Patent Publication Number: US-2019177964-A1

Title: Precast concrete formwork, floor system and a method of construction

Description:
TECHNICAL FIELD 
     The present invention relates to the field of construction and more specifically relates to a floor system and an associated method of forming a floor system. 
     BACKGROUND 
     Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge. 
     Suspended flooring systems with pre-cast components are gaining popularity for both residential and commercial construction projects. Formwork is a structural component that is temporarily used during construction phase and plays a significant role in the concrete building industry. Improper design of the formwork may cause partial or full collapse of a building during construction and/or excessive cracking and deformation at the operational stage. Furthermore, inappropriate stiffness of the formwork affects the surface finishes of the concrete structure. Therefore, a stiff formwork results in a flatter and smoother finish. 
     The shape of the formwork is also affected by the shape of the final structural elements. Hence, preparation and assembling of formworks can be time consuming and a costly process. Eliminating the step of preparation and assembling of formwork is also highly desirable because minimizing the use of formwork may enhance safety for construction personnel and increase the speed of construction whilst also decrease the cost associated with it. 
     Depending on the slab type, steel or timber formworks have been previously used. In some instances, where propping of the formworks is not possible precast concrete slabs have been used. 
     One of the commonly used floor systems with precast concrete slabs comprises joists and blocks. The joists are mostly placed with gaps ranging between 400 to 600 mm. The gap between the joists is filled with concrete or other types of masonry blocks and the joists and blocks are subsequently covered by a fresh concrete overlay of 60 to 120 mm thick concrete layer. The system acts as a one-way ribbed slab. Such a floor system uses a simple construction method but can be time consuming and is not suitable for use in long spans and normally results in a thick floor system. 
     Another commonly used floor system is known as the composite floor system. Composite floors are mostly used with steel structures. The distance between beams used in these systems varies from 900 mm to 3000 mm with economical distance of about 1200 mm to 2400 mm. Steel beams used in these system must be fire rated to meet relevant building code requirements which makes these floor systems expensive. Further, shear studs must be installed at the top flange of the beam to shape proper connections between the concrete slab and the supporting steel beam. The process of installing such composite floor systems can be time consuming and demands onsite welding and the integrity of the system depends on the strength of shear studs and their connections to the steel beam. 
     Yet another floor system is known as the waffle slab system. The waffle slab system comprises a two-way slab that is made of GRP (fibreglass) moulds. The system contains integrated joists that extend in both directions. The distance between joists varies between 600 mm to 1200 mm. Even though, the waffle slab system is suitable for covering long spans, this system is not economical for use in large scale construction. Construction of the waffle type slab system can also be time consuming. 
     There is a need for providing an improved floor system that overcomes the deficiencies of the prior art floor systems. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the invention provides formwork for constructing a floor system in a building, the formwork comprising:
         a plurality of pre-cast concrete joists positioned in a generally parallel arrangement, wherein one or more of the joists comprises: a horizontal base portion; and an upwardly directed portion extending substantially along the length of the joist, the upwardly directed portion having spaced apart surfaces extending upwardly from the base wherein respective shelf portions of the base are located adjacent said upwardly directed portion;   a plurality of pre-cast concrete members for extending along a length of the joists for receiving wet concrete; and   a supporting arrangement to support opposite ends each of the pre-cast concrete members upon oppositely arranged shelf portions of two adjacent joists.       

     In one embodiment, one or more of the pre-cast concrete members comprises a shell for receiving wet concrete, the shell being adapted to be coupled with respective downwardly directed supporting portions for supporting the shell on the oppositely arranged shelf portions of two adjacent joists. 
     In an embodiment, the supporting portions are integrally formed with the pre-cast members. 
     In an alternative embodiment, each of the pre-cast supporting portions comprises an in-use lower portion for being positioned on the respective shelf portions and an in-use upper portion for being coupled with lateral ends of the pre-cast members. 
     In an embodiment, the supporting portions are adapted to extend along a length of the joist. 
     In an embodiment, an outer surface of the pre-cast concrete members in combination with the surface of the upwardly directed portion of the supporting joists positioned at opposite ends defines an in-use receiving portion for receiving wet concrete. 
