WO1998053150A1

WO1998053150A1 - T-structure externally reinforced with composite material

Info

Publication number: WO1998053150A1
Application number: PCT/US1998/009898
Authority: WO
Inventors: Larry Cercone; Fred Policelli; Chris Pantelides; Janos Gergely; Lawrence Reaveley
Original assignee: The University Of Utah; Xxsys Technologies, Inc.
Priority date: 1997-05-22
Filing date: 1998-05-21
Publication date: 1998-11-26
Also published as: AU7573298A

Abstract

A T-structure (20), such as an internally reinforced concrete column (22) and cap beam (24), is reinforced with composite material applied to the beam (24) of the T-structure (20). The composite material is applied in layers, with a first layer (60) oriented at about +45 degrees to the longitudinal axis of the beam, a second layer (64) oriented at about -45 degrees, and a third layer (66) oriented at 90 degrees. The first (60) and second (64) layers are preferably applied on at least three sides of the beam (24), and the third layer (66) is preferably applied on all four sides.

Description

T-STRUCTURE EXTERNALLY REINFORCED WITH COMPOSITE MATERIAL

BACKGROUND OF THE INVENTION

This invention relates to the reinforcement of structures using composite materials, and, more specifically, to the reinforcement of T-structures using composite materials.

Earthquakes in California over the past 30 years have demonstrated that internally reinforced concrete structures may fail prematurely as a result of the shearing that results from some modes of ground movement. The shearing may cause the concrete near the surface of the structure to crack and spall, so that the internal reinforcing bar is exposed and thereafter bends. With the bending of the internal reinforcing bar, the strength of the structure is greatly reduced, and failure of the structure follows.

To guard against this premature failure, techniques have been developed to externally reinforce columns such as the columns that support highway overpasses. The techniques typically involve placing an external jacket around the column to contain the concrete at the surface and prevent it from spalling. Jackets have been made, for example, from grout-filled steel tubes welded around the columns, wraps of steel wire around the columns, and wraps of composite materials around the columns.

The inventors have observed that, with the columns externally reinforced to prevent premature failure, other components of the structures become the more- likely failure points during seismic activity. For example, the regions near T- joints may provide the source of failure initiation during shear of the structure. An example of such a T-joint and T-structure is a bridge column and its cap beam.

T-structures may be made stronger by providing heavier structure near the

T-joint, or by providing additional mass in the joint itself. However, these approaches are not practical in many cases of original construction, because of the additional mass and weight added to the structure, and are not practical in virtually all cases of retrofitting of existing construction, because they require a modification of the internal structure of the T-structure.

There is a need for an approach to improving the performance of T- structures during seismic and other events which apply shear loadings to the T- structures. The present invention fulfills this need, and further provides related advantages.

SUMMARY OF THE INVENTION

This invention relates to an external reinforcement for T-structures, particularly those made of internally steel-reinforced concrete. The external reinforcement is applied to the peripheral surfaces of the T-structure. The approach is therefore compatible with both original construction and retrofit. Shear-failure performance of the externally reinforced T-structure is improved from about 12 to about 51 percent over that of the externally unreinforced T- structure, yet very little weight and size are added to the structure. Additionally, the external reinforcement aids in reducing corrosion effects on the internal steel reinforcement and on the concrete itself.

In accordance with the invention, an externally reinforced T-structure comprises a column, and a beam attached to one end of the column at an intersection and oriented at 90 degrees to the column. The beam has a longitudinal axis and a peripheral surface. A cross-piece external reinforcement is applied to at least a portion of the peripheral surface of the beam. The cross- piece external reinforcement comprises a first layer of a first fiber-reinforced composite material having fibers oriented at an angle of from about +15 degrees to about +60 degrees, preferably about +45 degrees, to the longitudinal axis of the beam. Desirably, a second layer of a second fiber-reinforced composite material, having fibers oriented at an angle of from about -15 degrees to about -60 degrees to the longitudinal axis of the beam, is applied overlying the first layer. Even more desirably, a third layer of a third fiber-reinforced composite material, having fibers oriented at an angle of about 90 degrees to the longitudinal axis of the beam, is applied overlying the second layer. The third layer is located immediately adjacent to the intersection of the column and the beam, on either side thereof.

