WO1994024391A1 - Repair and reinforcement of load bearing members - Google Patents
Repair and reinforcement of load bearing members Download PDFInfo
- Publication number
- WO1994024391A1 WO1994024391A1 PCT/EP1994/001222 EP9401222W WO9424391A1 WO 1994024391 A1 WO1994024391 A1 WO 1994024391A1 EP 9401222 W EP9401222 W EP 9401222W WO 9424391 A1 WO9424391 A1 WO 9424391A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- structural member
- strip
- load bearing
- tension
- elongate
- Prior art date
Links
Classifications
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C3/00—Structural elongated elements designed for load-supporting
- E04C3/30—Columns; Pillars; Struts
- E04C3/34—Columns; Pillars; Struts of concrete other stone-like material, with or without permanent form elements, with or without internal or external reinforcement, e.g. metal coverings
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C3/00—Structural elongated elements designed for load-supporting
- E04C3/02—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
- E04C3/20—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of concrete or other stone-like material, e.g. with reinforcements or tensioning members
- E04C3/26—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of concrete or other stone-like material, e.g. with reinforcements or tensioning members prestressed
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
- E04G23/00—Working measures on existing buildings
- E04G23/02—Repairing, e.g. filling cracks; Restoring; Altering; Enlarging
- E04G23/0218—Increasing or restoring the load-bearing capacity of building construction elements
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
- E04G23/00—Working measures on existing buildings
- E04G23/02—Repairing, e.g. filling cracks; Restoring; Altering; Enlarging
- E04G23/0218—Increasing or restoring the load-bearing capacity of building construction elements
- E04G23/0225—Increasing or restoring the load-bearing capacity of building construction elements of circular building elements, e.g. by circular bracing
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
- E04G23/00—Working measures on existing buildings
- E04G23/02—Repairing, e.g. filling cracks; Restoring; Altering; Enlarging
- E04G23/0218—Increasing or restoring the load-bearing capacity of building construction elements
- E04G2023/0251—Increasing or restoring the load-bearing capacity of building construction elements by using fiber reinforced plastic elements
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
- E04G23/00—Working measures on existing buildings
- E04G23/02—Repairing, e.g. filling cracks; Restoring; Altering; Enlarging
- E04G23/0218—Increasing or restoring the load-bearing capacity of building construction elements
- E04G2023/0251—Increasing or restoring the load-bearing capacity of building construction elements by using fiber reinforced plastic elements
- E04G2023/0255—Increasing or restoring the load-bearing capacity of building construction elements by using fiber reinforced plastic elements whereby the fiber reinforced plastic elements are stressed
Definitions
- This invention relates to the repair and reinforcement of structural members, and more particularly to the external lateral reinforcement of load bearing structural members. Background to the invention
- a variety of repair and reinforcement methods are currently in use. These methods include, gluing of thin steel sheets, plate bonding, jacketing, heat tensioning of thin steel plates or tie plates, tying of steel ties using screws, heated and hammered spirals etc. Most such techniques are extremely costly, time consuming, need skilled personnel for welding and gluing, and require a further concrete jacket to be applied around the damaged member thereby increasing its dimensions. In addition, it is quite difficult to evaluate the effectiveness of any repair or reinforcement. Other proposals have involved wrapping or winding various materials around the structural member. In GB1446425 a concrete structural member of circular section is surrounded by a tensioned wire of high tensile strength wound helically onto the member.
- the invention provides a method of laterally reinforcing a load bearing structural member which comprises wholly or partly encircling the structural member with an elongate strip of high tensile strength, high stiffness material and applying a tension to the strip sufficient to put the material of the structural member into lateral compression such that an abnormal increase in the internal stresses in the structural member will cause yielding of the strip before compressive, bending, or shear failure of the structural member.
