WO2023172027A1

WO2023172027A1 - Inverted u-shaped pc modular structure with integral bottom part

Info

Publication number: WO2023172027A1
Application number: PCT/KR2023/003102
Authority: WO
Inventors: 이홍재; 배규웅
Original assignee: 주식회사 케이씨산업; 주식회사 케이씨엠엠씨; 한국건설기술연구원
Priority date: 2022-03-08
Filing date: 2023-03-07
Publication date: 2023-09-14
Also published as: KR20230132070A

Abstract

The present invention relates to an inverted U-shaped PC modular structure with an integral bottom part and, more specifically, to an inverted U-shaped PC modular structure with an integral bottom part, the structure having a bottom part integrally formed on the upper part of a body part that has an inverted U-shaped cross section, so that the upper surface of a lower PC modular structure becomes a bottom plate of an upper PC modular structure when the PC modular structure is stacked. One preferred embodiment of the present invention comprises: a horizontal plate-shaped ceiling plate; side plates each provided vertically downward from the ends on both sides thereof in the width direction of the ceiling plate; and a bottom part formed integrally with the ceiling plate so as to protrude upward from the upper surface of the ceiling plate by the width of the distance between a pair of side plates.

Description

Inverted U-shaped PC modular structure with integrated bottom

The present invention relates to an inverted U-shaped PC modular structure with an integrated bottom. More specifically, the bottom part is formed integrally with the upper part of the main body having an inverted U-shaped cross-section, so that when the PC modular structures are stacked, the upper part of the lower PC modular structure is formed. It relates to an inverted U-shaped PC modular structure in which an integrated bottom portion is formed so that the surface becomes the bottom plate of the upper PC modular structure.

Starting in 1988, the pillars and beams that make up the building's frame were converted to PC (Precast Concrete). Currently, the Singapore government mandates that more than 65% of the building's frame be made of PC, and in the 2000s, PBU (factory-made prefabricated toilet unit; Prefabricated Bathroom Unit (Prefabricated Bathroom Unit) has been activated, and the building's bathrooms are currently constructed with 100% PBU.

Therefore, in recent years, concrete PC units have been manufactured in the form of a box so that they can be freely inserted or removed into the frame for a wall structure or a frame for a ramen structure, as well as used for both remodeling and new construction and expansion of buildings.

However, the conventional box-shaped PC unit is not only very difficult to demold because a mold must be installed inside and then demolded when producing a box-shaped closed cross-section, and the weight of the PC unit itself is heavy, so the lifting load increases when lifting. In particular, there were problems such as difficulty in joining vertically or horizontally between unit structures made of PC.

The technology behind the present invention includes Patent Registration No. 0995646, “Building Unit Insertion Type Building” (Patent Document 1). In the above background technology, 'a frame for a wall structure consisting of a wall and a slab and equipped with facilities; And, a unit building unit consisting of a unit floor slab and a unit wall vertically coupled to the upper part of the unit floor slab, wherein the unit building unit includes a unit floor slab facing the outside, or a unit floor slab and a unit wall. A rail wheel coupled to a; is included, and the frame for the wall structure includes a slab or a guide rail coupled to the slab and the wall to correspond to the rail wheel. The unit building unit includes movement of the rail wheel along the guide rail. It can be inserted or removed by sliding into the frame for the wall structure, and the unit building unit is fixed to the frame for the wall structure by a post that penetrates the unit floor slab and is fixed to the slab of each floor, and the guide rail is attached to the slab. We propose ‘a unit building unit insertion type building characterized by being buried.’

However, the above background technology has a closed cross-sectional structure, which has the problem that not only is it difficult to remove the internal form during production, but also difficult to lift, and especially difficult to join vertically and horizontally between buildings.

The present invention is intended to solve the above problems, and the ceiling plate and the bottom are manufactured as one piece, which not only facilitates demolding from the mold, but also provides an inverted U-shaped PC with an integrated bottom that facilitates vertical and horizontal joining between PC modular structures. The purpose is to provide modular structures.

The present invention includes a horizontal plate-shaped ceiling plate; side plates each configured vertically downward from both ends of the ceiling plate in the width direction; The present invention seeks to provide an inverted U-shaped PC modular structure having an integrated bottom, including a bottom formed integrally with the ceiling plate so as to protrude upward from the upper surface of the ceiling plate.

