CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of the filing date of U.S. Provisional Application No. 63/325,894, filed on March 31, 2022, the disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] Contemporary structural members, such as girders and beams, in buildings or bridges or other structural systems are often required to resist higher loads than the original designs anticipated. These higher loads may be due to modem uses involving greater loads than during the time period of the design of the structure, or external environmental damage, like chloride attack or corrosion. In response to these situations, the load bearing capacity of such structural members can be increased using tensioned non-metallic tendons, which could produce low- maintenance girders with the same expected service life as steel tendons due to the non- corrosive nature of the non-metallic tendons.

[0003] There are numerous concrete and steel structures in North America and around the world that require repair, strengthening, or rehabilitation to ensure a certain level of safety in operation. Improvement of the bending moment resistant capacity structural members, and the repair of any damaged structural members, are an important application of this load increasing technology.

[0004] An effective method to enhance or restore the bending moment capacity of a structural member is to add external and/or internal tendons (depending on the prestressing system) and tension the tendons against the structure member. Using steel tendons increases potential corrosion issues, so non-metallic tendons may be a better option if an effective anchoring method is available.

[0005] A conventional reinforcing system for non-metallic, for instance, fiber reinforced polymer (FRP) tendons consists of bonding the non-metallic (e.g., FRP) tendon/rebar with epoxy, other adhesives, or any other method that does not damage the tendons. These tendons provide additional load resistance and ductility to the structural member. To achieve the maximum reinforcing effect, the stress carried by non-metallic (e.g., FRP) tendons must be transferred to the damaged/repaired structural member. An anchorage system that assures the effectiveness of the non-metallic (e.g., FRP) strengthening system is desirable for this application.

[0006] The anchorage system has been a significant challenge for each structural system that involves the use of non-metallic (e.g., FRP) tendons. There are many conventional designs and systems that been proposed by researchers to anchor and tension these tendons. However, these anchors are either expensive or difficult to fabricate. For external prestressing of structural members, non-metallic non-corrosive tendons would fit all the strength criteria if a suitable simple and effective anchorage system would be available. Accordingly, there is a need for an improved anchoring system that is affordable, simple, and effective enough to provide the capacity required for prestressing structural elements.

BRIEF SUMMARY OF THE INVENTION

[0007] The invention relates to anchorage systems that hold structural reinforcing non- metallic tendons or rebars made of fiber reinforced polymers (FRP) or any non-metallic materials prestressed against any structural member. The technologies proposed provide anchorage and locking systems for the tensioned tendon. The present invention allows the non- metallic (e.g., FRP) tendons to fully utilize their high strength without premature failure.

[0008] An anchorage system for prestressing a non-metallic tendon (e.g., FRP) against a support member and a method of prestressing a non-metallic tendon against a support member are disclosed.

[0009] The anchorage system may include a dead-end assembly and a live-end assembly configured to be placed on opposite sides of the support member. Each of the dead-end assembly and the live-end assembly may include a support sleeve affixed to a support plate and a hollow bolt removably coupled to an end of the support sleeve adjacent to the support plate. A longitudinal axis of each support sleeve may be perpendicular to a planar surface of the respective support plate, each support sleeve may have an interior that is configured to extend around a respective portion of the non-metallic tendon, each support sleeve may be configured to be affixed to the non-metallic tendon (e.g., FRP) using an expansive grout that extends therebetween, and each support sleeve may have one or more apertures extending into the respective interior that are configured to receive insertion of the grout therethrough. Each hollow bolt may have a lumen configured to slidably receive a portion of the tendon therethrough with a clearance that is sufficiently close to prevent the expansive grout from leaking out of the lumen when the non-metallic tendon extends therethrough. [0010] The anchorage system may also include a tensioning rod coupled to an end of the support sleeve of the live-end assembly that is remote from the respective support plate, and a removable support box extending around the support sleeve of the live-end assembly, the tensioning rod extending through an opening defined in the removable support box, the support box configured to be an abutment structure against which a jack may be placed. The anchorage system may also include one or more slotted shim plates interposed between the support plate of the live-end assembly and a first confronting surface of the support member, the one or more slotted shim plates having a total width approximately equal to a length that the non-metallic tendon has been stretched from a relaxed state thereof.

