Description:
This invention relates in general to structures and in particular to a method and apparatus for reinforcing and repairing structural members.
The necessity of establishing and maintaining the structural or load-bearing capacity of structural building members is well-understood and cannot be overemphasized as an aspect of structural safety. These considerations are especially significant where the structural members in question are used in or associated with the foundations of structures such as bridges, piers, buildings, and the like. Such foundation structural members, which are typically made of materials such as steel, steel-reinforced concrete, or wood in many applications, must not only meet the necessary design requirements for the structure to be supported, but must also maintain the necessary structural strength notwithstanding natural deterioration or degrading of the structural member tending to occur as an inevitable result of exposure to the elements.
Deterioration of steel structural members, and resulting degrading of the load-bearing capacity of the member, typically occurs through corrosion and rusting of the steel. Electrolysis, frequently referred to as galvanic corrosion, is another natural phenomenon which attacks structural metallic members and which is especially damaging to steel structural members used in marine applications such as pier supports and the like. Structural steel which is thus attacked becomes weakened by removal of the metal, as is known to those skilled in the art, with a resulting weakening in the load-bearing capacity of the structure.
Structural members made of concrete or steel-reinforced concrete are subject to different types of natural attrition. Since concrete is relatively brittle and non-elastic, the repeated expansion-contraction effects produced by thermal cycling of a concrete structural member exposed to temperature changes for a period of time will cause cracks to form in the concrete. The occurrence and growth of such cracks is greatly accelerated in climes where the concrete structural member undergoes periodic freeze-thaw cycles, since water has the opportunity to seep into the cracks and then expand upon freezing to cause further damage of the concrete. If the concrete structural member is internally reinforced by structural steel, such as an H-beam extending through the concrete structure, the existence of one or more cracks extending in the concrete from the exterior surface all the way to the structural steel provides a path for moisture to reach and attack the steel. The resulting corrosion products require a greater volume of space than previously occupied by the steel which was corroded, and so the pressure produced by such corrosion products causes still further damage and weakening of the surrounding concrete structure. Moreover, the presence of a concrete jacket surrounding a structural steel member may actually accelerate the rate at which galvanic corrosion of the steel occurs. Still other sources of damage to concrete structural members used in marine environments arise from the constant surface erosion produced by wave action, tidal currents, and water currents induced by other forces, and from physical impact of objects with the member.
The foregoing is intended to be no more than a brief summary of the forces which damage structural members, especially those subjected to marine environments, since those skilled in the art will immediately recognize many other aspects of this long-standing problem. While prior art attempts to overcome these problems have been partially successful in some instances, these attempts tend toward stop-gap solutions which only retard the inevitable occurrence of such damage. For example, various types of paints or paint-like coatings have been suggested for application to structural members for the prevention of the foregoing and other damaging effects. These coatings are intended to prevent rust and other corrosions on structural steel, to seal the pores of concrete pilings, or to inhibit attack of wooden pilings or other members by moisture and bacterial deterioration or by the ravages of various marine animal life forms. Such coatings cannot repair existing structural damage and have at best been partially successful in accomplishing the intended results. Moreover, the protective coatings generally require frequent periodic reapplication to the surface being protected, since the coatings generally lack substantial tensile strength and are thus easily cracked by corrosion-induced outward cracking of the concrete. It will be appreciated that the need for periodic application of a coating to a piling which supports a bridge or a dock, for example, and which is permanently installed in some substantial depth of water is difficult and expensive.
Furthermore, such efforts of the prior art have generally aimed toward preventing corrosion, cracking, and other damages but have not been capable of repairing damage existing in a structural member. Moreover, in the case of a structural member which has been already damaged to an extent which materially affects the load-bearing capacity or other structural integrity of the member, such prior art techniques cannot enhance the structural strength of the member without expensive and awkward substantial rebuilding of the member.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for treating a structural member.
It is another object of the present invention to provide a method and apparatus for reinforcing, protecting, and repairing a structural member.
It is yet another object of the present invention to provide method and apparatus for repairing, reinforcing, and protecting structural members in existing installations.
