Description

PRECAST STAIRWAY SYSTEM, UNIT STRUCTURE THEREOF, AND METHOD OF CONSTRUCTING STAIRWAY

SYSTEM USING THE SAME

Technical Field

[1] The present invention relates to a precast stairway system, a precast stair unit structure of such a precast stairway system, and a method of constructing a precast stairway system using such precast stair unit structures. In particular, the present invention relates to a high or ultra-high strength fiber-reinforced cement composite precast stairway system, the strength of which is in the range of 60 to 200 MPa, and which is relatively superior in flexible behavior and excellent in water-tightness and endurance, a precast unit structure for use in assembling such a precast stairway system, and a method of economically and efficiently constructing a precast stairway system while ensuring the good construction quality of the stairway system. Background Art

[2] In general, a vertical moving line in a building, in particular in a high-rise building is connected by installing an elevator together with a stairway system. However, difficult and complicate work conditions are accompanied when constructing such a stairway, because stairs of the stairway should be connected with top and bottom slabs within a narrow stair hall space and such a stairway takes a complicated shape including a vertically inclined shape, unlike conventional construction members, such as slabs and vertical wall bodies.

[3] At present a method of fabricating a one-piece type concrete stairway is usually employed when constructing a residential or commercial-residential apartment or a low-rise or high-rise building for business or shopping center.

[4] However, when such a stairway is constructed using ferroconcrete, there are several problems in that it is necessary to perform difficult and time-consuming processes, such as assembling of molds for fabricating an inclined stair slab, distribution of reinforcing rods, and assembling of molds for fabricating treads of respective stairs, and those processes should be followed by engineering works for finishing or plastering uneven surfaces of the treads. Moreover, constructing such a stairway system is inferior in view of economical efficiency and productivity because it is labor-intensive and requires a long construction period.

[5] In order to solve these problems, in the prior art, there has been proposed a ferroconcrete precast stairway system, which is constructed by a method comprising steps of: anchoring a floor landing and an intermediate landing to a wall body, placing a con-

ventional precast ferroconcrete stairway on the floor landing and intermediate landing and then adhering the stairway to the floor landing and intermediate landing using mortar. However, such a conventional ferroconcrete precast stairway system has a limitation in applicability as a transportable precast stairway because it fails to reduce the weight and volume as compared with a conventional cast-in-place concrete stairway due to its opposite lateral sides, which are formed by continuously connected right-angled triangle shapes. Furthermore, such a conventional precast stairway also has a problem in that because it has a continuous length from a floor landing to an intermediate landing or from an intermediate landing to a floor landing, which renders the precast stairway very massive and bulky, it is troublesome and inconvenient to transport and install such a precast stairway in position. In addition, in this method, it has been proposed to install a precast stairway through a process, which comprises steps of: constructing a stair hall, installing one or more intermediate landings and one or more floor landings, placing one or more precast stairways on the intermediate and floor landings, and anchoring the precast stairways using mortar. In practice, however, this process cannot be amicably employed in the construction field because such a precast stairway cannot provide a working space nor a moving line in the course of construction because the slabs and wall body are not simultaneously cast, thereby causing various inconveniences in construction.

[6] Therefore, in the prior art, there has been proposed another method for solving the above-mentioned problems. For example, U.S. Patent No. 5,203,128 discloses a precast stairway, wherein individual precast stairs, each of which consists of a generally vertical riser portion and a tread portion, are anchored to a pair of parallel stringers (i.e., flights) using screws. However, the '128 patent does not present a precast stair unit structure, which consist of a plurality of integrally interconnected stairs, at all, because a fiber-reinforced cement composite is not used for constructing such a precast stairway. Therefore, there is a troublesome in that it is necessary to anchor individual stairs using anchoring devices such as bolts so as to interconnect the stairs. Furthermore, each stair has a rib at the top portion of the front side of the stair so as to increase the strength thereof, and the rib projects from the front side of the stair. As a result, a walker may get wounded by tripping over the rib.

[7] In order to solve the problems encountered when constructing the above-mentioned conventional ferroconcrete stairway, it has been proposed to use a prefabricated iron- frame stairway connection structure in the prior art. In this method, iron-frame stairways, which are fabricated by coupling iron-frame units, are attached to a building structure. This method is superior in convenience in construction, stability, quality characteristic of stairway, and easiness of reducing construction period. However, because it is necessary to weld each tread unit when fabricating a stairway, serious

problems, such as high labor costs and deformation of the stairway caused by welding heat, are caused in the initial stairway fabrication stage in the method. In addition, due to the property of the metallic material of the finished iron-frame stairway, such a stairway is especially weak to fire and produces serious noise due to walking loads applied to the stairway when one or more persons ascend or descend the stairway. Moreover, because the sheet metals of the stairway are thin, geometrical moment of inertia is reduced, whereby the stairway may suffer from a deflection phenomenon by weight while the stairway is in use.

[8] In order to solve some of the above-mentioned problems of iron-frame stairways, there has been proposed another method for providing an improved iron-frame stairway, in which double tread units are lap-joined so as to reduce noise and deflection caused by walking loads and the tread units and stringers are connected by bolting so as to improve the easiness of fabrication and installation as well as the functionality of such a stairway. However, such a stairway is not sufficiently superior to a conventional ferroconcrete stairway in view of manufacturing costs. Furthermore, it is expected that the manufacturing costs of such an iron-frame stairway will be continuously increased for a long time in company with the recent increase of prices of row materials.

[9] As described above, constructing a ferroconcrete stairway in a ferroconcrete building is a labor-intensive and difficult work which requires accuracy and a long period of time. However, until now, there has not been proposed a suitable technique which is satisfactory in view of economical efficiency, utility and quality characteristic.

[10]

Disclosure of Invention Technical Problem

[11] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a fiber-reinforced cement composite precast stairway system, which has a high or ultra-high strength of 60 MPa to 200 MPa and is relatively superior in flexible behavior as compared to an existing high strength concrete structure, whereby exhibiting excellent endurance and high load carrying capacity, and which is also excellent in water-tightness and noise reduction characteristic for reducing noise which is produced by walking loads exerted to the stairs.

