US3736712A - Composite building structure and walls therefor - Google Patents

Abstract

A composite flexible-rigid building structure comprising a flexible skeleton structure and a plurality of bearing wall members having slits formed therein. The overall composite building structure normally behaves as a rigid structure for load smaller than a certain predetermined magntidue but transfers to a flexible structure upon occurrence of an extremely heavy load in excess of said magnitude. Each slit wall member normally acts as a rigid frame structure, and has a large ductility so as to absorb a large amount of seismic energy after being yielded at a certain predetermined load before complete failure.

Description

Uited States Patent [191 [111 3,736,712 Muto et al. [451 June 5, 1973 [54] COMPOSITE BUILDING STRUCTURE OTHER PUBLICATIONS AND WALLS THEREFOR Journal of American Concrete Institute, pages [75] Inventors: Kiyoshi Muto; Takao Itoh; Nobutsu- 909-918 June 1962.

all of Tokyo, Japan Engineering News-Record Jan. 9, 1947 pages 83, 84. [73] Assignee: Kajima Corporation, Tokyo, Japan i Primary Examiner-Alfred C. Perham [22] plied" 1972 Attorney-Roberts B. Larson, Andrew E. Taylor, [21] Appl. No.: 229,964 William R. Hinds et al.

Related US. Application Data [57] ABSTRACT I Continuation-impart of 5811 March 6, A composite flexible-rigid building structure compris- 1970* abandoned ing a flexible skeleton structure and a plurality of bearing wall members having slits formed therein. The ..52/l6E7645h25/ overall composite building Structure normally behaves [58] Field of Search ..52/l67,573, 198 as a Smaller than a i predetermined magntidue but transfers to a flexible [56] References Cited structure upon occurrence of an extremely heavy load in excess of said magnitude. Each slit wall member T D A E PATENTS normally acts as a rigid frame structure, and has a 845,046 2/1907 Bechtold ..52/l67 larlgfductmy as to a large amount 9 1,474,827 11/1923 Jones .52/174x seismic energy after being yielded at a certain 2,166,577 7/1939 Beckius ..52/l67 X predetermined l ad bef re comple e failure. 2,950,576 8/1960 Rubenstein ..52/l67X 16 Claims, 31 Drawing Figures D D D D D I I I I r Li I I I J I I I I I I I I I I I I B l I I I I I I I l I N I I I II I PAIENIEUJUH 5l975 $736,712

FIGJ lb PAIENIEUJUH 5191s SHEEI 5 [IF 9 PATENTEUJUH 5197s SHEET 7 BF 9 Mmmm-8642O Period, T (seconds) FIG.I3

Deformation (strain) FIG.I5

COMPOSITE BUILDING STRUCTURE AND WALLS THEREFOR This application is a continuation in part of application Ser. No. 17,062 filed March 6, 1970 and now abandoned.

This invention relates to a composite rigid-flexible building structure and a composite wall structure therefor. More particularly, the present invention relates to a composite rigid-flexible building structure applicable to a very tall multistoried building and a special wall structure therefor, which structure incorporates a plurality rows of slender slit walls vertically extending throughout the entire height of the building with suitable intervals between each other, whereby the rigidity of the structure varies in response to application of very large load thereto, e.g., an extremely large seismic force.

Generally speaking, the aseismatic structure of a very tall building is required to meet the following conditions.

1. The structure will not experience any excessively large deformation in the case of normally expected winds and frequently occurring earthquakes.

2. The structure should be capable of tenaciously bear sizeable deformations, if such deformations should be caused by rarely-happening extra heavy earthquakes.

3. The structure should warrant the necessary and sufficient levels of bearing strength.

4. The damping effects of a building skeleton, consisting of steel members alone, can be improved by using steel-reinforced concrete walls. The oscillation-absorbing effects and the specific bearing strength of such structure can further be improved as cracks are dispersed extensively throughout the concrete wall.

The inventors have succeeded in developing a composite rigid-flexible structure satisfying the aforesaid requirements. According to the present invention, there is provided a composite rigid-flexible structure for a multi-storied building, which comprises a steel skeleton and special steel reinforced concrete wall structures with slits, the wall structures being substantially integrally secured to the skeleton at each story. What is meant by the wall structure with slits" refers to a steel reinforced concrete wall structure which includes subsections separated by a plurality of pairs of mutually slidable abutting surfaces which are disposed in the wall structure in parallel with each other. Each pair of the mutually slidable surfaces is formed by embedding one or more strap-like members in the wall structure. The pair of mutually slidable surfaces defines a kind of slit, but the two surfaces abut with each other in such a manner that the abutting two surfaces do not allow air passage between them under normal conditions. The wall structures being cast in site or precast at works by using concrete having a high bearing strength against shearing while forming suitable slits therein. In one embodiment of the invention the wall structures thus formed are secured to the steel skeleton in a number of vertically extending groups at suitable intervals, each group consisting of two'or more rows of the wall structures extending vertically from the top to the bottom of the skeleton between a pair of adjacent columns of the skeleton. The steel skeleton is made by using shaped steels, such as H-shaped steels, boxshaped steels, cross steels, and the like.

Generally speaking, conventional aseismatic building structures use rigid wall members in order to prevent deformation of skeleton by the rigidity of the wall members, and to improve the strength of the skeleton. On the other hand, if the rigidity of the walls of a very tall multistoried building is too high, seismic load to the building becomes too large to adopt wall design with an economical cross section. Thus, the use of wall members with a large cross section tends to impair the elastic deformation characteristics of the structure.

