History of Beams

Brief History

• A beam in engineering was originally as simple as a solid piece of timber that was used as a beam for a house, a plow, or a balance.
• Beams were designed to carry a load in multiple different structures, such as buildings, bridges, etc.

First I-Beam 

• The first I-beam was developed in 1849 by Alphonse Halbou.
• The I-beam is an iconic beam in engineering because of sleek design and functionality.
• The world's first steel building which was constructed in 1889 used I-beams which showed engineers around the world the strength of the I-beam.
• The first I-beams could support approximately 20 stories, however when Henry Grey adjusted the design to reduce the internal stresses of the beam, then I-beams were able to be built larger and stronger which thus resulted in larger buildings [2].

Failures of Beams

Flexure Failures

• • Flexure tension failure occurs when the reinforcement ratio in the beam is lower than the balanced reinforcement ratio as per ACI 318-14.
  • Flexure compression failure occurs when the reinforcement ratio in the beam is higher than the balanced reinforcement ratio as per ACI 318-14.
  • Flexure balanced failure occurs when the amount of steel in the beam is equal to the balanced reinforcement ratio as per ACI 318-14.
  • This failure in tension is evident through the development of cracks either at the tension side of the beam which further extends to the compression side. These cracks are usually vertical and located in the middle of the beam. This failure happens gradually.
  • This failure in compression is sudden and doesn't provide warning.
  • The balanced failure occurs when concrete crushes and steel yields simultaneously [3].

Shear Failures

• • Shear failure occurs when the beam's shear resistance is lower than the flexural strength, and the shear force exceeds the shear capacity of the different materials in the beam.
  • These types of failures are sudden and provide no warning [3].

Diagonal Tension Failure

• • • This occurs when vertical cracks develop at the bottom of a beam due to flexural tensile stress.
    • As the load on the beam increases the crack grows as well, it expands in width and length and bends in a diagonal direction.
    • The beam then undergoes shear tension failure.
    • This failure occurs in beams with low to no web reinforcement [3].

Shear Compression Failure

• • • This occurs through the development of cracks in the beams cross-section. These cracks propagate and penetrate the compression zone of the beam.
    • The failure occurs when the compressive strength of the concrete is exceeded [3].

Splitting Shear Failure

• • • This occurs when the shear span to depth ratio of the beam is less than one.
    • These types of beams transfer loads directly to supports, while having a much higher shear strength than in common flexural beams [3].

Anchorage Failure

• • • This failure occurs when concrete splits along it's longitudinal reinforcement due to small diagonal cracks.
    • The main reinforcement is not adequately anchored beyond the small cracks [3].