In a common situation, the beam is generally rectangular in cross section, with two opposing lateral faces, an adjacent face adjacent to the column, and a distal face remote from the column. The first layer and the second layer of the cross-piece external reinforcement are applied to at least the lateral faces and the adjacent face. The first layer and the second layer may optionally be applied to the distal face. The third layer is preferably applied to all four faces.

The fiber-reinforced material used in the first, second, and third layers is preferably reinforced by unidirectional fibers (as distinct from cloths or other non- unidirectional forms, although other forms are operable). The same or different composite material may be used in the first, second, and third layers. The fiber- reinforced material comprises fibers embedded in a matrix. Operable fiber materials include inorganic fibers such as carbon (including graphite) and glass, and organic fibers such as aramids. Operable matrix materials include thermosetting resins such as epoxies, polyesters, and vinyl esters. Thermoplastic resins and inorganic matrix materials may be used for some applications, but are less preferred.

The column may also be externally reinforced, using any operable type of reinforcement approach. Wrapping with a fiber-reinforced composite material, such as the same material used in the external reinforcement of the beam, is preferred, but other approaches are also applicable.

The present invention provides an important advance in the art of reinforcement of structures, particularly those made of steel-reinforced concrete in building and other infrastructure construction. The shear strengths of the T- structures are improved by as much as about 50 percent over unreinforced T- structures.

Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1A and IB are an elevational view and a side view, respectively, of a T-structure;

Figure 2 is a sectional view of the cross-piece of the T-structure of Figures 1A and IB, taken generally along line 2-2 of Figure IB;

Figure 3 is a schematic perspective view of a fiber-reinforced composite material used as an external reinforcement;

Figures 4A and 4B are an elevational view and a side view, respectively, of a T-structure wrapped with a first layer of a first fiber-reinforced composite material;

Figures 5A and 5B are an elevational view and a side view, respectively, of a T-structure wrapped with a first layer of a first fiber-reinforced composite material and a second layer of a second fiber-reinforced composite material;

Figures 6A and 6B are an elevational view and a side view, respectively, of a T-structure wrapped with a first layer of a first fiber-reinforced composite material, a second layer of a second fiber-reinforced composite material, and a third-layer of a third fiber-reinforced composite material;

Figures 7A and 7B are an elevational view and a side view, respectively, of a T-structure wrapped with a first layer of a first fiber-reinforced composite material and a layer of a third fiber-reinforced composite material; and

Figure 8 is a block flow diagram of a preferred approach of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figures 1A and IB illustrate the general appearance of a T-structure 20 and present the applicable terminology. The T-structure 20 includes a column 22 (the downwardly extending central leg of the T) and a beam 24 (the crosspiece of the T). (Notwithstanding this terminology, the T-structure may be of any orientation, such as a horizontal column or a vertical column.) The beam 24 is affixed to an end 26 of the column 22 at an intersection 28. The column 22 has a longitudinal axis 30. The beam 24 has a longitudinal axis 32 and a peripheral surface 34. The angle between the longitudinal axis 30 of the column 22 and the longitudinal axis 32 of the beam 24 is 90 degrees or close thereto.

In a common construction exemplary of the application of the present approach, the column 22 is round or rectangular in cross-sectional shape. The beam 24 is rectangular in cross-sectional shape. The four faces of the beam 24 include two opposing lateral faces 36, an adjacent face 38 adjacent to the column 22 and to which the column 22 is joined, and a distal face 40 opposite to the adjacent face 38.

In a preferred application of the present invention, the T-structure 20 is internally reinforced concrete, as illustrated in the sectional view of Figure 2. A skeleton 42 of steel reinforcing bar lies inside a mass of concrete 44. Such reinforced structures are made by fabricating reinforcing bar into the desired shape, building a form around the reinforced bar, pouring concrete into the form, and allowing the concrete to cure. The internal reinforcement of the T-structure 20, which is a common construction practice, is to be distinguished from the external reinforcement of the T-structure 20 by the application of composite material to its external surfaces, as will be discussed subsequently. The invention is applicable to other constructions of T-structures, as well.