[0011] The anchorage system may also include the non-metallic tendon and the expansive grout, the expansive grout affixing the non-metallic tendon to an inner surface of each of the support sleeves. The end of the support sleeve of the live-end assembly may be threadedly coupled to an end of the tensioning rod. The anchorage system may also include the support member, the non-metallic tendon extending through each of the support sleeves and either through a duct extending through the support member, or outside of and along an outer surface of the support member and coupled to the outer surface.

[0012] The support member may have a recess extending into a second confronting surface thereof adjacent to the support sleeve of the dead-end assembly, the hollow bolt of the deadend assembly positioned within the recess such that the support plate of the dead-end assembly is positioned flush with a second confronting surface of the support member. The aperture of each support sleeve may have internal threads. The anchorage system may also include removable bolts configured to be threadedly coupled to respective ones of the apertures. The one or more slotted shim plates may be a plurality of shim plates each having a different thickness in a direction along the longitudinal axis of the support sleeve of the live-end assembly.

[0013] The method of prestressing a non-metallic tendon against a support member may include placing the non-metallic tendon extending either through a duct connecting opposite sides of the support member, or outside of and along an outer surface of the support member and coupled to the outer surface, and positioning a dead-end assembly and a live-end assembly on the opposite sides of the support member , each of the dead-end assembly and the live-end assembly having a support sleeve affixed to a support plate, a longitudinal axis of each support sleeve being perpendicular to a planar surface of respective support plate. The method may also include feeding first and second ends of the non-metallic tendon into the support sleeve of the dead-end assembly and the support sleeve of the live-end assembly, respectively, so that an interior of each support sleeve extends around a portion of the non-metallic tendon.

[0014] The method may also include coupling a tensioning rod coupled to an end of the support sleeve of the live-end assembly that is remote from the respective support plate, and pouring an expansive grout into apertures extending into an interior of each of the support sleeves, the expansive grout extending around exposed portions of the non-metallic tendon within the interior of each of the support sleeves. The method may also include curing the expansive grout so that the non-metallic tendon is affixed to the support sleeve of each of the live-end assembly and the dead-end assembly, and assembling a support box extending around the support sleeve of the live-end assembly, the tensioning rod extending through an opening defined in the removable support box.

[0015] The method may also include coupling a jack to the tensioning rod, an end surface of the support box serving as an abutment structure against which the jack is placed. The method may also include a first pulling of the tensioning rod along the longitudinal axis of the support sleeve of the live-end assembly to stretch the non-metallic tendon by a first elongation length, the first pulling of the tensioning rod creating a first gap extending between the support plate of the live-end assembly and a first confronting surface of the support member. The method may also include inserting one or more first slotted shim plates into the first gap, the one or more first shim plates having a first aggregate width approximately equal to the first elongation length that the non-metallic tendon has been stretched.

[0016] The method may also include a second pulling of the tensioning rod along the longitudinal axis of the support sleeve of the live-end assembly to further elongate/tension the non-metallic tendon by a second elongation length. The second pulling of the tensioning rod creates a second gap extending between the one or more first slotted shim plates and either the support plate of the live-end assembly or the first confronting surface of the support member. The method may also include inserting one or more second slotted shim plates into the second gap (i.e., the gap created by the elongation of the tendon) created after the second pulling is completed. The one or more second shim plates having a second aggregate width approximately equal to the second elongation length that the non-metallic tendon has been stretched. The second aggregate width may be less than the first aggregate width. [0017] The end of the support sleeve of the live-end assembly may be threadedly coupled to an end of the tensioning rod. The aperture of each support sleeve may have internal threads. The method may also include threadedly coupling removable bolts to seal respective ones of the apertures after the pouring and before the curing. The method may also include removing the removable bolts from the respective ones of the apertures after the curing period is completed. The method may also include removably coupling a hollow bolt to an end of each support sleeve adjacent to the respective support plate, each hollow bolt having a lumen that slidably receives a portion of the non-metallic tendon therethrough with a clearance that is sufficiently close to prevent the expansive grout from leaking out of the lumen.

