Creep and shrinkage for quad elements

SOFiSTiK
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Hello everyone :blush:

I did one model (bridge with 2 spans) with beam elements. I obtained all the Loads cases as 4XXX, 5XXX, 6XXX, 7XXX, 15XXX and 16XXX. The 7XXX Loads cases represents the “real stress” in the structure. However, I did the same model with quad elements, and I obtained only the 4XXX and 5XXX Loads cases. So, I didn’t have the effect of the pre-stress losses due to creep and shrinkage (LC 6XXX) in my quad model isn’t it ?

I read the notice and if I understood well, it stipulated inside that for beam model we use the AQB module and for quad model we use the BEMESS module.

To have the effect of the creep and shrinkage I used the CSM task. In the notice of the CSM module it’s writted that to have the creep and shrinkage effect for quad element we can added the command CREP … DEFQ to define the effective member thickness to calculate the effect of the creep and shrinkage.

However, I do so and it didn’t change anything :confused:

So, I would like to now if it’s possible to obtain the effect of the creep and shrinkage in quad a model ? It’s possible to obtain LC 7XXX as for the beam model with the “real stress” of the structure” at any construction stage ?

Thank you for your help :blush:

Sincerely

Antoine

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2

Hello

The effect of creep and shrinkage can be obtained from a QUAD-system. You have to look at the 4XXX or 5XXX load cases. I will do the calculation using the following TEDDY example.

TEDDY > File > Examples > csm > english > csm4_quad_singlespan.dat

  1. Open the Graphic (Wingraf) and visualise the tendon stresses (or forces)
    grafik
  2. The difference between the 4XXX load cases describe the losses due to relaxation, creep and shrinkage. For example:
    (1) load case 4011: 1279,73 MPa (on the rigth side of the singlespan)
    (2) load case 4027: 1147,98 MPa
    (3) Difference: 131,75 MPa
    The same result can be obtained by adding the load cases 5020+5025+5026+5027=131,75 MPa
  3. Now you know the loses due to k+s+r. If you want the loses due to kreep+shrinkage you need to subtract the relaxation proption.
    (1) total tendon relaxation in load case 4027: 4% → 0,04 * 1279,73 = 51,79 MPa
    (2) kreep+shrinkage: 131,75-51,79=79,96 MPa

I hope that with this example you understand how to calculate the stress losses within a tendon.

Best regards
Frederik Höller
Your SOFiSTiK Support Team

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