AU579733B2 - Expansion type anchor bolt - Google Patents

Description

EXPANSION TYPE ANCHOR BOLT

The present invention relates to anchor bolts to be set in concrete or the like.

The present invention generally relates to two-piece swage type fasteners or lockbolts of the type illustrated in ϋ. S. Patent Nos. 3,915,053, 2,531,048 and 4,472,096.

Bolts for anchoring workpieces to concrete frequently utilize a mandrel and an expansion sleeve, with the sleeve being expanded in response to relative movement by the mandrel resulting in an expansion type interference fit with a pre-drilled bore in the concrete. The latter is accomplished by a relative axial force applied between the pin and sleeve. In an over-sized hole condition or one in which the concrete is locally, excessively pulverized as the sleeve expands, the blind head type connection between the expanded portion of the sleeve and the concrete bore could be compromised. In fact in many instances the mandrel could move to such an extent relative to the sleeve that its final position would be unpredictable; in extreme cases the mandrel could move excessively to a position substan¬ tially through the sleeve.

Therefore, it is a general object of the present invention to provide a novel anchor bolt for securing workpieces to concrete via a pre-drilled hole in concrete.

The present invention provides an anchor bolt for fastening a workpiece to a structure of concrete or the like by a relative axial force applied by a pull tool to the anchor bolt when positioned within a fastening bore in the structure, said anchor bolt comprising a tubular expansion sleeve having a through bore, a pin including a shank, a pull portion on said pin shank, a lock portion on said pin shank having a plurality of circumferentially extending lock grooves, a breakneck groove defining the weakest portion of said pin shank and located between said pull portion and said lock portion, a shank portion located adjacent said lock portion and being of a diameter to be received within said sleeve bore, a sleeve expansion section located at the opposite end of said shank portion, a tubular collar adapted to be located on said pin shank and to be swaged into said lock grooves in response to a first preselected magnitude of said relative axial force, said sleeve expansion section adapted to be moved axially within said sleeve bore in response to said relative axial force to radially expand said confronting portion of said sleeve radially outwardly for gripping engagement with said structure bore.

In prior constructions, sleeve expansion has been provided by an enlarged expansion portion of a mandrel being drawn into the sleeve. However, where only a simple expansion grip is utilized, once- the sleeve has been expanded and engagement with the concrete bore has been established, the effectiveness of the grip may not increase significantly as relative movement of the pin through the sleeve continues. In the present invention, the pin is provided with an extended expansion section which will expand the associated^' portion of the sleeve radially outwardly to provide a first level of expansion grip or lock between the sleeve and the concrete bore. In the preferred embodiment, the expansion section of the pin terminates in an enlarged pin head having a flat or planar surface which is adapted to engage the expanded end of the sleeve. Where the first level of expansion forms a blind head connection with the concrete bore of adequate strength, this engagement acts as a positive stop between the pin and sleeve to locate the pin at a desired position relative to the opposite end of the sleeve. At the same time, however, if the connection at the first level of expansion grip is inadequate, the engagement of the enlarged pin head can provide further radial expansion of the inner end of the sleeve either by radially outward bulbing as in a column type buckling or by radial sleeve expansion if the head moves into the sleeve end. Thus, in the event of an over-sized hole condition or excessive local pulverizing, additional sleeve expansion and a second level of expansion grip will be provided by the pin head to enhance the lock between the sleeve and concrete bore. Even in this latter event, the additional movement of^" the pin can be relatively minor with the result that the final location of the pin will be within a predictable, acceptable range. The expandable end of the sleeve may be serrated or roughened to enhance the biting or frictional engagement with the walls of the concrete bore. A flanged collar may be used to provide an enlarged reaction bearing surface against the concrete'or workpiece outer surface. In still another form, a relatively straight collar is used with a flat washer to provide the reaction or bearing surface against the concrete or workpiece outer surface. Preferably, the lock grooves of the pin are in the form of a helical male thread. The collar is provided with a mating, female thread of a preselected limited extent such that a pre-assembly of the sleeve, pin and collar can be accommodated. The strength of the female collar thread is selected such that, in response to the relative axial setting force, at a level prior to the initiation of collar deformation or swaging into the lock grooves of the pin, it will shear or deform such that the collar will now be free to respond to the installation loads in the same manner as a collar without such limited female thread form. In some applications, it is desirable that the fasteners have a high strength, such that, in response to a predetermined high design ultimate tensile axial load applied to the swaged collar in a direction to remove the set anchor bolt from the concrete bore, either the concrete will fail or the pin will fail in tension diametrically across the helical lock grooves. At the same time, and in furtherance of the latter objective, it is desirable that the lock grooves not be distorted or weakened in response to the applied swage loads. To provide such a high tensile and distortion resistant characteristic, the helical lock grooves may be constructed to be of a unique configura¬ tion having the desired high strength to resist distortion. In a preferred form of the present invention, the lock grooves in the pin, are very shallow and are constructed to have roots of a simulated streamlined shape. While the lock grooves define a desired thread configuration, the shallow and simulated streamlined shape provide a resultant tensile strength, resistance to deformation during collar swage and fatigue life which is superior to that of comparable threaded fasteners or prior lock groove constructions. At the same time, the collar is constructed to have a predeter- mined wall thickness, and hence volume, not only to provide an over fill condition of the lock grooves during swaging to assure a good fill of the lock grooves but also to provide sufficient hoop stiffness to inhibit spring back of the collar material out of the shallow lock grooves in the pin. The latter retained clamp between the pin, sleeve and collar having a magnitude which is a high percentage of the installation load and of the yield strength of the pin in tension across the lock grooves.

