The quality of building structure construction directly impacts the safety and integrity of the building. Different types of structures require specific precautions during construction. Here, we have compiled a comprehensive list of key considerations for various building structures.
Steel Structures
Installation of Bolts for Column Foundation Floors
It is essential to control the elevation and level during installation, while securely fixing the nuts beneath the column base plate. Once the steel structure columns are installed, the upper fixing nuts should be welded to the embedded bolts, and the lower nuts spot-welded. The reserved gap under the column base plate must be filled with expansive concrete. Additionally, the portion of the column base below ground level should be wrapped with concrete, maintaining a protective layer thickness of at least 5 cm, with the wrapped concrete extending at least 15 cm above ground.
High-Strength Bolt Contact Surfaces
(1) When producing connection plates between main beams and columns, main beams and secondary beams, and the connection holes at beam ends, several installation defects commonly occur:
- The diameter of the high-strength bolt hole should be only 1-2 mm larger than the bolt itself. If the installation hole is too large, it must be repaired using a low-hydrogen welding rod compatible with the base material, ground smooth, and redrilled. Gas cutting or welding must not be used to enlarge holes.
- The distance between the first row of holes and the edge of the column or main beam web should be 5 cm. Holes should not be centered on the main beam flange plate or extended beyond the flange edge by 5 cm. Accurate drilling during fabrication is critical for smooth installation.
- At the connection plate between steel columns and main beams, horizontal stiffening plates should be installed above and below the beam connection holes at the flange plate positions. A bolted-welded assembly joint may be used, where the flange plate is connected by a single V-shaped groove with a pad and fully penetrated welds replace the use of steel bar heads with unequal strength.
- At intersections of main and secondary beams, if the secondary beam does not enter the main beam flange and the bolt holes are too far from the main beam web, a 1 cm connection gap should be maintained between the main beam and column, and between the main and secondary beams, especially in prefabricated housing.
(2) Welding points at the ends of main and secondary beams must be polished and rust removed promptly. The friction surface contacting high-strength bolts should be clean and free from burrs, welding slag, or dirt. This surface should be treated with sandblasting and an inorganic zinc-rich primer to ensure anti-slip performance, rather than anti-rust paint or other coatings.
(3) When tightening high-strength bolts and nuts, use a dedicated manual torque wrench, tightening symmetrically from the center toward the edges. Tightening should occur in two stages: initial tightening followed by final tightening. It is prohibited to complete all tightening in one step. After reaching the specified torque, mark the bolt ends with chalk to prevent loosening. Typical torque values at the construction site are an initial torque of 220 N·m and a final torque between 374–510 N·m, with a common test value of 440 N·m. Additionally, high-strength bolts must undergo slip coefficient testing on the friction surface and prestress testing before and after installation.
Welding Points
Before welding, thorough preparation is necessary. Weld seams should be uniform, neat, level, and smoothly transition into the base metal. The weld seam width-to-depth ratio should be approximately 1:1, with the seam height about twice the width. Each side of the weld seam should measure 2–4 mm. Welds made at 90° should form a 45° angle. The weld surface must be free of defects such as cracks, incomplete welds, root shrinkage, undercutting, poor joints, porosity, slag inclusion, weld bead irregularities, arc craters, burn-throughs, or arc abrasion.
Allowable deviations in weld size must be closely monitored: for every 10 cm length, deviation in depth before welding should not exceed 1 mm over 2.5 cm. For fully penetrated corner and butt welds, deviations should not exceed 10 mm.
Additional Considerations
- When transporting and stacking components, ensure the ground is leveled and cushion points are properly positioned. Upper and lower cushion blocks must align vertically to prevent deformation caused by uneven stress.
- Adopt a sensible welding sequence and process, or use fixtures and molds to secure components before welding, minimizing warping and deformation.
- During production, hoisting, and inspection, use a steel ruler with consistent accuracy. Component dimensions must strictly comply with allowable tolerances.
- Follow welding construction specifications rigorously to minimize defects.
- During installation, enlarging holes arbitrarily or replacing bolt connections with welding is prohibited. Such changes require consultation and agreement with the design team.
- Welders must hold valid work permits and identification numbers. All welds should be inspected and documented accordingly. If visual inspection reveals any welds failing standards, they must be re-inspected after repair.
- During installation, temporarily fix bolts according to specifications, adjust and tighten them, then install and replace with high-strength bolts.
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