Method for strengthening or repairing an existing reinforced concrete structural element

Abstract

A method for strengthening an existing concrete column having a concrete body and a plurality of parallel longitudinal steel reinforcements includes the steps of preparing a steel wire cable that includes strands of steel filaments, winding the steel wire cable on the longitudinal steel reinforcements in a spiral manner relative to a centerline of the concrete body, fastening two opposite ends of the steel wire cable to the longitudinal steel reinforcements, and casting a structural material around the steel wire cable, the longitudinal steel reinforcements, and the concrete body.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of Taiwanese application No. 091137352, filed on Dec. 25, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a method for strengthening or repairing an existing reinforced concrete structural element, more particularly to a method using a steel wire cable for strengthening or repairing an existing reinforced concrete structural element.

[0004] 2. Description of the Related Art

[0005] Conventional methods for forming a spiral-reinforced concrete column normally includes the steps of pre-forming lateral reinforcements, either circular hoop steel reinforcements or two C-shape stirrups lap spliced together reinforcements, that confine an inner space, placing longitudinal steel reinforcements in the inner space in the lateral steel reinforcements and tying the longitudinal steel reinforcements and the lateral steel reinforcements together, disposing form works around the steel reinforcements, and subsequently casting a structural material, such as concrete, around the lateral steel reinforcements and the longitudinal steel reinforcements so as to form the reinforced concrete structural elements.

[0006] The aforementioned conventional method is disadvantageous in that bending of a steel reinforcement to form the spiral steel reinforcement is difficult and requires a particular instrument to conduct. As such, the aforementioned conventional method is not suitable for strengthening or repairing an existing structural element. Moreover, there is an urgent need for effectively and rapidly strengthening or repairing a damaged structural element.

SUMMARY OF THE INVENTION

[0007] Therefore, the object of the present invention is to provide a method using a steel wire cable that is capable of effectively and rapidly strengthening or repairing existing structural elements.

[0008] According to one aspect of the present invention, there is provided a method for strengthening an existing reinforced concrete structural element that includes an elongated concrete body extending in a longitudinal direction, and a plurality of parallel longitudinal steel reinforcements extending in the longitudinal direction and embedded in the concrete body. The concrete body has an inner portion surrounded by the longitudinal steel reinforcements, and an outer portion surrounding the longitudinal steel reinforcements. The concrete body further has a segment with the outer portion removed in such a manner so as to expose the longitudinal steel reinforcements therefrom. The method includes the steps of: preparing a steel wire cable that includes strands of steel filaments; winding the steel wire cable on the longitudinal steel reinforcements, which are exposed from the segment of the concrete body, in a spiral manner relative to a centerline of the concrete body under a predetermined amount of tension; fastening two opposite ends of the steel wire cable to the longitudinal steel reinforcements; and casting a structural material around the steel wire cable, the longitudinal steel reinforcements, and the inner portion of the segment of the concrete body.

[0009] According to another aspect of the present invention, there is provided a method for strengthening an existing reinforced concrete structural element that has an outer surface. The method includes the steps of: placing a plurality of parallel longitudinal steel reinforcements around the outer surface of the structural element; preparing a steel wire cable that includes strands of steel filaments; winding the steel wire cable on the longitudinal steel reinforcements in a spiral manner relative to a centerline of the structural element under a predetermined amount of tension; fastening two opposite ends of the steel wire cable to the longitudinal steel reinforcements; and casting a structural material around the steel wire cable, the longitudinal steel reinforcements, and the outer surface of the structural element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In drawings which illustrate embodiments of the invention,

[0011] FIG. 1 is a schematic view showing how a structural load supported by a damaged reinforced concrete column is supported using a pair of temporary supports according to the first preferred embodiment of a method of this invention;

[0012] FIG. 2 is a fragmentary perspective view of a steel wire cable used in the method of the first embodiment;

[0013] FIG. 3 is a schematic view showing how the steel wire cable is wound on longitudinal steel reinforcements of the reinforced concrete column according to the method of the first embodiment;

[0014] FIG. 4 is fragmentary perspective view showing how an end of the steel wire cable is fastened to a selected one of the longitudinal steel reinforcements according to the method of the first embodiment;

[0015] FIG. 5 is a schematic view showing how the steel wire cable and the longitudinal steel reinforcements are surrounded by a set of form panels according to the method of the first embodiment;

[0016] FIG. 6 is a schematic sectional view showing how a steel wire cable is wound on longitudinal steel reinforcements that are disposed around an existing reinforced concrete column according to the second preferred embodiment of a method of this invention;

[0017] FIG. 7 is a diagram showing lateral force-displacement response during a cyclic loading test for a reinforced concrete column; and

[0018] FIG. 8 is a diagram showing lateral force-displacement response during a cyclic loading test for the reinforced concrete column which was repaired using a steel wire cable after the reinforced concrete column was damaged as a result of the test shown in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] For the sake of brevity, like elements are denoted by the same reference numerals throughout the disclosure.

