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US20060070338A1 - Shape modification and reinforcement of columns confined with FRP composites - Google Patents

Shape modification and reinforcement of columns confined with FRP composites Download PDF

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Publication number
US20060070338A1
US20060070338A1 US11/227,902 US22790205A US2006070338A1 US 20060070338 A1 US20060070338 A1 US 20060070338A1 US 22790205 A US22790205 A US 22790205A US 2006070338 A1 US2006070338 A1 US 2006070338A1
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fiber
frp
outer shell
reinforced polymer
fiber reinforced
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Chris Pantelides
Lawrence Reaveley
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Priority to US11/227,902 priority Critical patent/US20060070338A1/en
Priority to PCT/US2005/033207 priority patent/WO2006032033A2/fr
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Abandoned legal-status Critical Current

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    • 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

Definitions

  • FRP fiber reinforced polymer
  • the present invention provides fiber reinforced polymer (FRP) composite structures which include a core and a fiber reinforced polymer material at least partially surrounding the core.
  • the core includes an inner cement structure at least partially surrounded by an outer cement structure.
  • the outer cement structure comprises or consists essentially of expansive cement or non-shrink cement.
  • the inner cement structure of non-expansive cement can include steel reinforcements.
  • the materials and methods of the present invention can significantly reduce or even eliminate the need for steel reinforcement in cement structures.
  • the inner cement structure can have a cross-sectional shape which is different than a cross-sectional shape of the core.
  • a pre-existing structure having, for example, a rectangular cross-section can be modified into a structure having a circular, oval or elliptical cross-section. Modification of the cross-sectional shape can have multiple advantages. The elimination of corners can reduce stress concentration and early failure of the FRP jacket. Typically, the FRP shell is cured before the grout is poured in the space between the existing column and the FRP shell.
  • the effect on the FRP shell is a post-tensioning, and the effect on the existing column is radial compression.
  • the FRP materials and post-tensioning of the FRP jacket can provide improved mechanical properties as described in more detail below.
  • elliptical, oval and circular shapes can provide a greater degree of strength under asymmetric loads than comparable rectangular configurations.
  • the FRP jacket can be post-tensioned and have a hoop stress along the FRP material.
  • post-tensioning of the FRP jacket can be readily accomplished by using expansive concrete.
  • the post-tensioning induced in the present invention can be in the form of tensile stress along the FRP fibers, i.e. circumferential rather than axial.
  • the FRP material can include a fiber and a polymeric matrix.
  • Typical fibers can include, but are not limited to, glass fiber, carbon fiber, aramid fiber, and combinations thereof. Glass and carbon fibers tend to be cost effective and provide good mechanical properties. Aramid fibers are light, durable and are known to have high tenacity. The selection of the fiber can be based on factors such as cost, strength, rigidity, and long-term stability. Additionally, each type of fiber offers different performance characteristics and suitability for various applications. For example, aramids may come in low, high, and very high modulus configurations. Carbon fibers are also available with a large range of moduli; with upper limits nearly four times that of steel.
  • glass-based FRP reinforcement is least expensive and generally uses either E-glass or S-glass fibers.
  • the fiber material for use in FRP can be provided as sheets which can be cut to a desired size or as lengths of fiber which can be wrapped and/or laid as desired to form a particular shape.
  • the polymeric resins used as the matrix for the fiber are usually thermosetting resins. Most available FRP materials are provided with polymeric resins such as polyesters, vinylesters, or epoxies, although other polymeric materials can also be used. Additionally, the fibers and the FRP composites are heterogeneous and anisotropic which can make characterization and prediction of properties somewhat difficult.
  • existing structural columns can be reinforced. This is accomplished by placing a FRP outer shell around the existing column such that there is an open space between the existing column and the outer shell. Typically, this can be accomplished by placing two pieces of a shell around the column. Once the outer shell is in place, at least one additional layer of FRP material is wrapped around the outer shell to secure the two pieces together.
  • the outer shell can be formed and cured around the column while leaving an open space. The open space between the existing column and the outer shell can then be filled with expansive or non-shrink cement.
  • the existing column has a cross sectional shape which is different than a cross-sectional shape of the outer shell.
  • the existing column may be rectangular in shape while the outer shell is circular or elliptical in shape.
