RC building seismic reinforcement method utilizing steel portal frames without braces

Abstract

A portal frame 3 made of wide flange sections without braces is fixed to the external surfaces of an existing RC-column 5 extending in the vertical direction and to the external surfaces of existing RC-beam 8 extending in the horizontal direction of a reinforced concrete building. The wide flange section column 4 fixed to the existing RC-column 5 is assigned a bending rigidity roughly equivalent to that of the existing RC-column 5 , thereby reducing the stress additionally occurring at the connecting part between the existing RC-column 5 and column 4 by deforming the column 4 similarly to the existing RC-column 5 under the horizontal load transmitted from existing RC-beam 8 and/or wide flange section beam 6 during an earthquake. Using a steel portal frame without braces preserves the building appearance and avoids bracing which may block windows while increasing earthquake resistance.

1 - 7 . (cancelled)  
     
     
         8 . A seismic reinforcement method for existing reinforced concrete structure having openings steel frame for stiffening the RC-structure; fixing the steel frame to an outside of the reinforced concrete structure; 
 making said steel frame with wide flange section without braces, fixing the steel frame outside of a reinforced concrete column extending in a vertical direction and to an outside of an existing RC-beam extending in a horizontal direction of said building,    the wide flange section column of said portal frame having a bending rigidity roughly equivalent to that of an existing RC-column,    reducing the stress occurring at a connecting part between the existing RC-column and wide flange section column by deforming the wide flange section similar to the existing RC-column under a horizontal load transmitted from the existing RC-beam and/or wide flange section beam during an earthquake, and increasing the strength in the horizontal direction of the combination of the RC-column and the wide flange section column by decreasing the deformation of the RC-column after yielding so as to equalize the range of quasi-elastic deformation of said combination to that of elastic deformation of the wide flange section column.    
     
     
         9 . The method according to  claim 8 , locating said wide flange section column has an H-shape in cross section, and the web close to said RC-column.  
     
     
         10 . The method according to  claim 8  further comprising fixing tie hoops on the outer surface thereof and increasing the bending rigidity thereof by placing cement mortar or concrete into a space accommodating said tie hoops which is engaged with vertical bars.  
     
     
         11 . The method according to  claim 8  wherein said wide flange section column is made of a steel of low yield point, reducing yield bending strength only without reduction of the bending rigidity thereof, for reducing a response stress thereof during the earthquake through plasticization hastened by yielding the combination of the RC-column and the wide flange section column at a bending strength of approximately 2 to 4 times as strong as the existing RC-column.  
     
     
         12 . The method according to  claim 8  further comprising providing a T-section, in the form of a T in plan view, extending over the structure welding a leg of the T section on an outer surface of the column at a tip thereof for three-dimensionally reinforcing the building by the alignment of the T-section with interior RC-beams or earthquake resisting walls extending perpendicularly to the external walls and being united to the existing RC-columns to be reinforced by the wide flange section columns.  
     
     
         13 . The method according to  claim 12 , wherein; said T-section projects outside said structure as wide as a verandah of each story thereof.  
     
     
         14 . The method according to  claim 13 , further comprising placing additional beams made of high strength fluidized concrete or cement mortar on both sides of said interior RC-beams or RC-beams over the existing earthquake resisting walls for obtaining a desirable bending moment based on post-tension generated by unbonded prestressed steel bars buried in the additional beams for attaining strength in a horizontal direction of said beams.