What issues should be paid attention to when using flat anchors for prestressed anchorage construction?

Quality Problems and Phenomenon
The flat anchor is a new type of clip-type flat group anchor developed by the transportation system by absorbing foreign experience. It consists of a flat anchor head, a flat backing plate, a flat bell tube and a flat pipe section.
The advantages of flat anchors are: the tensioning slot is flat and small, which can reduce the thickness of the concrete slab. It can be tensioned by a single beam and is easy to construct. Therefore, flat anchors are particularly suitable for post-tensioned prestressed simply supported beams, hollow slabs, thin-walled structures such as low box girders with restricted urban heights, and transverse prestressing of bridge decks. They can effectively reduce The height of the trabeam or plate. However, there are also some quality problems in the application of flat anchors
① When using flat anchors, the steel strands should be threaded before pouring the slab beam concrete. It is easy to puncture the flat corrugated pipe during the threading, causing leakage when pouring the concrete.
The slurry blocks the prestressed channels.
② Since it is a single tension, the prestressed steel strands that are tensioned first have a large prestress loss. The final tensile stress of each bundle of steel strands is uneven.
③ Since the concrete has a thin-walled structure and the protective layer of the prestressed pipe is small, the concrete is prone to bursting when the pressure is too high during grouting.
Reason analysis
①The flat anchor adopts the method of first piercing the beam and then pouring
②The flat anchor prestressed beam adopts single tension
③The concrete slab is thin and the hole protection layer is small .
Preventive measures
①Before pouring concrete, be careful when stringing the flat corrugated pipe. Be careful not to puncture the flat corrugated pipe. If it is punctured, it should be wrapped tightly and firmly to
prevent grouting. When the slurry leaks out, it blocks the pores.
② When a single tensioned prestressed bundle is used, the tension control stress of each prestressed bundle should be reasonably controlled.
③ When designing beams and plates, try not to use flat anchors.

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