The preferred material for use in the external reinforcement of the T- structure 20 is fiber-reinforced composite material 46, one form of which is illustrated in Figure 3. The fiber-reinforced composite material 46 comprises reinforcing fibers 48 embedded in a matrix 50. The fibers 48 are preferably generally parallel to each other, which is termed a "unidirectionaF' fiber- reinforced composite material, although there may be deviations from a purely parallel arrangement. The unidirectional fiber-reinforced composite material is distinct from woven or unwoven mat structures wherein the fibers intentionally are not parallel to each other, or three-dimensional fiber structures. Fiber- reinforced composite material wherein the fibers are woven into a mat may be used in the present approach, although the unidirectional material is preferred. The fibers and the matrix of the composite material 46 may be any operable materials and present in any operable proportion. Preferably, the fibers are made of inorganic materials such as carbon (including graphite) and glass, or organic fibers such as aramids (e.g., Kevlar aramid fibers). Operable matrix materials include thermosetting resins such as epoxies, polyesters, and vinyl esters. Thermoplastic or inorganic resins may be used as the matrix for some applications, but are less preferred. The fibers usually occupy from about 50 to about 70 percent by volume of the composite material 46, although other volume fractions of fibers are operable as well. The fiber-reinforced composite material may be applied in arrangements according to the invention in any operable manner. In one approach, commercially available prepreg composite materials of fibers embedded in a slightly (i.e., B-stage) cured resin matrix are applied to a surface and cured in place. In another approach, the fibers are wound or otherwise applied onto the surface, a resin material is infiltrated between the fibers during or after application, and the resin is cured in place.

Figures 4 A and 4B illustrate a first embodiment of the invention. A first layer 60 of a first fiber-reinforced composite material is applied as an external reinforcement to the peripheral surface 34 of the beam 24. The peripheral surface 34 is first preferably prepared by cleaning and roughening. Cleaning may be accomplished by removing loose dirt and debris from the peripheral surface, preferably by sweeping or with a high-pressure water spray. Roughening may be accomplished by blasting the surface with an agent such as sand or shot, or in many instances the high-pressure water spray, where used, may provide sufficient roughening. The first layer 60 is preferably bonded to the surface of the beam 24 with a bond 61 in order to improve shear transfer between the beam and the first layer. The bonding agent is preferably an epoxy-based adhesive that is chemically compatible with the resin used as the matrix of the composite material. While such bonding of the first layer to the material of the beam is preferred, it is not necessary.

For the case of the preferred unidirectional fiber-reinforced composite material, the first layer 60 is applied such that an angle A between the fibers of the composite material and the longitudinal axis 32 of the beam 24 is from about +15 to about +60 degrees, most preferably +45 degrees. (As in all of Figures 4-7, the sets of parallel lines in Figures 4A and 4B are not section lines, nor do they indicate individual fibers, but are instead intended to indicate the angles of orientation of the fibers. Also, in Figures 4B, 5B, 6B, and 7B, the thicknesses of the layers such as layer 60 are exaggerated so as to be visible in the scale of the drawings.)

The first layer 60 may extend around the entire peripheral surface 34 of the beam 24, or only a portion of that surface on at least two faces. As shown in Figure 4B, the first layer 60 is applied only to the two lateral faces 36 and the adjacent face 38, but not to the distal face 40, in this embodiment.

The approach of the invention is compatible with the external reinforcing of the column 22 as well as the beam 24, an important advantage for infrastructure structural applications. Figures 4A and 4B illustrate the wrapping of the column 22 with an external column reinforcement 62 in the form of a fiber-reinforced composite material. The fiber-reinforced composite material used in the reinforcement 62 may be the same as that of the first layer 60, or it may be a different material. Figures 4, 5, 6, and 7 illustrate four different approaches to the external reinforcing of the column. Any of these approaches may be used with any of the described approaches to the reinforcement of the beam 24. The column 22 may be unreinforced as well.

Figures 5 A and 5B illustrate another embodiment of the invention. Here, the first layer 60 is applied as in the embodiment of Figures 4A and 4B, but with the following exception. In the embodiment of Figures 4A and 4B, the first layer 60 is applied only on three sides of the beam 24. In the embodiment of Figures 5A and 5B, the first layer 60 is applied on all four sides of the beam 24. It is often the case that the external reinforcement cannot be applied to the fourth side of the beam due to other structure that is present and interferes with the application process. Although it is preferred that the external reinforcement be applied on all four sides as in Figures 5A and 5B, the present studies have demonstrated that satisfactory performance may be obtained when the external reinforcement is applied to only three of the four sides.

