METHOD OF STRENGTHENING AN EXISTING INFRASTRUCTURE USING SPRAYED-FIBER REINFORCED POLYMER COMPOSITE

Abstract

A construction technique for strengthening existing infrastructure and its components (e.g. bridge columns) using sprayed fiber reinforced polymer (sprayed-FRP) made of randomly oriented chopped fibers and resins on the said existing deficient infrastructure. Sprayed-FRP composite laminates are applied to reinforced concrete (RC) or steel or wooden or masonry structure substrates as an external reinforcement as effective means for obtaining higher level of fiber utilization before premature failure.

Claims

1. A method of strengthening an existing seismically deficient infrastructure constructed from concrete, masonry, steel and/or timber wherein the infrastructure may have a first deficient area, the method comprising repairing any first deficient area of the infrastructure using cement motor and then externally jacking the infrastructure, including the cement motor, in a sprayed fiber reinforced polymer jacket.

2. A sprayed-fiber reinforced polymer composite member, for use in the method of claim 1, for increasing the compressive, tensile, shear and flexural strengths of reinforced concrete bridge column and supports, wherein the member includes: an external case of sprayed fibre and resin combination where the combination includes substantially 60 to 65% glass fiber and substantially 35 to 40% vinyl ester resin; wherein the external case encases an internal concrete core so as to provide an axial and circumferential reinforcement for the internal concrete core.

3. The member of claim 2 wherein the member is sprayed fiber reinforced polymer jacketing which includes randomly oriented chopped fibers chosen from the group: glass, carbon, basalt and aramid fibers group; in combination with a resin chosen from the group: vinyl ester, polymer and epoxy resin.

4. The member of claim 3 wherein the external case includes a multilayer of wraps.

5. The member of claim 4 wherein the multi-layer of wraps further includes randomly oriented chopped fiber laminated ply.

6. The member of claim 5 wherein the multi-layer of wraps further includes a layer of randomly distributed fibers sandwiching inner and outer layers of circumferential hoop wraps.

7. A sprayed fiber reinforced polymer composite member for increasing the compressive, shear and flexural strengths of concrete columns and supports comprising an external multilayer case of a fiber and resin combination, wherein the fiber includes at least one or more of: glass, carbon, basalt and aramid, and the resin includes at least one of vinyl ester, polymer and epoxy

8. The sprayed fiber reinforced polymer composite member of claim 7 comprising substantially 60 to 65% of the fibers, and substantially 35 to 35% of the resin by weight or by volume.

9. The sprayed fiber reinforced polymer composite member of claim 8 further comprising an external case formed solely from glass, one of the group comprising carbons.

10. The member of claim 9 wherein the member is adapted to snugly wrap onto a core concrete within the external case, whereby the external case provides axial and circumferential reinforcement for the core concrete.

11. The member of claim 10 wherein the core concrete is a support column or a pile.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a schematic diagram showing a sprayed-FRP wet lay-up process.

[0031] FIG. 2 is a schematic diagram of the manufacturing process of a sprayed-FRP laminate square plate.

[0032] FIG. 3 is schematic stress-strain behavior of sprayed-FRP coupon specimens.

[0033] FIG. 4 is the stress-strain behavior of sprayed-FRP confined concrete.

[0034] FIG. 5A is a schematic of the test set up in side view.

[0035] FIG. 5B is a top view of FIG. 5A.

[0036] FIG. 6 is a schematic diagram demonstrating sprayed-FRP applying an external confining pressure on circular reinforced concrete bridge columns

[0037] FIG. 7 is a typical single column reinforced concrete circular bridge column configuration.

[0038] FIG. 8 is a cross section of reinforced concrete circular bridge column

[0039] FIG. 9 represents a schematic of postposed experimental setup of sprayed-FRP retrofitted circular columns.

[0040] FIG. 10 represents stress-strain behavior of 3 mm thick sprayed-FRP specimen with 35 mm, and 25%, length and volume fibers, respectively.