In addition, it is intended to provide an inverted U-shaped PC modular structure with an integrated bottom, wherein the bottom is formed along the entire length of the ceiling plate or only in the central section excluding certain sections at both ends in the longitudinal direction.

In addition, a sleeve-type joint member is formed by joining a sleeve and a vertically constructed reinforcing bar to the upper end of the sleeve so that a plurality of sleeve-type joint members are embedded in the side plate so that the lower end of the sleeve is exposed to the lower end of the side plate, and from the upper surface of the ceiling plate to the upper side. The object is to provide an inverted U-type PC modular structure with an integrated bottom, characterized in that a vertical bar for joining is formed at a position corresponding to the sleeve-type joining member so as to protrude a certain length.

In addition, it is intended to provide an inverted U-shaped PC modular structure with an integrated bottom, wherein a side joining member made of metal is formed at the outer edge where the ceiling plate and the side plate meet.

In addition, the purpose is to provide an inverted U-shaped PC modular structure with an integrated bottom, wherein the side joining member is formed with a reinforcement plate to connect the inner edges.

In addition, it is intended to provide an inverted U-shaped PC modular structure with an integrated bottom, wherein a border beam is formed to protrude from the lower end of the side plate to the inside of the ceiling plate in the width direction.

In addition, it is intended to provide an inverted U-shaped PC modular structure with an integrated bottom, wherein the lower surface of the ceiling plate and the outer surface of the side plate protrude at regular intervals to form ribs.

In addition, it is intended to provide an inverted U-shaped PC modular structure with an integrated bottom, characterized in that a plurality of positive protrusions are formed between the side plate ribs or a plurality of negative grooves are formed on the surface of the ribs.

In addition, it is intended to provide an inverted U-shaped PC modular structure with an integrated bottom, characterized in that haunches are formed at the inner corners of the ceiling plate and side plates.

In addition, it is intended to provide an inverted U-shaped PC modular structure with an integrated bottom, characterized in that the haunches are composed of beam reinforcement consisting of main bars and stirrups.

In addition, the main body part is embedded in the side plate so that the end protrudes from the inner surface of the lower part of the side plate, and the bottom part embedment muscle is embedded so that it is exposed from the sides of both ends in the width direction of the bottom. The purpose is to provide an inverted U-shaped PC modular structure with a secondary structure.

In addition, an inverted U-type with an integrated bottom is formed, wherein fastening grooves are formed by blocking out at regular intervals in the longitudinal direction at both ends in the width direction of the bottom, and the bottom embedded roots are embedded in the bottom so that they are exposed in each fastening groove. We would like to provide a PC modular structure.

In addition, the bottom is not formed from the ends on both sides in the width direction of the ceiling plate to a portion of the central section, so the ends on both sides in the width direction are formed to have a step with the upper surface of the ceiling plate. An inverted U-shaped PC modular structure with an integrated bottom. We would like to provide.

The inverted U-shaped PC modular structure with an integrated bottom of the present invention is not only advantageous for demolding because the ceiling plate and two side plates are manufactured integrally in an inverted U shape, but also protrudes from the upper surface of the ceiling plate to form an integrated bottom portion. When stacking a PC modular structure, the bottom of the lower PC modular structure can be made to become the bottom plate of the upper PC modular structure, and the inverted U-shaped PC modular structure and the bottom can be stacked vertically using rebar joints and sleeve-type joint members. Modular structures can be combined very easily, and there is a very useful effect of making horizontal joining between PC modular structures very easy by pre-configuring side joining members.

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention along with the detailed description of the invention. Therefore, the present invention is limited to the matters described in the attached drawings. It should not be interpreted as limited.

Figure 1 is a perspective view of an inverted U-shaped PC modular structure with an integrated bottom of the present invention and a modified example.

Figure 2 is a partial enlarged view of the side of the inverted U-shaped PC modular structure with an integrated bottom of the present invention.

Figures 3 and 4 are cross-sectional views showing the vertical coupling structure of the inverted U-shaped PC modular structure with an integrated bottom of the present invention.

Figure 5 is a cross-sectional view and a partially enlarged view showing the horizontal coupling structure of the inverted U-shaped PC modular structure with the integrated bottom of the present invention.

Figure 6 is a diagram showing an example of use of the inverted U-shaped PC modular structure with an integrated bottom of the present invention.

