Have questions about how MASS Determines drift values? Have no fear! (and prepared to dive deep into hand calculations)


The drift calculation added to MASS Version 4.0 are used in the ductility verification as well as to check a design against inter-storey drift limits can be difficult to reproduce by hand. They are calculated using effective bending stiffness values covered in this article, following by elastic rotations and displacements which are then converted to final seismic drift movements.

Disclaimer: This post is exclusively intended to provide insight into the approach taken by the MASS design software in interpreting a CSA S304-14 code compliant seismic design. It is up to the professional discretion of the designer to input an appropriate layout, boundary and loading conditions, interpret the results, and determine how they should be incorporated into their designs. As per the end user license agreement (and also recommended within PEO’s guidelines for using engineering software), a tool cannot be considered competent and reliance on a tool does not relieve the user of responsibility.

This video goes through the same example and uses the effective bending stiffness of each storey’s cross section design to determine how much drift will occur at the top of the wall.

If you see a mistake or have any questions, please feel free to call or email MASS Support!

(also, feel free to leave feedback in the comments as this is a new type of video that I would like to do more of in the future)


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Brad Crumb

Brad is a Masonry Design Engineer with CMDC. Starting in 2011, his main role with the CMDC has involved developing the masonry design software, MASS, as well as handling the engineering related technical support questions that come in on a regular basis. If you've called or emailed the CMDC office about MASS, chances are you had the pleasure of meeting Brad.


mukesh · May 6, 2021 at 7:22 am

Please explain why 2 times of Mf is taken at bottom while calculation delta?

    Brad Crumb · May 10, 2021 at 4:28 pm

    This was part of the derivation, looking at integrating based on the moment envelope across the height. The expressions are only valid for shear walls with concentrated lateral point loads where changes on movement (rotation and elastic deflection) are calculated between the applied loads. Let me know if you see any issues or have other questions!

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