  • FIG. 1 is a perspective view of an exemplary FRP composite structure according to one embodiment of the present invention.
  • FIG. 2 is a cross sectional view of a FRP composite structure according to one embodiment of the present invention.
  • FIG. 3A is a cross sectional view of a FRP composite structure in accordance with one embodiment of the present invention wherein the inner cement structure has a circular cross-sectional shape and the core has a circular cross-sectional shape.
  • FIG. 3B is a cross sectional view of a FRP composite structure in accordance with one embodiment of the present invention wherein the inner cement structure has a square cross-sectional shape and the core has a circular cross sectional shape.
  • FIG. 3C is a cross sectional view of a FRP composite structure in accordance with one embodiment of the present invention wherein the inner cement structure has a rectangular cross sectional shape and the core has an elliptical cross sectional shape.
  • FIG. 4 is a perspective view of a FRP outer shell around an existing column, with outer shell being configured to leave an open space between the existing column and outer shell so that the open space may be filled with expansive or non-shrink cement in accordance with one embodiment of the present invention.
  • FIG. 5 is a perspective view of a FRP composite outer shell which has been divided into two pieces and place around an existing column in accordance with one embodiment of the present invention.
  • FIG. 6 is a perspective view of two pieces of a FRP composite outer shell that have been spliced with a vertical FRP composite strip along the seams between the two pieces in accordance with one embodiment of the present invention.
  • FIG. 7A is a perspective view of a mold used for forming a FRP composite outer shell in accordance with one embodiment of the present invention.
  • FIG. 7B is a perspective view of a mold that has been partially wrapped with at least one layer of fiber reinforced composite material to form an outer shell in accordance with one embodiment of the present invention.
  • FIG. 7C is a perspective view of an outer shell which has been divided into two pieces so that it can be used in applications requiring retrofitting existing columns in accordance with one embodiment of the present invention.
  • FIG. 8 is a graph of concrete strength vs. aging time in accordance with one embodiment of the present invention.
  • FIG. 9 is a graph of expansion hoop strain for expansive cement in accordance with one embodiment of the present invention.
  • FIG. 10A is a graph of the expansion history of 12′′ circular columns in accordance with one embodiment of the present invention.
  • FIG. 10B is a graph of expansion history of 16′′ circular columns in accordance with one embodiment of the present invention.
  • FIG. 10C is a graph of expansion history of elliptical (1:2) columns in accordance with one embodiment of the present invention.
  • FIG. 10D is a graph of expansion history of elliptical (1:3) columns in accordance with one embodiment of the present invention.
  • FIG. 11A is a perspective view for a wrapping method of a circular column in accordance with one embodiment of the present invention.
  • FIG. 11B is a cross sectional view of a circular column without a fiber reinforced polymer wrap.
  • FIG. 11C is a cross sectional view of a circular column with a fiber reinforced polymer wrap.
  • FIG. 11D is a cross sectional view of a circular column with a fiber reinforced polymer wrap.
  • FIG. 11E is a perspective view for a wrapping method of a circular column in accordance with one embodiment of the present invention.
  • FIG. 11F is a cross sectional view of a circular column of expansive concrete with a fiber reinforced polymer wrap.
  • FIG. 11G is a cross sectional view of a circular column of expansive concrete with a fiber reinforced polymer wrap.
  • FIG. 11H is a perspective view for a wrapping method of a circular column in accordance with one embodiment of the present invention.
  • FIG. 11I is a cross sectional view of a circular column with a fiber reinforced polymer wrap.
  • FIG. 11J is a cross sectional view of a circular column with a fiber reinforced polymer wrap.
  • FIG. 12A is a perspective view for a wrapping method of a square column in accordance with one embodiment of the present invention.
  • FIG. 12B is a cross sectional view of a square column without a fiber reinforced polymer wrap.
  • FIG. 12C is a cross sectional view of a square column with a fiber reinforced polymer wrap.
  • FIG. 12D is a cross sectional view of a square column encircled by regular concrete and a fiber reinforced polymer wrap.
  • FIG. 12E is a cross sectional view of a square column with a fiber reinforced polymer wrap.
  • FIG. 12F is a cross sectional view of square column encircled by regular concrete and a fiber reinforced polymer wrap.