Figure 7 is a diagram showing the joint structure of the inverted U-shaped PC modular structure with the integrated floor of the present invention and the wall of the core part of the building.

Figure 8 is a partial enlarged view of Figure 7.

Below, the present invention will be described in detail with reference to embodiments shown in the attached drawings, but the presented embodiments are illustrative for a clear understanding of the present invention, and the present invention is not limited thereto.

Hereinafter, the technical configuration of the present invention will be described in detail according to preferred embodiments.

Figure 1 is a perspective view of an inverted U-type PC modular structure with an integrated bottom of the present invention and a modified example, Figure 2 is a partial enlarged view of the side of the inverted U-type PC modular structure with an integrated bottom of the present invention, and Figures 3 and 3 4 is a cross-sectional view showing the vertical coupling structure of the inverted U-shaped PC modular structure with the integrated bottom of the present invention.

As shown in FIG. 1, the inverted U-shaped PC modular structure 1 with an integrated bottom of the present invention is formed to have an inverted U-shaped cross section in which the ceiling plate 11 and the two side plates 12 are manufactured integrally. In particular, the bottom portion 20 is configured to protrude toward the top of the ceiling plate 11.

The bottom part 20 is formed integrally with the ceiling plate 11 so as to protrude upward from the upper surface of the ceiling plate 11 by the width of the distance between the pair of side plates 12, and is an inverted U-shaped PC modular structure. When stacking (1) vertically, the bottom portion 20 formed on the upper part of the lower inverted U-shaped PC modular structure 1 functions as a bottom plate of the upper inverted U-shaped PC modular structure 1.

In the past, the PC modular structure was manufactured with a closed cross-section, making it difficult to install and remove the form inside. However, in the present invention, not only is it manufactured with an inverted U-shaped cross-section to facilitate demolding, but the bottom portion 20 is installed separately. It is possible to form a box-shaped module cross-section without manufacturing, assembling, or using it.

The ceiling plate 11 is formed in a horizontal plate shape, and side plates 12 are formed vertically downward from both ends in the width direction of the ceiling plate 11 to have an inverted U-shaped cross section.

The bottom portion 20 is formed to protrude upward from the upper surface of the ceiling plate 11, and the width of the bottom portion 20 is configured so that it does not extend from the ends on both sides in the width direction of the ceiling plate 11 to a portion of the central portion. It may be formed as the width of the distance between a pair of side plates 12 or may be formed as a width smaller than this. As shown in FIG. 6, both ends in the width direction of the bottom 20 are connected to the ceiling plate 11. By being formed to have a step, the upper surface of the ceiling plate 11 exposed to the outside in the width direction of the bottom portion 20 can be used as a mounting surface for mounting the slab 70, etc.

In addition, as shown in Figure 6b, when there is a difference in width between the PC modular structures 1, the PC modular structures 1 may be stacked vertically and a slab 70, etc. may be mounted on the outside.

The length of the bottom portion 20 can be formed along the entire length of the ceiling plate 11, as shown in Figure 1b, or formed only in the central section excluding certain sections at both ends in the longitudinal direction, as shown in Figures 1a and 1c. there is.

In this way, the bottom portion 20 is protruded with a step toward the upper part of the ceiling plate 11, so that a step is formed on the outside of the bottom portion 20, and the ceiling plate 11 is exposed to the outside of the bottom portion 20. ) can also be used as a mounting surface for holding slabs, etc.

In particular, the edge beam 13, which is formed to protrude from the lower end of the side plate 12 to the inside of the width direction of the ceiling plate 11, may be manufactured integrally, and in this case, the width of the bottom portion 20 is divided into two pairs. It can be made to an appropriate width within the distance between the border beams (13).

The lower surface of the ceiling plate 11 and the outer surface of the side plate 12 protrude at regular intervals to form

ribs

111 and 121, so that the ceiling plate 11 and the side plate 12 are made of thin plates. However, the strength can be strengthened and the shape can be maintained in response to deformation due to drying shrinkage.

At this time, a plurality of embossed protrusions 123 may be formed between the ribs 121 of the side plate 12, or a plurality of grooves 122 may be formed engraved on the surface of the ribs 111. there is.