- the present invention provides a structural member having an elongate strip of high tensile strength, high stiffness material positioned therearound, the strip having applied thereto a tension sufficient to put the material of the structural member into lateral compression such that an abnormal increase in the internal stresses in the structural member will cause yielding of the strip before compressive, bending, or shear failure of the structural member.
- the structural member is a solid (not hollow) element which may be, for example, a reinforced concrete column or beam, a cantilever, slab or wall section, a parapet, a brick or masonry lintel, a highway post, a timber or steel column, a composite material structural element, or a plate bonded, strengthened structural element.
- Other structural members such as the masts of ocean-going yachts may be strengthened using the method of the invention.
- the invention will be more particularly described with reference to load bearing reinforced concrete columns and beams, but it is to be understood that it is not limited thereto.
- the elongate strip is preferably flat and preferably has a thickness of less than 1.5 mm, most preferably from 0.5 to 1 mm.
- the strip preferably has a width of less than 40 mm, most preferably from 10 to 30 mm.
- the dimensions of the strip should be such that the strip will not break when bent under tension around tight corners.
- the material of the strip is preferably a high tensile, high stiffness material, such as for example high tensile steel, although other high tensile, high stiffness materials, for example structural polymers such as polypropylene and fibre reinforced plastics comprising for example carbon fibre, glass fibre and aramids are not excluded.
- the strip to be pre-stressed should have an ultimate stress value of greater than 350N/mm 2 , more preferably greater than 500 N/mm 2 .
- High tensile material is preferred because a lower volume of strip material can be used, but we have found that for a particular stiffness of material there is an optimum value for the ultimate stress of the strip beyond which, if no pre-stressing force is applied, no further strength and ductility improvement is obtained, and indeed poorer results may be achieved.
- the ultimate stress value of an unstressed (but not loose) steel strip preferably lies in the range of from 200 to 400 N/mm 2 .
- Suitable metal strips are currently manufactured having strengths of from 300 to lOOON/mm 2 .
- the applied tension should preferably induce a stress in the strip close to and preferably within 400N/mm 2 , more preferably within 200 N/mm 2 of its yield stress.
- the applied tension is preferably in the range of 600 to 800 N/mm 2 for moderate amounts of confinement, although the applied tension can be reduced if higher levels of confinement are used.
- the applied tension is sufficient to overcome any friction in the system and ensure that the strip is tightly applied to the structural member, however, and this generally requires the use of an applied tension of at least about lOON/mm 2 . It is important that the tension applied to the metal strip is sufficient to put the material of the structural member into lateral compression as determined by the relevant design calculations, which, for example, can be based on Eurocode 8 (EC8 1993) . Since the effect of the load on the structural member tends to cause cross sectional expansion of the load bearing member, the tension of the strip should be sufficient to counteract this tendency and to maintain the structural member in lateral compression.
- the strip may be applied to the load bearing structural member as a plurality of separate bands or as a spiral strapping and may be retained on the load bearing member by means of appropriately configured clips, which may be applied to the corner regions of the structural member. Whichever method is used, preferably adjacent turns of the strip are clipped together to prevent slippage and maintain the applied tension. Corner protectors may also be used, if desired, to minimise damage to the corners of the structural member by the strip and increase the confinement efficiency.
- the strip may be applied to the structural member by any suitable means, and a variety of commercial strapping machines for baling and packaging may be used, if necessary, with appropriate modifications. Suitable strapping machines can be either hand operated or powered, for example by compressed air or hydraulic pressure. Preferred machines can provide control of the level of tensioning force and may also incorporate a clip sealer. Metal clips are preferably used to ensure proper sealing of the tensioned strip.
- the metal strip may be applied to the load bearing member so that individual turns are overlapping, just touching, or are spaced apart, depending upon the application. It is usually possible to space apart the individual turns of the metal strip, in general, by an amount of from 0 to 300 mm.
- Structural members reinforced by the method of the invention can have improved strength and substantially improved ductility, imparting resistance to compressive failure, bending failure and shear failure. Localised failures such as buckling, pull-out or peeling of the concrete cover can also be reduced.