In short, for extra-heavy earthquakes, which occur only very rarely, the so-called flexible structure without any highly rigid wall members is preferable. The flexible structure has a comparatively long period of its natural vibration and allows a comparatively large interstory deformation, or deformation between adjacent stories of the building. Accordingly, the flexible structure can deal with huge energy of very rare extra-heavy earthquakes, without using any massive skeleton.

On the other hand, for comparatively frequently occurring less heavy earthquakes and for strong winds, a rigid structure is more practical and preferable to the flexible structure, because the former allows only a small amplitude of vibration for such less heavy earthquakes and winds, as compared with that of the latter.

Therefore, an object of the present invention is to provide an ideal composite structure for very tall multistoried buildings, which normally acts as a rigid structure, but upon occurrence of an extra-heavy earthquakes, transfers to a flexible structure, so as to ensure a desired high bearing strength while allowing desirable deformations. Such transfer from the rigid construction to the flexible construction can be effected by releasing the rigidity of the wall members of the rigid structure upon occurrence of the aforesaid extraheavy earthquake.

In a steel reinforced concrete wall structure, precast or cast-in-site, if the dynamic strength of the wall structure is not continuous but suitably distributed with intermittent strong and weak portions, the wall structure may normally behave as a rigid structure but may completely lose its shearing strength upon application of a shearing load surpassing a certain level. More particularly, such wall structure may act as a rigid-frame, from the dynamic standpoint, for shearing loads of frequently occurring magnitude. Upon occurrence of an extra-heavy earthquake with an extremely large acceleration, however, the weak portions of the wall structure may yield, so that the overall strength of the wall structure may gradually varies, until the shearing strength of the wall structure is completely lost. If such wall structures are incorporated in building with a steel skeleton of flexible structure, and if the wall structures are so designed as to normally behave as rigid-frames but to completely lose their rigidity at a predetermined shearing load, the overall building structure will become rigid for normal load with a frequently occurring magnitude, while upon occurrence of extremely heavy load surpassing a certain predetermined magnitude, the building structure will become flexible.

The wall structure with the aforesaid distributed strength can be constructed by disposing weakened portions in the wall structure at certain intervals.

Therefore, another object of the present invention is to provide a wall structure which normally behaves as a rigid structure, but completely yields upon application of an extremely heavy shearing load in excess of a certain predetermined level.

For a better understanding of the invention, reference is made to the accompanying drawings, in which:

FIGS. Ia and lb are diagrammatic illustrations of the manner in which a conventional rigid wall yields upon application of a heavy shearing load;

FIGS. 2a and 2b are views similar to FIGS. la and 1b, illustrating the manner in which a wall with slits is deformed by application of a heavy shearing load;

FIG. 3 is a graph, illustrating the relation between load P and deformation '0, in the walls of FIGS. Ia, lb, and FIGS. 2a, 2b;

FIGS. 4a to 4d are schematic elevations, illustrating different dispositions of slits in a steel reinforced concrete wall structure, according to the present invention;

FIG. 5 is a schematic plan view of a known building structure, illustrating the disposition of walls therein;

FIGS. 6 to 8 are schematic plan views of different embodiments of the present invention, illustrating the disposition of walls of special structure, respectively;

FIG. 9 is a schematic elevation of an embodiment of the present invention, illustrating a disposition of special wall structures in a composite building structure;

FIG. 10 is a schematic elevation of a wall structure, according to the present invention;

FIGS. 111a and 11b are detailed partial sectional views of the wall structure of FIG. 10;

FIG. 110 is a side view of the wall structure of FIG. I0;

FIG. 12 is a graph, illustrating the relation between the height of a building and its natural period of vibration;

FIG. 13 is a schematic diagram, showing a typical range of discomfortable building swaying;

FIG. I4 is a graph showing typical values of earthquake acceleration at different periods, or vibratory frequencies, of earthquake vibration;

FIG. 15 is a graph showing the stress-strain characteristics of a known rigid building structure and a composite building structure, according to the present invention;

FIGS. Ma and 16b are graphs, showing ductility characteristics of slit wall structure, for different slit dispositions; and

FIGS. 17a to 17g are fragmentary sectional views, illustrating different constructions of a slit, to be incorporated in the wall structure according to the present invention, respectively.

Before entering the details of slit wall members to be used in the structure of the present invention, the basic principles of seismic composite building structures will be described.

Generally speaking, a steel building skeleton has its natural (fundamental) period of vibration, as shown in FIG. 12. The approximate natural period T seconds of a skeleton of height H meters is given by the following relation.

T=aH

here, a is a constant related to the rigidity of the skeleton.

What the equation (1) means is simply that, for a given height of the skeleton, its natural period is proportional to its rigidity. The inventors found that for most tall buildings, the aforesaid constant a is greater than 0.025 for suppressing the earthquake load to the skeleton as will be described hereinafter.

When a tall building is exposed to strong earthquakes, it sways, and dwellers of the building may feel discomfort as the magnitude of the swaying increases. It is reported that the discomfort depends both on the period of the swaying and on the magnitude of the acceleration and displacement of the swaying. FIG. I3 reproduces one of such report, i.e., Wind and Movement in Tall Buildings by FU-KUEI CHANG, Journal of Civil Engineering-ASCE, Aug. 1967. For instance, referring to FIG. 13, when a swaying is caused at a period of 4 seconds, or at a rate of 0.25 cycle per second, the dwellers do not usually feel any discomfort as long as the magnitude of swaying, or displacement 8, is less than about 2 inches. However, the dwellers feel annoying discomfort for swayings of greater than 2 inches at 0.25 cycle per second, if the acceleration is kept constant at 1.5 percent g (g being gravitational acceleration).

