When I provide the prestressing force there is a problem in Sofistik with calculation the prestressing loss due to elastic shortening of concrete - Sofistik doesn’t do that. Is there any solution for it (the best with considering the Young Modulus change in time) or I must calculate it per hand?
Hello Paula,
the losses from elastic shortening are considered!
However, whether these losses occur or not depends on the point in time at which the tendon is grouted. Attached you find an adapted example with straight tendons without tensioning force losses.
If it is calculated with input line 361, grouting only takes place after prestressing. Then, of course, the full prestressing force is applied, see 01a and 01b.jpg.
If calculated with input line 362, the tendons are already grouted during shortening and then we obtain lower stresses, see 01c and 01d.jpg.
I hope that helps.
Best regards,
Jost
csm31_design.dat (43.2 KB)
though stress lost due to elastic shortening can be observed in the table, but why Axial force ‘N"‘ remains the same? stress results diagrams for 7000 series LCs also does not reflect the losses!
This is essentially a matter of perspective.
Our approach is that the prestressing force is applied with a magnitude of x, and the corresponding axial force N is also x. When determining the stresses, we use the transformed cross-section properties and calculate the stresses according to N/A ± M/W. In our comparison, the differences therefore arise from the cross-sectional properties A and W (see Figures 02a and 02b).
In other words, if the prestressing tendon has already been grouted, the axial force N acts on the entire composite cross-section, including the prestressing steel. As a result, the stresses in the prestressing steel are reduced accordingly.
If the prestressing tendon has not yet been grouted, the full axial force N acts only on the concrete cross-section.
No. If you start from the reduced prestressing force, the force must not be divided by the area of the entire cross-section, but only by the cross-sectional area of the concrete (ConSta 0). According to 02a, this area is only 5.13 m².
The same applies to the other cross-sectional properties.
Thankyou 