     In an embodiment, the pre-cast concrete members comprises edge portions extending along a length of the pre-cast concrete members wherein preferably at least a first edge portion extends along a first lateral side of the pre-cast concrete member and at least a second edge portion extends a second lateral side of the pre-cast concrete member. 
     In an embodiment, one or more of the pre-cast concrete members comprises:
         a pan for receiving the wet concrete; and   shoulder portions located at opposite ends of the pan, said shoulder portions being adapted to be supported on the oppositely arranged shelf portions of two adjacent joists.       

     In an embodiment, the pan in combination with the surface of the upwardly directed portion of the supporting joists positioned at opposite ends defines an in-use receiving portion for receiving wet concrete. 
     In an embodiment, the pre-cast concrete joists are supported by a plurality of beams extending generally in a perpendicular direction relative to the general direction of the said pre-cast concrete joists. 
     In an embodiment, the beam comprises a beam portion with a substantially flat profile with two spaced apart formations extending upwardly from the beam portion, the said formations extending along a length of the beam and joist receiving portions extending outwardly from the said formations for supporting an end portion of a plurality of joists. 
     In an embodiment, an outwardly projecting end portion of the plurality of joists is supported upon a joist receiving portion of the beam portion, the joist receiving portion of the beam preferably extending in a perpendicular direction relative to the said projecting end portions of the joist. 
     In an embodiment, an underside bottom surface of the beam substantially lies in the same plane as a bottom surface of the joist. 
     In an embodiment, the formwork further comprises:
         a first connecting mechanism for connecting a first joist positioned on a first lateral side of the beam with a second joist positioned on a second lateral side of the beam, said connecting mechanism being further adapted for preferably applying a negative bending force to the first and second joists during use; and   a second connecting mechanism for connecting two adjacently located beams supported simultaneously on a column, the connector being provided for applying negative bending to said adjacently located beams.       

     In an embodiment, the formwork further comprises column formwork members for forming columns to support said beams wherein each of the column formwork members can be inter-connected to define a hollow portion for receiving wet concrete. 
     In an embodiment, end portions of each of the column formwork members comprises connecting portions for inter-connecting the column formwork members such that imaginary plane of a first column formwork member is transversely arranged relative to an imaginary plane of second column formwork member inter-connected with the first column formwork member. 
     In an embodiment, said locking portions extend along a longitudinal edge of the column formwork member such that in an inter-connected configuration the locking member is adapted to be received in a recess of another of said column formwork, said recess extending along a longitudinal edge of said another column formwork. 
     In an embodiment, the formwork further comprises one or more permanent formwork members for being positioned in between two spaced joists and wherein preferably the permanent formwork members comprise a substantially L-shaped or U-shaped cross section. 
     In an embodiment, the joists of the formwork further comprise one or more apertures for receiving reinforcing bars, the reinforcing bars extending in a transverse direction relative to the general direction of the joists, the reinforcing bars being adapted for being tensioned (by way of post-tensioning) after pouring concrete into the pre-cast concrete receiving members. 
     In another aspect, the invention provides a pre-cast concrete joist comprising: a horizontal base portion; and an upwardly directed portion extending substantially along the length of the joist, the upwardly directed portion having spaced apart surfaces extending upwardly from the base wherein shelf portions of the base are located adjacent said upwardly directed portion, each of the shelf portions defining a seat for receiving a connecting portion of a pre-cast concrete pan member or a pre-cast concrete shell member wherein height of the upwardly directed portion is equal to or greater than vertical height of the said shelf portions. 
     In yet another aspect, the invention provides a pre-cast concrete member for being positioned in between and supported spaced apart joists or beams, the precast member extending along a length of the joists or beams for receiving wet concrete, the precast member comprising a supporting arrangement to support opposite ends each of the pre-cast concrete members upon oppositely arranged joists or beams. 