  • FIG. 12G is a perspective view for a wrapping method of a in accordance with one embodiment of the present invention.
  • FIG. 12H is a cross sectional view of a square column encircled by expansive concrete and a fiber reinforced polymer wrap in accordance with one embodiment of the present invention.
  • FIG. 12I is a cross sectional view of a square column encircled by expansive concrete and a fiber reinforced polymer wrap in accordance with one embodiment of the present invention.
  • FIG. 12J is a perspective view for a wrapping method of a square column in accordance with one embodiment of the present invention.
  • FIG. 12K is a cross sectional view of a square column with a fiber reinforced polymer wrap.
  • FIG. 12L is a cross sectional view of a square column with a fiber reinforced polymer wrap.
  • FIG. 13A is a perspective view for a wrapping method of a rectangular column in accordance with one embodiment of the present invention.
  • FIG. 13B is a cross sectional view of a rectangular column without a fiber reinforced polymer wrap.
  • FIG. 13C is a cross sectional view of a rectangular column with a fiber reinforced polymer wrap.
  • FIG. 13D is a cross sectional view of a rectangular column encircled by regular concrete and a fiber reinforced polymer wrap.
  • FIG. 13E is a cross sectional view of a rectangular column with a fiber reinforced polymer wrap.
  • FIG. 13F is a cross sectional view of a rectangular column encircled by regular concrete and a fiber reinforced polymer wrap.
  • FIG. 13G is a perspective view for a wrapping method of a rectangular column in accordance with one embodiment of the present invention.
  • FIG. 13H is a cross sectional view of a rectangular column encircled by regular concrete and a fiber reinforced polymer wrap.
  • FIG. 13I is a cross sectional view of a rectangular column encircled by regular concrete and a fiber reinforced polymer wrap.
  • FIG. 14A is a perspective view for a wrapping method of a rectangular column in accordance with one embodiment of the present invention.
  • FIG. 14B is a cross sectional view of a rectangular column without a fiber reinforced polymer wrap.
  • FIG. 14C is a cross sectional view of a rectangular column with a fiber reinforced polymer wrap.
  • FIG. 14D is a cross sectional view of a rectangular column encircled with regular concrete and a fiber reinforced polymer wrap.
  • FIG. 14E is a cross sectional view of a rectangular column with a fiber reinforced polymer wrap.
  • FIG. 14F is a cross sectional view of a rectangular column encircled by regular concrete and a fiber reinforced polymer wrap.
  • FIG. 14G is a perspective view for a wrapping method of a rectangular column in accordance with one embodiment of the present invention.
  • FIG. 14H is a cross sectional view of a rectangular column encircled by expansive concrete and a fiber reinforced polymer wrap in accordance with one embodiment of the present invention.
  • FIG. 14I is a cross sectional view of a rectangular column encircled by expansive concrete and a fiber reinforced polymer wrap in accordance with one embodiment of the present invention.
  • FIG. 15 is a side perspective view illustrating the placement of specimens in a compression machine in accordance with one embodiment of the present invention.
  • FIG. 16A is a cross sectional view illustrating placement of LVDT devices in accordance with one embodiment of the present invention.
  • FIG. 16B is a cross sectional view illustrating placement of LVDT devices in accordance with one embodiment of the present invention.
  • FIG. 16C is a cross sectional view illustrating placement of LVDT devices in accordance with one embodiment of the present invention.
  • FIG. 17 is a perspective view of a column compression machine used in testing the specimens in accordance with one embodiment of the present invention.
  • FIG. 18 is a graph of load versus displacement behavior of circular specimens.
  • FIG. 19 is a graph of stress versus strain relation for specimens with regular concrete.
  • FIG. 20 is a graph of stress versus strain relation for specimens with expansive cement concrete.
  • FIG. 21 is a graph of stress versus strain for several specimens in accordance with embodiments of the present invention.
  • FIG. 22 is a graph of stress versus strain for several specimens in accordance with embodiments of the present invention.
  • FIG. 23 is a graph of finite element results for CFRP-confined square and rectangular columns.
  • FIG. 24 is a graph of finite element results for CFRP-confined elliptical columns.
  • cement as any material which can be used to bind.