A second layer 64 of a first fiber-reinforced composite material is applied as an external reinforcement to the beam 24, overlying, contacting, and bonded to the first layer 60. The second layer 64 is preferably applied only in those portions of the peripheral surface 34 to which the first layer 60 is already applied. Where the first layer 60 is applied to only three sides of the beam 24, the second layer 64 is applied over the first layer 60 on those same three sides, but where the first layer 60 is applied to all four sides of the beam 24, the second layer 64 is applied over the first layer 60 on all four sides as well. For the case of the preferred unidirectional fiber-reinforced composite material, the second layer 64 is applied such that an angle B between the fibers of the composite material and the longitudinal axis 32 of the beam 24 is from about -15 to about -60 degrees, preferably so that the angle B is the negative of the angle A, and most preferably such that angle B is -45 degrees. The use of the plus (+) and minus (-) signs in relation to the respective angles A and B is a convention in this art and permits the specification of angles of the fibers in various layers relative to a common reference axis. As used herein, the + sign indicates a counter-clockwise rotation from the axis 32, and the - sign indicates a clockwise rotation from the axis 32. The second layer 64 may be made from the same composite material as the first layer 60, or a different composite material.

In the embodiment of Figures 5A and 5B, the column 22 is externally reinforced with a concrete-reinforced structure 65. In this approach, a new structure of steel reinforcement is built around the outside of the column 22. Then sprayable concrete, generally termed "shotcrete" in the art, is sprayed onto the new steel reinforcing structure, and the shotcrete is permitted to harden. This approach adds substantially to the weight of the T-structure and thence to the load on its footings. In another embodiment shown in Figures 6A and 6B, the first layer 60 and the second layer 64 are applied, as discussed previously. A third layer 66 of a third fiber-reinforced composite material is applied as an external reinforcement to the beam 24, overlying, contacting, and bonded to the second layer 64. The third layer 66 is applied over the first layer 60 and the second layer 64. Additionally, where possible, the third layer 66 is applied over the entire peripheral surface 34 of the beam 24. Thus, in the embodiment shown in Figures 6A and 6B, the third layer 66 is applied to the distal surface 40 as well as the other surfaces of the beam 24. For the case of the preferred unidirectional fiber- reinforced composite material, the third layer 66 is applied such that an angle C between the fibers of the composite material and the longitudinal axis 32 of the beam 24 is about 90 degrees, most preferably such that angle C is exactly 90 degrees. The third layer 66 may be made from the same composite material as either of the first layer 60 or the second layer 64, or a different composite material. The third layer 66 is located immediately adjacent to the intersection 28 and on either side thereof. It should extend from the intersection 28 for a distance D parallel to axis 32 that is at least 1/2 of the height H of the beam 24, in order to provide sufficient structural performance. In the embodiment shown in Figures 6 A and 6B, the column 22 is externally reinforced with a grout-filled steel jacket 68. The jacket 68 is provided as two semi-cylinders, which are assembled around the column 22 and welded together to make a complete cylinder. The cylinder is thereafter filled with grout. Figures 7 A and 7B illustrate yet another embodiment. Only one of the first layer 60 (as illustrated) and the second layer 64 is applied to the beam 24 as described earlier. The layer 66 of 90-degree fiber orientation is applied overlying that applied layer 60.

In the embodiment shown in Figures 7A and 7B, the column 22 is externally reinforced with steel wire 70 wound around the surface of the column 22.

The first layer 60, the second layer 64, and the third layer 66 may be of any operable thickness. In the preferred approach, the fiber-reinforced composite material is supplied as relatively thin unidirectional prepreg plies such as that depicted in Figure 3. A number of plies may be applied to form a single layer of the desired thickness. For most purposes, the thickness of each of the layers 60, 64 and 66 is from about 0.02 inches to about 0.03 inches, although thicker or thinner layers may be used. It will also be understood that additional layers may be added, as long as they do not adversely affect the performance of the layers 60, 64, and 66. Figure 8 illustrates a preferred approach for practicing the invention. This description specifically relates to the external reinforcement of the beam portion of the T-structure. However, if the column portion of the T-structure is also to be externally reinforced with, for example, a fiber composite material, the same steps may be used for it as well and conducted in parallel. The T-structure is provided, numeral 80. The surface to be externally reinforced is prepared, numeral 82, typically by cleaning and roughening as described previously. Optionally, the bonding agent is applied, numeral 84. The external reinforcements are applied, numeral 86, according to the previously described procedures, with as many layers as desired having the selected orientations. The resin matrix of the as-applied composite material is not fully cured, and after application it is cured, numeral 88. Curing is accomplished as recommended by the manufacturer of the resin. Some resins are cured at room temperature, while others must be heated to a temperature specific to that resin for a period of time. Optionally, the outer surface of the applied-and-cured composite material is post-processed, numeral 90. Such post processing may involve application of additional resin material to smooth the surface, because the as-applied composite material has a somewhat rough surface, and then painting the surface. If additional resin is applied, that portion of step 90 typically is accomplished prior to step 88, so that the additional resin may be cured in step 88. Painting may be performed as the final step. Any other type of post processing may also be used, such as the application of commercially available graffiti-resistant coatings.

