Seismosoft | Earthquake Engineering Solutions

I'm doing an Eigenvalue analysis with CON_CC material and inelastic frame. The Young Modulus of the Help System (4700*fc^0.5) is not equal to the modulus calculated by SeismoStruct obtained from the section characteristics. In fact knowing EA and A, I can obtain E but it is different from 4700*fc^0.5. Why?
Thank you Umberto

Hi Umberto,
is there reinforcement in your section? Maybe you are obtaining slightly different results because you are not taking into account the modulus of elasticity of the steel. In fact, if you consider e.g. a 0.30x0.30 m reinforced concrete rectangular section (rcrs) without reinforcement, in which you define the same material (concrete with fc = 30000 kPa) in each "material" field (reinforcement, concrete cover and concrete core), you should obtain EA = 2316866.41824685. Dividing by A = 0.09 mq => E = 25742960.2027428, which is equal to the hand-calculated Ec = 4700*fc^0.5 (where fc is in MPa).
Let me know.
Federica

I did as you said but I get the same result taking into account the steel. I made a mistake putting Fc in kPa rather than in MPa.
thank you very much

I defined a 0.30x0.30 m reinforced concrete rectangular section (rcrs) with reinforcement, in which different materials (concrete with fc = 30000 kPa, reinforcement with E=2.0e+8 kPa ) in each "material" field (concrete cover and concrete core, reinforcement), but EA is still equal to the same section without reinforcement. My version is 5.2.1-build101).Why? Thank you.

The EA, EI & GJ values are merely indicative (i.e not used in the analysis) and calculated using the elastic material properties of the main section material (i.e. concrete in R/C sections and steel in steel sections).

No discretisation of the section in monitoring points takes place in the Pre-Processor (as happens instead during the analysis).

Seismosoft Development