bridge using pc strand

Low relaxation pc strand

ISO 9001:2008, ISO14001:2004 Qualified ;
Low relaxation PC strand application for large-span bridges on railways and highway,rock-soil anchoring project,
multi-story industrial buildings,stadiums,coal mines,domes for nuclear power stations and etc.
Manufacturer comply to standard ASTM A416, BS5896, AS1311, JISG3536, ISO6934, EN10138

Low Relaxation PC Strand

Pc strand damage identification and analysis
Prestressing strand has been widely used in bridges, buildings, water conservancy and hydropower, ground anchor, the special structure of industrial and civil projects in the transport, storage, application and service stage, strand damage that may occur in various forms ( refers to the quality of strand damage), severe cases can cause the material can not be used or structural failure. This paper analyzes the common cause of the damage, the basic procedures provide investigative and preventive recommendations.
1, the classification of prestressing strand damage
(A) mechanical damage: refers to external strand tension and femoral mechanical damage occurs when served.
(2) corrosion damage: Due to inadequate protection and environmental factors caused by the corrosion damage.
(3) Heat damage: fire, welding and other thermal factors strand damage.
Damage phenomena can be classified according to the fracture, corrosion, deformation, mechanical injury.
2, strand breakage
2.1 Fracture
(1) due to quality problems or anchorage construction work of technical problems led to inefficiencies anchorage.
(2) Place the design or construction causes strand discontinuity when.
(3) fracture occurs at the thermal damage or mechanical lesion.
(4) Materials metallurgical defects.
(5) Specifications and Requirements strand deviation (eg level right).
Drawing strand caused structural organization make horizontal directional performance and longitudinal performance varies widely, the role of lateral pressure will reduce the strength of the strand, so that premature breakage. Curve pore, strand staggered, anchor and jack installation improper operation could increase the lateral pressure.
Close to 400 ℃ stabilization treatment has reduced the thermodynamic instability, if re-heated at 400 ℃ for a long time heating will accelerate and reduce the dislocation motion, strength began to decline, 537 ℃ for short heating will destroy drawing forming fiber structure, significantly decreased the intensity of use, fully annealed meal may fall 1100MPa less.
Table 1 is based on the number of faults in the last decade of the investigation summary.
Table 1 strand fracture classification, fracture factors and reasons
Factors may cause fracture classification
Slant fracture fracture within the common anchorage anchorage efficiency factor is not enough, installation problems caused by excessive pressure or lubricating; anchor strand exports have deflected side rodent bite place increasing pressure; slide wire problem changing the distribution of forces may result in broken wires
Pore ​​strand breaks staggered channel quality problems or tension problems
Ultra-tensioning fracture operational errors, excessive friction estimation or measurement problems caused by excessive tension
Fang Zhang Fang Zhang too fast or when breaking free section is too short
After the curing period fracture due Conservation cooling, concrete shrinkage or start cutting after leading strand stress increases, broken wires may occur, generally has no effect on the quality of components
Uneven fracture fracture heat damage from the flame cutting of metal, sparks, welding directly or indirectly caused by welding circuit sparking burning, strength and elongation decreased significantly
Mechanical damage and fracture unloading, transport, field operations and other issues
Other types of occasional metallurgical defects
There necking fracture tension is too large operational errors, excessive friction estimation or measurement problems caused; unloading violent pull hook
In welding, the welding circuit tempering heat strength decrease may occur
Fire fire resulting decrease in strength (package surface may have burning residues or color change)
Meanwhile there are other fracture necking is not the first fracture, probably due to the wire on the other
In accordance with the FIP (now changed FIB) acceptance specifications, anchorage efficiency to reach 95%, but the actual use of the greatest super-strength tensile force does not exceed 80% of the standard. Although the use of very good anchorage may be broken, but the actual application and the identification of the type of test chamber, often curved channel, the operation is difficult to control and there are environmental factors.
Since the stabilization process by strand tension equivalent to approximately 75% of the room temperature strength, poor quality of the strand can not be successfully produced by this process, so the residual metallurgical defects on the strand is very minimal.
2.2 Fracture Safety
(A) An Example 1: A site tensioned precast plant when broken wire frequently, because the plant while using a plastic film and grease. After various plastic film broken wire completely eliminated. Anchorage within the friction is too small will lead to high voltage stress on the strand, and the high strength steel strand opposite pressure sensitive, easily lead to broken wires.
(2) Case 2: A construction site next to the welding operation by strand damage occurred tensioned broken wire (strand surface can be found in welding burns), but very few people know that this site welding.
(3) Case 3: Tension occurs when the pores of thunderous sound, which is determined by the pores caused by excessive friction. The friction stresses the uniformity along the bore is very large, the elongation of the strand is not uniform. Increasing tensile force which will gradually overcome the friction, so that the extension strand leaps and bounds, every moment redistribution will reduce the stress ends, then jack and make it taut, this force causes rapid fluctuations pore air shocks, resulting in thunderous sound. If there are other issues, this process may also be in shock anchor position of some of the broken wire.
(4) Case 4: a bridge girder (transverse) tension occurs frequently broken wires are in the off position ends at about 450mm. Fracture in the vicinity of the current burn marks. Strand is a pre-site survey found that wear into the metal flat tube, fabric reinforcement near the end after a steel welding work. Welding ground ride in the strand tail. Strand in the welding circuit, poor contact with the pipe strand resulted ignition phenomena. If you do not change the construction process, should switch to plastic bellows.
2.3 investigate the general method of fracture
(1) The basic idea for the survey observed fracture characteristics of the sample, and then in accordance with Table 1 and in accordance with the fracture characteristics make a preliminary judgment, according to the survey site environment, work record, construction drawings and asked construction workers and field engineers.
(2) Do not be confused by the fracture normal, abnormal fracture individual may trigger a series of normal faults. Naked eye can not distinguish thermal damage can lead to decreased strength, fracture it may be the normal form of necking.

 

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