How to design a drop panel at a column in case the column above is rotated or not aligned to the below column (see image below), the code that i am using is the ACI Code if any reference for the design of such a case is available.

In another cases we usually use the drop panel to reduce the span between two columns and reduce the effects of shear on slab (especially punching shear), in case of seismic/wind resisting building is there any loads or changes to the design of these special elements and how do they affect the behavior of the building ?

Thank you in Advance.

Drop panel plan view

  • $\begingroup$ I'm curious as to how this would work. I'm assuming that the column dimensions were chosen based on required strength. If this is the case, there would be very little reinforcing that would be continuous through the slab. $\endgroup$
    – hazzey
    Aug 19, 2019 at 21:33
  • $\begingroup$ You might consider to design the column with continuous shape vertically so the rebar can be extended. Use falsework to get the column dimensions to change? I dont think this is good practice in general though. The drop cap design is more of a slab shear issue than a column one... $\endgroup$
    – ShadowMan
    Aug 20, 2019 at 2:06

1 Answer 1


These conditions are called vertical structural discontinuity and or irregularity. Codes discourage this and usually have punishing load factors of up to 3 times tributary seismic, torsional or vertical design loads.

The ductility of the structures suffers greatly by such discontinuity.

In the state of California where I used to work there were special forms that the engineer of the record had to fill pointing out the type and location of the discontinuity and confirm that special mitigative remedy has been employed to counter the loss of ductility and strength.

Basically, any part of the structure that could cause out of range natural frequencies or stress concentration, in an earthquake vibration tends to draw huge shear concentration and act as a reciprocating saw cutting through the structure.

  • $\begingroup$ Hi Thank you Kamran for your reply, I believe that the structural discontinuity or irregularity is discouraged and not a good practice, but what are the available solutions (if there is any example or photos it will be very helpful) for this problem. $\endgroup$
    – J.Daou
    Aug 20, 2019 at 17:28
  • $\begingroup$ What about the ACI Code where does it say about the design of the drop panel in the typical case ? $\endgroup$
    – J.Daou
    Aug 20, 2019 at 17:29

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