  • concrete can include crushed stone, sand, and a cement.
  • Portland cement is a fired mixture of limestone and clay which, when hydrated, forms interlocking crystals which bind to the sand, stone, and one another.
  • Cements can generally be classified as shrink, non-shrink, or expansive cements. The most commonly used cement for general construction is shrink cement.
  • post-tension refers to tension created or induced in a material subsequent to formation. For example, post-tensioning of FRP shells occurs after curing of the FRP shell to create a post-tensioned shell having circumferential, or hoop stress.
  • substantially refers to a degree of deviation that is sufficiently small so as to not measurably detract from the identified property or circumstance.
  • the exact degree of deviation allowable may in some cases depend on the specific context.
  • a numerical range of “about 1 inch to about 5 inches” should be interpreted to include not only the explicitly recited values of about 1 inch to about 5 inches, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. This same principle applies to ranges reciting only one numerical value. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.
  • FRP-confined concrete columns Due to the increasing need for repair of existing support structures, research has been carried out to investigate the behavior of FRP-confined concrete columns.
  • the compressive stress-strain behavior of FRP confined concrete cylinders is generally nonlinear and the initial portion of the stress-strain response typically follows that of the unconfined concrete.
  • the response of the FRP-confined concrete softens. This softening can occur with either a localized descending branch that may stabilize as the dilation of the concrete core progresses, or the concrete may exhibit a somewhat linear behavior until the FRP composite jacket fails.
  • FRP materials can be used to either reinforce existing structures regardless of shape, or form new structures with improved mechanical, structural and aesthetic properties.
  • a fiber reinforced composite structure 10 comprising a core 14 including an inner cement structure 18 at least partially surrounded by an outer cement structure 22 .
  • the inner cement structure can have steel reinforcements therein; however, the present invention reduces the need for steel reinforcements.
  • the outer cement structure 22 may include a non-shrink cement or an expansive cement. Alternatively, the outer cement structure 22 may consist exclusively of expansive cement.
  • Encircling the core 14 is an FRP material 26 , which makes up an FRP outer shell 30 .
  • the FRP material 26 preferably comprises a fiber and polymeric matrix.
  • the fiber is selected from the group consisting of glass fiber, carbon fiber, aramid fiber, and combinations thereof, although other FRP materials can also be used.
  • the composite structure 10 is shown in FIG. 2 with a core 14 having a cross sectional shape that is different from the cross sectional shape of inner cement structure 18 .
  • the core 14 may have a cross sectional shape similar to the cross sectional shape of the inner cement structure 18 , as shown in FIG. 3A .
  • the composite structure 10 is shown in FIGS. 3B and 3C having a core 14 with a cross sectional shape that is different from the cross sectional shape of the inner cement structure 18 .
  • FIG. 3B shows the composite structure 10 having a core 14 with a circular cross sectional shape and an inner cement structure 18 with a square cross-sectional shape
  • FIG. 3C shows the composite structure 10 wherein the inner cement structure 18 has a rectangular cross sectional shape and the core 14 has an elliptical cross sectional shape.
  • a FRP outer shell 30 is shown around an existing column 34 .
  • the existing column can have steel reinforcements therein; however, the present invention reduces the need for steel reinforcements.
  • the outer shell 30 is configured such that there is an open space 38 between the existing column 34 and the outer shell 30 .
  • the open space 38 can then be filled with cement 42 .
  • the cement 42 may be either expansive cement or non-shrink cement or a combination thereof.
  • pegs 15 can be placed between the inner cement structure and the FRP outer shell to secure the positioning of the outer column and existing column prior to filling the open space with cement.
  • FIG. 5 illustrates one embodiment of the present invention wherein the outer shell 30 comprises at least two pieces which can be placed around the existing column 34 to form the outer shell 30 .
  • This can be achieved by separating the FRP outer shell 30 into two pieces and placing the two pieces around the existing column to form the outer shell.
  • To reinforce an existing column 34 it is typically necessary to separate the outer shell 30 longitudinally into a first piece 46 and a second piece 48 .
  • the first piece 46 and second piece 48 can then be placed around the existing column 34 to reform the outer shell 30 .
  • the outer shell 30 is designed and shaped to leave an open space 38 between the existing column 34 and the outer shell 30 .
