Steel design using STAAD

Please check output file thoroughly. 2-sets of steel design outputs are available, one for loads 10 to 13 and another for 20 to 23.

Please check output file thoroughly. 2-sets of steel design outputs are available, one for loads 10 to 13 and another for 20 to 23.

Hi..

Thanks for your posting.. I failed to notice it.

But if u double click on a member & see the Steel Design tab, there the design ratio & the critical load specified are for the latest set of parameters. Isn' it??

I  generally check the interaction ratio n the governing load case this way.. so was cught unaware..

Anyway is this right.. the value in the steel design tab should be the critical case in the sense if design governs, it should be showing load case 10 to 13 & if deflection governsit should be showing load case 20 to 23..

 

Regards,

Arun.

Arun,

Your implementation of the LOAD LIST commands is correct.  Your are performing a code check (WITHOUT deflection checking) for your loads 10 to 13.  Then you are performing another code check (INCLUDING deflection checking for the specified beams) for loads 20 to 23.

The thing to keep in mind is that code checking will ALWAYS be evaluating stresses.  The only decision we have is whether or not to include a deflection check IN ADDITION TO evaluating stresses.

In your particular situation, the result was very easy to interpret, because the second CHECK CODE ALL command only revealed four failing members, and they all failed on the basis of deflection.  So you got a clean result that you can address, for instance, by increasing the moments of inertia of the four failing members and then rerunning your model to verify that the new sizes work for stress on the basis of factored loads and for deflection on the basis of service loads.

Keep in mind that the Prot Processor will always indicate the results of the LAST analysis (in a multiple analysis model) and the last CHECK CODE or SELECT command if more than one exists in the model.  That's why you are currently seeing beam design results that are all based on load conditions 20 to 23 in the post processor.

Cheers,

Chris

Thanks Chris !!!

Till this date after every analysis, i used to check the members which have failed by using the SELECT| BY SPECIFICATION| ALL FAILED BEAMS option.

This is a good knowhow. So in a multiple anlaysis model, we'll have to evaluate the design stresses by checking the output file only right?

I thought the post processor would always give the results for the most critical case, considering both service & design load combinations.. Is there any way by which this can be achieved?? It'd save considerable time..

Or is it possible to include two list commands for different parameters within the same set say PARAMETER 1?? Sorrry if I'm wrong, but just curious..

Regards,

Arun.

Arun,

 

These are some excellent points, so let's expand on this just a bit for the benefit of others who may not be aware of some of these concepts.

First, to reiterate from the last post, in a multiple analysis model, all results in the Post Processor will always be based on the last analysis.  If there is ever a need to observe results from analyses other than the last analysis, those results can be viewed in the output file.

Second, the Unity Check sub-tab of the Beam tab in the Post Processor always reports the results of the last CHECK CODE or SELECT command in the model.  Again, if there is ever a need to observe design results from code checks other than the last check, those results can be viewed in the output file.

Next, be aware that SELECT > BY SPECIFICATION > ALL FAILED BEAMS selects all members whose utilization ratio exceeds the upper limit on the "Pass" range as established by the user.  (The "Pass" range is range #2 in the Basic Diagram version of the Design Results tab of the Diagrams dialog.)  The important thing to understand here is that this gives the user the flexibility to alter the interpretation of the unity check ratio values.  This means that if the user establishes a value of 0.95 as the upper limit on the "Pass" range on the Design Results tab, then SELECT > BY SPECIFICATION > ALL FAILED BEAMS will select members with unity check values that exceed 0.95.  This is fundamentally different than viewing the design results in the output file, which always base the PASS/FAIL indication on a comparison of the actual unity ratio with an upper limit of 1.0 (potentially modified by parameters such as RATIO and OVR).

Finally, since there is significant value in being able to use the Post Processor to review design results, it may be more effective to separate a multiple analysis run into a series of single analysis runs by remming out selected portions of the model at a time.

Cheers ,

Chris

Chris !!! 

You threw a lot of light into the subject of using post processor!! Thanks !!

I have a clear picture now about the options.

I'd like to put in one more point, pertinent to my case atleast!!

Most of times I require a multiple analysis model, to check for deflection & evaluation of design stresses.

So in lieu of this, if a specific tab or option dedicated to check deflection alone for the specified members in a model is available, it'd do a lot of good. Because deflection check is done for service (unit) load combinations almost all the time. So Irrespective of a multiple analysis model for evaluating stresses (with factored load combinations), deflection check can be taken care of separately every time.

In such a case I'd use the post processor all the times to check for stresses, and a dedicated sub tab for cheking deflection under the BEAM tab in post processor can be used for deflection checking.

It'd ensure that DESIGN can be used to evaluate just stresses and the option of whether to have deflection cheeck or not, in the same is eliminated & done separately.

 Just a thought !! 

 Thanks again for your wonderful posting !!

 

Regards,

Arun.