GB2225597A

GB2225597A - A column base structure

Info

Publication number: GB2225597A
Application number: GB8828064A
Authority: GB
Inventors: Hideshige Matsuo; Nobukiyo Imagawa; Isamu Yamamoto; Michio Itoh; Kuniaki Sato
Original assignee: Kajima Corp; Hitachi Metals Ltd
Current assignee: Kajima Corp; Proterial Ltd
Priority date: 1988-12-01
Filing date: 1988-12-01
Publication date: 1990-06-06
Anticipated expiration: 2008-12-01
Also published as: HK44194A; GB8828064D0; GB2225597B

Abstract

A base for a steel column comprises four bolts in protecting tubes 11 which are held by anchor plates 2 and 3 at the top and bottom. The lower anchor plate is attached to a frame comprising horizontal and vertical members 29, 26 of angle section fixed to a concrete sub-slab 7. The attachment may be by welding or adjustable. The base is embedded in concrete to the level 8. A variety of shapes for the anchor plates are described. Lengths of angle section may be bolted between the anchor plates. <IMAGE>

Description

A COLUMN BASE STRUCTURE This invention relates to a column base structure in a steel-frame structure, or a steel-frame reinforced concrete structure, or a combined steel-frame and steelframe/reinforced concrete-structure.

The accuracy of a steel-frame structure depends largely on the positioning accuracy of steel-frame columns on the lowermost story, which are in turn greatly affected by the accuracy of the foundation structure.

Since shop-assembled steel-frame members are usually brought into the construction site within tolerances, errors in on-the-site steel-frame erection are often affected directly by the accuracy of the anchor bolts.

As a result, the quality of the erection of a steel-frame structure depends solely on the accuracy of the anchor bolts. For this reason, an anchor bolt fixing device in which anchor bolts are held in position via a steel-frame or an anchor retainer is usually used to prevent the anchor bolts from unwantedly moving due to the impacts applied by the pressure of concrete during concrete placement, as described on page 625 of Technical Guide for Steel-frame Construction with Detailed Description (Architectural Institute of Japan, April 25, 1979) published in Japan.

According to one embodiment of the present invention, a base structure for a steel-frame column comprises vertically extending first support members mounted on a concrete substrate; horizontal second support members mounted on and extending between the first support members; and an anchor bolt frame having anchor bolts extending vertically from the second support members to an upper anchor plate supported on the anchor bolts, the base structure having been embedded in a concrete foundation with the anchor bolts projecting upwardly therefrom.

According to another embodiment of the invention, a column base structure comprises a steel-frame column integrally joined to a column base metal fitting comprising a raised portion formed into a planar shape corresponding to the contour of an end face of said steel-frame column, and a base plate formed into a flat plate, the column base metal fitting being joined to a concrete foundation via anchor bolts and nuts both of which secure a central mortar provided in advance on the concrete foundation and a mortar case after the installation of the base fitting and are embedded into said concrete foundation, wherein horizontal support members are fixedly fitted to the upper ends of support members projecting on a concrete substrate; an anchor bolt retainer formed by joining together upper and lower anchor plates via a plurality of connecting members is fixedly fitted to the horizontal support members; anchor bolts having threaded parts at the upper and lower ends thereof are secured via through holes provided on the upper and lower anchor plates constituting said anchor bolt retainer; and wherein the anchor bolts, excluding the upper threaded parts thereof, are embedded in said concrete foundation, together with the anchor bolt retainer.

The present invention seeks to provide a column base structure having a high anchor bolt fixing accuracy, and to provide a column base structure in which the positioning and embedding of anchor bolts are made extremely easy. The invention facilitates the positioning of a steel-frame column and a column base metal fitting therefor, and the column base metal fitting and the concrete foundation. Consideration is also given to the adhesion of the column base metal fitting and the concrete foundation with the aim of improving the resistance to earthquakes and other external movements.

By predetermining the initial tensile strength of the anchor bolts, safety performance of the base structure can also be improved.

Various features and advantages of the invention will be apparent from the following description which discusses some prior structures and various embodiments of the invention by way of example and with reference to the accompanying drawings wherein.

Fig. 1 is a front view of the essential part of a convetional anchor bolt fixing device.

Figs. 2 and 3 are partially enlarged longitudinal sections illustrating the relationship between am anchor bolt and an upper anchor plate of the anchor bolt fixing device at tulle upper part of the anchor bolt.

Fig. 4 is a perspective view illustrating a conventional column base metal fitting.

Fig. 5 is a diagram illustrating center lines marked on the bottom surface of the column base metal fitting shown in Fig. 4.

Fig. 6 is a front view illustrating the state where the steel-frame column is anchored to a concrete foundation using the column base metal witting sow in Fig. 4.

Fig. 7 is a longitudinal section of the essential part corresponding to the column base structure shown in Fig. 6.

Fig. 8 is a diagram of assistance in explaining the flow of mortar in a form.

Flg. 9 is a diagram or assistance in explaining tie external force exerting on a column base structure.

Fig. 10 is a partially enlarged longitudinal section of the essential part illustrating tulle state where a flat washer is welded to a conventional colulllll base metal fitting.

Fig. 11 is a front view illustrating the state where anchor bolts are held in position in a first embodiment of this invention.

Fig. 12 is a cross-section taken along line U-E in Fig. 11.

Fig. 13 is a front view illustrating tie state where anchor bolts are held in position in a second embodiment of this invention.

Fig. 14 is a cross-section taken along line F-F . in Fig. 13.

Fig. 15 is a plan view illustrating an anchor plate in a third embodiment of tis invention.

Figs. 16 and 17 are cross-sections taken along lines G-G and H-H, respectively.

Fig. 18 is a partially enlarged cross-section illustrating the state where an anchor bolt is inserted into an anchor plate.

Figs. 19 and 20 are plan views illustrating anchor plates used in fourth and fifth embodiments of this embodiment.

Figs. 21 and 22 are plan views illustrating anchor plates used in sixth and seventh embodiments of this invention.

Fig. 23 is a plan view illustrating an anchor plate used in an eighth embodiment of this invention.

Figs. 2s and 25 are cross-section taken along lines I-I and J-J in Fig. 23.

Figs. 26 and 27 are a plan view and a cross-section of an anchor plate used 111 a ninth embodiment of this invention.

Fig. 28 is a plan view illustrating an anchor plate used in a tenth embodiment of this invention.

Fig. 29 is a cross-section taken along- line K-K in Fig. 28.

Figs. 30 and 31 are a front v view and a plan view of the essential part of an anchor bolt retainer used in an eleventh embodiment of this invention.

Fig. 32 is a cross-section taken along line L-L in Fig. 30.

Figs. 33 and 34 are a front view and a plan view of the essential part of an anchor frame used in a Lwelftl, embodiment of this invention.

Fig. 35 is a perspective view illustratiilg the state where a column base metal fitting is placed on a machining jig in a thirteenth embodiment of this invention.

Fig. 36 is a perspective view illustrating the thirteenth embodiment of this invention.

Figs. 37 and 38 are perspective views illustrating column base metal fittings used in fourteenth and fifteenth embodiments of tis invention.

Figs. 39 and 40 are a longitudinal section and a partially cross-sectional plan view of the essential part of a sixteenth embodiment of this invention.

Fig. 41 is a partially cross-sectional plan view illustrating a seventeenth embodiment of this invention.

Fig 42 is n plan view illustrating tic flow of mortar in an eighteenth embodiment of this invention.

Fig. 43 is a diagram illustrating the behavior of rota Live distortion caused by an external force applied to a column base structure in a nineteenth embodiment of this invention.

Fig. 44 is a schematic diagram of rotative distortion shown in Fig. 43.

Fig. 45 is a diagram illustratillg changes with time in the tensile force of an anchor bolt usecl in the nine- teenth embodiment of this invention.

Fig. 46 is a righting moment characteristic diagram for a conventional column base structure in which pretensioned anchor bolts are used.

Fig. 47 is a righting moment characteristic diagram for a conventional column base structure used in the nineteenth embodiment of this invention.

Figs. 48 and 49 are a plan view and a longitudinal section illustrating a test piece in the nineteenth embodiment of this invention.

Fig. 50 is a partial cross-section illustrating an anchor bolt assembly used in a twentieth embodiment of this invetion.

