Topic: Increased stiffness of system

i am modelling a reinforced concrete beam with ATENA sciene/GiD. It's a simple system: a short single span beam which is loaded centrically by a point load (modelled path controlled by increasing a displacement). All in all it's very similar to the GiD Tutorial.
Now, there is a load-deformation-curve given by experiments and my maximum load by ATENA is very similar to the result of these experiments. But my vertical deformation in the middle of the field is only about 50% of the experiment's deformation.

So my modelled system seems to be much stiffer than in real life. I've checked the geometry and material parameters several times. I've also tested different values for the Young's modulus but the gradient of my F-w-curve is still much bigger than the one of the experiments.

Do you know an input factor in ATENA/GiD that could lead to such a (wrongly) increase in stiffness?

Re: Increased stiffness of system

Dear Rudi,
1. are you 100% sure you are comparing the displacement at peak load to the same (and not for example displacement at peak from the analysis to the last recorded displacement)?

2. Frequently, there are some deformations included in the measurement but not represented in the model.

3. I assume you have 6 or more elements per thickness in the bending direction?

4. It is also quite easy to significantly change the stiffness by a relatively small difference in the boundary conditions.

5. I suggest to look at the frequent difference sources following ATENA Troubleshooting, 2.2.18 My analysis results do not match the experiment/expectations. How can I improve my model? The document is included in ATENA installation in PDF format and also available for separate download from our web (Products - ATENA - Documentation).

6. If you still can not trace the difference source, please follow Troubleshooting, 2.1.1 to send us your model etc.