First, the advantages of finish rolling threaded steel bars The application of finished rolled threaded steel bars in today's engineering construction is very extensive and effective, which can ensure the smooth implementation of the whole project. It is widely used in large-scale frame structures, large-scale water conservancy projects, continuous beams in industrial and civil buildings, nuclear power plants, highways, railways, large and medium-span bridges and ground anchors.
1. The finished rolled threaded steel bar has high strength and stable and reliable quality.
2. no open flame, safe operation, not affected by climate.
3. The connection method has strong adaptability. Connecting and anchoring are simple, with strong adhesion, safe and reliable tensioning and anchoring, and convenient construction.
4. Save steel bars and reduce the area and weight of components.
Second, the classification of finish rolling threaded steel bar Finishing rolled rebar can be roughly classified from the following three aspects: application field, geometric shape, material and specification. According to the application field, it can be divided into five categories:
1.Finished rolled threaded steel bars for building nondestructive testing: mainly used for building durability test and structural nondestructive testing.
2.Fine rolled threaded steel bars for geotechnical engineering monitoring: mainly used for field inspection of dams, tunnels and landslides and geotechnical engineering tests.
3.Advanced finish rolled threaded steel bars: mainly used for testing and evaluating the structural characteristics of coatings, pipes, metals, plates and other materials.
4.Fine-rolled threaded steel bars for laboratory materials: mainly used for geotechnical, cement, concrete, asphalt, rock and aggregate tests.
5.Fine-rolled threaded steel bars for highway bridges: mainly used for on-site inspection of highways, docks, airports, railways and bridges. Classification according to geometric shape, that is, according to the cross-sectional shape of ribs and different spacing of ribs. Classified according to materials and specifications: the finished rolled threaded steel bars are PSB500, PSB785, PSB830, PSB930 and PSB1080; Commonly used finish rolled rebar specifications are 15mm, 20mm, 28mm, 25mm, 32mm, 36mm and 40mm(20mm and 28mm are unique to PSB500 rebar).
Three, what is the finish rolling threaded steel bar? Finishing rolled rebar is a kind of straight rebar with high strength, high dimensional accuracy and large diameter, which has discontinuous external threads rolled on the whole rebar. The reinforcement can be connected or anchored at any cross section by connectors or anchors with internal threads. Finishing rolled threaded steel bar is also called threaded steel bar for prestressed concrete.
Fourth, the difference between finished rolled steel bars and ordinary rebar The difference between finish rolled rebar and common rebar can be distinguished from three aspects: chemical composition, shape and rules.
1.chemical composition difference: the finished rolled rebar is 42MNSIV with vanadium and high strength, so the finished rolled rebar is also called prestressed finished rolled rebar. Ordinary rebar is 20MNSI, which has low strength and cannot be used for tensioning.
2.Appearance difference: The appearance of finished rolled rebar is slightly different from that of ordinary rebar. The finished rolled rebar has no longitudinal ribs, so the nuts of finished rolled rebar can be directly connected.
3.Difference of specifications: Common specifications of finish rolled rebar are 15mm, 25mm, 32mm, 36mm and 40mm. Generally, the finished rebar does not have the specifications of 12mm, 14mm, 16mm and 28mm, while the ordinary rebar does not have the specifications of 15mm.
FIVE. Connection mode The finished rolled rebar is connected by spiral connector, and the rebar cut at any point along the length of rebar can be connected with rebar of any other length, and the strength of connection joint is higher than the ultimate breaking strength of rebar.
Sixth, distinguish between true and false finishing rebar Common unqualified finished rolled rebar usually has the following phenomena:
1. The length and outer diameter do not meet the design requirements.
2. Cracks appear.
3. The through-end thread plug gauge can't be screwed smoothly to connect both ends of the finish rolled rebar and reach the screwing length.
4. The screw-in amount of the stop thread plug gauge exceeds 3P(P is the pitch).
5. The end stop gauge passes through the small diameter of thread.
Seven, the application industry Finishing rolled rebar is widely used in various projects because of its advantages of economy, convenience and reliable quality. The construction industry is one of the fields where finish-rolled rebar has been used early. Now some countries have standardized and legislated finish-rolled rebar in construction. For example, in Japan, in 2000, it was stipulated that buildings below 60 meters should be built with finished rolled rebar, and it has become an industry trend to apply finished rolled steel to ordinary buildings. The following are the application fields of finish rolling rebar: High-rise buildings, water conservancy and hydropower dams, urban light rails, urban interchanges, highway bridges, port and wharf railway bridges, slip film intermittent propulsion, heavy lifting, tower buildings, warehouse buildings, bridge and tunnel jacking, large containers and ships, steel bar works, bridge bearing replacement, bridge and building reinforcement, sleepers, anti-magnetic and anti-corrosion works (fiber anchorage), subway, tunnel mine roof anchorage, foundation reinforcement, prestressed net rack, etc.
Eight, finish rolling threaded steel bar construction matters needing attention The construction process of finish rolling rebar and anchoring system includes material preparation, production of unbonded finish rolling rebar section, installation of anchoring system, pouring concrete, tensioning, anchoring, anchor sealing and other processes. Its construction method is simple, and matters needing attention in operation:
1.Before tensioning, check whether the reserved holes are unobstructed and whether there is slurry leakage in the corrugated pipe. If there is slurry leakage blocking the pipeline, be sure to clean it up. Especially the bell mouth of anchor pad at both ends of the tunnel must be cleaned up. As the connection between bellows and anchor pad can only be connected in the straight hole at the small end of anchor pad, and can not enter the bell mouth, the redundant bellows in the bell mouth should also be removed.
2.The steel strand between the tool anchor and the tool anchor shall not cross to ensure the anchoring quality.
3.Tools such as oil pump, oil pressure gauge and jack shall be calibrated before use. If the oil pressure gauge is bumped or a new gauge is replaced during use, it shall be calibrated again. When the tension elongation deviates greatly from the design value, check whether the pressure gauge is accurate. Jack is forbidden to apply force without load.
4.Clamping pieces of finishing rolled rebar ring shall be properly kept, and shall be strictly protected from moisture and rust, especially the teeth of clamping pieces. If serious corrosion occurs, they must be stopped. In addition, the anchor ring clips should be used to avoid sticking mud and sand.
5, steel strand can't have serious corrosion phenomenon. If there is floating rust and pitting, the strength of steel strand will be affected, and the phenomenon of broken wire will easily occur during tension. In the tension anchorage zone, the cement slurry, mud sand and floating rust on the steel strand should be cleaned to avoid affecting the anchorage quality.
5.When using finish rolling rebar, it is necessary to coat a layer of paraffin wax on the outer conical surface of the tool anchor clip so as to tension the back anchor.
Nine, finishing rebar industry trends Construction steel, which is mainly made of fine rolled rebar and wire rod, accounts for half of the steel production in China. 200 years ago, the proportion of small profiles was from 25%; From 2001 onwards, with the transfer of the world manufacturing industry to China, the proportion of production and sales of plate, pipe and strip in China gradually increased, while the proportion of construction steel decreased year by year. From 2001 to 2007, the output of finished rolled rebar in China increased from 43.897 million tons in 2001 to 101.366 million tons in 2007, but its proportion in steel production decreased from 28.0% to 18.0%. Affected by the economic crisis, the output of rebar in 2008 was 95.121 million tons, slightly lower than that in 2007. According to the new data from the State Computing Bureau, the cumulative output of rebar from January to September 2009 was 90.0337 million tons, an increase of 27.50%. It is estimated that the production capacity of finished rolled rebar in 2009 is about 133.2479 million tons, and the practical output is about 121.2822 million tons.