- Figure la schematically shows an end elevation of a fully encircled load bearing member according to the invention
- Figure lb shows an end elevation of a second fully encircled load bearing member according to the invention
- Figure lc shows an end elevation of a partially encircled load bearing member according to the invention
- Figure 2a shows a side elevational view of a load bearing member according to the invention encircled with individual strips;
- Figure 2b shows a side elevational view of a load bearing member according to the invention encircled with a spiral strip
- Figure 3 shows a graph of the stress/strain curves of Example 1
- Figure 4 shows a graph of the stress/strain curves of Example 2.
- Figure 5 shows a graph of the load/deflection curves of Example 3.
- a reinforced concrete member 4 of T- shaped section is partially encircled by pre-tensioned strips 5, which are secured by fixings 6 onto the member
- Corner protectors 7 are provided on those corners encompassed by the strips.
- Figures 2a and 2b show strip wrapping methods.
- individual strips 8 are wound around the member 9 and each is secured by its own clip 10.
- Figure 2b a single strip 11 is spiralled around the member 12 and secured on the corner protectors 13, which incorporate clips at suitable spacing ⁇ .
- This Example demonstrates the increase in load and longitudinal strain resulting from three laterally confined concrete cylindrical specimens reinforced according to the invention, and a comparison of these specimens with a control unconfined specimen in axial loading tests.
- the three concrete cylindrical specimens of 100 mm diameter and 200 mm height are cast vertically using standard steel forms. Each of the specimens is confined externally with Bryten type metal strips of 12.7 mm width and 0.5 mm thickness, having an average ultimate stress of 490N/mm 2 .
- the clear spacing (s') between strips for the three specimens were 0, 12.7, 25.4 mm respectively.
- the metal strips are tensioned around the specimens using a hand operated tensioning machine, and are secured in place by means of metal clips. The tension applied to the strips is determined to be lOON/mm 2 .
- a reinforced concrete specimen is prepared, 1 metre long with a square cross section of 100 mm.
- the placement of reinforcing rods is as shown in Figure 4.
- the specimen is tested in bending as a simply supported beam, with a mid-point load. After failure, the specimen is repaired, strengthened and re-tested. The results are shown in Figure 4.
- the specimen is designed to fail in shear. According to British Standard BS 8110 (BS 8110, 1985), stirrups of 4 mm diameter and 40 mm spacing are required to avoid shear failure, but instead, a 80 mm spacing is used. After the expected abrupt shear failure has taken place in the original specimen, crushed and loose concrete is removed and the compression side of the specimen is repaired by using an epoxy resin. The repaired specimen is strengthened externally by using the same metal strips as in Example 1. The spacing between the strips is 80 mm and the applied tension is determined to be lOON/mm 2 . The load deflection curve, before and after repair, is shown in Figure 4.
- This example demonstrates the use of the invention in providing ductility to potentially brittle members reinforced with new materials.
- a group of test pieces are made, consisting of concrete beams, 2.5 m long with a 150 x 250 mm cross section, each reinforced with two Glass Fibre Reinforced Plastic (GFRP) rods.
- the beams are tested in bending by applying a two point load at a distance of 700 mm from each support.
- the results obtained from one such beam, before and after repair are presented in Figure 5.
- the original beam being technically over- reinforced, failed due to concrete crushing in a brittle explosive manner. After failure, the beam is repaired by replacing the crushed concrete and strengthening with Superten metal strips of 12.7 mm width, 0.5 mm thickness and 950 N/mm 2 ultimate stress.
- Example 3 In a further experiment the procedure of Example 3 is repeated except that the strips are pre-stressed to a tension of 600N/mm 2 . A similar increase in the strength and ductility of the beam is observed.
