As a load-bearing structural system, steel structure possesses many advantages such as lightweight, high strength, good plastic toughness, superior seismic performance, the high degree of industrial assembly, short construction period, significant comprehensive economic benefits, flexible structural system, pretty appearance, etc. Therefore, it is more and more widely used in industrial buildings, garages, shopping malls, and other large-span buildings. Corresponding to its construction process, it is necessary to build large reinforced concrete foundations or equipment foundations for these steel structure buildings, and bury structural bolts connecting the steel structure (column) and reinforced concrete foundation. Due to the large foundation of the steel structure (the upper part is mostly quadrangular prism-shaped), it is not easy to fix the bolt, and the quality requirement of steel structure installation is pretty high. Therefore, the embedding accuracy of the connecting bolt has become a key technology for the installation and construction of the metal building.
Use the independent bracket system and shaping mold to locate the embedded bolts, use theodolite or total station to adjust and calibrate accurately, and then complete the pouring of the concrete at one time to achieve the accuracy of the embedded position. Below are the characteristics of this process:
1. Use a fixed mold steel plate to fasten the embedded bolts to ensure the bolts’relative position in the bolt group is accurate.
2. Use independent bracket systems and stereotyped molds to pre-buried the bolts. The bolts are tunable with high construction accuracy and a small overall deviation.
3. Make full use of the Φ48 mm steel pipe scaffold rod and fastener turnover materials which are commonly used for scaffolding. It has strong versatility with low cost, which can save a lot of engineering investment.
4. The construction process is simple and effective, and easy to learn for the operator.
a. The anchor bolts should be processed and customized according to the design requirements and must obtain the corresponding material certification and inspection report.
b. Mold design and processing
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, engrave the mold steel plate’s cross line of the longitudinal and horizontal axes. Then drilling determines the relative position of an embedded bolt according to the mold axis. The drilling position and hole diameter of the mold 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. Mold steel plate can be assembled on-site once finished processing. The poles adopt a short scaffold with a length of 2.0 m, and the standing rib adopts Φ18 mm screw steel or Φ20 mm steel pipe. The height of the standing rib should be 5-10 cm higher than the embedded bolt to facilitate the use of steel rulers to calibrate the axis.
3. If the top of the concrete foundation is a short column, then the holes could be dug in the steel plate center to facilitate the pouring of concrete.
c. Measurement accuracy control
According to the engineering design positioning coordinates and elevation, the encrypted survey axis and elevation control network are used to facilitate accurate measurement for different parts.
B. construction sequence
According to the plane layout of the steel structure column, start from the corner column or side column firstly, and fix the embedded bolts along the longitudinal axis. If it is a multi-span steel structure, it should be constructed from the middle span’s longitudinal axis to both sides’ longitudinal axis to reduce the measurement and construction errors, and improve the overall installation accuracy.
C. Independent bracket system installation
The size of the steel structure concrete foundation is large with a maximum width of 3.8 m. The upper part is often designed as a quadrangular prism shape. The supporting mold’s height is much lower than the embedded height of the anchor bolt, and the steel mold has a certain degree of flexibility, which couldn’t meet the accuracy requirements of embedded bolts. Therefore, an independent bracket system is needed.
picture2 - installation diagram of the independent bracket system
D. Adjusting the positioning of the mold
1. Use a theodolite or a total station to measure the horizontal and vertical axis points on the truss frame of the support system, and pull the wire to form a cross axis. Then place the stereotype mold poles on the horizontal bar of the truss frame to align the cross line on the mold steel plate with the axis line of the truss frame, and connect the poles to the horizontal rod with hand fasteners.
2. After setting mold in place, loosen the upper fastener of the pole, pull the wire from the axis of the ticket to the point on mold steel plate by use of small wire, and gently tap the pole to make the setting mold move slightly. The axis line on the rack is precisely adjusted to make the casting point coincide with the mold notch and then tighten the fastener.
E. Installation and adjustment of embedded bolts
1. Penetrate the embedded bolts from the drilling of mold steel plate, reserve the exposed thread length according to the design requirements, and fix it with two nuts. Use a spirit level to detect the elevation of bolt top, tune the upper and lower nuts to meet the elevation requirements, and tighten the nut.
2. Use a horizontal ruler to detect the verticality of every bedded bolt. The screw could be adjusted slightly until the verticality in both directions meets the requirements, and tighten the nut thoroughly.
3. When the elevation and verticality of each bolt are adjusted to be qualified, then use short bolts to connect the roots of the bolts to each other by spot welding to make a bolt group into a whole. If the embedded bolt is longer, one or two welding ribs can be added to ensure the accurate and stable positioning.
4. In order to ensure that the embedded bolt won’t occur the performance of overall settlement and full tilt, it is necessary to use diagonal reinforcement to spot weld the diagonal reinforcement with short steel bars, and diagonally weld two short steel bars at the bottom of the embedded bolts to support the foundation cushion.
5. When the internal space of the basic steel mesh is large enough and makes no effect on the overall installation of the embedded bolts, then the embedded bolts can be set up before installing the mold.
F. Review of embedded bolts
1. When the installation of the embedded bolts of each foundation platform is completed, use a total station to measure the axis intersection on the mold steel plate, and check whether the intersection of the steel plate score is coincided with the measured axis coincide intersection. If there is an error, tune the mold by taping the pole and loosening the fastener until it overlaps completely.
2. Use a steel ruler to check whether the distance between each foundation bolt group meets the design requirements, and 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 previous method to correct it.