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Equivalent Frame Stiffness

Equivalent Frame Stiffness

Equivalent Frame Stiffness

The new AS3600 says that for linear analysis of equivalent frames the stiffness of members should be representative of conditions at the limit state. The previous code allowed gross or "other resonable assumptions".

At the strength limit state, stiffnesses may be only 10-20% of gross properties, especially for PT which may lead to substantial "redistribution" of moments.

Most existing software (RAM Concept, RAPT I think, most FE programs) uses gross sections to reliably calculate moments.

Is this a issue?

RE: Equivalent Frame Stiffness

When you say the new AS3600 are you referring to the draft AS3600, or was this information that was presented in the national seminars on the new AS3600?

When you go through the calculations for cracked sections they can be significantly lower than the gross cross-section (10-20% of Igross) but it is increased slightly by tension stiffening. Stressed slabs and columns would be stiffer still because of the P/A component which increases the cracking moment.

RE: Equivalent Frame Stiffness

"Most existing software (RAM Concept, RAPT I think, most FE programs) uses gross sections to reliably calculate moments."

RAM concept, RAPT same sentence hehehe.
While RAPT is a FE program by definition, RAM concept is a whole new ball game. RAPT is based on an analysis that has been around for a while, with equivalent columns being the only time were torsion is taken into account. RAM concept, R/C building/slabs, ect haven't had the same time for development of techniques for modelling, there are some situations where you need to consider what you want, ie slabs to the core walls connections (walls in general), edge columns, heavy torsion members, how do you model the column to slab connections, joints ect now that is ultimate limit state, what about serviceabiltiy limit state, now we need to model everything correctly to get the correct defelction profile, but that is for another day.

There are a few good books such as "Finite Element Design of Concrete Structures" and there is a good publication by the cement and concrete centre UK (I am currently doing an Australian edition but I doubt mine will get any further than a pipe dream)

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Equivalent Frame Stiffness


Don't give up on the idea to publish an Australian textbook on concrete design. The engineering profession needs more textbooks written by practicing engineers for practicing engineers. And the Australian engineering professions needs more textbooks written to Australian design standards.

It's a shame your publishing thread was red-flagged.

RE: Equivalent Frame Stiffness

It is in the draft and I understand in the final version.

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