[12] Second object of the present invention is to provide a fiber-reinforced cement composite precast stairway system, which is excellent in construction characteristic in that it can be installed by being simply placed on a predetermined position without

performing a support installation work and a mold forming work for fabricating a stairway itself in the construction field, thereby reducing the period of fabricating a stairway and the labor cost, which result in the saving of construction cost and the shortening of period of construction work.

[13] Third object of the present invention is to provide a prefabricated fiber-reinforced cement composite precast stairway system.

[14] Fourth object of the present invention is to provide a prefabricated fiber-reinforced cement composite precast stairway system, which can reduce the manufacturing and transport costs.

[15] Fifth object of the present invention is to provide a unit structure which is applicable for economically and efficiently fabricating a precast fiber-reinforced cement composite stairway according to any of the first to fourth objects of the present invention.

[16] Sixth object of the present invention is to provide a method of economically and efficiently constructing a fiber-reinforced cement composite precast stairway system according to any of the first to fourth objects of the present invention.

[17]

Technical Solution

[18] According to first aspect of the present invention for achieving the above- mentioned first to fourth objects, there is provided a precast stairway system comprising: a stairway formed by connecting a plurality of stair unit structures one after another, each of which comprises at least one stair having at least one tread and at least one riser, which are integrally formed with each other; and a pair of stringers coupled with the stairway, wherein each of stair unit structures is a high-strength fiber reinforced cement composite body, which is formed of a mixture of cement, fine aggregate, filler, fine ceramic powder, water reducing agent, steel fiber, and water, the mixture ratio of which is 1: 0.9-1.7: 0.1-0.3: 0.02-0.1: 0.01-0.06: 0.03-0.2: 0.2-0.45, and which has a post-cure strength of 60 MPa to 100 MPa.

[19] According to second aspect of the present invention for achieving the above- mentioned first to fourth objects, there is provided a precast stairway system wherein each of the stair unit structures is an ultra-high strength fiber-reinforced cement composite body, which is formed of a mixture of cement, fine aggregate, filler, fine ceramic powder, water reducing agent, steel fiber, and water, the mixture ratio of which is 1: 0.8-1.5: 0.2-0.4: 0.05-0.3: 0.02-0.07: 0.05-0.4: 0.18-0.3, and which has a post-cure strength in the range of 100 MPa to 200 MPa.

[20] According to third aspect of the present invention for achieving the first to fourth objects, there is provided a precast stairway system, wherein at least one of the

stringers in the above-mentioned aspects is formed of a metallic material or a high strength or ultra-high strength fiber-reinforced cement composite as mentioned above.

[21] According to fourth aspect of the present invention for achieving the first to fourth objects, there is provided a precast stairway system, at least one reinforcing bar is embedded per one tread of each stair unit structure in the above-mentioned aspects so as to reinforce the load carrying capacity of the tread in the stair unit structure, and the opposite ends of the reinforcing bar are physically connected with and supported by both of the stringers.

[22] According to fifth aspect of the present invention for achieving the first to fourth, there is provided a precast stairway system further comprising connection members, each of which has a reinforcing member for interconnecting the top horizontal areas or bottom horizontal areas of the stringers in the first to third aspects, and a plurality of reinforcing bars which are perpendicularly connected to the reinforcing member.

[23] According to another aspect of the present invention for achieving the fifth object, there is provided a precast stair unit structure, wherein the stair unit structure is formed of a mixture of cement, fine aggregate, filler, fine ceramic powder, water reducing agent, steel fiber, and water, the mixture ratio of which is 1: 0.8-1.7: 0.1-0.4: 0.02-0.3: 0.01-0.07: 0.03-0.4: 0.18-0.45 and which has a post-cure strength of 100 MPa to 200 MPa, and the stair way unit comprises at least one stair having at least one tread and at least one riser, which are integrally formed with each other, wherein each stair has an insertion ridge formed at one end thereof and an elongated insertion groove formed at the other end, whereby a plurality of stairs are connected one after another so as to form a stairway.

[24] According to another aspect of the present invention for achieving the sixth object, there is provided method of constructing a precast stairway system comprising steps of: assembling a plurality of fiber-reinforced cement composite precast stair unit structures in the above-mentioned aspects, and fixing the stair unit structures to a pair of stringers using screws, thereby forming a precast stairway; after or simultaneously with forming the precast stairway system, anchoring two connection members to the top and bottom horizontal areas of the stringers, respectively, each of the connection members having a reinforcing member and a plurality of reinforcing bars which are perpendicularly connected to the reinforcing member; placing stair landing beams, each of which is provided with at least one reinforcing bar, on supports at the areas where one or more floor landings and an intermediate landing are formed; placing the precast stairway with the anchored connection members on the stair landing beams; assembling molds for constructing the floor landings, the intermediate landing and a wall body, in such a manner that one of the stringers can be used as a mold in a position where the stringer can be embedded in and fixed to the wall body to be

constructed; and pouring concrete into the molds so as to simultaneously and integrally form the floor landings, the intermediate landing, and the wall body.

[25]

Advantageous Effects

[26] As described above, the inventive fiber-reinforced cement composite precast stairway system is superior in endurance and load carrying capacity while having a high or ultra-high strength in the range of 60 MPa to 200 MPa, due to its relatively excellent flexible behavior. In addition, it has excellent water-tightness and excellent noise reducing performance as to walking noise. Furthermore, it is possible to simply and easily provide the inventive prefabricated high strength or ultra-high strength fiber-reinforced cement composite precast stairway system by using one or more the above-mentioned fiber-reinforced cement composite precast stairway unit structures. As a result, it is possible to install such a stairway system by bearing stairway landing beams without fabricating molds or supports for the stairway itself, and then simply placing one or more stairway unit structures on the stair landing beams. In addition, as a stringer may be used instead of some of molds for forming a wall body, it is possible to integrally form the wall body and stairway landings by assembling molds for stairway landings and the wall body and then simultaneously pouring concrete into all the moldings. In addition, in the course of construction, not only the precast stairway can serve as a working passageway, but also the wall body can support the load of one or both inclined stringers in the course of construction, as a result of which labor cost curtailment, construction cost curtailment owing to short construction period, manufacture/transport cost curtailment, and the shortening of construction time can be promoted. Moreover, by substituting the inventive prefabricated fiber-reinforced cement composite precast stairway system for a conventional concrete or steel frame stairway system, which is labor-intensive and time-consuming in construction, epochal improvements will be provided in view of saving construction costs and shortening construction period. Consequently, it is expected that the inventive stairways will be substituted for a considerable fraction of conventional concrete or steel frame stairway systems. Brief Description of the Drawings

