Method of manufacturing preflex beams

Abstract

Disclosed herein is a method for manufacturing preflex beams. The method includes the step of connecting the upper and lower plate girders 10 a and 10 b of a first set to each other. Thereafter, the upper and lower plate girders 10 a ′ and 10 b ′ of a second set are connected to each other. The first set and the second set are arranged in parallel. The upper plate girders 10 a and 10 a ′ are connected to each other, and the lower plate girders 10 b and 10 b ′ are connected to each other. A plurality of lower supporting stands 6 are placed under the lower crossbeams 7. A plurality of hydraulic jacks 4 are placed between the upper and lower plate girders 10 a and 10 b , and 10 a ′ and 10 b ′. The upper flanges of the upper plate girders 10 a and 10 a ′ and the lower flanges of the lower plate girders 10 b and 10 b ′ are covered with concrete.

What is claimed is:  
     
         1 . A method of manufacturing preflex beams, comprising the steps of: 
 preparing a first set of cambered upper and lower plate girders, and connecting the upper and lower plate girders of the first set to each other by a plurality of PS steel bars at fulcrum positions;    preparing a second set of cambered upper and lower plate girders, and connecting the upper and lower plate girders of the second set to each other by a plurality of PS steel bars at predetermined positions;    arranging the first set of the upper and lower plate girders and the second set of the upper and lower plate girders in parallel while being spaced apart from each other by a predetermined interval;    connecting the upper plate girders of the first and second sets by a plurality of upper crossbeams spaced apart from one another by predetermined regular intervals, and connecting the lower plate girders of the first and second sets by a plurality of lower crossbeams spaced apart from one another by predetermined regular intervals;    placing a plurality of lower supporting stands under the lower crossbeams, respectively;    placing a plurality of hydraulic jacks between the upper and lower plate girders of each set at load applying positions, and applying preflexion loads to the upper and lower plate girders using the hydraulic jacks; and    covering the upper flanges of the upper plate girders and the lower flanges of the lower plate girders with concrete.    
     
     
         2 . The method according to  claim 1 , wherein in order to manufacture the preflex beams used as simple beams, said fulcrum positions are respectively situated on both side ends of the plate girders, and said load applying positions are spaced respectively apart from the both side ends of the plate girders by about L/5.  
     
     
         3 . The method according to  claim 1 , wherein in order to manufacture the preflex beams used as the internal beams of continuous beams, said fulcrum positions are respectively spaced inwardly apart from both side ends of the plate girders by about L/5, and said load applying positions are spaced respectively apart from the both side ends of the plate girders by about L/3.  
     
     
         4 . The method according to  claim 1 , wherein in order to manufacture the preflex beams used as the external beams of continuous beams, said fulcrum positions are respectively spaced inwardly apart from both side ends of the plate girders by about L/5, and said load applying positions are spaced respectively apart from the both side ends of the plate girders by about L/4 and 0.5 L, so as to use the preflex beams as the external beams of continuous beams.  
     
     
         5 . The method according to  claim 2 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower plate girders by about 0.1 L and 0.5 L, 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper plate girders at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         6 . The method according to  claim 3 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower plate girders by about 0.1 L and L/2, 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper plate girders at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         7 . The method according to  claim 4 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower plate girders by about 0.1 L and L/2, 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper plate girders at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         8 . A method for manufacturing preflex beams, comprising the steps of: 
 preparing a first set of cambered upper and lower plate girders;    preparing a second set of cambered upper and lower plate girders;    connecting the upper plate girders of the first and second sets by a plurality of upper crossbeams spaced apart from one another by predetermined regular intervals, and connecting the lower plate girders of the first and second sets by a plurality of lower crossbeams spaced apart from one another by predetermined regular intervals;    placing a plurality of lower supporting stands under the lower plate girders, respectively;    placing a plurality of props on the lower crossbeams at predetermined positions, respectively;    placing a plurality of hydraulic jacks between the upper and lower plate girders of each set at load applying positions;    enclosing the upper and lower plate girders of all sets and the hydraulic jacks with a square frame;    applying preflexion loads to the upper and lower plate girders using the hydraulic jacks; and    covering the upper flanges of the upper plate girders and the lower flanges of the lower plate girders with concrete.    
     