' As a design basis for removing such discomfort, the inventors translated the annoying range of FIG. 13 to a tolerable discomfort range, as shown by the dotted lines of FIG. 12. The procedure of the translation is as follows.

i. In FIG. 13, an average annoying limit was determined as shown by the dash-dot lines. With such average annoying limit of FIG. 13 in mind, for the period of 3 seconds, the maximum allowable displacement 8 is 2 inches (about 5 cm), and for 4 seconds of period, the maximum allowable displacement is about 4 inches (about 10 cm).

ii. It is known that the aforesaid displacement 8 is proportional to the building height H and the initial rigidity of the skeleton, as given by the-following equation.

here, R is a constant related to the initial rigidity of the skeleton.

The typical value of R is about 0.001 for usual tall buildings.

Thus, the maximum allowable height of the skeleton for a given maximum allowable displacement 6 is given by H=8/R. For instance, for 8 of 5 cm, H is 50 meters, and for 8 of 10cm, H is meters.

Since such maximum allowable displacements correspond to the natural periods of the skeleton, the average annoying limit curve of FIG. 13 can be translated into the plane of FIG. 12, point by point, e.g., for T=3 seconds, H=50 meters, and for T=4 seconds, T=l 00 meters. Thus, the inventors have found that the tolerable discomfort limit may, for instance, be given by It should be noted here that such limit depends on many factors, such as the rigidity of the skeleton,

- the annoying range of dwellers, etc.

Accordingly, the equation (3) is just an indication,

but does not have any limiting significance.

Referring to FIG. 14, earthquakes have different periods and different shearing forces. Based on statistics, the heavy solid curve of FIG. 14 is recommended by professional organizations as the basis for aseismatic structural design. What the curve of FIG. 14 means is that earthquakes with a short period have a large shearing force. As compared with a unit shear force for about 2.5 second period, the shear force of earthquake of 1 second period is 4 units, or four times as great.

Accordingly, building skeletons should not have a short natural period, because a skeleton with a short natural period tends to resonate with earthquake vibration of short period, and is exposed to a large shear force. Thus, for a tall building, the skeleton has to be flexible, and should not be rigid. This is why the constant a of the equation (1) is usually selected to be greater than 0.025 for tall buildings.

Referring to FIG. 12, if a skeleton having a constant a of greater than 0.025 becomes very tall, or the height H becomes large, the displacement 8 of the skeleton due to winds and minor earthquakes falls in the aforesaid discomfort range. In order to mitigate this difficulty, it has been a practice to increase the rigidity of the building structure for reducing its natural period T by reducing the a value. However, the increased rigidity inevitably reduces the natural period of the structure, inviting an increased earthquake load as a result. To provide for the high earthquake load, the building structure was made very heavy and expensive in past design.

As an example, a flexible skeleton having a natural period characteristics of T=0.035H will be considered. When this skeleton is used for a building of 170 meter height, its wind or earthquake displacement exceeds tolerable discomfort limit, as shown by the point P1 of FIG. 12. According to the conventional practice, the rigidity of the skeleton is increased by adding brace members or monolithic walls, for instance to the point P2 of FIG. 12. The structure of the point P2 has a natural period T of about 1.7 second, to which period the earthquake shear force of about 1.75 unit is recommended as a design base. The monolithic reinforcedwalls cannot bear such shear force, as will be explained hereinafter. Thus, expensive structural materials, such as steel braces, must be used to achieve the desired increase of the rigidity, to make the building costly.

What the present invention intends to accomplish is to add the slit walls to the skeleton of the point P1, so as to shift it to the point P3, as shown in FIG. 12. For the structure of the point P3, the natural period is about 2.5 seconds, and the recommended shear force is about 0.80 unit, as shown in FIG. 14.

It is apparent from FIG. that the structure of the point P3 withstand such shear force. If the structure of the point P3 is exposed to the earthquake causing the shear force of 1.75 unit, it will be deformed to the point B2 of FIG. 15, but it bears the shearing load. As a result, the H-T characteristics of the structure of the point P3 may be shifted to point P4 of FIG. 12.

Theoretically, it is possible to increase the rigidity of the structure of the point P1 of FIG. 12 to the point P3 by using ventilation walls, such as those disclosed by HE. Jones in his U.S. Pat. No. 1,474,827. However, with such ventilation walls, the structure cannot withstand the shear load of, e.g., 1.75 unit, as described hereinafter by referring to FIG. 15. In this case, the structure of the point P3 of FIG. 12 is directly shifted back to the original point P1, but cannot stop at any intermediate point between P3 and P1. In fact, the structure with ventilation walls collapses when the shear force exceeds 1.0 unit.

Referring to FIG. 15, the curves A, B, and C represent stress-strain characteristics of a flexible skeleton, a first composite structure having the flexible skeleton plus the slit walls, a second composite structure having the flexible skeleton and the monolithic reinforcedwalls, respectively. When an earthquake shear force of about 1.75 unit, in terms of normalized shear force based on the shear force for earthquake vibration of about 2.5 second period (FIG. 14), is applied to the second composite structure represented by the curve C of FIG. 15, the monolithic reinforced wall cannot withstand the shear force and completely collapses (due to brittle failure), so that the remaining flexible skeleton of the second composite structure, as represented by the curve A of steel skeleton alone, tries to bear this shear force but the skeleton collapses at the point X.