[27] The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[28] FIGS. 1 to 3 are exploded perspective views of precast stairway systems according to preferred embodiments of the present invention, in which several parts are omitted;

[29] FIGs. 4 to 7 are perspective view showing female-screw type stair unit structures

according to preferred embodiments of the present invention; [30] FlGs. 8 to 11 are perspective view showing male-screw type stair unit structures according to preferred embodiments of the present invention; [31] FlGs. 12 and 13 schematic views exemplifying a tread for a female-screw type stair unit structure and a tread for a male-screw type stair unit structure, respectively, wherein the left part of each figure is a side view of the corresponding treads and the right part is a cross-sectional top plan view; [32] FlG. 14 is a schematic view exemplifying how an inner stress distributing joint member and an outer stress distributing joint member are joined together from the inner and outer surfaces of a stringer of a precast stairway system according to a preferred embodiment of the present invention; [33] FlG. 15 is a cross-sectional side view of a stringer for a precast stairway system according to a preferred embodiment of the present invention; [34] FlGs. 16 to 18 is a schematic view showing the connected condition of stair unit structures to a stringer according to a preferred embodiment of the present invention when the inventive precast stairway system is assembled; [35] FlG. 19 is a perspective view showing a stringer having a plurality of tread insertion grooves, which are formed on the inner surface of the stringer; [36] FlGs. 20 to 22 are perspective views of stair unit structures which are applicable to the stringer of FlG. 19; [37] FlG. 23 is a schematic view illustrating the inventive method of constructing a stairway system, in which a precast stairway according to a preferred embodiment of the present invention is placed on stair landing beams, and then floor landings and an intermediate landing are simultaneously constructed; [38] FlG. 24 is a schematic side view showing the inventive method for simultaneously constructing the floor landings, intermediate landing and a wall body in the embodiment of FlG. 23;

[39] FlG. 25 is a cross-sectional view taken along line I-I in FlG. 24; and

[40] FlG. 26 is a schematic view showing a preferred embodiment of a stairway landing beam to be used in the inventive method of constructing a stairway system. [41]

Best Mode for Carrying Out the Invention [42] Hereinafter, several preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same reference numerals are used to designate the same or similar components, so that repeated description on the same or similar components will be omitted.

[43] FlGs. 1 to 3 are exploded perspective views showing high strength or ultra-high strength fiber-reinforced cement composite precast stairway systems 1, Ia and Ib according to preferred embodiments of the present invention, wherein some parts are omitted in the drawings. Since the basic constructions of the precast stairway systems are substantially identical to each other, they are described in unison for the purpose of convenience in description.

[44] A precast stairway system 1, Ia or Ib comprises a stairway 10, and two inclined stringers 20 (optionally an inclined concrete stringer 20 and an inclined iron stringer 21), which are positioned at the both sides of the stairway 10, respectively, and connection members 31 for use in connecting top ends and bottom ends of the inclined lateral plates 20 to a floor landing (see reference numerals 3 and 4 in FlG. 23) or an intermediate landing (see reference numeral 2 in FlG. 23. Since such a stairway 10 is supplied to a construction field in a precast form, a complicated procedure for constructing a stairway can be simplified, thereby reducing labor costs and the time period for constructing such a stairway, which results in saving of construction costs. In addition, because such a stairway system is realized by assembling stringers (preferably, having a post-cure strength of 100 MPa to 200 MPa) and treads (typically, having a post-cure strength of 60 MPa to 200 MPa), which are formed of a high or ultra-high strength cement composite, it is possible either to prefabricate a precast stairway system with a transportable weight, which cannot be obtained in any sense using an existing concrete, or to install such a stairway system by simply placing the stairway in position without installing scaffolding (support) and fabricating molds.

[45] According to the present invention, the stairway 10 and stringers 20 (assuming that the stringers are not formed from an iron plate) are typically formed from a mixture of cement, fine aggregate, filler, fine ceramic powder, water-reducing agent, steel fiber, and water, the mixture ratio of which is 1: 0.9-1.7: 0.1-0.3: 0.02-0.1: 0.01-0.06: 0.03-0.2: 0.2-0.45, and which has a post-cure strength of 60 to 100 MPa and a post- cure void fraction of not more than 7%, typically in the range of 3 to 7%. If desired, the mixture ratio of cement, fine aggregate, filler, fine ceramic powder, water-reducing agent, steel fiber, and water may be 1: 0.8-1.5: 0.05-0.3: 0.02-0.07: 0.05-0.4: 0.18-0.3, the post-cure strength may be 100 to 200 MPa, and the post-cure void fraction may be not more than 5%, typically in the range of 3% to 5%. Preferably, the stairway 10 may be a high strength fiber-reinforced cement composite body, which has a post-cure strength of 60 to 100 MPa, and the stringers 20 may be ultra-high strength fiber-reinforced cement composite bodies, which has a post-cure strength of 100 MPa to 200 MPa.

[46] Due to the inclusion of steel fiber, the inventive precast stairway system 1 or Ia exhibits a flexible behavior, which has never been founded in a conventional high

strength concrete stairway system. In addition, it exhibits excellent water-tightness due to the low void fraction and has a sufficient structural load carrying capacity and endurance due to the high or ultra-high strength thereof. Moreover, the inventive precast stairway system 1 or Ia is excellent in noise reduction effect for reducing noises caused by walking loads.

