Hi all,

I’m performing a creep analysis in which I’d like to apply a series of nstress on a wall. Each applied nstress has to be applied on the wall for only 1 second.

**Premise**: I’m not performing a dynamic analysis because my idea is to model this applied stress pattern over a very large time window (days, months or years) that can not be easily modeled in a dynamic configuration.

I thus set the creep analysis in this way:

set cr 0

set fobl 10

set fobu 1E9

set lat 100

set lmul 2

set max 1E8

set min 1E3

set um 0.5

set crdt 0.1

set large

This is a tipical “time series” of applied nstress:

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

solve age 1

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

solve age 2

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

solve age 3

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

solve age 4

apply nstress -1694.29 var 0.0 -1694.29 from 258, 204 to 257, 234

solve age 5

apply nstress -15302.50 var 0.0 -15302.50 from 258, 204 to 257, 234

solve age 6

apply nstress -19457.20 var 0.0 -19457.20 from 258, 204 to 257, 234

solve age 7

apply nstress -14706.00 var 0.0 -14706.00 from 258, 204 to 257, 234

solve age 8

apply nstress -6932.76 var 0.0 -6932.76 from 258, 204 to 257, 234

solve age 9

apply nstress -1327.86 var 0.0 -1327.86 from 258, 204 to 257, 234

solve age 10

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

solve age 11

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

solve age 12

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

solve age 13

As you can see, it is a kind of sinusoidal “time series” (of 13 seconds) in which the applied stress starts from 0 Pa, reach a maximum value and then go back to 0 Pa.

If I plot the xdisplacement induced on a specific zone on which I apply the nstress it seems that the displacements are not affected by the increasing and decreasing stress trend.

I would expect, instead, that displacements would also increase and then decrease following the applied stress trend. It appears, in essence, that the applied stresses accumulate with each other instead of following an up-and-down trend.

Otherwise, if I set up a “classic” mechanical analysis (i.e., no creep) in which I define the number of solving steps for each applied nstress the results look different:

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

step 100

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

step 100

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

step 100

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

step 100

apply nstress -1694.29 var 0.0 -1694.29 from 258, 204 to 257, 234

step 100

apply nstress -15302.50 var 0.0 -15302.50 from 258, 204 to 257, 234

step 100

apply nstress -19457.20 var 0.0 -19457.20 from 258, 204 to 257, 234

step 100

apply nstress -14706.00 var 0.0 -14706.00 from 258, 204 to 257, 234

step 100

apply nstress -6932.76 var 0.0 -6932.76 from 258, 204 to 257, 234

step 100

apply nstress -1327.86 var 0.0 -1327.86 from 258, 204 to 257, 234

step 100

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

step 100

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

step 100

apply nstress -0.00 var 0.0 -0.00 from 258, 204 to 257, 234

step 100

The induced displacements agree with the applied stress trend, first increasing and then decreasing. Therefore, it seems that in this case the applied stresses do not accumulate but are overwritten with each new stress application.

Can anyone explain to me why this difference? Where am I going wrong with the creep analysis?

Thank you in advance