Steel structure has been more and more widely used in housing construction, especially in industrial plants and large public buildings, because of its advantages of high material strength, light weight, simple production and short construction period. Steel structure components are usually processed in the processing plant strictly according to the size of the drawing. In many cases, the steel structure column is connected with the reinforced concrete foundation through the embedded anchor bolt, so the accuracy of the position of the embedded anchor bolt is crucial in the construction of the steel structure. The positioning accuracy of anchor bolts in steel structure engineering foundation is relatively high, and the construction is relatively complicated. If the embedded anchor bolts are seriously offset, it will bring great difficulties to the installation of the superstructure.
1 Engineering Example
1.1 Project Overview

Erlian Truck wheel Change Depot is located in the north of Erlian City. The starting mileage of the depot is LDK332+109.225, and the end mileage is LDK332+960.775. It is 54.275m away from the center of the New China-Mongolia contact line, with a length of 851.55m and a width of 18.63m, and a construction area of 15 864.38m2. The roof ridge height is 10.85m, the cornice height is 10.25m, the foundation of the wheel change warehouse is an independent foundation, the upper part is a steel structure, the color steel plate enclosure, and the solid steel window

The upper and lower floors, the upper layer is the suspended steel window and the lower layer is the flat steel window. A wheel change wire for a four-wire sleeve and a wheel storage wire for a three-wire sleeve are provided inside.
50 sets of carriage machines (200) can disassemble a train for wheel change at the same time, and 8 cranes on the crane beam can lift the required running frame in place at any time. On the east side of the wheel change depot, there is a 45.5m wide wheel storage yard with 196 wheel storage lines, which can store 3,000 bogies.

The foundation is an independent foundation with a bearing capacity of 300KPa. Except the wind columns, the cross sections of 16 corner columns and deformation joints are 800mm×1 100mm, the cross sections of 6 wind columns are 400mm×800mm, the cross sections of the remaining 230 columns are 700 mm×1 100mm, and the width of the foundation beam is 400m. The top elevation of the beam and the top elevation of the column are -0.3m, and the beam is in line with the column. The upper structure of the wheel change warehouse is a steel structure, consisting of 123 rows of rigid frames and 7 wind-resistant columns, of which each row of rigid frames has two column feet connected with an independent foundation, and each independent foundation is anchored with 8 M39 bolts bolted with the column feet.

The hole diameter of the bolt at the end of the column foot is 44mm, the hole diameter of the bolt at the waist is 41mm, and the anchor bolt is made of M39 bolts. The installation accuracy is very high. The bolt length is 1 800mm, the weight of each bolt is 21kg, and the bolt anchoring is 1 580mm. The installation of anchor bolt has become an important factor restricting the construction and construction period.

At the end of 2003, the independent foundation column was constructed to the bottom of the embedded bolts, and the earth was backfilled to about 100mm below the concrete top surface of the foundation column.
1.2 Construction Points