.Thus, the entire second composite structure collapses.

This means the monolithic reinforced-walls cannot withstand such earthquakes.

On the other hand, when the same earthquake shear force of about 1.75 unit is applied to the first composite structure as represented by the curve B of FIG. 15, the slit walls yield at the point B1, but the composite structure tries to bear the shear force with the strength of the flexible skeleton plus the ductility of the slit wall. Consequently, this first composite structure bears the shearing force of about 1.75 unit at the point B2 of FIG. 15. The first structure can bear shear forces up to the point Y of FIG. 15. In short, the slit walls are free from the so-called brittle failure, but they are ductile.

Such anti-earthquake strength cannot be achieved by the ventilation walls, because ventilation wall completely collapses at the point B1 of FIG. 15, and the entire load is shifted to the flexible skeleton A.

After such large shear force is removed; or after the heaviest earthquake load is over, the cracked slit walls may be replaced. It is apparent that the reconstruction of the completely collapsed second composite structure is much more costly than the replacement of the slit walls. Above all, the first structure with the slit walls is much safer for dwellers than the second structure, because the former withstand larger earthquake shear forces than the latter.

The slit wall to be used for providing the desired composite flexible strain-stress characteristics, as shown by the curve B of FIG. 15, will now bedescribed.

FIG. 1a shows a solid wall structure A without slits, while FIG. 2a showsa composite wall structure B with a plurality of slits S formed therein. If a shearing load Pa is applied to the solid wall structure A, as shown in FIG. la, there is produced a deformation 8,, as shown in FIG. lb. In the case of the solid wall structure A without any slits, large cracks C are suddenly generated before the deformation 8,, increases to a material magnitude. FIG. 3, Curve A illustrates such relation between the load P and the deformation 8 of the wall structure A.

Upon application of shearing load Pb to the composite wall structure B with slits S, as shown in FIG. 2a, there isproduced a deformation 8,, as shown in FIG. 2b.

With the slit wall B according to the present invention, the critical deformation 8,, at which the wall structure begins to crack, is much larger than the corresponding critical deformation 8,, for the known solid wall A, as shown in FIG. 3. The loads corresponding to the critical deformation 8 8,, or yielding strengths of the walls A, B, are shown by Pa, Pb, respectively.

After the beginning of the cracking, the cracks in the wall structure growfas the load thereto increases, until the cracks spread throughout the wall structure. If the load to the wall further increases, the wall structure soon fails in the case of the conventional wall A. With the slit wall B, according to the present invention, the wall structure further deforms even after its yield or after the cracks are spread therethrough. The ability of the wall to deform after its cracking is usually referred to as ductility. In FIG. 3, the critical load at the boundary between the cracking deformation and the ductility deformation is represented by Pa for the conventional wall A, and by Pb" for the slit wall B according to the present invention.

It is apparent from FIG. 3 that the conventional wall A fails soon after the end of its cracking, because it has little ductility. On the other hand, the slit wall B according to the present invention has a large ductility, so that it experiences a considerably large deformation after the end of its cracking deformation before its failure or rupture, absorbing more earthquake energy, even though the maximum strength of the slit wall is smaller than ordinary monolithic walls. Thus the critical safety is assured by this invention.

One of the important features of the slit wall B, according to the present invention, is in that it can absorb a noticeable amount of energy during the period from the moment when it begins to be cracked to its complete failure or rupture. The rupture strength of the slit wall B, or the load at which the wall B is failed, is represented by a symbol D while the corresponding rupture strength of the conventional solid wall A is shown by a symbol D in FIG. 3.

If the rupture strength D, as defined in FIG. 3, is so selected as to represent the individual wall structures share of that specific load to a building structure, which necessitates the transfer of the dynamical nature of the building structure from rigid to flexible, it is possible to provide an ideal building structure that normally behaves as a rigid structure for comparatively small loads, but transfers to a flexible structure upon occurrence of an extremely heavy load in excess of the aforesaid specific load. The magnitude of the rupture strength D of individual composite wall structure can be controlled by suitably adjusting the number and the shape of the slits S.

The composite wall structure B with slits S, as shown in FIG. 20, can be made of a precast concrete wall or a cast-in-site concrete wall. I

The composite wall structure will now be described in further detail, referring to FIGS. 10 to 1 1c and FIGS. 17a to 17 In FIGS. 10, Ha, 11b, and 110, a building skeleton consists of columns 1 and beams 2, and wall structures are fitted in lattice spaces defined by the columns and beams. For simplicitys sake, two different kinds of wall structures, both embodying the present invention, are shown in one elevation of FIG. 10. The left-hand portion of FIG. 10 partially illustrates a castin-site wall structure 3 with steel reinforcement, while the right-hand portion of the figure shows a wall structure including two or more precast concrete wall sections 4, also with steel reinforcement. Steel bars 5 are used for the reinforcement, as is shown in FIG. Ill.

In both cases of precast and cast-in-site concrete wall structure 3, a plurality of slits 6 are formed in the wall structure, in parallel with each other at suitable intervals. Preferably, a part of the wall structure 3 is left continuous in one direction across the entire span, despite the presence of the slit 6; for instance, the upper and bottom edges, as shown in FIG. 10.

