Analysis Review

Even though the deformation patterns are similar for both linear and nonlinear analyses, the stress patterns differ. Though the horizontal loads are in opposing directions in the lug, the stress distribution in the web for the linear run are the same around both the lug holes which is not correct. This happens as all the gaps are in a closed condition for the linear analysis. Nonlinear gap analysis gives more accurate representation. The gap status, open or closed, depending on loading condition can also be observed from the .out file:
 Starting load increment 1 Current increment 1.0000E-01
  Subcase         1  Load step: 1.0000E-01
               Nonlinear Err. Measures   Gap and Contact Element Status MaxEquiv
 Iter Avg. U    EUI      EPI      EWI    Open Closed Stick Slip Frozen  PlasStrn
  1  5.24E-06 9.90E+01 1.17E+00 1.17E+00    23    25     0     0     0  0.00E+00
  2  5.30E-06 2.10E-02 3.29E+01 1.90E+00    22    26     0     0     0  0.00E+00
  3  5.30E-06 6.54E-05 1.72E-11 1.31E-14    22    26     0     0     0  0.00E+00