In one form of the present invention, the resultant preload on the pin is slightly below that at which yielding would occur in the helical lock grooves of the pin. The collar is longer than that required to provide engagement of the appropriate number of pin and collar shoulders to hold that preload; in this case fail- ure of the fastener under tensile loading will occur diametrically across the pin lock grooves. As noted the magnitude of the latter tensile loading will be equal to (and preferably greater) than the ultimate design tensile load for the fastened joint such that failure will occur in the concrete or across the lock grooves. It is advantageous that the pin be of a high strength construction such that there will be no signi¬ ficant yielding in response to the swage load. The utilization of the desirable shallow groove configuration is a significant factor in resisting such yielding. The latter feature is especially desirable in the present invention where the pin has a helical thread form. Now when the collar is finally swaged into the helical pin grooves, a complementary female thread will be formed in the collar. If the helical thread form of the pin lock grooves are distorted in swage, then they will not subsequently function effectively as a threaded fastener with the swaged collar. With the shallow grooved, high strength pin of one form of the present invention such distortion is inhibited. Now the integrity of the thread form is maintained and the swaged collar can be removed by a suitable wrenching tool and/or retorqued as with a conventional threaded fastener. Other features and advantages of the present invention will become apparent from the subsequent description taken in conjunction with the accompanying drawings, in which:

Figure 1 is an elevational view with some parts shown in section of an anchor bolt of the present invention in a concrete bore prior to being set by an installation tool;

Figure 2 is a view, similar to Figure 1 depicting the anchor bolt after it has been partially set with an end portion of the sleeve radially expanded against the concrete bore surface;

Figure 3 is a view similar to Figures 1 and 2 depicting the anchor bolt after the pin head has engaged the expanded end of the sleeve and the collar has been swaged onto the pin; Figure 4 is a view similar to that of Figure 1 showing a modified form of anchor bolt;

Figure 5 is a fragmentary view similar to Figure 1 of an anchor bolt having high strength helical lock grooves of a shallow configuration and embodying features of the present invention; and

Figure 6 is a fragmentary sectional view to enlarged scale of a preferred form of the helical lock groove for the pin of the anchor bolt of Figure 5.

Looking now to the drawings, an anchor bolt 10 is shown located in a pre-drilled bore 12 in a concrete member 14 prior to being set to secure a workpiece 16 to the outer surface 18 of the concrete member 14. The workpiece 16 has a bore 20 adapted to be aligned with concrete bore 12. The anchor bolt 10 has a pin or mandrel 22 having an elongated shank 24 terminating at one end in an enlarged head 26. The pin shank 24 has a straight shank section 28 of a uniform diameter adjacent the head 26 followed by an expansion, tapered portion 30. The tapered portion 30 connects the straight shank section 28 with a straight, reduced diameter shank section 32 of a uniform diameter wnich in turn is followed by a lock portion 34 comprised of a plurality of helical lock grooves 36. A pull portion 38 comprised of a plurality of annular pull grooves 40 terminates the opposite end of pin shank 24 and an annular breakneck groove 42 defines the weakest portion of the pin shank 24 and is located between the pull portion 38 and the lock portion 34.

The anchor bolt 10 also includes an elongated, tubular sleeve 44 of a generally uniform cross section throughout its length. The sleeve 44 has a central bore 45 which is in a close clearance fit with the reduced diameter pin shank section 32. At the same time the maximum diameter of the lock portion 34 is no greater than around that of the reduced pin shank section 32 while the pull groove portion 38 can be of a smaller maximum diameter than reduced shank section 32. Thus the sleeve 44 can be freely assembled onto the pin shank 24 down to the tapered portion 30 and can be lightly staked or othersie secured to the pin 22 such that the pin 22 and sleeve 44 can be handled as an assembly. The sleeve 44, being of a uniform cross section, can be assembled from either end onto the pin shank 24. A tubular locking collar 46 is adapted to be located over the portion of pin shank 24 protruding from the outer end of workpiece bore 20. Collar 46 has a relatively straight shank portion 48 and an enlarged flange 50 adapted to overengage the confronting or outer end of sleeve 44 and the workpiece bore 20 such that it partially engages the surrounding portion of outer surface 52 of the workpiece 16. As will be seen, the collar 46 is adapted to be swaged into the helical locking grooves 36 to lock the pin 22 and sleeve 44 together after the anchor bolt 20 has been set by a relative axial force applied between the pin 22 and collar 46 via a pull tool 54. The pull tool 54 can be of a conventional structure well known in the art and hence is only partially shown for illustration purposes. In one form, the collar 46 can be pre-assembled to the pin 22 whereby the pin 22, the sleeve 44 and the collar 46 will be held together as an assembly.

