gravity and mass

[tohamy]

i created two models for the same frame where,

model one has an permanent element vertical loads equal -24.4 KN/m, and from gravity and mass settings the mass defined (from both frame/mass elements and loads) and the loads defined from (loads in gravity direction are derived from mass based on g value) to take the effect of own weight of elements.

model two has a distributed mass equal 2.44 ton/m, and from gravity and mass settings the mass defined (from frame and mass elements only) and the loads defined from (loads in gravity direction are derived from mass based on g value)

it was observed that time period for the two frames is equal and also the vertical reaction is equal for them.

i think that is wrong because the mass in case two (2.44 ton/m) is equal the load in case one (-24.4 KN/m) and the results shouldn't be the same, i think it must be the same results if the mass equal the load divided by the g ( 24.4 KN = 2.44 ton force / 9.81 = 0.248 ton mass)

please some one clarify to my if there is some thing wrong in the program or i have misunderstand.

thank you

[z.gronti]

Dear tohamy,

The general relationship between weight and mass is:
W(N)= m(kgr) * g (m/s2)

Hence, the mass is not equal to the load, but it is equal to the load devided by the g value.

The imported values in the two models are almost equal, that's why you get the same results.

[tohamy]

so if i have an element has own weight equal 1 ton force (10 KN) and i want to replace it by lumped mass, this mass will be

1 ton force / 9.81 = 0.1 ton mass
or
10 KN / 9.81 = 1 ton ???
sorry but i have misunderstand with this point
thank you

[z.gronti]

Dear tohamy,

The correct relationship is the second one:
10KN/9.81≈ 1tn

[tohamy]

thank you very much