[0018] The support member may have a recess extending into a second confronting surface thereof adjacent to the support sleeve of the dead-end assembly. The method may also include positioning the hollow bolt of the dead-end assembly within the recess such that the support plate of the dead-end assembly is positioned flush with the second confronting surface of the support member. During the inserting of the first slotted shim plate into the first gap, the first shim plate may be inserted into an open side of the support box, and a slot extending into the first slotted shim plate may be positioned around a portion of the non-metallic tendon.

[0019] The method may also include, after the inserting of the first slotted shim plate into the first gap, uncoupling the jack from the tensioning rod, uncoupling the tensioning rod from the end of the support sleeve of the live-end assembly, and removing the support box from the live- end assembly. The non-metallic tendon may be made of a fiber reinforced polymer. The non- metallic tendon may be a first non-metallic tendon. The method may also include placing a second non-metallic tendon extending either through the duct or outside of and along an outer surface of the support member and coupled to the outer surface. The curing step may affix the second non-metallic tendon to the support sleeve of each of the live-end assembly and the deadend assembly, and the first pulling of the tensioning rod may stretch the second non-metallic tendon by the first length. The support member may be a concrete or steel beam, a girder, a slab, or any structural element that can uphold a tensioning force.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 shows a side view of an anchorage system, in accordance with aspects of the disclosure.

[0021] FIG. 2 shows an enlarged side view of the dead-end assembly of the anchorage system of FIG. 1. [0022] FIG. 3 shows an enlarged side view of the dead-end assembly support sleeve of the anchorage system of FIG. 1.

[0023] FIG. 4 shows an enlarged side view of the live-end assembly of the anchorage system of FIG. 1.

[0024] FIG. 5 shows an enlarged side view of the live-end assembly support sleeve of the anchorage system of FIG. 1.

[0025] FIG. 6 shows an enlarged perspective view of the support box of the anchorage system of FIG. 1.

[0026] FIG. 7 shows an enlarged front view of one of the slotted shim plates of the anchorage system of FIG. 1.

[0027] FIG. 8 is a flow chart of a method of installing and tensioning the anchorage system of FIG. 1 onto the concrete beam of FIG. 1.

DETAILED DESCRIPTION

[0028] The invention provides an anchorage system technology for non-metallic prestressed tendons. Disclosed is a simple anchorage system for non-metallic tendons to be prestressed against concrete structural members. The anchors proposed can assure achieving the full strength of the tendons attached without any grip failure. The non-metallic tendons can be easily un-tensioned anytime needed for any reason. The ability of the system to be un-tensioned makes it beneficial for performing maintenance.

[0029] Referring to FIG. 1, an example anchorage system 10 is installed into a portion of a concrete element 5. Although a concrete element 5 is shown, the anchorage systems 10 according to the invention may be installed into portions of many other types of support members, such as a metal support member, and the support member may have any other orientation relative to the ground, such as a 30° angle, a 45° angle, a 60° angle, or a horizontal angle parallel to the ground.

