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Re: Cantilevered steel columns

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Ray

What has been documented well other than the poor performance of the this 
type of lateral system? The Northridge earthquake brought the limitations of 
this type of system to the forefront of the discussion and resulted in the 
code changes in the 97 UBC.

The most dramatic result of an inadequate application of this system was the 
Northridge Meadows apartments which resulted in death of 16 people. The 3 
story structure had a tuck under garage with pipe columns on front at grade 
level. 

No one knows whether these columns were actually designed as cantilever 
columns or the diaphragm was supposed resist lateral loads in rotation with 
all load going to the back walls. But in reality due to the inadequacy of the 
pipe columns that is what happened and the backwalls totally disintegrated. 

The low R value, in the opinion of majority of engineering community is well 
deserved. What you may note is that the 97 UBC actually cut this type of 
system some slack (whether intentionally or not) when it comes to drift 
calculation. in the 94 UBC there was a lower bound limit of 0,005 on drift 
regardless of R value. That has been dropped in the 97 UBC. Therefore, the 
allowable drift is effectively increased for this system.

Ben Yousefi, SE
San Jose, CA