In the case of the wall structure including the precast wall sections 4, mutually abutting edges of the adjacent wall sections 4 are bonded together at suitable spaced positions, as portions 7 of FIG. 10, while forming slits 6 therebetween. The connection of the precast wall sections 4 to the building skeleton, directly or indirectly, is effected by applying cement mortar grout 7 between the top and bottom edges of the wall sections 4 and the building skeleton members. The bonding portions 7 between the adjacent precast wall sections 4 are made, for instance, by providing projecting steel rods 5 at such portions of each wall section 4 and welding the projecting rods 5 at the portions 7 As pointed out in the foregoing, each slit 6 in the wall structure according to the present invention is made by forming mutually slidable abutting surfaces at the position of the slit 6. FIGS. 17a to 17g are-sectional views of different wall structure B, illustrating the manner in which such sliding surfaces are formed. Referring to FIG. 17a, a pair of strap-like bar members Sm are embedded in each slit portion 6 of the wall structure B, in such a manner that the bar members Sm are integrally secured to the wall structure B, but the two bar members Sm are slidable with each other while forming mutually slidable surfaces at the abutting portions thereof. Such mutually slidable surfaces form a slit 6, as shown in FIG. 17a. The two mutually slidable surfaces at each slit 6 abut with each other in such a fashion that no air passage is normally expected through the gap therebetween.

-It is an important feature of the present invention that the wall structure B is divided into a plurality of subsections by such slits 6. As a result, if the rigidity of the wall structure B is measured at different points thereof, the rigidity at a point in the subsection will be different from that at the slit 6. Thus, the slit wall structure B has a discontinuous distribution of rigidity. Nevertheless, the slit wall structure B behaves as an integral member for a load within a certain limit; namely, for any loads smaller than the yielding stress of the wall structure B. When a load in excess of its yielding stress is applied to the wall structure B, the individual subsections, each being defined by the adjacent slits 6, tend to behave somewhat separately. All the subsections are, however, bonded together at a certain portion thereof, as pointed out in the foregoing. As a result, the individual subsections tend to swell in response to the load in excess of the yielding stress. The mutually slidable abutting surfaces at each slit 6, however, act to resist against such swelling. Consequently, the slit wall structure B according to the present invention has a high ductility; namely, the slit wall structure undergoes a considerably large deformation after being yielded but before being broken down. Referring to FIG. 3, the magnitude of such ductility is defined as follows.

ductility rupturing deformation 8 lyielding deformation 8,,

In order to achieve a large ductility, as defined above, it is preferable to dispose the reinforcing steel rods in the subsection in such a manner that shearing breakdown stress (Kg/cm of the subsection is greater than bending yielding stress (Kg/cm) thereof.

The magnitude of the above defined ductility depends on the size and the disposition of the slits 6 in the wall structure B. Referring to FIG. 4a, slits 6 of length I may be disposed in the wall structure B in parallel with one edge of the wall structure, while leaving spacings l from the longitudinal ends of the slits 6 to facing edges of the wall structure B. The slits 6 may be spaced by uniform distances D between adjacent slits and between the edge of the wall structure B and the nearest slit 6. Tests were made on the effects of different slit dispositions, by measuring the following sway deformation angle R (radian) for sample slit walls having different dimensions.

here,

8, is rupturing deformation of the slit, and l is the length of the slit.

The results are shown in the following Table and FIGS. 16a and 16b.

TABLE R i' 15 D L 1 Ductility (5111. 5111. 515. l/D 15 1) 10 40. s 51 151. 0 1.15 0. 559 14. 55 5. 40.8 01. 151. 0 1.15 0.000 14. 05 5. 40. s 51 151. 5 1.15 o. 059 15. 84 0. 49. 5 55 245 0. 00 0. 750 8.9 a. 36 24 132 2. 5 I. 500 25. 56 6. 36 24 132 2. 5 1. 500 20. 99 3. 35 27 132 2. 22 1. 333 22. 59 5. 36 30 132 2. 0 1. 200 16. 5 2. a5 30 132 2. 0 1. 200 19. 75 a. as as 132 1.82 1.001 17.18 1. 36 33 132 1. 82 1. 091 20. 42 4. 39.0 2.15 152.0 2.512 1.514 25. 052 a. 39. 0 21. 6 132. 0 2. 512 1. 814 28. 693 4. 30.0 27.0 132.0 2.000 1.444 22.049 3. a9. 0 27. 0 132. 0 2. 000 1. 444 22. 400 4. 3a. 0 20. 5 132. 0 2. 491 1. 245 10. 700 s. 33. 0 20. 5 1:12. 0 2. 401 1. 245 17. 300 4. 33. 0 33. 0 132. 0 2. 000 1.000 18.202 3. 33. 0 33. 0 132. 0 2.000 1.000 20.000 4.

The inventors have found out that, for purposes of aseismatic structures, the aforesaid sway deformation angle R should preferably be greater than 14X10". To obtain such rupturing angular deformation, the following conditions must be satisfied, provided that the slit disposition as shown in FIG. 4a is used.

l /D 0.5 and l/D 1.0

The strapJike bar members S, for making the slit 6, as shown in FIG. 17a, is made of hard yet flexible material, which can form a slidable surface. Typical examples of such material include asbestos slates, plaster boards, synthetic resin, iron, and non-ferrous metals.