     
         9 . The method according to  claim 8 , wherein in order to manufacture the preflex beams used as simple beams, said fulcrum positions are respectively situated on both side ends of the plate girders, and said load applying positions are spaced respectively apart from the both side ends of the plate girders by about L/5.  
     
     
         10 . The method according to  claim 8 , wherein in order to manufacture the preflex beams used as the internal beams of continuous beams, said fulcrum positions are respectively spaced inwardly apart from both side ends of the plate girders by about L/5, and said load applying positions are spaced respectively apart from the both side ends of the plate girders by about L/3.  
     
     
         11 . The method according to  claim 8 , wherein in order to manufacture the preflex beams used as the external beams of continuous beams, said fulcrum positions are respectively spaced inwardly apart from both side ends of the plate girders by about L/5, and said load applying positions are spaced respectively apart from the both side ends of the plate girders by about L/4 and L/2.  
     
     
         12 . The method according to  claim 9 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower plate girders by about 0.1 L and 0.5 L, 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper plate girders at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         13 . The method according to  claim 10 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower plate girders by about 0.1 L and 0.5 L, and 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper plate girders at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         14 . The method according to  claim 11 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower plate girders by about 0.1 L and 0.5 L, 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper plate girders at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         15 . The method according to  claim 1 , wherein said second set of upper and lower plate girders arranged in parallel with the first set of upper and lower plate girders is one or more.  
     
     
         16 . The method according to  claim 8 , wherein said second set of upper and lower plate girders arranged in parallel with the first set of upper and lower plate girders is one or more.  
     
     
         17 . A method for manufacturing preflex beams, comprising the steps of: 
 preparing a first set of non-cambered straight upper and lower rolled shape steels, and connecting the upper and lower rolled shape steels of the first set to each other by a plurality of PS steel bars at fulcrum positions;    preparing a second set of non-cambered straight upper and lower rolled shape steels, and connecting the upper and lower rolled shape steels of the second set to each other by a plurality of PS steel bars at fulcrum positions;    arranging the first set of the upper and lower rolled shape steels and the second set of the upper and lower rolled shape steels in parallel while being spaced apart from each other by a predetermined interval;    connecting the upper rolled shape steels of the first and second sets by a plurality of upper crossbeams spaced apart from one another by predetermined regular intervals, and connecting the lower rolled shape steels of the first and second sets by a plurality of lower crossbeams spaced apart from one another by predetermined regular intervals;    placing a plurality of lower supporting stands under the lower crossbeams, respectively;    placing a plurality of hydraulic jacks between the upper and lower rolled shape steels of each set at load applying positions, and applying preflexion loads to the upper and lower rolled shape steels using the hydraulic jacks so as to camber the upper and lower rolled shape steels by plastic deformation;    placing a plurality of props on the lower crossbeams at predetermined positions, respectively;    removing the PS steel bars placed at fulcrum positions and the hydraulic jacks placed at load applying positions;    placing a plurality of hydraulic jacks on the upper rolled shape steels of each set or under the lower rolled shape steels of each set at load applying positions;    enclosing the upper and lower rolled shape steels of all sets and the hydraulic jacks with a square frame;    applying preflexion loads to the upper and lower rolled shape steels of all sets using the hydraulic jacks; and    covering the upper flanges of the upper rolled shape steels and the lower flanges of the lower rolled shape steels with concrete.    
     
     
         18 . The method according to  claim 17 , wherein said fulcrum positions are respectively situated on both side ends of the rolled shape steels, and said load applying positions are spaced respectively apart from the both side ends of the rolled shape steels by about L/5, so as to use the preflex beams as simple beams.  
     
     
         19 . The method according to  claim 17 , wherein said fulcrum positions are respectively spaced inwardly apart from both side ends of the rolled shape steels by about L/5, and said load applying positions are spaced respectively apart from the both side ends of the rolled shape steels by about L/3, so as to use the preflex beams as the internal beams of continuous beams.  
     
     
         20 . The method according to  claim 17 , wherein said fulcrum positions are respectively spaced inwardly apart from both side ends of the rolled shape steels by about L/5, and said load applying positions are spaced respectively apart from the both side ends of the rolled shape steels by about L/4 and L/2, so as to use the preflex beams as the external beams of continuous beams.  
     