     In another aspect, the invention provides a method of constructing a suspended floor in a building, the method comprising the steps of:
         positioning a plurality of pre-cast concrete joists in a generally parallel arrangement, wherein one or more of the joists comprises: a horizontal base portion; and an upwardly directed portion extending substantially along the length of the joist, the upwardly directed portion having spaced apart surfaces extending upwardly from the base wherein shelf portions of the base are located adjacent said vertical portion;   positioning a plurality of pre-cast concrete members in between adjacently located joists, said pre-cast concrete members being positioned for extending along a length of the joists for receiving poured concrete;   supporting opposite ends of each of the pre-cast concrete members upon oppositely arranged shelf portions of two adjacent joists; and   pouring fresh concrete into a receiving portion defined by the pre-cast concrete members.       

     In at least some embodiments, the invention also comprises modular precast concrete formworks (MPCF) that includes joists, infill thin shells, beams, columns, and walls designed to eliminate or minimize the use of formwork and propping systems in concrete structures. The MPCF has been designed to withstand its self-weight together with construction related loads prior to on-site concreting. After installation, additional reinforcing bars (if required) are placed over the MPCF. A concrete overlay with a nominal thickness of not more than 70 mm is then placed over the MPCF to generate the final one-way or two-way flooring system. The MPCF looks a permanent formwork that is integrated and will be part of the final flooring system to bring the following superior benefits to the construction industry:
         High-Quality Soffit Finishes;   Less on-site concreting (in this invention 1 m3 covers between 11.5 m2 to 14 m2 of floor area where as in the traditional method it only covers between 3 m2 to 6 m2);   Less on-site reinforcing (Normally, single reinforcing mesh is enough even for long spans);   No additional formworks;   Minor propping (single prop at mid span of joists in large span floors or no prop for medium to small span floors);   Edge beams are equipped with proper connections for installation of temporary suspended scaffolding platform. Hence, no need for full scaffolding system;   The use of this invention offers a better serviceability limits in the final floor system;   The invention deems to satisfy minimum 2 hour fire rating.   A rapid increase in the construction speed and a reduction in construction costs.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows: 
         FIG. 1  is a perspective view of a one-way floor system  400  and a two-way floor system  400 ′ used in a building  1000  in accordance with a first and second embodiment of the present invention. 
         FIG. 2A  is a perspective view of a pre-cast concrete member in the form of a plank member  100  in accordance with an embodiment of the present invention. 
         FIG. 2B  is a right hand sectional view of the plank member  100 . 
         FIG. 2C  is a sectional view of a second embodiment of the plank member  100 ′. 
         FIG. 2D  is a sectional view of a third embodiment of the plank member  100 ″. 
         FIG. 2E  is a perspective view of a step plank unit  100 ′″. 
         FIG. 3  is an in-use sectional view of the plank member  100  having an indefinite length. 
         FIG. 4  is a sectional view of plank supporting member  110 ′ in accordance with an embodiment of the invention. 
         FIG. 5A  is an in-use sectional view of the plank member  100 ″ supported upon the supporting member  110 ′. 
         FIG. 5B  is a perspective view of the plank member  100 ″ supported upon the supporting members  110 ′ located at either lateral end of the plank member  100 ″. 
         FIG. 6A  is a perspective view of a pre-cast joist  140  in accordance with an embodiment of the invention. 
         FIG. 6B  is a sectional view of the pre-cast joist  140 . 
         FIG. 6C  is a sectional view of an alternative embodiment of a pre-cast joist  140 ′. 
         FIG. 7  is a sectional view of the two-way floor system  400 ″ in accordance with an embodiment of the present invention. 
         FIG. 8A  is a U-shaped permanent formwork member  120 ′ in accordance with an embodiment of the present invention. 
         FIG. 8B  is a sectional view of the U-shaped permanent formwork member  120 ′. 
         FIG. 9A  is an L-shaped permanent formwork member  120  in accordance with an embodiment of the present invention. 
         FIG. 9B  is a sectional view of the L-shaped permanent formwork member  120 . 
         FIG. 10A  is a perspective view of a pre-cast band beam  150  in accordance with an embodiment of the present invention. 
         FIG. 10B  is a sectional view of the pre-cast band beam  150 . 
         FIG. 11A  is a perspective view of a pre-cast edge beam  160  in accordance with an embodiment of the present invention. 
