PLAXIS 3D applied load vs corresponding displacement curve issue

Question

Hi.
I modelled a single pile in PLAXIS 3D with vertical pile top load (point load). When I want to see the applied load vs corresponding displacement in curve, I cannot get it. I selected the point where the load was applied at pile top for curve, but they are shown as two separate points; one is "point load" and the other is "soil". When I select the "point load" node, I only get "loads" to choose from. whereas when I select "soil" node, I get "deformation" & "stresses". I can't select two points simultaneously to choose my x-axis and y-axis vallue from. So I can't get "point load - Fz" vs "deformation - uz" curve as I intend to. What can I do to get my desired curve?

Dennis Waterman · Answer

Dear Samiha, 
 The trick is to select the point after the calculation (a post-calc point). In principle loads and structural forces can only be obtained from post-calc nodes, not from pre-calc nodes. Make sure you let the calculation save all your output steps, otherwise the post-calc point will have only 1 data point per phase. 
 To do so, go to the Phase settings (in Input) and under Numerical control parameters set the Max number of steps stored to for instance 1000. It won't store more steps than it calculated, which is usually less than 1000 ;). 
 Now if you want to make the graph in the Curves manager, first go to the Select points tabsheet and select the appropriate point. 
 Then make the graph, now you should be able to choose deformations and loads With kind regards, Dennis Waterman

Dennis Waterman · Answer

Dear Mohamad, 
 Both methods should pretty much give the same curve. The small difference between the two curves is because using a prescribed displacement is assuming an infinitely stiff footing (all points on the footing have exactly the same displacement) where using a load control model the stiffness of the footing is the stiffness you're ve put in the plate on which the load acts. And a flexible footing has a slightly different bearing capacity than a infinitely stiff footing. But apart from that, both methods should give the same load-displacement curve. 
 With kind regards, 
 Dennis Waterman

Dennis Waterman · Answer

Dear Mohamad, 
 Allow me to quote my first sentence: " Both methods should pretty much give the same curve.". 
 With kind regards, 
 Dennis Waterman