[47] In the above-mentioned mixed components, it is desired for the fine aggregate to contain silica sand (SiO ) not less than 90%, typically in the range of 90 to 99.9%, wherein the mean grain size of the silica is not more than 0.7 mm, typically in the range of 0.1 to 0.7 mm. However, the present invention is not limited to this.

[48] In the above-mentioned mixed components, it is desired for the filler to contain silica sand (SiO ) not less than 97%, typically in the range of 97 to 99.9%, wherein the mean grain size of the silica is not more than 20 D, typically in the range of 3 to 20 D. However, the present invention is not limited to this.

[49] In the above-mentioned mixed components, fine ceramic powder may be selected preferably but not exclusively from silica fume, blast furnace slag, fly ash, fine limestone powder, and combination thereof, and silica fume is more preferable.

[50] For the water-reducing agent in the above-mentioned mixed components, any water-reducing agent may be used, which is well-known or available as "ultra high performance water-reducing agent" in the art, wherein for a high strength fiber- reinforced cement composite which has a post-cure strength of 60 MPa to 100 MPa, the water-reducing agent should allow the cement composite to have sufficient flowability when the ratio of water to cement in the cement composite is in the range of 20% to 45%, and for an ultra-high strength fiber-reinforced cement composite, which has a post-cure strength of 100 MPa to 200 MPa, the water-reducing agent should allow the cement composite to have sufficient flowability when the ratio of water to cement in the cement composite is in the range of 18% to 30%. Because various kinds of such ultra high performance water-reducing agents are commercially available from various companies and well-known in the art, additional description thereof is omitted.

[51] In addition, in the above-mentioned mixed components, the steel fiber preferably but not exclusively has a mean length of not more than 30 mm, typically in the range of 0.3 mm to 30 mm, a mean diameter of not more than 0.5 mm, typically in the range of 0.1 mm to 0.5 mm, and a shape factor in the range of about 60 to 70, preferably of about 65. Any metallic wire may be used as the steel fiber without any limitation if it has a strong toughness. However, in general, steel wire may be preferably used as the steel fiber. The inclusion of steel fiber will alleviate the brittle behavior of a conventional high strength concrete and render a flexible behavior characteristic to the resultant composite.

[52] The stairway 10 and the stringers 20 (assuming that the stringers are not formed from an iron plate) are formed in high strength fiber-reinforced cement composite precast structures by thoroughly stirring the above-mentioned components using a mixer which can allow all the components, in particular, the steel fiber to be evenly dispersed, thereby forming a cement composite, pouring the cement composite into molds, stripping the molds after 0.5 to 2 days, in general 1 day have passed from the pouring of the components into the molds, steam-curing the cement composite for 48 to 72 hours under a temperature of not less than 20°C, typically in the range of 20°C to 100°C (in the case of a high strength fiber-reinforced cement composite) or under a temperature of not less than 70°C, typically in the range of 70°C to 100°C (in the case of an ultra-high strength fiber-reinforced cement composite), and under a relative humidity condition of 80% to 100%, whereby a precast structure having a post-cure strength of 60 MPa to 100 MPa is fabricated. AS being steam-cured under a high temperature, dry shrinkage and creep deformation are caused and completed in the high strength fiber-reinforced cement composite within a short time, no specific structural deformation occurs after the stairway system is constructed.

[53] The inventive high strength fiber-reinforced cement composite precast stairway system 1 is described again with reference to FlG. 1.

[54] In the example shown in the drawing, the inventive high strength fiber-reinforced composite precast stairway system 1 comprises: a stairway 10, which consists of a plurality of treads 11 and risers 12 with a riser 12 being interposed between two adjacent treads 11, whereby the treads 11 being continuously connected with each other via the risers 12; two metallic stringers 21 (for example, stringers made of iron); and two connection members 30 for connecting top ends and bottom ends of the stringers 21 with a floor landing or an intermediate landing (not shown), respectively, wherein although the treads 11 may have their own endurance against tension due to the inclusion of steel fiber, two reinforcing bars 117 (for example, iron reinforcing rods) may embedded in each tread 11 with female screws 16 being formed adjacent to opposite ends of the reinforcing bars 117, which will be described later, as shown in FlG. 12, so as to ensure firm endurance against tension, and screw holes 14 are exposed from the opposite sides of each tread 11, so that male screws 53 can be inserted into the screw holes 14 from the outer surfaces of the iron stringers 21, thereby being fitted in the screw holes 14, respectively.

[55] Whether the above-mentioned reinforcing bars 117 are arranged or not in each tread and how many reinforcing bars 117 are arranged in each tread are not critical but optional for the present invention. If arranged, two or three reinforcing bars are typically arranged.

[56] The above-mentioned stairway 10 comprises one or more precast stair unit struct

ures 110, 120, 130 and 140, each of which has one or more stairs (preferably one to four stairs), which are integrally formed with each other and each of which has a tread 113 and a riser 111. Each of the stair unit structures 110, 120, 130 and 140 has an insertion ridge 112 at one end and an elongated insertion groove 12 at the other end, so that two or more precast stairway unit structures 110, 120, 130 and 140 can be assembled with each other so as to form a precast stairway 10 and hence a precast stairway system 1 or Ia.

[57] The thickness of each tread 11 is not essential but optional for the present invention.

However, the thickness is preferably not more than 7 cm, and more preferably not more than 5cm, so as to reduce the weight of the treads 11.

[58] The high strength fiber-reinforced cement composite precast stairway unit structures, which are assembled to one another so as to form the above-mentioned stairway 10, will be described in more detail with reference FIGs. 4 to 13.

[59] Each of the stringers 21 has a top horizontal area 28, an inclined area 27, and a bottom horizontal area 29 as usual, and further comprises fastening holes 24, which are formed through the stringer 21 in such a way as to correspond in position to the screw holes 115, wherein female screws 16 are formed in the screw holes 115, respectively, adjacent to the opposite ends of the embedded reinforcing bars 117, (see FIG. 12), whereby it is possible to fasten the treads 11 to the stringer by inserting anchoring means such as bolts 53 so that the bolts 53 are engaged with the female screws 16.