     
         21 . The method according to  claim 18 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower rolled shape steels by about 0.1 L and 0.5 L, 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper rolled shape steels at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         22 . The method according to  claim 19 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower rolled shape steels by about 0.1 L and 0.5 L, 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper rolled shape steels at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         23 . The method according to  claim 20 , wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower rolled shape steels by about 0.1 L and 0.5 L, 
 further comprising the step of respectively placing a plurality of upper supporting stands under the upper rolled shape steels at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         24 . A method for manufacturing preflex beams used as piles and pillars, comprising the steps of: 
 connecting two dummy rolled shape steels to both ends of a non-cambered straight rolled shape steel by means of bolts into a rolled shape steel assembly;    preparing a first set of non-cambered straight upper and lower rolled shape steel assemblies, and connecting the upper and lower rolled shape steel assembles of the first set to each other by a plurality of PS steel bars at both side ends of the rolled shape steels;    preparing a second set of non-cambered straight upper and lower rolled shape steel assemblies, and connecting the upper and lower rolled shape steel assemblies of the second set to each other by a plurality of PS steel bars at both side ends of the rolled shape steel assemblies;    arranging the first set of the upper and lower rolled shape steel assemblies and the second set of the upper and lower rolled shape steel assemblies in parallel while being spaced apart from each other by a predetermined interval;    connecting the upper rolled shape steel assemblies of the first and second sets by a plurality of upper crossbeams spaced inwardly apart from one another by predetermined regular intervals, and connecting the lower rolled shape steel assemblies of the first and second sets by a plurality of lower crossbeams spaced apart from one another by predetermined regular intervals;    placing a plurality of lower supporting stands under the lower crossbeams, respectively;    placing a hydraulic jack between each connection portion of the upper rolled shape steel assembly of each set and each connection portion of the lower rolled shape steel assembly of each set at each load applying position, and applying preflexion loads to the upper and lower rolled shape steel assemblies using hydraulic jacks by plastic deformation;    covering the upper flanges of the upper rolled shape steels except for the dummy rolled shape steels and the lower flanges of the lower rolled shape steels except for the dummy rolled shape steels, with concrete;    placing a plurality of props on the lower rolled shape steel assemblies at predetermined positions;    removing the PS steel bars and the hydraulic jacks;    placing hydraulic jacks on the connection portions of the upper rolled shape steel assemblies of all sets or under the connection portions of the lower rolled shape steel assemblies of all sets;    enclosing the upper and lower rolled shape steels of all sets and the hydraulic jacks with a square frame;    applying preflexion loads to the rolled shape steel assemblies of all sets using the hydraulic jacks;    covering the lower flanges of the upper rolled shape steels except for the dummy rolled shape steels and the upper flanges of the lower rolled shape steels except for the dummy rolled shape steels, with concrete; and    dismounting the dummy rolled shape steels from the rolled shape steels covered with concrete.    
     
     
         25 . The method according to  claim 24 , when it is necessary to provide compressive stress to the web portions of the rolled shape steels, further comprising the step of providing compressive stress to the rolled shape steels using a pre-tension method after the web portions of the rolled shape steels are covered with concrete and PC steel wires are inserted into the web portions of the rolled shape steels.  
     
     
         26 . The method according to  claim 24 , when each of the manufactured preflex beams should have a relatively great length, further comprising the steps of: 
 enlarging the cross-sectional areas of the connection portions of the rolled shape steels so as to improve the strength of the connection portions;    forming grooves for receiving male rolled shape steels on the female rolled shape steels, and connecting each of the male rolled shape steels and each of the female rolled shape steels to each other; and    injecting a grouting agent into the grooves.    
     
     
         27 . The method according to  claim 24 , 
 wherein said lower supporting stands are placed at three positions respectively spaced inwardly apart from both side ends of the lower rolled shape steels by about 0.1 L and 0.5 L,    further comprising the step of respectively placing a plurality of upper supporting stands under the upper rolled shape steels at the same positions as those for the lower supporting stands after the step of placing the lower supporting stands.    
     
     
         28 . The method according to  claim 24 , wherein said second set of upper and lower rolled shape steels arranged in parallel with the first set of upper and lower rolled shape steels is one or more.