Elastic shorthening loss disregarded in the stress calculation

SOFiSTiK
1

Hi all,

I’ve recently come across to curious observation that Sofistik estimates in the tendon stress reduction due to ealstic shorthening but that does not affect the Normal force used for calculation of the stresses of the cross section.

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By the defintion I have removed or reduced all other losses :
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If we have consequence prestressing ( consequence prestressing of segments during balanced cantilever construction) the elastic shorthening due to second prestressing does not reduce normal force the first tendon.

My question is if check print of the tendon stress shows that tendon stress reuduction due to elastic shorthening is taken into account, why the normal force is not reduced as well - which leads to underestimate the stresses?

Kind regards

2

(My opinion) At least in the same CS the stress reduction by elastic shortening is (also in ASE) not taking in account. ASE sees only defined prestress loads and calculate the reactions.
On the other hand TENDON doesn’t know something about the system behavior, it is a standalone-module. To consider the influence of subsequent tendons (at leat in the same construction stage) you have for the insitu work separatly to calculate a prestress-instruction with gradually reduced overspan. Therefore you must have reserves in the modell-tendonforces.
(Or you work without TENDON, modellising real cables. Then you can see the force reduction.)

3

Hi Ragl,
Thanks for the repsonse.
“At least in the same CS the stress reduction by elastic shortening is (also in ASE) not taking in account.”
My concerns is that consequent stressing does not reduce the normal force in the first tendon - on the check print you can see the reduction of the stress in the tendon (1336-1314 = 22MPA) but that is not acounted in the Normal force (stay the same).
CS 11 first calbe is tensioned. CS 12 first tendon is grouted. CS 21 second cable is tensioned.

Kind regards

4

I think that in your quadsystem the calculation of subsequent tendons works. And probably you can see this in WINGRAF in quad-tendon-results.
(Beamsystems work not in this way, there you have to use AQB to obtain this.)

For instance you can take the TENDON-Instance “tendon_csm32.dat” and add this:

+prog sofiload $ Tests 98+99
head
lc 98 titl 'cooling '; quad grp 0 type dtxy p -30

lc 99 titl ‘compress’; line ref qgrp type pxx proj zz wide 0.2 p1 -1000 x1 #coor_x(302) #coor_y(302) #coor_z(302) x2 #coor_x(307) #coor_y(307) #coor_z(307)
ref = type = proj = wide = p1 +1000 x1 #coor_x(002) #coor_y(002) #coor_z(002) x2 #coor_x(007) #coor_y(007) #coor_z(007)
line ref qgrp type myy proj zz wide 0.2 p1 -10000.37 x1 #coor_x(302) #coor_y(302) #coor_z(302) x2 #coor_x(307) #coor_y(307) #coor_z(307)
ref = type = proj = wide = p1 +10000.37 x1 #coor_x(002) #coor_y(002) #coor_z(002) x2 #coor_x(007) #coor_y(007) #coor_z(007)
end $ ******************************************

+prog ase
grp cs 999
lc 98,99
end $ ******************************************

In WINGRAF you can see in both loadcases a change in the tendonforces.
At first the seems a little strange: The cooling leads to more tendon forces. But this is right due to different elongation coefficients (cooling of both, concrete and tendon steel),
And the shortening / compression leads to less tendon force.