[60] Next, inner stress-distributing joint members 40 and outer stress-distributing joint members 50 for use in interconnecting the stairway 10 and the stringers 21 are described with reference to FIG. 14 together with FIG. 1.

[61] The inner stress-distributing joint members 40 may be applied to the inner surfaces of the stringers 21 in order to alleviate stress concentration around the reinforcing bars 117 when interconnecting the treads 11 of the stairway 10 and the stringers 21. Each of the inner stress-distributing joint members 40 has a body 42, through which two through-holes 44 are formed, a pair of wings 41, which are vertically spaced with a distance corresponding to the thickness of the treads 11 and extend inwardly from the body 42, and a supporting and anchoring extension 43.

[62] Meanwhile, each of the outer stress-distributing joint members 50 is formed in a rectangular shape and has fastening holes 52, which are formed in such a way as to correspond in position to the screw holes 115 having female screws 16 adjacent to the opposite ends of reinforcing bars 117 embedded in a tread 11.

[63] Therefore, the screw holes 115 in the opposite sides of the respective treads 11 of the stairway 10 in FIG. 1, the through-holes 44 of the inner stress-distributing joint members, the fastening holes 24 in the stringers 21, and the fastening holes 52 in the inner stress-distributing joint members 40 are fastened with each other by the bolts 53.

At this time, because the opposite side portions of each tread 11 are respectively fitted in the spaces between the wings 41 of the stress distributing connectors 40, stresses can be effectively distributed.

[64] Consequently, plural inner stress-distributing joint members 40 are firmly secured to the inner surfaces of the stringers 21 in such a way that the extensions 43 and bodies 42 of the connectors 40 are abutted against and supported by the inner surfaces of the stringers 21, and plural outer stress-distributing joint members 50 are horizontally arranged on and abutted against the outer surfaces of the stringers 21 in such a manner as to correspond in position to the inner stress-distributing joint members 40, respectively. As a result, when the treads 11 and the stringers 20 are interconnected, the stress concentration occurring around the reinforcing bars 117 (for example, iron reinforcing bars) can be alleviated, thereby distributing stresses to the opposite sides of the treads 11. Furthermore, the spaces between the stringers 21 and the stairway 10 are filled up by the inner stress-distributing joint members 40, whereby either the permeation of water from the top side to the bottom side of the stairway 10 or the passage of contaminant can be prevented.

[65] Next, connection members 30 for use in interconnecting a precast stairway 10 and a floor landing or an intermediate landing (not shown) are described.

[66] Each of the connection members 30 shown in the drawing has a plurality of reinforcing bars 32, which are perpendicularly screwed or welded to a reinforcing member 31 as mentioned above. The reinforcing bars 32 have a length of not more than 1 m and each preferably take a form of a headed bar (not denoted by a reference numeral) so as to sufficiently increase the adhesion force in relation to the floor landing or intermediated landing. Meanwhile, it is also possible to form reinforcing bars 32a on the top and bottom horizontal areas 28 and 29 of both stringers 21.

[67] Although it is exemplified that screw holes (not denoted by a reference numeral) are formed adjacent to the opposite ends of the reinforcing members 31 of the connection members 30 and female screws (not denoted by a reference numeral) are positioned in the screw holes, it is possible to form male screws on the opposite ends of the reinforcing members 31, which extends beyond the opposite lateral sides of each tread.

[68] Simultaneously with or after assembling the stairway 10 and both of the stringers

21, bolts 28b and 29b are inserted into fastening holes (not denoted by a reference numeral) formed through reinforcing plates 28a and 28b (which are optional) of the top and bottom horizontal areas 28 and 29 of the stringers 21 in a state in which the opposite ends of the connection members 30 are abutted against the inner surfaces of the top and bottom horizontal areas 28 and 29 of the stringers 21, and then fitting the bolts 28b and 29b into the screw holes 37 formed at the opposite ends of the reinforcing members 31, whereby the reinforcing members 31 can be firmly anchored to

the stringers 20.

[69] The inventive precast stairway system 1 assembled in this manner is constructed in the following manner: temporarily supporting stair landing beams 60 (see FlGs. 23 to 26) using supports (not shown), placing the top and bottom ends of both stringers 31 of the precast stairway 1 on the stair landing beams 60, then fabricating molds over the above-mentioned connection members 30 and the reinforcing bars 32 exposed from the connection members 30, and pouring concrete into the molds, thereby forming floor landings 3 and 4 (see FlG. 23) and an intermediate landing 2 (see FlG. 23) along with a wall body (which will be described later with reference to FlGs. 24 and 25), wherein the top ends and bottom ends of the stairway 10 are integrally connected with a floor landing 3 or 4 and the intermediate landing 2, respectively, without a gap.

[70] In the inventive fiber-reinforced cement composite precast stairway system, it is of course possible that one of the stringers is formed from a metallic material and the other is formed of a fiber-reinforced cement composite material.

[71] Referring to FlG. 2, the fiber-reinforced cement composite precast stairway system

Ia according to another preferred embodiment of the present invention is substantially same with that shown in FlG. 1 in construction, except that the stringers 21 of FlG. 1 are formed of a metallic material whereas both of the stringers 20 for the fiber- reinforced cement composite precast stairway system Ia are formed of a fiber- reinforced cement composite material, and that as will be described with reference to FlGs. 8 to 11 and 13, reinforcing bars 117 project from the opposite sides of the treads 11, and male screws 118 are formed on the projecting ends of the reinforcing bars 117 so as to be firmly engaged with female screws 51 on the outer surfaces of outer stress- distributing joint members 50, which are positioned on the outer surfaces of the stringers 20. Therefore, the additional description of the fiber-reinforced cement composite precast stairway system Ia is omitted.