         FIG. 11B  is a sectional view of the pre-cast edge beam  160 . 
         FIG. 12  is a perspective view of the band beam  150  supported on column units  170 . 
         FIG. 13A  is a sectional view of a square-shaped column unit  170  in accordance with an embodiment comprising column formwork members  300  being inter-connected to form a hollow portion to receive fresh concrete. 
         FIG. 13B  is a sectional view of a rectangular column unit  170 ′. 
         FIG. 13C  is a sectional view of the column formwork member  300 . 
         FIG. 14  is a perspective view of the two-way flooring system  400 ′. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1  a building structure  1000  comprising a one-way floor system  400  and a two-way floor system  400 ′ in accordance with a first and second embodiment of the present invention. It shall be understood by the person skilled in the art that it is not necessary to use both flooring systems  400  and  400 ′ in the same building structure. By way of example, either a one-way floor system  400  or a two-way floor system  400 ′ may be used in an alternative building structure without departing from the spirit and scope of the invention. 
     Referring to  FIGS. 1 and 7 , the suspended one-way floor system is built by using modular precast concrete formworks. The system may comprise an array of parallel pre-cast concrete joists  140  positioned in a generally parallel arrangement. Each of the joists  140  spans between supporting elements such as a pair of elongate band beams  150 . Each of the joists  140  is supported upon two band beams  150  positioned along either end of the joists  140 . The band beams  150  and the joists  140  are generally arranged in a mutually perpendicular orientation. The band beams  150  are positioned and supported by upright columns or posts  170 . 
     A plurality of pre-cast concrete members in the form of pan units  110  extend in between adjacently located pre-cast joists  140 . Referring to  FIGS. 5A and 5B , it is clearly illustrated that each pan unit  110  comprises a pre-cast plank  100 ″ that extends in between two lateral sides  101 A and  101 B. At each of the lateral sides, supporting structures  110 ′ are provided for supporting the pan unit  110  upon the two adjacently located joists  140 . 
     Referring  FIGS. 2A to 2E  and  FIG. 3 , each of the plank units  100  or  100 ′ comprises a horizontal base portion  101 . The longitudinal edges of the plank unit  100  or  100 ′ contain a recess  102  positioned at either lateral ends  101 A and  101 B of the plank units  100 ,  100 ′, or  100 ′″. The recess  102  allows the plank unit  100 ,  100 ′,  100 ′″ to be seated upon the supporting structures  110 ′. The plank units contain a horizontal mesh  103  that extend through the length of the plank units. Z shape wire ties  104  is connected to the main horizontal mesh  103  to enhance the cracking capacity of the recess portion of the plank units. Furthermore, mechanical shear connector  105  may be provided at the top surface of the plank unit to ensure 100% bonding between the plank units and the fresh concrete  108  above that. The soffit of the plank units  100 ,  100 ′,  100 ′″ is equipped with equally spaced cast-in-ferrules  106  to ease installation of a ceiling structure  109  that supports ceiling plaster boards  109 ′. Since the plank unit  100 ″ is used to make the pan unit  110 , the top face of the pan unit  110  is also equipped with equally spaced cast-in-ferrules  107  for installation of the negative bending connectors  145  (refer to  FIG. 7 ). The thickness of the plank units  100 ,  100 ′, and  100 ″ may vary between 50 mm to 80 mm. The thickness of the step plank unit  100 ′″ depends on the step height and is only used when a step needs to be generated within the floor system. The step plank unit  100 ′″ contains an upwardly portion  106  that extend along the plank unit. This portion act as an edge formwork to keep the wet concrete in the required level. 
     Alternatively, the installation of the one-way floor system  400  or two-way floor system  400 ′ may involve positioning a plurality of the plank units  100  or the pan units  110  in between adjacently located joists  140  or  140 ′. As Shown in  FIGS. 4 and 5 , the pan unit  110  comprises of the plank unit  100 ″ and the plank supporting unit  110 ′. During the installation, opposite ends of each of the pre-cast concrete pan unit  110  are supported upon oppositely arranged shelf portions of two adjacent joists  140  or  140 ′ (as illustrated in  FIGS. 1 and 7 ). 
