The interaction between the fasteners and the durability of the reinforced concrete Yao Liwei (New Sun Real Estate (Shanghai) Co., Ltd., 200002, Shanghai) failed. By analyzing the interaction between the fastener and the concrete, it is proposed that the embedded parts should be reserved during the concrete construction, the fastener types should be changed, the fasteners should be set up for safety reserve and the maintenance system should be formulated.
As the building structure uses time, the concrete structure will gradually age. Exterior decoration materials and structures attached to the surface of concrete structures, especially dry-hanging stone materials, curtain walls, outdoor machine brackets, roller blinds, wire feet and awnings, which are highly stressed, require hard structures (especially concrete structures). Effective support, when the concrete can no longer provide reliable support, the surface of the exterior decoration materials, structures there is the risk of cracking, displacement or even falling off. In recent years, there have been frequent accidents in the high-rise building curtain wall in China. The relevant local departments have issued a series of requirements for the curtain wall installation, but no high requirements have been put forward for the non-curtain wall peripheral system.
1 Concrete durability failure mechanism Concrete materials are one of the most widely used building materials.
Due to the characteristics of the concrete structural material itself and the environment of use, the concrete structure inevitably has durability problems. Among them, steel corrosion is the most important factor. A series of engineering problems caused by steel corrosion have become very prominent in existing concrete structures, and have gradually become a serious problem facing concrete structures (~3).
2 The interaction between the fastener and the durability of the concrete, for the smaller gauge expansion bolt, generally between 35~90mm, and the range is also the steel bar in the concrete member (including the vertical rib and the horizontal rib) Corrosion affects the extent of damage to the surrounding concrete material. In addition, for general concrete members, such as beams, shear walls and columns, regardless of the vertical expansion bolt pressure contact position is determined according to the bolt type to determine the initial rust time of the transport process / 7; steel corrosion process ribs or horizontal ribs, The spacing is usually between 50 and 200 mm, so the possibility of the expansion bolt hitting the reinforcement is large and cannot be avoided.
When the expansion bolt hole is located near the steel bar, the expansion bolt may contribute to the corrosion of the steel bar.
Since the bore diameter of the borehole is generally larger than the outer diameter of the expander tube, there will always be a gap between the bore wall and the expander tube after installation, and the gap penetrates outside the hole, which provides convenience for the erosive medium 2, -, 2, 112) The transmission path makes the hole also have an unfavorable environment outside the hole. It should be specially pointed out that the presence of the gap may facilitate the aggregation of the erosive medium in the pores, is not easily diluted and volatilized, and tends to form a corrosive battery with a higher concentration after the steel is corroded, thereby accelerating corrosion.
The drilling makes the distance of the steel bar from the edge of the hole smaller than the thickness of the protective layer, shortening the transmission process of the erosive medium.
Once the corrosion of the steel bar begins, the volume of the rust product expands. Due to the existence of the gap, the pressure generated by the expansion tends to be pressed against the concrete on the side of the gap, eventually causing the crack to concentrate in the range between the steel bar and the bolt. The crack gradually develops and penetrates, causing the concrete to loosen and fall off. The support surface used to compress the tail of the expansion tube fails, and the bolt loses its bearing capacity. In the case of large force, the bolt may slip or even be pulled out. .
All in all, the fastener installation interacts with the durability of the concrete.
The fastener installation destroys the durability of the concrete, and the loss of concrete durability in advance reduces the safety of the fastener.
In fact, in the whole process, the corrosion of steel bars not only affects the fasteners, but also the rust-resistant steel bars have a great influence on the bearing capacity of concrete members (especially beams and columns). The reduced load carrying capacity reduces the reliability of the condition that the component can "provide a hard support", which also reduces the safety and reliability of the fastener.
3 Conclusion This paper discusses the failure mechanism of reinforced concrete durability, and the interaction between concrete durability and fastener safety. It presents potential unsafe factors for exterior decoration materials and structures connected by fasteners. Based on this, this paper proposes the following recommendations.
Pre-embedded parts are reserved during concrete construction. As far as possible, the size and positioning of the embedded parts are marked in the construction drawing, so as to ensure the bearing capacity (calculated by the professional), and it is convenient for the installation of the exterior decoration materials and structures. The most important thing is that the finished concrete has no concrete. Damage and durability meet the design requirements.
Change the fastener type. Taking the expansion bolt as an example, on the one hand, it is possible to use a long expansion bolt which can avoid a certain distance of the steel bar, so that even if the steel rust swells and damages the concrete, the bearing surface of the expansion tube can be avoided, and the bolt is still effective; Switch to the expansion bolts of the chemical bonding or injection anchor series. The gap between the bolt and the hole wall can fill the anchoring glue, so that the environment inside the hole is sealed and the erosive medium can not enter.
More fasteners are provided for safe storage. The safety margin should be appropriately enlarged to prevent the structure from becoming a maneuvering system for the maintenance system due to the failure of individual fasteners. Since durability damage is concealed and durable, it will not be destroyed in a short time. Regular inspection is very important. By recording and comparing, problems can be found and solved in advance to avoid accidents.
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