It is required that the deviation between the center of the bolt group and the positioning axis must not exceed 100 mm. Additionally, the deviation in the center distance between adjacent bolt groups should not be more than 100 mm, and the cumulative error along the coaxial line for the entire bolt group should also not exceed 100 mm. Furthermore, the positive error of all bolt elevations must not exceed 3900 mm. The construction period takes place in June and July, when the average outdoor temperature is around 12°C. For this reason, angle steel is used to create the mold, and a one-time pouring method is applied to ensure accuracy and stability.
The main idea behind the design is based on the high-quality requirements for pre-embedded components. Given that the column sections are large (typically 312200 mm by 332200 mm), with large diameter and length bolts, the mold needs to have sufficient rigidity and be convenient for concrete pouring. Therefore, a two-layer mold system was chosen. The threaded part of the bolts is appropriately extended, and during installation, the bolts are fixed at the lower part of the lower frame and the upper part of the upper frame. Different types of angle steel are used for different bolt sizes to ensure proper hole diameters and mold rigidity. Considering the connection between the mold and the short column formwork as well as the top ring beam ribbing, the short column formwork is designed with wood formwork at the top (not less than 92200 mm) and combined steel formwork at the bottom.
During the preparation phase, after the site is leveled, a gantry wall is built along the axis line, and the surface is smoothed with mortar to ensure flatness. The specifications and quantities of the bolts are determined and manufactured accordingly. Based on the dimensions and height of the short column, the number of templates for each specification is planned. A total station (with automatic temperature correction) is used to set up the vertical and horizontal axes on the gantry wall. A level instrument is used to transfer elevation control lines to the four corners of the gantry wall, which serve as the reference for controlling the height of the column and the embedded bolts. Molds are made according to the bolt diameters, such as B14, B7C, and B42. During processing, the hole size is slightly larger than the bolt diameter, with an allowable error of no more than 25 mm between adjacent holes and no more than 300 mm for diagonal errors. The upper and lower molds are fastened together using bolts, and the positions of the holes are uniformly marked and drilled to ensure concentricity and consistent size. To ensure compatibility with the short-column formwork, the lower mold is constructed with a spacing of 3200 mm between the upper and lower parts, connected via connecting elements.
Key construction points include: marking the release line using the control network on the gantry wall, projecting the column axis onto the concrete surface with a theodolite, and adjusting any displaced column reinforcement. The bottom of the column template is leveled using 3D1 cement mortar, with a screed thickness not exceeding 9200 mm. Due to the large cross-section of the short column (with the longest side measuring 3510 mm and the shortest side 3590 mm), pull-through screws are used for formwork support, spaced according to calculated values. After reinforcing the steel formwork, bamboo-glued formwork is installed and secured with bolts. Using the established control network, the vertical and horizontal axes are measured to the wooden formwork keel. The mold is then mounted on the wooden formwork, fixed with bolts, and the embedded bolts are inserted into the mold and secured with nuts at both ends. Since the bolts are long, the concrete is poured evenly around the perimeter of the short column to prevent displacement, and vibration is distributed evenly. A tarpaulin is placed over the bolts after they are fixed to protect them from contamination and damage during pouring. It is strictly prohibited to vibrate the rebar directly against the formwork, bolts, or anchors. Following this method, the steel frame columns and beams are installed in one go without reaming, saving costs and simplifying the production process.
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