Many of the other objects and attended advantages of the present invention will become more apparent from consideration of the following disclosure, including the annexed drawing, in which:
FIG. 1 is an isometric view according to an embodiment of the present invention used for reinforcing a structural member exemplified by an H-beam;
FIG. 2 is an isometric view showing the reinforcing member as used in the FIG. 1 embodiment, partially opened to be received around the beam;
FIG. 3 shows a partial section view of the reinforcing member of FIG. 2;
FIG. 4 is a section view taken along line 4--4 of FIG. 3;
FIG. 5 is a section view taken along line 5--5 of FIG. 1, before the filler material is added, showing centering and anchoring provisions according to a disclosed embodiment of the present invention;
FIG. 6 is a section view showing an alternative disclosed embodiment for centering and anchoring;
FIG. 7 shows an isometric view of another disclosed embodiment of the present invention, with one of the protective sheaths removed;
FIG. 8 shows the sheaths of FIG. 7 completely installed and strapped in place;
FIG. 9 shows a disclosed embodiment as an alternative to that shown in FIG. 8;
FIG. 10 shows a disclosed embodiment of the present invention as applied to a solid column;
FIG. 11 shows yet another disclosed embodiment of the present invention as applied to an H-beam; and
FIG. 12 shows still another embodiment of the present invention, partially removed from a structural member for illustrative purposes.
Stated in general terms, repair and reinforcement of a structural member is accomplished according to the present invention by enclosing at least part of the structural member with a surrounding cover and interposing a plastic layer of solidifiable material between the surrounding cover and the adjacent surface of the structural member. The solidifiable material in its plastic state enters and fills cracked, eroded, or otherwise-damaged portions of the structural member. The plastic layer of solidifiable material becomes structurally bonded to the structural member and to the surrounding cover, so that the surrounding cover and the solidified material become integral elements of a new composite structural member.
Stated more specifically and with reference to a specific embodiment of the present invention as shown in FIGS. 1-5, there is shown generally at 15 in FIG. 1 a composite reinforced structure which is installed around and in structural relation with an H-beam 16. Although the present embodiment and other disclosed embodiments of the present invention show the use of a particular shape of existing structural member, such as the H-beam 16, it will be understood that the use of an H-beam is illustrative only, and it will become apparent that the present invention can be applied as well to beams and other structural members having a variety of cross-section configurations.
In the example shown in FIGS. 1-5 and elsewhere herein, it is assumed that the repair and reinforcement according to the present invention is being accomplished with respect to a structural member 16 positioned in situ, that is, already installed in an existing location. For example, the structural member 16 is depicted in FIG. 1 as being driven or otherwise disposed in a marine embodiment and extending below a bottom surface 17 to reach a suitable foundation. Such a structural member typically would be used to support above-water structure such as a bridge, a dock, or the like.
In the first step of protecting the structural member 16 according to this embodiment of the present invention, the structural member 16 is surrounded with a housing 18 which is shown to be in the shape of a generally cylindrical pipe of substantially greater diameter than the greatest cross-section dimension of the structural member 16. As best shown in FIG. 2, the housing 18 is provided with a discontinuity such as the severed region 19 extending along the entire length of the housing. The housing 18 is preferably made of a material which is structurally rigid and affords substantial compressive strength, and which is also sufficiently resilient to permit the housing to be elastically deformed by moving apart the opened edges of the severed region 19, as depicted in FIG. 2, to permit the housing 18 to be disposed around an in situ structural member 16. It will be thus apparent that the housing 18 can be disposed around such a structural member without requiring removal or disassembly of either the structural member or of the load which such member normally supports. It has been found that the housing 18 can be suitably provided with pipe made of filament-wound glass fiber-reinformed polyester. A commercial source of such pipe is CorBan Industries, Tampa, Florida.
Since the housing 18 must become structurally anchored to be a unitary element of the reinforced structure as shown more clearly below, the interior wall 20 of the housing is provided with one or more suitable projections which extend inwardly into the open space defined by the housing and which are structurally anchored to the interior wall 20. As seen in FIGS. 2-4, for example, the anchor is provided in the disclosed embodiment by one or more spiral ribs 21 which extend substantially the entire length of the housing 18 and which are interrupted only by the severed region 19. As shown in the detail of FIG. 4, the spiral rib 21 is provided by one or more strands 22 of a suitable material such as glass fiber roving which are disposed to be integrally surrounded by an extension of the interior wall 20, which may consist of one or more layers 23 of polyester, glass fiber-reinforced polyester, or other suitable material of which the remainder of the housing 18 may be constructed.