Fig. 51 is a diagram illustrating a story deformation of a building in the twentieth embodiment of this invention.

Fig. 1 is a front view of the essential part of a conventional anchor bolt fixing device. In the figure, numeral 1 refers to an anchor frame formed in a square frame using equal angles in which an upper anchor plate 2 and a lower anchor plate 3 are fixedly fitted to the upper part thereof and at a location slightly higher than the lowermost part thereof, respectively, so that anchor bolts are held in position by retaining holes (not shown) provided on the upper and lower anchor plates 2 and 3.

The vertical positioning of the anchor bolts 4 is effected by interposing the lower anchor plate 3 between nuts 6 via a square washer plate 5. With this arrangement, an anchor frame 1 is placed at a predetermined location on a precast concrete subs lab 7 and secured in position by driving drill anchors 9, etc to form a concrete foundation 8 as shown by a chain line in the figure.

The anchor frame 1 consituting the above-mentioned conventional anchor-bolt fixing device, which is normally fabricated and assembled in advance at factory and transported to the erection site, has the following problems.

(1) The anchor frame 1, which has a large number of protruded parts, tends to be deformed during transportation due to stacking and collision of multiple anchor frames 1. This could result in the difficulty in embedding the anchor bolts 4 in the concrete foundation 8 with high accuracy.

(2) Since the anchor frame 1 is usually fabricated and assembled by welding, it is difficult to adjust the positions of the anchor bolts 4 in the horizontal or verticle direction on the erection site.

(3) Since the washer plate 5 to which the bottom end of the anchor bolt 4 is located has a large horizontal projected area, the anchor frame 1 must be made sufficiently large to accommodate the washer plate 5.

(4) The anchor frame 1 must have a sufficiently high rigidity to prevent the anchor bolts 4 from moving during placement of the concrete foundation 8. For this reason, anchor frame members must be of a rela tively large size. This could lead to increased pos sible interference of anchor frame members with rein forcing bars (not shown) used in the concrete founda tion 8.

(5) The outside surface of the anchor bolt 4 is covered by a non-stick covering sleeve (not shown in Fig. 1). As shown in Fig. 2, the top end of the anchor bolt 4 is supported by the upper anchor plate 2 of the anchor frame 1 via the covering sleeve- 11. The anchor bolt 4, however, tends to be secured in a tilted fashion, as shown in Fig. 3, due to a gap among the upper anchor plate 2, the sleeve 11 and the anchor bolt .

It is impossible, therefore, to improve the anchoring accuracy of the anchor bolts 4 a normal practice for erecting a steel-frame column on the concrete foundation 8 is such that a column base metal fitting is integrally joined to the column base portion of the steel-frame coulumn, and the column base metal flitting is tightly secured to the concrete founda- tion 8 by the anchor bolts 4. An example of the column base metal fitting is of a shape shown in Fig. 4. The column base metal fitting 10 has a square base plate - 12 and a square raised portion 13. On the base plate 12 provided are tick portions 14 at the four corner thereof, having anchor-bolt holes 15 drilled at each cor- ner thereof. The raised portion 13 is of a square, rectangular, circular, ii- or any other shape corresponding to the cross-sectional shape of the steel-frame column to be joined.

The column base metal fitting 10 is made usually by casting or forging, with the anchor bolt holes 15 thereof being formed after casting or forging. When forming the anchor bolt holes 15, two orthogonally intersecting center lines 16a and 16b passing through the center A of: the base plate 12 are marked, and ten center lines 17a and 17 b of the holes 15 are marked based on these center lines 16a and 16b to accurately determine the positions of title holes 15. The holes 15 are drilled on the centers 13 titus obtained.

When joining a steel-frame column to the raised portion 13, a center line 19a, as shown in Fig. 6, marked on the side surface of the raised portion 13 is matched with a center line 1 9b showing the center of the steel-frame column 18 to weld the steel-frame column 18 to the raised portion 13. Ttic column base thus formed by welding the column base metal fitting 10 to the steel-frame column 18 is secured to the concrete foundation n I:y the anchor bolts 4 and the nuts 6, as shown in Fig. 6.

This marking operation, however, has to be performed on each piece of the column base 10, requiring much labor and time. In other words, the conventional erection work using the column base metal fitting 10 involves high erection costs.

In the above-mentiolled column base structure, where the column base metal fitting 10 has to be brougllt in close contact with the concrete foundation 8, mortar must be cast into the gap between both. Fig. 7 is a longitu- dinal section of the essential part corresponding to a column base structure shown in Fig. 6. In the figure, the column base metal fitting 10 is integrally joined by welding to to steel-f ratote column 18 made of a steel material, and the assembly thus formed is placed on the concrete foundation 8 via a precast central mortar 20.In this case, since a predetermined number of anchor bolts 4 are embedded in the concrete foundation 8, positioning is performed by bolt holes (not shown) provided on the column base metal fitting 10. After that, mortar 21 is cast into the gap between the column base metal fitting 10 and the concrete foundation 8. After the mortar 21 has been hardened completely, the nuts 6 are fastened to the anchor bolts 4 via washers 22 to secure the steel-frame column 18 in place. Numeral 23 refers to a form for defining the outside dimensions when casting mortar 21.

With the above-mentioned c conventional column base structure, when the mortar 21 is cast in the gap between the column base metal fitting 10 and tlic concrete foundation 8 after L ite column base metal fitting 10 Ilas been placed on t Lhe central nor tar 20, a cavity 24 is often produced due to the air entrapped by the mortar 21, resalting in poor contact of the mortar 21 with the entire bottom surface of the column base metal fitting 10.

Fig. 8 is a diagram illustrating the flow of mortar in the form 23. In Fig. 8, shown by a chain line is tite outside contour of the column base metal fitting 1O. The central mortar 20 is most commonly formed in a quadrilate- ral form, as shown in the figure. When the mortar 21 is cast in the state shown in Fig. 8 from the direction shown by arrow C by means of a hopper or any other container, the mortar 21 flows along the flow lines shown by arrow but the flow of mortar is parted at the central mortar 20 and then joined together again on the downstream side of the central mortar 20.At this time, the flow of mortar entraps the air present between the column base metal fitting 10 and concrete foundation 8, forming a cavity 24 as shown by a shaded part.

The critical performance requirements for the column base structure include the adhesion between the mortar 20 and the column base metal fitting 10, as well as the rigidity of the column base metal fitting 10 and the fastening strength of toe anchor bolts 4. In tie presence of a cavity 24 on the bottom surface of the column base metal fitting 10, however, satisfactory performances for the column base structure cannot be maintained deteriorating remarkably t the earthquake resistance of the structure .

The coulmn base metal fitting 10 and the concrete foundation 8 are joined together by L the fastening ng strength of the anchor bolts 4 and the nuts 6. If a bending moment is exerted on the column base, toe column base metal fitting 10 is deformed locally and in a complicated man- ner. The tension value to be added to the anchor bolt A has not been clearly specified as ato industry standard value, and set for individual buildings. In addition, the evaluation method of performance (anchoring degree) has not been formally specified in the trade.

That is, the conventional column base structure has not necessarily accomplisll a high anchoring degree by fully utilizing the performance of tite anchor bolts 4 for the above reasons, and it is difficult to accurately grasp the anchoring degree at the time of tie design of a building. All this leaves a great uncertainty about the safety of buildings.

Next, the external forces exerting on the column base structure will be discussed. Fig. 9 is a diagram of assistance in explaining the external forces exerting on the column base structure. Like parts are indicated by like numerals in Fig. 6. In Fig. 9, an axial force N and a horizontal force F, both resulting front tite weight of the building, earthquake and storm, are applied onto the steel-frame column 18.The horizontal force F produces a bending moment M to bend the column base, and a shearing force Q to move the column base horizontally To cope with the bending moment M and Lite axial force N, the column base structure is designed in such a manner that the stresses are transmitted from the steel-frame column 18 to the column base metal fitting 10, the anchor bolts 4, and the concrete foundations 8. When the shearing force Q is small, the column base structure is designed in such a manner that the stresses are transmitted from the steel frame column 18 to the column base metal fitting 10, and the concrete foundation 8. In this case, tie transmission of stresses from the column base metal fitting 10 to the concrete foundation 8 is effected by a frictional resistance Qa1 between toe column base metal fitting 10 and tlle concrete foundation 8 caused toy tlic axial force N exerting on t the column base structure and the tensile force of the anchor bolts J. When the searing force Q is too large to be offset by the frictional resistance Qa1 between the column base metal fitting 10 and the concrete foundation 8, the column base structure is designed in such a manner that the stresses are transmitted front te steel- frame - column 18 to the column base metal fitting, the flat washer 22, the anchor bolts 4, and the concrete foundation 8. To this end, the inside diameter of the flat washer 22 is made relatively smaller so as to reduce the clearance between the inside diameter of the flat washer 22 and the outside diameter of the anchor bolts 4, and the entire outer periphery of the flat washer 22 is fillet-welded to the column base metal fitting 10, as shown in Fig. 10.