     The pre-cast plank supporting structure  110 ′ is elongate and extends along the length of the plank unit  100 ″. An outwardly facing surface of the pan unit  110  and the vertical surface of a supporting joist  140  or  140 ′ together define a receiving portion for receiving wet concrete during construction (best illustrated in  FIG. 7 ). Referring to  FIG. 4 , each supporting unit  110 ′ comprises a seat portion  111  at its top surface to bond it to the recess  102  of the plank unit  100 ″. Each supporting structure  110 ′ comprises a bottom reinforcing bar  112  and the top reinforcing bars  113 . The bottom reinforcing bars are connected to the top reinforcing bars using specific shear ligatures  114 . The top face of the supporting structure  110 ′ is also equipped with equally spaced cast-in-ferrules  115  for installation of the negative bending connectors  145  (refer to  FIG. 7 ). The pan unit  110  can be cast for providing span lengths of between 1750 mm and 2800 mm. The pre-cast concrete plank unit  110  or  110 ′ or  110 ″ are designed to withstand live loads of up to 4 kPa with total serviceability limit of span/250. The deflection under live load maybe kept under span/500. 
     Referring  FIGS. 6A to 6B  illustrate a joist  140  and  FIG. 7  illustrates an alternative embodiment of the joist  140 ′. Each of these joists ( 140  or  140 ′ comprises a horizontal base portion  141 ; and a vertically oriented portion  142  extending substantially along the length of the joist  140  or  140 ′. The vertically oriented portion  142  comprises spaced apart upwardly extending surfaces. The spacing between the vertical surfaces is denoted by b 1 . The length of the top surface (b 1 ) is less than the length of an in use bottom surface (b) of the base. The length of the top surface (b 1 ) is in the range of 150 mm to 300 mm and length of the bottom surface (b) is in the range of 300 mm to 500 mm. Each of the vertical surfaces includes a chamfered portion located in between the shelf portion  141  and the respective almost vertical surfaces. 
     Shelf portions  141  are located adjacent on lateral sides of the vertically oriented portion  142  and each of the shelf portions  141  defines a seat for receiving a connecting portion of a pre-cast concrete pan unit  110  or plank unit  100 ′. The joist unit also includes the bottom reinforcing bars  143  located in the shelf portion  141  and the top reinforcing bars  144  that are partially located in vertically oriented portion  142 . At least one of the top reinforcing bars, in some embodiments may be located outside of the vertically oriented portion  142  to enhance the connectivity between the joist and the fresh concrete  108  above that. The joist unit  140  may also be equipped with vertical ligature  146  that connect the bottom reinforcing bars  143  to the top reinforcing bars  144 . The top surface of the joist  140  may also be equipped with equally spaced cast-in-ferrules  147  that are used to assemble the negative bending connectors  145  (refer to  FIG. 7 ). To use the Joist  140  in the two-way action flooring system  400 ′, equally spaced voids  148  passing across the vertically oriented portions  142  to enhance the connectivity between joists  140  and the fresh concrete  108  and to assist with placing reinforcing bars or post-tensioning tendons/ducts for two-way floor system where the applied loads are transferred in direction of the joist  140  as well as in direction perpendicular to that. 
     The joists  140  or  140 ′ may be designed for covering spans of up to 12 m and the distance between adjacently located joists  140  and  140 ′ may vary between 1750 mm to 3300 mm. The joist unit  140 ′ (shown in  FIG. 6C ) is particularly useful when a step down in the floor system needs to be generated. The joist may be prestressed to shape downward curvature for covering longer spans or when high magnitude of construction loads are applied. The height of the vertically oriented portion may vary between 50 mm to 400 mm and the thickness of the base portion may vary between 50 mm and 120 mm. 
     In the presently described embodiment, the joist  140  has been designed to carry up to 6 kPa live load which is much higher than the required levels for both residential (less than 2 kPa) and commercial (mostly 3 kPa and in some location 4 kPa) buildings with a total deflection of less than span to 250 and deflection under live load of less than span to 500. Higher serviceability requirements can also be achieved by decreasing the clear distance between joists  140  when required. In the case when higher shear capacity is required, the web ( 142 ) of joists  140  and  140 ′ may be thickened at the support areas where the joist  140  or  140 ′ resting on the supporting elements (such as a band beam  150 , edge beam  160 , or a wall system  190 —shown in  FIG. 14 ). 