[0041] FIG. 11 represents stress-strain behavior of 6 mm thick sprayed-FRP specimen with 35 mm, and 25%, length and volume fibers, respectively.

[0042] FIG. 12 represents stress-strain behavior of 9 mm thick sprayed-FRP specimen with 35 mm, and 25%, length and volume fibers, respectively.

[0043] FIG. 13 represents axia stress-strain behavior unconfined and confined concrete cylinder with sprayed-FRP

[0044] FIG. 14 represents an elevation and cross-section of as-built columns

[0045] FIG. 15 represents load protocol adopted in the study.

[0046] FIG. 16 represents load-displacement (hysteretic) behavior of as-built column.

[0047] FIG. 17 represents load-displacement (hysteretic) behavior of as-built columns, and retrofitted column with 3.5 mm sprayed-FRP.

BRIEF DESCRIPTION OF THE TABLES

[0048] Table 1 represents levels of the factors considered for tensile strengths test of sprayed-FRP coupons.

[0049] Table 2 represents experimental results of tensile test of sprayed-FRP coupons with various length, volume fraction of fibers and length.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0050] In the first embodiment, the sprayed-FRP technique may contain the following: [0051] a) The material and mix proportion of sprayed-FRP [0052] b) Spraying process, one, two, three and multiple layers with different thickness [0053] c) Roll out process [0054] d) Curing of sprayed-FRP [0055] e) Prepare the dog-bone shape specimen from the prepared square sprayed-FRP plate [0056] f) Instrumentation of the sprayed-FRP specimens [0057] g) Uniaxial tensile strength test of sprayed-FRP coupon specimens [0058] h) Plot the stress-stain curve and find the Young's modulus of elasticity of sprayed-FRP

[0059] The material is chose from the group such as glass and/or carbon fiber, polyester, epoxy and vinyl ester resin. After the selection of the material, a preferred mix proportion of sprayed-FRP is chosen. Once the mix proportion is ready, the sprayed-FRP of 400 mm400 mm square plate is prepared with one, two and three layers. Rolling is applied as a rolling process to the square plate to get rid of the air from the sprayed-FRP. Then, the sprayed-FRP laminated square plate is cured at room temperature. The laminated cured specimen is cut in the desired shape and dimension to prepare the tensile strength test of dog-bone shape coupons. The strain gauge is installed on the sprayed-FRP coupons and a uniaxial tensile strength test is conducted to study the stress-strain behavior of the sprayed-FRP coupons.

[0060] Before describing the disclosed embodiment further, it is to be understood that the discovery is not limited to its use to the specific procedure revealed since the discovery is capable of further embodiments. Also, the terminology used herein is for the purpose of description and not of restriction.

[0061] The following are the preferred, but not necessarily the only, embodiments for the sprayed-FRP strengthening technique.

[0062] The present disclosure includes a study of sprayed-FRP coupons tensile strength test. The sprayed-FRP coupons are prepared with different thickness (3 mm to 9 mm) with different fiber length (15 to 45 mm) and various volume fractions of fibers (25 to 40%) in a vinyl ester resin. Table 1 and Table 2 show the full factorial design of sprayed-FRP coupon specimen. FIG. 1 shows the sprayed-FRP coupon specimen manufacturing process.

[0063] Types of fiber may be glass, carbon, basalt and/or aramid. Types of resin may be polyester, vinyl ester, epoxy, and the like as would be known to one skilled in the art. The fiber and resin combinations may be manufactured by processes such as but not limited to hand lay-up, filament winding, pultrusion and the like as would be known to one skilled in the art. FIG. 1 shows a schematic demonstration of a sprayed-FRP wet lay-up spray process. Hand lay-up spray process is a method of producing sprayed-fiber reinforced plastic components. The fibers can be pre-impregnated with resin (i.e., they are wetted by resin). Rolling can be done to consolidate the fibers in the resin and get rid of any air voids to get the proper bond. FIG. 2 is intended to illustrate that the tensile strength coupon specimens are cut from the cured sprayed-FRP laminated square plate to the desired shape/dimension and machined to the proper acceptances.

