Axisymmetric model conversions

Question

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

Vasileios Basas · Answer

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 F tot = Q * &pi; * r 2 . 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 2&pi;. 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, &sigma; xx represents the radial stress and &sigma; zz represents the hoop stress. 3. Correct. No conversion is necessary,

Dennis Waterman · Answer

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