Thus the collar 46 can be provided with a partial mating thread 62. This construction will facilitate pre- assembly of the pin 22, sleeve 44 and collar 46. Now the noted fastener components can be pre-assembled by threading the collar 46 onto the threaded lock portion 34 of the pin 22. To facilitate this pre-assembly the collar flange 50 can be provided with a conventional hex head or other irregular configuration to permit gripping by a suitable tool. At the same time, the pull portion 38 of the pin 22 can be provided with flats for gripping to prevent relative rotation during the threaded pre-assembly. Alternatively, ^■the end of the pin shank 24 can be provided with an Allen head type opening to assist in preventing relative rotation during pre-assembly. In another form, however, in order to inhibit removal of the collar 46 after installation, the flange 50 could be annular.

Looking now to Figures 1-3, in operation, the concrete bore 12 is drilled to a depth sufficient to accept the assembly of the pin 22, sleeve 44 and collar 46 such that with the workpiece 16 in place, the sleeve 44 will not extend above the surface 52 of the workpiece 16. At the same time a sufficient number of the pull grooves 40 will extend beyond the workpiece surface 52 to facilitate gripping by a gripping jaw assembly 56 of tool 54. Now with the workpiece bore 20 and concrete bore 12 in axial alignment, the pre-assembled fastener 10 including the pin 22, sleeve 44, and collar 46 is positioned in the concrete bore 12 and workpiece bore 20 with the collar flange 50 engaging the workpiece surface 52. Next the pull tool 54 is applied to the fastener 10 with the jaw assembly 56 gripping the pull grooves 40 and a swage anvil 58 engaging the outer end of the collar 46. Upon actuation of the tool 54, a rela¬ tive axial force is applied between the pin 22 and collar 46. As the magnitude of the pulling force is increased, the pin 22 moves the expansion tapered portion 30 of the pin shank 24 into sleeve bore 45 causing the inner end of the sleeve 44 to expand radially outwardly to engage the confronting surface of the concrete bore 12. As the tapered portion 30 moves further into the sleeve bore

45, the inner end of sleeve 44 is expanded to overengage of the enlarged smooth shank section 28 of the pin 22. This generally defines the maximum diameter of radial expansion of the sleeve 44 whereby an enlarged blind type head 59 is formed (see Figures 2 and 3) . The sleeve expansion continues as noted until the enlarged pin head 26 engages the expanded end of the sleeve 44; this defines the first level of expansion grip or lock between the sleeve 44 and concrete bore 12. The engagement of the pin head 26 with the expanded end of the sleeve 44 acts as a pin stop to inhibit f rther pin travel and also confines .the end of the sleeve 44 and inhibits it from extruding past the pin head 26. In this condition, the relative axial setting force can attain a magnitude such that the anvil 58 of the tool 54 will swage the collar 46 into the locking grooves 36 which are now in a desired alignment with the collar 46. After the collar 46 has been swaged, a further increase in relative axial force results in the pin shank 24 being severed at the breakneck groove 42. This completes the installation resulting in a set joint generally as shown in Figure 3.

The collar thread 62 is limited in number and radial depth, and hence strength, such that when the installation sequence is commenced the collar thread 62 will readily deform or shear as the pin 22 is moved axially relative to the collar 46; this will occur at a relatively low axial load such that premature swaging of the collar 46 into the pin lock grooves 36 will not occur. In one form of the invention, a single collar thread 62 of around a 360° circumferential extent was adequate for pre-assembly purposes while still being readily deformable during installation. Note that the pull groove portion 38 has a maximum diameter less than the inside diameter of the collar thread 62 whereby the collar 46 can be readily moved onto the pin 22 and the collar thread 62 engaged with the helical lock groove portion 34.