The construction of the individual slit 6 is not restricted to that as shown in FIG. 17a. Although the embodiment of FIG. includes the slit 6 extending through the entire thickness of the wall structure B, it is also possible to leave non-slitted portion or portions S, in its thickness, as shown in FIGS. 17b and 171:. Suitable sealing material S, may be applied to opposite edges of the mutually slidable abutting surfaces at the slit 6, as shown in FIGS. 17d and 17e. The slit 6 of FIG. 17d is almost as thick as the wall structure 8 itself, while the thickness of the slit 6 of the FIG. l7e represents only a small fraction of the thickness of the wall structure. FIG. 17f shows a slit 6 made by using only one metallic strap 8,, coated with frictionreducing films S thereon. FIG. 17g illustrates a slit construction, in which a metallic strap 8,, is sandwiched by a pair of non-metallic strap-like bar members S at the junction between two adjacent subsections of the wall structure B.

FIG. 4b shows a modification of the slit disposition of FIG. 4a by dividing each slit 6 into two parts which are spaced from each other in the longitudinal direction thereof. In the embodiment of FIG. 40, the slits 6 extend from one edge of the wall structure and terminate at about the central portion of the wall structure B, while FIG. 4d illustrates another slit disposition in which slits extend from opposite edges of the wall structure B and terminate at an intermediate portion of the wall structure B, so as to leave a suitable spacing between the extended ends of the slits 6. In other words, the length of each slit 6 is shorter than the distance between the opposite edges of the wall body, in the case of FIG. 4c; and the length of the slit 6 is shorter than one half of the distance between the opposite edges.

Thus, by incorporating those slit wall structures in a flexible skeleton structure, it is possible to provide a composite building structure, which behaves as a rigid structure by the initial rigidity of the wall structures for rather frequently occurring heavy seismic or wind load, but transfers to a flexible structure by yielding the wall structures upon occurrence of an extremely heavy rare seismic load. With the wall structures B of FIG. 2a, the entire wall of the composite building structure yields at a certain load and smoothly transfers to breakdown. Thus, the overall building structure smoothly and continuously transfers to the desired flexible structure. The wall structure B also ensures formation of a reliable flexible structure after being yielded.

FIG. 5 shows a schematic plan view of a building skeleton, according to a known system, which incorporates wall structures A without any slits. With conventional wall structures as depicted in FIG. 5, the desired aseismatic strength cannot be achieved. If slit wall structures A are disposed in a manner similar to FIG. 5, the building strength will somewhat be improved.

FIGS. 6 to 8 are schematic plan views of different embodiments of the composite building structure of the present invention, respectively. In the composite building structure of the invention, selected spans, each defined by adjacent steel columns, are vertically subdivided, so that a plurality rows of the slit wall structures B (two rows in the illustrated embodiments) are vertically disposed in each of the selected spans. Each row of the slit wall structures B extends vertically throughout the full height of the building, as shown in FIG. 9.

structure.

Conventional rigid building structure.

(FIG.

incapable of following large deformation.

Earthquake energy absorption is comparatively low, and hence, comparatively less safe.

Excessively large deformation is forcibly caused by the boundary beam effects.

Due to the concentration of rigid wall sections, stress level is high.

Due to the load concentration at rigid walls, stress distribution in the skeleton Composite building structure of the invention.

(FIGS. 6 to 10) Capable of following both small and large deformations. Earthquake energy absorption is comparatively high, and hence, comparatively safer.

The boundary beam effects are of reasonable magnitude.

Due to the distributed combination of wall structures with slits and skeleton, stress level is low.

Due to the load sharing to the skeleton, stress distribution between the skeleton and walls becomes and walls is uneven.

. even.

In other words, conventional rigid building structure with non-slender bearing walls, as shown in FIG. 5, is susceptible to bending deformation. Accordingly, excessively large stress is caused at lower stories, while excessively high reaction to bending of the skelton is generated at upper stories. Consequently, the conventional rigid building structure is less reliable and requires more steel structural material, resulting in an increased cost. Besides, floors at higher stories of the conventional building structure tend to considerably incline and horizontally move, in response to heavy loads. As a result, the habitability, or comfortableness, at the higher stories of the conventional building structure is inferior. The conventional building structure is also prone to breakdown due to excessive energy concentration therein.

On the other hand, the composite building structure of the present invention including wall structures with slits disposed in spaced vertical rows, as shown in FIGS. 6, 7, 8, 9, and 11, produces shearing deformation upon application of load thereto. The inclination and horizontal displacement at higher stories of the composite building structure of the invention are small. The stress caused in the composite building structure is comparatively small, to provide an improved bearing strength. In short, the composite building structure of the present invention fully utilizes the advantages of the flexible structure, while retaining the rigidity necessary for frequently occurring low stresses. Furthermore, with the composite structure of the present invention, the period of the natural vibration can easily be controlled, while maximizing the energy absorption therein.

Thus, the invention contribues greatly to the industry.