The embodiments of Figures 4 A and 4B, 5 A and 5B, and 6 A and 6B have been fabricated, except that in each case the column was externally unreinforced, so that the effect of the external reinforcement of the beam could be studied in a controlled manner. The beam 24 in each case was a steel-(internally) reinforced concrete piece about 14 inches by 16 inches in size. A similar comparison specimen, which had no external reinforcement at all, was also fabricated. The fabricated embodiments were tested in shear loading by applying reversed deformations in the direction indicated by the double-ended arrow 72 in Figure 1 A. The force required to cause the beam 24 to fail, which is proportional to the shear at the intersection 28, was measured. The embodiment of Figures 4 required a 12 percent greater applied force than the control specimen before failure occurred. The embodiment of Figures 5 and 7 required a 33 percent greater applied force than the control specimen before failure occurred. The embodiment of Figures 6 required a 51 percent greater applied force than the control specimen before failure occurred. These improvements are quite surprising in view of the fact that the beams were over 12 inches in cross-sectional dimensions, and the total thickness of the external reinforcing layers was well under 0.1 inch. The external reinforcement approach of the invention therefore provides a significant improvement to the shear strength of T-structures, as compared with T-structures that are not externally reinforced, but with very little added weight. The presence of the external reinforcing layers also reduces the susceptibility of the T-structures to corrosion-based damage to or failure of the steel internal reinforcement or the concrete.

Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A reinforced T-structure, comprising: a column; a beam attached to one end of the column at an intersection and oriented at 90 degrees to the column, the beam having a longitudinal axis and a peripheral surface; and a cross-piece external reinforcement applied to at least a portion of the peripheral surface of the beam, the cross-piece external reinforcement comprising a first layer of a first fiber-reinforced composite material having fibers oriented at an angle of from about +15 degrees to about +60 degrees to the longitudinal axis of the beam.

2. The reinforced T-structure of claim 1, wherein the beam is generally rectangular in cross section, with two opposing lateral faces, an adjacent face adjacent to the column, and a distal face remote from the column, and wherein the cross-piece external reinforcement is applied to the lateral faces and the adjacent face, but not to the distal face.

3. The reinforced T-structure of claim 1 or claim 2, wherein the fibers of the first layer are oriented at an angle of about +45 degrees to the longitudinal axis of the beam.

4. The reinforced T-structure of any of claims 1 -3, wherein the fibers of the first layer are unidirectional.

5. The reinforced T-structure of any of claims 1 -4, wherein the crosspiece external reinforcement further comprises: a second layer of a second fiber-reinforced composite material having fibers oriented at an angle of from about -15 degrees to about -60 degrees to the longitudinal axis of the beam.

6. The reinforced T-structure of claim 5, wherein the fibers of the second layer are oriented at an angle of about -45 degrees to the longitudinal axis of the beam.

7. The reinforced T-structure of claim 5, wherein the fibers of the first layer are oriented at an angle of about +45 degrees to the longitudinal axis of the beam and the fibers of the second layer are oriented at an angle of about -45 degrees to the longitudinal axis of the beam.

8. The reinforced T-structure of any of claims 1 -7, wherein the fibers of the second layer are unidirectional.

9. The reinforced T-structure of any of claims 1-8, wherein the crosspiece external reinforcement further comprises: a third layer of a third fiber-reinforced composite material having fibers oriented at an angle of about 90 degrees to the longitudinal axis of the beam, the third layer being located adjacent to the intersection and on either side thereof.

10. The reinforced T-structure of any of claims 1-9, wherein the column and the beam each comprise cement internally reinforced by a steel skeleton.

11. The reinforced T-structure of any of claims 1-10, further including a column external reinforcement comprising an external reinforcement fiber-reinforced composite material applied to the column.

12. The reinforced T-structure of any of claims 1-11, further including a bond between the first layer and the peripheral surface of the beam.