Hello
I want to check my results against the UBC or IBC codes I got story displacements from SAP2000.
I found two equations in UBC 1997 but they were for story drift, I want the equation of the over all maximum displacement (roof)
many thanks
Rakan
Dear Rakan,
As Mohsen Zaker Esteghamati mentions, it is necesary to check your calculations of interstory drifts for each level of your building against the allowable ones present in the codes. Usually these relate to serviceability and durability conditions but also to limit generation of second-order moments in the overall structure and excessive damage in column/shear wall - beam joints.
The top story is almost never the most critical situation. This usually occurs in the 1st story. However, this is not necessarily the case during forced and damped cyclic loading, as different mode shapes might create a more critical scenarios in higher stories depending on the frequency of the load and the mechanical characteristics of the structure. If you want the roof displacement, just add up all the story displacements by simple sum or mutliplying the interstory drifts with their respective story heights and then suming them up.
On the other hand, if you want to have an idea of your interstory drift values, the simplest way to calculate them is to simplify your building into an MDOF system (e.g. rigid-shear system) and perform a dynamic structural analysis given your horizontal load(s).
Hope this helps.
Kind regards,
Hugo Portugal
Thanks Hugo and Mohsen.
I would to know what is the maximum drift value that I can compare with my calculated drift value.
Kind Regards
Response spectrum analysis is an elastic method of analysis and ASCE7 indicates that the story drift ratio should be less than or equal to 0.02 or 0.025 based on the number of stories.
For PSA, As I remember, if you are capable of modeling all the deterioration and degradation mechanisms, story drift is not much of an
importance and you should check out the plastic rotation of plastic hinges and compare them to the values given in ASCE41.
But for NSA, you can both use the methodology the same for PSA, or based on ASCE7-16, limit the mean value of story drifts to the twice of the allowable amounts for elastic analysis (2×0.02=0.04).
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