What is claimed is: I

I. A steel reinforced concrete wall having a discontinuous distribution of rigidity, comprising a concrete wall body;

steel reinforcing members distributed in the concrete wall body to reinforce the body;

a plurality of elongated strap-like bar members, each.

having at least one elongated surface whose width taken in the direction of the thickness of the concrete wall body being substantially identical with the thickness of the concrete wall body, said plurality of the bar members being embedded in said concrete wall body in parallel with each other; a plurality of pairs of mutually slidable abutting surfaces distributed in said concrete wall member in parallel with each other, at least one of each pair of abutting surfaces being formed by the elongated surface of said bar member; and plurality of subsections of the concrete wall member being defined by severing said concrete wall body and said reinforcing members at said pairs of mutually slidable abutting surfaces, in such a manner that the concrete wall member has a rigidity which is discontinuous at said abutting surfaces and yet the concrete wall member being a rigid integral wall as a whole unless a shearing load in excess of a certain yielding stress is applied thereto; the longitudinal length of said abutting surfaces and the distribution of said steel reinforcing members being so related that said abutting surfaces act to prevent each subsection from swelling when a stress greater than said yielding stress but smaller than a breakdown stress thereof is applied thereto. 2. A steel reinforced concrete wall according to claim 1, wherein said reinforcing concrete members in each subsection being so distributed that each subsection has a shearing breakdown stress (Kg/cm) which is greater than a bending yielding stress (Kglcm of the same subsection. v

3. A steel reinforced concrete wall according to claim 2, wherein each of said subsection has a ductility factor not smaller than three, said ductility factor being a (strain at breakdown)/(strain at yield) ratio.

4. A composite building structure having a skeleton with a breakdown strain 0-,(radians) and a plurality of steel reinforced concrete walls joined to said skeleton, each of said steel reinforced concrete walls, comprising a concrete wall body;

steel reinforcing members distributed in the concrete wall body to reinforce the body;

a plurality of elongated strap-like bar members, each having at least one elongated surface whose width taken in the direction of the thickness of the concrete wall body being substantially identical with the thickness of the concrete wall body, said plurality of the bar members being embedded in said concrete wall body in parallel with each other;

a plurality of pairs of mutually slidable abutting surfaces distributed in said concrete wall member in parallel with each other, at least one of each pair of abutting surfaces being formed by the elongated surface of said bar member; and

a plurality of subsections of the concrete wall member being defined by severing said concrete wall body and said reinforcing members at said pairs of mutually slidable abutting surfaces, in such a manner that the concrete wall member has a rigidity which is discontinuous at said abutting surfaces and yet the concrete wall member being a rigid integral wall as a whole unless a shearing load in excess of a certain yielding stress is applied thereto;

the longitudinal length of said abutting surfaces and the distribution of said steel reinforcing members being so related that said abutting surfaces act to prevent each subsection from swelling when a stress greater than said yielding stress but smaller than a breakdown stress thereof is applied thereto, said reinforcing concrete members in each subsection being so distributed that each subsection has a shearing breakdown stress (Kg/cm which is greater than a bending yielding stress (Kg/cm of the same subsection, and

a ductility factor not smaller than three, said ductility factor being a (strain a (radian) at breakdown)/(- strain o' (radian) at yield) ratio, whereby said composite building structure has a breakdown strain a (radian) which is identical with the sum of said skeleton breakdown strain o-,(radian) and said wall subsection breakdown strain raidan) (o';,=o' +0' 5. A steel reinforced concrete wall according to claim 1, wherein each of said bar members is made of a material selected from the group consisting of asbestos slates, plaster boards, synthetic resin, iron, and nonferrous metals.

6. A steel reinforced concrete wall according to claim 5, wherein each of said bar members consists of a single bar made of a material selected from said group.

7. A steel reinforced concrete wall according to claim 5, wherein each of said bar members consists of two bars made of a material selected from said group.

8. A steel reinforced concrete wall according to claim 1, wherein said concrete wall body is of rectangular shape including one side length of (1+ 2l ),and the length of each of said strap-like bar members is l, and the bar members are disposed in said concrete wall member with a uniform spacings of D between each other in parallel with said wall member side of length (l l while leaving a spacing 1 from other sides of the wall member to facing ends of the bar member, the dimensions D, l, and l satisfying conditions of l /D 0.5 and l/D l.0..

9. A composite wall structure according to claim 4, wherein natural period T (second) of the skeleton is related to the height H (meter) of the skeleton as follows: T 0.025H.

10. A composite building structure according to claim 4, wherein said skeleton is a steel skeleton.

11. A steel reinforced concrete wall according to claim 1, wherein said subsections are precast steel rein- I forced concrete wall sections, and said strap-like bar members are disposed at joints between the adjacent precast wall sections.

12. A composite wall structure according to claim 4, wherein said steel reinforced concrete wall members are disposed in at least two vertical rows in parallel with vertical columns of said skeleton.

. 13. A steel reinforced concrete wall according to claim 1, wherein said strap-like bar member is coated with a friction-reducing film.

14. A steel reinforced concrete wall according to claim 8, wherein each said strap-like bar members is divided in two parts which are spaced from each other in the longitudinal direction thereof.

15. A steel reinforced concrete wall according to claim 1, wherein said strap-like bar members extend from one edge of the wall body toward the opposite edge to said one edge and terminate at an intermediate position before reaching the opposite edge.

16. A steel reinforced concrete wall according to claim 1, wherein said strap-like bar members extend from each of the two opposing edges of the wall body by a length shorter than one half of the distance between the two opposing edges.

