Design of Deep Beams for Bending Moment Only

Deep beams are structural elements with a depth-to-span ratio of less than two. They are generally used in structures such as transfer girders, pile caps, and foundation mats, where the span is too large for conventional beams. Deep beams are designed to resist bending moment, and they may also carry shear forces. The following are the reasons why deep beams are designed for bending moment only:

1. Stress Distribution

The stress distribution in a deep beam is complex, and it cannot be easily analyzed using conventional beam theory. Deep beams are subjected to a combination of bending and shear stresses that cause a triaxial stress state in the web. Therefore, the design of deep beams is based on the assumption that they are subjected to bending moment only.

2. Simplified Design

Designing deep beams for bending moment only simplifies the analysis and design process. It allows the engineer to use conventional beam theory to calculate the maximum bending moment and shear force, and then design the beam based on the bending moment capacity only. This approach is more straightforward than designing for combined bending and shear.

3. Conservative Design

Designing deep beams for bending moment only is a conservative approach. Since deep beams are subjected to both bending and shear stresses, designing for bending moment only results in a beam that is overdesigned for shear. This ensures that the beam will have sufficient shear capacity to resist any unexpected shear forces.

Conclusion

Deep beams are structural elements that are designed to resist bending moment. Although they may also carry shear forces, they are designed for bending moment only. This approach simplifies the analysis and design process and ensures a conservative design.

D=√(m/Qbd2)