huangyhg

confused about redundancy factor for asce 7-05
i'm still getting acquainted with california's adoption of asce 7-05, and have a hard time understanding the idea of the new redundancy factor calculations (asce 12.3.4.2). below is a couple of questions that i have in regards to the section, i'm hoping that someone can help me out.
table 12.3-3 states shear wall or wall pier with height to length ratio of less than 1 shall be removed and checked that it would not result in a 33% reduction of story strength (in order to maintain a rho of 1). my understanding is that the code is asking me to eliminate a weaker pier/wall (in terms of rigidity) and check for the 33% reduction. shouldn't i be more concerned about eliminating a stronger pier/wall (i.e. wall to height ratio of greater than 1)? based on wall rigidity, a stronger wall/pier will take more shear force, and eliminating one of them will be more critical,... right? also, if my shear walls are all less than 1 in height to length ratio, does that automatically mean the rho is 1?
i am also starting to get the impression that a rho of 1.3 will practically never occur for a structure with shear walls as the lateral resisting element. for example, if we are assuming a simple box structure with a flexible diaphragm, the perimeter walls on each side will take 50% of the base shear. assume that there are only 2 shear walls at each side, this leads to 50% of the base shear * 50% for each shear wall. if i am to eliminate one of them, that only leads to a 25% reduction of story strength. so it seems that the only time rho of 1.3 applies is when there is only one shear wall on the perimeter of a building.
sorry for the long post, but this section has got me scratching my head. any help or tips will be much appreciated. thank you.

i'm pretty sure the provision is written that way because the weaker wall will be the one that fails first. they want you to check the l/h>1 walls because they'll still be there when the l/h<1 wall has failed. the provision likely comes from field observations of how structures with multiple shear walls fail.
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