As a load-bearing structure system, steel structure has many advantages, such as light weight, high strength, good plasticity and toughness, superior seismic performance, high degree of industrial assembly, short construction period, remarkable comprehensive economic benefits, flexible structural system and beautiful appearance,Therefore, it is more and more widely used in industrial plants, urban rail (subway) depot warehouses, large shopping malls and supermarkets and other large-span or large-span buildings. 

Corresponding to its construction technology, it is necessary to build large reinforced concrete foundation or equipment foundation for these buildings, and to embed structural bolts connecting steel structure (column) and reinforced concrete foundation.Due to the large foundation of the steel structure (the upper part is mostly in the shape of a pyramid), it is not easy to fix the bolts hanging in the air, and the steel structure installation quality requirements are high. Therefore, the embedding precision of the connecting bolts becomes the key technology of the steel structure installation construction. 

01

Process principle

The independent support system and fixed mould are used to locate the embedded bolts. After precise adjustment and calibration by using theodolite or total station, the concrete bearing platform is poured at one time, so as to achieve the accuracy of embedded position.The characteristics of the process are as follows: 

(1) due to the use of shaped die steel plate to fix the embedded bolts, the relative position of the bolts in the bolt group is kept accurate.(2) using independent support system and fixed mould to embed bolts, the bolts have fine adjustment, high construction operation precision and small overall deviation.(3) make full use of the commonly used Φ 48 mm steel pipe scaffold and fastener turnover materials, with strong versatility and low cost, which can save a lot of project investment.(4) the construction technology is simple and fast, and the operator is easy to master. 

02

Key points of construction operation

2.1 Construction preparation

2. 1. 1 The processing of foundation bolt shall be customized and accepted according to the design requirements, and the corresponding material certificate and inspection report must be provided. 

2. 1. 2 Design and processing of shaping mould

(1) according to the relative position of the embedded anchor bolt and the axis of the concrete foundation, and considering the assembly requirements of the mold, determine the plane size of the mold steel plate, carve the cross line of the vertical and horizontal axis of the mold steel plate, and then determine the relative position of the embedded bolt according to the mold axis, and drill holes.The drilling position and hole diameter of the die should be completely consistent with the bolt hole location and hole diameter of the steel structure column, and the thickness of the steel plate should be ≮ 4 mm.(2) the die steel plate can be assembled on site after being processed. The short scaffold pole with a length of 2.0 m is used for the car pole, and the vertical bar is made of Φ 18 mm deformed steel or Φ 20 mm steel pipe. The height of the vertical bar shall be 5-10 cm higher than the embedded bolt, so as to facilitate the use of steel ruler to calibrate the axis.(3) if the top of concrete foundation is short column, it can be considered to dig holes in the center of steel plate to facilitate concrete pouring. 

2. 1. 3 Control of measurement accuracy

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

2.2 Construction sequence

According to the plane layout of steel structure column, the embedded bolts shall be fixed along the longitudinal axis starting from the corner column or side column.If it is a multi span steel structure, the longitudinal axis of the middle span should be used to flow along both sides of the longitudinal axis, so as to reduce the measurement and construction errors and improve the overall installation accuracy. 

2.3 Installation of independent support system

The design size of steel structure concrete foundation is large, the maximum width is 3.8 m, the upper part is usually designed as a pyramid shape, the height of formwork is far lower than the embedded height of anchor bolt. Moreover, the steel formwork or wood formwork have certain flexibility, which can not meet the accuracy requirements of embedded bolts. Therefore, an independent support system is adopted in the project.The installation points of the bracket are as follows: 

(1) along the longitudinal axis, the guy wire is about 0.75 m on both sides of the foundation axis (it should be ensured that it is outside the ground beam). Along the pull wire, the poles are set between the two sides of the cushion cap and the foundation cap, with the 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 soft and hard degree of soil), and the height should be about 20 mm higher than the longitudinal horizontal bar.The longitudinal horizontal bar must be set horizontally, and the height should ensure that the embedded bolt top conforms to the design height, and there is space for up and down adjustment and movement.(3) generally, the construction width of foundation bearing platform is greater than 2.0 m, so the vertical poles on both sides of the foundation and the upper horizontal bars can be connected with diagonal rods to form a portal frame; the node spacing between the diagonal tie rod and the horizontal bar is about 1.5 m, so as to ensure that the horizontal bar will not produce deflection deformation.(4) at the joint of the inclined rod and the horizontal bar, the diagonal support is erected to both sides (the support is driven into the foundation soil depth of about 30 cm), and then the transverse tie rod is installed near the support, and the well shaped frame is composed of the horizontal bar and the horizontal rod on the upper part of the foundation, forming a spatial geometric invariant body, so as to ensure the stiffness and stability of the frame body. 

 2.4 Positioning adjustment of setting mould

(1) use theodolite or total station to measure and set the vertical and horizontal axis points on the well frame of the support system, and then form the cross axis by pulling the wire. Then, put the shaped die car pole on the horizontal pole of the jig frame, so that the cross marking line on the die steel plate is aligned with the pull wire of the zigzag frame axis, and the car pole is connected with the horizontal bar with the scaffold fastener (not to be fastened temporarily for adjustment).(2) after the shaping mold is in place, loosen the fastener on the car pole, use a small wire drop to throw a point on the die steel plate from the axis of the zigzag frame, gently tap the car pole to make the molding mold move slightly from the front to the left, and then use the axis pull wire on the well bracket to make the casting point coincide with the mold notch, and then tighten the fastener. 

2..5 Installation and adjustment of embedded bolts

(1) insert the embedded bolt through the hole drilled in the die steel plate, reserve the exposed thread length according to the design requirements, and fix it with two nuts; use a level to detect the elevation of the bolt top, fine tune the upper and lower nuts to meet the elevation requirements, and tighten the nut (do not screw it tightly for the moment).(2) check the perpendicularity of the two directions of the embedded bolt screw facade one by one with a level ruler. The screw can be slightly pulled for adjustment until the perpendicularity of the two directions meets the requirements, and the nut is completely tightened.(3) when the elevation and perpendicularity of each bolt of a bolt group are adjusted to be qualified, the short steel bar is used to connect the bolt roots by spot welding, so that a bolt group can be pulled into a whole.If the embedded bolt is longer, one or two welding bars can be added to ensure accurate and stable positioning.(4) in order to ensure that the embedded bolt does not have overall settlement and overall inclination, it should be cable-stayed spot welded with the foundation reinforcement grid with short reinforcement, and two short steel bars should be spot welded diagonally at the bottom of the embedded bolt to support the foundation cushion.(5) when the internal space of the foundation 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 embedded bolts of each foundation bearing platform is completed, the total station is used to measure the intersection point of the axis on the die steel plate, and check whether the intersection point of the steel plate notch coincides with the intersection point of the measured axis. If there is an error, loosen the fastener and gently tap the car pole to fine tune the mold until it is completely re closed.If the deviation is too large, the fastener of the car pole and the reinforcement connection with the foundation reinforcement grid shall be loosened and adjusted again.(2) use steel ruler to check whether the distance between the bolt groups of each foundation bearing platform meets the design requirements, pull through the line to check whether the embedded bolts in the same row of each foundation bolt group are arranged in a straight line. If there is any error, repeat the above method to correct.(3) for the steel structure with long longitudinal axis, due to the limitation of vision and instrument, the method of segmented embedding and densification of control network can be adopted, and the recheck measurement with embedded bolts shall be strengthened to ensure the control accuracy meets the requirements.