In general the clearance between the concrete bore 12 and the outer surface of sleeve 44 will be such as to have a preselected magnitude to facilitate reception of the assembly of pin 22 and sleeve 44 in the bore 12 but still being of a restricted clearance such that, upon expansion of the inner end of sleeve 44, a secure lock between the sleeve and the concrete bore 12 will be attained. Note that the enlarged pin head 26 is of a diameter generally equal to the outside diameter of the inner end of sleeve 44. The adjacent straight shank portion 28 has a diameter which is generally equal to the mean diameter of the sleeve 44 i.e. half way between the sleeve outside diameter and sleeve inside diameter, or mean diameter = outside diameter - sleeve wall thickness. Note that the tapered, expansion portion 30 is of a relatively short length relative to the final expansion pin section or smooth section 28. Thus the sleeve 44 will be expanded over a significant length of provide a good lock relative to the surface of the concrete bore 12. Thus, in one construction of the present invention, for a sleeve 44 having an outside diameter of 1.587 cm (.625 inches) and an inside diameter of 1.155 cm (.455 inches), the pin shank 24 had its reduced diameter shank section 32 with a diameter of around 1.143 cm (.450 inches) and the enlarged diameter shank section 28 with a diameter of 1.435 cm (.565 inches). The enlarged pin head 26 had a diameter of around 1.587 cm (.625 inches). The axial length of the enlarged diameter shank section 28 was within a range of approx¬ imately around two to three times the length of the tapered expansion pin portion 30. The tapered portion 30 extended at an angle of around 15° with the axis of the pin 22. With the above diameters noted the enlarged shank section 28 had an axial length of 1.955 cm (.770 inches) while the tapered portion 30 had an axial length of 0.838 cm (.330 inches). The total diametrical clear¬ ance between the outside diameter of the sleeve 44 and the concrete bore 12 was between .0254 cm (.010 inches) and .101 cm (.040 inches) .

As noted, the lock formed upon final expansion of the sleeve 44 as the pin head 26 engages the expanded end of sleeve 44 will provide a desired, first level lock between the set fastener 10 and the concrete bore 12 to securely hold the workpiece 16 to the concrete member 14. However, in some situations the clearance between concrete bore 12 and the sleeve 44 may be larger than desired. In other situations the concrete bore 12 in the area of sleeve expansion may have excessive local pulverization. In these and other similar situations, the adequacy of the lock at the first level of radial expansion may be impaired. With the present construction, however, such variations can be reasonably accommodated while still providing an adquate lock at the second level of expansion. Thus when the pin head 26 engages the inner, expanded end of the sleeve 44, if the expanded end of sleeve 44 has not tightly engaged the wall of the concrete bore 12 it will still be capable of further radial expansion. In this case the pin head 26 can cause the sleeve end to bulb radially outwardly as in a column buckling type situation or the pin head 26 can move axially into the inner diameter 45 of the sleeve 44. Note that the engaging end surface 60 of the pin head 26 is generally .transverse or in quadrature to the pin axis; this will provide for a planar surface of engagement against the inner end of sleeve 44. Since the pin 22 is of a substantially harder material than the sleeve 44, the pin head 26 can move into the sleeve 44 generally without deformation to the pin head 26. In some circumstances the engaging surface 60 of the pin head 26 may shear a ring of material from the inner end of sleeve 44 facilitating its entry into the bore 45 and also facilitating radial expansion of the sleeve 44. Under any of the above noted circumstances the result is an increase in radial expansion of the sleeve 44 whereby the noted situations can be accommodated to provide a secure lock between the set fastener 10 and the concrete bore 12.

In one form of the invention, the pin 22 was constructed of AISI 4140 Alloy Steel having a hardness of Re 33-36 while the sleeve 44 was constructed of AISI 1020 Carbon Steel having a hardness of Rb 80-90. Note that the contour of the engaging surface of the collar 46 relative to that of the swage anvil 58 is constructed such that swaging of the collar 46 into the lock grooves 36 will not occur until the above described setting sequence has been completed i.e. collar^" swage will be held off until the blind head 59 has been finally formed and, where required, the second level of increased radial expansion via the pin head 26 has occurred. Note that the threaded lock section 34 in one form of the invention has an axial length such that upon completion of installation a substantial portion extends beyond the outer end of the collar 46, see Figure 3. This facilitates attachment of additional structures to the fastener assembly 10 with a threaded connection via a suitably threaded member. In addition in some installa- tions, it may be desirable to subject each or a number of the installed fasteners 10 to a proof load test. In these situations, an axial load of a preselected magnitude is applied between the pin 22 and the workpiece 16 attempting to pull the fastener 10 out of the concrete bore 12. The installed fastener 10 should sustain that design load without significant movement out from the concrete bore 12. The extra threaded portion extending beyond the end of collar 46 facilitates the application of a test tool to the pin 22 whereby the proof test can be conducted.

Another form of the invention is shown in Figure 4. Here components similar to like components in Figures 1-3 have been given the same numerical designation with the addition of the letter postscript "a" and hence a description of some of the components has been omitted for purposes of simplicity.

