topic Re: Mixed regulation in Robot Structural Analysis Forum

Mixed regulation

GabrieleNovembri1027 — Sat, 02 Jul 2011 08:05:46 GMT

Hi,

I'm trying to use RSA2012 and ......

I understand that NTC2008 for reinforced concrete structures are not available. We are waiting the full implementation of NTC2008 (at least in Italy) from the 2009 version !!!!..

This situation makes it impossible to use today the part of the software concerning real reinforcement.

Doing some test starting from beta version I noticed a different behavior of the real reinforcement module related to the regulation used.

In job preferences you can select simultaneously different regulations. For example, you can use the NTC2008 for seismic and loads combinations and the Eurocodes for the calculation of real reinforcement. The module for real reinforcement seems to create from scratch load combinations starting from simple load conditions. It is not clear which is the regulation is used in this operation.

The dialog box that appears at the beginning is rather obscure. Regulation used for real reinforcement calculation is not clearly indicated.

The real reinforcement uses the regulation selected in job preferences for loads combinations or the regulation selected for the design of concrete structures ?

if you select NTC2008 for combinations of loads and EN 1992-1-1:2004 AC:2008 for the design of concrete elements Robot seem to take the second one in order to create load combinations.

Using real reinforcement module the initial dialog box looks like:

In this case It seems that the regulation used for the calculation of load combination is Eurocode. In the printout of the real reinforcement calculus you can find the following information:

From NTC2008 (or Italian) point of view this in wrong because that loads combinations appears incorrect:

If you select NTC2008 for combinations of loads and EN 1992-1-1 plus Italian NAD for the design of real reinforcement of concrete elements the situation changes.

The dialog box informs you that the regulation that have been used is NTC2008

load combinations created in the real reinforcement module seems coherent with NTC2008

It's just a coincidence or you can use a sort of mixed regulation?.

In this case the user may have the opportunity to use part of the software not yet ready for a given regulation (wall design for example) with right load combination. (many of the regulation I know let you use other regulation with proven validity like Eurocodes for detailed design but not for loads and loads combinations).

Anyway…

in the first case (NTC 2008 + EN 1992-1-1:2004 AC:2008) it makes no sense to allow different regulation simultaneously.

In the second case It means instead that you can use mixed regulations.

Which is the correct interpretation?.

Thanks

Re: Mixed regulation

Artur.Kosakowski — Mon, 04 Jul 2011 06:51:47 GMT

The RC design modules generate its own code combinations based on the regulation that corresponds to the selected RC design code. The reason is that these modules are also accessible in the stand alone modes where there are no structures to import results of static analysis from but they have to be calculated based on loads defined inside of each of the design module itself. The other issue is that some of these modules (e.g. Spread footing) require additional set of combinations to be generated e.g. for geotechnical part of the design. In case you want to use exactly the same automatic combinations you generated for the model of the structure according to the selected regulation (e.g. when different that the one that corresponds directly to selected RC design code) you should convert them into manual combinations and then use such created manual combinations for the design in the RC design modules of Robot instead. The conversion of automatic code combinations into manual combinations can easily be done in the combination table (being on the values tab select all table using CTR+A and pres the right mouse button, then select Code combinations -> Combinations) and then all you have to do is to import manual combinations rather than simple cases.

Re: Mixed regulation

Artur.Kosakowski — Mon, 04 Jul 2011 06:59:04 GMT

We are waiting the full implementation of NTC2008...

In Robot v.2012 this code is named D.M. 14/01/2008

Re: Mixed regulation

GabrieleNovembri1027 — Mon, 04 Jul 2011 19:28:23 GMT

Hi Artur,
I'm sorry to insist on the topic but apparently I was not able to explain exactly what I meant.

It seems clear to me that the modules for the calculation of the real reiforcement should also work stand alone and therefore must recalculate the loads combinations from scratch.
The problem is that these modules behave differently using NTC 2008 + EN 1992-1-1:2004 AC: 2008 (oops DM 14/01/2008 ) or DM 14/01/2008 EN 1992-1-1 Italian NAD.
In the first case the EN 1992-1-1 is indicated as regulation for loads combinations, in the second case is indicated the DM 14/01/2008.
The question quite obvious.

In the first case seems that robot uses the coefficients of the Eurocodes in the second case it seems that those uses the DM 14/01/2008 ones. .....The question is more general.
What sense does it allowing a regulation for the calculation of loads combinations different from the rules to ber used for the design of concrete elements if I cannot combine them?

Thanks

Re: Mixed regulation

Artur.Kosakowski — Tue, 05 Jul 2011 09:38:06 GMT

I will try to explain in the best way I'm able to. First of all you can combine them but you should convert automatic code combinations into manual combinations and use these manual combinations for the design rather than import simple cases designing RC elements. As you know there are by far more load combination regulations than RC design codes in Robot and it is e.g. possible that you can use the one that is intended for steel structures in the model rather than the one intended for the concrete design (or use the one that is entirely 'different' than the one 'compatible' with available RC design codes in Robot). A quick example is e.g. a project you have for the US. You have a mixed structure and you want to design steel part using LRFD and concrete part using ACI codes. What you do is you generate code combinations for LRFD in the model and use them for steel code checking and then you import simple load cases onto the RC design modules which combines them using ACI regulation that is internally linked with selected ACI concrete design code. If the module uses LRFD combinations from the model they would be wrong for the RC design. In such a way we 'try' to avoid the situation that the user generates code combinations according to the rules that are not 'in line' with RC design code set for RC elements design without being aware of this fact. Finally the stand alone module and elements imported from the model should be designed in the same way - what I mean is that if simple load cases are defined in stand alone mode and the same load cases are defined in the model (I mean loads to be exact) the design should produce the same results.

Re: Mixed regulation

GabrieleNovembri1027 — Wed, 06 Jul 2011 23:22:40 GMT

hi Artur,

first of all thanks of the time you spent to treat this topic. I think that is what a user, perhaps somewhat pedantic, hopes.
From the discussion I realized this:

The regulation selected for the entire structure and the modules for the real reeifircement are in related in in a way that I can not understand (but it is not important).
Robot passes to the other modules only the elementary conditions. The loads combinations are generated again from scratch with the rules selected for the design of reinforced concrete elements.
The only way to pass to other modules the loads combinations of different regulation is to turn them into manual combinations
In the case I reported in which the two set of load combination generated automatically seemed consistent is accidental.

I still think that, from the user perspective, would be better that the modules of the in reinforced concrete elements design took care only of the requirements given from regulations for the design of real reinforcement starting from the theoretical reinforcement calculated in the main program and using the existing combinations for additional verification often required.
In this way, the workflow would seem consistent with the choices you can make in user preferences

But this is just a point of view

Thanks

Re: Mixed regulation

Artur.Kosakowski — Thu, 07 Jul 2011 07:04:02 GMT

This is what is actually done. If you decide to import simple cases then the RC Design module will automatically generate combinations which are then used for the design of the particular elements such as columns, beams etc. In other words regardless of the code combination regulation you selected in Job Preferences for the model, the selection of RC design code will govern the rules for generation of combinations inside the RC design modules (e.g. if you select EC2 code then combinations used for design of RC elements will be based on Eurocode rules, if you select ACI as your concrete design code the simple cases will be combined according to ACI rules). The only exception is the RC Slab reinforcement module that uses directly code combinations from the model.

In case you base your design on manual combinations then all RC design modules use them directly for calculations of reinforcement.