What’re the installation of double girder overhead crane?
（1）rail retest
We must retest the rails’ elevation, centerline spacing, straightness, key point and size about last procedure to meet the design requirement or construction rules, and 
measuring the setting point in suitable place of rails by theodolite which is presented squareness, the test item as following:
Two rails centerline limit deviation±5mm
Elevation limit deviation±2.0mm
（2）main girder test and end disposing
After the main girder goes into the site, put it on the sleeper or steel pier, it keeps horizontal, checking its side camber, upper camber and wheel’s span, dealing with the weld connecting surface of the main girder and crane traveling mechanism to meet the rules.
（3）20t overhead crane group layout
Main girder, end girder and two side crane traveling mechanism are assembled on the ground in factory, after ground layout, test the two sides traveling wheel’s depth of parallelism and centerline spacing.
Lifting trolley is installed on the rails in main girder after finishing the bridge frame installation.
