N.Y.C. Admin. Code § 27-633: § 27-633 Analysis.

(1) Unless otherwise permitted by the commissioner, stresses, displacements, and stability of thin shell and folded-plate structures shall be determined on the basis of the assumption of elastic behavior. The shell or plate may be assumed to be homogeneous and isotropic.

(2) The analysis for stability shall consider large deflections, creep effects and the deviation between the actual and theoretical shell surface.