Numeral 25 in the figure indicates a welded zone.

More recently, there is a growing demand for improv- ing the strength performance of the column base structure from considerations of aseismic design. In order to realize this, selection of good quality anchor bolts 4 having excellent mechanical properties (in terms of yield point and tensile strength) is of critical importance.

When anchor bolts 4 having a tensile strength pf over 50 kg/mm are used for the column base structure, however, flat washers 22, which are generally made of the same quality as the anchor bolts as set fasteners, cannot be welded to the column base metal fitting 10 because of the high carbon content and carbon equivalent (Ceq) thereof. For this reason, when anchor bolts 4 of this degree of strength (with a tensile strength of over 50 kg/mm2) are used, large shearing force Q cannot be Lransmitted to the column base metal fitting 10.The use of anchor bolts to of this degree of strength coultl therefore f ore help improve the flexural strength Ma (resistance to bending moment M) of the column base structure, but the shearing strength Qa thereof could be lowered because the shearing strength Qa can be maintained only by the frictional resistance Qa1.

Fig. 11 is a front view illustrating the state where anchor bolts are held in position in a first embodiment of this invention. Fig. 12 is a cross-section taken along line E-E in Fig. 11. Like parts are indicated by like numerals in Fig. 1. In the figures, an upper anchor plate 2 and a lower anchor plate 3 have anchor-bolt inserting holes drilled at predetermined intervals. Numeral 5 denotes a washer plate of a square shape, for example, provided on the upper part of the lower anchor plate 3. The lower anchor plate 3 is secured by the anchor bolts and the lower nuts 6 via the washer plates 5. The upper anchor plate 2 is secured by the anchor bolts 4 and the upper nuts 6a.

Covering sleeves 11 are provided over the shanks of the anchor bolts 4. By assembling in this manner, four pieces, for example, of anchor bolts 4 are held in place.

Next, support members 26 made of angles, for exaootple, are fixedly fitted by welding to a plurality of fixing members 27, and ten fixedly fitted at a predetermined location on the concrete subslab 7 by fixing bolts 28, etc. A plurality of horizontal support members 29, made of steel, are welded to a plurality of support members 26 at a predetermined height in such a manner tliat the top surface of the horizontal support members 29 forms a substantially horizontal plane. The anchor bolts 4, etc.

are then placed on the horizontal support members 29, centered and welded to the horizontal support members 29.

Thus, the anchor bolts 4 can be embedded into the concrete foundation 8 securely and witlo high accuracy by placing concrete around them.

Fig. 13 is a front view illustrating Lie state where anchor bolts are supported in a second embodiment of this invention. Fig. 14 is a cross-section taken along line F F in Fig. 13. Like parts are indicated by like numerals in Figs. 11 and 12. The arrangement of the anchor bolts 4 and others is the same as in the embodiment shown in Figs.

11 and 12, except that four support members 26 made of angles, for example, are embedded into the concrete sub- slab 7 by casting mortar 30, and tie horizontal support members 29 are fixedly fitted to the support members 26 in such a manner that the top surface of the horizontal support members 29 forms a substantially horizontal plane.

Other arrangements are the same as in tioc case of the first embodiment. In both the abovementioned embodiments the upper anchor plate 2 is not embedded into the concrete foundation, and the upper nuts 6a are removed before tite steel-frame column connected to the anchor bolts 4 is erected.

A column base metal fitting conected to te steelframe column (both not shown) is then placed on the concrete foundation 8, and the nuts 6 are fastened onto the anchor bolts 4 to complete the column base structure.

By adopting the abovementioned construction, the following effects can be obtained.

(1) Since only component members cato be cut to predeter- mined lengths and fabricated in advance at factory and then brought into the direction site for assembly, transport operations can be made quite easy.

(2) Since the column base structure of this invention has few protrusions, unlike the conventional. anchor frame, and is hardly subjected to deformation during trans portation for the reason mentioned in (1) above, the accuracy of tite anchor bolt retainer and the ancllor bolts 4 can be improved substantially.

(3) Since tic anchor bolt supporting assembly consists of a relatively few elements such as the ancloor bolts 4, the upper anchor plate 2 and the lower anchor plate 3, the interference of the anchor frame witli reinforcing bars in the concrete founelation 8 can be substantially reduced.

(4) As the lower anchor plate 3 is provided under the washer plate 5 the llorizontal support members 29 provided directly under tie lower anchor plate 3 do not interfcre with tite washer plate 5.As a result both the washer plate 5 and te lower anchor plate 3 can be disposed at a location closer to the nuts fastened to the lower threaded parts of the anchor bolts to 4 with the result that the intervals of the horizontal support members 29 can be increased. this could contribute much to reducing the deformation of the lower anchor plate 3 caused by the deposition of the concrete foundation 8, and therefore preventing the anchor bolts 4 from center misalignment.

(5) Since the upper anchor plate 2 is connected to the anchor bolts to without te use of the covering sleeve 11, the positioning accuracy of the anchor bolts 4 is not affected by te gap between the covering sleeve 11 and the anchor bolts 4.

Thus, witty the anchor bolt fixing device having the abovementioned construction tite anchor bolts 1 can be embedded I into the concrete foundation 8 in a an accurately positioned state.

Fig. 15 is a plan view illustrating an anchor plate in a third embodiment of tit Is invention. Figs. 16 and 17 are sections taken along lines G-G and 11-11 in Fig. 15. In the figures an n anchor plate 30 corresponds to the upper and lower anchor plates 2 and 3 in the abovementioned embodiments, and is formed into a hollow quadrilateral using steel plates having a thickness of t, with the cross-section of each side formed into an approximately U shape anti the height h made larger than t.At each corner of the anchor plate 30 fixedly fitted by welding are washers 31 made of steel plates having a thickness of t1 and drilled are anchor bolt holes 32 for inserting anchor bolts (not shown).

With the above arrangement, the rigidity of - the anchor plate 30 can be adequately maintained since the height h of the cross-section of each side of the anchor plate 30 is made larger than the thickness t of the steel plate. By fixedly fitting the washers 31 at each corner, the anchor bolts (not shown) can be passed through the anchor bolt holes 32 with ease, and the positioning accuracy of, the anchor bolts can be substantially improved.

Fig. 18 is an enlarged cross-section of the essential part illustrating the state where tite ancor bolts are inserted into the anchor plate. In the figure, if the thickness t of the anchor plate 30 is smaller than the pitch p of the thread 4a provided on the anchor bolt 4 the anchor plate 30 cuts into the root of the thread ta making it difficult to insert the anchor bolt to into the anchor bolt hole 32.This also causes the anchor bolt 4 to be tilted lowering the positioning accuracy of the bolt 4. This inconvenience can be eliminated by providing the washer 31 on the anchor plate 30, as shown in Figs. 15 through 17. In tiols case, the relationship among the thickness t of the anchor plate 30 and the thickness t1 of the washer 31 and the pitch p of the thread ta should preferably be such that (t + t1) ? p, where t may be equal to t1.

Figs. 19 and 20 are plan views illustrating anchor plates used in a fourth and fifth embodiments of t this invention. Like parts are indicated by like nunierals used for explaining the third embodiment. In the fourth embodiment shown in Fig. 19, the anchor plate 30 is formed into a hollow annular shape with the washers 31 formed into a hollow circular disc shape disposed at equal intervals. The cross-section of the anchor plate 30 is formed into an approximately U shape as in the third embodiment. In the fifth embodiment shown in Fig. 20, the anchor plate 30 is formed into a cross shape, with the anchor bolt holes 32 drilled in the vicinity of the ends of the cross-shaped anchor plate 30.In this embodiment, the washers as used in the above embodiments are omitted because the washers may be omitted, depending on toe diameter. tread pitch of anchor bolts (not shown).

