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As a load-bearing structural system, steel structure has many advantages such as light weight, high strength, good plastic toughness, excellent seismic performance, high degree of industrial assembly, short construction period, significant comprehensive economic benefits, flexible structural system, beautiful appearance, Therefore, it is more and more widely used in industrial buildings, urban rail (metro) depot warehouses, large-scale * fields * cities and other large-span or super-span buildings. Corresponding to its construction process, it is necessary to build large reinforced concrete foundations or equipment foundations for these buildings, and bury structural bolts connecting the steel structure (column) and reinforced concrete foundations. Due to the large steel structure foundation (the upper part is mostly quadrangular pyramid-shaped), it is not easy to fix the suspended installation of the bolts, and the installation quality of the steel structure requires high quality. Therefore, the embedding accuracy of the connecting bolts has become a key technology for the installation and construction of steel structures.

01 Process Principle

Using the unique bracket system and shaping mold to position the embedded bolts, after precise adjustment and calibration using theodolite or total station, the concrete cap is poured in one go, so as to achieve the accuracy of the embedded position. The characteristics of the process are:

(1) Because the fixed mold steel plate is used to fix the embedded bolts, the relative position of the bolts in the bolt group is kept accurate.

(2) The use of unique bracket system and stereotyped mold pre-embedded bolts, the bolts have fine adjustment, high construction operation accuracy, and small overall deviation.

(3) Make full use of the Φ 48 mm steel pipe, scaffold rod and fastener turnover materials commonly used for scaffolding. It has strong versatility and low cost, which can save a lot of engineering investment.

(4) The construction process is simple and fast, and the operator is easy to master.

02

Key points of construction operation

2.1 Preparation for construction

2. 1. 1 Processing of anchor bolts Anchor bolts should be customized according to the design requirements and enter the site for acceptance. * Must have the corresponding material certification and inspection report.

2. 1. 2 Design and processing of the mold

(1) According to the relative position of the embedded anchor bolts and the concrete foundation axis, and considering the assembly requirements of the mold, determine the plane size of the mold steel plate, engrave the cross line of the longitudinal and horizontal axes of the mold steel plate, and then determine the embedded bolt according to the mold axis Relative position, drilling. The drilling position and hole diameter of the die should be completely consistent with the bolt hole position and hole diameter of the steel structure column, and the thickness of the steel plate should be ≮4 mm.

(2) After the die steel plate is processed, it can be assembled on site. The car rod adopts a short scaffold with a length of 2.0 m, and the standing rib adopts Φ 18 mm screw steel or Φ 20 mm steel pipe. 5 ～ 10 cm, easy to use steel ruler to calibrate the axis.

(3) If the top of the concrete foundation is short column-shaped, consider digging holes in the middle of the steel plate to facilitate concrete pouring.

2. 1. 3 Control of measurement accuracy

According to the engineering design positioning coordinates and elevation, the encrypted survey axis and elevation control network are used to facilitate the accurate measurement of different parts.

2.2 Construction sequence

According to the plane layout of the steel structure column, first start from the corner column or side column, and fix the embedded bolts along the longitudinal axis. If it is a multi-span steel structure, it should be constructed by flowing water on both sides of the longitudinal axis of the middle span to reduce the measurement and construction errors and improve the overall installation accuracy.

2.3 The installation of stand-alone support system

The design size of the steel structure concrete foundation is large, the width is 3.8 m, the upper part is often designed in the shape of a quadrangular prism, the height of the supporting form is much lower than the embedded height of the anchor bolt, and the steel or wooden form has A certain flexibility can not meet the accuracy requirements of embedded bolts. Therefore, the project uses a unique bracket system. The installation points of the bracket are as follows:

(1) Along the longitudinal axis, about 0.75 m on both sides of the foundation axis (it should be ensured outside the ground beam), set up poles along the pull line between the two sides of the foundation platform cushion and the foundation platform with a spacing of 2.0 ~ 2. 5 m.