Claims (16)

1. A steel reinforced concrete wall having a discontinuous distribution of rigidity, comprising a concrete wall body; steel reinforcing members distributed in the concrete wall body to reinforce the body; a plurality of elongated strap-like bar members, each having at least one elongated surface whose width taken in the direction of the thickness of the concrete wall body being substantially identical with the thickness of the concrete wall body, said plurality of the bar members being embedded in said concrete wall body in parallel with each other; a plurality of pairs of mutually slidable abutting surfaces distributed in said concrete wall member in parallel with each other, at least one of each pair of abutting surfaces being formed by the elongated surface of said bar member; and a plurality of subsections of the concrete wall member being defined by severing said concrete wall body and said reinforcing members at said pairs of mutually slidable abutting surfaces, in such a manner that the concrete wall member has a rigidity which is discontinuous at said abutting surfaces and yet the concrete wall member being a rigid integral wall as a whole unless a shearing load in excess of a certain yielding stress is applied thereto; the longitudinal length of said abutting surfaces and the distribution of said steel reinforcing members being so related that said abutting surfaces act to prevent each subsection fRom swelling when a stress greater than said yielding stress but smaller than a breakdown stress thereof is applied thereto.

2. A steel reinforced concrete wall according to claim 1, wherein said reinforcing concrete members in each subsection being so distributed that each subsection has a shearing breakdown stress (Kg/cm2) which is greater than a bending yielding stress (Kg/cm2) of the same subsection.

3. A steel reinforced concrete wall according to claim 2, wherein each of said subsection has a ductility factor not smaller than three, said ductility factor being a (strain at breakdown)/(strain at yield) ratio.

4. A composite building structure having a skeleton with a breakdown strain sigma 1(radians) and a plurality of steel reinforced concrete walls joined to said skeleton, each of said steel reinforced concrete walls, comprising a concrete wall body; steel reinforcing members distributed in the concrete wall body to reinforce the body; a plurality of elongated strap-like bar members, each having at least one elongated surface whose width taken in the direction of the thickness of the concrete wall body being substantially identical with the thickness of the concrete wall body, said plurality of the bar members being embedded in said concrete wall body in parallel with each other; a plurality of pairs of mutually slidable abutting surfaces distributed in said concrete wall member in parallel with each other, at least one of each pair of abutting surfaces being formed by the elongated surface of said bar member; and a plurality of subsections of the concrete wall member being defined by severing said concrete wall body and said reinforcing members at said pairs of mutually slidable abutting surfaces, in such a manner that the concrete wall member has a rigidity which is discontinuous at said abutting surfaces and yet the concrete wall member being a rigid integral wall as a whole unless a shearing load in excess of a certain yielding stress is applied thereto; the longitudinal length of said abutting surfaces and the distribution of said steel reinforcing members being so related that said abutting surfaces act to prevent each subsection from swelling when a stress greater than said yielding stress but smaller than a breakdown stress thereof is applied thereto, said reinforcing concrete members in each subsection being so distributed that each subsection has a shearing breakdown stress (Kg/cm2), which is greater than a bending yielding stress (Kg/cm2) of the same subsection, and a ductility factor not smaller than three, said ductility factor being a (strain sigma 2(radian) at breakdown)/(strain sigma 2(radian) at yield) ratio, whereby said composite building structure has a breakdown strain sigma 3(radian) which is identical with the sum of said skeleton breakdown strain sigma 1(radian) and said wall subsection breakdown strain sigma 2(raidan) ( sigma 3 sigma 1+ sigma 2).

5. A steel reinforced concrete wall according to claim 1, wherein each of said bar members is made of a material selected from the group consisting of asbestos slates, plaster boards, synthetic resin, iron, and non-ferrous metals.

6. A steel reinforced concrete wall according to claim 5, wherein each of said bar members consists of a single bar made of a material selected from said group.

7. A steel reinforced concrete wall according to claim 5, wherein each of said bar members consists of two bars made of a material selected from said group.

8. A steel reinforced concrete wall according to claim 1, wherein said concrete wall body is of rectangular shape including one side length of (l + 2l0), and the length of each of said strap-like bar members is l, and the bar members are disposed in said concrete wall member with a uniform spacings of D between each other in parallel with said wall member side of length (l + l0) while leaving a spacing l0 from other sides of the wall member to facing ends of the bar member, the dimensions D, l, and l0 satisfying conditions of l0/D > or = 0.5 and l/D > or = 1.0.

9. A composite wall structure according to claim 4, wherein natural period T (second) of the skeleton is related to the height H (meter) of the skeleton as follows: T > or = 0.025H.

10. A composite building structure according to claim 4, wherein said skeleton is a steel skeleton.

11. A steel reinforced concrete wall according to claim 1, wherein said subsections are precast steel reinforced concrete wall sections, and said strap-like bar members are disposed at joints between the adjacent precast wall sections.

12. A composite wall structure according to claim 4, wherein said steel reinforced concrete wall members are disposed in at least two vertical rows in parallel with vertical columns of said skeleton.

13. A steel reinforced concrete wall according to claim 1, wherein said strap-like bar member is coated with a friction-reducing film.

14. A steel reinforced concrete wall according to claim 8, wherein each said strap-like bar members is divided in two parts which are spaced from each other in the longitudinal direction thereof.

15. A steel reinforced concrete wall according to claim 1, wherein said strap-like bar members extend from one edge of the wall body toward the opposite edge to said one edge and terminate at an intermediate position before reaching the opposite edge.

16. A steel reinforced concrete wall according to claim 1, wherein said strap-like bar members extend from each of the two opposing edges of the wall body by a length shorter than one half of the distance between the two opposing edges.

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