[0064] A tensile strength test of sprayed-FRP coupons was performed using an Instron 500 kN capacity universal testing machine. FIG. 3 shows how stress-strain data is plotted to obtain the ultimate tensile strength, the Young's modulus of elasticity and elongation to break.

[0065] In a sprayed-FRP durability test, the sprayed-FRP laminated cured coupons and the sprayed-FRP confined concrete cylinder is exposed to a freeze-thaw environment for about 300 to 400 freeze-thaw cycles. The sprayed-FRP laminated cured coupons and the sprayed-FRP confined concrete cylinder are kept in an oven at different temperatures (25 to 80 degrees celsius) for about a 24 hour period. For these durability tests, tensile stress-strain behavior of sprayed-FRP coupons and the sprayed-FRP confined concrete cylinder compressive strength and stress-strain behavior are observed.

[0066] In a constitutive model test of sprayed-FRP confined concrete, using not al concrete having a compressive strength of about 35 MPa of 100 mm200 mm, a concrete cylinder is manufactured, and then encased with the sprayed-FRP composite. The sprayed-FRP confined concrete cylinder was tested under uniaxial compression load with different percentage of mechanical load with respect to the axial capacity of unconfined concrete. FIGS. 5A and 5B show the test set-up of the uniaxial compression test of the sprayed-FRP confined cylinder. The stress-strain behavior was observed for the sprayed-FRP confined concrete with different percentage of axial load and plotted (FIG. 4).

[0067] Further testing included a sprayed-FRP strengthened circular reinforced concrete bridge column under constant axial load along with lateral reversed cyclic load to simulate earthquake induced loading and damage. Experimental and numerical investigations were conducted to study the performance of non-seismically designed reinforced concrete (RC) bridge columns retrofitted with sprayed-FRP. FIG. 6 shows schematic illustration of sprayed-FRP applying external confining pressure on a circular RC bridge column FIG. 7 is a typical single column reinforced concrete circular bridge column configuration. FIG. 8 is a cross section of a reinforced concrete circular bridge column. FIG. 9 is a test set up for reversed cyclic load test of circular RC bridge column. The damaged column specimen is retrofitted using sprayed-FRP then tested under reversed cyclic lateral load up to failure to assess remaining lateral load carrying capacity, energy absorption capacity and ductility.

[0068] In applicant's view, the sprayed-FRP strengthening technique using glass fiber and vinyl ester resin is preferable, although not intended to be limiting, from a variety of fibers and resin.

[0069] The mechanical properties of a sprayed-FRP coating were tested using a series of tensile strength tests on sprayed-FRP coupons using a factorial design. As described above, the factorial design showing three treatment levels (low, medium and high) are depicted in Table 1. The factorial design matrix and tensile strength test results are presented in Table 2. In the abbreviations in Table 2, for example GL35-V25-TH3, the first letter GL35 represent the glass fiber length is 35 mm, the second letter denotes the volume is fiber of 25%, and the third letters indicate the thickness of coupons is 3 mm The stress-stain behavior for the optimum material composition of the specimens that yielded the best strength are found in FIGS. 10-13 with 3, 6 and 9 mm thick coupons, respectively.

