Computing mass/length

[lacampos3]

Dear Seismosoft support,

On the verification report Ch4-blind-02A file, user defined element frames are used to model the slab. How did you obtain the mass/length for viga 1 (0.23 ton/m)?

Thanks.

[antonioacorreia]

Dear lacampos3,

The mass per length for that element, which represents a slab "slice" with 0.9m width and 0.1m height, was computed by multiplying the RC mass density of 2.55ton/m3 by the dimensions of the slab "slice".

Best regards,
Antonio

[lacampos3]

Antonioacorreia,

Thank you for your response. In order to corroborate the mass/length value of 0.23, I defined a section of 0.9x0.1m and used it to create the element class. In other words, instead of creating a user defined element class, I used an already defined section to obtain the mass/length.

The resulting mass/length is 0.71559633 tonn/m not 0.23 tonn/m. In addition, GJ=1388.58 kNm2 not 0. The other values (EA and EI) are the same.

Any idea, why this happens? Thanks.

[huffte]

I believe that you have defined an element class using a section composed of steel instead of concrete. This would explain the difference in the mass per unit length values which ensue.

The fact that GJ is a finite value in your definition is correct for a square section, but again it corresponds to steel, not concrete (different density, G, and E than steel).

So I think you can see the very reason that SeismoStruct developed a User-Defined element class. This the way to get properties exactly as you want them when using one type of element - a frame - to represent another - a slab. In this particular case, the modeler believed that GJ should be set to zero to obtain the behavior closest to the real structure in a computer model. The ensuing results would validate the choice.

[lacampos3]

Thanks a lot huffte. Your comments clarify many of the questions I had.