     The installation of the one-way floor system  400  may involve positioning a plurality of the pan units  110  or the plank unit  100 ′ or  100 ″ in between adjacently located joists  140  and  140 ′. Each of the pre-cast pan  110  or pre-cast plank unit  100 ′ and  100 ″ are adapted for receiving wet concrete, during construction, once these members ( 110 ,  100 ′, or  100 ″) are positioned in between the respective joists  140  or  140 ′. 
     Referring to  FIGS. 8 and 9 , permanent formwork flooring end plate units  120  and  120 ′ may also positioned, before pouring the wet concrete, at each of the respective edge portions of the pre-cast pan unit  110  or the plank units  100 ,  100 ′, and  100 ″. The flooring end plate units  120  or  120 ′ may be provided in the form of L-shaped  120  members ( FIG. 9 ) or U-shaped  120 ′ members ( FIG. 8 ). 
     The L-shaped end plate members  120  (depicted in  FIG. 9 ) are used at the connecting location between each of the joists  140  and the joist supporting members (band beam unit  150  or edge beam unit  160 , or wall unit  190 ). This arrangement has been more clearly illustrated in  FIG. 14 . The U-shaped end plate members  120 ′ (depicted in  FIG. 8 ) are used in the second embodiment of the invention ( 400 ′, refer  FIG. 15 ) when a two-way floor system is provided. The U-shaped flooring end plate  120 ′ can be positioned between the pre-cast pan units  110  and in line with rectangular or circular penetrations  148  in the joist  140  to allow two-way actions, one in direction of joist  140  and the other one in transverse direction relative to the joists  140 . The flooring end plates  120  and  120 ′ comprise a reinforcing mesh  121  that is bent to conform to the shape of the flooring end plates, i.e. U Shape or L Shape. To enhance the connectivity of the flooring end plates to the fresh concrete, these permanent formwork members have been equipped with mechanical shear connectors  122 . 
     Referring to  FIGS. 10 to 12  illustrates the sectional and perspective views of the band beam unit  150  and edge beam unit  160 . As discussed in the previous sections, the plurality of the pre-cast concrete joists  140  and  140 ′ are supported by a plurality of band beams  150  and or edge beams  160  that extends generally in a perpendicular direction relative to the general direction of the said pre-cast concrete joists  140  and  140 ′. When dealing with a low magnitude of the applied loads or dealing with short spans, the beam  150  may have a shape similar to the joist  140  but may be larger in size. Otherwise, the beam  150  comprises of two spaced apart formations  150 A and  150 B extending upwardly from the beam  150 . The edge beam  160 , contains one formation of  160 A extending upwardly from the beam  160 . The formations  150 A and  150 B extend along a length of the beam  150 . Similarly, formation  160 A also extends along a length of the edge beam. Joist receiving portions for the band beam  150  extend outwardly from the said formations  150 A and  150 B for supporting an end portion of a plurality of joists  140 . Similarly joist receiving portions for the edge beam  160  extends outwardly from the formation  160 A. The breadth for each of the formations (B) may vary between 100 to 300 mm depending on span of the band beam and magnitude of the applied loads. Thicker values may be used at the support areas of the beam to assist with transferring shear forces to the column  170 . The height of the formations (H) may vary between 200 mm to 600 mm depending on span of the band beam and magnitude of the applied load. The thickness of the beam (T) may vary between 80 mm to 150. 