  • the outer shell 30 provides a convenient avenue for shape modification of existing structures. Shape modification is particularly relevant with respect to retrofitting existing structures.
  • An existing column 34 with a square or rectangular cross-section may be modified such that the resulting composite structure 10 has a circular or elliptical cross-section.
  • FRP composite jackets subjected to membrane loading in accordance with the present invention are stronger than rectangular column sections having long flat sides. This is largely because of the dominant bending action of the flat sides. Therefore, shape modification of an existing column 34 using the present invention can be readily accomplished to provide improved structural and mechanical properties to the composite structure 10 .
  • first piece 46 and second piece 48 have been placed around the existing structure 34 they can be spliced, as shown in FIG. 6 , with a vertical FRP composite strip 56 along each seam 58 between the first piece 46 and second piece 48 so as to form a unitary outer shell 52 .
  • additional FRP material may be wrapped around the outer shell.
  • the wrapping can be done with a single continuous sheet; however, multiple sheets can be wrapped in a wet lay-up process followed by curing of the polymer resin. Most often, the number of layers can range from 1 to about 14 additional layers.
  • the existing column prior to placing the first piece 46 and second piece 48 around the existing column 34 , the existing column may be reshaped such that the edges of the existing column having an angle of about 90 degrees are rounded.
  • One important consideration in forming FRP-confined rectangular columns in accordance with the present invention is the issue of effectiveness of FRP confinement, which may significantly decrease due to the presence of 90° corners or abrupt change of direction around the perimeter. Small-scale tests illustrate the effect of rounding the column comers on confinement efficiency. The rounding of corners on concrete columns has been shown to have an effect in ultimate strength as high as an 80% increase with respect to square columns without rounding the corners.
  • FRP materials can be placed along the longitudinal axis of the existing column in direct contact with the existing column, either during or after formation of the FRP shell, for increased flexural resistance of the column, if required.
  • a mold can be prepared in order to form the FRP outer shell.
  • a mold can be prepared to correspond with a desired final shape of the column.
  • a mold is not necessarily the same shape as the existing column. Frequently, an existing rectangular or square column can be modified to produce a circular or elliptical column of slightly larger width.
  • a mold 60 is prepared.
  • the mold 60 is then wrapped with at least one layer of FRP material 64 to form an outer shell 72 .
  • the mold can then be removed leaving the outer shell as an independent structure.
  • the wrapping can be done with a single continuous sheet; however, multiple sheets can be wrapped in a wet lay-up process followed by curing of the polymer resin.
  • the sheets may be cut to a desired size or as lengths of fiber strands, as shown in FIG. 7B , which can be wrapped and/or laid as desired to form a particular shape. Most often, the number of layers can range from 1 to about 14 additional layers.
  • the FRP material 64 comprises a fiber and a polymeric matrix.
  • Typical fibers can include, but are not limited to, glass fiber, carbon fiber, aramid fiber, and combinations thereof. Any suitable FRP material can be used which includes a fiber material and a polymeric matrix.
  • Non-limiting examples of commercial products can include SikaWrap, Aquawrap, and the like.
  • Wrapping of the mold 60 may include a wet layup of resin coated fibers followed by a curing of the resin. Once the resin has cured, the outer shell 72 can be divided longitudinally into at least a first piece 76 and a second piece 78 so that it can be used in applications that require retrofitting existing columns.
  • the radii of curvature for the 90 degree corners of the square and rectangular columns were designed to be 3 ⁇ 4 in. This would allow modification of existing columns, taking into account typical existing steel reinforcement at 90 degree corners. Expansive cement was used for some examples, whereas non-shrink cement was used for other examples to fill the space between the outer shell and existing column.
  • FIG. 8 illustrates that the concrete strength increased during the first 6 months and after six months approaches a constant value of 2600 psi.
  • Unstressed FRP composite jackets do not participate in the confinement of concrete until the concrete starts expanding. Typically, this involves at least partial failure of the concrete and/or softening of the concrete.
  • expansive concrete can post-tension the FRP composites jacket in the hoop direction prior to application of vertical or axial loading to the column.
  • the expansive cement used in the following examples includes Type-K and KOMPONENT cements, manufactured by CTS Company, Cypress, Calif.