[72] Referring to FlG. 3, the fiber-reinforced cement composite precast stairway system

Ib according to another embodiment of the present invention is same with that shown in FlG. 2 beyond connection members 30. The connection members 30 shown in FlG. 3 are same with those shown in FlG. 2 in that they are perpendicularly connected with reinforcing members 31, respectively, and each of them has a plurality of reinforcing bars 32, which may be headed bars. Only one difference between the connection members 30 of FlG. 3 and those shown in FlG. 2 is that the above-mentioned reinforcing members 31 of FlG. 3 are embedded in a prismatic concrete body of a square, rectangular or trapezoidal cross-section. Therefore, the fiber-reinforced cement composite precast stairway system Ib is not described any further.

[73] Now, stair unit structures 110, 120, 130 and 140 according to preferred embodiments of the present invention, which are assembled to the inventive fiber-

reinforced cement composite precast stairway systems 1, Ia a and Ib, are described with reference to FlGs. 4 to 13.

[74] At first, the stair unit structures 110, 120, 130, 140, 110a, 120a, 130a and 140a may be classified into two types; in a first type (female screw type), female screws 115 and

114 are formed adjacent to the opposite ends of reinforcing bars 117, wherein the reinforcing bars 117 are embedded in treads 11 of a stairway 10 (see FlG. 1), a stringer 21 is placed in such a way as to be in contact with the one side of the stairway 10, respectively (see FlG. 1), and then bolts (not shown) are engaged with the female screws

115 and 116 through the stringer 21, thereby anchoring the stringer 21, as shown in FlGs. 4 to 7 and 12, and a second type (male screw type), male screws 118 are formed on the opposite ends of reinforcing bars 117, wherein the reinforcing bars 117 are embedded in the treads 11 of a stairway 10 and the opposite ends of the reinforcing bars 117 extend from the both sides of the treads 11 of the stairway 10 (see FlGs. 2 and 3), a stringer 20 is placed in such a way as to be in contact with one sides of the treads

11 and the male screws 118 formed on the corresponding ends of the reinforcing bars 117 extend through the stringer 20 (see FlGs. 2 and 3), and then nuts (not shown) are engaged with the male screws 118, which extend through the stringer 20, thereby anchoring the stringer 20, as shown in FlGs. 8 to 11 and 13.

[75] The inventive stairway sections 10 are constructed according to the following manner: the stringers 20 and stair unit structures 110, 120, 130, 140, HOa, 120a, 130a, and 140a are cast and cured (of course, if the stringers 21 are formed of a metallic material, only the stair unit structures 110, 120, 130, 140, HOa, 120a, 130a, and 140a are cast and cured), and then the stringers 20 and the stair unit structures 110, 120, 130, 140, 110a, 120a, 130a, and 140a are assembled with each other, thereby forming a one- piece precast stairway 10, and then moving the precast stairway 10 to a stairway placing position in the construction field using a crane, and then installing the stairway 10.

[76] According to the present invention, although the number and area of iron reinforcing bars as the reinforcing bars 117 are optional and variable depending on the magnitude of safety load for a finished stairway system, typically two or three iron reinforcing bars are embedded in each tread 11.

[77] FlGs. 4 to 7 are perspective views showing female type stair unit structures 110,

120, 130 and 140, respectively, wherein the inventive fiber-reinforced cement composite stair unit structures 110, 120, 130 and 140 may have a high or ultra-high strength. If they are have a high strength, they are formed of a mixture of cement, fine boding material, filler, fine ceramic powder, steel fiber and water, the mixing ratio of which are 1: 0.9-1.7: 0.1-0.3: 0.02-0.1: 0.01-0.06: 0.03-0.2: 0.2-0.45, and which has a post-cure strength of 60 MPa to 100 MPa, wherein each of the stair unit structures

has one to four stairs, each stair having a tread 113 and a riser 111, which are integrally formed. Each stair unit structure has an insertion ridge 113 at one end thereof and an elongated insertion groove 114 at the other end thereof, so that a plurality of such stair unit structures are connected one after another by fitting the insertion ridge of one stair unit structure into the elongated insertion groove in another stair, thereby forming a stairway section 10 (see FIGs. 1 to 3).

[78] Since the fabrication process of the stairway 10 has been described above with reference to FIG. 1, the additional description thereof is omitted.

[79] The stair unit structure 110 of FIG. 1, which is a female type, comprises a tread 113 having an elongated insertion groove 114 formed at the front end of the bottom side thereof, and a riser 111 having an insertion ridge 112 formed at the top end thereof and extending vertically from the tread 113, wherein the tread 113 and the riser 111 is integrally formed with each other. Alternatively, the tread 113 may be formed with a plurality of anti-slip grooves 116 at the front area of the top side thereof. Furthermore, plural reinforcing bars 117 (for example, iron reinforcing rods) are embedded in the tread 113, female screws (not denoted by a reference numeral) are formed adjacent to the opposite ends of the reinforcing bars 117 in the tread, respectively, and screw holes 115 are exposed in the opposite sides of the stair unit structure 110. Therefore, when forming a stairway section 10 (see FIG. 1), a plurality of stair unit structures 110 are assembled in such a manner that the insertion ridge 112 of one stair unit structure 110 is inserted into the elongated insertion groove 114 of a second unit structure, and the insertion ridge 112 of the second stair unit structure 110 is inserted into the elongated insertion groove 114 of a third stair unit structure 110.

[80] The female-screw type stair unit structures 120, 130 and 140 shown in FIGs. 5 to 7 are formed by integrally connecting two to four female-screw type stair unit structures 110 shown in FIG 4 and are essentially identical in detailed construction to the above- mentioned stair unit structure 110. Therefore, the additional description for the female- screw type stair unit structures 120, 130 and 140 is omitted.

[81] FIG. 12 schematically shows an example of a tread 113 for the female-screw type stair unit structures 110, 120, 130 and 140, wherein the left part of the drawing shows a left side view and the right part shows a cross-sectional top plan view. The tread 113 comprises two or three reinforcing bars 117 embedded in the tread 113, and female screws 16 in screw holes 15, which are formed in the tread 113 adjacent to the opposite ends of the embedded reinforcing bars 117 and opened to the outside of the tread 113.