In particular, the lower end of the side plate 12 of the present invention is formed with a border beam 13 so as to protrude inward in the horizontal direction to reinforce the end of the side plate 12, and at the same time, it is made of a thin plate to reinforce strength. It is possible to do so, and a haunch portion 16 is formed at the inner edge of the ceiling plate 11 and the side plate 12, so that the ceiling plate 11 and the side plate 12 are made of thin plates and have an open cross section. When configured in an inverted U shape, the haunch portion 16 prevents the deformation phenomenon in which the gap between the lower ends of the pair of side plates 12 becomes narrow during the drying shrinkage process, so that the inverted U shape can be maintained. In particular, the haunch portion 16 can be provided with beam reinforcement consisting of main bars 161 and stirrups 162 so that the haunch portion 16 behaves as a beam.

The side plate 12 and the bottom 20 have main body embedding muscles 15 of the side plate 12 and the ceiling plate 11 and bottom embedding roots 25 of the bottom 20 at regular intervals in the longitudinal direction. can be connected to resist the moment.

For this purpose, when necessary, the main body embedding roots 15 are embedded so that the ends protrude from the inner surface of the lower part of the side plate 12, and the end portions on both sides in the width direction of the bottom part 20 are blocked out at regular intervals in the longitudinal direction. A fastening groove 232 is formed and a bottom embedding bar 25 is formed in the bottom part 20 so that it crosses the bottom part 20 in the width direction and both ends are exposed in the fastening grooves 232, respectively, as shown in FIG. 3 When stacked vertically as shown, the bottom embedded root 25 of the bottom 20 of the lower PC modular structure 1 and the main body embedded root 15 of the upper PC modular structure 1 are connected to the coupler 50. ), etc., when the lower and upper PC modular structures (1) are combined, the main body embedded muscles (15) and the bottom embedded muscles (25) are connected as one to resist the moment.

When connecting the reinforcing bars of the main body embedded bar 15 and the bottom embedded bar 25, all known various rebar jointing methods, such as coupler jointing through welding and thread processing, can be used. As shown, the coupler (50 ) and joint reinforcement bars threaded at both ends can be used to fasten.

The bottom part 20 may be blocked out to a certain size at regular intervals in the longitudinal direction of the border beams 13 on both sides of the width direction, that is, at intervals where the main body embedded bars 15 are formed, so that fastening grooves 232 may be formed. .

When using such a fastening groove 232, the bottom embedded root 25 is configured so that the end is exposed. The bottom embedded root 25 is embedded in the width direction of the bottom 20, and both ends are each fastening groove ( 232) and is formed to protrude.

In particular, as shown, in order to connect the coupler 50, the main body embedded root 15 has one end protruding to the outside to be threaded to facilitate fastening with the coupler 50, and the bottom embedded root 25 ) is formed to be threaded at both ends, so that the positions of the main body embedding bar 15 and the bottom embedding bar 25 are aligned and fastened with the coupler 50.

1C and 4, a separate sleeve-type joint member 30 is embedded in the lower part of the side plate 12, so that the inverted U-shaped PC modular structure 1 with an integrated bottom is stacked vertically. It is possible to facilitate the joining of the upper PC modular structure 1 and the lower PC modular structure 1.

The sleeve-type joint member 30 is formed by joining a sleeve 31 and a reinforcing bar 32 configured perpendicularly to the upper end of the sleeve 31, and the lower end of the sleeve 31 is a side plate. A plurality of ribs are embedded in the side plate 12 so as to be exposed at the lower end of the side plate 12. In particular, they may be formed in the area where the ribs 121 are formed on the outer surface of the side plate 12 to ensure sufficient thickness. there is.

The sleeve 31 can be made of various known empty sleeves or can be made of structural steel pipes. As shown in the example, the upper and lower parts of the sleeve 31 have outlet ports 312, respectively. ) and the injection port 311 may be formed and buried so as to be exposed to the outside of the side plate 12.

At the upper end of the sleeve 31, anchoring reinforcing bars 32 of a certain length are joined using various methods such as screw jointing and mortar filling.

In addition, the vertical bar 60 for joining is configured to protrude a certain length upward from the upper surface of the ceiling plate 11, and the vertical bar 60 for joining is configured at a position corresponding to the sleeve-type joining member 30. This allows it to be inserted into the sleeve 31 of the sleeve-type joint member 30 of the inverted U-shaped PC modular structure 1 having an integrated bottom layered on the top.

When vertically stacking the PC modular structures (1) of the present invention, the vertical coupling structure between the PC modular structures (1) is such that the vertical bars (60) for joining the PC modular structures (1) are stacked on top of the PC modular structures (1). ) are stacked to be inserted into the sleeve 31 of the sleeve-type joint member 30, and the inside of the sleeve 31 is filled with non-shrink mortar to have a vertical coupling structure between the vertically stacked PC modular structures 1.

In addition, a separate side joining member 90 is formed at the corner where the ceiling plate 11 and the side plate 12 meet, as shown in FIGS. 1C and 5, for horizontal joining between the PC modular structures 1.

The side joining member 90 is made of a metal material and can be formed in various shapes such as an angle with an L-shaped cross section to be formed at the outer corner where the ceiling plate 11 and the side plate 12 meet. As shown, the PC It may be configured on both sides of the width of the modular structure (1) to enable jointing in the width direction between the PC modular structures (1). Although not shown, it may be configured at the longitudinal end of the PC modular structure (1) to form a PC modular structure (1). (1) can also be joined in the longitudinal direction.

It may be installed along the entire length of the PC modular structure 1, but as shown, one or more units may be installed only in necessary areas.

This side joining member 90 is made up of a plurality of fixing members 92 made of reinforcing bars, iron wires, studs, etc. on the inner surface, and is embedded in the ceiling plate 11 and the side plate 12 for fixation. In addition, as shown in Figure 5c, the side joining member 90 may form a reinforcing plate 93 to connect the inner edge, and the side joining member 90 may be reinforced to form a PC modular structure ( 1) It may be added to prevent the side joining member 90 from spreading when the liver is horizontally joined.

When joining the PC modular structures (1) of the present invention horizontally adjacent to each other, the horizontal coupling structure between the PC modular structures (1) connects the side joining member (90) on one side of the PC modular structure (1) to the adjacent PC modular structures ( It can be brought into contact with the side joining member 90 on the other side of 1), and as shown in FIG. 5b, the joining plate 91 covers the upper part of the joining member 90 of the PC modular structure 1 on both sides simultaneously. ) and welding the joining plate 91 to the joining members 90 on both sides to have a horizontal coupling structure between the PC modular structures 1. In particular, the lower part of the side joining member 90 A fixing member 92 made of reinforcing bars, wires, studs, etc. may be formed on the surface or inner surface to secure the side joining member 90.

Such a joining member 90 may be used for joining the PC modular structure 1 and the core wall 8 of the core part of the building, as shown in FIGS. 7 and 8. In this case, the core wall 8 of the core part The bonding plate 82 is configured so that the other side is exposed to the outer surface of the core wall 8, and the bonding member 90 on one side of the PC modular structure 1 is connected to the bonding plate of the core wall 8 (82). 82), add a fixing member 92 on top of the joining member 90, and weld the fixing member 92 to the joining plate 82 and the joining member 90, respectively, to form the core wall. Connect (8) and PC modular structure (1).

The anchoring member 92 is welded to the joint plate 82 and the joint member 90 using a plate-shaped plate as shown in FIG. 8A or an angle as shown in FIG. 8B, respectively, to form the core wall (8). ) and the PC modular structure (1) can be joined.

At this time, the bonding plate 82 is made in the form of a metal plate, and in order to anchor it to the core wall 8, a fixing member 81 such as a stud or anchoring rebar is attached to one side of the bonding plate 82 by a method such as welding. It is configured so that the anchoring member (81) is embedded in the core wall (8).

The inverted U-shaped PC modular structure with an integrated bottom of the present invention as described above is not only advantageous for demolding because the ceiling plate and two side plates are manufactured integrally in an inverted U shape, but also protrudes from the upper surface of the ceiling plate to integrate the bottom portion. When stacking PC modular structures, the bottom of the lower PC modular structure can become the floor plate of the upper PC modular structure, and the inverted U-shaped PC modular structure and the bottom can be vertically aligned using rebar joints and sleeve-type joint members. Stacked PC modular structures can be combined very easily, and there is a very useful effect of making horizontal joining between PC modular structures very easy by pre-configuring side joining members.

