topic Re: Load to mass conversion: mass and conversion directions in Robot Structural Analysis Forum

Load to mass conversion: mass and conversion directions

Anonymous — Fri, 22 Sep 2017 08:20:49 GMT

Hi Rafa,

Can you explane for me clear about Mass Direction & Conversion Mass, I feel some confuse of them.

@Anonymous Artur Kosakowski edited the topic for better findability

Re: Load to mass conversion: mass and conversion directions

Artur.Kosakowski — Fri, 22 Sep 2017 08:28:56 GMT

Hi @Anonymous

Conversion direction: it is to decide which load defined in a selected load case should be treated as masses. By default it is -Z which means that all vertical loads acting downwards (e.g. weight of some piece of equipment or machinery bolted to a floor) is treated as active mass for seismic analysis. If you set it as e.g. X+ you could convert wind load but I don't think you actually need this

Mass direction: allowable direction of vibrations e.g. you may exclude vertical; vibrations (of floors) while analysis a multi-story building with rigid floor systems or horizontal ones for a single slab (footfall analysis).

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Re: Load to mass conversion: mass and conversion directions

Anonymous — Fri, 22 Sep 2017 08:36:28 GMT

Thank you very much for your explanation, so how Mass Direction in Load to Mass Conversion tab relate to Active mass direction in Modal Analysis Parameter table ?

Re: Load to mass conversion: mass and conversion directions

Artur.Kosakowski — Fri, 22 Sep 2017 09:18:56 GMT

Hi @Anonymous

This is the same definition

In most of the situation you first decide which directions of the vibrations you want to consider defining the modal analysis and then you mark the same check boxes for the load to mass conversion unless you want to perform e.g. some comparison tests and e.g. unmark Z or (X and Y) in the modal analysis (or create a new modal case with such settings) to see the difference with all 3 marked.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: Load to mass conversion: mass and conversion directions

Artur.Kosakowski — Mon, 25 Sep 2017 10:36:47 GMT

Hi @Anonymous

I just wanted to check if you still need any additional clarification on the mass directions.

Re: Load to mass conversion: mass and conversion directions

Anonymous — Tue, 10 Mar 2020 07:48:19 GMT

In a multi story building, I perform a modal analysis. I am interested in only vertical vibrations in time historical results. Should I choose only active mass-z direction in modal analysis? When I chose it, Force-z of the nodes in time history analysis is all zeroes. I need help.

Re: Load to mass conversion: mass and conversion directions

structural.engineer79 — Wed, 11 Mar 2020 15:13:00 GMT

Dear Artur

In ASCE code in Static analysis the vertical seismic force add to dead load. In this case is z direction disregard or no in mass direction for load to mass conversation

Re: Load to mass conversion: mass and conversion directions

AnthonyMcTigue — Tue, 30 Jun 2020 03:43:28 GMT

It is possible to use the load to mass conversion tool to calculate and display the centre of mass of a particular subset of loads on the structure?