PSD scale factors

[UcfSE]

I'm modeling a small structure that is part of a large maintenance vehicle. The hood is to receive an additional load, and I am evaluating the hood and supporting frame for suitability and need for reinforcement. I have PSD data derived from accelerometer data, with gauges placed on the vehicle frame. I am using the PSD data to evaluate response of my frame, hood and new load to the vibration due to vehicle motion. Or attempting to do so anyway.

Question: I would like to include the dead load pattern in the PSD analysis since it is subject to the vehicle's vibration. Do I set the scale factor to the entire mass (154 lbf = 4.783 mass units = SF in slugs or lbf*s²/ft) of the structure contained in the DEAD load pattern? Or scale factor = the assembled joint mass at each node (in this case 0.77 slug - so I would have to use the highest joint mass since I cannot have multiple scale factors)?

 

[stressed]

I have not yet used the PSD analysis in SAP2000, but I have used the Steady state analysis. PSD load case doesn't necessarily need to be scaled to G unless your loading is acceleration. Anytime you scale to G for acceleration, you must use your current units (9.8 = 1 G if meters, 32.2 if feet, etc.). PSD can be based on load patterns such as DEAD load that don't need to be scaled to G.

You specify mass using the Define mass source dialogue. The default mass model is based on selfweight of modeled elements plus any additional assigned mass. I typically don't use the default but instead define mass models based on loads which can be factored. SAP2000 will convert these loads into mass. New versions of SAP can have multiple mass models, so that you can use different mass sources for different analyses.