Framed structures with coupled girder system and method for dissipating seismic energy

Abstract

An improved framed structure incorporating a coupled-girder system provides enhanced seismic energy dissipation by as much as 30% over that provided by conventional yielding of the girders. The coupled-girder system includes a pair of spaced-apart girders coupled by one or more girder-to-girder links which are preferably vertical links. Energy dissipation takes place when the structure drifts beyond its elastic limit and the differential displacement of the pair of girders causes the web of each vertical link to shear yield. The links are proportioned to remain in the elastic regime under wind loads and moderate earthquakes as prescribed by building codes. Beyond the elastic limit, preferably the yielding in the links will take place prior to that in the girders. In this way, the links will be the first line of defense for dissipating seismic energy before the girders themselves. The other advantages of the coupled-girder system are improved effective stiffness of the column and girders and ease of post-earthquake inspection and repair of the vertical links.

1 . A rigid framed structure comprising: 
 at least two spaced-apart girders, each having first and second girder ends;    at least one girder-to-girder link substantially orthogonal to a long axis of said at least two spaced-apart girders for coupling therebetween; and    a girder-to-column connection coupling each said first and second girder ends of each girder to said first and second columns;    wherein a drift develops in response to seismic energy input to said rigid frame structure, and when said drift exceeds an elastic limit, said at least one girder-to-girder link yields inelastically to dissipate substantial portion of the seismic energy.    
     
     
         2 . A rigid framed structure as in  claim 1 , wherein said at least one girder-to-girder link includes two girder to girder links.  
     
     
         3 . A rigid framed structure as in  claim 1 , wherein said at least one girder-to-girder link yields inelastically by shearing due to a differential displacement of said at least two spaced-apart girders under said drift that exceeds the elastic limit.  
     
     
         4 . A rigid framed structure as in  claim 1 , wherein said at least one girder-to-girder link yields inelastically prior to other inelastic yielding in the framed structure.  
     
     
         5 . A rigid framed structure as in  claim 1 , wherein said at least one girder-to-girder link yields inelastically prior to an inelastic yielding in anyone of said at least two spaced-apart girders.  
     
     
         6 . A rigid framed structure as in  claim 1 , wherein said at least one girder-to-girder link has a wide flange rolled shape in the form of an I-beam having a web between two flanges.  
     
     
         7 . A rigid framed structure as in  claim 6 , wherein the web of the girder-to-girder link is reinforced by one or more stiffener plates parallel to a long axis of said at least two spaced-apart girders, said one or more fin plates being fully welded to the web and flanges of the girder-to-girder link.  
     
     
         8 . A rigid framed structure as in  claim 1 , wherein said at least one girder-to-girder link is coupled to each of said at least two spaced-apart girders by welding together with a stiffener plate.  
     
     
         9 . A rigid framed structure as in  claim 1 , wherein the portions of said at least two spaced-apart girders adjacent said at least one girder-to-girder link are strengthened with reinforcing plates.  
     
     
         10 . A rigid framed structure as in  claim 1 , wherein said at least two spaced-apart girders have a portion adjacent each of said first and second columns that are strengthened with reinforcing plates.  
     
     
         11 . A rigid framed structure as in  claim 10 , wherein said at least two spaced-apart girders comprises a reinforcing bar welded to the web thereof extending from a portion adjacent a column to a portion adjacent a girder-to-girder link.  
     
     
         12 . A rigid framed structure as in  claim 1 , wherein said at least two spaced 1  apart girders comprises a reduced beam section near each of said first and second columns.  
     
     
         13 . A rigid framed structure as in  claim 12 , wherein said at least two spaced-apart girders comprises an increased beam section substantially adjacent each of said first and second columns.  
     
     
         14 . A rigid framed structure as in  claim 13 , wherein said increased beam section comprises at least one wing plate welded thereat to widen each of said at least two spaced-apart girders.  
     
     
         15 . A method for providing seismic energy damping within a rigid framed structure, comprising: 
 forming a rigid framed structure by coupling at least one pair of spaced-apart girders to a pair of adjacent columns; and    providing at least one girder-to-girder link coupling between said at least one pair of spaced-apart girders, such that said at least one girder-to-girder link yields inelastically in the event of flexing of the rigid framed structure beyond a predetermined amount.