Figs. 21 and 22 are plan views illustrating anchor plates used in sixth and seventh embodiments of this invention. Like parts are indicated by like numerals in the above embodiments. The anchor plate 30 in both figures can be formed integrally by welding channels, for example. When the anchor plate is of too large a size to be fabricated front a slngle steel plate, it is effective to fabricate the anchor plate from a plurality of members.

Fig. 23 is a plan view illustratitog en anchor plate used in an elgioth embodiment of titis invention, atod Figs.

24 and 25 are cross-sections taken along lines I-I and J3, respectively, in Fig. 23. The eighth embodiment shown in these figures is the same as te sixth and seventh embodiments in that the anchor plate 30 is integrally formed by welding channels, for example. In titis embodiment, however, componcnt members are overlapped aL tite corners. This constrllctioll makes it easy atod simple to assemble the anchor plate 30 by welding. In addition, this construction can can prevent anchor bolts from cutting into the anchor plate, as described earlier, and eliminate washers for preventing anchor bolts from cutting into the anchor plate because the thickness of t the anchor plate 30 around tite anchor bolt Stoles 32 can be made larger.

Next, Figs. 26 and 27 are a plan view and a crosssection of the essential part of a ninth embodiment of this invention. By providing prolonged oval-shaped projecting beads 33, as shown in both figures, on the component members of the anchor plate 30, the height h of the anchor plate 30 is made larger than te tickess t of the component members thereof.

Fig. 28 is a plan view illustrating an anchor plate used in a tenth embodiment of this invention, and Fig. 29 is a cross-section taken along line K-K in Fig. 29. Numeral 34 in both figures refers to a center titark; four center marks 34 provided at locations halving the distance between the two adjoining anchor bolt holes 32 for inserting anchor bolts (not shown). Tite center marks 34 cato be provided when the anchor plate 30 is formed, and/or when the anchor bolt holes 32 are drilled.By providing these center marks 34, it becomes easy to position the anchor plate 30 by matching tite center marks 34 with tite marker line indicating tite column center provided on the concrete subslab. Tie shape of the center mark 34 may be concave toward tic upside, contrary to tite shape shown 111 Fig. 29, and the cross-sectional shape thereof may toe freely selected.Aside from the shape mentioned above, tite center mark 34 may be provided by a punch or by marking.

Although the above embodiments employ the anchor plate 30 made of steel plate, te anchor plate 30 made of other structural materials than steel, including nonferrous materials has the same effects. The projected plane shape of the anchor plate 30 may be other shapes than the quadrilateral, circular, cross shapes described above. The cross-sectional shape thereof is not limited to a U-shape, but may be a hollow square cylindrical, hollow cylindrical or any other geometrical shape so long as the height h of the anchor plate can be made larger than the thickness t of the component members thereof.

Washers provided around the anchor bolt holes 32 may be omitted as necessary.

With the above construction, the weight of the anchor plate 30 having a predetermined rigidity can be reduced substantially, resulting in the ease of handling. In addition, tis 5 construction can reduce the thickness of the component members of the anchor plate, leading to reduced manufacturing costs.

Figs. 30 and 31 are front and plan views illustrating an elevent embodiment of tis invention and Fig. 32 is a cross-section taken along lioe L-L in Fig. 30. Like parts are indicated by like numerals in Fig. 1 atoct Figs. 11 14. In these figures, numeral 35 refers to a conectlng member, made of an angle, both ends of which are bent at right angles and fastened to tulle upper and lower atoctoor plates 2 and 3 via bolts and nuts 36 to form an anchor bolt retainer 37. Next, the anchor bolts -4 are secured via through-boles (not shown) of predetermined dimensions and pitch, provided on each of the upper and lower anchor plates 2 and 3.The means for positioning the anchor bolts 4 on the lower anchor plate 3 by means of the washer plate 5 and the nuts is the same as in the embodiments shown in Fig. 1 and Figs. Ii - 14. Next, four support members 26 me of angles, for example, are provided on the concrete subslab 7, and an anchor frame 38 is con struted by securing two horizontal members 29 made of angles on the upper ends of the support members 26 in such a manner that the top surface of the horizontal supports 29 forms a substantially horizontal plane.With the abovementioned construction, te anchor bolts 4 can be embedded in the concrete foundation 8, together wit tite anchor bolt retainer 37 and the anchor frame 38, by placing the anchor bolt retainer 37 on the anchor frame 38, joining both together by bolts and nuts (not shown) or welding, and casting concrete.

Figs. 33 and 34 are a front view and a plan view of te essential part of the anchor frame used I in a twelfth embodiment of this invention. Like parts are indicated by like numerals in the embodiments shown in Figs. 30 through 32. In Fig. 33, slots 39 extending in the vertical clirection are provided in tulle vicinity of toe upper ends of the support members 26 so as to permit bolts 40 to be passed through. Wit tiols construction, the top surface of the horizontal support members 29 can be levelled and the anchor bolts 4 shwon in Figs. 30 through 32 can be verti cal ly positioned since t the horizontal support members 2'9 can be moved in te vertical direction. Next, in Fig. 34 slots 41 and 42 are provided each on the lower anchor plate 3 and the horizontal support members 29 in an ortho- gonally intersecting manner so as to permit bolts 613 to be passed through. With this construction, the anchor bolts (not shown) passed through the througit-holes 3a provided on the lower anchor plate 3 can be positioned horizontally since the lower anchor plate 3 can be moved on a itori- zontal plane.

In the abovementioned embodiments, the anchor bolt retainer 37 is secured by bolts'and nuts, but they can be secured at the erection site by welding, or a combination of both. The number of the connecting members 35 forming the anchor bolt retainer 37 is not limited to four, but may be selected appropriately taking into account the number of anchor bolts 4. In addition, tite material used for the anchor bolt retainer 37 and the anchor frame 38 is not limited to angles, but other types of shape steels, tubes, rods, or any other structural itaterials, or a combination of these may be used.The support meotobers 26 may be provided at predetermined locations on the concrete subslab 7 by inserting the members 26 into the unsolidified concrete 7.

With the abovementioned construction, the following effects can be expected.

(1) Transportation is made quite easy since only component members fabricated in advance to predetermined dimen sions at factory can be assembled at te construction site.

(2) The accuracy of toe anchor bolt retainer 37 and the anchor frame 38 is substantially improved since vir tually no deformation of the frame occurs partly be cause of few protruded portions on toe frame, unlike the conventional one, and partly because of tic ease of transportation as described in (1) above.

(3) The positioning accuracy of tite anchor bolts 4 is substantially improved since the whole, or a part, of the component members can be joined togetiter by bolts and nuts, and the anchor bolts 4 can be positioned at the erection site.

(4) As tie anchor frame 38 can be installed extremely easily, there is no need at all for the use bf special tools or cumbersome work that have hitherto been needed, resulting in a marked reduction in the manu facturing process.

Fig. 35 is a perspective view of illustrating the state where the column base metal fitting used in a thir- teenth embodiment of this invention is placed on a machining jig. In Fig. 35, toe column base metal fitting 10 has a square base plate 12 aitci a square raised portion 13. On the base plate 12 provided are thick portions at the four corners thereof. Tlle raised portion 13 is a square projecting rim to which the steel-frame column ( (not shown) is joined.As is evident from Fig. 35, marks 45 are provided in advance on the central points of the sides of the square base plate 12. The mark 45 indicated in the figure is a linear projection, but column base metal fitting 10 of this invention is not limited to tis shape, and but the marks 45 may be of a spot-shaped projection, groove, recess or a any otter shape. Similar marks 46 are provided in advance on the central points of the sides of tile square raIsed portion 13.

