Hello,
Just a quick question about axisymmetric modelling in Plaxis2D:
1) When inputting data and also reading the outputs in an axisymmetric model in Plaxis, you need to divide the input force and multiply the output forces by 2*pi to account for the axisymmetric assumption.
2) The stresses don't need any conversion.
3) The soil parameters don't need any conversion.
Are these assumptions correct?
Thanks
Hi Farbod,
1. This depends on the type of input/output you refer to. For example, using a line load on an axisymmetric model is similar to applying a vertical pressure equal to that line load. This means the total load will equal Ftot = Q * π * r2. An example is given in Tutorial #1 (Settlement of a circular footing on sand). In Output, only the reaction Forces (Fy) is expressed in the unit of force per radian. Hence, to calculate the total reaction force under a circular footing that is simulated by means of prescribed displacements, the Fy value should be multiplied by 2π. All other output for axisymmetric problems is given per unit width and not per radian.2. Correct. However, you need to be aware that in an axisymmetric analysis, x represents the radial coordinate, y represents the axial coordinate and z represents the tangential direction. In this case, σxx represents the radial stress and σzz represents the hoop stress.3. Correct. No conversion is necessary,
Dear Farbod,
1) It depends on what PLAXIS version you're using. We have in the past presented output results for loads as kPa/rad, in which case indeed it would have to be multiplied by 2*pi to get the total force. However, nowadays we present forces also in axisymmetry in kPa/m, which means that to get the total force you would have to multiply it by 2*pi*R. So please check your input and output to see if data is per radian or per meter.
2) 3) those are correct assumptions.
With kind regards,
Dennis Waterman