Key technology of construction steel structure welding

1 Characteristic of steel structure buildings

Steel structure means that the main structure of the building adopts steel components, and through reasonable processing of steel, it is made into a structure that can bear pressure. Steel structures have the following characteristics:

1) High space utilization. Steel has high bending and compressive strength, and its performance is better than that of concrete. The application of steel structures in high-rise construction projects can reduce the cross-sectional area of the structure, thereby improving the utilization of engineering space.

2) The construction period is short. The use of steel structures in high-rise buildings can reduce the amount of scaffolding during construction, and the installation of steel structures can use profiled steel plates as templates for concrete floors. And in the construction process, the concrete and steel structure construction can also be carried out in a crossway, which improves the overall engineering strength and reduces the overall construction period of high-rise buildings.

3) Sustainable development can be achieved. The steel structure uses steel as the main material, and steel has the characteristics of reusability, which will not cause waste of materials, avoid excessive construction waste during construction, and meet the requirements of sustainable development of my country’s market economy.

2 Deficiencies in the welding technology of steel structures in construction engineering

2.1 Welding Technology and raw material issues

With the rapid development of the domestic economy, the industrial field has been greatly improved, and the number of steel structure construction projects is increasing year by year, and a variety of advanced steel structure welding technologies have been developed. The advancement of welding technology promotes the healthy development of construction steel structure projects. At this stage, although our country has a number of welding technologies, there are still many defects and deficiencies. The construction of building steel structures requires raw materials and welding materials to ensure the quality of construction projects.

2.2 The problem of porosity in the welding process

The occurrence of porosity is one of the most common and important problems in the application process of steel structure welding technology, and there are no good targeted measures to solve this problem in China at present, and more in-depth improvement and optimization are urgently needed. If no scientific wind protection measures are adopted during the welding process, it is very easy to cause gas to be mixed into the molten pool, and if the welding raw materials are not baked in place or the welding wire is not cleaned in place, it is easy to cause porosity. In order to effectively deal with this problem, the welding staff needs to clean the components and welding wire in place, choose the best welding rod baking process according to the actual construction quality requirements, and also need to choose certain windproof measures. Secondly, it is necessary to pay attention to the overall welding speed when connecting, and scientifically grasping many of the technologies. If there is a problem with surface pores, it is necessary to immediately select the best mechanical grinding technology to deal with it.

2.3 Local deformation occurs during the welding process

Under normal circumstances, in the process of steel structure welding construction, there are construction raw materials whose stiffness is not up to standard or the texture of raw materials is not uniform, resulting in local shrinkage of the steel after welding, which will cause uneven deformation of the overall steel structure, and in During the welding process, if the strength of the welding seam treatment is not increased, it will also cause uneven shrinkage of the steel. Secondly, if the welding staff does not operate in strict accordance with the relevant standards, the steel structure will be partially deformed due to the construction staff’s operating errors, which will lead to stress concentration and have a very serious impact on the use of the steel structure. Need to quickly select targeted measures to deal with. If you want to effectively control the local deformation problem, the staff need to ensure that the welding seam can be evenly distributed when designing the welding seam, which can effectively alleviate the occurrence of local deformation. The seams appear to cross, and the deployment of welding thin seams should not be too dense, which can effectively avoid the occurrence of local deformation. During the steel welding process, the staff need to strengthen the distinction between the primary and secondary welding seams. During the welding process, the key welding seams must be welded first, and then the secondary welding seams must be welded.

3 Steel structure welding technology

3.1 High-strength steel welding technology

When using a high-strength steel welding process, reasonable welding materials should be selected. In the construction process of strong joints and weak members, welding materials with impact toughness and strength higher than the minimum values specified in the timber standards should be selected to ensure that all aspects of welded joint performance meet the minimum values specified in the standards and improve the quality of welds. plasticity. When welding thick plates, construction personnel should choose welding materials with reasonable strength in combination with the thickness effect. When the joint constraints are large, the low-strength welding material should ensure the standard less than 1/4 of the plate thickness and the impact toughness of the steel. At the same time, the toughness of the welding material is reasonably selected according to the key construction process to ensure that the weld seam and toughness meet the basic standard requirements of steel. Construction personnel should choose the carbon equivalent evaluation method, heat-affected zone maximum hardness test evaluation method, and bolt test critical fracture stress evaluation method to evaluate high-strength weldability and conduct crack test control. When determining the minimum preheating temperature, construction personnel should fully combine the crack resistance test of the groove sample to achieve the expected hardness control effect. The construction personnel determine the weld energy according to the cooling temperature corresponding to the hardness of the T-joint fillet weld heat-affected zone of different plate thicknesses reaches 350hv and determine the minimum preheating temperature, crack sensitivity index, and diffusible hydrogen content of the deposited metal in combination with the plate thickness range, and determine the minimum preheat temperature based on the steel ratio curve, cooling time, and joint input.

