Post anchoring technology is now used in the reinforcement industry more reinforcement methods, post anchoring technology as a whole is mainly divided into: chemical planting steel, adhesive anchor bolt, mechanical anchor bolt, expansion anchor bolt.
Chemical planting steel bar
Chemical planting steel bar, referred to as planting steel bar, is a kind of post anchoring connection technology widely used in China's engineering field. It is a kind of component that uses chemical adhesive - anchoring glue to fix the ribbed steel bar and screw in the drilling hole of concrete substrate. Through the bonding and locking function, it can realize the anchoring of the connected parts.
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The anchoring principle of chemical planting steel bar is the same as that of adhesive anchor bolt, but the length of chemical planting steel bar and screw is not limited, which is similar to that of cast-in-place concrete reinforcement anchoring. The failure mode is easy to control, and generally can be controlled as the failure of anchor steel bar. Therefore, it is suitable for the anchoring connection of structural members and non structural members with static and seismic fortification intensity ≤ 8 degrees. As for the anchorage connection of structural members under fatigue load, we need to use it as appropriate.
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Adhesive anchor bolt
Adhesive anchor bolt, also known as chemical adhesive bolt, or adhesive bolt for short, is a kind of component that uses special chemical adhesive (anchoring glue) to fix bolts and internally threaded pipes in the drilling hole of concrete substrate, and realizes the anchoring of the connected parts through the bonding and seam locking between the adhesive and the screw, and between the adhesive and the concrete hole wall.
At present, the market fixed bond type anchor bolts are generally thick and short, the anchor depth is shallow, the adaptability to base material cracks is poor, and the bearing capacity is very low, which is not suitable for the post anchoring connection of structural members under tension, edge shear, tension shear composite stress and non structural members of lifeline engineering; in addition to the bond type anchor bolts specially used for cracking concrete, the general bond type anchor bolts are not suitable for cracking concrete The post anchoring connection of structural members with concrete base material under tension, edge shear and tension shear composite stress.
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Mechanical anchor bolt
The mechanical anchor bolt for load-bearing structure should be the back reamed anchor bolt with locking effect. This kind of anchor bolt can be divided into self expanding anchor bolt, die expanding anchor bolt and adhesive die expanding anchor bolt according to its different construction mode. The adhesive anchor bolt for load-bearing structure should be special inverted cone adhesive anchor bolt. Self tapping screw does not belong to anchor bolt system, so it should not be designed and calculated according to anchor bolt.
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Expansion bolt
Expansion bolt. The expansion bolt is wrapped with a ring tube. There is a gap on the ring tube. When it is used, make a hole in the wall. Put the expansion bolt into the hole. When tightening the bolt, the ring barrel will be squeezed and stretched. In this way, the bolt is stuck in the hole and plays a fixed role.
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The difference between them
1、 Stress principle
(1) The embedded steel bar must be full screw or ribbed steel bar, and the adhesive force is used to realize the stress and form the anchoring effect;
(2) The bolt is allowed to have smooth screw, which is forced by mechanical locking key force;
(3) The expansion anchor bolt mainly relies on the friction between the expansion pipe opening and the concrete to resist pulling. The pull-out force has a great relationship with the construction technology and human factors, so it is useless to do tensile test.
2、 Anchorage depth
(1) The anchorage depth of embedded bars is generally greater than 15d after calculated by calculation formula;
(2) The anchorage depth of anchor bolt should be less than 10d;
(3) The depth of expansion bolt is mainly determined according to concrete strength and expansion bolt specification.
3、 Form of destruction
In general, there is only one kind of reinforcement failure. The allowable failure modes of anchor bolt and expansion bolt are steel bolt failure and concrete cone failure.
Expansion bolts and chemical bolts are actually anchor bolts. In some cases, expansion bolts or chemical anchors are required because they are not pre embedded. But this situation should be avoided in the design. Because anchor bolts should be embedded. For example, anchor bolts at column base. Because only in this way can we ensure the best adhesion and stress. And after drilling, it often causes damage to the stressed steel bar in the concrete and the concrete itself.
Use status
In concrete specification, the components embedded in concrete are called embedded parts. According to the Ministry of construction documents, expansion bolts shall not be used for curtain walls. In general, it is strictly forbidden to use expansion anchor bolt in new construction, and it should be embedded.
In article 4.1.1 of jgj145 technical specification for post anchorage of concrete structures, adhesive anchor bolt points out: "adhesive anchor bolt is widely used in foreign countries, but recent research shows that its performance is poor, especially for cracked concrete substrate, its calculation method is not mature enough, and its failure mode is difficult to control.
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During the use of expansion bolts, stress concentration will occur on concrete, which greatly increases the probability of failure and makes the structure unsafe. Therefore, expansion bolts can not be used in cracked concrete. So now it has been banned in curtain wall design. If you want to review the drawing, the expansion bolt can't pass.
At present, planting steel bar technology is the mainstream reinforcement technology. Because of its mature technology, it has been seen in many new and reinforcement projects.