[0030] The anchorage system 10 has a non-metallic tendon 12 that is installed into a duct 6 extending through the concrete element 5. As used herein, the term “duct” may be a void extending through the concrete element 5, or the duct may comprise a surface (e.g., a cylindrical or box-shaped surface) that is disposed within a void extending through the concrete element. The non-metallic tendon 12 may be made of a fiber reinforced polymer (FRP), for example, which may include fibers made of carbon, glass, or aramid. Although a single tendon 12 is shown installed into a single duct 6, that need not be the case. In other examples, a plurality of tendons 12 may be installed into a single duct 6, or the anchorage system 10 may have a plurality of tendons each installed into a respective duct. Although the non-metallic tendon 12 is shown extending through a duct 6 extending through the concrete element 5, that need not be the case. In other examples (not shown), the non-metallic tendon may extend outside of and along an outer surface of the concrete element, and the non-metallic tendon may be coupled to the outer surface using one or more deviators, the deviators being configured to transfer stress from the non-metallic tendon to the concrete element.

[0031] The anchorage system 10 has a dead-end assembly 20 and a live-end assembly 30 that are configured to together apply a compressive force to the concrete element 5. Referring now to FIGS. 1-3, the dead-end assembly 20 has a support sleeve 21 that is affixed to a support plate 22. The sleeve 21 and the support plate 22 may each be made of a high strength metal, such as a high strength steel. The sleeve 21 and the support plate 22 may be welded to one another. The sleeve 21 may be oriented perpendicularly to the support plate 22, such that a longitudinal axis of the sleeve may be perpendicular to a planar surface of the support plate. The support plate 22 is configured to distribute force applied to the concrete element 5 over a wider surface area than the smaller cross section of the sleeve 21.

[0032] The sleeve 21 may define an interior 23 that is configured to extend around a portion of the non-metallic tendon 12. The sleeve 21 may be affixed to the non-metallic tendon 12 using an expansive grout 14 that extends therebetween. The grout 14 may be made of an epoxy or resin material. The grout 14 may be configured to expand when it is dried, so that a lateral clamping force is applied from the sleeve 21 to the tendon 12, thereby permitting the sleeve to effectively “grip” the portion of the tendon that extends within the interior 23. The grout 14 may occupy all of the interior 23 of the sleeve 21 that is not occupied by the tendon 12.

[0033] The sleeve 21 has first and second apertures 24 that are configured to be opened and closed by respective first and second bolts 24a and 24b. As can be seen in the enlarged FIG. 3, each of the apertures 24 may be threaded and configured to be placed in threaded engagement with a respective one of the first or second bolts 24a, 24b. The expansive grout 14 may be injected into the interior 23 of the sleeve 21 through the apertures 24.

[0034] The sleeve 21 has opposite ends that are configured to be closed by first and second hollow bolts 25a, 25b. As can be seen in FIG. 3, each of the opposite ends of the sleeve 21 may be threaded and configured to be placed in threaded engagement with a respective one of the first or second hollow bolts 25a, 25b. Each of the hollow bolts 25a, 25b has a lumen 25 extending therethrough. Each lumen 25 is configured to slidably receive a portion of the tendon 12 therethrough with a close clearance, so that the expansive grout 14 can not leak out of the sleeve 21 through the lumens 25.

[0035] As can be seen in FIG. 1, the support plate 22 is configured to be positioned flush with a confronting surface of the concrete element 5. To accommodate the second hollow bolt 25b, the concrete element 5 may have a recess 7 that is sized to receive the second hollow bolt 25b therein.

[0036] Referring now to FIGS. 1, 4, and 5, the live-end assembly 30 has a support sleeve 31 that is affixed to a support plate 32. The sleeve 31 and the support plate 32 may each be made of a high strength metal, such as a high strength steel. The sleeve 31 and the support plate 32 may be welded to one another. The sleeve 31 may be oriented perpendicularly to the support plate 32, such that a longitudinal axis of the sleeve may be perpendicular to a planar surface of the support plate. The support plate 32 is configured to distribute force applied to the concrete element 5 over a wider surface area than the smaller cross section of the sleeve 31.