To provide ancllor bolt holes 15 on tie the base metal fitting 10 having these marks 45 tite column base metal fitting 10 is first placed on a machining jig 47 of a machine tool having a center-aligning device, such as an NC machine tool. The machining jig 47 consists of tables 48 and 49, both extending in the X-Y direction and having center lines 50 and 51, respectively, so that center alignment can be automatically performed by matching the center lines 50 and 51 with the marks 45. Next, the anchor bolt holes 15 are automatically positioned on the thick portions 44 at the corners of the base plate 12, using an indexing device, and drilled.In this way, the anchor bolt holes 15 can be machined without marking operation.

Fig. 36 is a perspective view illustrating the state where the column base metal fitting 10, the steel-frame column 18 and the concrete foundation are joined together in a thirteeto embodiment of tis invention 8. In joining the steel-frame column 18 and the column base metal fitding 10 in Fig. 36, longitudinal center lines 52 and 53 are marked on toe centers of the sides of t the steel-frame column 18 and toe center lines 52 and 53 are matched witlo the marks 4 6 on tie e raised port loot 13.Then, the steel- frame column 18 is joined to the column base metal fitting 10 by welding, etc.

Furthermore, the use of the column base metal fitting 10 shown in Fig. 35 greatly facilitates tite positioning on the concrete foundation 8. That is, tie center lutes 54 and 55 of the column are first marked on the concrete foundation 8, as shown in Fig. 36, and te center lines 54 and 55 are matched wit te marks 45 of the base plate 12.

By using the column base metal fitting 10 having the abovementioned construction, marking operation for proving mark lines on tie base plate 12 and the raised portion 13 can be eliminated. Althougio this embodiment is concerned with a column base metal fitting supporting a column having a square cross section, the same applies to -a column having a ractangular cross section.

Fig. 37 is a perspective view illustrating a column base metal fitting used in a fourteenth embodiment of this invention. The column base metal fitting 10 has an 11- shaped raised portion 13 for supporting an ll-shaped steelframe column. In this embodiment, too, marks 45 and 46 are provided in advance on tile central points of the sides of the base plate 12 and te raised portion 13, respectively.

Fig. 38 is a perspective view illustrating a column base metal fitting used in a fifteenth embodiment of titis invention. The column base metal fitting 10 has a round raised port ion 13 for supporting a round column, wit to marks 46 provided In advance on tulle outer periphery of the raised portion 13 at intervals of 90 degrees. Tite marks 45 are lorovideci ott tita central points of tite sides of tite base plate 12, as in the above embodiment.

With this construction, the following effects can be expected.

(1) In machining tite anchor bolt holes 15 on the column base metal fitting 10, the marking operation cati be eliminated, leading to a reduction in the manufactur- ing cost of the column base metal fitting 10.

(2) By providing tite marks 46 in advance on the raised portion 13, the marking operation for indicating the centers of the steel-frame column 18 on t the ou t e r periphery of the raised portion 13 of the column base metal fitting 10 can be eliminated, leading to a reduction in manhours for the joining operation of the steel-frame column 18.

(3) Furthermore, when the column base is installed on toe concrete foundation 8 at the erection site, the steel frame column can be easily positioned by matching the centers on the column 18 provided on the concrete foundation 8 with the marks 45 on the base plate 12.

This results in a reduction in manhours at the con struction site.

FIgs. 39 and 40 are longitudinal section and partially cross-sectional plan view of a sixteenth embodiment of tis invention. Like parts are indicated by like numerals shown in Figs. 7 and 8. In Figs. 39 and 40, the column base metal fitting 10 is made of cast steel, for example, and ions n raised port loot 13 itavitog a plane corresponding to tie profile of the end face of toe foot of the steel frame column 18 which is integrally formed wi tlo a flat base plate 12. On the base plate 12 drilled are ancloor bolt holes (not shown) at locations corresponding to the anchor bolts 4.The projected plane shape of the raised portion 13 and the base plate 12 is almost a square corresponding to the cross-sectional shape of the steelframe column 18. Numeral 56 are holes provided at loca- tions almost corresponding to the contour of the central mortar 20 by piercing titrotoglo the column base metal fitting 10.

The steel-frame column 18 and te column base metal fitting 10 are joined together by welding to form the abovementiomed construction, and then positioned on the central mortar 20 provided in advance on the concrete foundation 8. After that, mortar 21 is cast lotto the form 23 in tite direction shown by arrow C. In this case, the mortar 21 tends to flow, as shown in Fig. 8, entrapping the air in te neighborhood of the central mortar 20.

Even if the air is entrapped, however, it can be easily discharged through the holes 56 provided on the column base metal fitting 10. Consequently, the mortar 21 can be cast without hindrance, ensuring perfect adesion of the mortar 21 to the bottom surface of the column base metal fitting 10. Thus, the cavities 24 as shown in Figs. 7 and 8 can be eliminated.

Like parts are indicated by like numerals in Figs. 39 and 40. In Fig. ll, numeral 57 refers to a groove provided in such a manner as to plercillg through t the central mortar 20 in the same direction as t the mortar casting direction C and in the horizontal direction. The holes 56 should be provided on the colurnn base metal fitting 10 in such a manner as to face the groove 57.

With this construction, as the nor tar 21 is cast in the direction C, tite mortar 21 not only flows in the same manner as described in the abovementioned embodimellts, S but also flows into the groove 57. The mortar flowing in the groove 57 passes through the groove 57 faster than the mortar flowing in other areas, reaching around the edge of the column base metal fitting 10. This prevents the air from being entrapped, ensuring perfect adhesion of the mortar 21 to the bottom surface of the colum base metal fitting 10.Provision of the hole 56 facing the groove 57 permits te air entrapped during the casting or flowing of the mortar 21 in the groove 57 to be easily discitarged.

Fig. 42 is a plan view of the mortar portion in an eighteenth embodiment of this invention. Like parts are indicated by like numerals in Figs. 39 through 41. In Fig. 42, the central mortar 20 is formed into an elliptical planar shape in such a manner that the major axis of the ellipse lies in te direction of the casting and flowing of the mortar 21. Other arrangements ore toe same as with the abovementioned embodiments.

With this construction, the steel-frame column and the column base metal fitting (both not shown) are joined together and placed on the central mortar 20, and the mortar 21 is cast in tite direction C. In this case, tie outside contour of the central mortar 21 almost coincides witit toe flow lines shown by arrows 58 because LIte central mortar 20 is formed ioto an elliptical planar shape, with the major axis thereof agreed with the mortar flowing direction. Thus, the mortar 21 encounters less fluidic resistance, ant the turbulence of tioe moo tar flow 11 toe can be prevented. This also eliminates the entrapping of the air in the mortar 21.

In the eighteenth embodiment, the cross-sectional shape of the steel-frame column 18 and the planar shape of the column base metal fitting 1 10 are formed into an almost square shape. However, other quadrilateral, circular or any other geometrical shape than a square leave the same effects. The column base metal flitting 10 may be formed not only by cast steel but also by steel plates or other steel materials. Tie hole 56 provided on tie column base metal fitting 10 may be of other cross-sectional shapes than the circular shape used in this embodiment.The horizontal through-groove 57 provided on the central mortar 20 may be provided in multiple numbes. The planar shape of the central mortar 20 may be of any desired shapes, other than a square, or circular shape. When the horizontal groove is not provided, the central mortar 21 should have a shape whose contour includes a curve corresponding to the flow line of toe mortar 21.

With this construction, the air existing between the column base metal fitting 10 and tie concrete foundation 8 during the placement of the mortar 21 can be easily discharged through tite hole 56 provided on toe column base metal fitting 10 , titus preventing t the unwanted formation of cavities in the mortar 21.

Fig. 43 is a diagram Illustrating the behavior of tite rotative clistortion of tlic column base structure caused by external force in a nineteenth embodiment of t this invell- Lion. Fig. 44 is a schematic diagram of the same rotative distortion. In the nineteenth embodiment of this invention, te column base structure is joined together by introducing to anchor bolts 4 sown in Fig. 44 a tensile force 0.15 - 1.2 times as large as the yield point thereof in order to obtain a high rotative rigidity k-, as shown in Fig. 43.This embodiment will be described in tic following.

As noted earlier in tlie above embodiments, the column base structure of this invention is such that the rotative rigidity of the column base metal fitting 10 is so high that deformation can be reduced to a very low level, thus reducing the rotative distortion of the column base to almost zero. By giving a predetermined tensile force to the anchor bolts 4, together with the use of a column base metal fitting 10 having a high rotative rigidity, the rotative rigidity of the column base structure can be accurately evaluated.