Thus the anchor bolt 10a is located in a pre- drilled bore 12a in*a concrete member 14a for securing a workpiece 16a to the concrete member 14a.

The pin or mandrel 22a is constructed substan¬ tially the same as pin 22 of Figures 1-3 except that the lock portion 34a is provided with one or more axially extending grooves 63 which act as an antirotation mechanism to prevent relative rotation between -collar 46a and pin 22a and hence inhibit removal of the collar 46a from the threaded lock grooves 36a after the fastener 10a has been set.

The inner end of the sleeve 44a is provided with a section 64 having a roughened outer surface which can be in the form of a knurl or serrations. The roughened section 64 has an axial length at least equal to around the axial length of the smooth pin shank section 28a. Prefer¬ ably, the length of section 64 is greater such that upon installation, the roughened section 64 will at least partially overengage the tapered expansion pin portion 30a. The roughened surface of section 64 will tend to bite into the confronting surface- of concrete bore 12a to enhance the gripping action or lock between the sleeve 44a and concrete bore 12a. The collar 46a has generally straight sidewalls except for an enlarged hold-off bead 66 at its outer end. The hold-off bead 66 along with the contour of the engaging swage surface of the swage anvil (not shown) will provide the desired resistance or hold-off from initial swage until a desired magnitude of relative axial setting force is attained. The inner end of the collar 46a is of a generally straight tubular configuration. In this form, a flat washer 68 is located between the collar 46a and the outer end of the sleeve 44a and is adapted to engage the workpiece surface 52a to provide the fastener reaction surface for the installation loads. The washer 68 has a bore 70 which is generally of the diameter of sleeve bore 45a. Here the helical collar thread 62a in cooperation with the threaded lock groove portion 34a will hold the pin 22a, sleeve 44a, reaction washer 68 and collar 46a together in a pre-assembly to facilitate handling.

The general operation of the anchor bolt 10a is similar to that of anchor bolt 10 of Figures 1-3 and will not be repeated.

As noted, it is desirable that a concrete joint fastened with the anchor bolt of the present invention have sufficient strength to accept a tensile load of a magnitude below a preselected ultimate load without failure either in the anchor bolt or in the surrounding concrete. While an annular lock groove configuration could be employed utilizing certain of the features of the present invention, in many applications a thread form (as shown in Figures 1-4) , having the advantages discussed, is desirable. However, a conventional thread form has a configuration which, in some cases, could result in a failure at a tensile load lower than the desired ultimate design tensile load or even at the installation loads. Also a conventional thread form would be susceptible to deformation from collar swage whereby its capability to function as a threaded connection could be impaired. Thus it has been found advantageous to provide the lock groove configuration for the pin 22 as illustrated in Figures 5 and 6.

In the embodiment depicted in Figures 5 and 6, components similar to like components of Figures 1-3 have been given the same numeral designation with the addition of the letter postscript "b" and hence the description of some of the components, will not be repeated. For example, except for the details of the lock groove 34b as shown in Figures 5 and 6 and as described, the pin 22b is the same as pin 22 of Figures 1-3. . _. .

As best seen in Figure 6, in one form of the invention, the lock grooves 36b of the lock groove portion 34b of pin 22b are of a shallow construction and have a closely approximated streamlined root configuration. A streamlined contour provides a transition between two different diameters with essentially no stress concentra¬ tion or an effective stress concentration factor (Kt) of one (1) . The helical lock grooves 36b, which are separated by annular crests or shoulders 78 can be considered to be defined by a root portion 72, which is connected at one end to a leading transition portion 74 and at the opposite end to a trailing transition portion 76. In order to approximate a streamlined shape as closely as possible, the root portion 72 is generally elliptically shaped and can be generally defined by the relationship: 2 L_ + y _ π

2 — 7 ^~ ' Da ob where (x, y) are the coordinates for a point of the root curvature surface. Actually, the elliptical shape simulates two streamlined controus, one from transition portion 74 and the other from transition portion 76. In addition to the above the lock grooves 36b are further defined by the following:

1. P is the pitch between successive helical lock grooves 36b;

2. P/X is the width of the shoulders 70 where X is selected to provide proportioned strength between the ultimate shear strengths of the material of collar 46b and the material of pin 22b such that, under tensile load, a failure in shear could occur at the effective shear plane across either the pin shoulders 78 or the resultant shoulders in the swaged collar; 3. h is the depth of helical lock grooves 36b;

