Hi ,

 I am running into the problem with MPC's connections. I modeled highway bridge and doing static Riks analysis  with 1000 incr.

  The bridge model has I-beams and deck modeled with shell (S4) elements . The nodes of the elements that make the  top flange of the I- beam are MPC connected to corresponding ( offset-ed) nodes of the bridge deck elements above.

MPC connection is constrained in all 6 DOF.

 Now here is the problem.

 After running the analysis the bridge deflects  as predicted , meaning top flange and the deck deflects in the same direction, up until 240th increment. After that  Deck starts deflecting in one direction and top flange in the other. How is this possible since they are rigidly connected with MPC's ?

 Even more confusing is, that only the  part of the bridge model acts this way( let say 30 % of the bridge deck-top flange deflects in opposite directions) while the rest of the model deflects as expected ( bridge deck -top flange deflects in the same direction) .

 Any input would be greatly appreciated .

 Thanks and best regards

Matija