According to experiments, the behavior of the rotative distortion of te column base structure of this embodiment caused by external force (bending moment) assumes a simplified form as shown by a solid line in Fig.

43. That is, the rotative rigidity (M/O) of the column base varies in three different sections: A section up to point a (in Fig. 43) where the bottom surface 10a of the column base metal fitting 10 at tie location of the tensioned anchor bolt in Fig. 44 is separated from the top surface of tic concrete futllldation 8; a section up to point b (in Fig. 43) where tlie tensioncd anchor bolt 4 Is yields; a rot a section thereafter.

The rotative rigidity indicated toy an alternate loe and short dash line in Fig. 43 is a theoretical value of the rotative rigidity in which the column base tO is regarded as a perfect rigid body and no tensile force is introduced to the anchor bolt 4, and geometrically expressed by equation (1).

E . AB . l K0 = ----- (1) L where K0: rotative rigidity of column base when no tensile force is introduced to anchor bolts (tm/rad) E: Young's modulus of anchor bolt (t/cm ) AB: total cross-sectional area of the group of ten sioned anchor bolts (cm) distance between anchor bolts (cm) L: effective insertion depth of anchor bolts (cm) The rotative rigidity K in the section of 0 - a of th column base obtained in this case is (I + α ) times as large as that obtained when no tensile force is introduce to anchor bolts 4, as indicated by equation (2).In this case, α is a spring constant ratio of te anchor bolt 4 and the concrete foundation 8, given by equation (3).

K = (1 + α)K0 ------------- (2) Ac α = -------------- (3) n . Ab were A : effective cross-sectional area of concrete C foundation (cm) Ab: cross-sectional area 1 area of a anchor bolt (cm) n: Young's modulus ratio of anchor bolt and concrete foundation The (1 + α) value is approximately 5 - 6 for commonly used SS41 and other anchor bolts. So, by introducing a tensile force to the anchor bolts 4 in tite section 0 - a in Fig 43 a substantially high rotative rigidity can be realized.In the section a - b In Pig. 43, however, as the bottom surface 10a of the column base metal fitting 10 is separated from t te top surface 8a of tlle concrete foundation 8, tite anchor bolts 4 are returned to the same state of simple tension as in the state where no tensile force is introduced. Thus, the rotative rigidity becoones the same value as K in equation (1), a level lower than the level in the section 0 - a.

In the construction industry, the allowable yield strength of the column base is generally defined as the yield point value of the entire column base. Tie allowable yield strength of the column base therefore becomes the H value (bending moment at which the anchor bolt 4 y yields) shown in Fig. 43. Consequently, when the allowable yield strength of the column base is My and the separating moment Ms is lower than My, the rotative rigidity of the column base has to be evaluated as K', and it is difficult to maintain a high rotative rigidity K. In order to maintain a high rotative rigidity K, on te contrary, the allowable yield strength of the column base has to be evaluated front M to H5, posing a disadvantage y in terms of yield strength.

In order to assore a high rotative rigidity nnti main- tain a high allowable yield strength My that is intrinsically possessed by the column base, therefore, It should s be equal to My. The separating moment Ms relates to the value of tension introduced to the anchor bolts 4 and is given by equation (4).

Ms = T0.l-------------(4) where T0:value of tension introduced to anchor bolts (t/cm) k: distance between anchor bolts (cm) Tite allowable yield strength of the column base is given by equation (5).

My = Ty.l=#y.AB.l------ (5) where Ty: yield tensile force of anchor bolts (t/cm).

#y: yield stress intensity of anchor bolts (t/cm) To ensure Ms = My, therefore, T0 should be such that T0 = Ty = #y.AB. This is the best way to give full play to the performance of the anchor bolts 4 in terms of both allowable yield strength and rotative rigidity.

Consequently, te effects of introducing tension to the anchor bolts 4 are basically produced in a range of O to 1 times the yield stress of te anchor bolts 4.

It is known, however, that the tension introduced to te anchor bolts 4 is released by te drying shrinkage and creep of the concrete foundation 8.

Fig 45 shows the results of tic anchor bolt tension unloading test the present applicant and others conducted.

The test shown in Fig. 45 was conducted to liovesti- gate secular changes (the ratio of a tensile T after the lapse of a predetermined time to tite initially introduced tension T0) in tite tetosiooo of tite anclior bolts 4 ott a test piece (No. 5 test specimen which will be described later) corresponding to a steel-frame column base in an actual steel-frame building as shown in Figs. 48 and 49, which will be described later.

This test revealed that the behavior of stress relaxation on the anchor bolts 4 has a certain regularity In the vicinity of the abovementioned #y of the tension introduced. That is, when a teitsioro is introduced to the anchor bolts 4 on a concrete foundation 8 which is more than 4 weeks old after placement, the stress relaxation is stabilized in about to days to approximately 20V. Titis shows good agreement with tite required amount of r-etightening of the anchor bolts 4 in the lapse of the above period after the placement of the concrete foundation 8, a level that is normally experienced by those skilled In the art.

It follows from the above test results ttiat by applying a tension of 1.2#y to the anchor bolts 4, the tension is eventually reduced to an ideal value of 1.0#y after secular changes. For this reason, the upper limit of the introduced tension is set at 1.2#y in this embodiment.

The lower limit of the tension - introduced to the anchor bolts 4 is set at 0.15#y in this embodiment for the following reasons. It ions been confirmed by a large number of experiment results tllat when tite tension intro duceel to toe anchor bolts 4 is 0, tite column base shows a righting moment characteristic of the slip type as shown in Fig. 46. That is, wherever the positive/negative pola rity of toe bending moment generated in t the column base is reversed, the column base tends to be subjected to a substantial rotative distortion even in te absence of a large bending moment. It is well known titan tolls tins an adverse effect on te superstructure.

In order to obtain a column base leaving a good performance (a spindle-shaped righting moment characteristic) as shown in Fig. 47, it is essential to prevent the tension introduced to the anchor bults 4 from being complete ly released. It was found that when te tension intro duced to the anchor bolts 4 is as low as 0.1 - 0.2 Cr . the y total stress relaxation in the anchor bolts 4 adds up to approximately 0.07#y; consisting of approximately 0.05#y that is attributable to the drying shrinkage of the con crete foundation 8, and approximately 0.02 #y that is at- tributable to the creep of the concrete foundation 8.As a result, when safety factor is set at about 2 and the introduced tension (stress intensity) is set at 0.15#y min., the tension introduced to the anchor bolts 4 is not completely released (with 0.08#y remaining) even after toe lapse of time, and thus a good performance of the column base as shown in Fig. 47 can be ensured.

Consequently, the lower limit of the introduced tension (stress intensity) of anchor bolts is set at 0.15.04 in this embodiment.

Figs. 48 and 49 are a plan view and a longitudinal section illustrating a test specimen in a nineteenth embo dine tot of thins invelltiorl. The measurement results of tite rotative rigidity of the column base using this test specimen are shown in the table below. K0 in the table is the rotative rigidity of the conventional column base when too tension is applied to the ancloor bolts 4. K is te rotative rigidity of title column base according to titis invention where tension is applied to tite anchor bolt' 4.

As is evident from the table, the rotative rigidity K of the column base in this cabodieient is as high as 5 - 6 times the rotative rigidity K0 of the conventional column base.

The column base of this embodiment tons a raised

Dimensions (mm) Rotational regidity No.

D A l t1 t2 t3 d L K0tm/rad) 1+a K(tm/rad) 1 200 380 280 10 32 32 30 600 3.9 x 10 5 19.5 x 10 2 " " " " " " 36 800 4.2 x 10 5 19.5 x 10 3 300 550 430 10 61 42 30 600 9.1 x 10 6 54.6 x 10 4 " " " " " " 36 800 9.9 x 10 " 59.4 x 10 5 " " " " " " 42 900 11.9 x 10 " 71.4 x 10 (Note) No.5 is a test specimen used in the anchor bolt tension unloading test.

portion 12 on the column base metal fitting 10 for joining the steel-frame column 18 to prevent the strain caused by welding to the steel-frame column 18 from affecting the bottom surface lOa of the column base metal fitting 10.

