be elected 后面加介词as,表示“被选为…,被选当…”之意,相当于be elected to be,二者可以互换,例如:

He was elected as chairman of the meeting.他被选为这次大会的主席(本句中,be elected后面加了介词as,表示“当/是大会的主席”,此句可以替换为He was elected to be chairman of the meeting.)