According to the opinions of the government planning department, a commercial and residential building project demolished the hall originally designed to face the outside of the community and readjusted the hall to face the atrium side of the community. According to the actual situation of the project, it is necessary to add 1 1 frame columns by planting steel bars. Four related shear walls in the original frame column were strengthened by planting steel bars; Add a roof panel 6.9m long and 4.5m short at the lighting well. The roof panel is made of cold-rolled and twisted steel bars, which are the same as the cast-in-place floor reinforcement in this project. One short side and two long sides need to be reinforced separately. Some steel bars in the newly-added frame beam also need to be planted with steel bars. Part of the text of the construction scheme of reinforcement planting project is as follows:
1. The scheme preparation, construction operation, inspection and acceptance of the rebar planting project are based on the Technical Specification for Reinforcement of Concrete Structures (CECS 25: 90).
2. The specifications, quantity and drilling depth of rebar planting are as follows:
Reinforcement planting specification (mm)φ8φ 18φ22φ25
Number of rebar planted (root) 36611648106.
Drilling depth (mm) 120 270 330375
3. Hilti structural adhesive is used for the upper reinforcement of the cantilever beam, and domestic grade A adhesive is used for other reinforcement. It is forbidden to touch and disturb the rebar within 7 days after implantation, and the maintenance and enclosure shall be strengthened according to the requirements of structural adhesive specification.
4. After the reinforcement is implanted and solidified 10, under the witness of the supervisor, entrust a testing unit with corresponding qualifications to conduct random sampling on-site pull-out testing. The number of steel bars pulled out on site for each specification shall not be less than one group. After passing the inspection, the subsequent work such as steel bar connection, installation and binding can be carried out.
5, on-site detection of pull-out resistance, when the steel bar for Ⅲ steel bar, pull-out resistance requirements must be ≥360 MPa； or higher; When the reinforcement is secondary reinforcement, the pullout resistance must be ≥ 300 MPa; When the reinforcement is grade I steel, the pullout resistance must be ≥2 10MPa.
Second, the steel planting technology related specifications and regulations
The scheme preparation, rebar planting construction, inspection and acceptance of this project are based on Technical Specification for Reinforcement of Concrete Structures (CECS 25: 90). In fact, this standard does not have very specific provisions on steel bar planting technology. This ancient code has been replaced by Code for Design of Reinforcement of Concrete Structures (GB50367-2006). The standard closely related to the acceptance of bar planting should be Technical Specification for Post-anchorage of Concrete Structures (JJ145-2004), and there are local standards in different regions, such as Chongqing local standard "Code for Construction and Acceptance of Inorganic Anchorage Materials for Concrete" DBJ/T50-032-2004 (hereinafter referred to as "Code")
Terminology in Article 2.10.5 of JJ145-2004: chemical planting of rebar-a kind of post-anchored rooting rebar that uses chemical adhesive (anchoring adhesive) to bond and fix ribbed rebar and long screw in the anchoring hole of concrete matrix; Terminology in article 2. 1. 10 of GB50367-2006: rebar planting-use special structural adhesive to anchor ribbed rebar or fully threaded screw in foundation concrete. These two terms about what is "rebar planting" define the type of rebar used for rebar planting: ribbed rebar or fully threaded screw. The transverse rib of ribbed steel bar can make the implanted steel bar colloid form a rib that engages with the transverse rib of the steel bar in the anchorage section. These ribs are mechanical splines to ensure the long-term anchoring performance of implanted steel bars. The spline is too shallow to form effective engagement with the transverse rib of steel bar, and the spline is too deep to resist the shear caused by engagement with the transverse rib of steel bar. Clause 12. 1.4 of GB50367-2006 stipulates that the relative rib area of ribbed steel bars shall meet the following requirements. The shape of cold-rolled and twisted steel bars can not only form mechanical teeth, but also make the local colloid too thick, which will lead to great shrinkage and affect the anchoring effect. Moreover, the colloid thickness of the anchorage section varies greatly. The thicker the colloid, the greater the shear deformation and the smaller the shear stress, while the thinner the colloid, the greater the shear stress, which leads to the uneven bonding shear stress between reinforcement and colloid and affects the effect of rebar planting. Therefore, the cold-rolled and twisted steel bars should not be used in the roof panel design of this project for planting steel bars!