The base portion of the column base structure is crowned by providing a slope from the base portion toward the edge portion to distribute the effects of the tension introduced to the anchor bolts 4 over the entire surface of the concrete foundation 8.

In addition, the use of a column base metal fitting 10 as disclosed in Japanese patent Publication No.

47963/1976, 13642/1977, 43330/1977, or 30425/1981, etc., for example, could give full play to the abovementioned effects.

As described above, since the tension (stress inten sity) introduced to the anchor bolts 4 is set at 0.15 1.2#y, the performance of the anchor bolts 4 can be fully utilized in terms of allowable yield strength, and toe rotative rigidity of t the column base can be evaluated at a high value. Furthermore, a good performance (spindle sha ped rigit t Itog moment nt characteristic) for t toe posi- tive/negative repetitive stress (bending moment generating in the column base) at an earthquake can also be maintained.In addition, by simplifying the dynamic mechanism of the column base, the performance (rotative rigidity and yield strength) of the column base can be accurately grasped, leading to increased safety of buildings.

Fig. 50 is a partially cross-sectional side view of an anchor bolt assembly used in a twentieth embodiment of this s invention. The anchor bolt assembly consists of an anchor bolt 4, a nut 6 screwed onto te upper threaded part 4a of the anchor bolt 4, a flat washer 22 interposed between the nut 6 and an object being fastened (not shown), a pair of nuts 59a and 59b screwed onto the lower threaded part 4b of the anchor bolt 4, and a washer 'plate 5 held in place by the nuts 59a and 59b.

The anchor bolt 4 is made of a material having a tensile strength of 50 - 70 kg/mm2; more specifically SS50, SS55, SR30, SRRR40, SD30, SD35, SD40, SD50, S30C, S35C, S40C, S45C, S50C, or S55C. The flat washer 22 is made of a steel material for welded structures; more specifically SM50 or SMASO. The outside diameter of the flat washer 22 is more than 1.73 times as large as the outside diameter of the threaded part of the anchor bolt 4, and the thickness thereof is more than 0.13 times as large as the outside diameter of the threaded part of the anchor bolt 4. The inside diameter of the flat washer 22 should preferably be set at somewhere between the outside diameter of the threaded part of the anclior bolt 4 and the outside diameter thereof plus 2 non. Tite nut 6 is desired to be made of the same material as the anchor bolt 4.

Tulle nut 6 may be made of any of a steel material for general structures or that for welded structures, such as SS41, SM41 or SMA41. The height of tbe nut 6 may be about 0.92 - 1.40 times as large as the outside diameter of the threaded part of the anchor bolt 4.

With the above construction, the anchor bolt 4 can have a high tensile strength of 50 - 70 kg/mm, and the use of the flat washer 22 of SM50 or SMASO pernoits the flat washer 22 to be properly welded to the column base metal fitting 10, ensuring a high shearing yield strength Q in the column base. Tious, the shearing force Q generated in the steel-frame column 18 can be smoothlyd transmitted to the concrete foundation 8 via the colutoin base metal fitting 10, the flat washer 22, and the anchor bolts 4.

Furthermore, the use of the flat washer having the above construction enables full-circle fillet welding. In this case, the use of the flat washer 22 whose outside diameter is more than 1.73 times the outside diameter of the threaded part of the anchor bolt 4. and whose thick- ness is more than 0.13 times the outside diameter of the threaded part of the anchor bolt 4 could cover the fullstrength shearing yield strength a of the anchor bolt 4, as can be seen from the following calculations.

(1) Full-strength shearing yield strength Bqa of anchor bolt

where d: outside diameter of threaded part of anchor bolt f1: yield point of anchor bolt= 2.8 t/cm (2) Shearing yield strength WQa of the fillet-welded part of the entire periphery of flat washer

where D: outside diameter of flat washer # 1.73d t: thickness of flat washer f2:

allowable tensile stress intensity of fillet welded part = 3.3t/cmZ (3) Conditions where the shearing yield strength WQa of the fillet-welded part of the entire periphery of flat washer becomes larger than the full-strength shearing yield strength BQa of anchor bolt BQa#WQa A0.95d # 7.3td At # 0.13d Moreover. according to a preferred embodimerlt of this invention, even when the column base is shifted sideways due to the shearing force Q exerted onto tite column base, the amount of displacement is 4 mm at the maximum because the inside diameter of the flat washer 22 lies between the outside diameter of the threaded part of the anchor bolt 4 and the outside diameter thereof plus 2 mm.Consequently, assuming that the hight of one story of a building is 3500 mm, which is a generally accepted value, the story deformation angle γ (= #/H) obtained by dividing the horizontal displacement 5 of the steel-frame colutsn 18 for one story of- the building by the height ti of one story is approximately 1/875, a value that can satisfy the present legal standard of 1/200, as shown in Fig. 51.

When the nut 6 is made of other material, as described above, the nut 6 has a yield strength equal to that of the anchor bolt 4. In addition the nut G made of such a material can be full-circle welded to the flat washer 22.Although the nut 6 made of a weldable material has low mechanical properties (in terms of yield point and tensile strength), the nut 6 has a height 1.15 - 1.75 times the height of a nut specified in JIS and made of the same material as the anchor bolt 4 so tnt re nut 6 can have a strength, in t te threaded part thereof and other parts, equal to that of a JIS standard nut made of, the same material as the anchor bolt 4.

Substantiation of these values is as follows.

(1) Strength Ta of the threaded part of a nut made of the same material as the anchor bolt hn Ta = Sn = S P where S: strength of the threads of a nut made of the same material as the anchor bolt n: number of threads of the nut t h : height, specified by JIS, of the nut n p: pitch of the nut (2) Strenght Ta' of the threaded part of a nut made of a steel for general structures hn Ta' = S'n' = S' P where S': strength of ttie threads of a nut made of a steel for general struc tures n': number of threads of the nut hn': height of the nut p: pitch of the nut (same as that of the nut in (1) above) (3) Conditions where the strength of tie threads of a nut made of a steel for general structures becomes equal to that of the nut made of the same material as the anchor bolt to it Ta = Ta' ,. Sp = S' p .hn = S where S/S' is te ratio of the yield points of an anchor bolt and a nut made of a steel : for general structures. With the combination used in this embodi ment, this value is 1.15 - 1.75.

1.15hn # hn' # 1.75hn.

By using the anchor bolt assembly described above, and full-circle fillet-welding te flat washer 22 to the column base metal fitting 10, anci tite flat washer 22 to the nut 6, the full-strength shearing yield strength Qa of the anchor bolt 4 can be maintained in the column base, and the nut 6 can be prevented from loosening.

By assembling the anchor bolt assembly as described above aimed at fastening an object being fastened, and using the anchor bolt assembly in the column base of a steel-frame building, the following effects can be expect ed.

(1) The bending yield strength Ma and shearing yield strength Qa can be increased simultaneously. (A ten sile strength of 50 - 70 kg/mm can be maintained for the anchor bolt, and at the same time, the full strength shearing yield strength 13Qa of the anchor bolt can also be maintained.) (2) The loosening of the anchor bolt having a tensile strength of 50 - 70 kg/mm can be prevented.

This invention having the aforementioned construction and functions have the following effects.

(1) The anchor frame or the anchor bolt retainer can be assembled at the direction site by transporting the component members. This facilitates the transporta tion of component members, and ensures- high accuracy in assembling the members, leading to improved posi tioning accuracy of the frame or the retainer with the anchor bolts.

(2) Because of a relatively few number of the component members involved, and of a 'simple overall construc tion, interference of the anchor frame with reinforc ing bars embedded in the concrete foundation can be reduced.

(3) The column base structure is hardly subjected to deformation due to the flow of concrete during place ant of the concrete foundation, making it possible to center align the anchor bolts with high accuracy.

(z) Connection of the anchor bolts to tite tipper anchor plate without the use of an anchor-bolt covering sleeve helps improve the anchorillg accuracy of the anchor bolts.

(5) By providing marks in advance on the outer periphery of the base plate of the column base metal fitting, the marking operation for machining anchor bolt holes on the column base metal fitting cato be eliminated.

This leads to reduced manufacturing cost of tite colunin base metal fitting.