After the housing 18 has been disposed to surround a structural member 16, it is desirable that the structural member be at least approximately centrally disposed with respect to the surrounding housing. This is accomplished according to the embodiment depicted in FIG. 5 with a plurality of spacing members such as the threaded bolts 26 which are inserted through corresponding tapped holes formed in the wall of the housing 18. The tapped holes through which the bolts 26 extend may be provided directly in the housing 18, if the thickness and material strength of the housing permits; alternatively, a threaded insert can be provided to receive each bolt 26 in a hole appropriately positioned in the housing. It can be seen from FIG. 5 that the bolts 26 extend into contact with the flanges 27, 28 and the web 29 of the structural member 16. It will be understood that the use of four bolts 26 is illustrative only, and that another number of such bolts may be usable to center the housing 18 around a structural member 16 having a cross-section configuration different from the depicted H-beam. The bolts 26 must be chosen of a material suitable to withstand the surrounding environment without causing or furthering the corrosion problem. In the case of an intended marine environment, for example, bolts made of an electrically nonconductive material such as fiber-reinforced polyester are preferred. Referring to FIG. 1, it can be seen that additional sets of bolts 20 and 21 are provided at locations spaced along the length of the housing 18 for centering at such locations.
A structural member 16 having the generally smooth wall configuration of the depicted H-beam preferably is provided with anchor structure which projects into the open space 33 between the structural member and the interior wall 20 of the housing 18. As shown in the FIG. 5 depicted embodiment, this anchor structure is provided by a plurality of studs 34 which are suitably attached to the flanges 27 and 28 and the web 29 of the H-beam. Although the studs 34 can be provided by any suitable structural member secured to the surfaces of the structural member 16, it has been found in the case of a steel H-beam that the studs 34 may be advantageously provided by exposive-cartridge attachment devices such as the Ramset process.
Once the housing 18 has been installed in place around the structural member 16 and suitably centered thereon by positioning of the bolts 26, it is necessary to connect the edges of the severed region 19. This is accomplished by allowing the edges to overlap as at 38 a predetermined amount which is established by the previous appropriate positioning of the adjacent one of the bolts 26, 30, and 31. A layer of an epoxy or other suitable cement that will bond together the confronting edges in the overlapped region 38 is then applied along the length and breadth of this region, and the region is then mechanically secured together with suitable devices such as blind rivets 39 or the like. The rivets 39 function primarily to secure the overlapped region 38 while the cement applied thereto becomes hardened or set. The overlapped region 38 may advantageously be cemented together by epoxy resins which are suitable for underwater use and which are chosen to be compatible with and to have the desired bonding properties for the material of which the housing 18 is made.
Following the completed installation of the housing 18 surrounding the structural member 16, the open space 33 is filled with any suitable material 40 which is provided in a plastic or semiliquid state and which subsequently hardens to provide a desired structural rigidity. The open space 33 can thus be filled with material such as concrete, epoxy mortar, or the like. The material 40 in its plastic state completely surrounds the spiral rib 31 on the interior wall 20 of the housing 18, and also completely surrounds the studs 34 secured to the structural member 16. It can be seen that the hardened material 40 is structurally interlocked with both the housing 18 and the structural member 16 to provide an essentially unitary composite structure having not only the load-bearing capability of the original structural member 16, but the additional load-bearing capabilities of both the rigid housing 18 and the material 40. In this way, the original strength of the structural member 16, which may have become degraded from rust, corrosion, or other flaws, can be restored to a level equalling or even exceeding the strength of the structural member 16 as originally installed. It can also be seen that the surrounding housing 18 as sealed along the overlapped region 38 provides an electrically nonconductive, impervious enclosure which is practically invulnerable to scour and errosion damage resulting from wave and tidal motion, and which is additionally highly resistant to cracking or other damage arising from physical impact against the housing, thermal stress, and the like. Since the tensile strength of the fiber-reinforced housing 18 is typically on the order of 600 times greater than the tensile strength of concrete, cracking of the filler material 40 by internal corrosion products is virtually impossible. The structural member 16 thus is provided with the double protection of the surrounding housing 18 and the intervening structural material 40.