  • the two principal constituents of KOMPONENT are calcium sulfoaluminate and gypsum (calcium sulfate).
  • the expansive cement induces tensile stress in the FRP composite jackets along the circumference of the FRP jackets.
  • FIGS. 10A-10D show the hoop expansion strain of the circular and elliptical columns for about 70 days.
  • a shrinkage compensated cement was also used to compare the differences between the expansive cement FRP jackets and the non-shrinkage FRP jackets.
  • the non-shrinkage concrete was used to modify the rectangular or square sections to elliptical or circular sections as detailed below. Once the aging of the concrete was stable, the FRP jackets were wrapped using a wet lay-up process. A structural grout, Sika Grout 212 was selected as the grout to make non-shrink concrete.
  • test structures were prepared such that each had nearly the same cross-sectional area prior to shape modification and the same height of 3 feet. Thus, comparisons were made for different cross sections and aspect ratios. Molds for specimens were made out of plywood and sonatubes.
  • FIGS. 11A through 11J , 12 A through 12 L, 13 A- 13 I, and 14 A- 14 I show details of the wrapping methods for each specimen. Regardless of the number of FRP layers, the entire bonded jackets were made of one continuous sheet of FRP fabric that was cut to the proper length and width. An additional 3′′ of overlap splice was provided. To expansive cement concrete specimens, the following steps were followed:
  • strain gauges employed in this testing program were manufactured by measurements Group, Inc. with model designation as EA-06-125BZ-350.
  • the resistance of these gauges at normal temperature (75° F.) is 350 ⁇ 0.15% ohms.
  • strain gauges were placed on fibers in the hoop direction, at about the mid-height of the specimens. Special care was taken during the installation to avoid damage of the strain gauges. Considering the geometry of the cross sections, the layout of strain gauges was varied for each shape.
  • Linear variable differential transducers are used to measure average strains when the use of strain gauges is impossible. In these tests, LVDTs are employed to measure the vertical and lateral strains. The data from LVDTs can be used to calculate the average axial and transverse strains over the column height and width. LVDTs are installed using aluminum angles with threaded rods at their ends. The angles must be solidly clamped to the specimen for accurate readings.
  • FIG. 15 shows the LVDT configuration. Two types of LVDTs used for experiments are MVL7C and MVL7, manufactured by Sensotec Company. They can measure a displacement in the range of ⁇ 0.500 in. and ⁇ 2.000 in., respectively, with high accuracy. For the square and rectangular columns, additional LVDTs are installed on the two sides of the cross section to measure the transverse strain in both directions as shown in FIGS. 16A-16C .
  • FIG. 17 illustrates the setup of the column compression tests. All of the specimens were loaded monotonically under a displacement control mode with a constant loading rate of 0.05 in. per minute.
  • a data acquisition system was used to record the values of the strain gauges and LVDTs.
  • the data acquisition system used in this testing program consisted of scanners, WIN5100 (manufactured by Measurements Group) with interface cards and the STRAINSMART software.
  • the scanners can read electrical signals from the sensors and send this information to a computer via the interface cards.
  • the software then converts these signals into the desired digital output.
  • a configuration file had to be written in the software to assign the measured quantities to input and output channels.
  • the calibration values of strain gauges and LVDTs were input into this configuration file. After the setup of the configuration file and immediately before testing, all of the initial values were set to zero to prepare for recording.
  • the specimens in this testing group exhibited several failure modes.
  • the governing failure mode was determined by the mechanical properties of the FRP composite material and the reinforcement scheme. It was observed from the tests that the most typical failure mechanism was crushing of concrete followed by the tensile failure of the FRP at or near the mid-height of the specimens. Because the fabric was unidirectional and oriented at 0 degrees, a band or ring was typically formed as a result of the shearing off, and separation of, the fabric in the hoop direction.
  • the stress-strain curves for regular concrete specimens and specimens with expansive cement concrete are shown in FIG. 19 and 20 , respectively.
  • the loading behavior of the FRP-confined specimens with regular concrete can be divided into three phases.
  • the first phase is from the origin to point A.
  • f co ′ is the strength of the baseline specimen C-0-0.