(6) By providing marks in advance on the raised portion of the column base metal fitting, tie marking operation to indicate the center of the steel-frame column can be eliminated in welding the steel-frame colun to te column base metal fitting. Tis leads to reduced onan- hours in joining the steel-frame column.

(7) During on-the-site installation of the column base on the concrete foundation, positioning of the column base can be facilitated by matching the marks indicat ing the center of the steel-frame column provided on the concrete foundation with the corresponding marks provided on the base plate. This results in a reduc tion in manhours at the construction site.

(8) By providing vertical trougti holes in te outer contour of the raised portion of the column base metal fitting, the air is prevented from being entrapped during casting mortar into toe gap between the column base metal fitting and the concrete foundation. Thus, cavities caused by the entrapped air can be completely eliminated. As to result, the mortar can perfectly adhere to the bottom surface of the column base metal fitting, leading to a substantial improvement in the aseismic performance required of the column base structure.

(9) By setting the tension (stress intensity) introduced to Lite anchor bolts to 0.15 - 1.2#y' tite allowable yield strength of tite anchor bolts can be fully otti- lize, and a higher rotative rigidity of the column base can be gtoaranteed.

(10) A good performance (spindle-shaped righting moment characteristic) can be maintained against the posi tive/negative repetitive stress (bending moment gene rated in the column base) at the time of an eartioquake ( 11) By simplifying the dynamic mechanism of the column base, the performance (rotative rigidity and yield strength) of the column base can be accurately grasp ed. This leads to increased safety of the building.

(12) By interposing a flat washer of a predetermined size between the column base metal fitting and the nut, the bending yield strength and shearing yield strength of the column base can be increased simultaneously.

Claims

1. A base structure for a steel-frame column comprising vertically extending first support members mounted on a concrete substrate; horizontal second support members mounted on and extending between the .

first support members; an anchor bolt frame having anchor bolts with screw threads at either end extending vertically from the second support members; a lower anchor plate attached to the anchor bolts and secured thereto adjacent the second support members; and an upper anchor plate supported on the anchor bolts, the upper and lower anchor plates being secured by nuts on the threaded ends of the anchor bolts, and the support members and the anchor bolts being embedded in a concrete foundation such that the upper ends of the anchor bolts project thereover.

2. A base structure according to Claim 1 wherein the lower ends of the first support members are embedded in the concrete substrate.

3. A base structure according to Claim 1 wherein the support members are fitted to said concrete substrate via fixing bolts.

4. A base structure according to any preceding Claim wherein the second support members are secured to the lower anchor plate via nuts and bolts.

5. A base structure according to any of Claims 1 to 3 wherein the second support members are secured to the lower anchor plate by welding.

6. A base structure according to any preceding Claim wherein the thickness of at least one-of the upper and lower anchor plates greater than the thickness of other component members of the column base structure.

7. A base structure according to any preceding Claim wherein the thickness of at least one of the upper and lower anchor plates is enlarged around anchor bolt holes therethrough.

8. A base structure according to any preceding Claim including a base fitting secured to the upper ends of the anchor bolts by nuts thereon, the fitting having a base plate with a raised portion for supporting a said column.

9. A base structure according to Claim 8 wherein marks indicating the centre of the base fitting are provided on the outer periphery of the base fitting.

10. A base structure according to Claim 8 or Claim 9 wherein at least one vertical through hole is provided within the outer contour of the raised portion of the column base fitting.

11. A base structure according to any of claims 8 to 10 wherein a central mortar is disposed on the concrete foundation below the base fitting.

12. A base structure according to Claim 11 wherein at least one through groove is provided on the central mortar.

13. A column base structure according to Claim 11 or Claim 12 wherein the central mortar is formed into a shape corresponding to the flow line of mortar therearound.

14. A column base structure according to any of Claims 8 to 13 wherein the base plate of the base fitting is formed in such a manner that the thickness thereof gradually decreases from the base portion coming in contact with the raised portion toward the end portion thereof, and wherein the anchor bolts embedded in the concrete foundation in an- axially unrestrained state are joined after a tensile force 0.15 - 1.2 times the yield point of the anchor bolts is imparted thereto.

15. A base structure according to any of Claims 8 to 14 wherein a flat washer made of a steel for welded structures is interposed between the base fitting and each nut, the outside diameter and thickness of said flat washer are respectively at least 1.73 times and at least 0.13 times the outside diameter of the threaded part of the anchor bolts, and wherein the anchor bolts are made of a material having a tensile strength of 50 - 70 kg/mm2.

16. A column base structure comprising a steel-frame column integrally joined to a column base metal fitting comprising a raised portion formed into a planar shape corresponding to the contour of an end face of said steel-frame column, and a base plate formed into a flat plate, the column base metal fitting being joined to a concrete foundation via anchor bolts and nuts both of which secure a central mortar provided in advance on the concrete foundation and a mortar case after the installation of the base fitting and are embedded into said concrete foundation, wherein horizontal support members are fixedly fitted to the upper ends of support members projecting on a concrete substrate; an anchor bolt retainer formed by joining together upper and lower anchor plates via a plurality of connecting members is fixedly fitted to the horizontal support members; anchor bolts having threaded parts at the upper and lower ends thereof are secured via through holes provided on the upper and lower anchor plates constituting said anchor bolt retainer; and wherein the anchor bolts, excluding the upper threaded parts thereof, are embedded in said concrete foundation, together with the anchor bolt retainer.

17. A base structure according to Claim 16 wherein the lower ends of the support members are embedded in the concrete substrate.

18. A column base structure as set forth in Claim 16 or Claim 17 wherein the upper and lower anchor plates are fixedly fitted to the connecting members via nuts and bolts.

19. A base structure according to any of Claims 16 to 18 wherein the horizontal support and members are fixedly fitted to the anchor bolt retainer via nuts and bolts.

20. A column base structure according to any of Claims 16 to 18 wherein the horizontal support members are fixedly fitted to the anchor bolt retainer by welding.

21. A base structure according to any of Claims 16 to 20 wherein marks indicating the centre of the base fitting are provided in advance on the outer periphery of the base plate thereof.

22. A base structure according to any of Claims 16 to 21 wherein one or a plurality of vertical through holes are provided within the outer contour of the raised portion of the base fitting.

23. A base structure according to any of claims 16 to 22 wherein at least one horizontal through groove is provided on said central mortar.

24. A base structure according to any of claims 16 to 22 wherein the central mortar is formed into a shape corresponding to the flow line of mortar.

25. A base structure according to any of claims 16 to 24 wherein the base plate of the base fitting is formed in such a manner that the thickness thereof gradually decreases from the base portion coming in contact with said raised portion toward the end portion thereof, and wherein anchor bolts embedded in the concrete foundation in an axially unrestrained state are joined after a tensile force 0.15 to 1.2 times the yield point of the anchor bolts is imparted thereto.

26. A base structure according to any of claims 16 to 25 wherein a flat washer made of a steel for welded structures is interposed between the base fitting and each nut, the outside diameter and thickness of said flat washer being respectively at least 1.73 times and at least 0.13 times the outside diameter of the threaded part of the anchor bolts, and wherein the anchor bolts are made of a material having a tensile strength of 50 70 kg/mm2.

27. A base structure for a steel-frame column comprising vertically extending first support members mounted on a concrete substrate; horizontal second support members mounted on and extending between the first support members; and an anchor bolt frame having anchor bolts extending vertically from the second support members to an upper anchor plate supported on the anchor bolts, the base structure having been embedded in a concrete foundation with the anchor bolts projecting upwardly therefrom.

28. A base structure according to Claim 27 wherein the upper anchor plate is support on the anchor bolts above the concrete foundation.

29. A base structure according to Claim 27 or Claim 28 including a lower anchor plate attached to the anchor bolts, and secured thereto adjacent the second. support members.

30. A base structure according to Claims 27 to 29 wherein the upper and lower ends of the anchor bolts are formed with screw threads, which screw threads secure the anchor bolts to the upper anchor plate and the second members.

31. A base structure according to Claim 30 including a base fitting for securement of a said column secured on the base structure by means of bolts on the upper ends of the anchor bolts.

32. A base structure for a steel frame column substantially and described herein with reference to any of Figures 11 to 51 of the accompanyihg drawings.