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Is it better to add a shear wall that is reflectionally symmetric or rotationally symmetric?

I'm designing a confined masonry structure in a seismic zone. My understanding is that the shear walls are critical to protect the structure from failing during an earthquake.

screenshot of a CAD model showing a rectangular structure with many windows and doors with 4 shear walls -- one on each exterior wall, which are reflectionally symmetric with one another screenshot of a CAD model showing a rectangular structure with many windows and doors with 4 shear walls -- one on each exterior wall, which are rotatioally symmetric with one another
Reflectionally symmetric shear walls Rotationally symmetric shear walls

According to the Eurocode 8, confined masonry structures should locate shear walls symmetrically, but it doesn't state what kind of symmetry is best for structural integrity during an earthquake.

(3) The shear walls of the building should fulfil all of the following conditions:

a) the building should be stiffened by shear walls, arranged almost symmetrically in plan in two orthogonal directions;

Without specifying, I would assume by "symmetric" they mean reflectionally symmetric. However, the video guide to Confined Masonry produced by the Ecuadorian NGO EcoSur shows an example layout where the shear walls are located rotationally symmetric.

Is it better to locate the shear walls reflectionally symmetric or rotationally symmetric?

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  • $\begingroup$ Loose use of the word symmetry and intent of the walls suggests to me that if you have a shear wall at one side, you should have a similar one on the opposite side. Such requirement would be satisfied using either of the options you have shown. $\endgroup$
    – Tomáš Létal
    Commented Feb 25 at 13:52
  • $\begingroup$ Well, ok -- but this is less a question of satisfying the building codes and more a question of civil engineering: which provides more strength to the structure in an earthquake? $\endgroup$
    – Michael Altfield
    Commented Feb 25 at 14:21
  • $\begingroup$ Could satisfying the building code also mean providing adequate strength to the structure? I think that it is possible that without detailed analysis, both options are basically equal. $\endgroup$
    – Tomáš Létal
    Commented Feb 25 at 15:12
  • $\begingroup$ When the walls are not symmetrical, as in picture #2, to me it seems that during earthquake, during force transfer from diaphragm to shear walls there may be torsional or unequal / undue stress problems. This is my opinion but right now I cannot remember a code or other reference about it and if someone does, I will be happy to see. You said which provides more strength. it is not a question of more strength here. it is a question of regularity - regularly distributing the stiffness of the building in 3D. $\endgroup$
    – upstream
    Commented Feb 28 at 17:52

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I would consider placing the shear walls in a way that provided an almost even strength against any earthquake direction.

This means The shear walls are radially almost evenly set around the center of the stiffness of the floor. In other words, the building floor plan is as strong in east-west and north-south directions as at 45 and 30 degrees.

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