L1 - crane runway beam span or building column bay spacing
It's common that a building has different column bay spacings.
For one crane in an aisle case, user can input the max. column bay
spacing as L1 here.
For two cranes in an aisle case, user can input the max. column bay
spacing as L1 here and the neighbor column bay spacing as L2 in the
next Crane-2 input.
