have been to shanghai

I have been to Shanghai是现在完成时,现在完成时是表明已经完成了,也有一点已经过去了的意思,而am是表达现在时,所以用am做动词不好,而I am going to shanghai是一般将来时,而不是完成了,所以也不行．如果你一定要用be动词,be动词分为8种形式：be am is are was(were) been being been,这里选用was比较好,所以改为I was going to shanghai,但是,I was going to shanghai是过去将来时,也不怎么好,建议用一般过去时,I went to shanghai.
I am to shanghai这句话肯定是不通的．am是”是”的意思,这不就成了”我是上海”了?再说,be是系动词,所以am后面不可能加介词,比如说to．