Moving Loads in seismic analysis

[sonyablade2010]

Dear All,

I wish to know how moving loading is taken into account during seismic calculations. What aroused my suspicion was, when I try to combine the other load natures(dead, wind snow etc..) with the moving loads, I observed that moving loads are been treated automatically as live loads in combinations.

Since moving load is assumed as live load I'm not sure whether they have been included with live load reduction factor or not during seismic load calculation.  I prefer all machinery loadings to be as is without any reduction factor if possbile.

Regards,

[Rafal.Gaweda]

Moving load case has LIVE nature as a default.

[sonyablade2010]

yes thank you very much

Is it possible to change that load nature to dead ?

What I wonder is whether RSA takes into account that moving load when calculates the seismic base shear/forces.  If RSA takes into account those moving loads then in which manner with reduction factor (live load reduction ) or w/o reduction as it is. 

For example, let's say that I have 10ton moving load(which has 4 wheel 2.5ton per wheel) and I prefered mass loads to be included as "only translation without rotation". Then how RSA  will include those moving load mass as reduced load by 0.3*10ton , 0.4*10 ton (depending on the live category)  into mass or will directly use it as 10ton into mass.

I hope that  this time my query is much clearer now,

[Rafal.Gaweda]

Is it possible to change that load nature to dead ?

[Rafal.Gaweda]

 

For example, let's say that I have 10ton moving load(which has 4 wheel 2.5ton per wheel) and I prefered mass loads to be included as "only translation without rotation". Then how RSA  will include those moving load mass as reduced load by 0.3*10ton , 0.4*10 ton (depending on the live category)  into mass or will directly use it as 10ton into mass.

If I understood you correctly:

You can do it in two ways:

1. Select the worst moving load position, convert it to simple load case, convert loads to masses from this loadcase with proper reduction factor, use it in (one) seimic case

2. select some \ many moving load positions, convert them to simple load cases, convert loads to masses from these loadcases with proper reduction factor(s)  assigning masses for different seismic case (one seismic case for one converted position(masses)).

[sonyablade2010]

The whole process now begins to take shape in my mind though it's a bit slow, but Im sure that I'll overcome it I'm also fololwing the online documentation for this, but sure it will take time.

In order to wrap it up in a brief, I itemized the list below for the issues I still have difficultiy to understand I l'll look for your confirmation please.

1. RSA doesn't take into account the loads (dead, live etc..)  during the dynamic calculation unless they are converted to mass manually by the  user with "load to mass conversion" Tab and are not taken into account during seismic base shear determination? Please confirm. 
2. Regarding your description for conversion from load to mass (described in 2 steps) it seems that conversion to the dead load case is crucial here. But how about, if I directly go to convert the move load to mass, where move will be moving loads with varying numerous steps? Will RSA take into account the mass conversion automatically for each different moving load steps or not ?
3. There are other move load case created automaticall with move+ and move- since there is no descritpition it is hard for me to guess for what they are, they seems like  an envelope?
4. Is that moving load, is simply linear static calculation for each moving load step?

Regards,

[Rafal.Gaweda]

1. RSA doesn't take into account the loads (dead, live etc..)  during the dynamic calculation unless they are converted to mass manually by the  user with "load to mass conversion" Tab and are not taken into account during seismic base shear determination? Please confirm

Correct.

[Rafal.Gaweda]

Regarding your description for conversion from load to mass (described in 2 steps) it seems that conversion to the dead load case is crucial here.

?????????

THis is your coice what you convert. Just remember not to include selfweight mass twice (take a look  MOdal case definition - Disregard Density and sw Load to mass conversion)

But how about, if I directly go to convert the move load to mass, where move will be moving loads with varying numerous steps? Will RSA take into account the mass conversion automatically for each different moving load steps or not ?

As I wrote before - approach 2, no automatic way ;  remember : you will have to use several seismic cases with different sets of masses

[Rafal.Gaweda]

There are other move load case created automaticall with move+ and move- since there is no descritpition it is hard for me to guess for what they are, they seems like  an envelope?

These are special automatically generated top(+) and bottom(-) envelope cases

[Rafal.Gaweda]

Is that moving load, is simply linear static calculation for each moving load step?

It depends of your settings (manually set nonlinear calculations) or model (if nonlinear).

As a default - linear static.