4. Dr is the effective root diameter of helical lock grooves 36b;

5. Du is the crest diameter αf pin shoulers 78 (or the diameter defined by the crests of the threaded pin 22b) ;

6. Da is the major axis of the ellipse defining the elliptical root contour of root portion 72;

7. Db is the minor axis of the ellipse defining the elliptical root contour of root portion 72;

8. Db/2 is one half of the minor axis or the distance along the minor axis

Db from root portion 72 up to the major axis Da; 9. L is the axial distance between the respective tangential intercepts of the leading transition portion 74 and the -trailing transition portion 76 with the ellipse portion defining root portion 72; and 10. W is the radial distance along the minor axis Db from root portion 72 to the axial line defined by the axial length L. In one form, the leading transition portion 74 was provided to be at a 40° angle with a plane transverse to the axis of pin 22b while the trailing transition portion 76 was provided to be at a steeper angle of 20°. The angle of the leading portion 74 facilitates flow of the material of collar 46b in swage while the steeper angled trailing portion 76 provides a buttressing effect relative to the swaged collar material. This buttressing effect facilitates clamping of the collar 46b and the sleeve 44b as the collar 46b elongates during swage. The transition portions 74 and 76 tangentially intercept the elliptical root portion 72 whereby a smooth transition in contour is provided. The elliptically shaped root portion 72 has an axial length L which is less_.than the major diameter Da with a radial width W which is less than the minor axis dimension Db/2. The root portion 72 will always have a length L and width W no greater than the major and minor axes Da and Db, respectively. However, in order to assure a smooth transition with the essentially straight transition portions 74 and 76, generally at the angles of inclination noted, it is desirable that the width W be no less than around 80% of the minor axis dimension Db/2 or 40% of Db. With the fastener construction of Figures 5-6, it has been foun^'d that the depth of each of the grooves can be selected to provide a desired minimum ratio of depth h to the crest diameter Du of the pin 22b. In this regard, the major criteria of groove depth h is that it be sufficiently deep as a practical matter to receive and retain the material of the collar 48b after swage.

A groove depth h of around 0.04 x Du or less is desirable

2 i.e. (h/Du) x 10 = 4. With such a shallow groove, the root diameter Dr will be maximized for a pin with a

- ) given crest diameter Du. This will provide that a pin 22b of a given material will have nearly the maximum tensile strength available since tensile failure would occur across the root diameter Dr which, when maximized, is only slightly less than the crest diameter Du. The maximized root diameter Dr will also provide improved fatigue life. Actually since the grooves 36b are helical the tensile failure would occur across some mean diameter Dm between the root diameter Dr and crest diameter Da. Thus, for a pin of a given diameter, the present invention will result in an increase in tensile strength and fatigue life over its conventionally threaded counterpart. At the same time, the groove 36b being shallow will permit the use of the simulated stream¬ lined or elliptical shape at root portion 72 resulting in a significantly reduced stress concentration factor Kt. Again, the result will be an increase in fatigue life over a comparable conventional threaded fastener. The same comparison, of course, holds true with regard to a comparison with anchor lock grooves of the prior art (supra) . With a shallow groove construction, it is desirable to provide the collar 46b with a volume such that when swaged into the locking grooves 36b it will have an excess volume over that required to fill the grooves 36b. in one embodiment, the volume of collar 46b was selected to provide 'overpacking' , i.e., a volume of collar 46b to provide substantially more volume of collar material for filling grooves 36b than they could normally accept within the swage envelope defined by the throat 80 of the swage cavity of anvil 58b and the confronting portion of the lock groove portion 34b of pin 22b. In the present system, it has been found desirable to provide a volume of collar material which has an excess of at least around 16%. With the shallow helical grooves 36b, excess collar volume over the noted 16% is not required since the amount of radial inward movement of collar material is not as great as with prior lock grooves of a deeper construction. The percentage 'overfill' or 'overpacking' noted can be generally determined for a finite length of the effective swage portion of throat 80 (see Figures 5 and 6) by the relationship:

-inn _v = % overfill where:

Da is the diameter of the throat 80 of anvil 58b;

Dc is the outside diameter of the collar 46b before swage; ID is the inside diameter of the collar 46b before swage;

Dm is the mean diameter of the lock grooves 36b; and dl is considered to be a finite length within the swage portion of throat 80.

Because of the shallowness of the lock grooves 36b; it is desirable that the pin 22b be hard enough relative to the hardness of the collar 46b to resist crushing or substantial yielding in tension or necking down from the high compressive swage loads. Thus, in one form of the invention of Figures 5 and 6, the pin 22b could be made of AISI 4140 alloy steel or AISI 1541 carbon steel having an ultimate shear strength of at least around 95 KSI. The collar 46b could be made of AISI 1035 (or AISI 1020) carbon steel having an ultimate shear strength of at least around 45 KSI. Generally, it is desirable to utilize a pin 22b having an ultimate shear strength relative to that of collar 46b in the ratio in a range of around 1.8:1 to around 2.4:1. Thus the pin 22b has a sufficient hardness to accept both the high tensile preloads desired and the swage loads on the collar substantially without yielding. It also should be noted that, from a manufacturing standpoint, the shallow grooves 36b are more easily formed than the prior, deeper lock grooves and, in fact, can be formed after the pin has been hardened.

