Status of Rebar Connection Technology Overseas

In the concrete construction field overseas, people use traditional binding technology to connect rebar over the years. It is easy to operate, no require skilled workers, and not be affected by climate, but waste steel, and eccentric connection of rebar will occur additional shearing stress, joint force transmission is not good. It will be difficult to pour vibration if the density of rebar arrangement is big, which will affect the compatibility of  vibration. Also needs to train arc welding workers, technical level of welders often affect the quality of welding. Construction speed is slow, which affect the progress of the project and increase the project cost. Flash welding requires workers with high skill level, but could not weld in construction site, so the usage range is restricted.

Electro-slag welding will save steel compared to the several above-mentioned methods, but with big power consumption. It needs special erection of power lines, and each welding machine needs to be equipped with a 400KVA transformer. The fluctuations of voltage often affect the quality of welding. The above-mentioned methods all require joint position is staggered lap, and have strict limit for the percentage of cross-sectional area of rebar joint and cross-sectional area of total rebar within the same section. Pressure welding technology is complicated, and is affected by climate, also not safe due to the fire.  

In order to solve these problems, in the mid-seventies, some developed countries such as the United States, Japan, Germany started to develop mechanical connection techniques such as: cold extrusion connection technology, taper threaded connection, straight thread connections, and developed a corresponding national standard, which is widely used in the subway, nuclear power plants, large-span aseismatic structure.