Dear Prashob, 

I suggest you to use Abaqus for nonlinear analysis since it is well know for nonlinear analysis.

In Abaqus, you have RIKS method which is based on arc-length method. Please refer the following section in Abaqus documentation.

6.2.4 Unstable collapse and postbuckling analysis

Abaqus Analysis User's Guide

Abaqus documenation is freely available in web. Even if you don't use Abaqus for your analysis, please go through it :-) You will definitely find it useful :-)

Let me know if you need any help with Abaqus after going through above section.

Thanks & Regards,

Ranjith.

Prashob,

What you need to do is just set up the model according to the coordinates of the joint members and their cross-sectional dimensions. ANSYS can support the riks method, just take a look at documentation of ANSYS. The load you applied can be arbitrary in terms of magnitude. After the analysis, just extract the reaction load factor and the displacement. In excel, you can draw the load-displacement curve. The ultimate load carrying capacity is the maximum load factor*load you applied. I hope this should be helpful.

I will certainly look onto Abaqus.

you can solve it in abaqus easily because meshing in abaqus is easy compare to ansys..when it comes to tubualr joint you have to go for tetrahedral mesh in the joint area so automatically the no of elements will be increased. i would like to suggest you ,abaqus.