(2) The vertical pole should be driven into the foundation soil by 30-50 cm (depending on the degree of softness and hardness of the soil), and the height is about 20 mm higher than the longitudinal horizontal pole. Longitudinal horizontal rods * must be set horizontally, and the height should ensure the top of embedded bolts

It meets the design height and leaves room for adjustment and movement.

(3) The construction width of the general foundation platform is greater than 2.0 m, and the vertical rods on both sides of the foundation and the upper horizontal rods can be connected with diagonal rods to form a gate-shaped frame; the node distance between the diagonal rods and the horizontal rods is 1.5 m Left and right, to ensure that the horizontal rod does not produce deflection deformation.

(4) Set up diagonal supports at the joints of the diagonal rods and horizontal rods to the both sides (the support penetrates into the foundation soil depth * about 30 cm), and then install lateral rods near the supports, and the horizontal rod and lateral rods form the well above the foundation The character frame forms a spatial geometrically invariable body, ensuring the rigidity and stability of the frame body 

2.4 In-position adjustment of the shaped mold

(1) Use theodolite or total station to measure the horizontal and vertical axis points on the truss frame of the support system, and draw the wire to form a cross axis, and then place the fixed mold car rod on the horizontal pole of the truss frame to make the cross on the mold steel The engraved line is aligned with the axis line of the tic-tac-toe frame, and the car pole is connected to the horizontal rod with a hand fastener (no need to fasten it for adjustment).

(2) After the setting mold is in place, loosen the upper fastener of the car rod, use a small wire to pull the wire from the axis of the ticket to the mold steel plate, and gently tap the car rod to make the setting mold move slightly front, back, left, and right. Use the axis pull line on the tic-tac-toe frame to finely adjust it to make the casting point coincide with the notch of the mold, and then tighten the fastener.

2..5 Installation and adjustment of embedded bolts

(1) Insert the pre-embedded bolt from the drilling of the die steel plate, reserve the length of the exposed thread according to the design requirements, and fix it with two nuts; use a spirit level to detect the elevation of the top of the bolt, and fine-tune it to meet the elevation requirements by the upper and lower nuts Nut (don't tighten it yet).

(2) Use a horizontal ruler to detect the verticality of the pre-embedded bolt and screw in two directions one by one. You can slightly adjust the screw until the perpendicularity in both directions meets the requirements. Tighten the nut.

(3) After the elevation and verticality of each bolt of a bolt group are adjusted, the short bolts are used to connect the roots of the bolts to each other by spot welding, making a bolt group integrated. If the embedded bolts are longer, one or two welding ribs can be added to ensure accurate and stable positioning.

(4) In order to ensure that the embedded bolts do not suffer from overall settlement and overall tilt, it is necessary to use diagonal reinforcement to spot weld the base reinforcement grid with short steel bars, and diagonally weld two short steel bars at the bottom of the embedded bolts to support Foundation cushion.

(5) When the internal space of the basic reinforcement grid is large enough to not affect the overall installation of the embedded bolts, the embedded bolts can be installed before installing the mold.

2.6 Review of embedded bolts

(1) After the installation of the embedded bolts of each foundation platform is completed, use a total station to measure the intersection point of the axis on the mold steel plate and check whether the intersection point of the steel plate score coincides with the intersection point of the measured axis.If there is an error, loosen the fastener to lighten Strike the car pole to fine-tune the mold until it completely overlaps. If the deviation is too large, loosen the car rod fasteners and the reinforced connection with the basic steel mesh frame and readjust.

(2) Use steel ruler to check whether the distance between each foundation bolt group meets the design requirements, pull the cable to check whether the same row of embedded bolts of each foundation bolt group are arranged in a straight line, if there is an error, repeat the above method to correct it.

(3) For the steel structure with a long longitudinal axis, due to the limitations of vision and instruments, it is possible to adopt the method of segmented embedded and encrypted control network, and strengthen the review measurement with the embedded bolts to ensure that the control accuracy meets the requirements.