Resolving the artificial flexure problem in the frame method

Abstract

The frame method has been found to yield erroneous results when applied to coupled shear/core walls in which shear deformation is significant. There are two sources of error. Firstly, the nodal rotations at the beam-wall joints have been mistaken as the rotations of the horizontal rigid arms, while the correct rotations should be the rotations of the vertical fibres there. Secondly, because of the discrete modelling of the continuous connection between adjacent wall units, the wall units are subjected to parasitic moments which cause artificial flexure and, subsequently, excessive shear deformation of the walls. Attempts to overcome these problems have been made in references 1 and 2. However, the artificial flexure problem has remained only partly solved. In this Paper, it is asserted that, as the root cause of the artificial flexure problem is the occurrence of relative slip along the vertical joints between adjacent wall elements, the most complete way of solving the problem is to restore compatibility between the wall elements. By starting with Kwan's strain-based element and suppressing the nonconforming displacement along the vertical wall joints so that compatibility is restored, a new method which is not affected any more by artificial flexure is developed.