3.2 Low-temperature welding technology

Since low-temperature welding technology is widely used in steel structure welding operations, from the perspective of the actual temperature requirements of low-temperature welding technology, although the temperature is not very high, it is still necessary to take corresponding welding insulation measures and set up a closed space in the welding area to reduce actual heat loss. If gas is used for welding protection during low-temperature welding, protective measures should also be taken for the cylinders storing the gas.

3.3 Thick steel plate welding technology

In the construction of building steel structures, thick steel plates have been widely used. For example, the maximum steel plate thickness of the National Stadium project can reach 110mm, and more and more steel structures are widely using thick steel plates, which promotes the rapid development of thick steel plate welding technology and expands the scope of steel used in construction. At the same time, during the welding process of thick steel plates, construction personnel should also do a good job in the control and prevention of cracks and deformation, and choose a reasonable groove method, such as an X-shaped groove or a double U-shaped groove. When single-sided welding is used, it is advisable to improve work efficiency on the basis of penetration, choose narrow gaps and small-angle grooves, reduce welding residual stress, reduce welding shrinkage, and ensure the rationality of the intermediate layer and preheating temperature.

4 Matters need attention during construction steel structure welding work

4.1 Preparation before processing and blanking work

A certain project adopts electrode arc welding and CO2 semi-automatic shielded welding. CO2 semi-automatic shielded welding is used for column-beam rigid connection and column butt joint, and electrode arc welding is used for the rest of the welds. In order to ensure the welding quality, a lot of energy has been invested in the pre-welding preparation work, including targeted safety technology disclosure, and formal welding will be carried out after the welding procedure is qualified. The low-hydrogen electrode should be dried at 350-380°C for 1.5-2 hours. After treatment, it should be kept warm in an incubator at 110-120°C and taken at any time. If the dry low hydrogen electrode is left in the atmosphere for more than 4 hours, it should be dried again. The welding rod should be dried twice at most, and wet welding rods, rusty welding wires, deteriorated welding cores and rusty welding rods or welding rods with peeling-off coatings should not be used. Before welding, the rust and clean oil stains within 20mm on both sides of the groove should be removed, and the same tack welding method as the back welding should be adopted, and it should be carried out according to the formal welding requirements to complete a firm and reliable tack welding. There should be no defects such as air holes. Slag and cracks. Before welding, the assembly quality should be rechecked to ensure the cleanliness of the welding parts and the quality of tack welding, otherwise targeted corrections should be made. When the on-site wind speed is greater than 8m/s, anti-wind measures should be taken for electrode arc welding. If the wind speed is greater than 2m/s, gas-shielded arc welding should also take wind protection measures.

4.2 Welding process

During the steel structure welding construction process, the steel columns installed in sections will form many small frame structures during the installation process. In order to reduce the damage to the structure caused by weld shrinkage, the welding sequence from the inside to the outside is adopted to ensure that there is always free weld shrinkage deformation. On-site welding is carried out after the steel columns and frame beams of the running water section are installed, corrected and fixed. Taking the bolted butt joint of H-beam and H-beam as an example, electrode arc welding and gas shielded welding are used. Welding needs to tighten the torque of the high-strength web bolts first, then weld the flange, and finally tighten the high-strength web bolts on the basis of cooling the flange weld. Welding flange: The same joint is welded by a welder to weld the lower flange and the upper flange sequentially. If two welders are responsible for welding the same joint, they should be welded symmetrically and multi-layer multi-pass welding should be used. The welding methods used for box-shaped rectangular column butt joints include flux-cored arc welding, electrode arc welding, and gas-shielded welding. The welding process shall be carried out symmetrically as a whole, and each welded joint shall be welded symmetrically by two welders at the same time. The web butt welds are welded first, and then the flange butt welds are fillet welded. It must be ensured that welded joints are staggered. Multi-layer multi-pass welding should also be used. The welds between every two layers should be staggered by 30-50mm. Each layer welded by two welders shall be staggered. In order to ensure the welding quality of the steel structure, the welding is protected in rainy and windy days to avoid problems such as a sudden drop in welding temperature and damp welding materials. For example, gas cylinders, welding wires, welding machines, etc. are placed in special work sheds. In order to ensure the smooth progress of high-altitude welding, if it is not convenient to set up a windproof shed, a small baffle made of profiled steel plate should be used to close the welding joint. In addition, a lot of effort has been invested in weld repair, such as removing defects such as air holes, slag inclusions and weld spatulas through electric shovel chiseling, drilling and grinding wheels, repairing undercuts, arc crater dissatisfaction, local defects and insufficient dimensions through welding, And supplemented by targeted welding inspection. Finally, the welding quality of the steel structure was guaranteed, and the follow-up construction was smoothly advanced.