[0037] The sleeve 31 may define an interior 33 that is configured to extend around a portion of the non-metallic tendon 12. The sleeve 31 may be affixed to the non-metallic tendon 12 using the expansive grout 14 that extends therebetween. The grout 14 may be configured to expand when it is dried, so that a lateral clamping force is applied from the sleeve 31 to the tendon 12, thereby permitting the sleeve to effectively “grip” the portion of the tendon that extends within the interior 33. The grout 14 may occupy all of the interior 33 of the sleeve 21 that is not occupied by the tendon 12.

[0038] The sleeve 31 has first and second apertures 34 that are configured to be opened and closed by respective first and second bolts 34a and 34b. As can be seen in the enlarged FIG. 5, each of the apertures 34 may be threaded and configured to be placed in threaded engagement with a respective one of the first or second bolts 34a, 34b. The expansive grout 14 may be injected into the interior 33 of the sleeve 31 through the apertures 34.

[0039] The sleeve 31 has opposite ends that are configured to be closed by a hollow bolt 36a and a tensioning rod 16. As can be seen in FIG. 5, each of the opposite ends of the sleeve 31 may be threaded, with the end adjacent to the concrete element 5 configured to be placed in threaded engagement with the hollow bolt 36a, and with the end 35 remote from the concrete element configured to be placed in threaded engagement with the tensioning rod 16. The hollow bolt 36a has a lumen 36 extending therethrough. The lumen 36 is configured to slidably receive a portion of the tendon 12 therethrough with a close clearance, so that the expansive grout 14 can not leak out of the sleeve 31 through the lumen 36.

[0040] Referring now to FIGS. 1, 4, 6, and 7, the live-end assembly 30 has a removable support box 40 extending around the sleeve 31 and one or more slotted shim plates 50 occupying a space between the support plate 32 and a confronting surface of the concrete element 5. The support box 40 has an opening 41 therein configured to receive insertion of an end of the tensioning rod 16 therethrough. The support box 40 has two open sides 42 that are configured to receive the shim plates 50 therein. Although the support box 40 is shown as having two open sides 42, in other examples, the support box may have only a single open side configured to receive the shim plates therein. The support box 40 may be made of high strength steel.

[0041] The one or more slotted shim plates 50 each have a flat shape with a recess 52 extending therein, the recess being configured to extend around a portion of the non-metallic tendon 12 that extends between the support plate 32 and a confronting surface of the concrete element 5. As will be explained more fully below, the one or more slotted shim plates 50 are configured to maintain tension in the tendon 12 after the tendon has been stretched by pulling the tensioning rod 16 away from the concrete element 5. The shim plates 50 may be made of high strength steel.

[0042] The total width W of the one or more slotted shim plates 50 will be approximately equal to the length that the tendon 12 has been stretched by the tensioning rod 16 during tensioning of the anchorage system 10. Each individual shim plate 50 may have any thickness, and the thicknesses of the shim plates may be the same as one another, or they may vary in thickness as shown in FIGS. 1 and 4, depending on the elongation required in the tensioned tendon 12.

[0043] Although the support box 40 is shown as having a substantially square cross section, this need not be the case. In other examples, the support box 40 may have any cross-sectional shape, as long as the support box can at least partially surround the sleeve 31, so that the support box may serve as an abutment structure against which to place a jack that is configured to pull the tensioning rod 16 (the process of which will be explained below).

[0044] Although the shim plates 50 are shown as having a shape that is a portion of a square and that corresponds to the shape of the interior of the support box 40, this need not be the case. In other examples, the shim plates 50 may have any cross-sectional shape, and the recess 52 may have any shape, as long as a portion of the tendon 12 can fit into the recess, and as long as the shim plates can fit into the open sides 42 of the support box 40.

[0045] Referring to FIG. 8, the process of installing the anchorage system 10 onto the concrete element 5 will now be described. FIG. 8 illustrates a flow chart 100 showing an example deployment of the anchorage system 10.