[82] Therefore, in the female-screw type stair unit structures 110, 120, 130 and 140, bolts are fitted into the screw holes 115 through the stringers 21 from the outer surfaces of the stringers 21, thereby interconnecting the stairway 10 and the stringers 21 as described above with reference to FIG. 1.

[83] FlGs. 8 to 11 are perspective views showing male-screw type stair unit structures

HOa, 120a, 130a and 140a, respectively, wherein the reinforcing bars 117 are essentially identical to those shown in FlGs. 4 to 7, except that the reinforcing bars 117 shown in FlGs. 8 to 11 are embedded in the tread 113 without any female screws, and male screws 118 are formed on the exposed ends of the reinforcing bars 117. Therefore, the additional description for the reinforcing bars 117 is omitted.

[84] FlG. 13 schematically shows an example of a tread 113 for the male-screw type stair unit structures HOa, 120a, 130b and 140a, wherein the left part of the drawing shows a left side view and the right part shows a cross-sectional top plan view. The tread 113 comprises two or three reinforcing bars 117, embedded in the tread 113 and the opposite ends of the reinforcing bars 117 are exposed to the outside of the tread 113, wherein male screws 118 are formed on the exposed ends of the reinforcing bars 117.

[85] Therefore, in the male-screw type stair unit structures 110a, 120a, 130a and 140a, nuts 51 are fitted on the male screws 118 extending through the stringers 20, thereby interconnecting the stairway 10 and the stringers 21, as described above with reference to FlG. 2.

[86] Iron molds may be usually used so as to fabricate the above-mentioned stair unit structures 110, 120, 130 and 140 because such molds are repeatedly used. However, in consideration of the easiness of fabricating molds and costs of the molds, it is possible to use plastic or fiber-reinforced plastic molds.

[87] Alternatively, it is also possible to fabricate a stair unit structure and/or a stringer according to the present invention in a desired color by previously mixing and stirring an organic or inorganic pigment with the materials of the stair unit structure and/or the stringers, and then casting and curing the materials, whereby it is possible to simplify or omit the coloring work, which is performed as finishing work after completing the construction of a stairway system.

[88] Now, a stringer 20 is further described with reference to FlG. 15. The stringer 20 is formed in a conventional form having a top horizontal area 28, an inclined area 27 and a bottom horizontal area 29, and a plurality of fastening holes 24 are formed through the stringer 20 in such a manner as to correspond in position to the reinforcing bars 117 embedded in the treads 11 (each tread may have two or three reinforcing bars 170 as described above) and extending from the opposite sides of the treads 11, thereby allowing the reinforcing bars 117 to extend through the fastening holes 24 so as to interconnect and support the treads 40 and the stringer 20. The stringer 20, which is a precast member fabricated from a fiber-reinforced cement composite, takes the tensile strength of the fiber-reinforced cement composite body (about 15 MPa), which is sufficient for a stringer. However, it is possible to ensure the reinforcement of such a

stringer in tensile strength by embedding one or more curved reinforcing bars (for example, bent iron reinforcing rods with upwardly oriented ends, which are not shown) or a reinforcing wire mesh 26 in the stringer 20 as shown in the drawing, wherein the amount and embedding position of the reinforcing bars or the reinforcing wire mesh 26 can be determined by calculating such a tensile strength that the stringer can sufficiently bear the tensile load occurring in the stringer 20.

[89] If desired, it is possible to provide a guide bar or a safety fence above the stringer

20 so as to protect the old and the weak.

[90] Although optional for the present invention, the thickness of the stringer 20 is preferably not more than 10 cm and more preferably not more than 7 cm, so as to reduce the weight of the stringer 20.

[91] FlGs. 16 to 18 schematically show examples for forming stairway systems by assembling a plurality of various stair unit structures 110, 110b and 110c, each of which forms a single stair, wherein reference numeral 27 denotes an inclined area of a stringer 20 or 21.

[92] FlG. 16 shows stair unit structures 110, each of which is identical to that shown in

FlG. 4, FlG. 17 shows stair unit structures 110b, each of which takes a variant form, as compared with that shown in FlG. 4, wherein a stair unit structure 110b comprises a tread (not denoted by a reference numeral) having an insertion ridge (not denoted by a reference numeral) at the rear end of the top side thereof, and a riser (not denoted by a reference numeral) extending downward from the front end of the tread and having an elongated insertion groove (not denoted by a reference numeral) formed at the lower end thereof, the tread and the riser being integrally formed with each other, and FlG. 18 shows stair unit structures 110c, each of which takes another variant form, wherein a stair unit structure 110c has a tread, a front riser extending downward from the front end of the tread and having an elongated insertion groove (not denoted by a reference numeral) at the lower end thereof, and a rear riser extending upward from the rear end of the tread and having an insertion ridge (not denoted by a reference numeral) at the top end thereof, the tread and the front and rear risers being integrally formed with each other.

[93] When interconnecting the inventive unit stair structures 110, 110b and 110c shown in FlGs. 16 to 18 as well as other stair unit structures HOa, 120, 130a, 130, 130a, 140, and 140a shown in FlGs. 5 to 11, no anchoring means such as bolts are used at all.

[94] Meanwhile, in order to more ensure the distribution of stresses in the inventive precast stairway and to obtain a stable precast stairway system, it is possible to form rectangular grooves 210 for inserting treads (denoted by reference numeral 11 in FlGs. 1 to 3) on the inner surface of the stringer 20 as shown in FlG. 19.

[95] If the stringer 20 has rectangular grooves 210 as shown in FlG. 19, it is necessary to

use stair unit structures 110', 110b' and 110c', which are modified to be suitable for such a stringer 20 as shown in FlGs. 20 to 22. The stair unit structures 110', 110b' and 110c' are essentially the same with the unit stair structures 110, 110b and 110c shown in FlGs. 16 to 18, respectively, except that each tread 113 has extensions 113a, which integrally extend from left and right sides of the tread 113, so that the extensions 113a can be inserted into and supported by the rectangular grooves 210 on a corresponding stairway carriage 20, thereby ensuring the distribution of stresses. Therefore, the additional description of the stair unit structures 110', HOb' and HOc' is omitted.