When the open space 33 to be filled with material 40 initially contains water, as is the case where the housing has been applied to a structural member 16 in marine environment, it may be necessary to remove the water before adding the material 40. Water removal can be accomplished without the necessity of a cofferdam, provided that a sufficiently watertight junction exists between the lower end of the housing 18 and the bottom surface 17. Depending on the maximum submerged depth of the housing 18 and the material of which the housing is made, internal bracing in addition to the support of the bolts 26 or the spacing members 41 may be necessary to overcome the surrounding hydrostatic pressure before the material 40 hardens.
An alternative to the arrangement of spacing bolts 26 and anchor studs 34 is shown in FIG. 6, where the functions of the aforementioned bolts and studs are combined in plural spacing members 41 attached to and extending outwardly from the flanges 27 and 28 of the H-beam toward locations adjacent the interior wall 20 of the housing 18. The spacing members 41 are suitably attached to the steel H-beam by connective techniques such as welding or the like before the housing 18 is installed, with the spacing members being not quite long enough to contact the interior wall 20 when the overlapped region 38 is connected together. It can be seen that these spacing members will become surrounded with the material 40 used to fill the open space 33, and the spacing members thus provide both the anchoring function previously afforded by the studs 34 in the embodiment depicted in FIG. 5 and the spacing function previously afforded by the bolts 26 of that embodiment. Since the spacing members 41 are completely encased by the surrounding material 40, these spacing members need not be made of electrically nonconductive and corrosion-resistant material and thus may be provided more economically than the bolts 26 of the previous embodiment.
The region of overlap 38 is defined in the FIG. 6 embodiment with one or more bolts 42 which extend through the wall of the housing 18 a distance sufficient to provide abutment for the end 43 of the severed region 19. The overlapped region 38 shown in FIG. 6 is coated with a suitable cement and initially mechanically secured with a plurality of rivets 39 in a manner as described above with respect to the embodiment shown in FIG. 5.
Although the embodiments of the invention as described thus far have been shown as used to repair or reinforce a structural steel member, these embodiments can as well be used for the repair and reinforcement of nonsteel structural members. For example, piles or other structural members made of materials such as wood or concrete can be surrounded by a suitable spaced-apart housing 18 and then filled with a suitable cementitious or other material 40 to provide a new, unitary structural member of enhanced strength. The functions of anchoring and/or spacing provided by the studs 34 and the spacing members 41 can be provided by similar members which are inserted into the existing structural member by techniques which are appropriate for the material composition of that member. In the case of wooden pilings, for example, the spacing and anchor functions could be provided by spikes or screws which are driven or turned into the pile at desired intervals of spacing. Similar spikes or anchor/spacing members can be driven into concrete pilings by explosive or other known techniques.
Turning next to the embodiment of the present invention as shown in FIGS. 7 and 8, the structural member 16 being reinforced (depicted as an H-beam) is provided with a surrounding cover taking the configuration of a sheath 50 which closely conforms to the external configuration of the structural member. The sheath 50 in the illustrated example is provided by a pair of sheath members 51 and 52, so that the sheath can be easily applied to a structural member 16 which is already installed in an existing environment. Although the sheath members 51 and 52 are shown having a length extending from the bottom 53 of a typical marine environment to the surface 54 thereof, this distance can be spanned by sheath members made in two or more segments as appropriate. Each of the sheath members 51 and 52 preferably is designed to present to the structural member 16 a confronting surface configuration which follows and closely fits the structural member. The sheath members 51 and 52, which may be made of glass fiber-reinforced epoxy or other suitable materials, preferably are prepared by employing as a mold form a structural member having an external configuration identical with that of the member 16, if such a member is available. In the alternative, the sheath members 50 and 51 can be prepared by conventional molding techniques.