[0020] FIGS. 1 to 5 illustrate consecutive steps of the first preferred embodiment of a method of this invention for repairing an existing reinforced concrete structural element 1, which is a damaged reinforced concrete column (see FIG. 1) in this embodiment, and which includes an elongated concrete body 10 extending in a longitudinal direction, a plurality of parallel longitudinal steel reinforcements 11 extending in the longitudinal direction and embedded in the concrete body 10, and a plurality of lateral steel reinforcements (ties) 12, each of which ties an adjacent pair of the longitudinal steel reinforcements 11 together. The concrete body 10 has an inner portion 101 surrounded by the longitudinal steel reinforcements 11, and an outer portion 102 surrounding the longitudinal steel reinforcements 11. The concrete body 10 further has a segment with the outer portion 102 removed in such a manner so as to expose the longitudinal steel reinforcements 11 therefrom. The method includes the steps of: preparing a steel wire cable 3 that includes strands of steel filaments 30 (see FIG. 2); winding the steel wire cable 3 on the longitudinal steel reinforcements 11 (see FIG. 3), which are exposed from the segment of the concrete body 10, in a spiral manner relative to a centerline of the concrete body 10 under a predetermined amount of tension, the distance between two adjacent turns of the spiral steel wire cable 3 ranging from 5 to 7 cm; fastening two opposite ends of the steel wire cable 3 to the longitudinal steel reinforcements 11 (see FIG. 3); disposing a set of form panels 5 around the steel wire cable 3 and the longitudinal steel reinforcements 11 (see FIG. 5); and casting a structural material around the steel wire cable 3, the longitudinal steel reinforcements 11, and the inner portion 101 of the segment of the concrete body 10 so as to form a concrete layer (not shown) at the segment of the structural element 1 and to thereby enclose the steel wire cable 3 and the longitudinal steel reinforcements 11.

[0021] In this embodiment, each end of the steel wire cable 3 is formed into a loop 31 that surrounds a selected one of the longitudinal steel reinforcements 11, and is fastened to an adjacent end portion of the steel wire cable 3 through a damper 4 so as to form the loop 31. The damper 4 includes first and second pieces 41, 42 that cooperatively clamp each end of the steel wire cable 3 and the adjacent end portion of the steel wire cable 3.

[0022] FIG. 6 illustrates the second preferred embodiment of a method of this invention for strengthening an existing reinforced concrete structural element 1 that includes a concrete body 10, a plurality of inner longitudinal steel reinforcements 11 embedded in the concrete body 10, and a plurality of lateral steel reinforcements (ties) 12, each of which ties an adjacent pair of the inner longitudinal steel reinforcements 11 together. The method of this embodiment includes the steps of: roughening an outer surface 110 of the structural element 11; disposing a plurality of parallel outer longitudinal steel reinforcements 61 around the outer surface 110 of the structural element 1; preparing a steel wire cable 3 that includes strands of steel filaments; winding the steel wire cable 3 on the outer longitudinal steel reinforcements 61 in a spiral manner relative to a centerline of the structural element 1 under a predetermined amount of tension; fastening two opposite ends of the steel wire cable 3 to the outer longitudinal steel reinforcements 61; and casting a structural material around the steel wire cable 3, the outer longitudinal steel reinforcements 61, and the outer surface 110 of the structural element 1 to form a concrete layer (not shown) to enclose the structural element 1.

[0023] The steel wire cable 3 possesses a higher tensile strength, a lower failure elongation ratio, and a lower modulus of elasticity than the steel reinforcement, does not have a distinct yielding point prior to failure, and exhibits an initial elongation when subjected to a force. The behavior of the stress-strain relationship for the steel wire cable 3 is a second order curve. The flexibility of the steel wire cable 3 permits rapid and effective repairing or strengthening of an existing structural element. Moreover, since grooves are formed among adjacent filaments 30 of the steel wire cable 3, engagement between the steel wire cable 3 and the concrete material is stronger as compared to that between the steel reinforcement and the concrete material. Since the steel wire cable 3 is made of strands of filaments 30, the defect in an individual filament 30 does not render the entire steel wire cable 3 defective. Unlike the steel reinforcement, which suffers from a sharp decrease in strength upon damage, the strength decreases sharply only for the damaged individual filament 30, and not for the entire steel wire cable 3.