     Referring to  FIGS. 10B and 11B , each of the band beams  150  further comprises top reinforcing bars  151  extending through an upper portion of the formation along a longitudinal direction of the band beam  150  and or the edge beam  160 . Positive reinforcing bars also  155  extend along the beam  150  and  160 . The beams  150  and  160  also comprise torsional and shear ligature bars  152  and  153  for providing additional shear strength characteristics to the beams  150  and  160 . The shear ligature bars also assist with transferring shear forces acting at the interface of the beam  150  or the edge beam  160  and the overlay concrete poured on site. Circular or rectangular penetration openings  156  may also be provided through the  150 A and  150 B vertical portion of the beam  150 . These openings reduce the total weight of the beam and generated interlock with the fresh concrete to enhance the composite actions between them. The beam  150  has also contains another penetration opening  157  within its horizontal portion along an underside to facilitate connection of the band beam  150  onto a supporting column, i.e. column  170 . The beam element  150  also contains a recess  158  around the penetration  157 . This will restrain the column head and transfer loads to the column via bearing at this area. A typical in-use perspective of assembly between column  170  and the band beam  150  has been shown in  FIG. 13 . Advantageously, each band beam  150  is provided as a single unit with a width of 800 to 2000 mm and no additional onsite works are required. 
     Referring  FIG. 13 , the cross section of column units  170  (square shape) and  170 ′ (rectangular shape) that are build using precast column formwork units  300 . The column formwork units  300  comprises of a horizontal portion with a thickness of 50 mm to 70 mm and also contain a recess  301  at one of its edge. A portion of the column builder is extend downwardly by about 50 mm ( 302 ). The element also comprises internal reinforcing mesh  303 . To enhance the cracking capacity of the edge of this unit, both external edges of the column formwork units  300  have been reinforced with edge wire ties  304 . The column formwork units also contain connector elements  305  that are located at each end of the unit  300 . Different widths of the column formwork units  300  can be connected to each other to shape a square shape ( 170 ) or a rectangular shape ( 170 ′) columns using structural adhesive. Mechanical connectors may also be used if required. Additional column cage containing longitudinal bars  306  and shear ligatures  307  may also be placed within the column cavity defined by the column formwork units  300  and secured in position using connector  305 . A perspective view of column unit  170  have been shown in  FIG. 13 . The cavity of the column will then be filled with fresh concrete  308  on site. 
     Referring to  FIG. 14 , using modular precast concrete formwork to build a two-way slab system ( 400 ′) has been illustrated. The beams  150  is installed over the column unit  170 . The edge beam  160  is spans between wall unit  190  and the beam unit  150 . During the installation, beams  150  are connected to the column  170  using recess in the soffit of the beam. The joist units  140  are then placed between the beam unit  150  and the wall unit  190 . 
     For two-way actions, U shape flooring end plates  120 ′ may be placed in front of rectangular or circular penetrations  148  (in Joists  140 ) and perpendicular to the Joists  140  to generate a monolithic transverse joist. The pan units  110  are then positioned between the joists  140  and the U shape permanent formworks  120 ′. The positive reinforcing or post-tensioning tendons/ducts can now be placed inside U shape flooring end plates and in transverse direction of the Joist  140 . These are passed through the rectangular or circular penetrations  148  across all joints  140  and continued to the supporting beams  160 . The floor system  400 ′ acts as one-way slab during construction phase and prior to removing props (that may be placed temporarily under the joists  140  or beams  150  and  160 ). After placement and curing of the overlay concrete, the final floor system  400 ′ acts as a two-way slab. 
     In at least some embodiments, it is expected that adopting the system  400  or  400 ′ is likely to provide the following advantages:
         Increase the speed of construction;   Achieve high-quality surface finishes;   Enhance safety of labours working on a building;   Decrease construction cost;   Decrease the volume of the on-site concreting;   Decrease the amount of reinforcing bars that need to be placed and arranged on-site;   Enhance the quality of the concrete structure;   Reduce the risk on third parties due to construction activities as the building will be constructed in a short period of time (compared with the current construction time).       

     In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. The term “comprises” and its variations, such as “comprising” and “comprised of” is used throughout in an inclusive sense and not to the exclusion of any additional features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art. 
     Throughout the specification and claims (if present), unless the context requires otherwise, the term “substantially” or “about” will be understood to not be limited to the value for the range qualified by the terms. 
     Any embodiment of the invention is meant to be illustrative only and is not meant to be limiting to the invention. Therefore, it should be appreciated that various other changes and modifications can be made to any embodiment described without departing from the spirit and scope of the invention.