Long-Term Deflection check and comparison between Tekla Structural Designer and Ram Concept

Dear Bentley team,

 

I’m performing a structural concept design of RC frame of residential development using EC2. I have models of the slab of one of the RC frame buildings in Tekla and Ram Concept. We made a comparison between the results for long-term deflections from both programmes. It appears that there a significant differences between the deflection in Tekla Structural Designer and Ram Concept.

In brief the deflections in Tekla using Slab Deflection tool with an event sequence similar to that recommended in the their Long-Term Deflection Webinar-part 2 are  less than those from Long term deflections in Ram Concept.

I’ve use the followings parameters for the slab:

 

Flat slab 250mm thk C32/40, columns 300x600mm C32/40 pinned at both ends, 100% restraint type for slab panels (which is conservatively and is equal to 20% in Ram) and following event sequence in Tekla:

I've created equivalent Load-History in Ram concept for comparison purpose using default load-History/ECR parameters:

I received the following long-term deflections for the slab model in Tekla with max deflection of 18.4mm in the span at the upper left corner of the slab:

and the following deflection of the slab model in Ram Concept:

and a snapshot from the same critical span in the upper left corner with 28.3mm long-term deflection or with 10mm more than the Tekla model:

After receiving these results I'm really confused of the big difference between the result from the programmes. I consider to change some of my column layouts to break down some of the spans in my 3D Tekla

model even its deflection are within the limit in order to control the greater deflections which I received in Ram concept for the same spans.

I sent a query to the Tekla Support Team as they usually respond within the same day but it's fear to do the same with your team in order to find what is the cause for the different result.

Please find below the answer/comments from Tekla Support Team:

We wonder if you have used all the default settings in the other program, or have altered the input?  Our expert had the following comments on some of the parameters set in the other program.  In particular he thought the Creep factor was oddly high and that the Ageing coefficient is more usually associated with the US design code/ method than EC.   Is this creep factor used for the entire load/sequence in the other product?  Does the program have recommended settings following Eurocode guidance that you have used?

You probably saw in the webinar that you can view the Effective modulus calculations in TSD by exporting this to Excel.  This gives the calculated creep factors – there are different values for each load sequence and we see they are quite a bit lower in general than the single value set in the other program:

No doubt you are similarly querying the other program vendor.  We hope the above is helpful and would be interested to know the results of your further investigations.

Kind regards

Trimble Support Team

Tekla also provides information for the locations and the extend of cracking on the slab for each of the events:

I compared the deflections in one of the other span for each of the events. They are pretty the same for the first three events (1-3) but after applying the sensitive finishes (event 4) there is a big raise in  the deflection of Ram Concept model compared to Tekla model. This event correspond to creep coefficient of 1.619 calculated by Tekla which is significant decrease from the initial value of 2.528:

Events                                                          Deflections in TDS                            Deflections in RAM

  1. Strike and backprop slab                               3.0mm                                                  2.5mm
  2. Propping slab above                                       7.2mm                                                  6.5mm
  3. Propping removed                                          7.9mm                                                  7.8mm
  4. Sensitive finishes added                                 9.6mm                                                  15.6mm
  5. Occupation                                                      13.3mm                                                21.4mm
  6. Final load event                                               13.8mm                                                24.0mm

My logical explanation is that the creep factor in RAM doesn’t change the same way as in Tekla.  Am I correct?

My question is how Ram Concept complies with EC2 requirements and recommended values for shrinkage, creep coefficient and ageing coefficient.

How the initial creep factor 3.35 differs from creep coefficient in Tekla /EC2 in physical way and how does it change in a similar way as in Tekla (e.g. from 2.528 to 0 at the final load event).

Please also find attached the model of the slab in Ram Concept:

Block C - additional YB load combinations.cpt

I'm looking forward a response from your team.

My desire is to find an explanation of the differences in order to use the both programmes in proper and effective way

Many thanks in advance.

Yavor Boshnakov