In order to ensure the construction quality and minimize the construction period, after getting the drawings, we should carefully review the forehead, check whether the position of the bolt is crossed with the steel bar in the foundation column and whether there are other construction contradictions, order the bolt, process the bolt and locate the steel plate early, and finish the preliminary preparation work; Determine the relative position and elevation of bolts, and arrange special personnel to operate the procedures such as pouring concrete, and check carefully after the completion of each process; The process flow as shown in Figure 1 should also be followed.
The main steps of the process are carried out according to the following methods and points.
1.2.1 Machining bolts and locating steel plates. In this project, the anchor bolt is processed by lathe, which requires the thread buckle to be uniform and the thread length to meet the design requirements and specification requirements. The anchor bolt bracket and stiffening plate are welded by artificial arc welding, and the weld is required to be uniform, full, without welding bumps and pores, and the weld size must meet the design requirements. After entering the site, the bolts shall be checked by the material personnel and quality inspectors to check whether the bolt specifications, dimensions, quantity and length of the bolts meet the design requirements. After passing the acceptance, the bolts shall be placed neatly according to the specifications and marked.
Considering that the weight of the 8 anchors should be supported by the positioning steel plate, the positioning steel plate is made of 8mm thick steel plate. The aperture of the positioning hole is all processed into 40mm, the positioning error is less than 140mm, and the number of processing should meet the construction flow.
1.2.2 Positioning steel plate After entering the steel plate, check the hole position and aperture of the positioning steel plate one by one. If the steel plate does not meet the requirements, it shall not be used.
1.2.3 Locating the steel plate The crosshair is carved to determine the bolt position. First of all, the location observed by the theodolite during positioning is determined according to the site situation (generally just with the axis), and then the cross line on the positioning steel plate is calculated according to the center line of the positioning hole and carved out with a hacksaw.
1.2.4 Bind the reinforcement of the foundation column, adjust the reinforcement and fix the position of the reinforcement. In order to control the correctness of the axis position of the bar cage of the upper column, the control line is shot on the concrete surface of the existing concrete foundation column. In order to ensure that the reinforcement cage does not move when the reinforcement of the bundling beam and concrete pouring, the reinforcement framework should be strengthened after the bundling adjustment of the reinforcement of the foundation column. Each stirrup of each column should be welded with the binding point of the main reinforcement, and the main reinforcement should not be damaged during welding. Inside the four sides of the cage, φ14 bars are welded diagonally to the main bar
To strengthen the integrity of the steel cage.
1.2.5 Place the positioning steel plate and fix the anchor bolt. Before placing the positioning steel plate, the top of the independent foundation column is laid down on the main bar of -500mm, and the upper side of the main bar is welded with 4 Φ22mm steel bars (the location should consider the location of the positioning hole on the positioning steel plate to prevent the conflict between the anchor bolt and the support steel bar). In order to facilitate the removal of the steel plate fixing bolts after the concrete pouring is completed, the top of the steel bar is -130mm (put the steel plate on, screw on the screw cap). There is also a 5mm wire buckle), which is used to support the positioning steel plate and control the embedded height of the bolts. Weld 5 vertical and horizontal tensile steel bars φ14 on the lower part of the bolt to the column, and use 16 steel bars to support the bottom of the bolt to ensure that the lower part of the bolt stands firm and does not move; The lower part of the anchor bolt is connected with φ14 steel bars between the steel plate and other steel bars.

Control of the longitudinal axis: Axis 1 in the south side and 123 in the north side of the extension direction of axis A and B are set up axis control piles, and the total station is used to make a control pile every 5 columns in the middle.

Horizontal axis axis control: axis control piles are set on both sides of axis A and axis B every 3-5 axes, and the total error is evenly distributed with steel ruler to reduce the installation error of each column.

After the axis control of the steel plate meets the requirements, weld 5 vertical and horizontal tension steel bars φ14 on the upper part of the bolt and the column to ensure that the bolt does not move.
1.2.6 Determine the position of the locating steel plate. After the foundation beam reinforcement and beam column template are installed, the position of the positioning steel plate should be further confirmed, and the concrete can be poured after confirming that it is correct.
2 Other precautions

The welder must hold the certificate to work, and shall not injure the main rib and welding slag when welding. The steel rules and instruments used must be corrected and within the service life; In the concrete pouring process, the material should be uniformly and symmetrically cut around the foundation to avoid the displacement of bolt position caused by uneven concrete flow. Check the bolt position and elevation at any time, find that the bolt position deviation and elevation change should be adjusted in time.
3 Finished product protection measures

The appearance of bolts, nuts and washers should be coated with oil to protect them from rust and dirt. The bolts should be covered with nylon sleeves to ensure that the threads are not damaged. During bolt transportation and fixing, it is strictly prohibited to collide threads; Wrap the threaded part of the bolt with a plastic sheet before pouring the concrete.
4 Closing remarks

The accuracy of the position of the embedded anchor bolt in the construction of the steel structure is very important. By taking the above measures, not only the construction progress is accelerated, but also the construction quality is ensured, and no anchor bolt is found to be skewed, which also creates a good condition for the next step of the main installation of the steel structure.