  • lateral expansion was very small and the FRP stresses were very low (about 16%-33% of their ultimate strength as observed from the tests).
  • the load exceeded point A the FRP stress and strain started to increase quickly.
  • phase AB the concrete expands and FRP composite jacket is put into tension. Therefore, the FRP material provides partial confinement against expansion.
  • phase AB the concrete goes into a flowing state until FRP fracture and the failure is very brittle.
  • the behavior of the specimens with expansive cement concrete was somewhat different. Specifically, the initial slope of the stress-strain curve is lower than that of the regular concrete specimens, but the later slope after the turning point is similar to that of the regular concrete specimens. The comparisons show that the axial stress capacity was equivalent to the FRP-confined regular concrete specimens and the axial strain capacity was much larger.
  • FIGS. 21 and 22 Testing results for several square columns are shown in FIGS. 21 and 22 .
  • S- 0 - 0 shows results for an 11 in. square column without FRP composites
  • S-G 6 - 0 shows results for an 11 in. square column with 6 layers of glass FRP composite directly wrapped thereon
  • S-GT-E shows results for an 11 in. square column with expansive concrete modified into a 16 in. diameter circle with 6 layers of glass FRP composite in accordance with the present invention.
  • FIG. 21 illustrates that the GFRP expansive composite column has a strength of about 3.3 times that of the unwrapped column and about 2.3 times that of the directly wrapped column.
  • FIG. 22 illustrates that strain, i.e. ductility, for the GFRP expansive composite column is about 8 times that of the unwrapped column.
  • FRP composites are very effective in increasing the load-carrying capacity and deformation ability of existing columns.
  • Significant increases in both ultimate stress and strain are observed from the tests.
  • the specimens with expansive cement concrete show more deformation ability and ductility at failure. In addition, they have a higher increase in the ultimate strength.
  • the strengthening method with FRP strips should be used with caution for the normal retrofit of bridge columns. Otherwise, the maximum spacing of FRP strips should be limited.
  • strengthening with FRP strips offers the advantage of easy inspection.
  • the FRP composites can significantly improve the axial behavior of the columns. It is recommended that at least two layers of FRP composites be used for the retrofit of existing columns.
  • ANSYS6.0 ANSYS 2000
  • SOLID65 which is an eight-node brick element with 3 DOFs at each node, was used to model concrete.
  • SHELL181 is a four-noded element that is well-suited to model FRP composite materials.
  • the material properties for the unconfined concrete and FRP composites were obtained from compression cylinder and tensile coupon tests, respectively. Considering the symmetry of each column, only one-quarter of the column section along its longitudinal direction was modeled; symmetrical boundary conditions were applied at the symmetrical borders along the X and Y axes.
  • the output of ANSYS results consists of the nodal displacement, element stress, element strain and other information.
  • a mean value was calculated by taking the average of the longitudinal 6 elements along the central line of the model. By entering this value into the element result tables, circumferential or hoop strain was obtained. Then, the curves of axial stress versus axial strain and hoop strain were developed by joining a series of data for each loading step.
  • FIGS. 23 and 24 The results of finite element analysis for some rectangular/square specimens are summarized in the stress-strain curves in FIGS. 23 and 24 . It is noted from FIG. 23 that the confinement provided was not sufficient to significantly increase the axial stress for the square and rectangular sections. Both the square and rectangular models demonstrated a typical softening behavior which is characterized by a sudden drop from the peak stress (as seen from FIG. 23 ). Observations from the results of the normal elliptical models (as shown in FIG. 24 ) also demonstrated the softening behavior. However, this softening is not as much as that of the rectangular columns. This result illustrates that the confinement effect is directly related to the shape of the section and that the confinement efficiency of circular columns is much better than the sections with 90 degree corner radius.