As shown in FIG. 7, the external surface of the structural member 16 is preferably coated as at 55 with a suitable material which seals the structural member surface from the surrounding water and which provides a binder for subsequent application of the sheath members. The coating 55 should be of a material which will become bonded to the structural member and to the subsequently-applied sheath member, and obviously should be capable of application in a submerged environment as applicable; suitable coatings having these properties are provided by polyamide epoxy resins formulated in a sufficiently liquid state to be applied by techniques such as brushing or rolling onto the exposed surfaces of the structural member 16. After the coating 55 has been applied to the structural member 16, the confronting surface 56 of the sheath member 51, for example, is liberally coated as at 57 with a suitable sealing and adhesive compound which may advantageously be provided by a polyamide epoxy resin having the consistency of a gel to prevent the resin from flowing off the sheath member during the provess of installation onto the structural member. Once the coating 55 and the gel layer 57 have been appropriately applied, the respective sheath members 51 and 52 are placed in closely confronting contact with the structural member 16. The sheath members are designed to provide regions of overlap, one of which is shown at 58, along the regions where the two sheath members join each other, and these overlap regions are supplied with an epoxy or other suitable adhesive which will bond the overlapped regions of the sheath members to each other.
After the two sheath members are disposed on the structural member 16, a number of straps 59 are provided at spaced positions along the length of the ensheathed structural member 16. These straps may be suitably provided by plastic webbing or other material of the type conventionally and economically used to strap boxes or other packages, since the straps 59 must function only to hold together the sheath members 51 and 52 for the time required for the gel layer 57 and the coating 55 to set. This time typically is provided by the passage of one or two days, after which the sheath members 51 and 52, the structural member 16, and the intervening solidified coatings for a unitary bonded-together structural member having the strength of the original structural member 16 and also of the bonded sheath 50. Moreover, the water-repellent properties of the coating 55 and the gel layer 57, followed by the enclosing presence of the sheath 50, completely isolate the structural member from subsequent exposure to the surrounding environment. In the instance of a structural member 16 installed in a marine environment, this means that the structural member is no longer exposed to wave action and the corrosive effects of a water-air environment. In the case of steel structural members exposed to a salt water environment, moreover, the presence of a sheath 50 made of an electrically nonconductive material such as glass fiber-reinforced polyester or the like effectively insulates the structural member from electrolytic corrosion.
A modified version of the embodiment as described with reference to FIGS. 7 and 8 is shown in FIG. 9, where the sheath 50 is provided by a pair of modified sheath members 63 and 64 which have confronting flanges 65a, 66a and 65b, 66b, respectively, substituted for the sheath edges which are overlapped as shown at 58 in FIG. 8. Application of the sheath members 63 and 64 to the beam 16 of FIG. 9 is accomplished as described previously with respect to the embodiment of FIGS. 7 and 8, with the difference that the installed sheath members 63 and 64 are secured in place by bolts or other suitable fasteners disposed through confronting holes 69 in the adjacent flanges. It will be appreciated that the bolted flanges provide a function functionally similar to that provided by the straps 59 of the FIG. 8 embodiment, namely, retaining the sheath members 63 and 64 in place on the structural member 16 for the time required for the interposed adhesive material to become hardened and to bond together the sheath members and the structural member 16.
Another modified embodiment of the present invention is shown in FIG. 10, wherein a sheath 73 comprised of separate sheath members 74 and 75 is shown installed on a structural member 76 comprised by a pillar depicted as being of solid concrete and which may alternatively contain appropriate reinforcing structural steel, as is known to those skilled in the art. The sheath members 74 and 75 are provided in closely conforming relation to the external surface of the structural member 76, in a manner analogous to the sheath members 51 and 52 of FIG. 8. Prior to installing the sheath members 74 and 75, the external surface of the structural member 76 is first suitably provided with an adhesive filler or coating and the interior surfaces of the sheath members are likewise provided with a suitable adhesive gel, analogous to the above-described embodiment depicted in FIG. 7. If the concrete pillar 76 has cracks or other external structural damage, these should be first repaired by techniques such as pressure grouting or the like. It will be appreciated that the choice of adhesives is determined to some extent by the material of which the structural member 76 is made, since it is essential to provide a bond which combines the sheath 73 and the enclosed structural member 76 into an effectively unitary structural member. The straps 77 are provided as aforementioned to retain the sheath members 74 and 75 in place pending hardening of the adhesive.