However, in order to realize the advantages noted, the collar 46b must have a sufficient wall thickness and, hence, volume to insure that enough collar material will move axially in elongation. At the same time it is desirable that the swaged collar have sufficient wall thickness and, hence, have sufficient strength to resist any significant spring back from the shallow lock grooves 36b. The collar wall also should have sufficient thickness to resist significant radial expansion under tensile load such that the pin shoulders 70 and collar shoulders remain in substantially full engagement as the design tensile load on the joint is reached. If the collar wall after swage does not provide sufficient radial stiffness, the collar 46b could expand radially under tensile load, reducing the effective shear plane carrying the load. The result could be a premature failure in shear at the tips of the pin shoulders 70 or corresponding collar shoulders. Thus, the collar wall thickness is selected to provide the necessary material to promote swaging into the shallow helical lock grooves 36b and flow in elongation to provide the desired clamp load. At the same time, the collar wall thickness at final swage is also selected to provide sufficient, radial stiffness or hoop strength to resist significant radial spring back from the grooves 36b both during initial swage and also under subsequent tensile loading. Also, the volume of the collar 46b and swage cavity 80 are selected to provide movement of the material of collar 46b into the grooves 36b to assure a good fill. With the above relationship and an anvil throat portion to provide approximately 16% overfill, satisfactory results were obtained. In this regard an overfill significantly under 16% would not provide the desired high preloads while an overfill significantly over 16% could result in excessive installation loads which could yield the^* pin 22b. For a pin 22b and collar 46b of the ferrous materials having the relative shear strengths previously noted, the following dimensional relationships in centimeters (in inches) were found satisfactory:

Collar Collar

Pin Depth O.D. I.D. Anvil Pin Mean Crest of Before Before Throat Lock Groove Diameter Grooves Swage Swage Diameter Diameter

NOM DIA. Du h Dc ID Da Dm

1.27 1.27 .0393 2.057 1.325 1.912 1.234

(1/2) (.500) (.0155) (.810) (.522) (.753) (.486)

1.587 1.587 .0050 2.562 1.645 2.385 1.536

• (5/8) (.625) (.0200) (1.009) (.648) (.939) (.605) t to

10 1.905 1.905 .0622 3.081 1.988 2.857 1.841

(3/4) (.750) (.0245) (1.213) (.783) (1.125) (.725)

The above dimensions are exemplary only, with the Nominal Diameter being related to the diameter of reduced shank section 32b and the pin crest diameter Du which are approximately the same. Actual dimensions could be varied, and extrapolated, to accommodate different sized concrete bores 12b and sleeves 44b.

It is also desirable, that the width of the helical pin grooves 36b and pin shoulders 78 and the complementary grooves and shoulders of the swaged collar 46b be proportioned in width relative to the respective shear strengths of the materials of pin 22b and collar 46b such that both the shoulders defined by pin grooves 36b of the pin 22b and the shoulders defined by interlocking grooves of the swaged collar 46b are in incipient or simultaneous failure in shear at or above the preselected minimum ultimate design tensile load on the fastened joint. It is preferred that the design provide for the shoulders defined by the grooves of collar 46b to fail prior to the shoulders defined by pin lock grooves 36b, i.e. the shoulders 78 of pin lock grooves 36b would fail in shear at approximately 110% of the tensile load at which the shoulders of swaged collar 46b would fail. By proportioning the grooves as noted, the engaged length of pin and collar can be minimized for a given tensile load. Of course, by providing sufficient collar length, the above shear strength relationship can be maintained while providing for a tensile failure diametrically across the pin lock groove portion 34b. The application of proportioned strength permits the pin grooves 36b to be elongated relative to the shoulders 78 whereby the use of an approximated, stream¬ lined root shape can be more effectively employed. At the same time the shallow groove structure permits smooth transitions between the root 72 and the connecting side- walls 74 and 76. While the elliptical contour employed will closely approximate the desired streamlined shape other similar continuous curves could be utilized.

Another advantage of employing proportioned strength as noted is that the shear strength of the limited collar thread 62b can now be maximized permitting the pre-fastened clamp via torquing to be at a relatively high magnitude. This is achieved by virtue of the fact that the width of collar thread 62b is substantially the same as the width of the groove 36b of lock thread 34b.

With the fastener 10b installed, the swaged collar 46b will have a complementary female thread formed in its bore. This will now permit the collar 46b to be removed by torquing it off the pin 22b. At the same time the collar 46b could, in some circumstances, have additional torque applied.