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US11/227,902 2004-09-15 2005-09-14 Shape modification and reinforcement of columns confined with FRP composites Abandoned US20060070338A1 (en)

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US20120124937A1 (en) * 2010-05-24 2012-05-24 Jin-Guang Teng Hybrid frp-concrete-steel double-skin tubular beams and hybrid dstb/slab units using the beams
US20130081342A1 (en) * 2011-09-30 2013-04-04 Siemens Aktiengesellschaft Wind turbine tower
US20140157715A1 (en) * 2011-07-17 2014-06-12 Philipp Wagner Method and Sliding Form for Producing a Structure and Corresponding Structure
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US9669579B2 (en) 2008-11-13 2017-06-06 The Boeing Company Aircraft skin attachment system
US20120124937A1 (en) * 2010-05-24 2012-05-24 Jin-Guang Teng Hybrid frp-concrete-steel double-skin tubular beams and hybrid dstb/slab units using the beams
US20140157715A1 (en) * 2011-07-17 2014-06-12 Philipp Wagner Method and Sliding Form for Producing a Structure and Corresponding Structure
US9657722B2 (en) * 2011-07-17 2017-05-23 X-Tower Consructions GmbH Method and sliding form for producing a structure and corresponding structure
US20140237919A1 (en) * 2011-09-30 2014-08-28 Siemens Aktiengesellschaft Wind turbine tower and method of production thereof
US9567981B2 (en) * 2011-09-30 2017-02-14 Siemens Aktiengesellschaft Wind turbine tower and method of production thereof
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US20140245695A1 (en) * 2013-03-04 2014-09-04 Fyfe Co. Llc Method of reinforcing a column positioned proximate a blocking structure
US9085898B2 (en) * 2013-03-04 2015-07-21 Fyfe Co. Llc System and method of reinforcing a column positioned proximate a blocking structure
US10227786B2 (en) 2013-08-08 2019-03-12 University Of Utah Research Foundation Elongate member reinforcement with a studded collar
US9976315B2 (en) 2013-08-08 2018-05-22 University Of Utah Research Foundation Elongate member reinforcement
CN103967214A (zh) * 2014-04-12 2014-08-06 北京工业大学 多腔钢管混凝土内嵌圆钢管再生混凝土带缀板组合柱
US11174637B2 (en) * 2014-08-11 2021-11-16 Hpc Okinawa Co., Ltd. Prestressed concrete for non-primary structural members
US9580908B2 (en) 2014-11-12 2017-02-28 King Saud University Fiber reinforced composite system for strengthening of wall-like RC columns and methods for preparing such system
CN104712099A (zh) * 2015-03-15 2015-06-17 北京工业大学 异形截面多腔钢管内置圆钢管混凝土组合巨型柱及作法
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US11421414B2 (en) * 2018-05-02 2022-08-23 South China University Of Technology Concrete-filled steel tubular column-steel plate concrete ring beam joint and construction method thereof
CN109164852A (zh) * 2018-07-27 2019-01-08 同济大学 一种大体积混凝土自适应温度与应力控制方法
CN110029596A (zh) * 2019-05-22 2019-07-19 福州大学 复合式桥墩抗震加固结构及其施工方法
CN113638545A (zh) * 2019-12-08 2021-11-12 王哲 一种适用于宽温度范围的组合结构和制作方法
CN111350370A (zh) * 2020-03-11 2020-06-30 天津大学 基于闭合截面预应力frp的钢柱加固修复结构及方法
CN113898373A (zh) * 2021-10-19 2022-01-07 辽宁工业大学 Frp-pvc膜壳内填自密实煤矸石混凝土防火组合煤柱及加固方法
CN114352058A (zh) * 2021-12-30 2022-04-15 华润水泥(南宁)有限公司 一种建筑物结构加固水泥绳及其加固施工方法
CN116104327A (zh) * 2023-02-24 2023-05-12 山西北斗钢结构实业发展有限公司 一种网架结构焊接空心球节点的加固方法
CN116427621A (zh) * 2023-03-24 2023-07-14 武汉大学 Frp永久模板海水海砂混凝土柱及制作方法
CN118728120A (zh) * 2023-03-30 2024-10-01 中国石油化工股份有限公司 一种海洋平台焊接管节点碳纤维修复方法
CN116988618A (zh) * 2023-07-06 2023-11-03 哈尔滨工业大学 约束粘结双增强uhpc壳模frp型钢混凝土柱及施工方法
CN117071476A (zh) * 2023-10-17 2023-11-17 山西交通科学研究院集团有限公司 一种复合隔离栅立柱
CN119047042A (zh) * 2024-08-20 2024-11-29 天津大学 一种基于纤维单元法的frp约束钢管混凝土柱设计方法

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