[0070] From FIG. 10, it can be observed that the 3 mm thick specimen's average tensile strength and strain were 56 MPa and 0.84%, respectively. From FIG. 11, it can be observed that the 6 mm thick specimen's average tensile strength and strain were 92.3 MPa and 0.72%, respectively. From FIG. 12, it can be observed that the 9 mm thick specimen's average tensile strength and strain was 101.6 MPa and 0.68%, respectively. All the specimens, tensile strength and Young's modulus of elasticy are depicted in Table 2 along with their standard deviation (SD) and coeficient of varation (COV). The results of the material properties tests assist in identifying the otimum materials properties for the sprayed-FRP system for seismic strengthening. The test results indicate that the tensile strength increases with the length of chopped fibers under the condition that the quantity of the fibers in the mixture was greater compared to resin. Based on the performance and construction workability of the chopper gun, seen by way of example in FIGS. 1 and 6, a fiber length of 35 mm and with volume of fiber 30% produced the best strength with the least fiber jumbling.

[0071] The effectiveness of sprayed-FRP coating was studied by conducting an axial compression test. In the compression test the length and volume of fiber were 35 mm and 30%, respectively. The unconfined compressive strength of the concrete tested was 42 MPa. FIG. 13 shows the axial compression stress-strain relationship of unconfined and confined concrete with 2 and 4 mm thick sprayed-FRP coating. The results show that the sprayed-FRP coating significantly increased the compression strength (41%) and strain (75%) of the confined concrete as compared to the unconfined concrete. It was observed that confined and unconfined specimen stress-strain slope were same, but after a certain limit seen in FIG. 13 cracking occurred on the sprayed-FRP confined specimen which developed the lateral tri-axial state of stress, and the slope of the stress-strain diagram changed. Hence, it may be that the effectiveness of sprayed-FRP confinement is most effective after cracking occurs in the confined specimen. Based on the experimental results, it may be concluded that the sprayed-FRP coating is effective in increasing the compressive strength and strain of concrete.

[0072] FIG. 14 shows the dimensions of an as-built column and also shows the steel reinforcement detailing. The effective height, and diameter of the columns is 1745 mm, 300 mm, respectively. The column is supported by 1400 mm800 mm660 mm footing. In its longitudinal direction the column is reinforced with 18-11.3 mm reinforcing bars, while in the lateral direction, 9 gauge 3.5 mm diameter wire hoops are placed every 91 mm The column was cast using ready mix concrete of 35 MPa. A reduced scale single-cantilever damaged reinforced concrete column was repaired and retrofitted with sprayed-FRP, and tested under cyclic loading.

[0073] FIG. 9 shows the experimental set-up of the column under lateral revise cyclic load along with constant axial load. The column was damaged under an incrementally increasing displacement-controlled lateral cyclic load. Both columns were subjected to the same load protocol as shown in FIG. 15. To mimic the effect of gravity loads, the axial load on the column was maintained during testing at a value of 116 kN which represents 5% of the column's gross section compressive strength. The reversed cyclic load was applied to the column using hydraulic actuator mounted on the reaction frame.

[0074] The lateral load versus top lateral displacement response of experimental and numerical results of as-built and sprayed-FRP retrofitted columns under reverse cyclic loading are presented in FIGS. 16 and 17, respectively. It should be noted that both figures are plotted in the same scale. From FIG. 16, it can be observed that the as-built specimen shows stable behavior up to 20 mm displacement, and the strength is degrading. The lateral load carrying capacity of as-built column and sprayed-FRP retrofitted columns specimen differed considerably. The sprayed-FRP retrofitted column started yielding at a drift ratio of 0.73%, and the average maximum strength recorded under pulling and pushing was 110 kN. Comparing the average strength of the retrofitted and as-built columns showed that damaged column was fully restored to the as-built column's lateral strength. The hysteretic behavior of sprayed-FRP-retrofitted column shows superior load carrying capacity compared to the as-built column up to a displacement ductility level of 6. The sprayed-FRP retrofitted column was able to maintain its load-carrying capacity until the end of the loading protocol without evidence of significant structural deterioration. The sprayed-FRP retrofit provided additional confinement to existing core concrete, and was effective at preventing the columns from bond failure of longitudinal bar buckling, and therefore greatly increased the earthquake resistance of the column.

[0075] As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof.