System for joining precast concrete columns and slabs

A precast concrete system is provided that consists of columns and slabs joined together in one point. Each corner of the slab is equipped with a steel pipe mounted on a steel plate that is attached at and covers the top surface of the column. Each column is equipped with high tensile steel reinforcement strands protruding at the top end to penetrate the steel pipes of the four corners of four slabs, through the holes in the steel base plate attached at the bottom surface of the next column above it, and through the pipes implanted vertically at the lower section of the next column. The implanted pipes are in line with the holes on the base plate. The four steel pipes of four slabs meeting on one column are tied together with high tensile steel wire rope through three holes drilled horizontally at three places of the pipe length: upper, middle, and lower sections. The pipes of the slab corners and the gaps between pipes and slabs are filled with a special mortar cement that hardens fast. Then a special mortar cement is injected to the implanted pipes through each pipe's opening on the side surface of the column.

FIELD OF THE INVENTION 
This invention concerns a method of constructing a multistory building from 
precast concrete using columns and slabs as its structural elements. 
BACKGROUND OF THE INVENTION 
The use of precast concrete components for multistory buildings has earned 
significant position in the building construction industry for the 
benefits it offers. Benefits include: 
Shorter construction time; 
Better quality assurance; 
Smooth concrete surfaces; 
Cleaner construction area; and 
Lower cost of production from standardized mass production. 
In pre-fabricated precast systems, the joints between the components are 
the most crucial elements. Joining several precast concrete components in 
one single joint or at one place has to be done fast and efficiently, and 
more importantly is the assurance of its construction strength. The joint 
has to withstand all forces resulting from external load, such as its own 
weight, live load, and seismic forces. In the conventional construction 
system, where the columns, slabs, and beams are cast on site, structural 
problems at the joint between columns and beams or floor do not appear. As 
the components are cast on site together, they form a monolithic 
structure. 
The use of precast concrete systems as the structure of multistory 
buildings has been limited by the difficulty in creating a joint system 
that is practical and economical, and able to overcome all forces 
resulting from its own weight, especially from seismic forces. Some 
popular and simple methods such as connecting columns and beams or floors 
with bolts or welding, have a handicap in their capability to withstand 
horizontal forces imposed by seismic forces. Those simple methods were 
designed only for withstanding gravitational force. 
The objective of this invention is to produce a seismic resistant and fast 
method for connecting and joining precast concrete elements, consisting of 
reinforced concrete columns and beams, which indeed form the floor itself 
(hereafter called slab). 
SUMMARY OF THE INVENTION 
The floor element in this system is a panel made from ribs and concrete 
with thin plates in between, where the ribs function as beams. The 
sequence of assembling the precast elements is as follows. 
Firstly, precast concrete columns are positioned vertically so that the 
steel anchors at the base floor fit in the steel pipe holes implanted in 
the lower section of the columns. Each concrete column is able to stand 
firmly by bonding it to steel anchors mounted on the base floor or at the 
head of the foundation. Special mortar cement is poured or injected 
through the other openings of the said pipes that are on the side surface 
of the column. The mortar cement flows down by gravity and fills up the 
passage of the pipes. As the mortar cement hardens, the column is 
sufficiently firm to stand without support. Then precast slabs are placed 
on top of the columns. 
One slab with four corners is supported by four columns. One column is the 
junction of four slab corners of four slabs. A column of the next story of 
the building is placed on top of the junction. Hence at one junction meet 
six ends of precast structural elements consisting of the top of the lower 
column, the four corners of four slabs, and the base of the next higher 
column, where they all form a single joint. 
There is a structural bond among the reinforcement of the lower column, the 
structure of the four corners of slabs, and the upper column from the 
existence of high tensile steel strands rooted in the upper section of the 
lower column and anchored at the lower section of the upper column, There 
is also a structural bond among the slab corners by means of tying the 
steel pipes of the slabs'corners with high tensile steel wire rope through 
the holes drilled horizontally on the pipes'walls. The pipes and the gaps 
among the pipes are filled with mortar cement so that the wire rope and 
the four pipes of the four slabs come in contact and bind together. This 
system results in a practical and economical method of assembly and a 
reliable construction in terms of its strength. The following drawings are 
presented to illustrate the above description.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows in perspective the precast concrete elements: the upper 
section of the lower column (1), the four corners of the four slabs (3), 
and the lower section of the upper column (2) separately before joining. 
On the top of the lower column (1), there are a number of steel strands 
protruding (16), which are embedded in the lower column (1). In the lower 
section of the upper column (2) are implanted a number of steel pipes (17) 
vertically positioned at the bottom surface of the column (2) and bent 
toward the side surface of the column, so the other openings of the pipes 
are on and flat to the side surface of the column, The number of the steel 
pipes (17) is equal to the number of the steel strands (16) protruding 
from the lower column (1). FIG. 1 shows a partial view of four slabs (3) 
between the lower column (1) and the upper column (2). The corner of each 
slab (3) is laid on the surface of the steel plate (12) that is mounted on 
the top surface of the column (1). Steel pipes (20) which are firmly 
integrated in a vertical position to the corner of the slab (3) will 
convey the steel strand (16) protruding from the lower column (1) to enter 
the pipes (17) in the lower section of upper column (2). 
FIG. 2 shows in perspective the six structural elements in unity. A gap 
(25) between adjacent slabs (3) will be filled with special mortar mixed 
from portland cement, sand, and finely crushed stone. The perimeter of the 
slab has shear keys (28) which provide binding strength to one another at 
the meeting line. 
FIG. 3a shows the vertical cross-section of a lower column (1). Steel 
strands (16) which penetrate through holes (32) on the steel plate (12) 
are made of high quality steel with flexible properties. A single steel 
strand (16) consists of seven steel wires, each of approximately 4 mm. 
diameter, as illustrated in FIG. 3b. A steel strand made of seven 4 mm 
wires is standard in production and commerce and is known as pc strand. 
The main reinforcements (7) are surrounded by a stirrup reinforcement (8), 
and the ends of the main reinforcement (7) are connected by welding (24) 
them to the steel plate (12) along the edge of the holes on the plate 
surface that is in contact with the lower concrete column (1). 
FIG. 4 shows the vertical cross-section of the upper column, (2). The steel 
pipes (17) function to take the steel strands (16) from the lower column 
(1), and through the pipe openings (19) which are on and flat to the side 
surface of the column (2). The special mortar cement (18) is injected to 
bind the steel strands (16) and the pipes (17) together (see FIG. 6a). The 
bottom ends of the pipes (19) are welded at the edge of the hole (34) on 
the steel base plate (11) surface that is in contact with the bottom of 
the upper column (2). The ends of the main reinforcements (10) are welded 
to the edge of the hole (33) on the surface of steel base plate (11) that 
is in contact with the concrete column. Hence, the free outer surface of 
the steel base plate (11) is flat and smooth. The main reinforcement (10) 
is surrounded by stirrup reinforcement (9) at a predetermined distance. 
FIG. 5 shows the vertical cross-section of a slab corner (3). A steel pipe 
(20) with a height equal to the thickness of the slab (3) is mounted 
perpendicularly to the two pairs of steel anchors (4 and 6) that are in 
perpendicular position to each other, by welding at the pipe holes (23), 
(25), and (26). A high tensile wire (29) of the prestress precast slab 
beam will slip through the holes (28) and (30) on the pipe wall (20). 
FIGS. 6a and 6b show the vertical cross-section of the upper section of 
lower column (1), the slab side (3), and the lower section of the upper 
column, (2), in an integrated position as one single joint. The steel 
strand (16), protruding from the lower column (1), is inside the steel 
pipe (20) of the beam (3) and the steel pipe (17) of the upper column (2). 
The four steel pipes (20) of four slabs (3) have holes (13), (14), and 
(15) through which slips flexible wire rope (31), (31a), and (31b) to tie 
the four steel pipes (20) together. Each steel pipe (20) and the gap 
between the pipes are filled with mortar cement (21) and (27). 
FIG. 7 shows the horizontal cross-section of the joint of four slab corners 
(3). The steel strand (16) protruding from the lower column (1) penetrates 
the steel pipe (20) of the slab (3), with two steel strands through each 
pipe (20). The drawing also shows a wire rope (31) tying together four 
steel pipes (20) through the pre-bored holes (13) on each pipe wall. The 
passage of the steel pipe (21), the gaps between pipes (27), and also the 
gaps between slabs (25), are filled with mortar cement. To the holes (23) 
of each steel pipe (20) are welded the ends of two pairs of anchors (6) in 
perpendicular position to each other. 
As shown in FIG. 2, the precast structure components of the system are 
columns and slabs. The shape of the slab can be rectangular, but can also 
be a combination of small beams connected with thin concrete plates. The 
most important and critical part of construction is that the corners meet 
at the column ends. The firm integration of the structural elements which 
in this system consists of the joint of the top of the lower column with 
the bottom of the upper column, the joint of the top of the lower column 
and the four slab corners, and the tying of the slab corners together, all 
in one single joint and the practicality in assembly are the essence of 
this invention The interconnection of the reinforcement of each structural 
element meeting at the single joint is able to take and distribute 
vertical forces, horizontal forces, moment, and shear forces. This has 
been proven in a series of tests conducted by the Structural Laboratory of 
Housing Research Center, Department of Public Works of the Republic of 
Indonesia. 
The steel strands (16) rooted at the upper section of the lower column (1) 
are to extend the reinforcement from the lower column (1) to the upper 
column (2). The passage of the steel pipe (17) with the steel strand (16) 
inside, is filled with special mortar cement so that the steel strand (16) 
adheres to the pipes, thus uniting firmly to the upper column (2). The 
adherence of the steel strand (16) and the lower column (2) results from 
the confined nature of the steel pipe (17) and the steel strand (16). For 
columns of 26.times.26 cm with four main reinforcement of diameter of 19 
mm, to transfer maximum force that can be endured by the columns, that is 
from the lower column to the upper column or vice versa, eight high 
tensile steel strands of a diameter of 1/2 inch are used (16). From the 
technical specification of each main reinforcement (10) and steel strand 
(16), the tensile strength of two steel strands (16) is 2 to 3 times of 
the tensile strength of one main steel reinforcement (7) or (10). The high 
quality steel strand (16) consists of seven wires, each of 4 mm diameter. 
High tensile steel strands are commonly used for main reinforcement of 
prestressed concrete, but in this invention, the strand is not tensioned 
and does not function as prestressed steel. The characteristics of the 
steel strand suitable for this invention are the high tensile strength and 
the flexibility, so it is easy to direct the eight strands (16) to slip 
through the steel pipe holes (17) of upper column (2). The rugged surface 
of the strand (16) helps to increase the adherence between the mortar (18) 
and the strand (16). The steel strand of a relatively short length in this 
invention, is easily acquired as a waste from the high tensile steel 
strand usage in the prestress pretension concrete industry. FIG. 5 and 7 
show the construction detail and the connection with the slab corners (3). 
Steel rods (4) and (6) that are welded to the steel pipe (20) at a point 
(23) with the steel rods (4) and (6) of approximately 100 cm in length 
function as anchors for the steel pipe (20) of the concrete slab (3). 
Several pairs of straight steel rods (5) are welded at uniform distances 
connecting the two steel anchors (4) and (6) to serve two functions: as a 
steel reinforcement to receive shear force, especially around the slab 
corner or around the steel pipe (20), and as a link for reinforcement (4) 
and (6) to become one construction frame that works together and as a 
strengthening reinforcement system in critical spots at corners where the 
load can come from external forces such as an earthquake, with a changing 
load direction. On the steel pipe wall (20) and between steel anchors (4) 
and (6), there are holes (30). The holes (30) enable steel rods (29) to 
cross steel pipe (20) from the peripheral beams of the slab and to 
function as prestress pretension reinforcement on the said beams. 
FIG. 7 shows four slab corners (3) on column (1). It also shows a 
connection between the steel pipes (20) of the slabs (3) which are tied 
together by three high tensile wire ropes (31) that are slipped through 
pre-bored holes (13), (14), (15) on the pipe wall (20). The three wire 
ropes (31), (3la), and (31b), are also shown in FIG. 6b. The passage of 
the steel pipe (21), the gaps between pipes (27) on the lower column (1), 
and the gaps between the slabs (25) are filled with special mortar. 
Observing FIGS. 6a and 6b, the flow of forces from one component to 
another especially those resulting from moment at the peripheral beams of 
the slab (3) and shear force from earthquake at the joint, can be 
explained as follows. Positive or negative moment from the peripheral 
beams of the slab (3) is firstly transferred to the steel pipe (20), then 
through the wire rope (31a) or (31b), some is conveyed to the next steel 
pipe (20) and some is taken by the high tensile steel strand (16) inside 
the pipe (20). The steel strand (16) in the upright position is confined 
in the pipe (17) with special mortar cement. The wire rope (31) positioned 
in the middle, functions to take shear force in the center of the joint, 
with the direction of the shear force being at a 45 degree angle due to 
the shear force. The uniting characteristic of the structural construction 
at the bottom of the upper column (2) and also the top of lower column (1) 
is provided by the firm connection between the main reinforcement of each 
column (7) and (10) with the steel plate (1 1) and (12), so that the 
horizontal force or shear force between the column and the top surface of 
the pipe of the four corners (20) can be transferred from the main 
reinforcement (10) to the steel strand (16) through the steel plate (11).