Still another modified embodiment of the present invention is shown in FIG. 11, where an exposed exemplary H-beam 78 is provided with a surrounding cover 79 having functional aspects both of a sheath and a housing as aforedescribed. This surrounding cover is provided by a pair of substantially U-shaped cover members 80 and 81 which are adhesively bonded to the surfaces of H-beam flanges 82 and 83 to define a pair of open spaces 84 and 85 bounded by the H-beam and the respective cover members. After the cover members 80 and 81 have become securely bonded to the H-beam, the open spaces 84 and 85 are filled with a suitable structural material 86 in a plastic state, such as concrete or epoxy mortar, which is then allowed to harden. The resulting composite structure provided by the unitary combination of the H-beam 78, the surrounding cover 79 bonded thereto, and the solidified filler material 86 provides a structural strength which is greatly enhanced over that previously afforded by the H-beam per se.
Yet another embodiment of the present invention is shown in FIG. 12 in partially exploded view attached to a structural member 90 depicted as a solid pillar of concrete. Surrounding the pillar 90 is a sheath comprising a pair of sheath members 91 and 92, with the sheath member 91 shown detached from the pillar 90 for illustrative purposes. Each of the sheath members 91 and 92 is provided along the respective edges 93 and 94, which are lowermost as installed in place around the structural member 90, with seals 95 and 96, respectively, preferably made of a resilient compressible material such as open-cell sponge rubber or the like. Immediately prior to installing the sheath members 91 and 92 in place surrounding the structural member 90, the seals 95 and 96 are soaked or otherwise coated wth a suitable sealing material such as epoxy resin or the like. The sheath members 91 and 92 are then disposed around the structural member with the seals 95 and 96 in confronting contact with the structural member to provide sealing contact between the structural member and the lower edges 93 and 94 of the respective sheath members. Sealing by epoxy resin or the like is also accomplished along the confronting edges of the sheath members 91 and 92, which are overlappingly sealed together as shown at 58 in FIG. 8. An adhesive coating or adhesive gel, corresponding to the coating 55 and the gel layer 57 of FIG. 7, is omitted with respect to the initial installation of the sheath members 91 and 92 on the structural member 90, and it will be appreciated that the presence of the seals 95 and 96 on the sheath members as installed provides a discrete substantially annular space defined by the structural member 90 and the surrounding, spaced-apart sheath members 91 and 92. Each of these sheath members is provided with a plurality of apertures 97 disposed at spaced-apart locations along the sheath length, and each of these apertures is provided with a one-way valve 98 which is operative to permit the flow of fluid through the valve into the aforementioned annular space but which blocks fluid attempting to exit this annular space.
After the sheath members 91 and 92 have been secured in position surrounding the structural member 90, a suitable adhesive compound such as the aforementioned epoxy resin and having a viscosity suitable to permit the compound to be flowable, is injected into the surrounding annular space by way of the one-way valves 98. The adhesive compound injection may be accomplished with any suitable pressure-driven arrangement such as a pump and interconnecting hose fitting; the hose fitting would be first attached to the lowermost one-way valve 98 and adhesive pumped into the annular space to approximately fill such space to the level of the next one of the apertures and valves. The hose fitting is then connected to this next valve, and the filling process is repeated until the entire annular space is filled with the adhesive compound. If the filling process is being accomplished in an underwater environment, it will be appreciated that the adhesive must be heavier than water so that the adhesive will fill the annular space and displace the water therein upwardly as the adhesive filling progresses.
Although the pumped-adhesive embodiment of the present invention as depicted in FIG. 12 is shown in conjunction with a structural member of square or rectangular cross-section, it will be appreciated that this embodiment can be applied as well to the protection and reinforcement of other structural shapes.
Although the foregoing relates to several disclosed embodiments of the invention disclosed and described herein, it will be apparent that numerous alterations and modifications thereof may be made without departing from the spirit and the scope of the invention as described in the following claims.