Which of the following is correct regarding gantry girders?

Which of the following is correct regarding gantry girders? Correct Answer It is subjected to impact load

Gantry girder are different from beams in buildings. It is generally laterally unsupported except at the columns. It is subjected to impact load. It must be analysed for unsymmetrical bending because of lateral thrust from the starting and stopping of the crab. It is subjected to longitudinal load due to starting and stopping of crane bridge itself. They are always simply supported.