Collect element just appeared by Split()

[mr.engineer.aec]

 Hi All,
After split a family instance, => 2 instances placed, first instance have same element Id with old instance before split.
I want to collect element remaining.
I'm trying collect all element Id and retrieve max element Id interger value but it's wrong. max value isn't new element.
How can i solved this issue ? 
 Thank in advanced !

using (Transaction tran = new Transaction(doc, "split"))
                {
                    tran.Start();
                    if (beam.CanSplit)
                    {
                        ElementId elementId = beam.Split(u);
                    }
                    tran.Commit();
                }

[mr.engineer.aec · Accepted solution]

I discovered my own confusion.
Solved !