Footfall Analysis - Damping Results

[simon.weda]

Hi All,

After running footfall analysis on a staircase, I noted that increasing the damping in the parameters box, the acceleration increased and the Rf resonant factor increased (Noted transient did reduce). See below image for a simple beam check. 

I am not overly experienced in vibration checks, but I would of expected these values to also reduce. Can anyone please comment on these results.

Thankyou

rtygyjh

[Pawel.Pulak]

Hi @simon.weda,

can you attach the model for which you observe such effects?

Regards,

[simon.weda]

Thanks Pawel,

I have tested this on a number of models. Attached are 2 simple checks.

[Pawel.Pulak]

Hi @simon.weda,

thank you for sending these models,

The shell one correspond to "high frequency floor" where the transient response dominates.

When I increased load to mass conversion 10 times to "shift" it to "low frequency floor" the Rf resonant factor starter to behave as expected when changing damping.

But it seems that the same should be observed for Rf resonant factor in "high frequency floor" domain.

I will update this post after more detailed analysis.

Regards,

[simon.weda]

Yes based on the SCI guidance I would expect similar. I look forward to your response.

[Pawel.Pulak]

It occurred that there is some issue in considering the resonance build-up factor (part 6.5.3 of SCI P354) for SCI P354 floors and slabs.

It is necessary to specify the Number of footsteps about 1000 to consider fully build up resonance. In such case the resonant Response factor for your shell model is equal to:

96.2785 for 0.5% damping and 96.2775 for 1% damping

For not fully build-up resonance there are some issues in calculations - reported to the dev team to be analysed and fixed.

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Regards,

[simon.weda]

Thanks Pawel,

On a side note could you please explain for what analysis case is the 'energy' column populated in the dynamic analysis results table? 

Simon

[Pawel.Pulak]

Hi @simon.weda,

the data shown in the 'energy' column in the dynamic analysis results table depends on the active load case:

1. For the default settings of  the dynamic modal load case this columns shows zeros
2. When "Include damping in calculations (according to PS92)" is active in advanced settings of dynamic modal load case this column shows non zero values and units correspond to energy (force*length) but these values have no physical meaning. It is only the "flag" information that in case of seismic/spectral cases following this modal case and the model composed from various materials with various structural damping the spectrum for the specific mode will be modified to consider the average damping of this mode calculated considering the energy corresponding to appropriate parts as the pondering factor (vibration mode (eigenvector) treated as displacement when calculating energy). It is made according to point 6.2.3.4.3) of PS 92 (NF P 06-013) French code
3. For the response spectra method (seismic or spectral load cases) energy for each mode is a potential elastic energy calculated for the displacement for this mode (corresponding to pseudo-static forces for this mode). Such energy has physical meaning – similar to potential energy calculated for each static load case (but displayed in Analysis > Calculation Notes > Full Note)

---------------------------------------------
If this post answers your question please click the "ACCEPT AS SOLUTION" button (the button visible when logged to the forum). It will help everyone to find answer more quickly!

Regards,

[simon.weda]

Yes it would be interesting to understand how robot uses footsteps to calculate the resonance build-up factor (part 6.5.2 of SCI P354), and how does it adopt a 'length of walking path'. I assume it calculates a velocity, though there is no clear formula for higher pace frequency's in the SCI. It would perhaps be useful to have the option of a 'velocity' input box.

[Pawel.Pulak · Accepted solution]

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@Pawel.Pulak wrote:

It occurred that there is some issue in considering the resonance build-up factor (part 6.5.3 of SCI P354) for SCI P354 floors and slabs.

It is necessary to specify the Number of footsteps about 1000 to consider fully build up resonance. In such case the resonant Response factor for your shell model is equal to:

96.2785 for 0.5% damping and 96.2775 for 1% damping

For not fully build-up resonance there are some issues in calculations - reported to the dev team to be analysed and fixed.

---

Fixed in Update 1 for RSA 2019

Regards,