Deformed Bar (Rebar)

 

Inferior joint of a reinforcing rebar on gas pressure welding.
   A reinforcing rebar (bar for concrete) is a very familiar steel product to us, and is used for almost every structures of our surroundings.
   The terrible Hanshin Earthquake occurred on January 17, 1995.
   By this earthquake, the serious damage occurred in many buildings and structures.
   Unintentionally, the spectacular full-sized breaking test which didn't realize in the history was done.
   I was froze when I saw bridge pier of Hanshin highway collapsing by 635m on TV.
   Since, the day of the earthquake, I spend full day to get broken articles in a room out of the way, I went to see the spot for satisfying my curiosity next day.
   Main reason of broken building was pillar damage by compression force, and concrete of the pillar central part was crush to pieces, and burst out to the outside.
   On the other hand, there are no damage on the main reinforcing rebar, nevertheless many hoop bars were broke or disconnected by tension stress.
   Contrary to this, and, as for bridge pier of Hanshin highway, a joint part of main reinforcing rebar are separated.
   Essentially, break of reinforcing rebar should run out with the main body part, and there must not be separated with joint part.
The joining of a reinforcing rebar.
   I think that a cause should be made clear sometime soon by the person concerned, but a theme of this time is the joining of this reinforcing bar.
   There are some methods that the joining of a reinforcing bar;
   Most simple way is puts a reinforcing rod, and tie up by thin steel wire, second is gas pressure welding, and last is mechanical joint.
   Gas pressure welding process and mechanical joint are used for high quality construction in Japan.
   Process of gas pressure welding are heat up the joint parts of rebar by gas flame, and compressed together.
   This method is applied in the construction spot.
   As for mechanical joint, there are various kinds of methods.
   A common point of these process are using screw for jointing rebar and screw parts are manufactured in a factory
   Manufactured in a factory mean easy to get high quality assurance.
   Roughly saying, at the joining point that strength is necessary in Japan are 80 million place par year, and 90% is joined with gas pressure welding process.
   Cost of mechanical joint process is expensive as compared with gas pressure welding, so it gets only 10 % of market share this time, but the ratio is increasing year by year because of high quality assurance and easy constructionability.
   Mechanical joint process doesn't demand a skill of a high working man.
   This process will increase in future when considers aging of the working population, security of skill working man, rank stability of execution quality.
G-Joint
   My company has started to produce a mechanical joint (G-Joint) from 3 years ago.

   We use special steels for screw parts, and adopt friction weld process which is popular process for automobile parts,
   G-Joint have high quality stability and supports safety of all construction projects.

   Above photographs show the situation of rebuild construction of a building in Nishinomiya city which collapsed by buckling by the Great Hanshin Earthquake.
   G-Joint is used number of 60 thousand for this building.
   In Southeast Asia countries, they couldn't obtain high quality stable concrete, they need to get safety of construction by reinforcing rebar.
   They use high tensile rebar and high density of rebar.
   Gas pressure welding process will be hardly used in these area, because it have an effect on weather greatly, it needs specially skilled worker, and difficult to apply for high tensile rebar.
   Interest of mechanical joint becomes high recently in these countries.
   I think that mechanical joint technology introduction from Japan progresses in future.