Flexural Strength

Definition - What does Flexural Strength mean?

Flexural strength is a measure of the tensile strength of concrete beams or slabs. Flexural strength identifies the amount of stress and force an unreinforced concrete slab, beam or other structure can withstand such that it resists any bending failures.

Flexural strength is also known as bend strength or modulus of rupture or fracture strength.

Corrosionpedia explains Flexural Strength

In order to test the flexural strength of a concrete beam, its span length should be at least three times the depth. The flexural strength is expressed as the modulus of rupture (MR) in psi (MPa). There are two standard test methods to determine the flexural strength of a concrete beam:

  1. Center point loading test (as per ASTM C 293) – In this test method, the entire load is applied at the center of the beam’s span length. Here the flexural strength or modulus of rupture is higher than the modulus of rupture of the third point loading test. The maximum stress is present only at the center of the beam.
  2. Third point loading test (as per ASTM C 78) – In this test method, half the load is applied at each third of the beam’s span length. Here the flexural strength or modulus of rupture is lower than that of the modulus of rupture found in the center point loading test. In this test, the maximum stress is present over the center one-third portion of the beam.

Flexural MR is about 10% to 20% of the compressive strength depending on the type, size and volume of coarse aggregate used in a concrete beam. However, the best correlation for specific materials is obtained by laboratory tests for the given materials and mix design. The MR determined by third point loading is lower than the MR determined by center point loading, sometimes by as much as 15%.

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