So far, the present invention has been described in detail with reference to the presented embodiments, but those skilled in the art can make various variations and modifications without departing from the technical spirit of the present invention with reference to the presented embodiments. will be. The present invention is not limited by such variations and modifications, but is limited by the claims appended below.

The inverted U-shaped PC modular structure with an integrated bottom of the present invention is not only advantageous for demolding because the ceiling plate and two side plates are manufactured integrally in an inverted U shape, but also protrudes from the upper surface of the ceiling plate to form an integrated bottom portion. When stacking a PC modular structure, the bottom of the lower PC modular structure can be made to become the bottom plate of the upper PC modular structure, and the inverted U-shaped PC modular structure and the bottom can be stacked vertically using rebar joints and sleeve-type joint members. It is a very useful invention that allows modular structures to be combined very easily and makes horizontal joining between PC modular structures very easy by pre-configuring side joining members.

Claims

A horizontal plate-shaped ceiling plate (11);

side plates 12 each configured vertically downward from both ends in the width direction of the ceiling plate 11;

An inverted U-shaped PC modular structure with an integrated bottom, comprising: a bottom (20) that protrudes upward from the upper surface of the ceiling plate (11) and is formed integrally with the ceiling plate (11).
In claim 1,

The bottom 20 is an inverted U-shaped PC modular structure with an integrated bottom, characterized in that it is formed along the entire length of the ceiling plate 11 or only in the central section excluding certain sections at both ends in the longitudinal direction.
In claim 1,

The sleeve 31 and the reinforcing bar 32 formed vertically at the upper end of the sleeve 31 are joined so that the lower end of the sleeve 31 is exposed to the lower end of the side plate 12. A plurality of pieces are embedded in the side plate 12. A sleeve-type joint member 30 is constructed as much as possible,

An inverted U-shaped PC module with an integrated bottom, characterized in that a vertical bar 60 for joining is formed at a position corresponding to the sleeve-type joining member 30 so that a certain length protrudes upward from the upper surface of the ceiling plate 11. structure.
In claim 1,

An inverted U-shaped PC modular structure with an integrated bottom, characterized in that a side joining member 90 made of metal is formed at the outer corner where the ceiling plate 11 and the side plate 12 meet.
In claim 1,

The side joining member 90 is an inverted U-shaped PC modular structure with an integrated bottom, characterized in that a reinforcement plate 93 is formed to connect the inner edges.
In claim 1,

An inverted U-shaped PC modular structure with an integrated bottom, characterized in that a border beam (13) is formed to protrude from the lower end of the side plate (12) to the inside of the ceiling plate (11) in the width direction.
In claim 1,

An inverted U-shaped PC modular structure with an integrated bottom, characterized in that the lower surface of the ceiling plate 11 and the outer surface of the side plate 12 protrude at regular intervals to form ribs 111 and 121.
In claim 7,

A plurality of embossed protrusions 123 are formed between the ribs 121 of the side plate 12, or

An inverted U-shaped PC modular structure with an integrated bottom, characterized in that a plurality of grooves 122 are formed engraved on the surface of the ribs 111.
In claim 1,

An inverted U-shaped PC modular structure with an integrated bottom, characterized in that haunches 16 are formed at the inner corners of the ceiling plate 11 and the side plates 12.
In claim 9,

An inverted U-shaped PC modular structure with an integrated bottom, characterized in that the haunch portion (16) is composed of beam reinforcement consisting of main bars (161) and stirrups (162).
In claim 1,

The main body embedding muscle 15 is embedded in the side plate 12 so that the end protrudes from the inner surface of the lower part of the side plate 12,

An inverted U-shaped PC modular structure with an integrated bottom, characterized in that the bottom embedding roots (25) are embedded so as to be exposed from the sides of both ends in the width direction of the bottom part (20).
In claim 11,

Fastening grooves 232 are formed by blocking out the ends at both ends in the width direction of the bottom portion 20 at regular intervals in the longitudinal direction, and the bottom embedding bars 25 are positioned on the bottom portion 20 so that they are exposed in each fastening groove 232. An inverted U-shaped PC modular structure with an integrated bottom, characterized in that it is buried.
In claim 1 or claim 2,

The floor portion 20 is not formed from the widthwise ends of the ceiling plate 11 to a portion of the central portion, so that the widthwise both ends are formed to have a step with the upper surface of the ceiling plate 11. An inverted U-shaped PC modular structure with additional parts.