[96] Of course, it is possible to form stair unit structures 110', 110b' and 110c having extensions 113a, which are integrally formed with treads 113 at the left and right sides of the treads 113 as mentioned above, in a male screw type like the above-mentioned male screw type stair unit structures, and the existence of reinforcing bars 117 is not essential but optional for the present invention.

[97] FlG. 23 schematically shows the inventive method of constructing floor landings 3 and 4 and an intermediate landing 2 together with a wall body (denoted by reference numeral 80 in FlG. 25) after placing the inventive precast stairways 10 on stair landing beams 60, which are carried by supports 90.

[98] At first, the stair landing beams 60 are described with reference to FlG. 26.

Although it is possible to form such a stair landing beam 69 with a high strength fiber- reinforced cement composite, it is desired to form it with an ultra-high strength fiber- reinforced cement composite.

[99] Specifically, such a stair landing beam may be formed from a mixture of cement, fine aggregate, filler, fine ceramic powder, water reducing agent, steel fiber and water, the mixture ratio of which is 1: 0.9-1.7: 0.1-0.3: 0.02-0.1: 0.01-0.06: 0.03-0.2: 0.2-0.45, and has a post-cure strength of 60 MPa to 100 MPa, a void fraction of not more than 7%, typically in the range of 3% to 7%. However, it is more preferable that such a stair landing beam is formed from a mixture of cement, fine aggregate, filler, fine ceramic powder, water reducing agent, steel fiber and water, the mixture ratio of which is 1: 0.8-1.5: 0.2-0.4: 0.05-0.3: 0.02-0.07: 0.05-0.4: 0.18-0.3, and has a post- cure strength of 100 MPa to 150 MPa, a void fraction of not more than 5%, typically in the range of 3% to 5%.

[100] The above-mentioned stair landing beam 60 has at least two reinforcing bars 61 embedded in the stair landing beam 60, and reinforcing members 62 provided adjacent to the opposite ends of the reinforcing bars 61, respectively, wherein the reinforcing bars 61 extend beyond the reinforcing members 62, whereby the extensions 63 of the reinforcing bars 61 are exposed to the outside of the stair landing beam 60. In addition, a plurality of ribs 64 are embedded in the stair landing beam 60 and extend from the top surface of the stair landing beam 60, thereby being exposed. The front side of the

stair landing beam 60 may be formed in an inclined extension 65, which is not essential but optional for the present invention.

[101] The extensions 63 of the reinforcing bars 61 extending from the stair landing beam

60 are provided for the purpose of integrating the stair landing beam 60 with an wall body after concrete casting, thereby enhancing the structural stability of the stairway, and the ribs 64 exposed to the top of the stair landing beam 60 are provided for the purpose of giving sufficient adhesion strength between the stair landing beam 60 and concrete after concrete casting, wherein the stair landing beam 60 and the concrete will form a floor landing or an intermediate landing.

[102] The stair landing beam 60 has a thickness (height) of about 5 cm if a stair landing (a generic term for floor landing and intermediate landing) has a thickness of about 15 cm, for example. Further, the stair landing beam 60 should have a minimum width to be capable of supporting a stringer 20 and take a form for facilitating the arrangement of iron reinforcing rods in a stair landing slab.

[103] As shown in FIG. 23, the above-mentioned stair landing beams 60 are employed in order to reinforce the bearing force of molds, because such molds do not provide sufficient bearing force to such an extent for allowing a precast stairway 10 to be placed on the molds, and such a precast stairway 10 is placed on the stair landing beams 60, which are born by supports 90.

[104] In the drawing, reference numeral 32 indicates reinforcing bars.

[105] FIG. 24 is a schematic side view showing the inventive method for simultaneously constructing floor landings 3 and 4, an intermediate landing 2 and a wall body (denoted by reference numeral 80 in FIG. 25), and FIG. 25 is a cross-sectional view taken along line I-I in FIG. 24.

[106] Referring to FIG. 24, the top horizontal area 29 and the bottom horizontal area 28 are placed on the stair landings 60, respectively, and the stair landings 60 are born by supports 90. In the shown example, molds for forming the wall body may consist of a plurality of standardized rectangular molds 80 (i.e., an area positioned outside of the region defined by Vl, hi, V2 and h2) and a plurality of standardized triangular molds 70a, which are in contact with an inclined area 27 in a region which is positioned on a stringer 20 (i.e., an area positioned inside of the region defined by Vl, hi, V2 and h2), wherein the stringer 20, which is one of the stringers for the precast stairway 10, serves as a mold. In the drawing, reference numerals 2 and 4 indicate an intermediate landing and a floor landing, respectively.

[107] As shown in FIG. 25, the stringer 20, which serves as a mold, is located at a position where it can be embedded and anchored in a wall body 80 to be constructed (i.e., at a position on a plane which is not coplanar with the molds 70 and 70a but offset into the wall body 80, so that the stringer 20 can be fixedly supported by the wall

body 80), whereby the wall body 80, the floor landings 3 and 4, and the intermediate landing 2 are simultaneously formed, so that the precast stairway 10 is capable of providing a work space and a moving line in the course of construction. As a result, such a precast stairway can be very economically and effectively utilized.

[108] Meanwhile, regardless of the fact that the molds of a wall body are either permanent molds or temporary molds, it is easy to form the wall body molds, some of which are formed by a stringer instead of existing molds.

[109] Although several preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Industrial Applicability

[110] The present invention relates to a precast stairway system, a precast stair unit structure of such a precast stairway system, and a method of constructing a precast stairway system using such precast stair unit structures. In particular, the present invention relates to a high or ultra-high strength fiber-reinforced cement composite precast stairway system, the strength of which is in the range of 60 to 200 MPa, and which is relatively superior in flexible behavior and excellent in water-tightness and endurance, a precast unit structure for use in assembling such a precast stairway system, and a method of economically and efficiently constructing a precast stairway system while ensuring the good construction quality of the stairway system.

[Ill]

[112]