steel structure is generally welded, and some important welds are generally full penetration welding.In the process of local heating and melting, the temperature difference between the metal in the heating zone and the surrounding base metal is very large, and the instantaneous stress in the welding process occurs.After cooling to the original temperature, the tensile stress area of the whole joint area and the near joint area is in balance with the value of the base metal in the compressive stress area, which causes the welding residual stress of the structure itself.At this moment, under the action of welding stress, the structure of weldment has many forms of deformation.The existence of residual stress and the occurrence of deformation are transformed from each other. It is not difficult to find out the way to prevent the reduction and correction of deformation from knowing the deformation rules.

1）Reduce the cross-sectional area of the weld: on the premise that the weld is intact and free of over support defects, select a smaller groove size (view point and clearance) as much as possible.

2）For steel with yield strength less than 345mpa and less hardenability, choose a smaller heat input, try not to preheat or reduce the preheat and interpass temperature properly; choose a welding method with smaller heat input, such as CO2 gas shielded welding.

3）As far as possible, multi-layer welding shall be selected to replace single layer welding for thick plate welding.

4）When both sides can be welded, the double-sided symmetrical groove shall be selected, and the welding sequence symmetrical to the neutral axis of the component shall be selected during multi-layer welding, as shown in Figure 2 below:

5）When the thickness of T-joint plate is large, the fillet butt weld of the opening is selected, as shown in Figure 3:

6）The method of anti deformation before welding is used to control the angle deformation after welding. This method is a common method in production, and the weldment is offset (compensated) in advance.The zigzag reverse deformation after welding can prevent the deformation after welding.Table 1 and Figure 4 are the reference values of anti deformation of box column and H-beam before welding

7）Rigid fixed law: also known as compulsory law.In the actual production, the post welding deformation of the members with large rigidity is generally less. For the members with small rigidity, the rigidity of the members can be strengthened before welding, and the post welding deformation should also be reduced.When selecting this method, it is necessary to remove the fixture and support after welding and cooling. Several common methods include fixture method, support method, mould method, temporary fixation method (such as welding nail fixation and compression fixation method), and positioning welding method.

8）Hammering weld method: this method is mainly applicable to the welding of thin plates.When the welding seam of the thin plate and its heat affected area have not been cooled thoroughly, hammer the area immediately, and use the air gun to knock the thick plate.

9）The reserved length method is used to compensate the longitudinal shrinkage deformation of the weld.

10）In the planning, the number and scale of welds shall be reduced as far as possible; in addition to preventing the weld from being densely distributed, the weld orientation shall be as close to the neutral axis of the component as possible, and the placement of the weld shall be symmetrical with the neutral axis of the component.

11）Select the welding sequence correctly.When there are butt welds and fillet welds in steel structure, in principle, butt welds shall be welded first and fillet welds shall be back filled.For cross weld and t-weld, the correct sequence shall be adopted to prevent the welding stress from converging and ensure the welding quality of the joint.It is very beneficial to reduce the deformation by adopting the welding of the neutral axis symmetrical to the whole steel structure and adopting the welding of two sections from the middle phase.For the welding of important parts with high strength requirements in steel structure, the joints should be able to contract freely without binding.