What is Pre-stressing Force Method for Crane Main Girder Deformation?

Principle for using pre-stressing force method to correct main girder down-warp: use pre-stressing force to stretch-draw many steel bars or steel wire ropes at two ends of main girder bottom cover plate by fixed support, make main girder bear a bending moment (main girder upper half bears tensile stress, lower half press stress), and main girder recovers up-warp influenced by the bending moment. When main girder bears loads, working pressure is rightly opposite to the steel bar pre-stressing force which at the same time can counterbalance part of working press stress, thus improve load capacity of main girder.

double girder bridge crane

Pre-stressing force method is an effective method to correct main girder down-warp

Advantages:

1. Accurate and stable up-warp value after main girder correction, and it can be adjusted anytime in accordance with different purpose;

2. Simple correction technology, short period, low cost

Disadvantages:

1. It is just suitable to correct box type main girder down-warp of bridge (gantry) crane, not suitable for main girder horizontal bend, local deformation, set-back correction for gantry crane cantilever

2. External appearance is not beautiful after correction

Pre-stressing force method is most appropriate to be used in below conditions:

1. Cranes that have been used many years

2. Main girder stiffness is not enough

3. Bad bearing capacity

4. Crane works with full load for a long term

5. Bad working environment