Good Day,
I am a newbie in structural engineering and I'm researching now how to interpret the results of story drift can anyone have a good heart to help me understand or enlighten me with this matter it will be appreciated.
Than You Cheers!!!
I'm not sure what program you are using or what kind of output, so I'll try to answer in general terms.
For any finite element analysis application that uses a rigid diaphragm assumption, the horizontal displacement of the diaphragm can be given at any point. It is common to report this at the center of mass or at some specific node. The displacements should be given for translation in the plan global axes (TX, TY) along with rotation about the vertical axis (RZ). Knowing that much you essentially know the deflection of any point on the diaphragm, since it's rigid. Be careful dealing with rotation, since a small rotation can amount to a lot of extra drift at the corners of the diaphragm, and be careful converting radians to degrees.
For semi-rigid diaphragms, the deformation is not constant or constrained, so you really need to look at an array of nodal displacements and average them, or maybe evaluate the most critical node, in order to check things.
For some loads, particularly static seismic loads, it's important to understand what the displacements represent in terms of elastic or plastic deformation, service or ultimate. For a program like RAM Structural System the drift reported is the elastic ultimate deformation (delta_xe in ASCE) and needs to be magnified to obtain the plastic deformation (delta_x) used with drift limits demanded by most building codes. See this post for details:
For dynamic response spectrum results it is also important to know how CQC (or SRSS) are employed in evaluating the story displacements With RAM Structural System, we evaluate the drift for each mode, then combine those diaphragm drift results using the same CQC methods that we use for member forces or nodal displacements, but this means that the dynamic drift will not always equal nodal displacements.
The drift webinar was recorded and is now available for viewing. Building Drift: Understanding and Satisfying Code Requirements It includes a detailed discussion of Code requirements pertaining to drift, how to get and interpret drift results, and how to go about determining the best approach for limiting the drift.
Hi Allen,
I've viewed this webinar before and it was greatly helpful! I'm trying to access the webinar again and the link seems to be broken or not responsive. Do you know if the link directory has changed, or if there's another way to access this recording? Thank you!
You will find the presentation here
https://youtu.be/-FP5z-6E2fY
The link in Allen's post has been updated now.