness and, therefore, considerable portions of the noncircular cross-section remain unconfined. Significantly, most columns or walls are noncircular. Accordingly, there is a need for a wrapping system that is adaptable to all types of columns or walls.
SUMMARY OF THE INVENTION
To overcome the disadvantages of the prior art, and in accordance with the purposes of the invention, as embodied and broadly described herein, there is provided a method for strengthening an existing structure, such as a column or wall, comprising winding a sheet of resin impregnated fiber around a concrete structural member to form a multi-layer wrap and interposing a substantially stiff inner element between layers of the wrap prior to completing the winding step, thereby sandwiching the substantially stiff inner element within the wrap. The structure usually is made of concrete or cement, but also may include brick and cinder block among others, all of which are referred to herein as masonry.
Also in accordance with the purposes of the invention, as embodied and broadly described herein, there is provided a reinforced support structure comprising a masonry column or wall, layers of resin impregnated fiber tightly wrapped around a peripheral portion of the masonry column or wall, and stiffening means either interposed within the layers along the wall or disposed immediately adjacent the column or wall.
Preferably, the stiffening means includes one or more stiff inner elements substantially enveloping the exterior of the support structure. If the support structure is noncircular, the stiffening means may include one or more planar stiff inner elements arranged along each side of the support structure. Alternatively, if the support structure is substantially circular, the stiffening means may be shaped or configured to conform to the exterior of the support structure.
In addition, it is preferable if the stiffening means is formed from a substantially lightweight material having a high ratio of strength to weight and a high ratio of stiffness to weight. In a preferred embodiment, the stiffening means includes a plurality of planar support members which substantially encapsulate the column or wall, when assembled.


REFERENCES:
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patent: 2924546 (1960-02-01), Shaw
patent: 3793104 (1974-02-01), Harrowing
patent: 4543764 (1985-10-01), Kozikowski
patent: 4786341 (1988-11-01), Kobatake
patent: 5043033 (1991-08-01), Fyfe
patent: 5218810 (1993-06-01), Isley
patent: 5657595 (1997-08-01), Fyfe
patent: 5924262 (1999-07-01), Fawley
patent: 5946880 (1999-09-01), Morrison

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