Construction requirements for rear anchoring components
Rear anchorages are widely used in the construction of building curtain walls, especially in curtain wall projects for the renovation and expansion of old buildings, where a large number or even all of them use rear anchorages. In curtain wall engineering, a large number, or even all, of rear anchors are used, and the construction quality is not well controlled, which can bring safety hazards to the use of curtain walls.
The construction requirements for rear anchoring components are clearly specified in the technical specification for rear anchoring of concrete structures JGJ 145-2004.
1) The rear anchoring components include expansion bolts, expansion bolts, chemical planting bolts, and other types of bolts.
When using rear anchoring components, in addition to considering the performance differences of various types of bolts themselves, factors such as the properties of the substrate, the stress properties of the anchoring connection, the type of connected structure, and the absence of seismic fortification requirements should also be considered.
Expansion type bolts and expansion type bolts shall not be used for rear anchor connections of structural components subjected to tension and edge shear (with a margin C<10hcf and an effective anchoring depth of the anchor), structural components subjected to tension shear composite forces, and non structural components of lifeline engineering. (Non structural components of buildings include: exterior walls, partition walls, curtain walls, suspended ceilings, billboards, etc.)
Chemical planting bars and screws can be used for post anchoring connections of structural and non structural components subjected to tensile, edge shear, and tensile shear composite forces with seismic fortification intensity not exceeding level 8, provided that the anchoring depth is met.
2) Pay attention to the construction quality of anchor bolts. For the construction of anchor bolts, it is stipulated in the standard "Technical Specification for Post Anchoring of Concrete Structures" JGJ 145-2004 that:
(1) Requirements for drilling anchor bolts:
Construction of pre embedded parts for building curtain walls and related issues
Note: A. When drilling, the main load-bearing bars should be avoided, and chemical anchoring glue or high-strength resin cement mortar should be used to fill the waste holes;
B. After drilling, use a compressor or manual air cylinder to remove dust and debris from the hole, then wipe the hole with acetone and keep it dry.
(2) The minimum effective anchoring depth of the anchor bolt hmin: hmin/d=6, where d is the diameter of the anchor bolt.
If a 12mm anchor bolt is used, its minimum effective anchoring depth should be 72mm. (The fortification intensity is level 7, concrete C30), and the effective anchoring depth should not include the thickness of the plaster layer and decorative layer on the wall.
(3) Pay attention to the minimum edge distance of drilling: expansion bolt Cmin ≥ 12d, expansion type anchor bolt Cmin ≥ 10d, chemical planting reinforcement Cmin ≥ 5d. (d is the outer diameter of the bolt).
(4) Considering the adverse effects of high welding temperatures on chemical anchoring agents, effective cooling measures should be taken.
III Quality issues in the construction of embedded parts
1. Design calculation problems
Some curtain wall projects, especially small and medium-sized curtain wall projects, do not attach enough importance to the professional design of curtain walls. Some designs only have a few simple design drawings, without the location diagram of embedded parts or structural mechanics calculation sheets. Some designs have calculation sheets, but do not include the calculation of embedded parts and have not been reviewed.
2. Welding quality of embedded flat parts
1) The common form of embedded parts is composed of welded anchor bars on the anchor plate. Cold rolled steel bars shall not be used for anchor bars. When the diameter of the anchor bar is ≥ 10mm, Grade II deformed steel bars, including crescent shaped and threaded steel bars, shall be used. See "Reinforced Concrete Structure Embedded Parts" JSJT-203. The early practice was to bend the steel bars and weld them directly to the anchor plate. Now, the method of drilling holes on the anchor plate and then plug welding is basically adopted, which is more reliable. The welding quality of anchor plates and anchor bars is the key to the quality of embedded parts. To ensure welding quality, welding operators must be trained and certified before taking up their posts. The acceptance of embedded parts is also crucial, not only checking the appearance quality to prevent virtual welding and detachment, but also conducting a weld strength inspection of anchor plates and steel bars according to regulations.
2) The embedded parts are mostly buried away from the design position, resulting in their inability to be used.