IntermediateTopic 60 of 106Engineering Mechanics
Combined loading
Superpose axial, bending, shear and torsion stresses at critical points.
In depth
Members often experience axial, bending, torsion and shear together. Calculate stress components at the critical point, add normal stresses algebraically and combine shear with normal using Mohr's circle or failure criteria.
Key points
- Superposition valid in the linear range
- Critical point may be at the surface
- Eccentric loads create bending
ExampleA pole with a lateral wind load has bending plus axial stress from its weight.
Real members carry axial, bending, shear and torsion at once, so you must superpose stresses at the critical point to find the true state of stress.
What is Combined loading?
Superpose axial, bending, shear and torsion stresses at critical points.
Why is it important to understand combined loading?
Real members carry axial, bending, shear and torsion at once, so you must superpose stresses at the critical point to find the true state of stress.
How do I combine stresses?
Add the normal stresses from axial load and bending at the critical point, and combine shear from torsion and transverse load separately, then use a failure criterion.
Why do I check several points?
The maximum combined stress may occur at the outer fibre, at the neutral axis or at a hole, so each critical location must be checked.
How is Combined loading used in practice?
Typical applications include checking a crane arm under combined bending and axial load, designing a drive shaft that carries torque and bending from a gear and checking a bracket with eccentric loads that cause both bending and direct stress.
What should I learn before Combined loading?
Study "Shear stress in beams" first (topic 59 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Combined loading?
Superposition valid in the linear range. Critical point may be at the surface. Eccentric loads create bending.
Can you give an example of Combined loading?
A pole with a lateral wind load has bending plus axial stress from its weight.
What comes after Combined loading?
The next topic is "Mohr's circle", which builds directly on this one.
How difficult is Combined loading?
It is classed as Intermediate in Engineering Mechanics (topic 60 of 106). It is an intermediate topic. Work through the beginner topics in Engineering Mechanics first.