Static load calculation of a vibrating mass

[precast123]

Hi everyone,

How to calculate equivalent static load due to vibrating mass.

To be specific, it is vibrating roller load.

Drum Load = 14.9 Ton

Frequency = 28 Hz (1680 vpm)

Amplitude = 0 - 2.5mm

Total load on soil considering vibration will be how much?

Thanks.

 

[WARose]

Is that amplitude the level of soil vibration? If so, you have a means to figure the (dynamic) soil spring constant. With that, you should be able to figure the DLF (Dynamic Load Factor) pretty easy.

 

[precast123]

Thats amplitude of drum vibration.

 

[WARose]

I think the "amplitude" in those things is the weight of the drum divided by eccentric moment. In other words: the eccentricity of the drum as it rolls about it's axis. Therefore your sinusoidal forcing equation will be:

F_o=m*e*ω²

Where:

m=mass of your drum
e=eccentricity of the drum (0-2.5mm)
ω=circular frequency of rotation [for 28 Hz that would 175.9 rad/sec]

As far as the equivalent static load, it would be = the drum weight + (F_o*DLF)

Since you [I assume] don't have a spring constant for the soil (and you also cannot guarantee the time period it will be applied), it will be best to just use 2 as your DLF. Conceivably, it could be more than that (thinking of it as a transmissiblity problem)......but I have a hard time picturing the frequencies getting so close as to causing that.

EDIT: I kind of have to re-think my statement above (i.e. about the DLF/transmissiblity not exceeding a factor of 2). Running some rough numbers, I can see the possibility of the frequencies getting close depending on the site characteristics. However, I think damping would bail you out here to some degree. Again running some rough numbers I came out with a (minimal) damping ratio of about 15%. With that, the transmissiblity factor would be about 3.4

 

[precast123]

@WARose, Thanks for your reply. I have attached the specs of roller. Centrifugal force generated is given here. Is it the total load(365 kN) the drum is transferring to the soil considering vibrations also?

 

[WARose]

Centrifugal force generated is given here. Is it the total load(365 kN) the drum is transferring to the soil considering vibrations also?

I don't know. But that might let you calculate/verify the equivalent mass that is rotating. Since you have contact info for them......you may want to contact them and explain the problem.