Relate measured strains to input load

[BevanSmith]

I am working on a project where strain has been measured on various places on a bridge structure that supports an agitator. I have been tasked to relate the measured strains to the input load from the agitator in the center of the bridge structure.

Is there any literature or examples that I can follow to obtain this outcome? I know I need to obtain coefficients that relate the applied force to the measured strain but am lacking some direction of how to do this.

Any help would be appreciated.

 

[Ron]

That's the concept of an electronic scale. Proper placement of strain gages can allow you to backcalculate the applied load, typically based on the bending stress in the material. Should be calibrated for accuracy, though.

 

[rb1957]

The stress analysis of the bridge should provide you the means of estimating the stress at the strain gauge location, to compare with the strain gauge reading.

 

[dhengr]

Bevan:
Get your Mechanics of Materials text books out and do a little review. You might be a bit over tasked if you don’t remember that stress and strain are related through the modulus of elasticity of the material. You should get some info. from the people who installed and read the strain gages, as to their orientation, correction factors, etc. for a meaningful and usable strains. Knowing the material, you can then calc. the stress in the member, in that particular point and orientation. Someone must have known the stresses and their orientation which you were ultimately looking to check. Then you must understand the structure well enough to track that stress back to the machine actually inducing the load. Is it a pure tension stress in a hanger? Is it a bending stress in a beam on which the machine rests? Is it a stress on a member of the structure far removed from the machine inducing the load? That req’rs. some structural analysis. Maybe all you want to know is that the machine in question is not stressing the material beyond yield; then you must know the grade of the material.