4.3 Continuously improve the comprehensive quality of welding technical staff

With the rapid development of welding technology, various types of welding technology and construction raw materials are constantly emerging. If welding technicians want to ensure the construction quality of building steel structure projects, they need to continuously strengthen their overall quality and continuously improve their technical capabilities. In the steel structure link, welding technology is a highly professional technology. The construction steel structure welding technicians need to undergo strict and professional training and assessment before taking up the job. Only those who pass the assessment can obtain the corresponding qualification certificate. Work with a certificate for actual operation. With the rapid development of the economy of the times, in the process of carrying out the construction of steel structures in construction projects, if you want to break through various types of welding technical difficulties, relevant technical personnel need to keep pace with the times, follow the trend of the times, constantly improve their technical capabilities, and constantly improve themselves The overall literacy of the students, and constantly improve their knowledge reserves in practical work. Secondly, the relevant departments of construction enterprises need to increase the training of welding technicians’ professional ethics and train a group of high-quality, high-professional and high-tech technical teams, so as to promote the healthy and sound development of construction projects.

4.4 Control welding joint structure

When designing welded joints of steel structures, deformation problems should be avoided, and the number and size of welds should be strictly controlled. During the welding process of steel structure, problems such as a large number of welds and large size are prone to occur, resulting in frequent welding deformation. Therefore, the staff should strictly control the size and number of welds, and choose the appropriate size and shape of the weld groove as much as possible to ensure the bearing capacity of the steel structure and reduce the cross-sectional area. At the same time, when the steel structure is welded, the position of the welding node should be determined on the symmetrical section of the object as much as possible to ensure that the welding point of the neutral axis is as close as possible to the neutral axis and avoid approaching the high-stress area. In addition, the joint form should be reasonably selected to avoid deformation problems caused by stress concentration and high-temperature concentration, and nodes should not be set at multi-directional intersections.

4.5 Control of welding construction conditions

A large number of investigations and practices have shown that there are many factors that affect the welding construction process of steel structures, and the external factors mainly include wind force and the external environment. Therefore, in order to effectively complete the steel structure welding operation, it is necessary to continuously optimize the construction conditions and reduce the impact of environmental factors. First, control the temperature of the welding environment. During the welding process, if the ambient temperature is too low, the temperature value should be adjusted reasonably on the basis of the normal welding temperature to make it consistent with the operating parameters of the equipment, and the equipment used should be preheated to ensure the operating status of the equipment for the next step. One welding construction. And determine the welding method and welding position, select the appropriate welding material, and carry out the steel structure welding construction when the welding operation requirements are met. Second, control the air humidity and try to keep the regional humidity within 90 degrees. If the hair layer of the equipment to be welded is relatively wet, preparations for dehumidification and heat removal should be done in advance to ensure that the surface of the welded component is dry, so as not to affect the welding effect. When dealing with heat and humidity problems, it is necessary to combine the construction situation to clarify the specific characteristics and properties of the steel structure and welded components on the construction site, and then do optimal control; the third is to reasonably control the wind conditions at the construction site. The main control principle is to ensure the stability of the wind speed and welding conditions under the original wind conditions.

4.6 Key Points of welding deformation control

The welding quality of steel structure engineering should focus on controlling welding deformation. The welding process that can reduce the deformation and shrinkage of components should be adopted, and the welding sequence should be strictly controlled. When cross joints, T-joints, and butt joints are used, components that are easy to flip or placed in good condition can be welded symmetrically on both sides. For members with symmetrical cross-sections, welding can be carried out around the neutral axis of the member. If there are member nodes that are symmetrical to the connecting rod, then symmetrical welds can be made around the axis of symmetry of the node axis. For asymmetric double-sided groove welds, welding construction should be carried out in strict accordance with a certain order. If the plate is thick, several times of symmetrical welding should be carried out in sequence. For longer steel structure welds, welding methods such as multi-person symmetrical welding, jump welding, and segmented back welding should be preferred. In the welding process of components, in order to achieve effective control of shrinkage deformation, pre-set anti-deformation methods or reserved welding can also be used. The amount of anti-deformation and shrinkage allowance can be determined according to the target test or calculation. In the process of assembling welded components, welding should be carried out in the order of joint shrinkage from large to small, and the joint constraints can be effectively controlled.

4.7 Innovative construction steel structure welding

The building steel structure itself belongs to a new type of building system, which has good seismic performance in actual use. Moreover, this new type of technology meets the needs of ecological development, because the steel structure itself is environmentally friendly, which is an essential component of modern buildings, and will also promote the development and progress of the construction industry to a certain extent.

Therefore, under the influence of this general environment, if the construction industry wants the structure to fully play its role, it must proceed from reality and continuously improve the welding technology of steel structures, thereby fundamentally improving the welding level. With the continuous development and change of the times, the original manual welding and cutting technology has gradually become intelligent. Such a transformation can not only reduce the working pressure of the staff, but also improve its safety and help promote the further development of steel structures. Generally speaking, steel structure welding technology has many advantages, and it can be found in various regions of the country. Future development may only increase, and more stringent requirements are put forward for welding technology in steel structure construction of construction projects. At this stage, the level of domestic welding technology has reached the level of globalization and is at the forefront of the world. Even so, there are still many problems and defects in welding technology. How to better deal with these problems and defects requires the relevant departments of our country and those engaged in Technicians in welding dig deeper.