[0024] The present invention will be described in greater detail in the following Comparative and Illustrated Examples.

COMPARATIVE EXAMPLE

[0025] A standard test sample of a rectangular reinforced concrete column was prepared. The reinforced concrete column has a 50 cm×50 cm cross-section and a height of 170 cm, and includes twelve #8 longitudinal steel reinforcements, each of which has a yield strength of 412.0 MPa, and a number of #3 lateral steel reinforcements (which serve as ties), each of which has a yield strength of 274.4 MPa. The spacing is about 40 cm for two adjacent lateral steel reinforcements. The concrete of the reinforced concrete column has a strength of about 20.5 MPa. The reinforced concrete column has a foundation with a size of 245 cm×180 cm×74 cm (length×width×height) The foundation includes eleven #8 steel reinforcements which are evenly distributed along a periphery of the foundation.

[0026] During the cyclic loading test, a hydraulic axial force (52.5 tons) was applied to the top end of the reinforced concrete column, and a lateral force was applied to one side of the reinforced concrete column adjacent to the top end of the reinforced concrete column so as to observe the lateral force-displacement response of the reinforced concrete column. The test was terminated when the reinforced concrete column was damaged. FIG. 7 shows the lateral force-displacement relationship of the reinforced concrete column during the cyclic loading test. The test shows that the reinforced concrete column has a drift ratio (i.e., the ratio of displacement to the height of the column) of about 2.8%.

ILLUSTRATIVE EXAMPLE

[0027] The reinforced concrete column, which was prepared and damaged as a result of the cyclic loading test in the Comparative Example, was repaired using a steel wire cable according to the method of this invention. The repaired reinforced concrete column was then subjected to the same cyclic loading test as that of the Comparative Example. FIG. 8 shows the lateral force-displacement relationship of the repaired reinforced concrete column during the cyclic loading test. The test shows that the repaired reinforced concrete column has a drift ratio of about 10.5%, which is much higher than that (2.8%) of the comparative Example, which represents a higher flexural strength than that of the originally undamaged reinforced concrete column prepared in the Comparative Example. In addition, the size of each Hysteresis loop shown in FIG. 8 is larger than that in FIG. 7, which indicates that the repaired reinforced concrete column of the Illustrative Example is more effective in dissipating energy applied thereto as compared to the original reinforced concrete column of the Comparative Example.

[0028] By virtue of the steel wire cable 3 employed in the method of this invention, the aforementioned drawbacks as encountered in the prior art can be eliminated.

[0029] With the invention thus explained, it is apparent that various modifications and variations can be made without departing from the spirit of the present invention.

Claims

1. A method for strengthening an existing reinforced concrete structural element that includes a concrete body extending in a longitudinal direction, and a plurality of parallel longitudinal steel reinforcements extending in the longitudinal direction and embedded in the concrete body, the concrete body having an inner portion surrounded by the steel reinforcements, and an outer portion surrounding the longitudinal steel reinforcements, the concrete body further having a segment with the outer portion removed in such a manner so as to expose the longitudinal steel reinforcements therefrom, the method comprising the steps of:

preparing a steel wire cable that includes strands of steel filaments;

winding the steel wire cable on the longitudinal steel reinforcements, which are exposed from the segment of the concrete body, in a spiral manner relative to a centerline of the concrete body under a predetermined amount of tension;

fastening two opposite ends of the steel wire cable to the longitudinal steel reinforcements; and

casting a structural material around the steel wire cable, the longitudinal steel reinforcements, and the inner portion of the segment of the concrete body.

2. The method of claim 1, wherein each of the ends of the steel wire cable is formed into a loop that surrounds a selected one of the longitudinal steel reinforcements.

3. The method of claim 2, wherein each of the ends of the steel wire cable is fastened to an adjacent end portion of the steel wire cable through a damper so as to form the loop.

4. A method for strengthening an existing reinforced concrete structural element that has an outer surface, the method comprising the steps of:

disposing a plurality of parallel longitudinal steel reinforcements around the outer surface of the structural element;

preparing a steel wire cable that includes strands of steel filaments;

winding the steel wire cable on the longitudinal steel reinforcements in a spiral manner relative to a centerline of the structural element under a predetermined amount of tension;

fastening two opposite ends of the steel wire cable to the longitudinal steel reinforcements; and

casting a structural material around the steel wire cable, the longitudinal steel reinforcements, and the outer surface of the structural element.