[0046] The method of installing the anchorage system 10 includes two processes. The first process is bonding the non-metallic tendons 12 to the support sleeves 21 and 31, and the second process is securing the force in the tensioned non-metallic tendons using the slotted shim plates 50. Both processes presented offer a system for non-metallic tendons 12 that anchors the tendons, secures the tensioning force, and is simple and affordable compared to the systems available in the market or proposed by other researchers. The anchorage system 10 allows for destressing tendons after tensioning for any reason such as maintenance and can be applied on metallic (steel) and non-metallic (FRP) strands.

[0047] In block 110, the duct 6 may be formed extending through the concrete element 5, and the recess 7 that is sized to receive the second hollow bolt 25b therein may be formed extending into the concrete element. In block 111, the non-metallic tendon 12 may be inserted through the duct 6, with sufficient length on both sides of the concrete element 5 to extend through the sleeves 21 and 31. In block 112, the support sleeves 21 and 31 may be assembled onto opposite ends of the non-metallic tendon 12.

[0048] In block 113, the hollow bolts 25a and 25b may be tightened, and the non-metallic tendon 12 may be passed through the lumen 25 of each of the hollow bolts. The hollow bolt 36a may be tightened, and the non-metallic tendon 12 may be passed through the lumen 36 of the hollow bolt. The tensioning rod 16 may be threaded onto the end 35 of the support sleeve 31. The non-metallic tendon 12 may be pretensioned with a small force (< 5 kips) to keep it aligned until the grout 14 starts to cure.

[0049] In block 114, the grout 14 may be poured into the interiors 23 and 33 of the support sleeves 21 and 31 through the apertures 24 and 34, so that the grout occupies the space between the tendon 12 and inner surfaces of the support sleeves. In block 115, the apertures 24 and 34 may be closed with the bolts 24a, 24b, 34a, and 34b. In block 116, the grout 14 may be permitted to cure and expand, so that the tendon 12 is affixed to inner surfaces of each of the support sleeves 21 and 31. In block 117, the bolts 24a, 24b, 34a, and 34b may be removed from the apertures 24 and 34, to avoid interference with the tensioning process. [0050] In block 118, the support box 40 may be placed over the live-end assembly support sleeve 31, so that the tensioning rod 16 extends out of the opening 41. The support box 40 functions to secure a gap between the concrete element 5 and the support plate 32 for the slotted plates 50 to be installed until the desired strength is achieved.

[0051] In block 119, a hydraulic jack may be attached to the tensioning rod 16 and pulled in a longitudinal direction of the tendon 12 to stretch the tendon. The jack may press against an end surface of the support box 40 while pulling the tensioning rod 16 to stretch the tendon 12. Once the tensioning starts, the support box 40 will apply pressure onto the concrete element 5 that makes the tendon 12 elongate in the opposite direction, and a gap will appear between the support plate 32 and a confronting surface of the concrete element. In block 120, while the tendon 12 is being stretched, one or more first shim plates 50 may be inserted into the support box 40 and placed around the tendon between the support plate 32 and a confronting surface of the concrete element 5.

[0052] In block 121, the tensioning rod 16 may be pulled again in the longitudinal direction of the tendon 12 to further stretch the tendon. In block 122, while the tendon 12 is being stretched, one or more second shim plates 50 may be inserted into the support box 40 and placed around the tendon between the support plate 32 and a confronting surface of the concrete element 5. The second shim plates 50 may be placed adjacent to the first shim plates.

[0053] In block 123, the steps of blocks 121 and 122 may be repeated to stretch the tendon 12 and add further shim plates 50. In some examples, each successively added shim plate 50 or group of shim plates 50 may have a smaller thickness than the previously placed one, although that need not be the case. The steps of blocks 121 and 122 may be repeated until the desired pretensioning force or elongation length of the tendon 12 is achieved. In block 124, the jack may be removed from the tensioning rod 16, the tensioning rod may be removed from the end 35 of the support sleeve 31, and the support box 40 may be removed from the support sleeve.

[0054] Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.