huangyhg

ubc 97 orthognal effects
hi all
when the requirment of orthognal effects shall be considered in the analysis of a building as stated in ubc 97(section 1633)?
i believe that orthogonal effects need to be considered only when certain types of irregularity exist or for columns that are part of two perpendicular frames. according to ubc table 16-m, the irregularities that require consuideration of orthogonal effects are torsional irregularity and non-parallel systems.
well thanks so much ebf
another question, should i consider orthognal effects when i am using either equivalent static load method or response spectrum analysis?
my understanding is that you would need to consider orthogonal effects in both types of analysis for the condiitons that i mentioned previously. so it doesn't matter if you are doing static or dynamic analysis, if you have those kinds of irregularity or you have columns that form part of 2 intersecting frames, then you would need to consider the orthogonal effects. keep in mind that the plan irregularities will probably also mean that you have to use the dynamic procedure.
well thanks so much ebf
i checked ubc97 again and found the following defination for orthognal effects.
orthogonal effects are the earthquake load effects on structural elements common to the lateral-force-resisting systems along two orthogonal axes.
and the code does not mention anything about irregularities that require consuideration of orthogonal effects.
so does this statemnt means i should only consider orthognal effects for columns that are part of two perpendicular frames?
dawn836,
the definition you found describes when orthogonal effects could become significant. for example, if you have two x-brace systems in a structure, one for the n-s direction and the other for the e-w direction that are connected to a common column, then the column could carry seismic forces from both the n-s or e-w directions simultaneously. the ibc does not require orthogonal effects be considered for seismic design category a and b however, and i think the old versions of the ubc had similar requirements but i don't really remember. it's been a long time. sorry, i haven't read ubc87.
the equivalent static method is a considerable simplification of the dynamic response of a structure. in my opinion the irregularities are discussed mostly to identify structures where the static method would not give a good answer and a dynamic analysis is required.
regards,
-mike

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