Steel structure welding

In the construction of steel structure engineering, the installation and function of steel components and steel structures are directly affected by welding deformation. And because of the additional bending moment, secondary stress, etc. during the bearing, which indirectly affects the performance of the steel structure engineering, so the control of welding deformation is very important.

According to the causes and influencing factors of welding deformation, the following measures to control deformation can be taken:

1. Reduce the cross-sectional area of the weld: under the premise of obtaining a sound weld without exceeding the standard defect, use a smaller groove size (angle and gap) as much as possible.

2. For steels with a yield strength below 345MPa and weak hardenability, use a small heat input, do not preheat as much as possible or appropriately reduce the preheating and interlayer temperature: priority is given to welding methods with small heat input, such as CO2 gas Protected welding.

3. For thick plate welding, multi-layer welding should be used instead of single-layer welding as much as possible.

4. In the case of meeting the design requirements, the welding of longitudinal stiffeners and transverse stiffeners can adopt the intermittent welding method.

5. When both sides can be welded, double-sided symmetrical grooves should be used, and a welding sequence that is symmetrical to the neutral axis of the component should be used in multi-layer welding.

6. When the thickness of the T-shaped joint is large, the bevel angle butt weld is adopted.

7. Use the anti-deformation method before welding to control the angle deformation after welding.

8. Adopt rigid fixture fixing method to control post-weld deformation.

9. Use the component reserved length method to compensate for the longitudinal shrinkage and deformation of the weld. For example, 0.5mm-0.7mm can be reserved for each meter length of the H-shaped steel longitudinal weld, and 0.5mm can be reserved for the length of the section steel corresponding to each pair of transverse bars. The reserved perimeter method is adopted. Compensate the longitudinal and transverse shrinkage deformation of the weld of the cylindrical pipe member. If the thickness of the plate is greater than 10mm, each longitudinal and circumferential weld shall reserve a circumference of 2.0mm.

10. For the distortion of long components, it is mainly by improving the flatness of the plate and the assembly accuracy of the components, so that the groove angle and gap are accurate, and the direction or centering of the arc is accurate, so that the weld angle deformation and the longitudinal deformation of the flange and web Consistent along the length of the member.

11. In the design, the number and size of welds should be reduced as much as possible; in addition to avoiding dense welds, the welds should be arranged as close as possible to the neutral axis of the component, and the layout of the welds should be consistent with the components. The neutral axis is symmetrical.

12. When assembling and welding components with many welds or when installing steel structures, a reasonable welding sequence should be adopted.

Control and Correction of Welding Distortion

Improved welding design——

(1) Minimize the number of welds

Unnecessary welds should be avoided when designing the weld structure, and steel and stamping parts should be used instead of welded parts as much as possible to reduce the number of ribs to reduce the workload of welding and correcting deformation.

(2) Reasonable selection of weld shape and size

For butt joints with a large share of plate thickness, X-shaped grooves should be selected instead of V-shaped grooves. Reduce the total amount of deposited metal to reduce weld distortion. Under the condition of ensuring sufficient capacity, the smaller weld size should be selected as much as possible. For T-shaped joints that do not require strength calculation, the minimum weld leg size reasonable in process shall be selected. And the use of intermittent welds can reduce deformation more than continuous welds.

When the T-joint fillet weld is determined according to the design calculation, continuous welds shall be used instead of intermittent welds of equal strength, and double-sided continuous welds shall be used instead of single-sided continuous welds of equal strength. to reduce the fillet size.

For T-shaped or cross joints with high stress, under the condition of ensuring the same strength, fillet welds with openings should be used, which can greatly reduce weld metal and weld deformation compared with ordinary fillet welds.

(3) Reasonable design of structural form and weld position

When designing the structure, the minimum welding workload and the minimum welding deformation during component assembly should be considered. For the thin plate structure, the appropriate plate thickness should be selected, the spacing of the skeleton and the size of the weld angle should be reduced to improve the stability of the structure and reduce the wave deformation. In addition, curved structures should be avoided as much as possible. Because the use of a plane can make the welding equipment in a fixed state relatively simple, and it is easy to control the welding deformation.

Since the transverse shrinkage of the weld is usually more significant than the longitudinal shrinkage, the weld should be arranged parallel to the direction that requires the least welding deformation as much as possible. The position of the weld should be as close to the central axis of the section as possible and symmetrical to the central axis as possible to reduce the bending deformation of the structure.

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