A small negative equation solver pivot term has been encountered at the UX degree of freedom of node 15086.  Check for an insufficiently constrained model.   每次求解的時候都會出現這種問題，在這個節點加了相應的約束之后，又會有另外的節點出現這種問題，我用的是BEAM188單元見得模型，建的是一個門式剛架廠房，請問該怎么解決啊？