Abstract
Description
Claims
Priority Applications (7)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP94914411A EP0694108B1 (en) | 1993-04-17 | 1994-04-15 | Repair and reinforcement of load bearing members |
DE69403074T DE69403074D1 (en) | 1993-04-17 | 1994-04-15 | REPAIR AND REINFORCEMENT OF SUPPORTING CONSTRUCTION PARTS |
AU66796/94A AU6679694A (en) | 1993-04-17 | 1994-04-15 | Repair and reinforcement of load bearing members |
JP6522779A JPH08509037A (en) | 1993-04-17 | 1994-04-15 | Repair and reinforcement of load bearing members |
US08/535,041 US5799451A (en) | 1993-04-17 | 1994-04-15 | Repair and reinforcement of load bearing members |
PCT/EP1994/001222 WO1994024391A1 (en) | 1993-04-17 | 1994-04-15 | Repair and reinforcement of load bearing members |
GR970402007T GR3024360T3 (en) | 1993-04-17 | 1997-08-06 | Repair and reinforcement of load bearing members |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9307979A GB2277332A (en) | 1993-04-17 | 1993-04-17 | Repair and reinforcement of load bearing members |
GB9307979.6 | 1993-04-17 | ||
PCT/EP1994/001222 WO1994024391A1 (en) | 1993-04-17 | 1994-04-15 | Repair and reinforcement of load bearing members |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1994024391A1 true WO1994024391A1 (en) | 1994-10-27 |
Family
ID=26070100
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/EP1994/001222 WO1994024391A1 (en) | 1993-04-17 | 1994-04-15 | Repair and reinforcement of load bearing members |
Country Status (1)
Country | Link |
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WO (1) | WO1994024391A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5505030A (en) * | 1994-03-14 | 1996-04-09 | Hardcore Composites, Ltd. | Composite reinforced structures |
WO1999049155A1 (en) * | 1998-03-24 | 1999-09-30 | University Of Ottawa | Retrofitting existing concrete columns by external prestressing |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1446425A (en) * | 1972-08-04 | 1976-08-18 | Kuei Fan Yu | Structural members |
DE3806759A1 (en) * | 1988-03-02 | 1989-09-14 | Dyckerhoff & Widmann Ag | Process for repairing a hollow-cylindrical structural body, in particular a chimney consisting of reinforced concrete, and set of structural elements for carrying out this process |
US5043033A (en) * | 1991-01-28 | 1991-08-27 | Fyfe Edward R | Process of improving the strength of existing concrete support columns |
WO1993020296A1 (en) * | 1992-04-06 | 1993-10-14 | Eidgenoessische Materialpruefungs- Und Forschungsanstalt Empa | Process and device for increasing the shearing resistance of a structure component |
-
1994
- 1994-04-15 WO PCT/EP1994/001222 patent/WO1994024391A1/en active IP Right Grant
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1446425A (en) * | 1972-08-04 | 1976-08-18 | Kuei Fan Yu | Structural members |
DE3806759A1 (en) * | 1988-03-02 | 1989-09-14 | Dyckerhoff & Widmann Ag | Process for repairing a hollow-cylindrical structural body, in particular a chimney consisting of reinforced concrete, and set of structural elements for carrying out this process |
US5043033A (en) * | 1991-01-28 | 1991-08-27 | Fyfe Edward R | Process of improving the strength of existing concrete support columns |
WO1993020296A1 (en) * | 1992-04-06 | 1993-10-14 | Eidgenoessische Materialpruefungs- Und Forschungsanstalt Empa | Process and device for increasing the shearing resistance of a structure component |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5505030A (en) * | 1994-03-14 | 1996-04-09 | Hardcore Composites, Ltd. | Composite reinforced structures |
WO1999049155A1 (en) * | 1998-03-24 | 1999-09-30 | University Of Ottawa | Retrofitting existing concrete columns by external prestressing |
US6247279B1 (en) | 1998-03-24 | 2001-06-19 | University Of Ottawa | Retrofitting existing concrete columns by external prestressing |
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