Bend test for steel

The steel bars are bent to form a specific shape such as shear stirrups, L-bars, and other shapes. therefore steel should have sufficient ductility to enable the bending of reinforcement bars without affecting the steel strength The bending test of reinforcement steel performed to verify that steel ductility and to ensure that no fracture or cracks will occur during the bending. the reinforcing steel may fracture or crack due to the following reasons:

• the ribs of steel are a location of concentrated stress, and it is considered as a weak point. these locations may fracture if steel bends.
•  The steel possesses high strength. Therefore a larger force is required to bend steel, and this could cause steel to crack.
• Also, the radius of bending the reinforcement, smaller radius of bending will have a greater adverse effect on reinforcement steel.
• The low temperature playing an important role in reducing the steel bar's toughness, and this may result in bars cracking or fracture if bent.

Figure 1

After performing the bending test, the convex surface of the tested bar should be checked by the unaided eye to identify any cracks or fractures. The test is performed by the support of the specimen at two pin locations. The distance between supports equal three times the bar diameter plus the plunger, then a force given to the plunger to bend the bar specimen. The test will stop when the bar bends to an angle of 180, as shown in figure 2.

A rebend test can be conducted to determine the effects of strain aging on steel. Strain aging can cause embrittlement effects, which can occur after bending the cold deformation by the diffusion of nitrogen in steel. Therefore some codes limit the content of nitrogen to 0.012%. the rebending testing can be conducted by bending the reinforcement bar at an angle of 45 degrees at 100 C for an hour and then bent it back by 23 degrees.  

Figure 2