Claims (13)

1. An anchor bolt for fastening a workpiece to a structure of concrete or the like by a relative axial force applied by a pull tool to the anchor bolt when positioned within a fastening bore in the structure, said anchor bolt comprising a tubular expansion sleeve having a through bore, a pin including a shank, a pull portion on said pin shank, a lock portion on said pin shank having a plurality of circumferentially extending lock grooves, a breakneck groove defining the weakest portion of said pin shank and located between said pull portion and said lock portion, a shank portion located adjacent said lock portion and being of a diameter to be received within said sleeve bore, a sleeve expansion section located at the opposite end of said shank portion, a tubular collar adapted to be located on said <pin shank and to be swaged into said lock grooves in response to a first preselected magnitude of said relative axial force, said sleeve expansion section adapted to be moved axially within said sleeve bore in response to said relative axial force to radially expand said confronting portion of said sleeve redially outwardly for gripping engagement with said structure bore.

2. The anchor bolt of claim 1, wherein said pin includes an enlarged pin head at one end of said pin shank, said pull portion being located at the opposite end of said pin shank from said pin head, said sleeve expansion section, being located between said shank portion and said pin head, said enlarged pin head having a diameter greater than said tubular expansion bore at the confronting por¬ tion of said expansion sleeve, said enlarged pin head being adapted to engage the confronting portion of said sleeve after its radial expansion and to locate said lock grooves at a preselected location in line with said collar and to inhibit further axial move¬ ment of said pin relative to said expansion sleeve, said first preselected magnitude of said relative axial force for swaging said collar being greater than that required to move said enlarged pin head into engagement with said confronting portion of said sleeve after said radial expansion.

3. The anchor bolt of claim 2, wherein said enlarged pin- head has an engaging surface being generally operable on said confronting sleeve portion to effectuate further radial expansion of said confronting portion of said sleeve to a second level of said radial expansion, and said tubular collar has a through bore of a diameter to be generally in a clearance relationship with said pull portion and said lock^' grooves.

4. The anchor bolt of claim 3, wherein said engaging surface is generally in quadrature with said axis of said pin shank and has a diameter generally equal to the outside diameter of said expansion sleeve.

5. The anchor bolt of any of claims 1 to 4, wherein said tubular collar has a limited female thread formed in said through bore and adapted to thread- ably engage said lock grooves whereby said pin, said expansion sleeve and said collar can be pre-assembled and held together prior to installation, said limited female thread having a preselected strength adapted to deform out of said lock grooves in response to the application of a second preselected magnitude of said relative axial force less than said first preselected magnitude.

6. The anchor bolt of any of claims 1 to 5, wherein said collar has an enlarged flange on one end adapted to engage the opposite end of said expan¬ sion sleeve and to engage the adjacent surface of the workpiece to be fastened.

7. The anchor bolt of any of claims 1 to 5, wherein said collar has a generally straight tubular shank portion and an enlarged generally flat washer located between said collar and said expansion sleeve, said flat washer extending radially outwardly to engage ^■• the adjacent surface of the workpiece to.be fastened.

8. The anchor bolt of any of claims 1 to 7, wherein said sleeve expansion section includes a tapered expansion portion having a tapered surface o extending at an angle of around 15 relative to the axis of said pin shan .

9. The anchor bolt of any of claims 1 to 8, wherein said expansion sleeve has a roughened exterior surface at said confronting portion having an axial length at least equal to around 'the axial length of said straight expansion portion.

10. The anchor bolt of any of claims 1 to 9, wherein said lock grooves extend helically to define a thread form.

11. The anchor bolt of any of claims 1 to 10, wherein said lock grooves comprise a plurality of circumferentially extending pin grooves and associated pin shoulders, said pin grooves being shallow and having a radial depth defined by the relationship of:

2 (h/Du) x 10 , where h is said radial depth and Du is the diameter as defined by said pin shoulders and with said depth h selected to be shallow relative to said shoulder diameter Du to provide a result to said relationship of no greater than around 4, said pin member being of a different material and having an ultimate shear strength of a different magnitude from that of said collar with the ratio of the shear strength of said member to said collar being such that crushing of said pin member in swage is substantially avoided, said ratio of ultimate shear strengths of said pin member to said collar being in a range of around 1.8 to around 2.4, the axial widths of said pin grooves and shoulders and said collar grooves and shoulders formed during swage being preselected in accordance with the relative shear strengths of said different materials whereby said i ^"shoulders and said collar shoulders formed in swage are adapted to fail in shear generally at the same tensile load applied between said pin member and said collar.

12. The anchor bolt of claim 11, wherein said pin grooves are substantially wider than said pin shoulders, said pin grooves having a simulated streamlined root contour being generally defined by a continuous curve.

13. The anchor bolt of claim 11, wherein said pin grooves have a simulated streamlined root contour being generally defined by a portion of an ellipse, said ellipse portion being no greater than one half and no less than around 80% of an ellipse along the minor axis.^'